Network construction type and network type energy storage combined control method, electronic equipment and storage medium

Abstract

The invention discloses a network construction type and network type energy storage combined control method, electronic equipment and a storage medium, and the method comprises the steps: firstly obtaining the inertia of a power grid and the short-circuit capacity of a grid-connected point of an energy storage power station, and calculating the short-circuit ratio of the grid-connected point of the power station; dynamically adjusting the basic operation proportion of the two types of energy storage according to the inertia and short-circuit ratio of the power grid; then determining the frequency deviation and the frequency change rate of the power grid, calculating the initial output of two types of energy storage in combination with the basic operation proportion, and executing hierarchical control: constructing network type energy storage dominated virtual inertia control based on the frequency change rate, and preferentially responding to the network type energy storage to primary frequency modulation control based on the frequency deviation of the power grid; and finally, dynamically distributing a real-time output weight by combining the power grid frequency deviation, the frequency change rate and the short-circuit ratio through the coordination controller, and carrying out weighted optimization on the initial output to realize collaborative adaptation of primary frequency modulation and virtual inertia control. According to the scheme, weak power grid stability improvement and fast frequency modulation active supporting capability are effectively considered, and the operation requirements of a high-proportion new energy power grid are met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage control of power systems, and in particular to a grid-forming and grid-following energy storage joint control method, an electronic device and a storage medium. BACKGROUND

[0002] At present, the installed capacity of wind power and photovoltaic power has reached 1.4 billion kilowatts, which has historically surpassed coal power. The annual newly installed capacity of wind power and photovoltaic power is 358 million kilowatts, accounting for 82.6% of the total annual newly installed capacity of power generation. The installed capacity of new energy is still maintaining a rapid growth trend. Unlike the traditional synchronous generator dominated power grid, new energy power generation is connected to the power grid through power electronic converters. The large mechanical inertia of the rotor of the synchronous generator can effectively suppress the rapid fluctuation of the power grid frequency, and the output voltage of the synchronous generator is nearly an ideal sinusoidal wave. With the continuous increase of the penetration rate of new energy, the inertia of the power system decreases significantly, and the frequency stability problem is increasingly prominent.

[0003] At the same time, due to the limitation of wind and light resource distribution, new energy power generation bases are mostly located in remote areas such as grasslands, mountains and deserts. Long-distance transmission lines result in weak power grid structure in these areas. New energy grid-connected converters often operate in a weak alternating current grid environment. Early grid-connected converters have small capacity and small quantity, and the power grid can be approximated as an infinite power source. The control and parameter design are based on the premise that the grid impedance is zero. However, with the increase of the penetration rate of new energy grid-connected converters and the weakening of the characteristics of the power grid, the ideal grid assumption is no longer valid. The connection of new energy grid-connected converters to a weak grid can easily cause wideband oscillation problems.

[0004] Grid-forming control simulates the characteristics of the generator in maintaining the stability of the terminal voltage during power grid disturbance by not directly following the power grid state and enhancing the overcurrent capability of power electronic devices. A large number of simulations and laboratory tests have verified that this control strategy can improve the frequency and voltage stability of the power system in the "double high" scenario, and strengthen the synchronization stability and wideband oscillation suppression capability of low short-circuit ratio new energy stations.

[0005] However, traditional energy storage control mostly adopts a single mode (grid-following or grid-forming), which is difficult to adapt to the dynamic changes of the power grid strength. In the prior art, grid-forming energy storage can autonomously provide voltage and frequency support, but the dynamic response is slow; grid-following energy storage has fast response speed, but it depends on the voltage phase of the power grid, and oscillation easily occurs between devices, affecting the operation stability. SUMMARY

[0006] The present application provides a grid-forming and grid-following energy storage joint control method, an electronic device and a storage medium, which are suitable for high-proportion new energy power grids and can improve the stability of the power grid and the utilization efficiency of energy storage.

[0007] According to an aspect of the present application, a grid-constructing and grid-following energy storage joint control method is provided, comprising:

[0008] The grid inertia and the short-circuit capacity of the energy storage power station grid-connected point are obtained, and the short-circuit ratio of the power station grid-connected point is calculated based on the short-circuit capacity;

[0009] The basic operation ratio of the grid-constructing energy storage and the grid-following energy storage is dynamically adjusted according to the grid inertia and the short-circuit ratio of the power station grid-connected point;

[0010] The grid frequency deviation and the grid frequency change rate are determined, and the initial output of the grid-constructing energy storage and the initial output of the grid-following energy storage are calculated based on the grid frequency deviation, the grid frequency change rate and the basic operation ratio, so as to perform hierarchical control on the two types of energy storage; wherein the hierarchical control includes virtual inertia control based on the grid frequency change rate dominated by the grid-constructing energy storage, and primary frequency modulation control based on the grid frequency deviation preferentially responded by the grid-following energy storage;

[0011] The real-time output weight of the two types of energy storage is dynamically allocated by the coordination controller in combination with the grid frequency deviation, the grid frequency change rate and the short-circuit ratio of the power station grid-connected point, and the initial output of the grid-constructing energy storage and the initial output of the grid-following energy storage are weighted and optimized based on the real-time output weight, so as to adapt the primary frequency modulation and virtual inertia control.

[0012] According to another aspect of the present application, a grid-constructing and grid-following energy storage joint control device is provided, comprising:

[0013] The short-circuit ratio calculation module is used to obtain the grid inertia and the short-circuit capacity of the energy storage power station grid-connected point, and calculate the short-circuit ratio of the power station grid-connected point based on the short-circuit capacity;

[0014] The operation ratio adjustment module is used to dynamically adjust the basic operation ratio of the grid-constructing energy storage and the grid-following energy storage according to the grid inertia and the short-circuit ratio of the power station grid-connected point;

[0015] The hierarchical control module is used to determine the grid frequency deviation and the grid frequency change rate, and calculate the initial output of the grid-constructing energy storage and the initial output of the grid-following energy storage based on the grid frequency deviation, the grid frequency change rate and the basic operation ratio, so as to perform hierarchical control on the two types of energy storage; wherein the hierarchical control includes virtual inertia control based on the grid frequency change rate dominated by the grid-constructing energy storage, and primary frequency modulation control based on the grid frequency deviation preferentially responded by the grid-following energy storage;

[0016] The coordination control module is configured to dynamically allocate real-time output weights of the two types of energy storages by a coordination controller in combination with the grid frequency deviation, the grid frequency change rate and the station grid point short-circuit ratio, and perform weighted optimization on the initial output of the grid-forming energy storage and the initial output of the grid-following energy storage based on the real-time output weights, so as to adapt the primary frequency modulation and the virtual inertia control.

