Interphase charge state rapid balancing method and device of high-voltage direct-hanging energy storage system

Abstract

The invention discloses an inter-phase charge state rapid equalization method and device of a high-voltage direct-hanging energy storage system. The method comprises the steps of obtaining active and reactive components of zero-sequence current in each phase; acquiring external active and reactive current instruction values of the system in real time; judging whether a first condition is met or not; if yes, entering the second mode, otherwise, running the first mode; the first condition comprises that the absolute value of the maximum SOC deviation value among the three phases is smaller than or equal to a preset threshold value; the first mode comprises the following steps: continuously acquiring zero-sequence current regulation factors of each phase according to a preset phase current maximum threshold value, a current instruction value and active and reactive components of zero-sequence current in each phase, and selecting a real-time minimum value in the zero-sequence current regulation factors of each phase as a real-time regulation factor; multiplying the real-time regulation factor by the zero-sequence current, and injecting into the PCS; the second mode comprises the steps of multiplying the real-time regulation factor at the moment of entering the second mode by the zero-sequence current and injecting into the PCS; when the current command value changes, a first mode is entered.

Description

Technical Field

[0001] The present invention relates to the technical field of battery energy storage conversion, and particularly to a method and device for quickly equalizing the inter-phase state of charge of a high-voltage directly-connected energy storage system. Background Art

[0002] With the rapid development of the new power system, the power grid's demand for high-performance battery energy storage is gradually increasing. A battery energy storage system mainly consists of batteries, a battery management system, a PCS (Power Conversion System), and a monitoring and management system. Due to reasons such as differences in switching devices between modules in the battery energy storage system, inconsistent battery cell manufacturing processes, and power imbalance, the differences in the SOC (State of Charge) of the battery packs in each phase of the battery energy storage system will gradually increase during the operation of the PCS, thereby resulting in a reduction in the actual available capacity of the energy storage unit. Therefore, the inter-phase SOC equalization control of the energy storage system is particularly important.

[0003] The existing SOC equalization technologies mainly include hardware equalization methods and software equalization methods. The hardware equalization method mainly realizes the dissipation or transfer of energy through an externally added hardware equalization circuit. Although this method has good equalization effects, it increases the cost and volume of the system, has low system efficiency, and is more complex to control, reducing the system reliability. The software equalization method does not require additional hardware and cost and is widely applied. It redistributes power among the battery packs of each sub-module through a control algorithm, so that the SOC of all battery packs tends to be consistent. However, although the existing software equalization method avoids additional hardware costs, there are still obvious technical limitations in practical applications: on the one hand, traditional methods represented by zero-sequence voltage injection are simple to implement but face the inherent defect of slow equalization speed, especially insufficient adjustment ability when the initial SOC imbalance degree is large, and may violate the power quality standard in grid-connected applications; on the other hand, most existing algorithms are based on the ideal assumption that the capacities of all batteries are the same. When the capacity decays inconsistently during the actual operation of the battery packs, the equalization effect of the conventional proportional coefficient control strategy will deteriorate significantly. These limitations make the existing software equalization method often need to compromise between equalization speed, control accuracy, and stability when dealing with actual engineering scenarios such as large-scale energy storage systems, high-dynamic working conditions, and battery aging, and it is difficult to meet the multi-objective optimization requirements simultaneously.

[0004] Therefore, there is an urgent need for a new technical solution to solve the technical problem of how to equalize the SOC of the battery packs between phases of a dynamically operating high-voltage directly-connected chain-type energy storage system. Summary of the Invention

[0005] The present invention provides a method and device for quickly balancing the state of charge (SOC) between phases of a high-voltage direct-connected energy storage system, aiming to solve the technical problem of how to balance and control the SOC of battery packs between phases of a dynamically operating high-voltage direct-connected chain-type energy storage system.

[0006] To achieve the above object, the present invention provides a method for quickly balancing the state of charge between phases of a high-voltage direct-connected energy storage system, including: Obtaining the active and reactive components of the zero-sequence current based on the positive and negative sequence components of the three-phase voltage, the SOC deviation between phases ab, and the SOC deviation between phases bc; obtaining the zero-sequence current based on the active and reactive components of the zero-sequence current; Obtaining the active and reactive components of the zero-sequence current in each phase based on the zero-sequence current; obtaining the current command values of the active and reactive power of the system to the outside in real time; determining in real time whether the first condition is satisfied; when the first condition is satisfied, entering the second mode, otherwise operating in the first mode; the first condition includes that the absolute value of the maximum SOC deviation among the three phases is less than or equal to a preset threshold; The first mode includes: continuously obtaining the zero-sequence current adjustment factor for each phase based on the preset maximum threshold of the converter phase current, the current command value, and the active and reactive components of the zero-sequence current in each phase, and selecting the real-time minimum value among the zero-sequence current adjustment factors for each phase as the real-time adjustment factor; multiplying the real-time adjustment factor by the zero-sequence current and injecting it into the PCS; The second mode includes: multiplying the real-time adjustment factor at the moment of entering the second mode by the zero-sequence current and injecting it into the PCS; when the current command value changes, entering the first mode.

