CN109067003B - SOC balance control system for cascade energy storage system - Google Patents

Abstract

The SOC balance control system for the cascade energy storage system comprises a plurality of control devices with the same structure, wherein each control device is connected with each energy storage module in the cascade energy storage system in a one-to-one correspondence mode and can independently perform SOC balance control on the corresponding energy storage modules. The system is a distributed control system, the SOC balance control device corresponding to each energy storage module can realize SOC balance control on the energy storage module only through local information, and other external communication is not required. Therefore, compared with the conventional SOC balance control system, the system has the advantage that the cost is greatly reduced.

Description

A SOC balance control system for cascaded energy storage systems

technical field

The present invention relates to the technical field of power electronics, in particular to an SOC balance control system for cascaded energy storage systems and a centralized large-capacity energy storage system.

Background technique

In the application of energy storage projects, in order to enable the energy storage system to be charged and discharged at the same time to increase its service life, the State of Charge (SOC) of each energy storage module needs to be balanced. Different initial SOC of the system and different output power during operation will cause SOC imbalance among various energy storage modules in the system, resulting in overcharge or overdischarge of individual energy storage modules, thereby reducing the service life of energy storage modules and system efficiency.

With the continuous improvement of people's awareness of sustainable energy development and environmental protection, renewable energy and electric vehicles have been vigorously developed, and traditional small-capacity energy storage systems have been unable to meet current needs. With the continuous expansion of the scale of energy storage, the value of cascaded energy storage systems has been recognized by the market in medium and high voltage applications. The voltage of a single energy storage unit is low, and a higher voltage level can be directly obtained by cascading inverters without the need for expensive and bulky transformers. At the same time, each energy storage module can be controlled individually, making it more convenient to manage each energy storage unit.

At present, the SOC balance control methods for cascaded energy systems all rely on high-bandwidth centralized communication. With the increase in the number of energy storage modules, on the one hand, the cost of communication bandwidth will continue to increase, and on the other hand, communication packet loss, failure, etc. It will greatly reduce the system robustness.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention provides an SOC balance control system for a cascaded energy storage system, characterized in that the system includes a plurality of control devices with the same structure, and each control device is respectively connected with each energy storage device in the cascaded energy storage system. The modules are connected in one-to-one correspondence and can independently perform SOC balance control on the corresponding energy storage modules. For an energy storage module to be controlled, the corresponding control device includes:

an output voltage reference value generation module, configured to generate an output voltage reference value for the energy storage module to be controlled according to the obtained state of charge and output power of the energy storage module to be controlled;

a closed-loop control module, configured to generate a corresponding modulation reference signal according to the output voltage reference value based on a closed-loop control strategy;

The pulse modulation module is configured to generate a corresponding switching pulse signal according to the modulation reference signal, so as to adjust the state of charge of the energy storage module to be controlled by the switching pulse signal.

According to an embodiment of the present invention, when the energy storage modules in the cascaded energy storage system share a filter circuit, the output voltage reference value generation module is configured to The preset reference voltage of the energy storage module determines the output power of the energy storage module to be controlled.

According to an embodiment of the present invention, the output voltage reference value generating module includes:

A phase angle reference value generating unit, which is used for determining an angular frequency reference value of the output voltage according to the state of charge and output power of the energy storage module to be controlled, and generating a phase angle reference value of the output voltage according to the angular frequency reference value ;

an amplitude reference value generating unit, which is used for determining the amplitude reference value of the output voltage according to the voltage amplitude reference value at the common point of the cascaded energy storage system;

A reference voltage generating unit, configured to generate a reference value of the output voltage of the energy storage module to be controlled according to the reference value of the phase angle and the reference value of the amplitude of the output voltage.

According to an embodiment of the present invention, the amplitude reference value generating unit is configured to:

Determine the voltage amplitude reference weight of the energy module to be controlled according to the maximum electric energy capacity of the cascaded energy storage system and the maximum electric energy capacity of the energy storage module to be controlled;

The amplitude reference value of the output voltage of the energy storage module to be controlled is determined according to the voltage amplitude reference weight and the voltage amplitude reference value at the common point of the cascaded energy storage system.

