Battery state-of-charge balancing method and device and electronic equipment

Abstract

The invention provides a battery state of charge balancing method and device and electronic equipment, in the method, under the condition that a modular multi-level energy storage system is disconnected from a power grid, direct current circulation is injected to realize inter-phase SOC balancing, and the SOC of each bridge arm in the modular multi-level energy storage system is balanced according to the direction of the direct current circulation and the SOC of each bridge arm in the modular multi-level energy storage system. DC voltage of upper and lower bridge arms of the same phase is changed, and power distribution of the upper and lower bridge arms is changed by using injected DC ring current and DC power generated by the DC ring current, so that SOC balance between the upper and lower bridge arms in the same phase is realized. Therefore, the inter-phase and in-phase SOC balance of the modularized multi-level energy storage system when the modularized multi-level energy storage system is disconnected from the power grid is effectively realized.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to a battery state of charge equalization method, device and electronic equipment. Background Art

[0002] As the intermediate energy storage link of AC and DC power grids, energy storage systems can improve the reliability of power grid power supply. Among them, Modular Multilevel Converter Based Battery Energy Storage System (MMC-BESS) not only improves the reliability and flexibility of battery energy storage systems, but also facilitates system integration and coordinated control, and therefore has a wide range of applications.

[0003] In order to maximize the use of battery energy and extend the system life, it is necessary to balance the SOC (State Of Charge) between different power sub-modules of MMC-BESS. At present, there are certain strategies for SOC balancing of MMC-BESS in the grid-connected state, but there is still a lack of SOC balancing strategies when MMC-BESS is disconnected from the grid. Summary of the invention

[0004] In view of the above problems, the present application provides a battery state of charge equalization method, device and electronic equipment, which can solve the SOC equalization problem of MMC-BESS when it is disconnected from the power grid.

[0005] In a first aspect, the present application provides a battery state of charge balancing method, comprising: when a modular multi-level energy storage system is disconnected from a power grid, injecting a DC circulating current into the modular multi-level energy storage system; according to the direction of the DC circulating current and the state of charge of each bridge arm in the modular multi-level energy storage system, adjusting the DC voltage of each bridge arm to balance the state of charge of the upper and lower bridge arms of the same phase.

[0006] In the above implementation process, when the modular multi-level energy storage system is disconnected from the grid, the DC circulating current is injected to achieve inter-phase SOC balance, and according to the direction of the DC circulating current and the SOC of each bridge arm in the modular multi-level energy storage system, the DC voltage of the upper and lower bridge arms of the same phase is changed, and the injected DC circulating current is used to generate DC power, thereby changing the power distribution of the upper and lower bridge arms, and then achieving SOC balance between the upper and lower bridge arms in the same phase. In this way, the inter-phase and intra-phase SOC balance of the modular multi-level energy storage system when it is disconnected from the grid is effectively solved.

[0007] In some embodiments, the DC circulating current is determined based on the overall average state of charge in the modular multi-level energy storage system, the average state of charge of each phase, the DC terminal voltage of each phase, and the phase balancing coefficient; the average state of charge of each monomer is the average value of the state of charge of all submodules in the phase; the overall average state of charge is the average value of the average state of charge of the three-phase monomers.

[0008] In the above implementation process, the DC circulating current of each phase is calculated according to the charge state of each submodule of each phase of the MMC-BESS, the DC terminal voltage and the phase balancing coefficient, and a DC power circulating between the three phases is generated between the MMC-BESS, thereby balancing the phase SOC.

[0009] In some embodiments, the DC circulating current is calculated based on the following method: calculating the difference between the overall average state of charge and the monomer average state of charge of the target phase, multiplying the difference by the inter-phase balancing coefficient, and then dividing the product by the DC terminal voltage of the target phase to obtain the DC circulating current of the target phase; the target phase is any phase of the modular multi-level energy storage system.

[0010] In the above implementation process, a specific method for calculating the DC circulating current of each phase is provided.

[0011] In some embodiments, adjusting the DC voltage of each bridge arm according to the direction of the DC circulation and the charge state of each bridge arm in the modular multi-level energy storage system includes: comparing the charge states of upper and lower bridge arms of the same phase in the modular multi-level energy storage system, and adjusting the DC voltage of the upper and lower bridge arms according to the comparison result and the direction of the DC circulation.

[0012] In the above implementation process, in the same phase, the bridge arm with a higher SOC and the bridge arm with a lower SOC are determined, and then combined with the direction of the DC circulation current, the DC voltage of the upper and lower bridge arms is adjusted accordingly to change the power distribution of the upper and lower bridge arms, thereby balancing the charge state between the upper and lower bridge arms in the same phase.

[0013] In some embodiments, the DC voltage of the upper and lower bridge arms is adjusted according to the comparison result and the direction of the DC circulation, including: when the direction of the DC circulation is positive, if the charge state of the upper bridge arm is greater than the charge state of the lower bridge arm, the DC voltage of the lower bridge arm is increased and the charge state of the upper bridge arm is reduced; if the charge state of the lower bridge arm is greater than the charge state of the upper bridge arm, the charge state of the upper bridge arm is increased and the charge state of the lower bridge arm is reduced; when the direction of the DC circulation is negative, if the charge state of the upper bridge arm is greater than the charge state of the lower bridge arm, the DC voltage of the upper bridge arm is increased and the charge state of the lower bridge arm is reduced; if the charge state of the lower bridge arm is greater than the charge state of the upper bridge arm, the charge state of the lower bridge arm is increased and the charge state of the upper bridge arm is reduced.

