A battery state of charge equalization method, device and electronic equipment

Abstract

This application provides a battery state-of-charge (SOC) balancing method, apparatus, and electronic device. In this method, when a modular multilevel energy storage system (MMES) is disconnected from the grid, a DC circulating current is injected to achieve inter-phase SOC balancing. Furthermore, based on the direction of the DC circulating current and the SOC of each arm in the MMES, the DC voltage of the upper and lower arms of the same phase is changed. The injected DC circulating current generates DC power, thereby altering the power distribution of the upper and lower arms and achieving SOC balancing between the upper and lower arms within the same phase. This effectively solves the problem of inter-phase and intra-phase SOC balancing for MMES in MMES systems disconnected from the grid.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and more specifically, to a battery state-of-charge balancing method, apparatus, and electronic device. Background Technology

[0002] Energy storage systems, serving as intermediate energy storage links in AC / DC power grids, can improve the reliability of power supply. Among them, the 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, thus having wide applications.

[0003] To maximize battery energy utilization and extend system lifespan, it is necessary to balance the State of Charge (SOC) among different power submodules of the MMC-BESS. Currently, there are some strategies for SOC balancing in grid-connected MMC-BESS, but strategies for SOC balancing when the MMC-BESS is disconnected from the grid are still lacking. Summary of the Invention

[0004] In view of the above problems, this application provides a battery state of charge balancing method, apparatus and electronic device that can solve the SOC balancing problem when MMC-BESS is disconnected from the power grid.

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

[0006] In the above implementation process, when the modular multilevel energy storage system is disconnected from the grid, a DC circulating current is injected to achieve inter-phase SOC equalization. Furthermore, based on the direction of the DC circulating current and the SOC of each arm in the modular multilevel energy storage system, the DC voltage of the upper and lower arms of the same phase is changed. The injected DC circulating current generates DC power, thereby altering the power distribution of the upper and lower arms and ultimately achieving SOC equalization between the upper and lower arms within the same phase. This effectively solves the problem of inter-phase and intra-phase SOC equalization of the modular multilevel energy storage system when disconnected from the grid.

[0007] In some embodiments, the DC circulating current is determined based on the overall average state of charge (SOC) of the modular multilevel energy storage system, the individual average SOC of each phase, the DC terminal voltage of each phase, and the phase-to-phase equalization coefficient; the individual average SOC is the average value of the SOC of all sub-modules within a phase; and the overall average SOC is the average value of the individual average SOC of the three phases.

[0008] In the above implementation process, the DC circulating current of each phase is calculated based on the state of charge and DC terminal voltage of each sub-module of each phase of MMC-BESS and the phase balance coefficient. A DC power circulating between the three phases is generated in MMC-BESS, thereby playing the role of balancing the state of charge between phases.

[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 individual average state of charge of the target phase, multiplying the difference by the phase-to-phase equalization 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 multilevel 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 circulating current and the state of charge of each bridge arm in the modular multilevel energy storage system includes: comparing the state of charge of the upper and lower bridge arms of the same phase in the modular multilevel 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 circulating current.

[0012] In the above implementation process, in the same phase, the bridge arm with higher SOC and the bridge arm with lower SOC are identified. Then, in combination with the direction of DC circulating 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 state of charge between the upper and lower bridge arms in the same phase.

[0013] In some embodiments, adjusting the DC voltage 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 circulating current is positive, if the state of charge of the upper bridge arm is greater than that of the lower bridge arm, then increase the DC voltage of the lower bridge arm and decrease the state of charge of the upper bridge arm; if the state of charge of the lower bridge arm is greater than that of the upper bridge arm, then increase the state of charge of the upper bridge arm and decrease the state of charge of the lower bridge arm; when the direction of the DC circulating current is negative, if the state of charge of the upper bridge arm is greater than that of the lower bridge arm, then increase the DC voltage of the upper bridge arm and decrease the state of charge of the lower bridge arm; if the state of charge of the lower bridge arm is greater than that of the upper bridge arm, then increase the state of charge of the lower bridge arm and decrease the state of charge of the upper bridge arm.

