WO2010103332A1

WO2010103332A1 - Current measuring device

Info

Publication number: WO2010103332A1
Application number: PCT/GB2010/050439
Authority: WO
Inventors: Mike Bird; Chris Poulton; Alistair Edwin May
Original assignee: Energeno Limited
Priority date: 2009-03-13
Filing date: 2010-03-12
Publication date: 2010-09-16
Also published as: GB2465638A; GB0904324D0; GB2465638B

Abstract

A device (5; 5'; 6;6') comprising means for measuring amplitude, phase and/or change in phase of an alternating current in a section of wiring (2), means for generating a message in response to a change in the amplitude and/or a change in the phase of the alternating current, the message including information about the amplitude, the phase and/or the change in phase of the alternating current, and means for sending the message to a server (9).

Description

Current measuring device

Field of the Invention

The present invention relates to a current - and, optionally, voltage - measuring device, particularly but not exclusively for use in monitoring energy usage.

Background

Information about electrical energy usage in the home and in commercial buildings is extremely valuable. Not only is this information important to energy companies for billing, planning, etc., it can also be used by individuals for a number of different purposes. For example, individuals can analyse their energy usage in order to identify ways of increasing efficiency, such as by changing patterns of usage, replacing appliances and/or switching energy tariffs.

Thus, it can be useful to provide energy usage information which is detailed and/or provided in real time or near real time and which can be analysed appropriately and communicated to an appropriate recipient. For systems which are to be used by individuals rather than electricity companies, there may also be considerations relating to cost, ease of installation and ease of use.

Several factors to consider include: the number and placement of sensors, how these sensors measure energy usage, how the energy usage information is analysed in the various parts of the system and how the information is communicated between these various parts.

Systems for capturing information about energy usage are known.

US-A-4,858,141 describes a monitor in which analogue voltage and current signals are converted to digital format, processed to detect changes in certain residential load parameters, and logic is applied to identify individual appliances.

WO-A-2003/055031 describes a system for the remote acquisition of data and for the remote control of electricity meters which comprises a central server in bi- directional communication with a plurality of concentrators. To each concentrator, a set of electricity meters is connected. The intelligence of the system is distributed between the central server, the concentrators and the electricity meters.

GB-A-2451001 describes a smart metering system comprising an information display unit coupled for communication with at least one metering device and a memory device, for example by low power radio. The information display unit displays graphically or otherwise instantaneous energy consumption, historical energy consumption, etc.

The present invention seeks to provide an improved system.

Summary of the Invention

According to a first aspect of the present invention, there is provided a device comprising means for measuring amplitude, phase and/or change in phase of an alternating current in a section of wiring, means for generating a message in response to a change in the amplitude and/or a change in the phase of the alternating current, the message including information about the amplitude, the phase and/or the change in phase of the alternating current, and means for sending the message to a server.

Thus, the device can provide pertinent information efficiently to a server, enabling analysis of energy usage by one or more electrical devices powered via the section of wiring. A single device or network of devices can then be used to flexibly monitor energy usage in a site such as a home or commercial building.

The generating means may be configured to include in the message information about the time when the change in amplitude and/or the change in phase of the alternating current occurred. The generating means may configured to include in the message information identifying the device. The sending means may be configured to send the message to a gateway via the wiring and according to a power line communication protocol or via a wireless communication link.

The measuring means may comprise a phase lock loop configured to generate an output signal in response to a change in phase of an alternating current input signal.

The phase lock loop may comprise means for generating an error signal which is dependent on the difference between an input signal and a feedback signal, means for integrating the error signal, and means for generating the feedback signal with a frequency which is dependent on the integrated error signal, wherein the phase lock loop is configured so that the feedback signal varies until it has the same phase and frequency as the input signal, wherein the output signal is the integrated error signal, and wherein the device may further comprise means for converting the output signal from an analogue to a digital signal.

The measuring means may be configured to measure the phase difference or the change in phase difference between the alternating current and alternating voltage in the wiring. The measuring means may be further configured to measure the frequency and/or the amplitude of the alternating voltage and the message generating means may be configured to include the information about the frequency and/or the amplitude of the alternating voltage in the message.

The measuring means may comprise a non-contact sensor, for example a capacitive sensor, configured to sense the alternating voltage. The measuring means may comprise a coil, for example a Rogowski coil, configured to sense the alternating current.

The measuring means may be configured to calculate the phase difference between the current and the voltage by digital signal processing. The measuring means may be configured to apply a Hubert transformation to a first copy of a voltage signal, determine a first product which is the product of the Hilbert-transformed first copy of the voltage signal and a first copy of a current signal, determine a second product - A -

which is the product of a second copy of the voltage signal and a second copy of the current signal, low-pass filter the first and second products, and determine the arctangent of the quotient of the low-pass filtered first and second products.

The measuring means may be configured to determine real and reactive power in the section of wiring, and the message generating means may be configured to generate a message in response to a change in the real and/or the reactive power, the message including information about the real and/or the reactive power. The measuring means may be configured to determine the apparent power from the amplitude of the current and the voltage. The measuring means may be configured to determine the real and the reactive power from the apparent power and the phase difference between the current and the voltage. The measuring means may be configured to determine the real power by multiplying the current and the voltage waveforms and to determine the reactive power from the real power and the apparent power.

The device may further comprise switching means and means for controlling operation of the switching means in response to receiving a message from the server including an instruction about operation of the switching means. The generating means may be configured to include in the message to the server information about status of the switching means.

According to a second aspect of the present invention, there is provided a device comprising a sensor configured to measure amplitude, phase and/or change in phase of an alternating current in a section of wiring, a controller configured to generate a message in response to a change in the amplitude and/or change in the phase of the alternating current, the message including information about the amplitude, the phase and/or the change in phase of the alternating current, and a network interface configured to send the message to a server.

According to a third aspect of the present invention, there is provided a server configured to receive a message from a device, the message generated in response to a change in amplitude and/or a change in phase of alternating current in a section of wiring and the message including information about the amplitude, the phase and/or the change in phase of the alternating current, and determine, from the information about the amplitude, the phase and/or the change in phase of the alternating current, the energy usage of one or more electrical devices powered via the section of wiring.

The message may include information about the amplitude of the voltage, and the server may be configured to determine the energy usage of the one or more electrical devices from the information about the amplitude of the voltage.

The message may include information about the time when the change in amplitude and/or the change in phase of the alternating current occurred and the server may be configured to determine the energy usage of the one or more electrical devices from the information about the time when the change occurred.

The server may be configured to calculate the phase difference between voltage and current in the section of wiring by comparing the information about the change in phase of the alternating current with information about the change in phase of the alternating current at one or more earlier times.

The server may be configured to store an energy usage profile of one or more of the electrical devices, the energy usage profile including information about the amplitude and/or the phase of the alternating current at one or more times. The server may be configured to assign the change in amplitude and/or the change in phase of the alternating current to one or more of the electrical devices by determining whether the change in amplitude and/or the change in phase of the alternating current at one or more times matches any of a plurality of energy usage profiles of electrical devices. The server may be configured to read one or more of the plurality of energy usage profiles of electrical devices from a database.

The server may be configured to determine whether energy usage by one or more of the electrical devices matches any of a predefined plurality of energy usage conditions and, in response to matching the condition, send a message to a device comprising switching means, the message including an instruction about operation of the switching means, and/or send a message to a user.

According to a fourth aspect of the present invention, there is provided a system comprising one or more of the devices and a gateway, wherein the gateway is configured to receive the messages from the one or more devices and to send the messages from the one or more devices to the server.

The system may further comprise the server, wherein the gateway is configured to receive the messages from the server and to send the messages from the server to the one or more devices.

The gateway may be configured to store the messages from the one or more devices and/or the messages from the server for sending at a later time.

According to a fifth aspect of the present invention, there is provided a method comprising measuring amplitude, phase and/or change in phase of an alternating current in a section of wiring, generating a message in response to a change in the amplitude and/or a change in the phase of the alternating current, the message including information about the amplitude, the phase and/or the change in phase of the alternating current, and sending the message to a server.

The message may further include information about the time when the change in the amplitude and/or the change in phase of the alternating current occurred.

The method may comprise measuring the phase or change in phase of the alternating current by phase locking.

