Energy Storage Management System

Abstract

A method for managing an energy storage system (ESS) having one or more supercapacitors, comprising: obtaining a desired power transfer between the ESS and a power grid; and determining a reference voltage for providing the desired power transfer between the ESS and the power grid based on a state of health (SoH) of the ESS. Further disclosed herein is a non-transitory computer-readable medium configured to perform such a method, an energy storage management system (ESMS) comprising the non-transitory computer-readable medium, and a power system comprising the ESMS.

Description

[Technical Field]

[0001] Technical Field The present disclosure relates to a method for managing an energy storage system (ESS), an energy storage management system (ESMS) for performing the method in an ESS, and a power system comprising an ESS including such an ESMS. [Background technology]

[0002] background An energy storage system (ESS) is a system for storing large amounts of electrical energy. Electrical energy may be generated by inconsistent generation means, and an ESS therefore conveniently provides a way to store the generated electrical energy for later use, as desired, even if the generation means itself is offline. Thus, an ESS may form an important part of a renewable energy distribution grid, including, for example, solar or wind power generation.

[0003] An ESS can be integrated with a converter to form an enhanced power grid system. One example of such a system is an enhanced static synchronous compensator (E-STATCOM), which integrates a converter system (e.g., a full-bridge-based modular multilevel converter (MMC)) with a supercapacitor-based energy storage system (ESS).

[0004] An E-STATCOM can supply active and / or reactive power to the power grid. However, an ESS contains a limited amount of electrical energy, and therefore it is conventional for such systems, especially the ESMS therein, to track the SoC of the ESS and operate accordingly, i.e., regulate the power transfer between the ESS and the power grid.

[0005] It is desired to provide an improved method for managing an ESS, where such an improvement may result in slower degradation of the ESS components and thus extend the operational life of the ESS and therefore the operational life of any E-STATCOM system in which the ESS is installed. Summary of the Invention [Means for solving the problem]

[0006] overview As part of this disclosure, it is recognized that the power and energy capabilities of an ESS may change over time due to component aging, such as the reduction in capacitance of a supercapacitor. Accordingly, aspects of the present disclosure provide methods for managing an ESS that incorporate such changing capabilities into control operations, for example, when implementing an ESS in an E-STATCOM system. Aspects of the present disclosure provide an overall control strategy that takes into account the SoC, SoH, current, power, and / or energy limitations of the ESS and advantageously improves the operating life of the ESS.

[0007] In particular, according to one aspect of the present disclosure, a method for managing an ESS having one or more supercapacitors is provided, the method including obtaining a desired power transfer between the ESS and a power grid, and determining a reference voltage (i.e., a reference capacitor voltage) for providing the desired power transfer between the ESS and the power grid based on a state of health (SoH) of the ESS.

[0008] The method may then include initiating a desired power transfer between the ESS and the power grid using the determined reference voltage and controlling, with the controller, the power transfer between the ESS and the power grid based on a desired state of charge (SoC) of the ESS.

[0009] According to a further aspect of the present disclosure, the control method is implemented as or performed by an energy storage management system (ESMS) having a control unit or the like that is implemented as a transient or non-transitory computer-readable medium that includes instructions that, when executed by a processor, cause the processor to perform the control method.

[0010] According to yet a further aspect of the present disclosure, there is provided an electric power system comprising: a converter coupled to an electric power grid; and an ESS operably coupled to the converter and configured to transfer electric power to and from the electric power grid via the converter, the ESS comprising the above-mentioned ESMS configured to implement the control method described herein.

[0011] Those skilled in the art will appreciate that a STATCOM can inject power into and absorb power from a power grid. For example, if a frequency drop is detected on the power grid, an E-STATCOM may respond by providing power from an ESS to the power grid, thereby providing frequency support to the power grid.