[0014] In the above implementation process, when the DC circulating current is positive, it indicates that the batteries in both the upper and lower bridge arms will be charged. At this time, increasing the DC voltage of the bridge arm with the lower SOC and decreasing the DC voltage of the bridge arm with the higher SOC increases the power of the bridge arm with the lower SOC and decreases the power of the bridge arm with the higher SOC. Conversely, when the DC circulating current is negative, it indicates that the batteries in both the upper and lower bridge arms will be discharged. At this time, increasing the DC voltage of the bridge arm with the higher SOC and decreasing the DC voltage of the bridge arm with the lower SOC increases the power of the bridge arm with the higher SOC and decreases the power of the bridge arm with the lower SOC. This achieves SOC balance between the upper and lower bridge arms within the same phase.

[0015] In some embodiments, the adjusted DC voltage of each bridge arm is calculated based on the following method: the superposition component of the state of charge of the upper and lower bridge arms of the target phase when the state of charge is balanced is calculated according to the difference in the state of charge of the upper and lower bridge arms of the target phase, the direction of the DC circulating current, and the phase balancing coefficient; the target phase is any phase of the modular multilevel 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; the adjusted DC voltage of the upper and lower bridge arms of the target phase is calculated based on the superposition component, the initial DC voltage of the target phase, and the DC terminal voltage.

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

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

[0018] dU 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 The superposition component of the upper and lower arms of phase j when the state of charge is balanced; SOC j_p State of charge (SOC) of the upper arm of phase j. j_n U represents the state of charge of the lower arm of phase j; γ is the phase balancing coefficient; sign(x) is the sign function, which is 1 when x>0, 0 when x=0, and -1 when x<0; U dc_j_ref Let be the initial DC voltage of phase j; G(s) is the transfer function of the proportional-integral link with respect to the complex variable s; I dc_j For phase j, DC circulating current; I cir_j For the total circulation of phase j; U j_p_ref U is the DC voltage after adjustment of the upper bridge arm of phase j; j_n_ref The DC voltage after adjustment of the lower bridge arm of phase j.

[0023] In the above implementation process, the DC voltage of each phase after adjustment of the upper and lower bridge arms can be quickly calculated using the above formula, and then the corresponding modulation wave can be generated to achieve intra-phase SOC balance.

[0024] In some embodiments, the intra-phase equalization coefficient is determined based on the state of charge of the upper and lower arms of each phase, the number of sub-modules in each arm, the minimum value of the sub-module 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 intraphase equilibrium coefficient is provided.

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

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

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

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

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

[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 For the switching function of the j-phase upper / lower bridge arm; I lim This is the maximum current value that the submodule's battery can withstand when it is operating.

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

[0036] Secondly, this application provides a battery state-of-charge balancing method, comprising: an injection module for injecting a DC circulating current into the modular multilevel energy storage system when the system is disconnected from the grid; and an adjustment module for adjusting the DC voltage of each arm according to the direction of the DC circulating current and the state of charge of each arm in the modular multilevel energy storage system, so as to balance the state of charge of the upper and lower arms of the same phase.

[0037] Thirdly, this application provides an electronic device, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the method as described in any of the first aspects.

[0038] Fourthly, this application provides a computer-readable storage medium storing instructions that, when executed on a computer, cause the computer to perform the method as described in any of the first aspects.

[0039] Fifthly, this application provides a computer program product that, when run on a computer, causes the computer to perform the method described in any of the first aspects.

[0040] Other features and advantages disclosed in this application will be set forth in the following description, or some features and advantages may be inferred from the description or determined without doubt, or may be learned by practicing the above-described technology disclosed in this application.

[0041] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0042] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 A schematic diagram of the topology of MMC-BESS provided in some embodiments of this application;

[0044] Figure 2 A flowchart of a battery state-of-charge balancing method provided for some embodiments of this application;

[0045] Figure 3 The diagram below illustrates the power distribution of three phases A, B, and C in MMC-BESS according to some embodiments of this application. The horizontal axis represents time in seconds (s), and the vertical axis represents power in watts (W).

[0046] Figure 4a This is a schematic diagram of the power distribution of the upper and lower arms of phase A in MMC-BESS provided in some embodiments of this application, where the horizontal axis represents time in seconds (s) and the vertical axis represents power in watts (W).

[0047] Figure 4b This is a schematic diagram of the power distribution of the upper and lower arms of phase B in MMC-BESS provided in some embodiments of this application, where the horizontal axis represents time in seconds (s) and the vertical axis represents power in watts (W).

[0048] Figure 4c This is a schematic diagram of the power distribution of the upper and lower arms of phase C in MMC-BESS provided in some embodiments of this application, where the horizontal axis represents time in seconds (s) and the vertical axis represents power in watts (W).