The method may comprise measuring the phase difference or change in phase difference between the alternating current and alternating voltage in the wiring. The method may comprise measuring the frequency and/or the amplitude of the alternating voltage and may comprise including the information about the frequency and/or the amplitude of the alternating voltage in the message. The method may comprise calculating the phase difference between the current and the voltage by digital signal processing. The method may comprise applying a Hubert transformation to a first copy of a voltage signal, determining a first product which is the product of the Hilbert-transformed first copy of the voltage signal and a first copy of a current signal, determining a second product which is the product of a second copy of the voltage signal and a second copy of the current signal, low- pass filtering the first and second products, and determining the arctangent of the quotient of the low-pass filtered first and second products.

The method may comprise determining real and reactive power in the section of wiring and generating a message in response to a change in the real and/or the reactive power, the message including information about the real and/or the reactive power.

The method may further comprise controlling operation of switching means in response to receiving a message from the server including an instruction about operation of the switching means.

According to a sixth aspect of the present invention, there is provided a method comprising receiving a message from a device, the message generated in response to a change in amplitude and/or a change in phase of alternating current in a section of wiring and the message including information about the amplitude, the phase and/or the change in phase of the alternating current, and determining, from the information about the amplitude, the phase and/or the change in phase of the alternating current, the energy usage of one or more electrical devices powered via the section of wiring.

The message may include information about the amplitude of the voltage, and the method may comprise determining the energy usage of the one or more electrical devices from the information about the amplitude of the voltage. The method may comprise storing an energy usage profile of one or more of the electrical devices, the energy usage profile including information about the amplitude and/or the phase of the alternating current at one or more times. The method may comprise assigning the change in amplitude and/or the change in phase of the alternating current to one or more of the electrical devices by determining whether the change in amplitude and/or the change in phase of the alternating current at one or more times matches any of a plurality of energy usage profiles of electrical devices.

The method may comprise determining whether energy usage by one or more of the electrical devices matches any of a predefined plurality of energy usage conditions and, in response to matching the condition, sending a message to a device comprising switch means, the message including an instruction about operation of the switching means, and/or sending a message to a user.

According to a seventh aspect of the present invention, there is provided a computer program comprising instructions which when executed by a data processing apparatus perform the method.

According to an eighth aspect of the present invention, there is provided a computer-readable medium storing the computer program.

Brief Description of the Drawings

Certain embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows an energy monitoring system in accordance with the present invention;

Figure 2 is a schematic block diagram of a first meter sensor in accordance with the present invention; Figure 3 is a schematic block diagram of circuitry included in the meter sensor shown in Figure 2 for measuring a change in phase of an alternating current;

Figure 4 illustrates examples of input and output signals of the circuitry shown in

Figure 3; Figure 5 is a schematic block diagram of a messaging manager included in the meter sensor shown in Figure 2;

Figure 6 is a flowchart illustrating an example of a method by which the messaging manager shown in Figure 5 monitors an alternating current; Figure 7 is a schematic block diagram of a first socket sensor in accordance with the present invention;

Figure 8 is a schematic block diagram of a messaging manager included in the socket sensor shown in Figure 7;

Figure 9 is a schematic block diagram of a second meter sensor in accordance with the present invention;

Figure 10 is a schematic block diagram of a processing module included in the meter sensor shown in Figure 9;

Figure 11 is a flowchart illustrating an example of a method by which a phase detection module included in the processing module shown in Figure 10 determines the phase difference between current and voltage;

Figure 12 is a schematic block diagram of a gateway in accordance with the present invention;

Figure 13 is a sequence flow diagram illustrating an example of energy monitoring and control in accordance with the present invention; Figure 14 is a schematic block diagram of a server in accordance with the present invention; and

Figure 15 illustrates examples of screenshots showing energy usage information produced by a user interface module included in the server shown in Figure 14.

Detailed Description of Certain Embodiments of the Invention

System for energy monitoring

Referring to Figure 1, a system 1 for energy monitoring in accordance with the present invention is shown. Alternating current (AC) electricity is supplied via wiring 2, such as electrical power cables, from a source 3 to one or more devices 4, hereinafter referred to as "appliances", which may consume electrical power. Appliances 4 can include fridges, freezers, dishwashers, washing machines, televisions, other audio-visual equipment, computers, heating systems, lights and industrial machines, for example. A meter sensor, i.e., a first meter sensor 5 or a second meter sensor 5', is coupled, for example inductively, capacitively or conductively coupled, to a section of the wiring 2 between the source 3 and most or all of the appliances 4. For example, the meter sensor 5, 5' is situated near the standard electricity meter (not shown). There are also one or more socket sensors, i.e., first socket sensors 6 and/or second socket sensors 6'. Electricity is supplied to appliance(s) 4_l5 4₂...4_m via a corresponding socket sensor 6, 6'. Alternatively, appliance(s) 4_m+1...4_n may be powered via a path which does not include a socket sensor 6. The meter and socket sensors 5, 5', 6, 6' each communicate with a gateway 7 by way of the wiring 2 and/ or a wireless communication link 8. The gateway 7 communicates with a server 9 via a router 10 and the Internet 11. A computer 12 can also communicate with the server 9 via the router 10 and the Internet 11.

The meter sensor 5, 5' monitors current, hereinafter referred to as "meter current", supplied to the collection of appliances 4 and the socket sensors 6, 6' monitor currents, hereinafter referred to as "socket currents" supplied to individual appliances 4. In some embodiments, the meter sensor 5, 5' also monitors voltage supplied to the collection of appliances 4 and the socket sensors 6, 6' monitor voltages supplied to individual appliances 4. In particular, the meter and socket sensors 5, 5', 6, 6' each monitor the phase and amplitude of the alternating current and, in some embodiments, the alternating voltage. The phase, or phase difference between the current and the voltage, can be inferred from measurements of current alone or calculated from measurements of current and voltage. The amplitude of the current or voltage can be represented, for example, by a root mean square (RMS) value. Whenever a meter or socket sensor 5, 5', 6, 6' detects a change in amplitude and/or a change in phase of a meter or socket current, it sends a message to the gateway 7. This message includes information, hereinafter referred to as a "reading", about the amplitude and/or about the change in phase of the meter or socket current. If voltages are also monitored, then the message can include information about the amplitude of the voltage, the phase difference between the current and voltage, the frequency of the voltage and/or the power. In turn, the gateway 7 sends a message including the reading to the server 9. The server 9 stores the meter and socket readings, e.g. current and/or voltage readings, received from the gateway 7 in a database 72 (Figure 14) and analyses the data in various ways. For example, the energy consumption of each appliance A₁, 4₂...4_m connected via a socket sensor 6, 6' can be calculated. Furthermore, the energy consumption of each appliance 4_m+1...4_n not connected via a socket sensor 6, 6' may be inferred from a comparison of one or more meter current readings with a set of readings that are characteristic of a particular type of appliance. A user can view the energy consumption and related data by using the computer 12 or a different device, such as a portable device, connected to the server 9. The user can also control actions which the system 1 may carry out in response to particular conditions. For example, a socket sensor 6, 6' may be used to switch off the electrical power to a particular appliance 4 in response to its energy consumption exceeding a certain value in a certain period of time. In this case, the server 9 sends a message to the gateway 7 including information identifying a particular socket sensor 6, 6' and a switching instruction. The gateway 7 then sends a message to the particular socket sensor 6, 6' instructing the socket sensor 6, 6' to switch off the power to the appliance 4. Other actions which the system 1 may catty out include sending messages to alert the user about energy consumption levels, for example via email or short message service (SMS). The server 9 receives information from different gateways 7 associated with different users. The server 9 also performs additional functions such as updating the software in the gateway 7, meter sensor 5, 5' and/or socket sensors 6. Further details of how the system operates will be provided below.

First meter sensor

Referring to Figure 2, the first meter sensor 5 is shown in more detail. The meter sensor 5 has circuitry for measuring a change in phase of the meter current, including a signal conditioner 12, phase lock loop (PLL) 13 and an analogue-to- digital (A/D) converter 14, and circuitry for measuring amplitude of the meter current, including a signal conditioner 15 and an A/D converter 16. The meter sensor 5 may also include circuitry 17 for harvesting power from the meter current and circuitry for generating and sending messages to the gateway 7, including a messaging manager 18 and an isolating transformer 19. In the meter sensor 5 shown in Figure 2, messages are sent to the gateway 7 via the wiring 2. An alternative or additional way of sending messages to the gateway 7 via the wireless communication link 8 may also be provided.