[0017] According to another aspect of the present application, an electronic device is provided, comprising:

[0018] at least one processor;

[0019] and a memory in communication connection with the at least one processor;

[0020] wherein the memory stores a computer program executable by the at least one processor, and the computer program is executed by the at least one processor to enable the at least one processor to perform the grid-forming and grid-following energy storage joint control method of any embodiment of the present application.

[0021] According to another aspect of the present application, a computer readable storage medium is provided, which stores computer instructions for enabling a processor to implement the grid-forming and grid-following energy storage joint control method of any embodiment of the present application when executed by the processor.

[0022] The technical scheme of the embodiment of the present application acquires the grid inertia and the short-circuit capacity of the grid point of the energy storage station, and calculates the station grid point short-circuit ratio based on the short-circuit capacity; dynamically adjusts the basic operation ratio of the grid-forming energy storage and the grid-following energy storage according to the grid inertia and the station grid point short-circuit ratio; determines the grid frequency deviation and the grid frequency change rate, and calculates the initial output of the grid-forming energy storage and the initial output of the grid-following energy storage based on the grid frequency deviation, the grid frequency change rate and the basic operation ratio, to perform hierarchical control on the two types of energy storages; wherein the hierarchical control includes the virtual inertia control based on the grid frequency change rate dominated by the grid-forming energy storage, and the primary frequency modulation control based on the grid frequency deviation preferentially responded by the grid-following energy storage; a coordination controller is used to dynamically allocate real-time output weights of the two types of energy storages in combination with the grid frequency deviation, the grid frequency change rate and the station grid point short-circuit ratio, and perform weighted optimization on the initial output of the grid-forming energy storage and the initial output of the grid-following energy storage based on the real-time output weights, to adapt the primary frequency modulation and the virtual inertia control. This technical scheme can solve the technical problems that the traditional single-mode energy storage control is difficult to adapt to the dynamic changes of the grid, the grid-forming energy storage and the grid-following energy storage lack a cooperative optimization mechanism, and the inertia support and the rapid frequency modulation demand cannot be considered, by adjusting the ratio of the grid-forming energy storage and the grid-following energy storage through real-time grid short-circuit capacity detection, and dynamically allocating the output based on the frequency fluctuation, the weak grid stability and the rapid frequency modulation active support capability are considered, and the energy storage utilization efficiency is improved.

[0023] It is to be understood that the embodiments described herein are merely exemplary of the application and that a myriad of modifications, both as to the nature and number of elements within the execution of the application and as to the modes of execution thereof, can be made by those skilled in the art, and that in its broader aspect, the application is directed to those who have, or promise to have the skills in the art. Any and all such modifications are intended to be included within the scope of the following claims. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiments description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0025] Figure 1 A flow chart of a network-constructing and network-following combined energy storage control method provided by the embodiment of the present application;

[0026] Figure 2 A flow chart of another network-constructing and network-following combined energy storage control method provided by the embodiment of the present application;

[0027] Figure 3 A structural schematic diagram of a network-constructing and network-following combined energy storage control device provided by the embodiment of the present application;

[0028] Figure 4 A structural schematic diagram of an electronic device for implementing the network-constructing and network-following combined energy storage control method of the embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to make the technical personnel in the art better understand the present application scheme, the following will combine the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort should be within the scope of the present application.

[0030] It should be noted that the terms "first", "second", and the like in the specification and claims of the present application and the above-described drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not necessarily limit to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0031] Figure 1 A flow chart of a network construction type and network following type energy storage combined control method is provided for an embodiment of the present application. The embodiment can be applicable to the case of improving weak power grid stability and active support capability of fast frequency modulation. The method can be executed by a network construction type and network following type energy storage combined control device. The device can be realized in the form of hardware and / or software, and can be configured in an electronic device. As shown in the figure, the method specifically includes the following steps. Figure 1

[0032] S110, obtain the inertia of the power grid and the short-circuit capacity of the energy storage power station grid-connected point, and calculate the field station grid-connected point short-circuit ratio based on the short-circuit capacity.

[0033] The inertia of the power grid can represent the ability of the power grid to resist frequency changes, and can be represented by H G . The short-circuit capacity S k of the energy storage power station grid-connected point can refer to the product of the three-phase short-circuit current and the nominal voltage of the energy storage power station grid-connected point. When the actual value is calculated, it is 3 times the product of the three-phase short-circuit current I and the nominal voltage U nom . The field station grid-connected point short-circuit ratio can refer to the ratio of the short-circuit capacity of the energy storage power station to the rated capacity of the energy storage power station.

[0034] In some optional embodiments, obtaining the inertia of the power grid and the short-circuit capacity of the energy storage power station grid-connected point includes: obtaining the inertia of the power grid through data interaction with the power grid dispatching center; obtaining the short-circuit capacity of the energy storage power station grid-connected point by using a preset detection method, the preset detection method including a disturbance injection method and a harmonic impedance analysis method; and performing ratio operation on the short-circuit capacity of the energy storage power station grid-connected point and the rated capacity of the energy storage power station to obtain the field station grid-connected point short-circuit ratio.

[0035] The preset detection method can refer to a detection method preset for obtaining the short-circuit capacity, including the disturbance injection method and the harmonic impedance analysis method. The data interaction can refer to real-time information transmission between the energy storage control system and the power grid dispatching center.