[0049] Figure 5a This is a schematic diagram of the DC circulating current injected into phase A of the MMC-BESS according to some embodiments of this application, where the horizontal axis represents time in seconds (s) and the vertical axis represents current in amperes (A).

[0050] Figure 5b This is a schematic diagram of the DC circulating current injected into phase B of the MMC-BESS according to some embodiments of this application, where the horizontal axis represents time in seconds (s) and the vertical axis represents current in amperes (A).

[0051] Figure 5c This is a schematic diagram of the DC circulating current injected into the C phase of the MMC-BESS according to some embodiments of this application, where the horizontal axis represents time in seconds (s) and the vertical axis represents current in amperes (A).

[0052] Figure 6a This is a schematic diagram of the voltage waveforms of the upper and lower arms of phase A in MMC-BESS provided in some embodiments of this application, where the horizontal axis represents time in seconds (s) and the vertical axis represents voltage in volts (V).

[0053] Figure 6b This is a schematic diagram of the voltage waveforms of the upper and lower arms of phase B in MMC-BESS provided in some embodiments of this application, where the horizontal axis represents time in seconds (s) and the vertical axis represents voltage in volts (V).

[0054] Figure 6c This is a schematic diagram of the voltage waveforms of the upper and lower arms of phase C in MMC-BESS provided in some embodiments of this application, where the horizontal axis represents time in seconds (s) and the vertical axis represents voltage in volts (V).

[0055] Figure 7 A block diagram of a battery state-of-charge balancing device provided in some embodiments of this application;

[0056] Figure 8 This is a structural block diagram of an electronic device provided for some embodiments of this application. Detailed Implementation

[0057] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0058] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this application, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0059] MMC-BESS features high efficiency, low harmonic content, and strong fault tolerance, making it suitable for medium- and high-voltage, large-capacity energy storage applications. Figure 1 As shown, Figure 1 This is a schematic diagram of the MMC-BESS topology. The MMC-BESS consists of three phases (A, B, and C), each divided into an upper arm and a lower arm. Each arm consists of N sub-modules and an arm inductor connected in series. Each sub-module comprises a full / half-bridge power module and a battery cluster. Each battery cluster consists of M battery cells connected in series and directly connected to the DC terminal of the power module. When the state of charge (SOC) distribution of the batteries in the various sub-modules of the MMC-BESS is dispersed, it can easily affect the safe and stable operation of the entire system. Currently, there are certain strategies for SOC balancing in grid-connected MMC-BESS, such as controlling the DC circulating current and AC baseband circulating current to achieve SOC balancing control between phases and between the upper and lower arms of the same phase. However, these strategies do not consider the operating 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. In this case, the original control strategies are difficult to implement.

[0060] To address the aforementioned technical problems, this application provides a battery state-of-charge (SOC) balancing method. When the MMC-BESS is disconnected from the grid, a DC circulating current is injected to achieve phase-to-phase SOC balancing. Based on the direction of the DC circulating current and the state of charge of each arm, the DC voltage of each arm is adjusted. The injected DC circulating current generates DC power, altering the power distribution between the upper and lower arms, thereby balancing the SOC in the upper and lower arms of the same phase. This achieves SOC balancing when the MMC-BESS is disconnected from the grid.

[0061] The embodiments of this application will be described below:

[0062] like Figure 2 As shown, Figure 2 This is a flowchart of a battery state-of-charge balancing method provided in an embodiment of this application. The method can be applied to the control system of MMC-BESS, which can control the sub-modules of MMC-BESS by generating PWM (Pulse Width Modulation) waves.

[0063] The method includes:

[0064] Step 101: When the modular multilevel energy storage system is disconnected from the grid, inject a DC circulating current into the modular multilevel energy storage system;

[0065] In practical applications, grid-connected operation and grid-off operation are the two working modes of MMC-BESS. The difference lies in whether or not it is connected to the power grid. In other words, grid-off operation means that the MMC-BESS is disconnected from the power grid. When the MMC-BESS is disconnected from the power 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 circulating current into the MMC-BESS, a DC power circulating between the three phases is generated between the MMC-BESS, thereby achieving the function of balancing the inter-phase SOC.