The amplitude and phase-change measuring circuitry 12, 13, 14, 15, 16 and the power harvester 17 are coupled to a section of the wiring 2 by way of a current transformer 20 which is inductively coupled to the live wire 21, i.e., the wire carrying the electrical current from the source 3 to the appliances 4. For example, the current transformer 20 may include two 'C'-shaped ferrite core parts (not shown) which can be clipped together to form a closed core around the live wire, with one of the core parts wound by a wire which is operatively connected to the measuring circuitry. Other ways of inductively coupling to the live wire 21 may also be used, such as by using a differently shaped transformer 20. The transformer 20 and other parts of the meter sensor 5 may be located in the same physical housing or in separate housings. If separate housings are used, they may be connected using insulated wiring. In many domestic and commercial buildings, the live wire 21 and neutral wire 22 are located in separate cables in between the electricity meter and the fuse box, thereby facilitating coupling of the current transformer 20 to the live wire 21 by the user. The power harvester 17 may be coupled to the wiring 2 by a transformer other than the current transformer 20, for example it may have its own transformer.

Referring also to Figures 3 and 4, the phase-change measuring circuitry includes the signal conditioner 12 connected to the PLL 13 which is, in turn, connected to the A/D converter 14. The signal conditioner 12 converts an AC current from the transformer 20 into an AC voltage which acts as the input signal to the phase lock loop 13. The PLL 13 includes three elements connected in series: a phase comparator 23, a loop filter 24 and a voltage-controlled oscillator 25. The phase comparator 23 compares the phases and frequencies of two signals (the input signal from the signal conditioner 12 and a feedback signal from the voltage-controlled oscillator 25) and generates an error signal which is a function of the phase difference and/or frequency difference between the two signals. The loop filter 24 integrates the error signal. The voltage-controlled oscillator 25 generates a signal whose frequency is a function of the integrated error signal and this signal is fed back to the phase comparator 23. The circuit provides a negative feedback loop wherein the feedback signal is varied until it has the same phase and frequency as the input signal, as shown in the region between t_α and t₂ in Figures 4B and 4C. When the PLL 13 is "locked" in this way, any changes in the phase and/or frequency of the input signal result in an integrated error signal from the loop filter 24. Thus, as shown in the region between t_x and t₂ in Figure 4D, the integrated error signal is a dynamic measurement of any changes in frequency and/or phase of the input signal and, ultimately, of the electrical current in the wiring 2. Such frequency and/or phase changes will occur whenever the reactance of the load changes, as shown in Figure 4A, for example when an appliance 4 is switched on or off. The integrated error signal from the loop filter 24 is passed to the A/D converter 14, which converts, with a particular sampling rate, the signal to a digital signal and passes this to the messaging manager 18.

Referring to Figure 2, the amplitude measuring circuitry includes the signal conditioner 15 connected to the A/D converter 16. The signal conditioner 15 filters and/or otherwise conditions the AC current from the transformer 20 and passes a signal to the A/D converter 16. The A/D converter 16 passes a digital signal indicative of the amplitude of the meter current to the messaging manager 18.

Referring to Figures 2, 5 and 6, operation of the messaging manager 18 will now be described. The messaging manager 18 includes, for example, one or more processors, a system clock, volatile and non-volatile memory, a network interface and/or a transceiver. The messaging manager 18 receives signals indicative of the amplitude and the change in phase of the meter current from the current measuring circuitry (step S601). These signals are analysed by a current monitoring module 26 which determines whether there is a change of at least a predetermined amount in the amplitude and/or phase of the meter current (in the latter case, whether the signal differs from zero by at least a predetermined amount) (step S602). The predetermined amounts are chosen so as to ignore most or all changes which are due merely to electrical noise, etc., and not to the effects of any changes in operation of an appliance 4 or in the characteristics of the supplied power. Additionally, filtering will be carried out by the server 9 (Figure 1) as described below. The signals are monitored until a significant change in amplitude and/or phase is detected (i.e., more than the predetermined amount), in which case a message generating module 27 generates a message including information about the amplitude and/or the change in phase of the meter current (step S603). The message also includes information indicating the present time and an identifier of the meter sensor 5. Identifiers of the message type and of the software version of the meter sensor 5 may also be included in the message, as well as any other information which may be useful. The message is formatted using a markup language such as XML, thereby allowing flexibility as regards the number of fields and their contents. The message generating module 27 may also encrypt all or a part of the message. A message sending/receiving module 28 then sends the message to the gateway 7 via the wiring 2 or via the wireless link 8 (step S604). Messages may also be stored in memory for sending at a later time.

The message may be sent using a protocol stack comprising the HomePlug 1.0 protocol or any other suitable power line communication protocol. In this case, the signals are passed through the isolating transformer 19 to the wiring 2 via a direct electrical connection to the live 21 and neutral 22 wires. These connections may be achieved in various ways. For example, an assembly may be provided which can be clipped onto the cable and which includes a screw which can be moved so as to penetrate the insulating sheath of the cable and make electrical contact with the wire. Of course, the assembly must be arranged so that the making of the connections is a safe procedure for the user. Furthermore, the meter sensor 5 may be provided with an indicator such as a light- emitting diode (not shown) to indicate to the user when the electrical connections have been made. Alternatively, the messaging manager 18 may pass signals to the wiring 2 via, for example, a transformer which is inductively coupled to the wiring 2.

The message sending/receiving module 28 may also receive messages from the gateway 7 which include software update information. Such messages are passed to the software updating module 29 which will store and verify the information, and update some or all of the software stored in the meter sensor 5. The meter sensor 5 may also be provided with an alternative or additional way of sending messages to the gateway 7 via the wireless communication link 8. The wireless communication may be carried out using any suitable wireless protocol, such as Wi-Fi, ZigBee or another standard or a proprietary wireless protocol. In this case, the meter sensor 5 will include hardware (not shown), such as a radio transceiver and an antenna, and the message sending/receiving module 28 will include suitable software (not shown).

Referring to Figure 2, the meter sensor 5 includes power-harvesting circuitry 17 which is connected to the current transformer 20 and which includes rectifying and filtering circuitry or other suitable elements arranged to supply a suitable direct current (DC) voltage to power the meter sensor 5. Rechargeable batteries (not shown) may also be provided to act as a power reservoir. The meter sensor 5 may also be provided without power harvesting circuitry 17, in which case power may be obtained by any standard means. The meter sensor 5 may also include other components (not shown), such as indicators to indicate the status of the meter sensor 5 and/or buttons to control various functions such as resetting the meter sensor 5 or connecting to the gateway 7.

First socket sensor

Referring to Figure 7, the first socket sensor 6 is shown in more detail. The socket sensor 6 includes many of the same or similar elements as the meter sensor 5 (Figure 2). In particular, the socket sensor 6 includes a signal conditioner 30, phase lock loop 31 and A/D converter 32 for measuring the change in phase of the socket current, and a signal conditioner 33 and A/D converter 34 for measuring the amplitude of the socket current. All of these elements are generally arranged in the same way as described earlier in relation to the meter sensor 5. The socket sensor 6 has a plug 36 and socket 37 to enable the socket sensor 6 to be plugged into a power socket and to enable an appliance 4 to be plugged into the socket sensor 6. The plug 36 and socket 37 may be integral to the socket sensor 6. In any case, the plug 36 and socket 37 are electrically connected via live 38, neutral 39 and (where used) earth 40 wires. In contrast to the meter sensor 5 (Figure 2), a current transformer 41 is generally located inside the device housing and is permanently coupled to the live wire 38. The current transformer 41 may include a closed ferrite core around the live wire, wound by a wire which is operatively connected to the measuring circuitry. Other ways of coupling to the live wire 38 may also be used, such as, for example, a direct electrical connection. A DC power supply 35 is electrically connected to the wires 38 and 39.

Referring to Figures 7 and 8, the socket sensor 6 also includes a messaging manager 42 which, similar to that in the meter sensor 5 (Figure 2), is connected to the measuring circuitry and is connected via an isolating transformer 43, to the live 38 and neutral 39 wires. In contrast to the meter sensor 5 (Figure 2), the electrical connections to the live 38 and neutral 39 wires are generally internal to the device housing and permanent. The socket sensor 6 may also include software and hardware (not shown) associated with an alternative or additional way of sending messages to the gateway 7 via the wireless communication link 8. The socket sensor 6 also has a switch 44, which is arranged so that it can make or break the part of the electrical circuit formed by the live wire 38, thereby enabling the power supply to an appliance 4 to be switched on or off. The switch 44 includes a solid-state or other type of relay and is operatively connected to and controlled by the messaging manager 42 as described below. The socket sensor 6 need not include a switch 44.