[0007] Preferably, obtaining the active and reactive components of the zero-sequence current based on the positive and negative sequence components of the three-phase voltage, the SOC deviation between phases ab, and the SOC deviation between phases bc; obtaining the zero-sequence current based on the active and reactive components of the zero-sequence current includes: Obtaining the positive and negative sequence components of the three-phase voltage, the SOC deviation between phases ab, and the SOC deviation between phases bc; obtaining a system of equations for solving the active and reactive components of the zero-sequence current based on the positive and negative sequence components of the three-phase voltage, the zero-sequence current calculation formula, and the control objective of inter-phase SOC balance; The system of equations for solving the active and reactive components of the zero-sequence current includes Expressions for and expressions for the SOC deviation between phases; where represents the active power generated by the zero-sequence current in phase x, x = ab, bc, ca; represents the reactive component of the zero-sequence current, represents the active component of the zero-sequence current; Solving the system of equations for solving the active and reactive components of the zero-sequence current and the SOC deviation between phases ab and bc to obtain the reactive component of the zero-sequence current ​ and the active component of zero-sequence current ; according to the reactive component of zero-sequence current , the active component of zero-sequence current and the zero-sequence current calculation formula to obtain the zero-sequence current.

[0008] Preferably, obtaining the positive and negative sequence components of three-phase voltage, the SOC deviation between ab phases and the SOC deviation between bc phases includes:[[]] Obtain the grid voltage and perform filtering to obtain the grid voltage and ; obtain the phase of the grid voltage ; ; According to the phase for , and perform positive and negative sequence dq transformation to obtain the positive and negative sequence components of three-phase voltage; The positive and negative sequence components of three-phase voltage include the positive sequence active voltage amplitude , the positive sequence reactive voltage amplitude , the negative sequence active voltage amplitude and the negative sequence reactive voltage amplitude , including:[[]] ; ; Among them, represents a notch filter for filtering out the second harmonic component generated by negative sequence voltage; represents a notch filter for filtering out the second harmonic component generated by positive sequence voltage; Obtaining the SOC deviation between ab phases and the SOC deviation between bc phases includes:[[]] ; ; Among them, represents the SOC deviation between x phases; represents the SOC value between x phases; represents the average value of three-phase SOC; x = ab, bc, ca.

[0009] Preferably, according to the positive and negative sequence components of three-phase voltage, the zero-sequence current calculation formula and the control target of inter-phase SOC balance, the solution equations for the active and reactive components of zero-sequence current include:[[]] According to the positive and negative sequence components of three-phase voltage and the phase to obtain , and The expressions of are:[[]] ; According to and the expression and the zero-sequence current calculation formula, we get the expressions about and : ; ; The control objective of the inter-phase SOC balance is that the of each phase is zero, then there is the expression about the inter-phase SOC deviation: ; Among them, represents the inter-phase SOC balance coefficient, which determines the speed of the balance and takes a constant according to the capacity; represents the zero-sequence current.

[0010] Preferably, solve the system of equations according to the active and reactive components of the zero-sequence current and the inter-phase SOC deviation between ab and the inter-phase SOC deviation between bc to obtain the reactive component of the zero-sequence current and the active component of the zero-sequence current; according to the reactive component of the zero-sequence current, the active component of the zero-sequence current and the zero-sequence current calculation formula, the zero-sequence current includes: the reactive component of the zero-sequence current and the active component of the zero-sequence current include: ; According to the active component of the zero-sequence current and the reactive component of the zero-sequence current, combined with the zero-sequence current calculation formula, the zero-sequence current can be obtained.

[0011] Preferably, the active and reactive components of the zero-sequence current in each phase obtained according to the zero-sequence current include: Decompose the zero-sequence current in each phase to obtain the active component of the zero-sequence current in the x phase and the reactive component : The component of the zero-sequence current in the ab phase: ; The component of the zero-sequence current in the bc phase: ; The zero-sequence current Component in ca phase: ; in, Indicates the grid voltage The phase of Indicates the grid voltage phase.

[0012] Preferably, continuously obtaining the zero-sequence current adjustment factor of each phase according to the preset converter phase current maximum threshold, current command value and active and reactive components of zero-sequence current in each phase includes: The current command amplitude of each phase is obtained according to the current command value and the active and reactive components of the zero-sequence current in each phase. Regarding the expression of the zero-sequence current regulation factor; assuming that the maximum threshold of the converter phase current is preset to be ,in is the proportionality factor used to retain the preset current safety margin. is the phase current limit value; each phase current command amplitude Should be less than or equal to , so establish The expression of zero-sequence current regulation factor is The inequality between them is solved by taking the equal sign to obtain the zero-sequence current regulation factor of each phase; Continuously calculating the zero-sequence current adjustment factors of each phase means continuously obtaining the zero-sequence current adjustment factors of each phase.

