WO2009007459A2

WO2009007459A2 - Method for power supply control

Info

Publication number: WO2009007459A2
Application number: PCT/EP2008/059141
Authority: WO
Inventors: Denis Waucampt; Jean-Philippe Vanhulst
Original assignee: Cherokee Europe S.C.A.
Priority date: 2007-07-11
Filing date: 2008-07-11
Publication date: 2009-01-15
Also published as: WO2009007459A3

Abstract

The present invention relates to the field of methods for supplying power as used for example in telecommunication systems.

Description

METHOD FOR POWER SUPPLY CONTROL

Field of the invention [0001] The present invention relates to the field of methods for supplying power as used for example in telecommunication systems.

State of the art [0002] In telecommunication systems used for various applications such as mobile telephony and triple play

(voice/data/image) the energy is generally provided by a power system (see Fig.l) combining several AC/DC power supplies connected in parallel on both AC and DC sides. A monitoring unit is generally placed into the same power system, gathering alarms and other parameters . The monitoring generally also enables active control of each power supply. [0003] It is of common knowledge that for improvement of the power conversion efficiency, it is preferable to activate only the number of power supplies that is necessary to provide the power at a given time and to keep the other power supplies out of operation. This is due to the fact that power supplies have a significant consumption at no-load and that power conversion stages are optimized on the upper range of their rated power. The use of this method is facilitated when batteries are connected on the DC side, allowing unexpected peak load demand. [0004] Several ways of selecting the power supplies to be placed in OFF mode are presently used, according to the number of units optimized for a given power level. One method is to assign a permanent list of priority order for turning off power supplies as a function of the load. In this way the power supplies which are the last ones in the priority list for turning off will show higher ageing than those which are in first priorities, leading to accelerated ageing of the overall power system. Another method is to assign turn-off priorities cyclically. Another method is to assign turn-off priorities in a random way. The two last methods are clearly more optimized in terms of ageing than the first one. However, in case some of the power supplies of a power system are replaced for maintenance reasons, these methods lose part of their interest.

Aims of the invention

[0005] The present invention aims to provide a method for monitoring the ageing of power supplies working in parallel, and particularly when a subset of power supplies is replaced for maintenance reasons.

Short description of the drawings

[0006] Fig. 1 represents a general view of an AC/DC power system feeding an application with battery back-up

(prior art) .

[0007] Fig. 2 illustrates power supply ageing as a function of time, in an example of ON/OFF control after a load variation, for four power supplies.

Summary of the invention

[0008] The present invention aims to provide a method for defining, by means of a monitoring unit employing electronics and/or software technologies, the turn-off/turn-on priorities of power supplies included in a same system, comprising the steps of

— measuring the instantaneous power consumption of the load or application and evaluating power consumption parameters,

— calculating, according to said power consumption parameters, the number of power supplies to turn- off or turn-on in order to optimize the power conversion efficiency, — measuring and recording for each power supply, the history of a number of ageing parameters such as starting dates and stopping dates, cumulated durations of functioning, internal temperature, output power stresses, input voltage stresses, - evaluating from the previous recordings, the degree of ageing of each power supply,

— assigning, at each time interval Ti, to each power supply a level of priority based on the ageing, such as the level of priority is increasing with the degree of ageing of power supply,

— accordingly to the number of power supply to turn- off or turn-on in order to optimize said power conversion efficiency, turning-off power supplies with the highest level of priority or turning-on power supplies with the lowest level of priority.

[0009] Preferably, the degree of ageing of each power supply is evaluated at first order by application of the Arrhenius law for the action of ambient temperature on effective on-time duration and at second order by further correcting the effective on-time duration in regards to local stresses such as input voltages stresses or output power stresses. [0010] Preferably, the method further comprises the step of turning-on and turning-off, at each time interval

Ti, power supplies so that the power supplies running, after this step, are the ones with the lowest priority. [0011] Preferably, the value of Ti is randomly determined.

[0012] More preferably, the value of Ti is identical for all the values of i.

[0013] Preferably, the value of Ti is superior to 24h.

[0014] Preferably, the value of Ti is superior to

12h.

[0015] Preferably, the value of Ti is superior to

Ih. [0016] Preferably, the value of Ti is superior to 1 sec .

[0017] Preferably, all the power supplies have the same specifications.

[0018] Preferably, the power (consumption parameters are the average power level and the peak power level, within a given period of time, defined from acquired data of the slow rate power consumption variations of the application .

[0019] Preferably, the measuring and recording are performed for each power supply, either separately inside each power supply or, totally or partially, inside the monitoring unit.

[0020] Preferably, the degree of ageing of each power supply is stored in the corresponding power supply. [0021] Preferably, the evaluation from the previous recordings is performed, either separately inside each power supply or, totally or partially, inside the monitoring unit. Detailed description of the invention

[0022] The present invention aims to provide a monitoring method to improve life time and mean time between failure (MTBF) , while optimizing the efficiency of power conversion of several power supplies operating in parallel, in order to deliver power to an electrical or an electronic application.