[0012] Aspects of the present disclosure relate primarily to replenishing the energy stored in the ESS. That is, during normal operation of the E-STATCOM, the ESS is recharged using power from the power grid. However, as part of this disclosure, it is recognized that excessively high voltage levels during the discharge and recharge of the ESS (including one or more supercapacitors) can result in premature degradation of the ESS if its State of Health (SoH) is not considered.

[0013] Therefore, the life of the ESS may be extended by obtaining a desired power transfer between the ESS and the power grid based on the state of charge (SoC) of the ESS (i.e., indicating whether the SoC is below or above a set point) and determining a reference voltage for providing the desired power transfer between the ESS and the power grid based on the state of health (SoH) of the ESS.

[0014] In other words, the reference voltage across the ESS, which is used to provide power to the ESS and thereby change its SoC, can be periodically adapted according to the SoH estimate with the goal of minimizing the voltage across the ESS and thereby extending its lifetime. The reference voltage may be updated according to, or in response to, an SoH update, thereby being updated "automatically" with each SoH update.

[0015] The SoC of the ESS may be estimated using any suitable estimator, such as the terminal voltage of the ESS, and may be estimated online (i.e., while the ESS is operating) or offline (when the ESS is not operating). However, according to advantageous refinements of the control method of the present disclosure, the SoC is additionally or alternatively determined online based on an estimated (or measured) voltage across at least one of the one or more supercapacitors.

[0016] In some instances where an ESS comprises multiple supercapacitors, adequate accuracy may be achieved to estimate the SoC of the entire ESS based on the voltage (and / or estimated SoC) of only one of the supercapacitors, since the SoCs of all of the supercapacitors may be expected to be balanced according to some balancing scheme.

[0017] The State of Health of the ESS may also be estimated using any suitable estimator. For example, the State of Health of the ESS may be determined based on the terminal voltage and / or current of the ESS, depending on the implementation. The State of Health of the ESS may be affected by the temperature and / or voltage experienced by the capacitors of the ESS over their lifetime. Temperature fluctuations may be approximated, for example, based on current values ​​or measured directly using a thermometer. However, it will be understood that while the temperature of the supercapacitor may be assumed to remain substantially constant over its lifetime, a non-constant temperature does not substantially affect the resulting control.

[0018] Over its lifetime and as its SoH changes, the equivalent capacity of the ESS also changes. Because the equivalent capacity of the ESS changes over time, if the SoC regulator uses a fixed controller gain, the dynamic response of the ESS (i.e., during changes in SoC, such as during recharging of the ESS) will change over time due to aging. It will be understood that the "controller gain" is that used in control functions such as proportional-integral (PI) or proportional-integral-derivative (PID) control.

[0019] Therefore, according to an exemplary refinement of the present disclosure, the control method further includes determining one or more gain factors based on the SoH of the ESS, and the controller is configured to control the power transfer according to the one or more gain factors.

[0020] The ability to adapt the control gains during operation based on SoH estimates that take into account changes in the equivalent capacity of the ESS allows the same dynamic response of the ESS to be maintained over its lifetime, even if the equivalent capacity changes significantly due to SoH variations. This provides a more intuitive way to tune the SoC control parameters compared to direct selection of the controller parameters.

[0021] Optionally, the control method according to aspects of the present disclosure can be suspended or disabled when the connected grid leaves a defined frequency band. In other words, according to an optional refinement of the control method of the present disclosure, if it is determined that the power grid has a grid frequency outside the frequency band, no power is transferred between the ESS and the power grid. The determination that the power grid has a grid frequency outside the frequency band may be measured directly or indirectly, such as by using the output of a phase-locked loop that controls the converter reference signal.

[0022] Advantageously, such a technique reduces the load on the grid when the frequency is not at its nominal value (e.g., 50 Hz). If the frequency deviates significantly from the nominal frequency, the grid can be assumed to be vulnerable. Therefore, recharging the ESS (i.e., transferring power between the ESS and the power grid) can have a negative impact on the grid. Furthermore, the grid may recover from a low-frequency or high-frequency episode and return to the nominal frequency, thereby reducing the error between the reference voltage and the actual voltage again. If the ESMS was active during that time, there is a risk of overcharging (or discharging) the ESS, which would require the ESMS control to act again. Consequently, disabling the ESMS in a frequency band can result in reduced power exchange during frequency transients and ensure that power for energy management purposes is only exchanged during steady-state conditions of the grid.