[0013] Preferably, the current command amplitude of each phase is obtained according to the current command value and the active and reactive components of the zero-sequence current in each phase. The expressions for the zero-sequence current regulation factor include: Define the zero-sequence current regulation factor as ,Will With zero sequence current After multiplication, the new zero-sequence current for injection into PCS is obtained , expressed as: ; in, Indicates the phase of the x-phase grid voltage; Active component in phase x and reactive components for: ; but It can be expressed based on the x phase as: ; Total current command Expressed as: ; Wherein, and respectively represent the external active current command value and the external reactive current command value of the x-phase.

[0014] According to the total current command and the active component and reactive component in the x-phase, the amplitude value of the current command for each phase is obtained : ; Preferably, an inequality between the expression of the zero-sequence current adjustment factor and is established, and the inequality is solved by taking the equal sign to obtain the zero-sequence current adjustment factor for each phase, including: The inequality includes: ; Thus, the zero-sequence current adjustment factor satisfying the requirements of each phase is obtained, denoted as ; If it is required that all three phases satisfy , the value of should be the intersection of The expressions of are similar. Let take the equal sign, and two different real number solutions and of are calculated: ; Wherein, is an intermediate quantity.

[0015] The value range of is: Considering that the SOC equalization speed is positively correlated with the magnitude of the power transferred by the zero-sequence current, that is, the larger the injected , the faster the SOC equalization speed. Therefore, when reaches the maximum value allowed under the current limiting constraint, the inter-phase SOC equalization speed also reaches the fastest under the current limiting constraint. At this time, the amplitude limit value is taken as the equal sign, that is, it satisfies: ; Then the value of the zero-sequence current adjustment factor for each phase should be: ​​The present invention also provides a device for quickly balancing the inter-phase state of charge of a high-voltage direct-connected energy storage system, which is used for the method of the present invention. The device includes a first module, a second module, and a third module; The first module is used to obtain the active and reactive components of the zero-sequence current based on the positive and negative sequence components of the three-phase voltage, the SOC deviation between phases a and b, and the SOC deviation between phases b and c; and obtain the zero-sequence current based on the active and reactive components of the zero-sequence current; The second module is used to obtain the active and reactive components of the zero-sequence current in each phase based on the zero-sequence current; and obtain the current command values of the active and reactive power of the system to the outside in real time; The third module is used to judge in real time whether the first condition is satisfied; when the first condition is satisfied, enter the second mode, otherwise operate in the first mode; the first condition includes that the absolute value of the maximum value of the SOC deviation between the three phases is less than or equal to a preset threshold; The first mode includes: continuously obtaining the zero-sequence current adjustment factor for each phase according to the preset maximum threshold of the converter phase current, the current command value, and the active and reactive components of the zero-sequence current in each phase, and selecting the real-time minimum value among the zero-sequence current adjustment factors for each phase as the real-time adjustment factor; multiplying the real-time adjustment factor by the zero-sequence current and injecting it into the PCS; The second mode includes: multiplying the real-time adjustment factor at the moment of entering the second mode by the zero-sequence current and injecting it into the PCS; when the current command value changes, enter the first mode.

[0016] The present invention has the following beneficial effects: The method for quickly balancing the inter-phase state of charge of the high-voltage direct-connected energy storage system of the present invention calculates the optimal adjustment factor value under the current limit of each phase in real time, which greatly improves the balancing speed while ensuring safe operation. For the problem of sudden change of the zero-sequence current at the end of the balancing period, a smooth transition strategy is introduced in the second mode. Instead of simply pursuing the maximum balancing speed, the zero-sequence current follows the reduction of the inter-phase SOC deviation, and the balancing speed is gradually slowed down to avoid frequent changes of the zero-sequence current, realizing the smooth transition of the zero-sequence current, thereby ensuring more important indicators such as current limiting and system stability compared with the balancing speed. In this method, the first mode realizes the dynamic maximization of the SOC balancing speed, and the zero-sequence current in the first mode decreases smoothly, ensuring the system stability at the end of the balancing period.

[0017] The present invention realizes the active re-distribution of three-phase power through dynamic adjustment of zero-sequence current injection. Based on the adaptive adjustment mechanism of the SOC deviation, it ensures the fast inter-phase SOC balancing of the energy storage system under strict current limiting constraints. The present invention can achieve fast dynamic balancing under the full range of SOC imbalance, improves the system performance and safety, can significantly reduce the full life cycle cost, improve the return on investment, and can be applied to the energy storage system in a weak grid environment, with outstanding advantages such as accurate current limiting, fast balancing speed, excellent power quality, and good stability.

[0018] The inter-phase state of charge rapid equalization device of the high-voltage direct-connected energy storage system of the present invention is used for the method of the present invention and has the same beneficial effects as the method of the present invention.

[0019] In addition to the purposes, features and advantages described above, the present invention has other purposes, features and advantages. The following will refer to the accompanying drawings and make a further detailed description of the present invention. Brief Description of the Drawings

[0020] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings: Figure 1 is a schematic topology diagram of a high-voltage direct-connected chain-type energy storage system according to a preferred embodiment of the present invention.