According to an embodiment of the present invention, the amplitude reference value generating unit is configured to determine the amplitude reference value of the output voltage of the energy storage module to be controlled according to the following expression:

表示第i个储能模块的电压幅值参考权重，V^*表示表示级联储能系统的公共点处电压幅值参考值，E_{max_i}和∑E_{max_i}分别表示第i个储能模块和级联储能系统的最大电能容量。Among them, V _i represents the amplitude reference value of the output voltage of the ith energy storage module, and the ith energy storage module is used as the energy storage module to be controlled,

Represents the voltage amplitude reference weight of the i-th energy storage module, V ^* represents the voltage amplitude reference value at the common point of the cascaded energy storage system, E _{max_i} and ∑E _{max_i} represent the i-th energy storage module and the cascaded energy storage, respectively The maximum power capacity of the system.

According to an embodiment of the present invention, the phase angle reference value generating unit is configured to generate an angular frequency correction term of the energy storage module to be controlled according to the state of charge of the energy storage module to be controlled, and The correction term and the output power generate the angular frequency reference value of the energy storage module to be controlled, and the phase angle reference value is obtained by integrating the angular frequency reference value.

According to an embodiment of the present invention, the phase angle reference value generating unit is configured to generate the angular frequency correction term of the energy storage module to be controlled according to the following expression:

Δω _i = _ki ·SOC _i

Among them, Δω _i represents the angular frequency correction term of the ith energy storage module, _ki represents the correction coefficient of the angular frequency correction term of the ith energy storage module, and SOC _i represents the state of charge of the ith energy storage module.

According to an embodiment of the present invention, the correction coefficients of the angular frequency correction terms of each energy storage module in the cascaded energy storage system are all equal.

According to an embodiment of the present invention, the phase angle reference value generating unit is configured to generate the angular frequency reference value according to the following expression:

ω _i =ω ^* +sgn(Q _i )(m _i P _i -Δω _i )

Among them, ω _i represents the angular frequency reference value of the ith energy storage module, ω ^* represents the angular frequency of the _ith energy storage module at no load, and Qi and mi represent the reactive power of the _ith energy storage module, respectively and droop control coefficient, Pi represents the output power of the _{ith energy storage module, and Δω i represents} the angular frequency correction term of the ith energy storage module.

The present invention also provides a centralized large-capacity energy storage system, which is characterized by comprising a cascaded energy storage system and the SOC balance control system described in any one of the above.

The SOC balance control system for cascaded energy storage systems provided by the present invention is a distributed control system, and the SOC balance control device corresponding to each energy storage module can realize the SOC balance control of the energy storage modules only through local information, without the need for Depends on other external communication. Therefore, compared with the existing SOC balance control system, the cost of the present system is greatly reduced.

Other features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the description, claims and drawings.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings required in the description of the embodiments or the prior art will be briefly introduced below:

Figure 1 is a schematic structural diagram of a cascaded energy storage system;

2 is a schematic structural diagram of a control device for an i-th energy storage device according to an embodiment of the present invention;

3 is a schematic structural diagram of an output voltage reference value generation module according to an embodiment of the present invention;

4 and 5 are schematic diagrams of P-ω curves of two energy storage modules with the same maximum electrical energy capacity in different modes according to an embodiment of the present invention;

6 is a schematic diagram of a simulation model of a cascaded energy storage system according to an embodiment of the present invention;

7 to 10 are schematic diagrams of SOC values and active power change curves when each energy storage module operates in four different modes according to an embodiment of the present invention;

11 to 12 are schematic diagrams of SOC value change curves and power change curves of each energy storage module under charging and discharging switching according to an embodiment of the present invention;

13 is a schematic diagram of an SOC conversion curve and a power change curve when the load characteristics of the energy storage module are switched according to an embodiment of the present invention.