[0023] The present invention provides an optimized solution for both efficiency of power conversion and for life time and mean time between failure (MTBF) optimization, combined with a method for turn-off that takes into account the ageing of each power supply. [0024] This control method is intended to be used mostly but not restrictively in various telecommunication applications employing AC/DC power supplies with battery back-up connected to the DC side.

[0025] The method also applies to applications employing AC/DC power supplies without battery back-up and to applications employing DC/DC power supplies with or without battery back-up.

[0026] When working in parallel on the same output power DC bus, all the power supplies contribute in supplying current to the load. [0027] It is generally preferred that all the power supplies have the same specifications.

[0028] It is generally preferred that all the power supplies evenly contribute to the load current. [0029] It is of common practice to balance the output current of all the power supplies by a current sharing control circuit.

[0030] The power supplies share a common signal being an image of the average value of the output currents of each power supplies. [0031] Each power supply is than controlled in such a way that its output current converges to that average value .

[0032] Power supplies, as all electronics circuits, have a limited life time.

[0033] In the same operating conditions, all power supplies - having the same specifications - will have the same life time within tolerances, equal to the life time of its weaker component (e.g. an electrolytic capacitor drying out with temperature and going out of tolerances) .

[0034] The ageing is mainly linked to temperature, but it can also be linked to external stresses like output power stresses, input power stresses, AC mains over- voltages, mechanical vibrations, etc. [0035] The evaluation of the degree of ageing takes into account at first order the effect of temperature on the life time, according to the Arrhenius law (for electrolytic capacitors and for fans, the life time is decreased by a factor 2 for each increase of 10 degrees Celsius of the ambient temperature), so by applying a major multiplicative factor on the effective on-time duration regarding to a common reference ambient temperature (e.g. 25 degrees Celsius) . [0036] Furthermore, corrections to the calculation of the ageing of each power supply can be applied.

[0037] These corrections are based on recordings of other stresses than temperature, such as output power peaks or input voltages peaks (amplitude and occurrences) , that can increase the stress of specific sub-circuits of the power supply and in that way affect the life time.

[0038] The invention relates to a method to control, by means of a monitoring unit employing electronics and/or software technologies, the turn-off priorities of power supplies included in a same system, comprising the steps of - measuring the instantaneous power consumption of the load (application) and evaluating significant power parameters such as (but not limited to) for example the average power level and the peak power level, within a given period of time, defined from acquired knowledge of the slow rate power consumption variations of the application.

- calculating, according to these power consumption parameters, the number of power supplies to turn-off in order to optimize the power conversion efficiency,

- measuring and recording for each power supply, either separately inside each power supply or, totally or partially, inside the monitoring unit, the history of a number of parameters such as (and not restrictively) , starting dates and stopping dates, cumulated durations of functioning, internal temperature, output power, input voltage,

- evaluating from the previous recordings, either separately inside each power supply or, totally or partially, inside the monitoring unit, the degree of ageing of each power supply,

- when all power supplies are running and one or more have to be turned-off in order to increase efficiency because of reduced load, assigning the turn-off priorities with highest priority for turn-off on the higher aged power supplies (illustrated in Fig.2),

- at steady-state load, reassigning at regular time intervals T₁ the turn-off states with highest priority for turn-off on the higher aged power supplies (Fig.2) - when more than one power supply has to be either turned-off or turned-on after a load variation or after a given time T₁, these power supplies will be controlled by the monitoring unit in such a way that they change their ON/OFF state one after the other, with an interval of time At₁ (t_± in the priority document) between each change of state that is significantly lower than T₁ (e.g. T₁ is one day, At₁ ( t_x in the priority document) is one minute) . This has to be applied in the case represented by Fig.2 (although the time scale of Fig.2 does not allow representing it) .

[0039] The degree of ageing of each power supply is stored in the corresponding power supply. [0040] Preferably, a additional step of the method is the evaluation, as a function of the last temperature recordings and of the long term temperature history, of a possible reduction of the number of power supplies running, in order to limit overheating of the power supplies remaining in the "on" state, and so optimize their life time and MTBF.

[0041] If one or more power supplies have to be turned-on in order to respond to an increasing demand of power, assigning the turn-on priority to the lower aged power supplies.

[0042] If one or more power supplies are added by an operator to the system, due to a structural increasing demand of power (e.g. increasing number of users of the application) , the newly added power supplies enters into the turn ON/OFF strategy, taking into account the age of the newly introduced power supplies and assigning a level of priority corresponding to their ages relatively to the ages of the other power supplies.

[0043] Figure 2 elaborates more in detail an example of ON/OFF control for four power supplies according to the present invention after a load variation.

[0044] Before time ti, all four power supplies are needed to provide the power required by the application. [0045] In this example, all the units share the load current at the same value and have the same ambient temperature. As a result all four power supplies are showing the same ageing slope. [0046] At time to, the ambient temperature reduces, for example because of the starting of a heat exchanger controlled by the application. As a result the ageing slope of all four power supplies is reduced. [0047] At ti the application reduces the load requirement (for example because of a lower demand of transactions at night) and the monitoring controls the turn-off of two power supplies in order to optimize the efficiency of the power conversion. [0048] In this example, it is assumed that all other conditions (like temperature, etc) remain the same, so after ti, the ageing slope of the two power supplies remaining operational increases slightly, because of increased power level per power supply remaining in ON state . [0049] Simultaneously, the ageing of the two power supplies turned off remains constant.