[0014] In the above implementation process, when the DC circulating current is positive, it indicates that the batteries of the upper and lower bridge arms will be charged. At this time, the DC voltage of the bridge arm with a lower SOC is increased, and the DC voltage of the bridge arm with a higher SOC is reduced, so that the power of the bridge arm with a lower SOC is increased and the power of the bridge arm with a higher SOC is reduced; and when the DC circulating current is negative, it indicates that the batteries of the upper and lower bridge arms will be discharged. At this time, the DC voltage of the bridge arm with a higher SOC is increased, and the DC voltage of the bridge arm with a lower SOC is reduced, so that the power of the bridge arm with a higher SOC is increased and the power of the bridge arm with a lower SOC is reduced. In this way, the SOC balance between the upper and lower bridge arms in the same phase is achieved.

[0015] In some embodiments, the regulated DC voltage of each bridge arm is calculated based on the following method: according to the difference in the charge state of the upper and lower bridge arms of the target phase, the direction of the DC circulating current and the intra-phase balancing coefficient, the superimposed component when the charge state of the upper and lower bridge arms of the target phase is balanced is calculated; the target phase is any phase of the modular multi-level energy storage system; the DC circulating current and the total circulating current of the target phase are input into the transfer function of the proportional integral link to obtain the initial DC voltage of the target phase; based on the superimposed component, the initial DC voltage of the target phase and the DC terminal voltage, the regulated DC voltage of the upper and lower bridge arms of the target phase is calculated.

[0016] In the above implementation process, a specific method for calculating the regulated DC voltage of each bridge arm is provided.

[0017] In some embodiments, the regulated DC voltage of each bridge arm is calculated based on the following formula:

[0018] Ud j =γ((SOC j_p -SOC j_n )+sign(I dc_j ))

[0019] U dc_j_ref=G(I dc_j -I cir_j )

[0020] U j_p_ref =0.5(U dc -dU j -U dc_j_ref )

[0021] U j_n_ref =0.5(U dc +dU j -U dc_j_ref )

[0022] Among them, dU j is the superposition component when the charge state of the upper and lower bridge arms of phase j is balanced; SOC j_p is the state of charge of the upper bridge arm of phase j; SOC j_n is the charge state of the lower bridge arm of phase j; γ is the phase balance coefficient; sign(x) is the sign function, when x>0, sign(x)=1, when x=0, sign(x)=0, when x<0, sign(x)=-1; U dc_j_ref is the initial DC voltage of phase j; G(s) is the transfer function of the proportional integral link for the complex variable s; I dc_j is the DC circulating current of phase j; I cir_j is the total circulation current of phase j; U j_p_ref is the DC voltage of the upper bridge arm after adjustment of phase j; U j_n_ref is the regulated DC voltage of the lower bridge arm of phase j.

[0023] In the above implementation process, the above formula can be used to quickly calculate the adjusted DC voltage of the upper and lower bridge arms of each phase, and then generate the corresponding modulation wave to achieve intra-phase SOC balance.

[0024] In some embodiments, the intra-phase balancing coefficient is determined based on the charge state of the upper and lower bridge arms of each phase, the number of submodules in each bridge arm, the minimum value of the submodule capacitor voltage, and the direction of the DC circulating current.

[0025] In the above implementation process, a specific method for determining the boundary of the intra-phase equalization coefficient is provided.

[0026] In some embodiments, the intra-phase equalization coefficient γ satisfies the following conditions:

[0027] -NU cmin ≤γ(SOC j_p -SOC j_n )sign(I dc_j )≤NU cmim

[0028] Where N is the number of submodules in each bridge arm; U cmin is the minimum value of the submodule capacitor voltage.

[0029] In the above implementation process, a boundary of the intra-phase equalization coefficient is provided, thereby effectively preventing overshoot and preventing the modulated wave from being a negative value.

[0030] In some embodiments, the DC circulating current of the target phase is determined based on a maximum current value that a battery of a submodule of the target phase can withstand when operating.

[0031] In the above implementation process, a specific method for determining the boundary of the DC circulating current is provided.

[0032] In some embodiments, the DC circulating current of phase j satisfies the following conditions:

[0033] abs(I dc_j M p / n_j )≤I lim

[0034] Where abs(x) is the function for finding the absolute value of x; M p / n_j is the switching function of the upper bridge arm / lower bridge arm of phase j; I lim It is the maximum current value that the battery of the submodule can withstand when working.

[0035] In the above implementation process, a boundary of the DC circulating current is provided, thereby effectively reducing the occurrence of battery overcurrent.

[0036] In a second aspect, the present application provides a battery state of charge balancing, including: an injection module, used to inject a DC circulating current into the modular multi-level energy storage system when the modular multi-level energy storage system is disconnected from the power grid; a regulation module, used to adjust the DC voltage of each bridge arm according to the direction of the DC circulating current and the state of charge of each bridge arm in the modular multi-level energy storage system, so as to balance the state of charge of the upper and lower bridge arms of the same phase.