Detailed ways

The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and examples, so as to fully understand and implement the implementation process of how the present invention applies technical means to solve technical problems and achieve technical effects. It should be noted that, as long as there is no conflict, each embodiment of the present invention and each feature of each embodiment can be combined with each other, and the formed technical solutions all fall within the protection scope of the present invention.

Meanwhile, in the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present invention. It will be apparent, however, to those skilled in the art that the present invention may be practiced without the specific details or in the specific manner described herein.

In view of the above problems existing in the prior art, the present invention provides a new distributed SOC balance control system for cascaded energy storage systems and a centralized large-capacity energy storage system using the distributed SOC balance control system. The distributed SOC balance control system can realize the SOC balance of the cascaded energy storage system without communication.

Figure 1 shows a schematic structural diagram of a cascaded energy storage system. As shown in FIG. 1 , the cascaded energy storage system may include N (N greater than or equal to 2) cascaded energy storage modules (ie, the first energy storage module 101_1 to the Nth energy storage module 101_N) with the same structure. Each energy storage module is composed of an energy storage unit, a conversion circuit and a filter circuit. The N energy storage modules are connected in series to a common bus through a feeder, and provide electrical energy to the load 102 through the common bus. The common bus is also connected with other types of micro-sources 103 (eg photovoltaic power generation equipment or wind power generation equipment) to obtain the electric energy provided by these micro-sources.

According to the different load characteristics and energy storage operating modes, the operating modes of the cascaded energy storage system can be divided into four categories: I quadrant (discharge mode and the load is an inductive load), II quadrant (charge mode and the load is an inductive load), In quadrant III (charging mode and the load is capacitive load), quadrant IV (discharging mode and the load is capacitive load), the control system provided by the present invention can realize each energy storage in the cascaded energy storage system in four different modes SOC balance between modules and unified control for four different operating modes.

The SOC balance control system for the cascaded energy storage system provided by the present invention is a distributed control system. The control system includes a plurality of control devices with the same structure, and each control device is in a one-to-one correspondence with each energy storage module in the cascaded energy storage system. connect. Wherein, these control devices can independently perform SOC balance control on the corresponding energy storage modules.

Since the structure and working principle of each control device in the SOC balance control system are the same, in order to more clearly illustrate the realization principle and advantages of the SOC balance control system provided by the present invention, one of the control devices is taken as an example for further explanation below. .

Taking the i-th energy storage module in the cascaded energy storage system as the energy storage module to be controlled, the control device corresponding to the energy storage module is the i-th control device in the SOC balance control system. Figure 2 shows this implementation. The structure diagram of the control device in the example.

As shown in FIG. 2 , in this embodiment, the control device 200 includes: an output voltage reference value generation module 201 , a closed-loop control module 202 and a pulse modulation module 203 . The output voltage reference value generating module 201 can generate an output voltage reference value for the energy storage module 101_i to be controlled according to the obtained state of charge and output power of the energy storage module 101_i to be controlled.

In this embodiment, the energy storage module 101_i to be controlled preferably includes: an energy storage unit, a bridge conversion circuit and a filter circuit. The output voltage reference value generation module 201 preferably determines the output power of the energy storage module 101_i to be controlled according to the voltage and current flowing through the filter circuit.

It should be noted that, in other embodiments of the present invention, the output voltage reference value generating module 201 also adopts other reasonable methods to determine the output power of the energy storage module 101_i to be controlled according to the actual situation, and the present invention is not limited thereto. For example, in an embodiment of the present invention, when the energy storage modules in the cascaded energy storage system share a filter circuit, the output voltage reference value generation module 201 can be based on the obtained current flowing through the filter circuit and corresponding to the to-be-controlled The output power of the energy storage module 101_i to be controlled is determined by the preset reference voltage (eg, rated voltage) of the energy storage module 101_i.

The closed-loop control module 202 is connected to the output voltage reference value generation module 201, which can generate a corresponding modulation reference signal according to the above-mentioned output voltage reference value based on the closed-loop control strategy, and transmit the modulation reference signal to the pulse modulation module 203 connected to it. .