[0036] Specifically, for the inertia of the power grid, it can be directly obtained through data interaction with the power grid dispatching center. For the short-circuit capacity of the energy storage power station grid-connected point, the disturbance injection method or the harmonic impedance analysis method can be used for detection. Then, ratio operation is performed on the detected short-circuit capacity and the rated capacity of the energy storage power station to obtain the field station grid-connected point short-circuit ratio.

[0037] In some possible implementation manners, the short-circuit ratio SCR is the ratio of the short-circuit capacity S k of the energy storage power station grid-connected point to the rated capacity of the energy storage power station:

[0038] ​

[0039] In some optional embodiments, the short-circuit capacity of the energy storage power station grid-connected point is obtained by using a disturbance injection method, including: injecting a sinusoidal disturbance signal with preset parameters through the energy storage converter to the power grid during steady-state operation of the power grid, the preset parameters including an amplitude of 1%~5% of the rated voltage and a frequency of 45~55 Hz; collecting voltage waveforms and current waveforms before and after the disturbance, and calculating the equivalent impedance of the power grid according to the ratio of the voltage variation to the current variation; substituting the rated voltage of the power grid and the equivalent impedance of the power grid into a preset short-circuit capacity calculation formula to obtain the real-time short-circuit capacity.

[0040] Specifically, during steady-state operation of the power grid, a sinusoidal disturbance with an amplitude of 1%~5% of the rated voltage (the frequency is 45~55 Hz, avoiding the power frequency) can be injected to the power grid through the energy storage converter, the voltage V and current I waveforms before and after the disturbance are collected, and the preset formula is used to calculate the grid impedance Zgrid=ΔV / ΔI.

[0041] For the new energy high penetration scenario, a harmonic analysis method can be used, that is, the background harmonics of the power grid (such as 5th and 7th harmonics) are extracted, the phase difference between the harmonic voltage and current is analyzed by FFT (Fast Fourier Transform), and the equivalent impedance is calculated. In order to realize redundant checking, the real-time short-circuit capacity can be compared with the offline data provided by the dispatching center, and when the deviation exceeds 10% of the preset threshold, secondary detection is started. In this way, the reliability and accuracy of data detection are improved by matching the redundant checking mechanism.

[0042] S120, according to the grid inertia and the field station grid-connected point short-circuit ratio, dynamically adjusting the basic operation proportion of the grid-forming energy storage and the grid-following energy storage.

[0043] The basic operation proportion can be understood as the proportion of the equipment investment scale of the two types of energy storage under the current grid state; the embodiment of the application can dynamically adjust the basic operation proportion of the grid-forming energy storage and the grid-following energy storage according to the grid inertia and the field station grid-connected point short-circuit ratio.

[0044] In some optional embodiments, dynamically adjusting the basic operation proportion of the grid-forming energy storage and the grid-following energy storage includes: dividing the grid strength level based on the size relationship between the field station grid-connected point short-circuit ratio and the preset reference short-circuit ratio, the grid strength level including a strong grid, a medium grid and a weak grid; determining the basic operation proportion of the grid-forming energy storage according to the inertia level corresponding to the grid inertia and the grid strength level, the inertia level including high inertia, medium inertia and low inertia; determining the basic operation proportion of the grid-following energy storage based on the basic operation proportion of the grid-forming energy storage, wherein the sum of the basic operation proportions of the two types of energy storage is 1.

[0045] The preset reference short-circuit ratio can be a reference value preset for dividing the grid strength level; the grid strength level can be three types of grid states of strong, medium and weak divided according to the short-circuit ratio; the inertia level can be three types of states of high, medium and low divided according to the grid inertia; and the preset proportion matrix can be a proportion matrix of network-forming energy storage corresponding to different inertia levels and grid strength levels.

[0046] In the embodiment of the application, the grid can be divided into three strength levels of strong, medium and weak according to the size relationship between the short-circuit ratio of the site grid connection point and the preset reference short-circuit ratio; and the high, medium and low inertia levels corresponding to the grid inertia are determined; the basic operation proportion of the network-forming energy storage is obtained by querying the preset proportion matrix, and the basic operation proportion of the network-following energy storage is obtained by subtracting 1 from the proportion, so that the dynamic adaptation of the basic operation proportions of the two types of energy storages is realized.

[0047] In some embodiments, the strategy for dynamically adjusting the basic operation proportion of the network-forming energy storage is as shown in Table 1:

[0048] Table 1

[0049] Proportion of networked energy storage Short-circuit ratio of field station grid connection point (H) Short-circuit ratio of field station grid connection point (N) Short-circuit ratio of field station grid connection point (L) Grid inertia (H) 0 0.25 0.5 Grid inertia (N) 0 0.5 0.75 Grid inertia (L) 0.25 0.75 1

[0050] SCR base is a preset reference value, and defines the grid strength level (strong / medium / weak grid):

[0051] Strong grid (H): SCR≥2SCR base ;

[0052] Medium grid (N): SCRbase<SCR<2SCR base ;

[0053] Weak grid (L): SCR≤SCR base .

[0054] In S130, the grid frequency deviation and the grid frequency change rate are determined, and the initial output of the network-forming energy storage and the initial output of the network-following energy storage are calculated based on the grid frequency deviation, the grid frequency change rate and the basic operation proportion, so as to perform hierarchical control on the two types of energy storages.

[0055] The hierarchical control includes virtual inertia control based on the grid frequency change rate dominated by the network-forming energy storage and primary frequency modulation control based on the grid frequency deviation preferentially responded by the network-following energy storage; and the initial output can be understood as the preliminary output power of the two types of energy storages calculated.

[0056] Specifically, the grid frequency deviation and the frequency change rate are determined, and the initial output of the two types of energy storages is calculated in combination with the basic operation proportion, so as to perform hierarchical control on the two types of energy storages.

[0057] S140, through the coordination controller, the real-time output weight of the two types of energy storages is dynamically allocated in combination with the grid frequency deviation, the grid frequency change rate and the short-circuit ratio of the station grid-connected point, and the initial output of the grid-constructing energy storage and the initial output of the grid-following energy storage are weighted and optimized based on the real-time output weight, so that the primary frequency modulation and the virtual inertia control are cooperatively adapted.