[0050] At t₂, no change occurs in the ON/OFF states, since the two power supplies in OFF mode are still those showing the highest age. [0051] At t3 power supply 3 shows a higher age than power supply 2.

[0052] Therefore, the level of priority of power supplies 2 and 3 are reassigned, as consequence power supply 2 has a lower priority than power supply 3. [0053] Power supply 2 is first turned-on (for a short instant At₁ (t_± in the priority document) , three power supplies are running) , followed after the time interval At₁ (t_± in the priority document) , by the turning off of power supply 3.

[0054] In this way it is made sure that the number of power supplies in ON state is always greater than or equal to the minimum number required to power the application adequately.

[0055] The same method is applied at t₄ and t₅. [0056] At tβ it appears that the two power supplies in ON state are of higher age than the two power supplies in OFF state.

[0057] In the same way as before, each power supply in OFF mode is first controlled in ON mode, before its counterpart is controlled in OFF mode. At tβ, all four power supplies have changed of state within three time intervals t_±.

[0058] A method according to the present invention can be applied to control the ON and OFF states of the power supplies, based on the same principle that the power supplies with higher age having to be turned off first as a function of the load level.

[0059] For instance, this method can be based on instantaneous comparison of ages between the power supplies, which yields the advantage that the need to define the time intervals T₁ is avoided. [0060] In this case, this method has to comprise steps such as it avoids high-frequency turn ON/OFF once all the power supplies have reached very close ages. [0061] In this case also, this method has to comprise steps such as it avoids simultaneous turn ON/OFF of power supplies.

[0062] In this case also, when there is no battery on the DC, or when these batteries are unloaded, methods have to comprise steps such as it avoids turning OFF one ore more powers supplies, before having turned ON lower age power supplies.

[0063] Preferably, the time intervals Ti are defined randomly. [0064] Preferably, in order to avoid high-frequency turn ON/OFF once all the power supplies have reached very close ages, the time intervals Ti are superior to 1 sec. [0065] More preferably, the time intervals Ti are superior to Ih. [0066] More preferably, the time intervals Ti are superior to 12h.

[0067] More preferably, the time intervals Ti are superior to 24h.

Claims

1. A method for defining, by means of a monitoring unit employing electronics and/or software technologies, the turn-off/turn-on priorities of power supplies included in a same system, comprising the steps of

- measuring the instantaneous power consumption of the load or application and evaluating power consumption parameters, - calculating, according to said power consumption parameters, the number of power supplies to turn- off or turn-on in order to optimize the power conversion efficiency,

- measuring and recording for each power supply, the history of a number of ageing parameters such as starting dates and stopping dates, cumulated durations of functioning, internal temperature, output power stresses, input voltage stresses,

- evaluating from the said recordings, the degree of ageing of each power supply,

- assigning, at each time interval Ti, to each power supply a level of priority based on the ageing, such as the level of priority is increasing with the degree of ageing of power supply, - accordingly to the number of power supply to turn- off or turn-on in order to optimize said power conversion efficiency, turning-off power supplies with the highest level of priority or turning-on power supplies with the lowest level of priority.

2. A method as claimed in claim 1, wherein the degree of ageing of each power supply is evaluated at first order by application of the Arrhenius law for the action of ambient temperature on effective on-time duration and preferably at second order by further correcting the effective on-time duration in regards to local stresses such as input voltages stresses or output power stresses.

3. A method as claimed in claim 1-2, wherein it further comprise the step of turning-on and/or turning-off, at each time interval Ti, power supplies so that the power supply running , after this step, are the ones with the lowest priority.

4. A method as claimed in any of the previous claims, wherein the value of Ti is randomly determined.

5. A method as claimed in claim 1-3, wherein the value of Ti is identical for all the values of i.

6. A method as claimed in claim 5, wherein the value of Ti is superior to 24h.

7. A method as claimed in any of the previous claims, wherein the value of Ti is superior to 12h.

8. A method as claimed in any of previous claims, wherein the value of Ti is superior to Ih.

9. A method as claimed in any of previous claims, wherein the value of Ti is superior to 1 sec.

10. A method as claimed in any of previous claims, wherein all the power supplies have the same specifications, such as the maximal power output, maximal voltage input.

11. A method as claimed in any of the previous claims, wherein the power consumption parameters are the average power level and the peak power level, within a given period of time, defined from acquired data of the slow rate power consumption variations of the application .

12. A method as claimed in any of the previous claims, wherein measuring and recording are performed for each power supply, either separately inside each power supply or, totally or partially, inside the monitoring unit,

13. A method as claimed in any of the previous claims, wherein the degree of ageing of each power supply is stored in the corresponding power supply.

14. A method as claimed in any of the previous claims, wherein the evaluation from the previous recordings is performed, either separately inside each power supply or, totally or partially, inside the monitoring unit.