[0066] In some embodiments, the DC circulating current can be determined based on the overall average state of charge (SOC) in MMC-BESS, the individual average SOC of each phase, the DC terminal voltage of each phase, and the inter-phase equalization coefficient; the individual average SOC is the average of the SOCs of all submodules within a phase; the overall average SOC is the average of the individual average SOCs of the three phases. That is, assuming the individual average SOCs of the three phases are SOCs... a SOC b SOC c Defined as the average state of charge (SOC) of each phase and each submodule, the overall average SOC of MMC-BESS is then... 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 was calculated. bess And the average state of charge (SOC) of individual cells in phase j. j Then, combined with the DC terminal voltage U of phase j dc_j With the phase-to-phase equalization coefficient λ, the DC circulating current I of phase j can be calculated. dc_j .

[0069] Furthermore, in some embodiments, the DC circulating current can be calculated as follows: the difference between the overall average state of charge and the individual average state of charge of the target phase is calculated; the difference is multiplied by the inter-phase equalization 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 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 in 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 point, the sum of the injected DC circulating currents in the three phases is 0. The DC circulating current of each phase can be calculated using the above formula. The value of the interphase balance coefficient λ can be set according to the specific requirements of the scenario, such as the requirements for interphase SOC balance and power quality. Optionally, the absolute value of the interphase balance coefficient λ does not exceed 1, that is, the value of λ is within the open interval (-1, 1).

[0072] Step 102: 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 multilevel energy storage system so as to balance the state of charge of the upper and lower bridge arms of the same phase.

[0073] In the upper and lower arms of the same phase, the power P of the upper arm is... jp =U dc_jp I dc_j The power P of the lower bridge arm jn =U dc_ jn I dc_j , among which, U dc_jp U is the voltage of the upper bridge arm. dc_jn The voltage of the lower bridge arm is the voltage of the upper and lower bridge arms. Therefore, changing the voltage of the upper and lower bridge arms can change the power distribution in the upper and lower bridge arms within 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 circulating current and the state of charge of each bridge arm. The injected DC circulating current generates DC power with it, thereby achieving SOC balance between the upper and lower bridge arms within the same phase.

[0074] In some embodiments, this step may include: comparing the state of charge (SOC) of the upper and lower arms of the same phase in the MMC-BESS, and adjusting the DC voltage of the upper and lower arms according to the comparison results and the direction of the DC circulating current. That is, the SOC of the upper and lower arms of the same phase in the MMC-BESS is compared to determine the arms with higher SOC and those with lower SOC. Then, combined with the direction of the DC circulating current, the DC voltage of the upper and lower arms is adjusted accordingly to change the power distribution of the upper and lower arms, thereby balancing the state of charge between the upper and lower arms within the same phase.

[0075] Furthermore, the aforementioned adjustment of the DC voltage of the upper and lower bridge arms based on the comparison results and the direction of the DC circulating current can include: when the direction of the DC circulating current is positive, if the state of charge of the upper bridge arm is greater than that of the lower bridge arm, then increase the DC voltage of the lower bridge arm and decrease the state of charge of the upper bridge arm; if the state of charge of the lower bridge arm is greater than that of the upper bridge arm, then increase the state of charge of the upper bridge arm and decrease the state of charge of the lower bridge arm; when the direction of the DC circulating current is negative, if the state of charge of the upper bridge arm is greater than that of the lower bridge arm, then increase the DC voltage of the upper bridge arm and decrease the state of charge of the lower bridge arm; if the state of charge of the lower bridge arm is greater than that of the upper bridge arm, then increase the state of charge of the lower bridge arm and decrease the state of charge of the upper bridge arm. In other words, taking the direction of current flow from the positive terminal to the negative terminal as positive, when the DC circulating current is positive, it indicates that the batteries in both the upper and lower bridge arms will be charged. Therefore, increasing the DC voltage of the bridge arm with the lower SOC and decreasing the DC voltage of the bridge arm with the higher SOC will increase the power of the bridge arm with the lower SOC and decrease the power of the bridge arm with the higher SOC. Similarly, when the DC circulating current is negative, it indicates that the batteries in both the upper and lower bridge arms will be discharged. Therefore, increasing the DC voltage of the bridge arm with the higher SOC and decreasing the DC voltage of the bridge arm with the lower SOC will increase the power of the bridge arm with the higher SOC and decrease the power of the bridge arm with the lower SOC. In this way, SOC balance is achieved between the upper and lower bridge arms within the same phase.