[0058] The real-time output weight refers to a weight coefficient adjusted according to the dynamic state of the grid.

[0059] Specifically, the real-time output weight can be allocated by the coordination controller in combination with the frequency deviation, the frequency change rate and the short-circuit ratio, the initial output is weighted and optimized, the dynamic change of the grid is adapted, and the inertia support and the fast frequency modulation demand are taken into account.

[0060] The technical scheme of the embodiment of the present application acquires the grid inertia and the short-circuit capacity of the grid-connected point of the energy storage power station, calculates the short-circuit ratio of the station grid-connected point based on the short-circuit capacity, dynamically adjusts the basic operation proportion of the grid-constructing energy storage and the grid-following energy storage according to the grid inertia and the short-circuit ratio of the station grid-connected point, determines the grid frequency deviation and the grid frequency change rate, calculates the initial output of the grid-constructing energy storage and the initial output of the grid-following energy storage based on the grid frequency deviation, the grid frequency change rate and the basic operation proportion, performs hierarchical control on the two types of energy storages, wherein the hierarchical control includes the virtual inertia control based on the grid frequency change rate dominated by the grid-constructing energy storage and the primary frequency modulation control based on the grid frequency deviation preferentially responded by the grid-following energy storage, dynamically allocates the real-time output weight of the two types of energy storages by the coordination controller in combination with the grid frequency deviation, the grid frequency change rate and the short-circuit ratio of the station grid-connected point, and performs weighted optimization on the initial output of the grid-constructing energy storage and the initial output of the grid-following energy storage based on the real-time output weight, so that the primary frequency modulation and the virtual inertia control are cooperatively adapted. The technical scheme can solve the technical problems that the traditional single-mode energy storage control is difficult to adapt to the dynamic change of the grid, the grid-constructing energy storage and the grid-following energy storage lack a cooperative optimization mechanism, and the inertia support and the fast frequency modulation demand cannot be taken into account, adjusts the proportion of the grid-constructing energy storage and the grid-following energy storage through real-time grid short-circuit capacity detection, dynamically allocates the output based on the frequency fluctuation, takes into account the improvement of the weak grid stability and the fast frequency modulation active support capability, and improves the energy storage utilization efficiency.

[0061] Figure 2 Another flowchart of the grid-constructing and grid-following energy storage joint control method provided by the embodiment of the present application is based on the above-mentioned embodiment, and the process of the hierarchical control of the two types of energy storages is optimized. As shown in the figure, Figure 2 the method specifically includes the following steps:

[0062] S210, the grid inertia and the short-circuit capacity of the grid-connected point of the energy storage power station are acquired, and the short-circuit ratio of the station grid-connected point is calculated based on the short-circuit capacity.

[0063] S220, dynamically adjusting the basic operation proportion of the grid-constructing energy storage and the grid-following energy storage according to the grid inertia and the short-circuit ratio of the field station grid-connected point.

[0064] S230, determining a virtual inertia time constant and a damping coefficient, and calculating an initial output of the grid-constructing energy storage according to the virtual inertia time constant, the damping coefficient, a grid frequency change rate, and the basic operation proportion of the grid-constructing energy storage.

[0065] The virtual inertia time constant can be dynamically adjusted according to the change of the grid inertia. When the grid inertia drops to a first threshold value, the virtual inertia time constant increases in a linear relationship. When the grid inertia drops to a second threshold value, the virtual inertia time constant is switched to a preset maximum virtual inertia value. The virtual inertia time constant can represent the virtual inertia capability provided by the grid-constructing energy storage. The first threshold value and the second threshold value are preset critical values of the grid inertia. The preset maximum virtual inertia value refers to an upper limit value of the virtual inertia time constant.

[0066] Specifically, the virtual inertia time constant and the damping coefficient can be set, wherein the virtual inertia time constant and the short-circuit ratio are inversely adjusted. Then, the initial output is calculated in combination with the virtual inertia time constant, the damping coefficient, the grid frequency change rate, and the basic operation proportion of the grid-constructing energy storage. When the grid inertia drops to the first threshold value, the virtual inertia time constant is linearly increased. When the grid inertia drops to the second threshold value, the virtual inertia time constant is switched to the preset maximum virtual inertia value.

[0067] In some implementations, the virtual inertia constant H GFM is related to the grid inertia H G , and the expression is:

[0068]

[0069] When H G >2H base , H GFM =1 / 3H max is fixed.

[0070] The dynamic adjustment of the virtual inertia time constant H GFM satisfies:

[0071] When H G drops to the first threshold value, H GFM increases in a linear relationship;

[0072] When H G further drops to the second threshold value, H GFM is switched to a fixed maximum value H max .

[0073] With examples, the virtual inertia time constant of the energy storage is dynamically adjusted according to different grid inertia, and the first threshold (which can be set to 10) can not be adjusted, which belongs to the normal inertia level of the grid; below the first threshold, the inertia of the energy storage increases linearly, and below the second threshold (which can be set to 5), the grid inertia is in urgent shortage, and all energy storages are adjusted to the maximum inertia.

[0074] For network-type energy storage, the frequency response control output (i.e. the initial output of the network-type energy storage) satisfies:

[0075]

[0076] wherein H GFM is the virtual inertia time constant, D GFM is the damping coefficient, and H GFM is adjusted according to the SCR in reverse; the damping coefficient , wherein ξ = 0.7-1.2; Δf is the grid frequency deviation, and dΔf / dt is the grid frequency change rate.

[0077] S240, adopting a droop control strategy, setting a reference droop coefficient and a maximum output limit value of the grid-following type energy storage; dynamically adjusting the droop coefficient according to the short-circuit ratio of the station grid connection point, and the droop coefficient and the short-circuit ratio of the station grid connection point are in a reverse adjustment relationship.

[0078] S250, calculating the initial output of the grid-following type energy storage according to the adjusted droop coefficient, the grid frequency deviation and the basic operation ratio of the grid-following type energy storage.