[0021] Figure 2 is a schematic flowchart of the method according to a preferred embodiment of the present invention.

[0022] Figure 3 is a control block diagram of the method according to a preferred embodiment of the present invention.

[0023] Figure 4 is a schematic diagram of the current comparison waveform between the traditional control strategy and the control strategy of the method of the present invention when the SOC imbalance degree is relatively large according to a preferred embodiment of the present invention.

[0024] Figure 5 is a schematic diagram of the SOC comparison waveform between the traditional control strategy and the control strategy of the method of the present invention when the SOC imbalance degree is relatively large according to a preferred embodiment of the present invention.

[0025] Figure 6 is a schematic diagram of the current comparison waveform between the traditional control strategy and the control strategy of the method of the present invention when the SOC imbalance degree is relatively small according to a preferred embodiment of the present invention.

[0026] Figure 7 is a schematic diagram of the SOC comparison waveform between the traditional control strategy and the control strategy of the method of the present invention when the SOC imbalance degree is relatively small according to a preferred embodiment of the present invention.

[0027] Figure 8 is a schematic diagram of the current comparison waveform before and after adding the control strategy of the method of the present invention when the three-phase current is asymmetric according to a preferred embodiment of the present invention.

[0028] Figure 9 is a schematic diagram of the SOC comparison waveform before and after adding the control strategy of the method of the present invention when the three-phase current is asymmetric according to a preferred embodiment of the present invention. Detailed Embodiments

[0029] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways defined and covered by the claims.

[0030] See Figure 1 , the high-voltage direct-connected chain-type energy storage system of the present invention includes an AC filter inductor , a fuse, a contactor, and n H-bridge power conversion units; the H-bridge power conversion unit includes a DC-side inductor, an energy storage battery, a full-bridge converter, and a DC-side capacitor. The positive pole of the DC side of the full-bridge converter is sequentially connected in series with the DC-side inductor and the energy storage battery and then connected to the negative pole of the DC side of the full-bridge converter. The DC-side capacitor is connected in parallel between the two poles of the DC side of the full-bridge converter; the AC sides of the n H-bridge power conversion units are cascaded into a PCS link, and the PCS links of each phase are connected in sequence in a delta connection; each phase of the PCS link is connected to the medium-voltage and high-voltage power grid in a conductive state through an AC filter inductor , a fuse, and a contactor.

[0031] In Figure 1 , represents the nth H-bridge power conversion unit; is the grid voltage; is the phase current of the PCS link; ; wherein, x = ab, bc, ca, respectively representing the ab phase, the bc phase, and the ca phase; and respectively represent and amplitude; represents the phase of the x-phase grid voltage; represents the phase of the PCS link phase current relative to the grid voltage .

[0032] See Figures 2 to 3 , in a preferred embodiment of the present invention, a method for quickly balancing the state of charge between phases of a high-voltage direct-connected energy storage system is provided, including: S1. Obtain the active and reactive components of the zero-sequence current according to the positive and negative sequence components of the three-phase voltage, the SOC deviation between the ab phases, and the SOC deviation between the bc phases; obtain the zero-sequence current according to the active and reactive components of the zero-sequence current. S1 specifically includes: Obtain the positive and negative sequence components of the three-phase voltage, the SOC deviation between the ab phases, and the SOC deviation between the bc phases; obtain the solution equations for the active and reactive components of the zero-sequence current according to the positive and negative sequence components of the three-phase voltage, the zero-sequence current calculation formula, and the control target of the inter-phase SOC balance.

[0033] The solution equations for the active and reactive components of the zero-sequence current include Regarding and Expression of Expression of the inter-phase SOC deviation; where represents the active power generated by the zero-sequence current in phase x, x = ab, bc, ca; represents the reactive component of the zero-sequence current, represents the active component of the zero-sequence current.

[0034] In the preferred embodiment of the present invention, obtaining the positive and negative sequence components of the three-phase voltage, the SOC deviation between phases ab, and the SOC deviation between phases bc includes: Obtaining the grid voltage and filtering it to obtain the grid voltage and ; Obtaining the phase of the grid voltage ; According to the phase to perform positive and negative sequence dq transformation on and to obtain the positive and negative sequence components of the three-phase voltage; The positive and negative sequence components of the three-phase voltage include the positive sequence active voltage amplitude , the positive sequence reactive voltage amplitude , the negative sequence active voltage amplitude and the negative sequence reactive voltage amplitude , including: ; ; wherein, represents a notch filter for filtering the second harmonic component generated by the negative sequence voltage; represents a notch filter for filtering the second harmonic component generated by the positive sequence voltage; Obtaining the SOC deviation between phases ab and the SOC deviation between phases bc includes: ; ; wherein, represents the SOC deviation between phases x; represents the SOC value between phases x; represents the average value of the three-phase SOC; x = ab, bc, ca.