The messaging manager 42 includes a current monitoring module 45, message generating module 46, message sending/receiving module 47 and software updating module 48, which generally function in the same way as described earlier in relation to the meter sensor 5. However, the messages sent in response to a change in amplitude and/or phase of the socket current include additional information indicating the status of the switch 44, e.g., whether the switch is on or off. Furthermore, the message sending/receiving module 47 may also receive messages from the gateway 7 which include instructions to switch on or off the switch 44. Such messages are passed to a switching module 49 which responds by appropriately adjusting the control signal to the switch 44. The switching module 49 also provides information about the status of the switch to the message generating module 46. The socket sensor 6 may also include other components, such as indicators and/or control buttons (not shown). Furthermore, in place of the switch 44, the socket sensor 6 may include circuitry arranged to set the power supply to the appliance 4 to a particular value between zero and a maximum value. Furthermore, the socket sensor 6 may be arranged so that it can be incorporated into an appliance 4. In this case, the socket sensor may not include the plug 36 or socket 37.

Second meter sensor Referring to Figure 9, the second meter sensor 5' is shown in more detail. The meter sensor 5' includes measuring circuitry including two or more sensors 50, 51 and optional processing circuitry. The sensors 50, 51 include a Rogowski coil 50 or other current transformer for measuring current and a capacitive sensor 51 for measuring voltage. The Rogowski coil 50 and capacitive sensor 51 are operatively connected to amplifiers 52 and then to an A/D converter 53. The A/D converter 53 is operatively connected to a processing module 54 which is operatively connected in turn to a communications interface 55. The meter sensor 5' also includes, amongst other things, a power supply 56 such as a power harvester similar to the power harvester 17 used in the first meter sensor 5.

In use, the relatively weak signals from the sensors 50, 51 are fed to the amplifiers 52 and then digitised by the A/D converter 53 before being sent to the processing module 54. The processing module 54 analyses the digital signals and generates a stream of data representing RMS current, RMS voltage, phase difference and voltage frequency. The processing module 54 may also determine the real and reactive power consumption. At least some of these data are uploaded via the communications interface 55 to the server 9, for example in response to a change in the data values.

Rogowski coil

Referring still to Figure 9, the Rogowski coil 50 is an air-cored toroidal coil which can be positioned around the live wire 21 near the electricity meter. The voltage output from the Rogowski coil 50 is given by the following expression: _{γ =} _ ^MNμ_o d_L

2πR dt ^M in which r is the minor radius and R is the major radius of the coil 50, M is the number of major loops which the coil 50 makes around the wire 21 (or vice versa), JV is the number of windings per major loop of the coil 50, μ₀ is the permeability of free space (4π x 10^~7 Hm^"1) and di/ dt is the slew rate of the mains current. It is assumed that no current flows in the coil. The expression shows that the Rogowski coil 50 responds only to changes in current, not, for example, changes in voltage.

This expression can be rewritten as:

V = -^≡^2πfi , Eq. 2

2πR in which /is the frequency of the mains current i, and then as:

V = τιr²Mnμ₀2πfi , Eq. 3 in which n is the density of the windings in turns per metre and the sign of the voltage has been ignored. Thus, the output voltage is proportional to the frequency.

The mutual conductance of the coil 50 and, thus, its sensitivity is then given by the following expression:

in which p is the side-by-side winding compactness factor and φ is the outer radius of the wire used in the coil 50. Values for r, M, p and φ that are practical and provide sufficient sensitivity are chosen. For example, a coil 50 with values of r — 2.62 mm, M = 2.1, p = 0.95, φ = 0.2 and/= 50 Hz gives a measured vale of g_m = 85 μV/A.

The meter sensor 5' uses an air-cored Rogowski coil 50 to reduce measurement errors due to the dependence of the permeability of ferrite cores upon magnetic field. Although the output from the Rogowski coil 50 will be lower than a similar ferrite-cored transformer, it is generally sufficient. Moreover, a Rogowski coil can be wound on a flexible former, enabling production of a sensor which the user can £lex in order to fit around the live wire 21 and so which is easier to install. Alternatively, the meter sensor 5' may use a ferrite-cored transformer with a compensating winding to apply an opposing field and thus keep the magnetic field in the transformer close to zero. However, such a compensating winding requires a large and quickly servoed current.

The Rogowski coil 50 — or the transformer 20 (Figure 2) — can be fitted with conductive contacts on the surfaces where it is split and the meter sensor 5, 5' can include circuitry to detect whether or not the sensor is closed correctly and, if not, to indicate to the user that there is an error, e.g., by means of an indicator light. This can help to avoid any slight openings which will cause erroneous, lower currents to be measured.

Voltage sensor Referring still to Figure 9, the capacitive voltage sensor 51 includes a three-terminal capacitor which can be positioned around the live wire 21. When in position, the capacitive sensor 51 includes a first cylindrical conducting layer (not shown) arranged concentrically around a section of the live wire 21 and a second cylindrical conducting layer (not shown) arranged concentrically around the first conducting layer. The first and second conducting layers may be formed from copper tape. They are electrically insulated from one another, and the exterior and interior surfaces of the capacitive sensor 51 are also insulated. The capacitive sensor 51 and the Rogowski coil 50 may be integrated into a single sensor unit. For example, the first and second conducting layers may be arranged inside the Rogowski coil 50. Other sensor configurations which also provide sufficient coupling to the live wire 21 may also be used.

The second conducting layer is earthed and so the output signal from the first conducting layer is less affected by phase-shifts, for example, due to people touching the sensor. This output signal is proportional to the rate of change of the voltage, άV/ at, in the live wire 21 and also depends upon capacitances in the system. For example, a typical output signal is around 4 V (peak- to-peak) into 1 MΩ. The capacitive sensor 51 uses the body of the meter sensor 5' as its earth. In certain circumstances, this may not have sufficient capacitance to ground for the capacitive sensor 51 to operate. Moreover, people touching or moving close to the meter sensor 5' may change this capacitance and so affect the measurements. Therefore, a balanced capacitive system may be used which includes the capacitive sensor 51 on the live wire 21 and a similar sensor on the neutral wire 22. Other types of voltage sensors may also be used.

Amplifiers

Referring still to Figure 9, the meter sensor 5' includes amplifiers 52a and 52b for the Rogowski coil 50 and the capacitive sensor 51 respectively. The amplifiers 52a and 52b are low-noise operational amplifiers.

The amplifiers 52a and 52b include circuitry to integrate the signals from the Rogowski coil 50 and the capacitive sensor 51. Both of these signals are proportional to frequency and so this integrating circuitry is to avoid the possibility of strong harmonics or high-frequency noise overdriving the A/D converter 53.

Analogue-to-digital converter

Referring still to Figure 9, the A/D converter 53 will now be described in more detail.

The A/D converter 53 has a sample rate which is sufficient to sample a number of harmonics of the mains current. Lower sample rates reduce power consumption and digital signalling processing requirements. For example, the sample rate may be of the order of 1 kHz.

The resolution of the A/D converter 53 is determined by the dynamic range of the mains current to be measured. For example, a resolution of 16 bits may be sufficient. Processing module

Referring to Figure 10, the processing module 54 includes various modules 57, 58, 59, 60, 61, 63. A detector module 57 reads blocks of voltage and/or current data from the interface with the A/D converter and then calls, in turn, each of the various digital signal processing modules 58, 59, 60, 61 with each of the blocks of data. The digital signal processing modules 58, 59, 60, 61 calculate phase, voltage, current and frequency respectively and output these data to memory 62. A main module 63 carries out further analysis of the data and controls sending of the data to the server 9 via the communications interface 55 and the gateway 7. The processing module 54 may include other modules and may carry out other functions. For example, it may check the inputs from the A/D converter 53 for clipping. The various modules are implemented using hardware and/or software. For example, the processing module 54 may include, amongst other things, one or more processors, a system clock, and volatile and non-volatile memory, and the processor(s) may operate under the control of software. The software may employ multitasking and the modules be implemented as threads operating in a shared memory space.