[0037] In a third aspect, the present application provides an electronic device comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the steps of the method described in any one of the first aspects are implemented.

[0038] In a fourth aspect, the present application provides a computer-readable storage medium having instructions stored thereon. When the instructions are executed on a computer, the computer is caused to execute the method as described in any one of the first aspects.

[0039] In a fifth aspect, the present application provides a computer program product, which, when executed on a computer, enables the computer to execute the method as described in any one of the first aspects.

[0040] Other features and advantages disclosed in the present application will be described in the following description, or some features and advantages can be inferred or determined without doubt from the description, or can be learned by implementing the above-mentioned technology disclosed in the present application.

[0041] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, preferred embodiments are specifically cited below and described in detail with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0043] Figure 1 A schematic diagram of the topological structure of an MMC-BESS provided in some embodiments of the present application;

[0044] Figure 2 A flow chart of a battery state of charge equalization method provided in some embodiments of the present application;

[0045] Figure 3 A schematic diagram of power distribution of three phases A, B, and C in an MMC-BESS provided in some embodiments of the present application, wherein the horizontal axis is time in s (seconds), and the vertical axis is power in W (watts);

[0046] Figure 4a A schematic diagram of power distribution of the upper and lower bridge arms of phase A in the MMC-BESS provided in some embodiments of the present application, wherein the abscissa is time in s (seconds), and the ordinate is power in W (watts);

[0047] Figure 4b A schematic diagram of power distribution of the upper and lower bridge arms of the B phase in the MMC-BESS provided in some embodiments of the present application, wherein the abscissa is time in s (seconds), and the ordinate is power in W (watts);

[0048] Figure 4c A schematic diagram of power distribution of the upper and lower bridge arms of the C phase in the MMC-BESS provided in some embodiments of the present application, wherein the abscissa is time in s (seconds), and the ordinate is power in W (watts);

[0049] Figure 5a A schematic diagram of a DC circulating current injected into phase A of an MMC-BESS provided in some embodiments of the present application, wherein the abscissa is time in seconds (s), and the ordinate is current in amperes (A);

[0050] Figure 5b A schematic diagram of a DC circulating current injected into the B phase of an MMC-BESS provided in some embodiments of the present application, wherein the abscissa is time in s (seconds), and the ordinate is current in A (amperes);

[0051] Figure 5c A schematic diagram of a DC circulating current injected into the C phase of an MMC-BESS provided in some embodiments of the present application, wherein the abscissa is time in s (seconds), and the ordinate is current in A (amperes);

[0052] Figure 6a A schematic diagram of voltage waveforms of upper and lower bridge arms of phase A in MMC-BESS provided in some embodiments of the present application, wherein the abscissa is time in s (seconds), and the ordinate is voltage in V (volts);

[0053] Figure 6b A schematic diagram of voltage waveforms of upper and lower bridge arms of phase B in an MMC-BESS provided in some embodiments of the present application, wherein the abscissa is time in s (seconds), and the ordinate is voltage in V (volts);

[0054] Figure 6c A schematic diagram of voltage waveforms of upper and lower bridge arms of phase C in an MMC-BESS provided in some embodiments of the present application, wherein the abscissa is time in s (seconds), and the ordinate is voltage in V (volts);

[0055] Figure 7 A block diagram of a battery state of charge equalization device provided in some embodiments of the present application;

[0056] Figure 8 A structural block diagram of an electronic device provided for some embodiments of the present application. DETAILED DESCRIPTION

[0057] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0058] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. At the same time, in the description of this application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0059] MMC-BESS has the characteristics of high efficiency, low harmonic content, and strong fault tolerance, and is suitable for medium- and high-voltage large-capacity energy storage applications. Figure 1 As shown, Figure 1 This is a schematic diagram of the topological structure of MMC-BESS. MMC-BESS consists of three phases, A, B, and C. Each phase is divided into an upper bridge arm and a lower bridge arm. Each bridge arm is composed of N submodules and a bridge arm inductor in series. Each submodule consists of a full / half-bridge power module and a battery cluster. Each battery cluster is composed of M battery cells in series and is directly connected to the DC end of the power module. When the battery charge state of each submodule in the MMC-BESS is dispersed, it is easy to affect the safe and stable operation of the entire system. At present, there are certain strategies for the SOC balancing of MMC-BESS in the grid-connected state, such as controlling the DC circulating current and the AC baseband circulating current to balance the SOC between phases and between the upper and lower bridge arms of the same phase. However, it does not take into account the working conditions when the system is disconnected from the grid. When the MMC-BESS is disconnected from the grid, its port voltage is no longer clamped by the grid voltage, and there is no AC power exchange with the grid. At this time, the original control strategy is difficult to implement.

[0060] In view of the above technical problems, the embodiment of the present application provides a battery state of charge balancing method. When the MMC-BESS is disconnected from the power grid, a DC circulating current is injected to achieve inter-phase SOC balancing, and the DC voltage of each bridge arm is adjusted according to the direction of the DC circulating current and the charge state of each bridge arm. The injected DC circulating current is used to generate DC power, and the power distribution of the upper and lower bridge arms is changed, thereby balancing the SOC in the upper and lower bridge arms of the same phase. In this way, the SOC balancing is achieved when the MMC-BESS is disconnected from the power grid.