[0076] In some embodiments, the adjusted DC voltage of each arm can be calculated as follows: based on the difference in the state of charge of the upper and lower arms of the target phase, the direction of the DC circulating current, and the phase balancing coefficient, the superposition component when the state of charge of the upper and lower 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 superposition component, the initial DC voltage of the target phase, and the DC terminal voltage, the adjusted DC voltage of the upper and lower arms of the target phase is calculated.

[0077] Continuing with the previous example, in MMC-BESS, the SOC of the upper arm of phase j is SOC. j_p The SOC of the lower axle arm is SOC j_n Then, based on the difference in SOC between the two bridge arms and the DC circulating current I... dc_j Based on the direction and the intra-phase equilibrium coefficient γ, the superposition component dU during SOC equilibrium of the upper and lower arms of phase j can be calculated. j Meanwhile, the total circulating current can be considered to consist of an AC circulating current component and a DC circulating current component, and the transfer function of the proportional-integral element is G(s) = k p +k i / s, where k p It is the gain of the proportional element, k iis the gain of the integral element, 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), the initial DC voltage U of phase j can be obtained. dc_j_ref Subsequently, based on this superimposed component dU j The initial DC voltage U dc_j_ref and DC terminal voltage U dc The DC voltage of the upper and lower bridge arms of phase j can be calculated after adjustment.

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

[0079] dU 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] Where sign(x) is the sign function, sign(x) = 1 when x > 0, sign(x) = 0 when x = 0, and sign(x) = -1 when x < 0; U j_p_ref U is the DC voltage after adjustment of the upper bridge arm of phase j; j_n_ref Let be the DC voltage of the lower bridge arm of phase j after adjustment. Using the above formula, the DC voltage of each phase after adjustment of the upper and lower bridge arms can be quickly calculated, and thus the corresponding modulation wave can be generated to achieve intra-phase SOC equalization.

[0084] In addition, some embodiments of this application provide boundaries for the intra-phase equalization coefficient. Optionally, the intra-phase equalization coefficient can be determined based on the state of charge of the upper and lower arms of each phase, the number of submodules in each arm, the minimum value of the submodule capacitor voltage, and the direction of the DC circulating current. Specifically, in order to ensure that the arm voltage does not overshoot and the voltage command is not negative, the intra-phase equalization coefficient γ should satisfy 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 sub-modules in each bridge arm; U cmin This is the minimum value of the submodule capacitor voltage. This effectively prevents overshoot and avoids negative values ​​in the modulation wave.

[0087] Furthermore, some embodiments of this application also provide a boundary for 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 during operation. Specifically, to prevent the injected DC circulating current from causing battery current overcurrent, the DC circulating current I... dc_j The following conditions must 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 For the switching function of the j-phase upper / lower bridge arm; I lim This is the maximum current value that the submodule's battery can withstand while operating. Under the most extreme conditions, the DC voltage is completely distributed across either the upper or lower bridge arm; in this case, the DC circulating current I... dc_j The following conditions must be met:

[0090] abs(I dc_j )≤I lim

[0091] This effectively reduces the occurrence of battery overcurrent.

[0092] In this embodiment, when the modular multilevel energy storage system is disconnected from the grid, a DC circulating current is injected to achieve inter-phase SOC equalization. Furthermore, based on the direction of the DC circulating current and the SOC of each arm in the modular multilevel energy storage system, the DC voltage of the upper and lower arms of the same phase is changed. The injected DC circulating current generates DC power, thereby altering the power distribution of the upper and lower arms and achieving SOC equalization between the upper and lower arms within the same phase. This effectively solves the problem of inter-phase and intra-phase SOC equalization for the modular multilevel energy storage system when disconnected from the grid.

[0093] To provide a more detailed explanation of the solution in this application, a specific embodiment is described 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 with a series resistor. The DC power supply voltage is 800V and the resistance is 0.1Ω. Each bridge arm of the MMC-BESS includes 30 sub-modules. The bridge arm inductance is 4mH. The sub-modules use LC filters with a filter inductance of 7.5mH and a filter capacitor of 30mF.

[0095] Under one operating condition, the SOC of the upper arm and the lower arm of phase A of this MMC-BESS are both 0.9, meaning the average SOC of phase A is 0.9; the SOC of the upper arm and the lower arm of phase B are both 0.7, meaning the average SOC of phase B is 0.6; and the SOC of the upper arm and the lower arm of phase C are both 0.4, meaning the average SOC of phase C is 0.5. Therefore, the average SOC of the three phases is 2 / 3.