[0079] wherein the initial output does not exceed the maximum output limit value of the grid-following type energy storage; the droop control strategy refers to a control method for realizing frequency regulation by adjusting the proportional relationship between the energy storage output and the frequency deviation; the reference droop coefficient can refer to the initial value preset as the reference for adjusting the droop coefficient; the maximum output limit value can be understood as the maximum power upper limit allowed to be output by the grid-following type energy storage.

[0080] Specifically, the droop control strategy can be adopted to set a reference droop coefficient and a maximum output limit value of the grid-following type energy storage, and the droop coefficient is dynamically adjusted according to the short-circuit ratio, and the two are in a reverse relationship; further combining the adjusted droop coefficient, the grid frequency deviation and the basic operation ratio of the grid-following type energy storage, the initial output is calculated to ensure that the output does not exceed the maximum limit value, which can improve the frequency regulation sensitivity in a weak grid scenario and avoid overloading of the energy storage equipment.

[0081] In some implementations, the droop coefficient Kf is dynamically adjusted according to the SCR, and the formula is:

[0082]

[0083] wherein K f0The droop coefficient is used as a reference to ensure the improvement of frequency modulation sensitivity in a weak power grid.

[0084] For the grid-following energy storage, a droop control strategy is adopted, and the output P GF Satisfies:

[0085]

[0086] Wherein, K f is the droop coefficient, also known as the primary frequency modulation coefficient, P GF_max is the maximum output limit of the grid-following energy storage; T J is the virtual inertia time constant of the grid-following energy storage, f N is the rated frequency, i.e. 50 Hz.

[0087] S260, input the grid frequency deviation, grid frequency change rate and field station grid connection point short circuit ratio into the coordination controller.

[0088] S270, the coordination controller outputs the real-time output weight of the grid-forming energy storage and the grid-following energy storage according to different stages of grid frequency fluctuation, and the sum of the real-time output weights of the two types of energy storage is 1.

[0089] S280, based on the real-time output weight, the initial output of the grid-forming energy storage and the initial output of the grid-following energy storage are weighted and optimized to adapt the primary frequency modulation and virtual inertia control.

[0090] In some embodiments, the coordination controller outputs the real-time output weight of the grid-forming energy storage and the grid-following energy storage according to different stages of grid frequency fluctuation, including: increasing the real-time output weight of the grid-forming energy storage in the early stage of frequency change, wherein the grid frequency deviation is small and the grid frequency change rate is large; reducing the real-time output weight of the grid-forming energy storage in the middle stage of frequency change, wherein the grid frequency deviation is large and the grid frequency change rate is small; further reducing the real-time output weight of the grid-forming energy storage in the late stage of frequency change, wherein the grid frequency deviation decreases and is opposite to the direction of the grid frequency change rate.

[0091] Wherein, the coordination controller is used for dynamically allocating the output weight and optimizing the collaborative effect of the two types of energy storage; the frequency fluctuation stage can be understood as the complete process from slight fluctuation to serious deviation and then to gradual recovery, including the early stage, the middle stage and the late stage.

[0092] Specifically, the grid frequency deviation, the frequency change rate and the short circuit ratio can be input into the coordination controller, and the controller outputs the real-time output weight of the two types of energy storage according to the frequency fluctuation stage, the weight of the grid-forming energy storage is increased in the early stage, the weight is evenly distributed in the middle stage, and the weight of the grid-following energy storage is increased in the late stage; the initial output of the two types of energy storage is multiplied by the corresponding real-time output weight to obtain the final output.

[0093] In some implementations, the input variables can be Δf, dΔf / dt and SCR, and the output is the output weight of two types of energy storage: the output weight of grid-forming energy storage , and the output weight of grid-following energy storage (meeting );

[0094] In the early stage of frequency change, Δf is small and dΔf / dt is large, so the proportion of grid-forming energy storage output is increased: β GFM = 0.8;

[0095] In the middle stage of frequency change, Δf is large and dΔf / dt is small, so the proportion of grid-forming energy storage output is reduced: β GFM = 0.5;

[0096] In the late stage of frequency change, Δf is reduced and dΔf / dt is opposite to Δf, so the proportion of grid-forming energy storage output is further reduced: β GFM = 0.2.

[0097] In some embodiments, the hardware implementation of the technical solution of the present application can adopt an energy storage converter with grid-forming / grid-following dual-mode switching function, whose DC side is connected with a battery energy storage system, and whose AC side is connected with a power grid through a circuit breaker; the controller adopts a multi-core processor architecture, wherein the first core performs short-circuit capacity detection and proportional distribution, the second core runs a hierarchical control algorithm, and the third core implements coordination optimization.

[0098] The technical scheme of the embodiment of the present application obtains the inertia of the power grid and the short-circuit capacity of the grid connection point of the energy storage power station, and calculates the short-circuit ratio of the grid connection point of the station based on the short-circuit capacity; the basic operation ratio of the grid-forming energy storage and the grid-following energy storage is dynamically adjusted according to the inertia of the power grid and the short-circuit ratio of the grid connection point of the station; the frequency deviation of the power grid and the frequency change rate of the power grid are determined, and the initial output of the grid-forming energy storage and the initial output of the grid-following energy storage are calculated based on the frequency deviation of the power grid, the frequency change rate of the power grid and the basic operation ratio, so as to perform hierarchical control on the two types of energy storage; wherein, the hierarchical control includes the virtual inertia control based on the frequency change rate of the power grid, which is dominated by the response of the grid-forming energy storage, and the primary frequency modulation control based on the frequency deviation of the power grid, which is preferentially responded by the grid-following energy storage; the real-time output weight of the two types of energy storage is dynamically allocated by the coordination controller in combination with the frequency deviation of the power grid, the frequency change rate of the power grid and the short-circuit ratio of the grid connection point of the station, and the initial output of the grid-forming energy storage and the initial output of the grid-following energy storage are weighted and optimized based on the real-time output weight, so as to make the primary frequency modulation and the virtual inertia control adapt to each other. The technical scheme can solve the technical problems that the traditional single-mode energy storage control is difficult to adapt to the dynamic change of the power grid, the grid-forming energy storage and the grid-following energy storage lack a cooperative optimization mechanism, and the inertia support and the rapid frequency modulation demand cannot be considered, the ratio of the grid-forming energy storage and the grid-following energy storage is adjusted by real-time power grid short-circuit capacity detection, the output is dynamically allocated based on the frequency fluctuation, the weak power grid stability and the rapid frequency modulation active support ability are considered, and the energy storage utilization efficiency is improved.