[0035] In the preferred embodiment of the present invention, the system of equations for solving the active and reactive components of the zero-sequence current obtained according to the positive and negative sequence components of the three-phase voltage, the zero-sequence current calculation formula, and the control objective of inter-phase SOC balance includes: According to the positive and negative sequence components of the three-phase voltage and the phase to obtain and The expressions of are: ; According to and 's expression and the zero-sequence current calculation formula, we get the expression about and : ; ; The control objective of the inter-phase SOC balance is that the of each phase is zero, then there is the expression about the inter-phase SOC deviation: ; Among them, represents the inter-phase SOC balance coefficient, which determines the speed of the balance and takes a constant according to the capacity; represents the zero-sequence current.

[0036] Solve the equations according to the active and reactive components of the zero-sequence current and the inter-phase SOC deviation between phases ab and bc to obtain the reactive component of the zero-sequence current and the active component of the zero-sequence current; According to the reactive component of the zero-sequence current, the active component of the zero-sequence current and the zero-sequence current calculation formula, the zero-sequence current is obtained.

[0037] The reactive component of the zero-sequence current and the active component of the zero-sequence current specifically include: ; S2. Obtain the active and reactive components of the zero-sequence current in each phase according to the zero-sequence current. S2 specifically includes: Decompose the zero-sequence current in each phase to obtain the active component of the zero-sequence current in the x phase and the reactive component : The component of the zero-sequence current in the ab phase: ; The component of the zero-sequence current in the bc phase: ; The component of the zero-sequence current in the ca phase: ; Among them, Represents the phase of the grid voltage ; Represents the phase of the grid voltage ; The phase information of each phase is independently obtained by a single-phase phase-locked loop.

[0038] S3. Obtain the current command values of active and reactive power of the system in real time; Judge in real time whether the first condition is satisfied; When the first condition is satisfied, enter the second mode, otherwise operate in the first mode; The first condition includes that the absolute value of the maximum inter-phase SOC deviation is less than or equal to a preset threshold.

[0039] The first condition can be expressed as: .

[0040] The first mode includes: Continuously obtain the zero-sequence current adjustment factor of each phase according to the preset maximum converter phase current threshold, current command value, and the active and reactive power components of the zero-sequence current in each phase, and select the real-time minimum value among the zero-sequence current adjustment factors of each phase as the real-time adjustment factor; Multiply the real-time adjustment factor by the zero-sequence current and inject it into the PCS; The second mode includes: Multiply the real-time adjustment factor at the moment of entering the second mode by the zero-sequence current and inject it into the PCS; When the current command value changes, enter the first mode.

[0041] In the preferred embodiment of the present invention, the first mode is the Figure 3 unbalanced end stage part in Figure 3 , and the second mode is the balanced end stage part in . In the second mode, that is, the balanced end stage, instead of simply pursuing the maximum balancing speed, the zero-sequence current is made to follow and continuously decrease. By gradually slowing down the balancing speed, the frequent change of the zero-sequence current is avoided, and the smooth transition of the zero-sequence current is realized, so as to ensure more important indicators such as current limiting and system stability compared with the balancing speed.

[0042] In the preferred embodiment of the present invention, continuously obtaining the zero-sequence current adjustment factor of each phase according to the preset maximum converter phase current threshold, current command value, and the active and reactive power components of the zero-sequence current in each phase includes: Obtain the current command amplitude of each phase according to the current command value and the active and reactive power components of the zero-sequence current in each phase expression about the zero-sequence current adjustment factor; Assume that the preset maximum converter phase current threshold is , where is the proportional coefficient multiplied to reserve the preset current safety margin, is the phase current limiting value; The current command amplitude of each phase should be less than or equal to , so establish expression about the zero-sequence current adjustment factor and The inequality between them is solved by taking the equality of the inequality to obtain the zero-sequence current adjustment factor for each phase. Specifically, it includes: Define the zero-sequence current adjustment factor as , multiply by the zero-sequence current to obtain the new zero-sequence current for injection into the PCS , which is expressed as: ; Among them, represents the phase of the grid voltage of phase x; The active component and the reactive component in phase x are: ; Then can be expressed based on phase x as: ; The total current command is expressed as: ; Among them, and respectively represent the external active current command value and the external reactive current command value of phase x.

[0043] According to the total current command and the active component and reactive component in phase x, the current command amplitude for each phase is obtained: ; Assume that the preset maximum threshold of the converter phase current is , and the current command amplitude of each phase should be less than or equal to , so an inequality between the expression of the zero-sequence current adjustment factor and is established: ; Thus, the zero-sequence current adjustment factor that meets the requirements of each phase is obtained, denoted as ; if it is required that all three phases meet , the value of should be the intersection; The expressions of are similar. Let take the equality, and calculate to obtain two different real solutions and of ; ; Among them, is an intermediate quantity.