[0096] Through simulation testing, the power distribution of phases A, B, and C was obtained as follows: Figure 3 As shown, curve 31 indicates the power of phase A, curve 32 indicates the power of phase B, and curve 33 indicates 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 phases A, B, and C are as follows: Figure 4a , Figure 4b , Figure 4c As shown, curve 41 indicates the power of the upper arm of phase A, curve 42 indicates the power of the lower arm of phase A, curve 43 indicates the power of the upper arm of phase B, curve 44 indicates the power of the lower arm of phase B, curve 45 indicates the power of the upper arm of phase C, and curve 46 indicates the power of the lower arm of phase C. Figure 4a It can be seen that since the State of Charge (SOC) of the upper and lower arms of phase A is the same, the power distribution of the upper and lower arms is also equal. From... Figure 4b It can be seen that since the SOC of the upper bridge arm of phase B is greater than that of the lower bridge arm, and phase B is currently in a charging state, the power of the lower bridge arm of phase B is greater than that of the upper bridge arm. Similarly, from Figure 4c It can be seen that since the SOC of the upper bridge arm of phase C is less than that of the lower bridge arm, and phase C is in a charging state, the power of the upper bridge arm of phase C is greater than that 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 as follows: Figure 5a , Figure 5b , Figure 5c As shown, curve 51 indicates the DC circulating current injected into phase A, curve 52 indicates the DC circulating current injected into phase B, and curve 53 indicates the DC circulating current injected into phase C. The voltage waveforms of the upper and lower bridge arms of the three phases are respectively shown in the figure. Figure 6a , Figure 6b , Figure 6c As shown, curve 61 indicates the DC voltage of the upper bridge arm of phase A, curve 62 indicates the DC voltage of the lower bridge arm of phase A, curve 63 indicates the DC voltage of the upper bridge arm of phase B, curve 64 indicates the DC voltage of the lower bridge arm of phase B, curve 65 indicates the DC voltage of the upper bridge arm of phase C, and curve 66 indicates the DC voltage of the lower bridge arm of phase C.

[0099] Experiments have shown that the SOC between and within phases in MMC-BESS is balanced during offline operation, thus verifying the effectiveness of the SOC balancing strategy proposed in this embodiment.

[0100] Corresponding to the embodiments of the aforementioned methods, this application also provides embodiments of a battery state-of-charge balancing device and a terminal thereof:

[0101] like Figure 7 As shown, Figure 7 This is a block diagram of a battery state-of-charge balancing device provided in an embodiment of this application. The device includes:

[0102] Injection module 71 is used to inject DC circulating current into the modular multilevel energy storage system when the modular multilevel energy storage system is disconnected from the grid.

[0103] The adjustment module 72 is 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 multilevel energy storage system, so as to balance the state of charge of the upper and lower bridge arms of the same phase.

[0104] The specific implementation process of the functions and roles of each module in the above device can be found in the implementation process of the corresponding steps in the above method, and will not be repeated here.

[0105] This application also provides an electronic device, please refer to [link to application]. Figure 8 , Figure 8This is a structural block diagram of an electronic device provided in an embodiment of this 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 enable direct communication between these components. In this embodiment, the communication interface 820 of the electronic device is used for signaling or data communication with other node devices. The processor 810 may be an integrated circuit chip with signal processing capabilities.

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

[0107] The memory 830 may be, but is not limited to, random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), etc. The memory 830 stores computer-readable instructions. When these computer-readable instructions are executed by the processor 810, the electronic device can perform the aforementioned operations. Figure 2 The various steps involved in the method implementation examples.

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

[0109] The memory 830, storage controller, processor 810, peripheral interface, and input / output unit are electrically connected directly or indirectly to achieve data transmission or interaction. For example, these components can be electrically connected to each other through 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 electronic devices.

[0110] The input / output unit is used to provide users with the ability to create tasks and to set optional start periods or preset execution times for those tasks, thereby enabling user-server interaction. The input / output unit may be, but is not limited to, a mouse and keyboard.

[0111] Understandable. Figure 8 The structure shown is for illustrative purposes only; the electronic device may also include components that are more advanced than those shown. Figure 8 The more or fewer components shown, or having the same Figure 8 The different configurations shown. Figure 8 The components shown can be implemented using hardware, software, or a combination thereof.

[0112] This application also provides a storage medium storing instructions. 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 again here.