[0061] Next, the embodiments of the present application are introduced:

[0062] like Figure 2 As shown, Figure 2 It is a flow chart of a battery state of charge equalization method provided in an embodiment of the present application. The method can be applied to the control system of MMC-BESS, and the control system can control the submodules of MMC-BESS by generating PWM (Pulse Width Modulation) waves.

[0063] The method comprises:

[0064] Step 101: When a modular multi-level energy storage system is disconnected from a power grid, injecting a DC circulating current into the modular multi-level energy storage system;

[0065] In practical applications, grid-connected operation and off-grid operation are two working modes of MMC-BESS. The difference between the two is whether they are connected to the grid. That is to say, off-grid operation is the situation where MMC-BESS is disconnected from the grid. When MMC-BESS is disconnected from the grid, its port voltage is no longer clamped by the grid voltage, and there is no AC power exchange with the grid. In this embodiment, by injecting a DC loop current into the MMC-BESS, a DC power circulating between the three phases is generated between the MMC-BESS, thereby playing a role in balancing the inter-phase SOC.

[0066] In some embodiments, the DC circulating current can be determined based on the overall average state of charge in the MMC-BESS, the average state of charge of each phase cell, the DC terminal voltage of each phase, and the phase balancing coefficient; the average state of charge of each cell is the average state of charge of all submodules in the phase; the overall average state of charge is the average state of charge of the three-phase cells. In other words, assuming that the average states of charge of the three-phase cells are SOC a , SOC b , SOC c , defined as the average state of charge of each submodule per phase, then the overall average state of charge SOC of MMC-BESS is bess It can be calculated based on the following formula:

[0067] SOC bess =(SOC a +SOC b +SOC c ) / 3

[0068] The overall average state of charge SOC of MMC-BESS is calculated. bess , and the average state of charge SOC of the monomers in phase j j After that, combined with the DC terminal voltage U of phase j dc_j And the phase balance coefficient λ, the DC circulating current I of phase j can be calculated dc_j .

[0069] Further, in some embodiments, the DC circulating current can be calculated based on the following method: calculate the difference between the overall average state of charge and the average state of charge of the monomers of the target phase, multiply the difference by the interphase balancing coefficient, and then divide the product by the DC terminal voltage of the target phase to obtain the DC circulating current of the target phase; the target phase is any phase of the MMC-BESS. In the MMC-BESS, the injected DC component should satisfy P j =U dc_j I dc_j =λ(SOC bess -SOC j ), therefore, the DC circulating current I of phase j dc_jIt can be calculated based on the following formula:

[0070] I dc_j =λ(SOC bess -SOC j ) / U dc_j

[0071] At this time, the sum of the DC circulating currents injected into the three phases is 0. The DC circulating current of each phase can be calculated by the above formula. Among them, the value of the phase balancing coefficient λ can be set according to the needs of the specific scenario, such as the requirements for the balance of the phase SOC and the requirements for the power quality. Optionally, the absolute value of the phase balancing coefficient λ does not exceed 1, that is, the value of λ is within the open interval (-1, 1).

[0072] Step 102: According to the direction of the DC circulating current and the charge state of each bridge arm in the modular multi-level energy storage system, adjust the DC voltage of each bridge arm to balance the charge state of the upper and lower bridge arms of the same phase.

[0073] In the upper and lower bridge arms of the same phase, the power P of the upper bridge arm is jp =U dc_jp I dc_j , the power of the lower bridge arm P jn =U dc_ jn I dc_j , where U dc_jp is the voltage of the upper bridge arm, U dc_jn is the voltage of the lower bridge arm. Therefore, changing the voltage of the upper and lower bridge arms can change the power distribution in the upper and lower bridge arms in the same phase. Based on this, in this embodiment, the DC voltage of each bridge arm is adjusted according to the direction of the DC circulation and the charge state of each bridge arm, and the injected DC circulation is used to generate DC power therewith, thereby achieving SOC balance between the upper and lower bridge arms in the same phase.

[0074] In some embodiments, this step may include: comparing the charge states of the upper and lower bridge arms of the same phase in the MMC-BESS, and adjusting the DC voltages of the upper and lower bridge arms according to the comparison result and the direction of the DC circulation. That is, the SOCs of the upper and lower bridge arms of the same phase in the MMC-BESS are compared to determine the bridge arm with a higher SOC and the bridge arm with a lower SOC, and then the DC voltages of the upper and lower bridge arms are adjusted accordingly in combination with the direction of the DC circulation to change the power distribution of the upper and lower bridge arms, thereby balancing the charge states between the upper and lower bridge arms in the same phase.