-Phase detection module- Referring to Figures 10 and 11, the operation of the phase detection module 58 will now be described in more detail. Blocks of voltage data and blocks of current data are received and are, firstly, low-pass filtered to below the Nyquist limit and, secondly, decimated, for example, to 220.5 Hz (steps SlOIa and Sl OIb). The decimated voltage and current data are then band-pass filtered to a relatively narrow bandwidth centred on the mains frequency, e.g., a bandwidth of 40-60 Hz (steps S102a and S102b). This band-pass filtering is carried out using an identical digital filter for both the voltage and the current data. The band-pass filtering improves tolerance to noise. The resulting voltage signal will be referred to as v(t) and the resulting current signal will be referred to as a(t).

A copy of the voltage signal v(t) is taken and is passed through a Hubert transformer (step S 103). The Hubert transform includes a finite impulse response filter that shifts the phase of the signal by 90° regardless of frequency. The Hubert- transformed signal will be referred to as q(t). Another copy of the voltage signal v(t) is delayed by the same amount of time as the latency introduced by the Hubert transformer (step Sl 04). This delayed voltage signal will be referred to as i(t).

The delayed voltage signal i(t) is then multiplied by a copy of the current signal a(t) (step S 105a). The resulting signal, m,(t), includes two main frequency components, one at twice the mains frequency, e.g., 100 Hz, and one at 0 Hz. The 0-Hz component of mft) is linearly dependent on the amplitudes of the a(t) and i(t), and also on the phase relationship between a(t) and i(t). In particular, the 0-Hz component of m, reaches a maximum when a(t) matches i(t) in phase, that is when the current and voltage are in-phase. Similarly, the Hilbert-transformed voltage signal q(t) is multiplied by a copy of the current signal a(t), giving rise to a signal, τn_q(t), including 100-Hz and 0-Hz frequency components (step S 105b). In the case of m_q, the 0-Hz component is a maximum when the current is 90° out-of-phase with the voltage.

The 100-Hz components of m,(t) and m_q(t) ate removed by low-pass filtering (steps S 106a and 106b). Identical filters are used for the two signals. The resulting signals, m,_j(t)and mjt), have the same dependence on current amplitude and voltage amplitude and so this dependence can be removed by dividing the signals, i.e., calculating m \_j(t) / ' m Jt) (step S107). Moreover, when m_qf > 0, calculating arctan (m^t) I m JtJ) gives the phase angle between the current and the voltage (step S 108). More generally, the atan2 function is used to calculate the phase angle. The values of phase angle are subject to further low-pass filtering (step S109) to remove far-out phase noise and then stored in the memory 62.

The performance of the phase detection module 58 is limited by noise and by mains-frequency stray hum. Typically, changes of 0.01° are detectable when around 1 A (RMS) is flowing. At larger currents, smaller changes may be detectable. At lower current flows, e.g. around 0.1 A (RMS), the signal-to-noise ratio is worse and the typical phase noise is around 0.2°. The phase detection has a settling time (to 90%) of around 0.5 seconds for a 90° change. This can be reduced at the expense of increased phase noise. The calculations of phase are independent of any voltage and current amplitude changes. Nevertheless, phase changes will be reported if there are sudden current pulses. For example, if a resistive load is turned on 90° through the mains cycle, then a pulse at 90° will be reported before settling to 0°. This is correct because a pulse of current has been drawn out of phase.

-Modifications of the phase detection module-

The phase detection module 58 may use a pure, synthesised sine in place of the measured voltage signal. This synthesised sine is phase-locked to the measured voltage signal by a PLL function that has a loop response time of, for example, several minutes. Such a response time gives good immunity against noise present on the voltage signal. The mains voltage signal generally drives a PLL relatively well compared to the mains current signal, since it is much more constant in shape and amplitude.

Such an approach may also be used in a modification of the analogue phase- measuring circuitry included in the first meter sensor 5 (Figure 2). In particular, the PLL 13 (Figure 3) may be operated in open-loop mode in which the integrated error signal not used to control the voltage-controlled oscillator 24 (Figure 3). Instead, the voltage-controlled oscillator 24 may be phase-locked to the mains voltage signal using a second PLL. Thus, the PLL 13 operates as a phase comparator. Amongst other things, such a modification would enable the meter sensor 5 to detect gradual phase changes which would otherwise be undetectable. For example, some devices, such as washing machines, draw current at gradually varying phase angles as they control their motor speed over several minutes. Of course, the meter sensor 5 would have to include a voltage sensor such as the capacitive sensor 51.

Furthermore, the phase detection module 58 may include a digital delay line (DLL) in place of a Hubert transformer. However, since the mains frequency generally varies by at least ± 0.5 Hz, a fixed length of the DLL cannot create a fixed 90° phase shift. The variation in mains frequency can be compensated for by adjusting the phase data in dependence upon the difference between the mains frequency and a local crystal oscillator, or by locking the sample rate of the entire system to a multiple of the mains frequency.

The phase detection module 58 may operate by using edge detection to detect the phase difference between the current and the voltage. In particular, the time between a zero crossing of the voltage signal and the corresponding zero crossing of the current signal is measured and used to calculate the phase difference. To improve noise immunity, the current and voltage signals are filtered to improve monotonicity, i.e., to reduce the harmonics and/or noise which cause the signals to pass through zero multiple times instead of once. Further immunity to low- frequency noise disturbances can be achieved by separately measuring the relative timing of rising edges, T_πse, and the relative timing of falling edges, T_faih and calculating the mean of T_nsβ and T_jall. This is because, in general, noise which affects T_nsβ will also affect Tr_aII but with opposite polarity. The point of zero-crossing is calculated using linear interpolation between data points on either side of the zero- crossing. This may be required because a reasonable sampling rate of, for example, 44.1 kHz provides a phase resolution of about 0.4° (at 50 Hz) whereas a resolution of about 0.1° is required to detect small inductive loads (~ 0.1 A) in the presence of large resistive loads (~ 50 A). Outliers are removed from the timing measurements. More advanced statistical methods can also be used, e.g., constructing a histogram to determine the modal value. Hysteresis can also be used when determining the point of zero crossing to improve rejection of low-level noise.

-Frequency detection module- Referring to Figure 10, the frequency detection module 61 uses reciprocal counting and averaging, together with sub-sample interpolation, to detect the frequency of the voltage. The frequency detection module 61 operates in a similar way to the edge detection described above, except that it determines times between edges of only the voltage waveform. After band-pass filtering, the voltage signal is hysteresis thresholded, i.e., to qualify as a cycle, the signal must traverse a higher threshold value and then a lower threshold value, in order. The upper and lower threshold values are automatically calculated from the RMS voltage of the signal so that they track the voltage. As well as measuring the time period between successive rising edges, the module 61 also measures the time period between successive falling edges. By taking the mean of these rising and falling periods, the effect of measurement errors is reduced, particularly errors due to low-frequency noise. Further immunity to noise is obtained by calculating the variance of the time periods and discarding any outliers before averaging.

The typical resolution of the frequency detection module 61 is around 10 μHz. For measurements of mains frequency, only a resolution of about 1 mHz is required due to the inherent wander of the mains frequency.

Since the frequency detection module 61 is aware of the exact start and end of a mains cycle, it can generate very fast RMS voltage data, i.e., RMS averages over just one cycle. These data can be provided for use by other modules if required.

-Voltage and Current Measurement Modules-

The voltage and current measurement modules 59, 60 both operate in similar ways. After low-pass filtering, a rolling true RMS average of the current or voltage signal is taken. The averaging is performed using a multipole recursive filter, the feedback coefficient of which can be dynamically adjusted to tailor the response speed. The RMS values are filtered using a second-order Butterworth filter to a bandwidth of 200 Hz. This bandwidth can be changed, although not dynamically. Higher bandwidths will include more energy from harmonics and so give a more accurate representation of the actual power. However, the data will be more susceptible to fluctuations due to noise. The RMS voltage and current data are delayed before being stored in the memory 62. This is for synchronisation with the data from the phase detection module, which includes the slowest part of the system, namely the Hubert transformer. For example, the delay may be set to 0.61 s.

The voltage in the mains wiring 2 will typically vary abruptly by around +2 V (RMS) every second. This is due to the combination of wiring resistance and loads being turned on and off. Thus, long-term averaging is required to provide stable readings. For a nominally 240 V supply, variation over 24 hours is typically between 220 V and 250 V. -Calibration-

The meter sensor 5' is calibrated using values stored in non-volatile memory (not shown). These calibration values are set at the time of manufacture and/or installation. The calibration values may also be received from the server 9 via the gateway 7 and communications interface 55, so that the sensor 5' can be remotely calibrated, for example based on analysis of previous measurements sent to the server 9. Calibrations values for voltage, current, frequency and phase offset may be provided.