The pulse modulation module 203 is connected to the closed-loop control module and the energy storage module 101_i to be controlled, and is used for generating a corresponding switching pulse signal according to the modulation reference signal, so as to adjust the state of charge of the energy storage module 101_i to be controlled through the switching pulse signal.

Specifically, in this embodiment, the pulse modulation module 203 preferably controls the on-off state of the controllable switch tube in the bridge conversion circuit with the switch pulse signal generated and output by itself, thereby realizing the charging of the energy storage module. Status adjustment.

FIG. 3 shows a schematic structural diagram of the output voltage reference value generating module 201 in this embodiment.

As shown in FIG. 3 , in this embodiment, the output voltage reference value generation module 201 preferably includes: a phase angle reference value generation unit 301 , an amplitude reference value generation unit 302 and a reference voltage generation unit 303 . The phase angle reference value generating unit 301 is connected to the energy storage unit and the filter circuit in the energy storage module 101_i to be controlled, and can acquire the state of charge SOC _i of the energy storage module 101_i to be controlled by detecting the energy storage unit, At the same time, the output power P _i of the energy storage module 101_i to be controlled can also be obtained by detecting the output voltage and output current of the filter circuit.

According to the state of charge SOC _i and the output power P _i of the energy storage module 101_i to be controlled, the phase angle reference value generating unit 301 can determine the angular frequency reference value of the output voltage of the energy storage module 101_i to be controlled, and according to the angular frequency reference value to generate a phase angle reference for the output voltage.

Specifically, in this embodiment, the phase angle reference value generating unit 301 can generate the angular frequency correction term of the energy storage module 101_i to be controlled according to the state of charge SOC _i of the energy storage module 101_i to be controlled, and then according to the angular frequency correction term and The output power P _i of the energy storage module 101_i to be controlled generates an angular frequency reference value of the energy storage module 101_i to be controlled.

For example, the phase angle reference value generating unit 301 is preferably configured to generate the angular frequency correction term of the energy storage module 101_i to be controlled according to the following expression:

Δω _i = _ki ·SOC _i (1)

Among them, Δω _i represents the angular frequency correction term of the ith energy storage module (ie, the energy storage module to be controlled), and _ki represents the correction coefficient of the angular frequency correction term of the ith energy storage module.

In this embodiment, in order to control the SOC balance, the correction coefficients of the angular frequency correction terms of each energy storage module in the cascaded energy storage system are preferably equal. i.e. exists:

k ₁ =k ₂ =...=k _N =K (2)

Among them, N represents the total number of energy storage modules included in the cascaded energy storage system, and K represents a positive number.

In this embodiment, the phase angle reference value generating unit 301 preferably generates the angular frequency reference value according to the following expression:

ω _i =ω ^* +sgn(Q _i )(m _i P _i -Δω _i ) (3)

Among them, ω _i represents the reference value of the angular frequency of the ith energy storage module, ω ^* represents the angular frequency of the ith energy storage module at no-load, Qi represents the reactive power of the _{ith energy storage module, and m i represents} the angular frequency of the ith energy storage module. Droop control coefficient of the i-th energy storage module.

It should be pointed out that, in order to ensure the stable operation of the system, the droop control coefficient m _i preferably needs to meet the following conditions:

Among them, θ _i , θ _j and θ _k are the phase angle reference values of the i, j, and kth energy storage modules, respectively, θ _load represents the impedance angle of the load, and Z _load represents the load impedance modulus value. It can be seen from this that a smaller K/m _i value is easier to stabilize the system. Therefore, in this embodiment, in the process of selecting the value of the droop control coefficient m _i , the value of K needs to be referred to.

Of course, in other embodiments of the present invention, the phase angle reference value generating unit 301 may also determine the angular frequency reference value ω _i according to other reasonable methods, and the present invention is not limited thereto.

After obtaining the angular frequency reference value ω _i , the phase angle reference value generating unit 301 can obtain the phase angle reference value δ _i by integrating the angular frequency reference value.