[0075] Furthermore, the aforementioned adjustment of the DC voltages of the upper and lower bridge arms according to the comparison results and the direction of the DC circulation current may include: when the direction of the DC circulation current is positive, if the state of charge of the upper bridge arm is greater than the state of charge of the lower bridge arm, then the DC voltage of the lower bridge arm is increased and the state of charge of the upper bridge arm is decreased; if the state of charge of the lower bridge arm is greater than the state of charge of the upper bridge arm, then the state of charge of the upper bridge arm is increased and the state of charge of the lower bridge arm is decreased; when the direction of the DC circulation current is negative, if the state of charge of the upper bridge arm is greater than the state of charge of the lower bridge arm, then the DC voltage of the upper bridge arm is increased and the state of charge of the lower bridge arm is decreased; if the state of charge of the lower bridge arm is greater than the state of charge of the upper bridge arm, then the state of charge of the lower bridge arm is increased and the state of charge of the upper bridge arm is decreased. That is to say, with the direction of current flowing from the positive electrode to the negative electrode as the positive direction, when the DC circulation is positive, it means that the batteries of the upper and lower bridge arms will be charged. Therefore, the DC voltage of the bridge arm with a lower SOC is increased, and the DC voltage of the bridge arm with a higher SOC is reduced, so that the power of the bridge arm with a lower SOC is increased, and the power of the bridge arm with a higher SOC is reduced; similarly, when the DC circulation is negative, it means that the batteries of the upper and lower bridge arms will be discharged. Therefore, the DC voltage of the bridge arm with a higher SOC is increased, and the DC voltage of the bridge arm with a lower SOC is reduced, so that the power of the bridge arm with a higher SOC is increased, and the power of the bridge arm with a lower SOC is reduced. In this way, the SOC balance between the upper and lower bridge arms in the same phase is achieved.

[0076] In some embodiments, the regulated DC voltage of each bridge arm can be calculated based on the following method: according to the difference in the charge state of the upper and lower bridge arms of the target phase, the direction of the DC circulating current and the intra-phase balancing coefficient, the superimposed component when the charge state of the upper and lower bridge arms of the target phase is balanced is calculated; the DC circulating current and the total circulating current of the target phase are input into the transfer function of the proportional integral link to obtain the initial DC voltage of the target phase; based on the superimposed component, the initial DC voltage of the target phase and the DC terminal voltage, the regulated DC voltage of the upper and lower bridge arms of the target phase is calculated.

[0077] Using the previous example, in the MMC-BESS, the SOC of the upper bridge arm of phase j is SOC j_p , the SOC of the lower bridge arm is SOC j_n , then according to the difference in SOC between the two bridge arms and the DC circulating current I dc_j The direction and the phase balance coefficient γ can be used to calculate the superposition component dU when the upper and lower bridge arms of phase j are balanced. j At the same time, the total circulating current can be considered to be composed of AC circulating current components and DC circulating current components, and the transfer function of the proportional integral link G(s) = k p +k i / s, where k p is the gain of the proportional link, k iis the gain of the integral link, s is a complex variable, and this transfer function can be used to describe the dynamic response characteristics of the control system. In this embodiment, the DC circulating current I of phase j is dc_j and total circulation I cir_j By inputting the transfer function G(s), we can get the initial DC voltage U of phase j. dc_j_ref ; Then, based on the superposition component dU j , the initial DC voltage U dc_j_ref And the DC terminal voltage U dc , the regulated DC voltage of the upper and lower bridge arms of phase j can be calculated.

[0078] Optionally, the calculation process of the DC voltage after adjustment of the upper and lower bridge arms of the j-phase can be expressed as the following formula:

[0079] Ud j =γ((SOC j_p -SOC j_n )+sign(I dc_j ))

[0080] U dc_j_ref =G(I dc_j -I cir_j )

[0081] U j_p_ref =0.5(U dc -dU j -U dc_j_ref )

[0082] U j_n_ref =0.5(U dc +dU j -U dc_j_ref )

[0083] Wherein, sign(x) is the sign function, when x>0, sign(x)=1, when x=0, sign(x)=0, when x<0, sign(x)=-1; U j_p_ref is the DC voltage of the upper bridge arm after adjustment of phase j; U j_n_ref is the DC voltage of the lower bridge arm after adjustment of the j-phase. Through the above formula, the DC voltage of the upper and lower bridge arms after adjustment of each phase can be quickly calculated, and then the corresponding modulation wave can be generated to achieve SOC balance within the phase.

[0084] In addition, some embodiments of the present application also provide the boundary of the intra-phase balancing coefficient. Optionally, the intra-phase balancing coefficient can be determined based on the charge state of the upper and lower bridge arms of each phase, the number of sub-modules in each bridge arm, the minimum value of the sub-module capacitor voltage, and the direction of the DC loop current. Specifically, in order to prevent the bridge arm voltage from being over-regulated and the voltage command from being negative, the intra-phase balancing coefficient γ should meet the following conditions:

[0085] -NU cmin ≤γ(SOC j_p -SOC j_n )sign(I dc_j )≤NU cmin

[0086] Where N is the number of submodules in each bridge arm; U cmin is the minimum value of the submodule capacitor voltage. In this way, overshoot and negative modulation wave can be effectively prevented.