-Main module-

The main module 63 may calculate real power (P = S cosθ) and reactive power

(Q = S sinθ) from the phase angle, θ, of the fundamental frequency (e.g., 50 Hz) and the apparent power, S = V_RMS xI_RMS.

This standard method of calculating real and reactive power provides accurate results for linear loads, but not for devices with extremely non-linear voltage- current characteristics. For example, a triac dimmer switch draws current in short bursts every mains cycle. In this case, the phase detection module 58 correctly records the phase angle of the fundamental frequency, but the reactive power calculated from this phase angle using the standard method is misleading. In particular, it will indicate that the switch is acting as a reactive load, i.e., drawing a period of negative current when a positive voltage is present, and vice-versa. However, in fact, the switch only draws a positive current when a positive voltage is present, and vice-versa.

Therefore, another method of calculating real and reactive power that is more accurate for non-linear loads may be used. In particular, an additional module (not shown) is provided to directly calculate real power, P, by summing V.I for a plurality of sample points along the voltage (V) and current (T) waveforms. As in the standard method, apparent power, S, is calculated as V_RMS x I_RMS and, thus, reactive power, Q, can be calculated from S²—P^2jrQ^. The meter sensor 5' may provide power data calculated using both of the methods, thus enabling the appliance detection algorithms used in the server 9 to discriminate more effectively between truly reactive loads, such as motors, and loads which have non-zero phase angle but are non-reactive, namely non-linear loads such as triac dimmer switches.

The main module 63 also performs similar functions to the messaging manager 18 included in the first meter sensor 5. For example, the main module 63 monitors the data and, if it detects a change, it sends a message to the server 9 which includes information about the changed data. However, in the second meter sensor 5', the main module 63 monitors the amplitude of the current, the amplitude of the voltage, the phase difference between the current and the voltage, the frequency of the voltage, the real power and/or the reactive power. Thus, the message can be sent in response to a change in any of these quantities and can include information about any of these quantities. For example, the message may be sent in response to a change in the amplitude of the current or the phase difference between the current and the voltage, or it may be sent in response to a change in the real or reactive power.

Second socket sensor

A second socket sensor 6' (Figure 1) includes many of the same components as the meter sensor 5', namely the Rogowski coil 50, the amplifiers 52, A/D converter 53, processing module 54 and communications interface 55 (see Figure 9). These elements generally operate in the same way as described earlier. The differences between the second socket sensor 6' and the second meter sensor 5' are similar to the differences between the first socket 6 sensor and first meter sensor 5. For example, the socket sensor 6' has a plug and socket to enable it to be placed into a mains electricity circuit. The current sensor, e.g., the Rogowski coil 50, is positioned inside the device housing and is permanently coupled to the live wire. The capacitive sensor 51 is replaced by a sensor with a direct, conductive connection to the mains wiring and which is also located insider the device housing. The socket sensor 6' may also include a switch to control the power supply to an appliance 4 in response to messages received from the server 9, as described earlier in relation to the first socket sensor 6.

Gateway Referring to Figure 12, the gateway 7 is shown in more detail. The gateway 7 includes one or more processors 64, memory 65, network interface 66 and power line communication interface 67, operatively connected to each other by a bus 68. The processor(s) operate under the control of software. The power line communication interface 67 is arranged to send and receive messages via the wiring 2 to and from the meter sensor 5, 5' and socket sensors 6, 6'. The messages may be sent or received using a protocol stack comprising the HomePlug 1.0 protocol or any other suitable power line communication protocol. The gateway 7 includes a plug to enable it to be plugged into a power socket, thereby establishing the electrical connection with the wiring 2. Such a connection is also used for the power supply 69 of the gateway 7. The gateway 7 may also include software and hardware (not shown) associated with an alternative or additional way of communicating with the meter and socket sensors 5, 5', 6, 6' via the wireless communication link 8. The network interface 66 includes a wired or wireless local area network interface, which is arranged to send and receive messages via the router 10 to and from the server 9. These messages are sent and received using

HTTP and TCP/IP protocols or any protocol or protocol stack which is suitable for communication with the server 9.

The gateway 7 is arranged to pass messages between the meter sensor 5, 5' or socket sensors 6, 6' and the server 9. Thus, the gateway 7 converts between the protocol stack related to the power line communication network and/or the wireless communication link 8 and the protocol stack related to the wired or wireless local area network. In addition, the gateway 7 may edit the headers and/or contents of any messages which are being passed, encrypt and/or decrypt messages, and/or it may combine a message with one or more other messages. However, analysis of meter or socket current readings etc. is generally performed by the server 9, as described below. When a message is received from the meter sensor 5, 5', the gateway 7 may include an identifier of the gateway 7 in the message, may establish a TCP/IP connection with the server 9 and may send the message to the server 9 by using e.g. a HTTP POST method. In the event that a connection with the server 9 cannot be established, the gateway 7 may also store one or more messages in memory 65 for sending at a later time. The gateway 7 may also carry out a corresponding process when passing messages from the server 9 to the meter or socket sensors 5, 5', 6, 6'. In this case, the TCP/IP connection may be initiated by the server 9 or, alternatively, the gateway 7 may periodically connect to the server 9 and may receive any messages from the server 9 by using e.g. a HTTP GET method. Messages received from the server 9 may also be stored in memory 65 for sending to a sensor 5, 5', 6, 6' at a later time. The gateway 7 may also enable the user to change settings stored in the gateway 7, for example by connecting to a configuration web page. The gateway 7 can also receive messages from the server 9 including software update information and store, verify and use the information to update some or all of the software stored in the gateway 7.

Energy monitoring and control

Referring to Figure 13, an example of energy monitoring and control in accordance with the present invention is shown. At step SlOOl, a socket sensor O₁, O₁' detects a change in amplitude and/or phase of the socket current and, at step S1002, it generates a message which includes an identifier (Device_ID) of the socket sensor 6_{l 5} O₁', an identifier (Message_ID) of the message type, the status (Switch_Status) of the switch, the amplitude of the socket current, the change in phase of the socket current, and the time. At step S1003, the message is sent from the socket sensor O₁, O₁' to the gateway 7, which establishes a connection to the server 9 at step S1004 and sends the message to the server 9 at step S1005, the message including an identifier (Gateway _ID) of the gateway 7. At step S1006, the meter sensor 5, 5' detects a change in amplitude and/or phase of the meter current and, at step S 1007, it generates a message which includes an identifier of the meter sensor 5, 5', an identifier of the message type, the amplitude of the meter current, the change in phase of the meter current, and the time. At step S1008, the message is sent from the meter sensor 5, 5' to the gateway 7. At step S 1009, the gateway 7 attempts to establish a connection to the server 9 but this attempt is unsuccessful because, for example, the server 9 is busy. Therefore, at step SlOlO, the gateway 7 stores the message and, at step SlOI l, reattempts to establish a connection to the server 9 and, after successfully doing so, sends the message, including the identifier of the gateway 7, to the server 9 at step S1012. At steps S1013 to S1017, a second socket sensor 6₂, 6₂' detects a change in the socket current and sends a message via the gateway 7 to the server 9. At step SlOl 8, the server 9 determines that the second socket sensor 6₂, 6₂' should be switched. Therefore, at step S1019, the server 9 sends a message to the gateway 7 including an identifier of the gateway 7, an identifier of the socket sensor 6₂, 6₂' to be switched and a switching instruction. At step Sl 020, the gateway 7 sends a message to the socket sensor 6₂, 6₂' including an identifier of the socket sensor 6₂, 6₂' and the switching instruction. At step S1021, the socket sensor 6₂, 6₂' switches.

Server

Referring to Figure 14, the server 9 is shown in more detail. The server 9 includes a web server module 70, a data storage module 71, a database 72, a data processing module 73, a user interface module 74, a monitoring module 75 and a device software updating module 76. The server 9 may include one or more server computers and/or hardware such as processor(s), memory, storage and network interface(s).

The web server module 70 sends information to and receives information from the gateway 7 (Figure 1), the computer 12 (Figure 1), and other devices (not shown) such as a user's mobile telephone, an administrator computer and an energy company server. The web server module 70 may also catty out other functions, such as processing of messages, encryption or decryption of messages, access control, etc.