[0044] The value range of is: ; Considering that the SOC balancing speed is positively correlated with the magnitude of the zero-sequence current transfer power, that is, the larger the injected, the faster the SOC balancing speed. Therefore, when reaches the maximum value allowed under the current limiting constraint, the inter-phase SOC balancing speed also reaches the fastest under the current limiting constraint. At this time, the amplitude limit value is taken as an equal sign, that is, it satisfies: ; Then the value of the zero-sequence current adjustment factor for each phase should be: ; Continuously calculate the zero-sequence current adjustment factors corresponding to each phase, that is, continuously obtain the zero-sequence current adjustment factors for each phase.

[0045] The method for quickly balancing the inter-phase state of charge of the high-voltage direct-connected energy storage system of the present invention calculates the optimal adjustment factor value under the current limit of each phase in real time, which greatly improves the balancing speed while ensuring safe operation. Aiming at the problem of zero-sequence current mutation at the end of the balancing period, a smooth transition strategy is introduced in the second mode. Instead of simply pursuing the maximum balancing speed, the zero-sequence current is made to follow the inter-phase SOC deviation and continuously decrease. By gradually slowing down the balancing speed, the frequent change of the zero-sequence current is avoided, and the smooth transition of the zero-sequence current is realized, thereby ensuring more important indicators such as current limiting and system stability compared with the balancing speed. In this method, the first mode realizes the dynamic maximization of the SOC balancing speed, and the zero-sequence current smoothly decreases in the first mode, ensuring the system stability at the end of the balancing period.

[0046] The present invention realizes the active reallocation of three-phase power by dynamically adjusting the zero-sequence current injection. Based on the adaptive adjustment mechanism of the SOC deviation, it ensures the fast inter-phase SOC balancing of the energy storage system under strict current limiting constraints. The present invention can achieve fast dynamic balancing under the full range of SOC imbalance degrees, improves the system performance and safety, can significantly reduce the full life cycle cost, improve the return on investment, and can be applied to the energy storage system in a weak grid environment, with outstanding advantages such as accurate current limiting, fast balancing speed, excellent power quality, and good stability.

[0047] In the method of the present invention, the power distribution coefficient is adjusted in real time according to the SOC differences of each phase battery pack, which can effectively solve problems such as slow balancing speed and deteriorated power quality in traditional methods, and ensure efficient energy balance among the three-phase battery packs. At the same time, the method of the present invention avoids system stability problems and grid pollution, has a simple and reliable control structure, is easier to implement in actual energy storage systems, and has a faster response speed.

[0048] The method of the present invention introduces a zero-sequence current regulation factor to dynamically regulate the zero-sequence current, avoiding the decisive influence of the inter-phase SOC balancing coefficient on the magnitude of the zero-sequence current. At the same time, the method of the present invention does not need to limit the additional power to avoid the influence of the amplitude limit on the phase of the zero-sequence current. Since the zero-sequence current regulation factor comprehensively considers the internal and external current commands and the current limiting constraint, it solves the problem of the lack of current limiting mechanism for the zero-sequence current and the over-current problem caused by the independence of the internal and external current commands. It can also dynamically regulate the zero-sequence current according to the external current command and the current limiting value, and then dynamically maximize the balancing speed within the current limiting constraint on the basis of giving priority to ensuring the response of the external current command.

[0049] In a preferred embodiment of the present invention, a device for quickly balancing the state of charge between phases of a high-voltage direct-connected energy storage system is also provided for the method of the present invention. The device is characterized in that it includes a first module, a second module, and a third module; The first module is used to obtain the active and reactive components of the zero-sequence current according to the positive and negative sequence components of the three-phase voltage, the SOC deviation between phases ab, and the SOC deviation between phases bc; and obtain the zero-sequence current according to the active and reactive components of the zero-sequence current; The second module is used to obtain the active and reactive components of the zero-sequence current in each phase according to the zero-sequence current; and obtain the current command values of the active and reactive power of the system externally in real time; The third module is used to judge in real time whether the first condition is established; when the first condition is established, enter the second mode, otherwise run the first mode; the first condition includes that the absolute value of the maximum SOC deviation among the three phases is less than or equal to a preset threshold; The first mode includes: continuously obtaining the zero-sequence current regulation factor for each phase according to the preset maximum converter phase current threshold, the current command value, and the active and reactive components of the zero-sequence current in each phase, and selecting the real-time minimum value among the zero-sequence current regulation factors for each phase as the real-time regulation factor; multiplying the real-time regulation factor by the zero-sequence current and injecting it into the PCS; The second mode includes: multiplying the real-time regulation factor at the moment of entering the second mode by the zero-sequence current and injecting it into the PCS; when the current command value changes, enter the first mode.

[0050] The inter-phase state of charge rapid equalization device of the high-voltage direct-connected energy storage system of the present invention is used for the method of the present invention and has the same beneficial effects as the method of the present invention.