[0087] At the same time, some embodiments of the present application also provide a boundary of the DC circulating current. Optionally, the DC circulating current of the target phase can be determined based on the maximum current value that the battery of the submodule of the target phase can withstand when working. Specifically, in order to prevent the injected DC circulating current from causing the battery current to overcurrent, the DC circulating current I dc_j The following conditions should be met:

[0088] abs(I dc_j M p / n_j )≤I lim

[0089] Where abs(x) is the function for finding the absolute value of x; M p / n_j is the switching function of the upper bridge arm / lower bridge arm of phase j; I lim It is the maximum current value that the battery of the submodule can withstand when working. Under the most extreme conditions, the DC voltage is completely distributed in the upper bridge arm or the lower bridge arm. At this time, the DC circulating current I dc_j The following conditions should be met:

[0090] abs(I dc_j )≤I lim

[0091] In this way, the occurrence of battery overcurrent can be effectively reduced.

[0092] In the embodiment of the present application, when the modular multi-level energy storage system is disconnected from the power grid, a DC circulating current is injected to achieve inter-phase SOC balance, and according to the direction of the DC circulating current and the SOC of each bridge arm in the modular multi-level energy storage system, the DC voltage of the upper and lower bridge arms of the same phase is changed, and the injected DC circulating current is used to generate DC power with it, thereby changing the power distribution of the upper and lower bridge arms, and then achieving SOC balance between the upper and lower bridge arms in the same phase. In this way, the inter-phase and intra-phase SOC balance of the modular multi-level energy storage system when it is disconnected from the power grid is effectively solved.

[0093] In order to explain the solution of this application in more detail, a specific embodiment is introduced below:

[0094] In this embodiment, a 10kV MMC-BESS is used for simulation testing. The battery of the MMC-BESS is replaced by an ideal DC power supply series resistor, the voltage of the DC power supply is 800V, and the resistance is 0.1Ω; a single bridge arm of the MMC-BESS includes 30 submodules; the bridge arm inductance is 4mH; the submodule uses an LC filter, the filter inductance is 7.5mH, and the filter capacitor is 30mF.

[0095] Under one working condition, the SOC of the upper bridge arm of the A phase of the MMC-BESS is 0.9, and the SOC of the lower bridge arm is 0.9, that is, the average SOC of the A phase is 0.9; the SOC of the upper bridge arm of the B phase is 0.7, and the SOC of the lower bridge arm is 0.5, that is, the average SOC of the B phase is 0.6; the SOC of the upper bridge arm of the C phase is 0.4, and the SOC of the lower bridge arm is 0.6, that is, the average SOC of the C phase is 0.5. Then, the average SOC of the three phases is 2 / 3.

[0096] Through simulation test, the power distribution of phases A, B, and C is obtained as follows Figure 3 As shown, curve 31 is a curve indicating the power of phase A, curve 32 is a curve indicating the power of phase B, and curve 33 is a curve indicating the power of phase C. Figure 3 It can be seen that the average SOC of phase A is higher than the average SOC of the three phases, so its power is negative, and it discharges to phases B and C. The difference between the average SOC of the three phases and the average SOC of phase C is greater than the difference between the average SOC of the three phases and the average SOC of phase B. Therefore, the charging power of phase C is higher than that of phase B.

[0097] At this time, the power distribution of the upper and lower bridge arms of the three phases A, B, and C are as follows: Figure 4a , Figure 4b , Figure 4c As shown, curve 41 is a schematic diagram indicating the power of the upper bridge arm of phase A, curve 42 is a schematic diagram indicating the power of the lower bridge arm of phase A, curve 43 is a schematic diagram indicating the power of the upper bridge arm of phase B, curve 44 is a schematic diagram indicating the power of the lower bridge arm of phase B, curve 45 is a schematic diagram indicating the power of the upper bridge arm of phase C, and curve 46 is a schematic diagram indicating the power of the lower bridge arm of phase C. Figure 4a It can be seen that since the SOC of the upper and lower bridge arms of phase A is the same, the power distribution of the upper and lower bridge arms is also equal. Figure 4b It can be seen that since the SOC of the upper bridge arm of phase B is greater than the SOC of the lower bridge arm, and phase B is in a charging state at this time, the power of the lower bridge arm of phase B is greater than the power of the upper bridge arm. Figure 4c It can be seen that since the SOC of the upper bridge arm of the C phase is less than the SOC of the lower bridge arm, and the C phase is in a charging state, the power of the upper bridge arm of the C phase is greater than the power of the lower bridge arm.

[0098] Based on this, a DC circulating current is injected into the MMC-BESS, and the DC voltage of the upper and lower bridge arms of each phase is changed. The injected A, B, and C three-phase circulating currents are respectively as follows: Figure 5a , Figure 5b , Figure 5c As shown, curve 51 is a curve indicating the DC circulating current injected into phase A, curve 52 is a curve indicating the DC circulating current injected into phase B, and curve 53 is a curve indicating the DC circulating current injected into phase C. The voltage waveforms of the upper and lower bridge arms of the three phases are respectively as shown in FIG. Figure 6a , Figure 6b , Figure 6c As shown, curve 61 is a curve indicating the DC voltage of the upper bridge arm of phase A, curve 62 is a curve indicating the DC voltage of the lower bridge arm of phase A, curve 63 is a curve indicating the DC voltage of the upper bridge arm of phase B, curve 64 is a curve indicating the DC voltage of the lower bridge arm of phase B, curve 65 is a curve indicating the DC voltage of the upper bridge arm of phase C, and curve 66 is a curve indicating the DC voltage of the lower bridge arm of phase C.