Messages from the gateway 7 (Figure 1) including readings from meter and/or socket sensors 5, 5', 6, 6' (Figure 1) are passed to the data storage module 71, which stores the readings in an appropriate location in the database 72 dependent, for example, on the identifier of the gateway 7 included in the message. The readings may include readings of current amplitude, change in phase, voltage amplitude, phase difference between the current and voltage, frequency and/or real and reactive power.

The data processing module 73 reads data from the database 72, analyses the data in various ways and stores the results of the analysis in the database 72. If information about the phase difference between the current and voltage is not received, the data processing module 73 can calculate this phase difference by combining a reading of a phase change with previous readings of phase changes. Readings may also be filtered and/or averaged. Averaging over short time periods, e.g., one or more power line cycles, may be used, for example, when identifying appliances. If frequency data is not received, averaging over longer time periods may be used, for example, to determine frequency drift in the power being supplied, e.g., due to peak demand in the electricity grid. A change in amplitude, phase difference or power can also be calculated by comparing a reading with a previous reading. If voltage amplitude data is not received, the amplitude of the voltage can be taken to have a constant value determined by the standard supply voltage, e.g., 120 V, 220 V or 240 VAC. If power data is not received, values of time, phase difference and amplitude for a particular appliance 4 or collection of appliances 4 can then be used to calculate power consumption. Power consumption data can then be used to calculate energy usage in a specified period of time. The data processing module 73 "learns" the typical energy usage of an appliance 4 (Figure 1). In particular, vectors comprising values of time, phase difference and amplitudes for a particular appliance 4 are built up over a period of time to produce a typical operating envelope for the appliance 4. This information about typical energy usage is stored in the database 72 and may be shared between different users. The database 72 may also store typical energy usage information obtained from other sources such as, for example, from the manufacturer of the appliance 4.

The user can assign a particular appliance 4 (Figure 1) to a particular socket sensor 6 (Figure 1) by using a web interface provided by the user interface module 74. An appliance 4 may be identified by inputting the name and type of the appliance 4 and/or selecting the appliance 4 from a predetermined list. Any such information is stored in the database 72. Socket sensors 6, 6' may be labelled so that they can be easily identified by the user. Thus, a user can obtain typical energy usage data for a plurality appliances 4 by successively connecting these appliances 4 to a single socket sensor 6, 6'. The learning process may also be interactive, with the user prompted to switch an appliance 4 off or on. Such an interactive learning process may also be used to obtain typical energy usage data for appliances 4 which are only connected via the meter sensor 5, 5' (Figure 1), such as lighting, central heating systems, etc.

The data processing module 73 uses typical energy usage data from the database 72 in various ways. For example, a typical operating envelope can be compared with new data to detect a potential malfunctioning of an appliance 4 (Figure 1). Furthermore, a typical operating envelope can be used to automatically identify devices which have been connected via either a meter or socket sensor 5, 5', 6, 6' (Figure 1). Particularly in the case of data originating from the meter sensor 5, 5' each reading will be associated with energy usage by one or more of a plurality of appliances 4. In this case, the data processing module 73 will compare one or more readings with typical energy usage data for a series of devices in order to attempt to assign with a reasonable degree of certainty a particular reading to a particular appliance 4. The assignment or classification process may also take into account other factors such as correlations with readings from socket sensors 6, 6' and any information provided by the user. Generally, this analysis is performed heuristically.

The user interface module 74 may also provide various other services to the user via a web interface. These include inputting basic profile information, such as type of house, name of energy company, etc., viewing and interpreting energy consumption data, and recording instructions to be carried out in response to particular power consumption levels or patterns.

Referring to Figures 15A and 15B, examples of energy usage information provided by the user interface module 74 in the form of screenshots are shown. The screenshot in Figure 15A shows energy usage by different categories of appliance 4 (Figure 1) in a period of seven days. The user may also choose to view total energy usage, energy usage by individual appliances 4 or categories of appliances 4 and/or energy usage in different time periods. Information may also be presented in other graphical or tabular forms. Other measures of energy usage such as financial cost or environmental (CO₂) cost may also be used. The tariff period (e.g., peak or off- peak) during which energy has been consumed may also be shown. The user can also choose to have information sent periodically to an email address or to an energy company. Furthermore, energy usage data can be compared with corresponding data for different time periods, for different homes or buildings or for alternative, e.g., more efficient, appliances 4. For example, the screenshot in Figure 15B shows a comparison of energy usage in a particular month with corresponding data for the previous year. The user can also view or choose to receive additional information such as, for example, methods of running appliances 4 more efficiently, financial benefits of replacing particular appliances 4 and/or opportunities to save money by switching to a different tariff or a different energy company. Data can also be provided to energy companies for planning purposes, e.g., allowing energy companies to vary tariffs so as to encourage off-peak energy consumption.

The user interface module 74 also enables the user to record instructions specifying actions to be carried out in response to particular conditions. Examples of these actions include switching on or off a socket in response to particular levels of energy usage, at particular times, e.g., when off-peak tariffs apply, or in response to particular patterns of energy usage by other appliances 4 (Figure 1), e.g., so that peripheral devices will switch on or off when a main device is switched on or off. Sockets may also be switched on or off in response to dynamic demand regimes applied by an energy company, e.g., temporarily turning off a fridge or a battery charger at times of peak demand. Other examples include alerting the user by email or SMS, for example, about high, low or abnormal energy usage. The monitoring module 75 compares new energy usage data in the database 72, and other parameters, such as the time, with the conditions recorded in the instructions and carries out the corresponding action whenever the conditions are satisfied. For example, the monitoring module 75 may generate a message instructing a particular socket sensor 6 to switch off. This message will be passed to the web server module 70, which will send the message to the gateway 7 (Figure 1) as described earlier.

Finally, the device software updating module 76 monitors the software versions of meter sensors 5, 5' socket sensors 6, 6' and gateways 7 (Figure 1) present in the system 1, for example by reading software version identifiers included in the messages from the devices. When newer versions of the software are available, the device software updating module 76 may cause the web server module 55 to send the new software to the device in a series of messages.

It will be appreciated that many other modifications may be made to the embodiments hereinbefore described.

For example, there may be no meter sensor 5, 5' included in the system 1 or there may be no socket sensors 6, 6' included in the system 1. There may also be more than one meter sensor 5, 5' included in the system 1. There may also be more than one appliance 4 connected via one or more socket sensors 6, 6'.

Furthermore, the network and devices via which the gateway 7 communicates with the server 9 may differ. For example, the network may include an Ethernet local area network, a wireless local area network and/or a mobile telecommunications network. Additional network devices may also be present. There may be no router 9 included in the system 1 and/or the gateway 7 and server 9 may be connected to the same network. The computer 12 may not be included or it may communicate with the server 9 via a different network.

The sensors 5, 5', 6, 6' need not send information to the server, but may store the information for retrieval at a later time, e.g., by the user connecting a memory stick or other storage device to the sensor 5, 5', 6, 6'. Thus, the sensors 5, 5', 6, 6' need not include a sending means, e.g., need not include a network interface.

An appliance 4 may also be replaced by a device which is a generator of electricity, such as, for example, a solar panel or wind turbine. In this case, one or more of the sensors 5, 5', 6, 6' may be replaced by special sensors which are capable of monitoring power generation.

A display device may also be provided which receives messages from the server 9 via the router 7 and the wiring 2 and/or the wireless link 8, the messages including pre-selected information and alerts, and which displays this information on an LCD or other type of screen.

Monitoring of polyphase electrical power can also be performed by using one or more sensors 5, 5', 6, 6' arranged to measure the alternating current in a plurality of live wires.

Other types of devices, such as gas and water meters, and fire and intruder alarms, may also send information to and be controlled by the server 9.

Any features described in relation to particular embodiments may also be included in any suitable manner in any other embodiments. For example, the second meter sensor 5' may include any suitable features from the first meter sensor 5 and vice versa.

Claims

1. A device comprising: means for measuring amplitude, phase and/or change in phase of an alternating current in a section of wiring; means for generating a message in response to a change in the amplitude and/or a change in the phase of the alternating current, the message including information about the amplitude, the phase, and/or the change in phase of the alternating current; and means for sending the message to a server.

2. A device according to claim 1, wherein the generating means is configured to include in the message information about the time when the change in amplitude and/or the change in phase of the alternating current occurred.

3. A device according to claim 1 or 2, wherein the generating means is configured to include in the message information identifying the device.

4. A device according to any preceding claim, wherein the sending means is configured to send the message to a gateway via the wiring and according to a power line communication protocol or via a wireless communication link.