[0051] Verification part: Verify the effectiveness of the method of the present invention through MATLAB / Simulink software. Among them, the traditional control strategy is based on zero-sequence current for control; the control strategy of the method of the present invention is based on the new zero-sequence current for control; See Figures 4 to 5 , which is the comparison waveform of the traditional control strategy and the control strategy of the method of the present invention when the SOC imbalance degree is large. Set the battery SOC of each sub-module in phases ab, bc, and ca to 80%, 100%, and 60% respectively, and the inter-phase equalization coefficient is 10000. The initial three-phase output active power of the system is 5MW. Add the traditional control strategy at 2s and switch to the control strategy of the method of the present invention at 2.1s. The simulation waveform is as Figures 4 to 5 shown. It can be seen from Figures 4 to 5 that after adding the traditional control strategy, although the SOC equalization speed is relatively fast (seen from the SOC change rate), the phase current has serious overcurrent. After switching to the control strategy of the method of the present invention, although the equalization speed slows down, the phase current amplitude is limited to the maximum allowable current =140.7A. Therefore, the control strategy of the method of the present invention can ensure that the phase current does not overcurrent when the inter-phase SOC imbalance degree is large, and maximize the zero-sequence current within the current limiting constraint, thereby maximizing the SOC equalization speed under this working condition.

[0052] See Figures 6 to 7 , which is the SOC waveform of the traditional control strategy and the control strategy of the method of the present invention when the SOC imbalance degree is small. Set the battery SOC of each sub-module in phases ab, bc, and ca to 80%, 80.2%, and 79.8% respectively, and the rest remains unchanged. Add the traditional control strategy at 2s, and then switch to the control strategy of the method of the present invention at 2.1s. The simulation waveform is as Figures 6 to 7 shown. It can be seen from Figures 6 to 7 that when the inter-phase SOC imbalance degree is small, the zero-sequence current injected by the traditional control strategy is small, so that the SOC change rate before and after injecting the zero-sequence current does not change significantly, and the SOC equalization speed is too slow at this time. After switching to the control strategy of the method of the present invention, the zero-sequence current reaches the maximum value within the phase current limit , making the SOC change rate change significantly. Therefore, the control strategy of the method of the present invention still ensures a relatively large SOC equalization speed when the inter-phase SOC imbalance degree is small.

[0053] See Figures 8 to 9, which are the current waveforms before and after adding the control strategy of the method of the present invention when the three-phase current is asymmetric. The SOC of each sub-module battery in the ab, bc, and ca phases is set to 80%, 100%, and 60% respectively. The initial three-phase output active power of the system is 5 MW, and at the same time, 2 MVar of reactive power is additionally output in the bc phase and 0.5 MVar of reactive power is additionally output in the ca phase, making the three-phase output current asymmetric. The control strategy of the method of the present invention is added at 2 s, and the simulation waveform is as Figures 8 to 9 shown. It can be seen from Figures 8 to 9 that even in the case of severe asymmetry of the three-phase current amplitude and phase, the control strategy of the method of the present invention can still ensure that each phase does not overcurrent, and makes the zero-sequence current reach the maximum under the current-limiting condition, thus effectively improving the equalization speed of the SOC.

[0054] The above simulation shows that the method of the present invention has a strong adaptability to the degree of SOC imbalance, and solves the problems existing in the traditional equalization strategy, such as the difficulty in selecting the equalization coefficient λ , phase current over-limit, and too slow equalization speed, etc., and realizes the maximization of the zero-sequence current within the current-limiting constraint, making the equalization ability reach the limit, thus dynamically realizing the maximization of the equalization speed.

[0055] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for quickly balancing the state of charge between phases of a high-voltage direct-connected energy storage system, characterized in that, including: obtaining the active and reactive components of the zero-sequence current based on the positive and negative sequence components of the three-phase voltage, the SOC deviation between phases a and b, and the SOC deviation between phases b and c; obtaining the zero-sequence current based on the active and reactive components of the zero-sequence current; obtaining the active and reactive components of the zero-sequence current in each phase based on the zero-sequence current; acquiring the current command values of the active and reactive power of the system externally in real time; judging in real time whether the first condition is satisfied; when the first condition is satisfied, entering the second mode, otherwise operating in the first mode; the first condition includes that the absolute value of the maximum value of the inter-phase SOC deviation is less than or equal to a preset threshold; the first mode includes: continuously obtaining the zero-sequence current adjustment factors for each phase according to the preset maximum converter phase current threshold, the current command value, and the active and reactive components of the zero-sequence current in each phase, and selecting the real-time minimum value among the zero-sequence current adjustment factors for each phase as the real-time adjustment factor; multiplying the real-time adjustment factor by the zero-sequence current and injecting it into the PCS; the second mode includes: multiplying the real-time adjustment factor at the moment of entering the second mode by the zero-sequence current and injecting it into the PCS; when the current command value changes, entering the first mode.