[0099] It is determined through experiments that during off-grid operation, the SOC between phases and within phases in the MMC-BESS are balanced, thereby verifying the effectiveness of the SOC balancing strategy proposed in this embodiment.

[0100] Corresponding to the embodiments of the aforementioned method, the present application also provides embodiments of a battery state of charge equalization device and a terminal using the same:

[0101] like Figure 7 As shown, Figure 7 is a block diagram of a battery state of charge equalization device provided in an embodiment of the present application, the device comprising:

[0102] An injection module 71, configured to inject a DC circulating current into the modular multi-level energy storage system when the modular multi-level energy storage system is disconnected from the power grid;

[0103] The regulating module 72 is used to regulate the DC voltage of each bridge arm according to the direction of the DC circulating current and the charge state of each bridge arm in the modular multi-level energy storage system, so as to balance the charge state of the upper and lower bridge arms of the same phase.

[0104] The implementation process of the functions and effects of each module in the above-mentioned device is specifically described in the implementation process of the corresponding steps in the above-mentioned method, which will not be repeated here.

[0105] This application also provides an electronic device, see Figure 8 , Figure 8A block diagram of an electronic device provided in an embodiment of the present application. The electronic device may include a processor 810, a communication interface 820, a memory 830, and at least one communication bus 840. The communication bus 840 is used to realize direct connection and communication between these components. The communication interface 820 of the electronic device in the embodiment of the present application is used to communicate signaling or data with other node devices. The processor 810 may be an integrated circuit chip with signal processing capabilities.

[0106] The processor 810 may be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it may also be a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components. The methods, steps and logic block diagrams disclosed in the embodiments of the present application may be implemented or executed. The processor 810 may be a microprocessor, or the processor 810 may be any conventional processor, etc.

[0107] The memory 830 may be, but is not limited to, a random access memory (RAM), a read only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electric erasable programmable read-only memory (EEPROM), etc. The memory 830 stores computer-readable instructions. When the computer-readable instructions are executed by the processor 810, the electronic device can execute the above-mentioned Figure 2 The method embodiment involves various steps.

[0108] Optionally, the electronic device may further include a storage controller and an input / output unit.

[0109] The memory 830, storage controller, processor 810, peripheral interface, input and output unit components are directly or indirectly electrically connected to each other to achieve data transmission or interaction. For example, these components can be electrically connected to each other via one or more communication buses 840. The processor 810 is used to execute executable modules stored in the memory 830, such as software function modules or computer programs included in the electronic device.

[0110] The input and output unit is used to provide users with the task creation and to create a start optional time period or preset execution time for the task to realize the interaction between the user and the server. The input and output unit can be, but is not limited to, a mouse and a keyboard.

[0111] Understandably, Figure 8 The structure shown is for illustration only, and the electronic device may also include Figure 8 More or fewer components as shown, or with Figure 8 Different configurations are shown. Figure 8 Each component shown in the figure can be implemented by hardware, software or a combination thereof.

[0112] An embodiment of the present application further provides a storage medium having instructions stored thereon. When the instructions are run on a computer, the computer program is executed by a processor to implement the method described in the method embodiment. To avoid repetition, the method will not be described here.

[0113] The present application also provides a computer program product, which, when executed on a computer, enables the computer to execute the method described in the method embodiment.

[0114] In several embodiments provided in the present application, it should be understood that the disclosed devices and methods can also be implemented in other ways. The device embodiments described above are merely schematic. For example, the flowcharts and block diagrams in the accompanying drawings show the possible architecture, functions and operations of the devices, methods and computer program products according to multiple embodiments of the present application. In this regard, each box in the flowchart or block diagram can represent a module, a program segment or a part of a code, and the module, a program segment or a part of a code contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in a different order from the order marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or flowchart, and the combination of boxes in the block diagram and / or flowchart can be implemented with a dedicated hardware-based system that performs a specified function or action, or can be implemented with a combination of dedicated hardware and computer instructions.

[0115] In addition, the functional modules in the various embodiments of the present application may be integrated together to form an independent part, or each module may exist separately, or two or more modules may be integrated to form an independent part.

[0116] If the functions are implemented in the form of software function modules and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application can be essentially or partly embodied in the form of a software product that contributes to the prior art. The computer software product is stored in a storage medium, including several instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in each embodiment of the present application. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0117] The above description is only an embodiment of the present application and is not intended to limit the scope of protection of the present application. For those skilled in the art, the present application may have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings.

[0118] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

[0119] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

Claims

1. A battery state of charge equalization method, characterized in that: include: In the case where the modular multi-level energy storage system is disconnected from the power grid, injecting a DC circulating current into the modular multi-level energy storage system; According to the direction of the DC circulating current and the charge state of each bridge arm in the modular multi-level energy storage system, the DC voltage of each bridge arm is adjusted to balance the charge state of the upper and lower bridge arms of the same phase.

2. The method according to claim 1, characterized in that The DC circulating current is determined based on the overall average state of charge in the modular multi-level energy storage system, the average state of charge of each phase, the DC terminal voltage of each phase, and the phase balancing coefficient; the average state of charge of each monomer is the average value of the state of charge of all submodules in the phase; the overall average state of charge is the average value of the average state of charge of the three-phase monomers.