[0023] According to aspects of the present disclosure, the customizable reference voltage profile may be expressed as follows:

[0024]

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[0025] In other words, a control method according to the presently disclosed aspects may include the optional steps of determining a voltage margin based on an estimated reference voltage at the end of life of the ESS and / or a current State of Health (SoH) of the ESS (i.e., the last determined State of Health for the ESS), and determining a reference voltage further based on the determined voltage margin. The voltage margin may be determined based at least in part on a minimum required reference voltage of the ESS at the end of life of the ESS.

[0026] In conventional power systems, most grid-forming control scheme designs assume there is a large energy storage, e.g., a battery, with a time constant much longer than the electromechanical dynamics associated with the inertial response required for an ESS. Therefore, the SoC of the battery can be considered to be effectively constant when designing the control system.

[0027] However, in E-STATCOMs, for example, using supercapacitors, much smaller energy storage is typically used, and the SoC dynamics are not sufficiently separated in time from the inertial emulation dynamics required for the ESS, often on a second-by-second basis. Therefore, it is advantageous to consider the SoC of the ESS when calculating its active and reactive power capabilities to reduce the risk of overcharging or undercharging the ESS. As used herein, the active and reactive power capabilities of an ESS are the amount of active or reactive power that the ESS is deemed capable of providing at any instant, e.g., from the perspective of a controller. This refers to the reported availability of active or reactive power.

[0028] To this end, dynamic active and reactive power capability strategies can be incorporated into control methods according to aspects of the present disclosure that implement advantageous, accurate, and rapid enforcement of active and reactive power limitations provided by the underlying grid-forming control scheme.

[0029] In particular, according to an optional refinement of the control technique of the present disclosure, the method further includes dynamically varying a threshold power capability of the ESS based on the SoC of one or more supercapacitors included in the ESS, the threshold power capability corresponding to a threshold amount of power that can be transferred between the ESS and the power grid. As described above, the threshold power capability includes a minimum or maximum active and / or reactive power that can be transferred between the ESS and the power grid, or at least a value thereof that can be provided to the controller when devising an overall control strategy for the ESS. Power transfer between the ESS and the power grid can then be limited based on the threshold power capability.

[0030] The threshold power capability may be further modified based on the total energy storage capacity of the ESS and / or parameters indicative of the converter capacity, such as one or more of the SoC, DC voltage, AC side current, DC side current, modulation index, etc.

[0031] Such an approach can maintain the SoC and / or energy storage current between minimum and maximum values, and maintain the magnitude of the converter AC side output current below the maximum. Additionally, the converter can be configured to operate in an active power priority mode so that the remaining current margin is available for reactive power compensation.

[0032] It will be appreciated that the various elements of the control methods disclosed herein may be implemented individually or in any combination, depending on the particular implementation, while still achieving the associated advantageous effects.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects of the present disclosure will now be described in more detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0034] [Figure 1] 1 illustrates a schematic diagram of a power system according to an aspect of the present disclosure. [Figure 2]1 illustrates a schematic diagram of an exemplary embodiment of an energy storage management system. DETAILED DESCRIPTION OF THE INVENTION

[0035] Detailed Description The present disclosure is described below by means of some illustrative examples, which it will be understood are provided for purposes of illustration and description only and are not intended to limit the scope of the present disclosure.

[0036] 1 schematically illustrates a power system 100 according to an embodiment of the present disclosure. The power system 100 comprises a converter 120 coupled to an energy storage system (ESS) 130 to form an energy storage enhanced converter system 140. The converter 130 is coupled to a power grid 110 and configured to transfer power between the power grid 110 and the ESS 130, the details of which are outside the scope of this disclosure and are well understood by those skilled in the art.