[0113] This application also provides a computer program product that, when run on a computer, causes the computer to perform the method described in the method embodiment.

[0114] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can also be implemented in other ways. The apparatus embodiments described above are merely illustrative. For example, the flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of apparatus, methods, and computer program products according to various embodiments of this application. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than those marked in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in a block diagram and / or flowchart, and combinations of blocks in block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

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

[0116] If the aforementioned functions are implemented as software functional 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 this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0117] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application. It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0118] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0119] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

Claims

1. A battery state-of-charge balancing method, characterized in that, include: When the modular multilevel energy storage system is disconnected from the grid, a DC circulating current is injected into the modular multilevel energy storage system. Based on the direction of the DC circulating current and the state of charge of each arm in the modular multilevel energy storage system, the DC voltage of each arm is adjusted to balance the state of charge of the upper and lower 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 (SOC) of the modular multilevel energy storage system, the individual average SOC of each phase, the DC terminal voltage of each phase, and the phase balance coefficient; the individual average SOC is the average value of the SOC of all sub-modules within a phase; the overall average SOC is the average value of the individual average SOC of the three phases.

3. The method according to claim 2, characterized in that, The DC circulating current is calculated based on the following method: Calculate the difference between the overall average state of charge and the individual average state of charge of the target phase, multiply the difference by the phase-to-phase equalization 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 one phase of the modular multilevel energy storage system.

4. The method according to claim 1, 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 state of charge of each bridge arm in the modular multilevel energy storage system includes: By comparing the state of charge of the upper and lower bridge arms of the same phase in the modular multilevel energy storage system, the DC voltage of the upper and lower bridge arms is adjusted according to the comparison results and the direction of the DC circulating current.

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

6. The method according to any one of claims 1 to 5, characterized in that, The adjusted DC voltage of each bridge arm is calculated based on the following method: The superposition component when the upper and lower arms of the target phase are balanced is calculated based on the difference in the state of charge of the upper and lower arms of the target phase, the direction of the DC circulating current, and the phase balance coefficient. The target phase is any one phase of the modular multilevel energy storage system; The initial DC voltage of the target phase is obtained by inputting the DC circulating current and the total circulating current of the target phase into the transfer function of the proportional-integral element. Based on the superimposed components, the initial DC voltage of the target phase, and the DC terminal voltage, the adjusted DC voltage of the upper and lower bridge arms of the target phase is calculated.

7. The method according to claim 6, characterized in that, The adjusted DC voltage of each bridge arm is calculated based on the following formula: in, The superposition component is the upper and lower bridge arms of phase j when their charge states are balanced. The state of charge of the upper arm of phase j; The state of charge of the lower arm of phase j; This is the phase equilibrium coefficient; For a sign function, when hour, ,when hour, ,when hour, ; Let be the initial DC voltage of phase j; Let be the transfer function for the proportional-integral stage with respect to the complex variable s; For phase j, the DC circulating current; For the total circulation of phase j; The DC voltage after adjustment of the upper bridge arm of phase j; The DC voltage after adjustment of the lower bridge arm of phase j; This is the DC terminal voltage.

8. The method according to claim 7, characterized in that, The phase balance coefficient is determined based on the state of charge of the upper and lower arms of each phase, the number of sub-modules in each arm, the minimum value of the sub-module capacitor voltage, and the direction of the DC circulating current.

9. The method according to claim 8, characterized in that, The intra-phase equilibrium coefficient The following conditions must be met: in, The number of submodules for each bridge arm; This is the minimum value of the capacitor voltage in the submodule.

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 target phase submodule can withstand when it is working.

11. The method according to claim 10, characterized in that, The DC circulating current of phase j satisfies the following condition: in, In order to obtain A function of the absolute value; For the switching function of the upper / lower arm of phase j; This is the maximum current value that the submodule's battery can withstand when it is operating.

12. A battery state-of-charge balancing device, characterized in that, The device includes: An injection module is used to inject DC circulating current into the modular multilevel energy storage system when the system is disconnected from the grid. The adjustment module is 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 multilevel energy storage system, so as to balance the state of charge of the upper and lower bridge arms of the same phase.

13. A computer-readable storage medium, characterized in that, It stores a computer program thereon, which, when executed by a processor, implements the method as described in any one of claims 1 to 11.

14. An electronic device, characterized in that, It includes a processor, a memory, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the method as described in any one of claims 1 to 11.

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