[0099] Figure 3 A structural schematic diagram of a grid-forming and grid-following energy storage joint control device is provided for the embodiment of the present application. As shown in the figure, Figure 3 the device comprises:

[0100] The short-circuit ratio calculation module 310 is used for obtaining the inertia of the power grid and the short-circuit capacity of the grid connection point of the energy storage power station, and calculating the short-circuit ratio of the grid connection point of the station based on the short-circuit capacity;

[0101] The operation ratio adjustment module 320 is used for dynamically adjusting the basic operation ratio of the grid-forming energy storage and the grid-following energy storage according to the inertia of the power grid and the short-circuit ratio of the grid connection point of the station;

[0102] The hierarchical control module 330 is used for determining the frequency deviation of the power grid and the frequency change rate of the power grid, calculating the initial output of the grid-forming energy storage and the initial output of the grid-following energy storage based on the frequency deviation of the power grid, the frequency change rate of the power grid and the basic operation ratio, so as to perform hierarchical control on the two types of energy storage; wherein, the hierarchical control includes the virtual inertia control based on the frequency change rate of the power grid, which is dominated by the response of the grid-forming energy storage, and the primary frequency modulation control based on the frequency deviation of the power grid, which is preferentially responded by the grid-following energy storage;

[0103] The coordination control module 340 is configured to dynamically allocate real-time output weight of the two types of energy storage by a coordination controller in combination with the power grid frequency deviation, the power grid frequency change rate and the short-circuit ratio of the power station grid-connected point, and perform weighted optimization on the initial output of the grid-forming energy storage and the initial output of the grid-following energy storage based on the real-time output weight, so as to adapt the primary frequency modulation and the virtual inertia control.

[0104] In some embodiments, the short-circuit ratio calculation module 310 comprises:

[0105] The power grid inertia acquisition submodule is configured to acquire the power grid inertia by interacting with a power grid dispatching center.

[0106] The short-circuit capacity detection submodule is configured to acquire the short-circuit capacity of the energy storage power station grid-connected point by using a preset detection method, and the preset detection method comprises a disturbance injection method and a harmonic impedance analysis method.

[0107] The grid-connected point short-circuit ratio calculation submodule is configured to perform ratio operation on the short-circuit capacity of the energy storage power station grid-connected point and the rated capacity of the energy storage power station to obtain the power station grid-connected point short-circuit ratio.

[0108] In some embodiments, the short-circuit capacity detection submodule is specifically configured to:

[0109] When the power grid is in a steady state, a sinusoidal disturbance signal of a preset parameter is injected into the power grid through an energy storage converter, and the preset parameter comprises an amplitude of 1% to 5% of the rated voltage and a frequency of 45 to 55 Hz.

[0110] The voltage waveform and the current waveform of the grid-connected point before and after the disturbance are collected, and the power grid equivalent impedance is calculated according to the ratio of the voltage change amount to the current change amount.

[0111] The real-time short-circuit capacity is obtained by substituting the rated voltage of the power grid and the power grid equivalent impedance into a preset short-circuit capacity calculation formula.

[0112] In some embodiments, the operation ratio adjustment module 320 is specifically configured to:

[0113] The power grid strength level is divided based on the size relationship between the power station grid-connected point short-circuit ratio and a preset reference short-circuit ratio, and the power grid strength level comprises a strong power grid, a medium power grid and a weak power grid.

[0114] The basic operation proportion of the grid-forming energy storage is determined by a preset proportion matrix according to the inertia level corresponding to the power grid inertia and the power grid strength level, and the inertia level comprises high inertia, medium inertia and low inertia.

[0115] The basic operation proportion of the grid-following energy storage is determined based on the basic operation proportion of the grid-forming energy storage, and the sum of the basic operation proportions of the two types of energy storage is 1.

[0116] In some embodiments, the hierarchical control module 330 is specifically configured to:

[0117] determine a virtual inertia time constant and a damping coefficient;

[0118] calculate an initial output of the grid-forming energy storage according to the virtual inertia time constant, the damping coefficient, and the grid frequency change rate, in combination with a basic operation ratio of the grid-forming energy storage;

[0119] wherein the virtual inertia time constant is dynamically adjusted according to the change of the grid inertia: when the grid inertia drops to a first threshold value, the virtual inertia time constant increases in a linear relationship; and when the grid inertia drops to a second threshold value, the virtual inertia time constant is switched to a preset maximum virtual inertia value.

[0120] In some embodiments, the hierarchical control module 330 is specifically further configured to:

[0121] adopt a droop control strategy, and set a reference droop coefficient and a maximum output limit value of the grid-following energy storage;

[0122] dynamically adjust the droop coefficient according to the short-circuit ratio of the station grid connection point, the droop coefficient and the short-circuit ratio of the station grid connection point being in an inverse adjustment relationship;

[0123] calculate an initial output of the grid-following energy storage according to the adjusted droop coefficient, the grid frequency deviation, and the basic operation ratio of the grid-following energy storage;

[0124] wherein the initial output does not exceed the maximum output limit value of the grid-following energy storage.

[0125] In some embodiments, the coordination control module 340 comprises:

[0126] an input sub-module configured to input the grid frequency deviation, the grid frequency change rate, and the short-circuit ratio of the station grid connection point into the coordination controller;

[0127] a coordination controller configured to output real-time output weight of the grid-forming energy storage and the grid-following energy storage according to different stages of grid frequency fluctuation, the sum of the real-time output weights of the two types of energy storage being 1.