[0037] According to the illustrated example, power grid 110 is an alternating current (AC) power grid. Accordingly, converter 120 is configured to convert direct current (DC) from ESS 130 to AC for distribution on power grid 110, and to convert AC from power grid 110 to DC for providing power to ESS 130. In an alternative example, power grid 110 may be a high-voltage DC (HVDC) power grid, and in this example, converter 120 may be a DC-DC converter.

[0038] The converter 120 may be a static synchronous compensator (STATCOM), and thus the energy storage enhanced converter system 140 may be an energy storage enhanced STATCOM system, also referred to as an E-STATCOM system.

[0039] 1 includes multiple supercapacitors 132 that function as energy storage units. In alternative examples, depending on the implementation, only one energy storage unit may be implemented within the ESS 130, and / or the energy storage unit may be a battery cell, a fuel cell, or a conventional capacitor.

[0040] The operation and status of ESS 130 is monitored and controlled (such operation is generalized as ESS being "managed") by an energy storage management system (ESMS) 134. The ESMS may be implemented as hardware and / or software, and while the ESMS is shown as part of ESS 130, it will be understood that in some examples the ESMS may be implemented as a separate unit from ESS 130 that may be remote from supercapacitor 132.

[0041] Among other things, the ESMS may monitor the state of charge (SoC) of the supercapacitors 132, the terminal voltage of each supercapacitor 132 and / or the entire ESS 130, and / or the current flowing through the ESS 130 (e.g., including through an individual supercapacitor 132). The ESS 130 may be configured with sensors for measuring information related to such monitoring and control. Such sensors may be included in the ESMS 134 and may communicate with a controller configured to implement the management process. It will be understood that such a controller may be implemented as a transient or non-transitory computer-readable medium containing instructions that, when executed by a processor, cause the processor to perform such management processes.

[0042] Figure 2 illustrates schematically an exemplary embodiment of an ESMS 134 as described above in connection with Figure 1. As shown in this figure, the ESMS 134 may be considered to comprise multiple subsystems or modules.

[0043] In the example shown in FIG. 3, the ESMS 134 comprises an SoC estimation module 302 configured to estimate the SoC of the ESS and an SoH estimation module 310 configured to estimate the SoH of the ESS.

[0044] The energy stored in a capacitor is proportional to the capacitance of the capacitor and the square of the voltage from the capacitor. Thus, the SoC estimation module receives as input the terminal voltage of the ESS and / or the voltage across one or more capacitors 316, as well as the estimated equivalent capacitance of the supercapacitors of the ESS 320 from the SoH estimation module 310. The SoC estimation module 302 then provides as an output an estimated SoC of the ESS. This output of the estimated SoC of the ESS 322 is then provided as a usable output from the ESMS 134, for example, to inform other processes in the power system. The output of the estimated SoC of the ESS 322 is further provided to other internal modules of the ESMS 134.

[0045] The ESMS 134 further comprises a dynamic power capability calculation module 304 that receives the estimated SoC of the ESS 322 as an input and provides the dynamic active and reactive power limits of the ESS 328 as an output.

[0046] The ESMS 134 further comprises an error metric calculation module 306 configured to determine the difference between a reference amount of energy stored in the ESS (i.e., a set point for the SoC) and the actual amount of energy (or SoC) stored in the ESS. The error metric calculation module 306 receives as input the estimated SoC of the ESS 322 and outputs an error metric signal 326.

[0047] The error reference signal 326 is provided to a controller 308 configured to control the power transfer between the ESS and the power grid, i.e., the charging and discharging of the ESS. Accordingly, the output of the controller 308 is a power reference signal 332.