As shown in FIG. 3 again, in this embodiment, the amplitude reference value generating unit 302 can determine the amplitude reference value of the output voltage of the energy storage module to be controlled according to the voltage amplitude reference value V ^* at the common point of the cascaded energy storage system value V _i .

Specifically, in this embodiment, the amplitude reference value generating unit 302 preferably first determines the voltage amplitude of the energy storage module to be controlled according to the maximum electrical energy capacity of the cascaded energy storage system and the maximum electrical energy capacity of the energy storage module to be controlled Reference weight, and then determine the amplitude reference value of the output voltage of the energy storage module to be controlled according to the voltage amplitude reference weight and the voltage amplitude reference value V ^* at the common point of the cascaded energy storage system.

Preferably, the amplitude reference value generating unit 302 can determine the amplitude reference value of the output voltage of the energy storage module to be controlled according to the following expression:

表示第i个储能模块的电压幅值参考权重，E_{max_i}和∑E_{max_i}分别表示第i个储能模块的最大电能容量和级联储能系统的最大电能容量。Among them, V _i represents the amplitude reference value of the output voltage of the ith energy storage module,

Represents the voltage amplitude reference weight of the ith energy storage module, E _{max_i} and ∑E _{max_i} represent the maximum electrical energy capacity of the ith energy storage module and the maximum electrical energy capacity of the cascaded energy storage system, respectively.

Of course, in other embodiments of the present invention, the amplitude reference value generating unit 302 may also use other reasonable methods to determine the amplitude reference value V _i of the output voltage of the energy storage module to be controlled, but the present invention is not limited thereto.

As shown in FIG. 3 , in this embodiment, the reference voltage generation unit 303 is connected to the phase angle reference value generation unit 301 and the amplitude reference value generation unit 302 , which can be based on the above-mentioned phase angle reference value δ _i and amplitude reference value V _i to generate the output voltage reference value for the energy storage module 101_i to be controlled. Specifically, the output voltage reference value can be expressed as V _i sinδ _i .

Figures 4 and 5 show the P-ω curves of two energy storage modules with the same maximum energy capacity in different modes. Among them, curve 1 represents the uncorrected P-ω curve, curve 2 represents the P-ω curve of the energy storage module with a large SOC, and curve 3 represents the P-ω curve of the energy storage module with a small SOC. It can be seen from Figure 3 and Figure 4 that in the discharge mode, the output power per unit capacity of the energy storage module with a larger SOC is greater than that of the energy storage module with a smaller SOC. In the charging mode, an energy storage module with a larger SOC absorbs less power per unit capacity than an energy storage module with a smaller SOC.

FIG. 6 shows the simulation model of the cascaded energy storage system in this embodiment. As shown in Fig. 6, the simulation model of the cascaded energy storage system includes three energy storage modules (the maximum electric energy capacity of these three energy storage modules is the same), common load and line impedance. In this simulation model, the initial SOC values of the first energy storage module, the second energy storage module and the third energy storage module in the discharge mode are 90%, 80%, and 70% respectively, and the initial SOC values in the charging mode are 10%, 20%, and 30%, respectively.

Figures 7 to 10 respectively show that each energy storage module in the cascaded energy storage system works in quadrant I (discharge mode and the load is an inductive load), quadrant II (charging mode and the load is an inductive load), and quadrant III (charging mode and an inductive load). The load is capacitive load) and the IV quadrant (discharge mode and the load is capacitive load) SOC value and active power change curve in four operating modes.

It can be seen from FIG. 7 to FIG. 10 that when the SOC balance control system provided in this embodiment operates, the output active power and SOC value of the energy storage module in the four quadrant modes gradually converge, and the SOC error ΔSOC and The power errors are all approximately equal to zero. At this time, the cascaded energy storage system reaches a steady state, and the SOC value and output power of the energy storage module reach a balance. It can be seen that the SOC balance control system proposed in this embodiment can make the cascaded energy storage system operate stably in four different modes. Active power sharing.