[0128] In some embodiments, the coordination controller is specifically configured to:

[0129] increase the real-time output weight of the grid-forming energy storage in a pre-frequency change period, wherein the grid frequency deviation is small and the grid frequency change rate is large in the pre-frequency change period;

[0130] In the frequency change middle period, the real-time output weight of the grid-forming energy storage is reduced, wherein the grid frequency deviation is large and the grid frequency change rate is small in the frequency change early period;

[0131] In the frequency change late period, the real-time output weight of the grid-forming energy storage is further reduced, wherein the grid frequency deviation is reduced and opposite to the direction of the grid frequency change rate in the frequency change late period.

[0132] The grid-forming and grid-following energy storage joint control device provided by the embodiment of the application can execute the grid-forming and grid-following energy storage joint control method provided by any embodiment of the application, and has the corresponding function modules and beneficial effects of the execution method.

[0133] Figure 4 A structural schematic diagram of an electronic device for implementing the grid-forming and grid-following energy storage joint control method of the embodiment of the application. The electronic device is intended to represent various forms of digital computers, such as laptops, desktops, workstations, personal digital assistants, servers, blade servers, mainframes, and other appropriate computers. The electronic device can also represent various forms of mobile devices, such as personal digital assistants, cellular telephones, smartphones, wearable devices (such as helmets, glasses, watches, etc.), and other similar computing devices. The components shown herein, their connections and relationships, and their functions, are meant to be examples only, and are not intended to limit the implementations of the applications described and / or claimed in this document.

[0134] As shown in Figure 4 The electronic device 10 includes at least one processor 11, and a memory, such as a read-only memory (ROM) 12, a random access memory (RAM) 13, etc., which is in communication connection with the at least one processor 11, wherein the memory stores a computer program that can be executed by the at least one processor, and the processor 11 can execute various appropriate actions and processes according to the computer program stored in the read-only memory (ROM) 12 or the computer program loaded from the storage unit 18 to the random access memory (RAM) 13. In the RAM 13, various programs and data required for the operation of the electronic device 10 can also be stored. The processor 11, the ROM 12, and the RAM 13 are connected to each other through a bus 14. An input / output (I / O) interface 15 is also connected to the bus 14.

[0135] A plurality of components in the electronic device 10 are connected to the I / O interface 15, including: an input unit 16, such as a keyboard, a mouse, etc.; an output unit 17, such as various types of displays, speakers, etc.; a storage unit 18, such as a magnetic disk, an optical disk, etc.; and a communication unit 19, such as a network card, a modem, a wireless communication transceiver, etc. The communication unit 19 allows the electronic device 10 to exchange information / data with other devices through a computer network, such as the Internet, and / or various telecommunication networks.

[0136] The processor 11 can be various general and / or special purpose processing components with processing and computing capabilities. Some examples of the processor 11 include, but are not limited to, a central processing unit (CPU), a graphics processing unit (GPU), various specialized artificial intelligence (AI) computing chips, various processors running machine learning model algorithms, a digital signal processor (DSP), and any appropriate processor, controller, microcontroller, etc. The processor 11 performs various methods and processes described above, such as the grid-forming and grid-following energy storage co-control method.

[0137] In some embodiments, the grid-forming and grid-following energy storage co-control can be implemented as a computer program tangibly embodied in a computer readable storage medium, such as the storage unit 18. In some embodiments, part or all of the computer program can be loaded and / or installed onto the electronic device 10 via the ROM 12 and / or the communication unit 19. When the computer program is loaded onto the RAM 13 and executed by the processor 11, one or more steps of the grid-forming and grid-following energy storage co-control method described above can be performed. Alternatively, in other embodiments, the processor 11 can be configured to perform the grid-forming and grid-following energy storage co-control method by any other appropriate means, such as by means of firmware.

[0138] Various implementations of the systems and techniques described above can be realized in digital electronic circuitry, integrated circuitry, a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), a system on a chip (SOC), a complex programmable logic device (CPLD), computer hardware, firmware, software, and / or combinations thereof. These various implementations can include implementation in one or more computer programs that are executable and / or interpretable on a programmable system including at least one programmable processor, which can be special or general purpose, coupled to receive data and instructions from, and to transmit data and instructions to, a storage system, at least one input device, and at least one output device.

[0139] Computer programs for implementing the methods of the present application can be written in any combination of one or more programming languages. These computer programs can be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the computer program, when executed, enables the functions / acts specified in the flowcharts and / or block diagrams to be implemented. The computer program can be executed entirely on a machine, partially on a machine, partially on a machine as a standalone software package and partially on a remote machine or entirely on a remote machine or server.

[0140] In the context of the present application, a computer-readable storage medium can be a tangible medium that can contain or store a computer program for use by or in connection with an instruction execution system, apparatus, or device. A computer-readable storage medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. Alternatively, a computer-readable storage medium can be a machine-readable signal medium. More specific examples of a machine-readable storage medium will include one or more lines of a program of instructions in a transitory signal, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0141] To provide for interaction with a user, the systems and techniques described here can be implemented on an electronic device having a display device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information to the user and a keyboard and a pointing device (e.g., a mouse or a trackball) by which the user can provide input to the electronic device. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user can be received in any form, including acoustic, speech, or tactile input.

[0142] The systems and techniques described herein can be implemented in a computing system that includes a back end component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a front end component, e.g., a user computer having a graphical user interface or a Web browser through which a user can interact with an implementation of the systems and techniques described herein, or any combination of such back end, middleware, or front end components. The components of the system can be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (LAN), a wide area network (WAN), a blockchain network, and the Internet.

[0143] The computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other. A server can be a cloud server, also known as a cloud computing server or cloud host, which is a host product in the cloud computing service system, to solve the defects of large management difficulty and weak business scalability in traditional physical host and VPS service.

[0144] It should be understood that the various forms of flow shown above can be re-ordered, added to, or deleted from without departing from the scope of the present disclosure. For example, the steps recited in the present disclosure can be executed in parallel, executed in series, or executed in different orders, as long as the desired results of the technical solutions of the present disclosure can be achieved, and the present disclosure is not limited herein.