3. The method according to claim 2, characterized in that The DC circulating current is calculated based on the following method: The difference between the overall average state of charge and the average state of charge of the monomers of the target phase is calculated, the difference is multiplied by the inter-phase balancing coefficient, and the product is divided by the DC terminal voltage of the target phase to obtain the DC circulating current of the target phase; the target phase is any phase of the modular multi-level energy storage system.

4. The method according to any one of claims 1 to 3, characterized in that: The step of adjusting the DC voltage of each bridge arm according to the direction of the DC circulating current and the charge state of each bridge arm in the modular multi-level energy storage system includes: The charge states of the upper and lower bridge arms of the same phase in the modular multi-level energy storage system are compared, and the DC voltages of the upper and lower bridge arms are adjusted according to the comparison result and the direction of the DC circulating current.

5. The method according to claim 4, characterized in that The step of adjusting the DC voltages of the upper and lower bridge arms according to the comparison result and the direction of the DC circulating current includes: When the direction of the DC circulation is the positive direction, if the state of charge of the upper bridge arm is greater than the state of charge of the lower bridge arm, the DC voltage of the lower bridge arm is increased and the state of charge of the upper bridge arm is reduced; if the state of charge of the lower bridge arm is greater than the state of charge of the upper bridge arm, the state of charge of the upper bridge arm is increased and the state of charge of the lower bridge arm is reduced; When the direction of the DC circulation is negative, if the charge state of the upper bridge arm is greater than that of the lower bridge arm, the DC voltage of the upper bridge arm is increased and the charge state of the lower bridge arm is reduced; if the charge state of the lower bridge arm is greater than that of the upper bridge arm, the charge state of the lower bridge arm is increased and the charge state of the upper bridge arm is reduced.

6. The method according to any one of claims 1 to 5, characterized in that: The DC voltage after adjustment of each bridge arm is calculated based on the following method: Calculate the superposition component when the charge states of the upper and lower bridge arms of the target phase are balanced according to the difference in charge states of the upper and lower bridge arms of the target phase, the direction of the DC circulating current, and the intra-phase balancing coefficient; The target phase is any phase of the modular multi-level energy storage system; Inputting the DC circulating current and the total circulating current of the target phase into the transfer function of the proportional-integral link to obtain the initial DC voltage of the target phase; Based on the superimposed component, the initial DC voltage of the target phase and the DC terminal voltage, the adjusted DC voltages of the upper and lower bridge arms of the target phase are calculated.

7. The method according to claim 6, characterized in that The DC voltage after adjustment of each bridge arm is calculated based on the following formula: you j =((SOC j_p -OC j_n )+ign(I dc_ )) U dc__ =(I dc_ -cir_j) IN j_p_ref =0.5(U dc -IN j -dc__) IN j_n_ref =0.5(U dc +U j -dc__) Among them, dU j is the superposition component when the charge state of the upper and lower bridge arms of phase j is balanced; SOC j_ is the state of charge of the upper bridge arm of phase j; SOC j_ is the charge state of the lower bridge arm of phase j; γ is the phase balance coefficient; sign(x) is the sign function, when x>0, sign(x)=1, when x=0, sign(x)=0, when x<0, sign(x)=-1; U dc__ is the initial DC voltage of phase j; G(s) is the transfer function of the proportional-integral link for the complex variable s; I dc_ is the DC circulating current of phase j; I cir_j is the total circulation current of phase j; U j__ref is the DC voltage of the upper bridge arm after adjustment of phase j; U j__ is the regulated DC voltage of the lower bridge arm of phase j.

8. The method according to claim 7, characterized in that The intra-phase balancing coefficient is determined based on the charge states of the upper and lower bridge arms of each phase, the number of submodules in each bridge arm, the minimum value of the submodule capacitor voltage, and the direction of the DC circulating current.

9. The method according to claim 8, characterized in that The intra-phase equalization coefficient γ satisfies the following conditions: -U cmin ≤γ(SOC j_p -OC j_n )sign(I dc_ )≤NU cmin Where N is the number of submodules in each bridge arm; U cmin is the minimum value of the submodule capacitor voltage.

10. The method according to claim 7, characterized in that The DC circulating current of the target phase is determined based on the maximum current value that the battery of the submodule of the target phase can withstand when working.

11. The method according to claim 10, characterized in that The DC circulating current of phase j satisfies the following conditions: abs(I dc_j M p / n_j )≤I lim Where abs(x) is the function for finding the absolute value of x; M p / _ is the switching function of the upper bridge arm / lower bridge arm of phase j; I lim It is the maximum current value that the battery of the submodule can withstand when working.

12. A battery state of charge equalization device, characterized in that: The device comprises: An injection module, used for injecting a DC circulating current into the modular multi-level energy storage system when the modular multi-level energy storage system is disconnected from the power grid; The regulating module is used to regulate the DC voltage of each bridge arm according to the direction of the DC circulation and the charge state of each bridge arm in the modular multi-level energy storage system, so as to balance the charge state of the upper and lower bridge arms of the same phase.

13. A computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the computer program is executed by a processor, the method according to any one of claims 1 to 11 is implemented.

14. An electronic device, characterized in that: The method comprises a processor, a memory, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the method according to any one of claims 1 to 11 is implemented.

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