[0048] The gains used by the controller (e.g., as part of a PI or PID control scheme or the like) are adjusted based on the SoH of the ESS. That is, the estimated SoH, expressed as an equivalent capacity 320, is provided to a control parameter determination module 314, which determines the control parameters (i.e., gains) for use by the controller 308 based on the estimated SoH 320 of the ESS and provides these to the controller 308.

[0049] The controller 308 is further provided with the dynamic power capability of the ESS 328 calculated by the dynamic power capability calculation module 304 so as to further base the control of the power transfer between the ESS and the power grid on the power capability of the ESS.

[0050] The ESMS 134 further comprises a voltage reference calculation module 312 configured to determine a reference voltage 324 for providing a desired power transfer between the ESS and the power grid based on the estimated SoH of the ESS 320 provided by the SoH estimation module 310. The reference voltage 324 is provided to the error criterion calculation module 306 such that the desired power transfer can be controlled by the controller 308 according to an error criterion 326.

[0051] It will be understood that the above-described modules and their interconnections are entirely schematic and are provided as examples for understanding possible implementations of the control methods described herein, i.e., individual modules may be implemented alone or in any other combination, with or without further possible modules, depending on the intended implementation.

[0052] While the present disclosure is susceptible to various modifications and alternative forms, specific examples have been shown and described in connection with the drawings to clearly explain various advantageous aspects of the disclosure. It should be understood, however, that the detailed description herein and the drawings accompanying this specification are not intended to limit the disclosure to the particular forms disclosed. Rather, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the following claims, including all possible combinations of the various elements of these examples.

Claims

1. 1. A method for managing an energy storage system (ESS) having one or more supercapacitors, comprising: Obtaining a desired power transfer between the ESS and a power grid; determining a reference voltage for providing the desired power transfer between the ESS and the power grid based on a state of health (SoH) of the ESS; A method comprising:

2. determining the desired power transfer between the ESS and the power grid based on a state of charge (SoC) of the ESS; using a controller to control the power transfer between the ESS and the power grid using the determined reference voltage; The method of claim 1 further comprising:

3. determining one or more gain factors based on the SoH of the ESS, wherein the controller is configured to control the power transfer according to the one or more gain factors; The method of claim 2 further comprising:

4. determining the SoC online during operation of the ESS based on an estimated voltage across at least one of the one or more supercapacitors; The method of claim 2 or 3, further comprising:

5. Determining the SoH of the ESS based on a terminal voltage and / or current of the ESS.

10. The method of any preceding claim, further comprising:

6. If the power grid is determined to have a grid frequency outside a frequency band, power is not transferred between the ESS and the power grid.

10. A method according to any preceding claim.

7. determining a voltage margin based on an estimated reference voltage at the end of life of the ESS; determining the reference voltage further based on the determined voltage margin; 10. The method of any preceding claim, further comprising:

8. the voltage margin is determined based at least in part on a current State of Health and / or a minimum required reference voltage of the ESS at the end of life of the ESS; The method of claim 7.

9. dynamically varying a threshold power capability of the ESS based on the SoC of one or more supercapacitors included in the ESS, the threshold power capability corresponding to a threshold amount of power that can be transferred between the ESS and the power grid; 10. The method of any preceding claim, further comprising:

10. The method of claim 9 , wherein the threshold power capability comprises a minimum or maximum active and / or reactive power that can be transferred between the ESS and the power grid.

11. The method of claim 9 or 10, wherein the threshold power capability varies further based on a total energy storage capacity of the ESS.

12. limiting power transfer between the ESS and the power grid based on the threshold power capability; The method of any one of claims 9 to 11, further comprising:

13. A non-transitory computer readable medium comprising instructions that, when executed by a processor, cause the processor to perform a method according to any of the preceding claims.

14. 14. An energy storage management system (ESMS) comprising the non-transitory computer readable medium of claim 13.

15. a converter coupled to a power grid; an energy storage system (ESS) operably coupled to the converter and configured to transfer power to and from the power grid via the converter, the ESS comprising the ESMS of claim 14; A power system comprising:

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