[0145] The above detailed description does not constitute a limitation on the protection scope of the present application. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for joint control of grid-type and grid-type energy storage, characterized in that, include: Obtain the grid inertia and the short-circuit capacity of the energy storage power station's grid connection point, and calculate the short-circuit ratio of the power station's grid connection point based on the short-circuit capacity; Based on the grid inertia and the short-circuit ratio at the grid connection point of the substation, the basic operating ratio of grid-connected energy storage and grid-connected energy storage is dynamically adjusted. The grid frequency deviation and grid frequency change rate are determined. Based on the grid frequency deviation, the grid frequency change rate, and the basic operating ratio, the initial output of grid-based energy storage and grid-connected energy storage are calculated to perform hierarchical control on the two types of energy storage. The hierarchical control includes virtual inertia control based on grid frequency change rate, which is dominated by grid-based energy storage, and primary frequency regulation control based on grid frequency deviation, which is prioritized by grid-connected energy storage. By coordinating the controller, the real-time output weights of the two types of energy storage are dynamically allocated based on the grid frequency deviation, the grid frequency change rate, and the short-circuit ratio of the power station's grid connection point. The initial output of the grid-connected energy storage and the initial output of the grid-connected energy storage are then weighted and optimized based on the real-time output weights, so that primary frequency regulation and virtual inertia control can be coordinated and adapted.

2. The method according to claim 1, characterized in that, The acquisition of grid inertia and short-circuit capacity at the grid connection point of the energy storage power station includes: The power grid inertia is obtained by interacting with the power grid dispatch center. The short-circuit capacity of the grid connection point of the energy storage power station is obtained by using a preset detection method, which includes the disturbance injection method and the harmonic impedance analysis method. The short-circuit capacity of the energy storage power station's grid connection point is calculated as a ratio to the rated capacity of the energy storage power station to obtain the short-circuit ratio of the grid connection point.

3. The method according to claim 2, characterized in that, The short-circuit capacity of the grid connection point of the energy storage power station is obtained using the perturbation injection method, including: During steady-state operation of the power grid, a sinusoidal disturbance signal with preset parameters is injected into the power grid through an energy storage converter. The preset parameters include an amplitude of 1% to 5% of the rated voltage and a frequency of 45 to 55 Hz. Collect the voltage and current waveforms at the grid connection point before and after the disturbance, and calculate the equivalent impedance of the power grid based on the ratio of voltage change to current change; Substituting the grid's rated voltage and equivalent impedance into the preset short-circuit capacity calculation formula yields the real-time short-circuit capacity.

4. The method according to claim 1, characterized in that, The dynamic adjustment of the basic operating ratio of grid-connected energy storage and grid-linked energy storage includes: Based on the relationship between the short-circuit ratio at the grid connection point of the power station and the preset benchmark short-circuit ratio, the power grid strength level is divided into strong power grid, medium power grid and weak power grid. Based on the inertia level corresponding to the grid inertia and the grid intensity level, the basic operating proportion of grid-type energy storage is determined by a preset ratio matrix. The inertia level includes high inertia, medium inertia and low inertia. Based on the basic operating ratio of the grid-type energy storage, the basic operating ratio of the grid-connected energy storage is determined, wherein the sum of the basic operating ratios of the two types of energy storage is 1.

5. The method according to claim 1, characterized in that, The initial output of the computationally constructed grid-type energy storage includes: Determine the virtual inertia time constant and damping coefficient; Based on the virtual inertia time constant, the damping coefficient, and the grid frequency change rate, combined with the basic operating ratio of grid-type energy storage, the initial output of grid-type energy storage is calculated. The virtual inertia time constant is dynamically adjusted according to the change of the power grid inertia: when the power grid inertia drops to a first threshold, the virtual inertia time constant increases linearly; when the power grid inertia drops to a second threshold, the virtual inertia time constant switches to a preset maximum virtual inertia value.

6. The method according to claim 1, characterized in that, The calculation of the initial output of the grid-type energy storage includes: A droop control strategy is adopted, and a benchmark droop coefficient and a maximum output limit for grid-connected energy storage are set. The droop coefficient is dynamically adjusted based on the short-circuit ratio of the grid connection point of the power station, and the droop coefficient is inversely related to the short-circuit ratio of the grid connection point of the power station. The initial output of the grid-connected energy storage is calculated based on the adjusted droop coefficient, the grid frequency deviation, and the basic operating ratio of the grid-connected energy storage. Wherein, the initial output does not exceed the maximum output limit of the grid-connected energy storage.

7. The method according to claim 1, characterized in that, The dynamic allocation of real-time output weights for the two types of energy storage, and the weighted optimization of the initial output of the grid-type energy storage and the grid-connected energy storage based on the real-time output weights, includes: The grid frequency deviation, the grid frequency change rate, and the short-circuit ratio at the power station's grid connection point are input into the coordination controller. The coordination controller outputs real-time output weights for grid-connected energy storage and grid-linked energy storage based on different stages of grid frequency fluctuations, with the sum of the real-time output weights for the two types of energy storage being 1.

8. The method according to claim 7, characterized in that, The coordination controller outputs real-time output weights for grid-connected energy storage and grid-linked energy storage based on different stages of grid frequency fluctuations, including: In the early stage of frequency change, the real-time output weight of grid-type energy storage is increased, wherein the grid frequency deviation is small and the grid frequency change rate is large in the early stage of frequency change; In the middle of the frequency change, the real-time output weight of grid-type energy storage is reduced, wherein the grid frequency deviation is large and the grid frequency change rate is small in the early stage of the frequency change. In the later stages of frequency change, the real-time output weight of grid-type energy storage is further reduced, wherein the grid frequency deviation decreases in the later stages of frequency change and is opposite to the direction of the grid frequency change rate.

9. An electronic device, characterized in that, The electronic device includes: At least one processor; and a memory communicatively connected to the at least one processor; The memory stores a computer program that can be executed by the at least one processor, which is then executed by the at least one processor to enable the at least one processor to perform the grid-type and grid-type energy storage joint control method according to any one of claims 1-8.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions that are used to cause a processor to execute the combined control method of grid-type and grid-type energy storage as described in any one of claims 1-8.

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