5. A device according to any preceding claim, wherein the measuring means comprises a phase lock loop configured to generate an output signal in response to a change in phase of an alternating current input signal.

6. A device according to claim 8, wherein the phase lock loop comprises: means for generating an error signal which is dependent on the difference between an input signal and a feedback signal; means for integrating the error signal; and means for generating the feedback signal with a frequency which is dependent on the integrated error signal; wherein the phase lock loop is configured so that the feedback signal varies until it has the same phase and frequency as the input signal; wherein the output signal is the integrated error signal; and wherein the device further comprises: means for converting the output signal from an analogue to a digital signal.

7. A device according to any one of claims 1 to 6, wherein the measuring means is configured to measure the phase difference or change in phase difference between the alternating current and alternating voltage in the wiring.

8. A device according to claim 7, wherein the measuring means is further configured to measure the frequency and/or the amplitude of the alternating voltage, and, optionally, the message generating means is configured to include the information about the frequency and/or the amplitude of the alternating voltage in the message.

9. A device according to claim 7 or 8, wherein the measuring means comprises a non-contact sensor, for example a capacitive sensor, configured to sense the alternating voltage.

10. A device according any one of claims 7 to 9, wherein the measuring means comprises a coil, for example a Rogowski coil, configured to sense the alternating current.

11. A device according to any one of claims 7 to 10, wherein the measuring means is configured to calculate the phase difference between the current and the voltage by digital signal processing.

12. A device according to claim 11, wherein the measuring means is configured to apply a Hubert transformation to a first copy of a voltage signal, determine a first product which is the product of the Hilbert-transformed first copy of the voltage signal and a first copy of a current signal, determine a second product which is the product of a second copy of the voltage signal and a second copy of the current signal, low-pass filter the first and second products, and determine the arctangent of the quotient of the low-pass filtered first and second products.

13. A device according to any one of claims 7 to 12, wherein the measuring means is configured to determine real and reactive power in the section of wiring, and the message generating means is configured to generate a message in response to a change in the real and/or the reactive power, the message including information about the real and/or the reactive power.

14. A device according to claim 13, wherein the measuring means is configured to determine the apparent power from the amplitude of the current and the voltage.

15. A device according to claim 14, wherein the measuring means is configured to determine the real and the reactive power from the apparent power and the phase difference between the current and the voltage.

16. A device according to claims 14 or 15, wherein the measuring means is configured to determine the real power by multiplying the current and the voltage waveforms, and to determine the reactive power from the real power and the apparent power.

17. A device according to any preceding claim, further comprising: switching means; and means for controlling operation of the switching means in response to receiving a message from the server including an instruction about operation of the switching means.

18. A device according to claim 17, wherein the generating means is configured to include in the message to the server information about status of the switching means.

19. A device comprising: a sensor configured to measure amplitude, phase and/or change in phase of an alternating current in a section of wiring; a controller configured to generate a message in response to a change in the amplitude and/or a change in the phase of the alternating current, the message including information about the amplitude, the phase and/or the change in phase of the alternating current; and a network interface configured to send the message to a server.

20. A server configured to: receive a message from a device, the message generated in response to a change in amplitude and/or a change in phase of alternating current in a section of wiring and the message including information about the amplitude, the phase and/or the change in phase of the alternating current; and determine, from the information about the amplitude, the phase and/or the change in phase of the alternating current, the energy usage of one or more electrical devices powered via the section of wiring.

21. A server according to claim 20, wherein the message includes information about the amplitude of the voltage, and the server is configured to determine the energy usage of the one or more electrical devices from the information about the amplitude of the voltage.

22. A server according to claim 20 or 21, wherein the message includes information about the time when the change in amplitude and/or the change in phase of the alternating current occurred and wherein the server is configured to determine the energy usage of the one or more electrical devices from the information about the time when the change occurred.

23. A server according to any one of claims 20 to 22, configured to calculate the phase difference between voltage and current in the section of wiring by comparing the information about the change in phase of the alternating current with information about the change in phase of the alternating current at one or more earlier times.

24. A server according to any one of claims 20 to 23, configured to store an energy usage profile of one or more of the electrical devices, the energy usage profile including information about the amplitude and/or the phase of the alternating current at one or more times.

25. A server according to any one of claims 20 to 24, configured to assign the change in amplitude and/or the change in phase of the alternating current to one or more of the electrical devices by determining whether the change in amplitude and/or the change in phase of the alternating current at one or more times matches any of a plurality of energy usage profiles of electrical devices.

26. A server according to claim 25, configured to read one or more of the plurality of energy usage profiles of electrical devices from a database.

27. A server according to any one of claims 20 to 26, configured to determine whether energy usage by one or more of the electrical devices matches any of a predefined plurality of energy usage conditions and, in response to matching the condition, send a message to a device comprising switching means, the message including an instruction about operation of the switching means, and/or send a message to a user.

28. A system comprising: one or more devices according to any one of claims 1 to 19; and a gateway; wherein the gateway is configured to receive the messages from the one or more devices and to send the messages from the one or more devices to the server.

29. A system according to claim 28, further comprising: a server according to any one of claims 20 to 27; wherein the gateway is configured to receive the messages from the server and to send the messages from the server to the one or more devices.

30. A system according to claim 28 or 29, wherein the gateway is configured to store the messages from the one or more devices and/or the messages from the server for sending at a later time.

31. A method comprising; measuring amplitude, phase and/or change in phase of an alternating current in a section of wiring; generating a message in response to a change in the amplitude and/or a change in the phase of the alternating current, the message including information about the amplitude, the phase and/or the change in phase of the alternating current; and sending the message to a server.

32. A method according to claim 31, wherein the message further includes information about the time when the change in the amplitude and/or the change in phase of the alternating current occurred.

33. A method according to claim 31 or 32, comprising measuring the phase or change in phase of the alternating current by phase locking.

34. A method according to any one of claims 30 to 33, comprising measuring the phase difference or change in phase difference between the alternating current and alternating voltage in the wiring.

35. A method according to any one of claims 30 to 34, comprising measuring the frequency and/or the amplitude of the alternating voltage, and, optionally, including the information about the frequency and/ or the amplitude of the alternating voltage in the message.

36. A method according to any one of claims 30 to 35, comprising calculating the phase difference between the current and the voltage by digital signal processing.

37. A method according to claim 36, comprising applying a Hubert transformation to a first copy of a voltage signal, determining a first product which is the product of the Hilbert-transformed first copy of the voltage signal and a first copy of a current signal, determining a second product which is the product of a second copy of the voltage signal and a second copy of the current signal, low-pass filtering the first and second products, and determining the arctangent of the quotient of the low-pass filtered first and second products.

38. A method according to any one of claims 30 to 37, comprising determining real and reactive power in the section of wiring and generating a message in response to a change in the real and/or the reactive power, the message including information about the real and/or the reactive power.

39. A method according to any one of claims 30 to 38, further comprising controlling operation of switching means in response to receiving a message from the server including an instruction about operation of the switching means.

40. A method comprising: receiving a message from a device, the message generated in response to a change in amplitude and/or a change in phase of alternating current in a section of wiring and the message including information about the amplitude, the phase and/or the change in phase of the alternating current; and determining, from the information about the amplitude, the phase and/or the change in phase of the alternating current, the energy usage of one or more electrical devices powered via the section of wiring.

41. A method according to claim 40, wherein the message includes information about the amplitude of the voltage, and the method comprises determining the energy usage of the one or more electrical devices from the information about the amplitude of the voltage.

42. A method according to claim 40 or 41, comprising storing an energy usage profile of one or more of the electrical devices, the energy usage profile including information about the amplitude and/or the phase of the alternating current at one or more times.

43. A method according to any one of claims 40 to 42, comprising assigning the change in amplitude and/or the change in phase of the alternating current to one or more of the electrical devices by determining whether the change in amplitude and/or the change in phase of the alternating current at one or more times matches any of a plurality of energy usage profiles of electrical devices.

44. A method according to any one of claims 40 to 43, comprising determining whether energy usage by one or more of the electrical devices matches any of a predefined plurality of energy usage conditions and, in response to matching the condition, sending a message to a device comprising switching means, the message including an instruction about operation of the switching means, and/or sending a message to a user.

45. A computer program comprising instructions which when executed by a data processing apparatus perform a method according to any one of claims 31 to 44.

46. A computer-readable medium storing a computer program according to claim 45.