11 and 12 respectively show the SOC value change curve and the power change curve of each energy storage module in the cascaded energy storage system under the switching of charging and discharging. 11 shows switching from discharge to charging, and FIG. 12 shows switching from charging to discharge.

It can be seen from Figure 11 and Figure 12 that whether switching from discharge to charge or from charge to discharge, the output active power and SOC value of each energy storage module gradually converge, and the SOC error and power error before and after switching are almost the same. constant. At the same time, it can also be seen from the figure that the dynamic response of the energy storage module is fast and the overshoot is small during the switching process, which shows that the SOC balance control system has a good response performance.

FIG. 13 shows the SOC conversion curve and the power change curve when the load characteristics of the energy storage module are switched. It can be seen from Figure 13 that during the load switching process, the cascaded energy storage system initially works under the inductive load condition, and the load characteristics of the cascaded energy storage system change at the time of 20s (that is, the inductive load is switched to the capacitive load). Before and after the load characteristic switching, the SOC error of the energy storage module remains almost unchanged, and the convergence can eventually reach the SOC balance among the energy storage modules.

Of course, in other embodiments of the present invention, according to actual needs, the SOC balance control system further includes other reasonable modules or devices, but the present invention is not limited thereto. For example, in an embodiment of the present invention, the SOC balance control system may further include an auxiliary service module, and the auxiliary service module can realize auxiliary services such as system synchronous startup and battery safety protection. On the other hand, when a certain energy storage module cannot operate safely, the corresponding bypass switch can be controlled to bypass the energy storage module.

It can be seen from the above description that the SOC balance control system for the cascaded energy storage system provided by the present invention is a distributed control system, and the SOC balance control device corresponding to each energy storage module can realize the energy storage system only through local information. The SOC balance control of the module does not need to rely on other external communication. Therefore, compared with the existing SOC balance control system, the cost of the present system is greatly reduced.

At the same time, the SOC balance control system provided by the present invention can ensure that the cascaded energy storage system can realize the SOC balance of each energy storage module in the system under four different working modes. And, for the above four different operation modes, the control system can realize unified control.

In addition, the SOC balance control system not only realizes the SOC balance control of each energy storage module in the cascaded energy storage system, but also can realize the active power sharing of each energy storage module.

Reference in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "one embodiment" or "an embodiment" in various places throughout the specification are not necessarily all referring to the same embodiment.

While the above examples serve to illustrate the principles of the invention in one or more applications, it will be apparent to those skilled in the art that the invention can be made in form, usage, and implementation without departing from the principles and spirit of the invention. Various modifications can be made to the details without creative labor. Accordingly, the invention is defined by the appended claims.

Claims (8)

1. A SOC balance control system for a cascaded energy storage system, characterized in that the system comprises a plurality of control devices with the same structure, and each control device is respectively connected with each energy storage module in the cascaded energy storage system in a one-to-one correspondence And can independently perform SOC balance control on the corresponding energy storage module, for an energy storage module to be controlled, the corresponding control device includes: an output voltage reference value generation module, configured to generate an output voltage reference value for the energy storage module to be controlled according to the obtained state of charge and output power of the energy storage module to be controlled; a closed-loop control module, configured to generate a corresponding modulation reference signal according to the output voltage reference value based on a closed-loop control strategy; a pulse modulation module, which is configured to generate a corresponding switching pulse signal according to the modulation reference signal, so as to adjust the state of charge of the energy storage module to be controlled through the switching pulse signal; The simulation model verification module is used to verify the state of charge and power changes of the cascaded energy storage system in various operation modes through the simulation model of the cascaded energy storage system; wherein, the operation mode includes the load characteristic switching function of the cascaded energy storage system. condition; The output voltage reference value generating module further includes: A phase angle reference value generation unit, which is used for determining the angular frequency reference value of the output voltage according to the state of charge and output power of the energy storage module to be controlled and the droop control coefficient of the energy storage module to be controlled, and according to the angular frequency The reference value generates the phase angle reference value of the output voltage; where the droop control coefficient m _i satisfies the following conditions:

In the formula, θ _i , θ _j and θ _k are the phase angle reference values of the i, j, and kth energy storage modules, respectively, θ _load represents the impedance angle of the load, and Z _load represents the load impedance modulo value; SOC _i and SOC _k respectively represent the state of charge of the ith and kth energy storage modules, N represents the total number of energy storage modules in the cascaded energy storage system, K represents the correction coefficient of the angular frequency correction term of the energy storage module, and m _i represents the ith energy storage module. For the droop control coefficient of the energy storage module, the K/m _i value is set to a preset value according to the demand, so as to make the system stable; an amplitude reference value generating unit, which is used for determining the amplitude reference value of the output voltage according to the voltage amplitude reference weight of the energy storage module to be controlled and the voltage amplitude reference value at the common point of the cascaded energy storage system; Wherein, the amplitude reference value generating unit is configured to determine the amplitude reference value of the output voltage of the energy storage module to be controlled according to the following expression:

Among them, V _i represents the amplitude reference value of the output voltage of the ith energy storage module, and the ith energy storage module is used as the energy storage module to be controlled,

Represents the voltage amplitude reference weight of the i-th energy storage module, V ^* represents the voltage amplitude reference value at the common point of the cascaded energy storage system, E _{max_i} and ∑E _{max_i} represent the i-th energy storage module and the cascaded energy storage, respectively The maximum power capacity of the system; A reference voltage generating unit, configured to generate a reference value of the output voltage of the energy storage module to be controlled according to the reference value of the phase angle and the reference value of the amplitude of the output voltage. 2 . The system according to claim 1 , wherein when the energy storage modules in the cascaded energy storage system share a filter circuit, the output voltage reference value generation module is configured to be based on the obtained current flowing through the filter circuit. 3 . and a preset reference voltage corresponding to the energy storage module to be controlled to determine the output power of the energy storage module to be controlled. 3. The system of claim 1, wherein the amplitude reference value generating unit is configured to: Determine the voltage amplitude reference weight of the energy module to be controlled according to the maximum electric energy capacity of the cascaded energy storage system and the maximum electric energy capacity of the energy storage module to be controlled; The amplitude reference value of the output voltage of the energy storage module to be controlled is determined according to the voltage amplitude reference weight and the voltage amplitude reference value at the common point of the cascaded energy storage system. 4 . The system according to claim 1 , wherein the phase angle reference value generating unit is configured to generate the energy storage to be controlled according to the state of charge of the energy storage module to be controlled. 5 . The angular frequency correction term of the module, and the angular frequency reference value of the energy storage module to be controlled is generated according to the angular frequency correction term and the output power, and the phase angle reference value is obtained by integrating the angular frequency reference value. 5. The system of claim 4, wherein the phase angle reference value generating unit is configured to generate the angular frequency correction term of the energy storage module to be controlled according to the following expression: Δω _i = _ki ·SOC _i Among them, Δω _i represents the angular frequency correction term of the ith energy storage module, _ki represents the correction coefficient of the angular frequency correction term of the ith energy storage module, and SOC _i represents the state of charge of the ith energy storage module. 6 . The system according to claim 5 , wherein the correction coefficients of the angular frequency correction terms of each energy storage module in the cascaded energy storage system are equal. 7 . 7. The system of claim 5, wherein the phase angle reference value generating unit is configured to generate the angular frequency reference value according to the following expression: ω _i =ω ^* +sgn(Q _i )(m _i P _i -Δω _i ) Among them, ω _i represents the angular frequency reference value of the ith energy storage module, ω ^* represents the angular frequency of the _ith energy storage module at no load, and Qi and mi represent the reactive power of the _ith energy storage module, respectively and droop control coefficient, Pi represents the output power of the _{ith energy storage module, and Δω i represents} the angular frequency correction term of the ith energy storage module. 8 . A centralized large-capacity energy storage system, characterized by comprising a cascaded energy storage system and the SOC balance control system according to any one of claims 1 to 7 .

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