2. The rapid state of charge balancing method between phases of the high-voltage direct-connected energy storage system according to claim 1, wherein the obtaining the active and reactive components of the zero-sequence current based on the positive and negative sequence components of the three-phase voltage, the SOC deviation between phases a and b, and the SOC deviation between phases b and c; the obtaining the zero-sequence current based on the active and reactive components of the zero-sequence current includes: acquiring the positive and negative sequence components of the three-phase voltage, the SOC deviation between phases a and b, and the SOC deviation between phases b and c; obtaining a system of equations for solving the active and reactive components of the zero-sequence current according to the positive and negative sequence components of the three-phase voltage, the zero-sequence current calculation formula, and the control objective of inter-phase SOC balance; The system of equations for solving the active and reactive components of the zero-sequence current includes Regarding And Expressions of Expressions for the phase-interval SOC deviation; where Represents the active power generated by the zero-sequence current in phase x, x = ab, bc, ca; Represents the reactive component of the zero-sequence current, Represents the active component of the zero-sequence current; Solve the system of equations based on the active and reactive components of the zero-sequence current and the SOC deviation between phase a and phase b and the SOC deviation between phase b and phase c to obtain the reactive component of the zero-sequence current and the active component of the zero-sequence current ; According to the reactive component of the zero-sequence current , the active component of the zero-sequence current and the zero-sequence current calculation formula to obtain the zero-sequence current.

3. The method for rapid state of charge equalization between phases of the high-voltage direct-connected energy storage system according to claim 2, wherein Solve the system of equations based on the active and reactive components of the zero-sequence current and the SOC deviation between phases a and b and the SOC deviation between phases b and c to obtain the reactive component of the zero-sequence current and the active component of the zero-sequence current ; According to the reactive component of the zero-sequence current , the active component of the zero-sequence current and the zero-sequence current calculation formula, the obtained zero-sequence current includes: The zero-sequence current reactive component and the zero-sequence current active component include: ； the zero-sequence current calculation formula includes: ； Among them, represents the positive-sequence active voltage amplitude; represents the positive-sequence reactive voltage amplitude; represents the negative-sequence active voltage amplitude; represents the negative-sequence reactive voltage amplitude; represents the SOC deviation between phases a and b; represents the SOC deviation between phases b and c; represents the inter-phase SOC balance coefficient, which determines the speed of balancing and takes a constant value according to the capacity; represents the grid voltage phase; According to the active component of the zero-sequence current and the reactive component of the zero-sequence current Combining the zero-sequence current calculation formula, the zero-sequence current can be obtained .

4. The method for quickly equalizing the inter-phase state of charge of the high-voltage directly-connected energy storage system according to claim 3, characterized in that the continuously obtaining the zero-sequence current adjustment factors for each phase according to the preset maximum converter phase current threshold, the current command value, and the active and reactive components of the zero-sequence current in each phase includes: Obtain the current command amplitude of each phase based on the current command value and the active and reactive components of the zero-sequence current in each phase Expression regarding the zero-sequence current regulation factor: Define the zero-sequence current adjustment factor as , multiply by the zero-sequence current to obtain the new zero-sequence current for injection into the PCS, expressed as: ； Among them, represents the phase of the x-phase grid voltage; represents the zero-sequence current active component in the x-phase; represents the zero-sequence current reactive component in the x-phase; In the active component of the x-phase and the reactive component are as follows: ； Then It can be expressed based on the x phase as: ； Total current command Expressed as: ； Among them, and respectively represent the external active current command value and the external reactive current command value of the x-phase; Based on the total current command and the active component and reactive component in the x-phase to obtain the amplitude of each phase current command : ； Assume that the preset converter phase current maximum threshold is ,in is the proportionality factor used to retain the preset current safety margin. is the phase current limit value; each phase current command amplitude Should be less than or equal to , so establish The expression of zero-sequence current regulation factor is The inequality between them is solved by taking the equal sign to obtain the zero-sequence current regulation factor of each phase: the inequality includes: ； The zero-sequence current adjustment factor that meets the requirements of each phase is obtained accordingly , denoted as ; if it is required that all three phases meet , the value of should be the intersection of The expressions of are similar. Let take the equal sign, and two different real solutions of and are calculated as follows: ； ； Among them, is an intermediate quantity; The value range is: ； Considering that the SOC balancing speed is positively correlated with the magnitude of the power transferred by the zero-sequence current, that is, the injected is larger, the SOC balancing speed is faster. Therefore, when reaches the maximum value allowed under the current-limiting constraint, the inter-phase SOC balancing speed also reaches the fastest under the current-limiting constraint. At this time, the amplitude limit is taken as an equal sign, that is, it satisfies: ； Then the zero-sequence current adjustment factors of each phase are obtained should take the value of: ； continuously calculating the corresponding zero-sequence current adjustment factors for each phase, that is, realizing continuously obtaining the zero-sequence current adjustment factors for each phase.

5. An inter-phase state of charge rapid equalization device for a high-voltage directly-connected energy storage system, used for the method according to any one of claims 1 to 4, characterized in that, the device includes a first module, a second module, and a third module; the first module is configured to obtain the active and reactive components of the zero-sequence current based on the positive and negative sequence components of the three-phase voltage, the SOC deviation between phases a and b, and the SOC deviation between phases b and c; obtaining the zero-sequence current based on the active and reactive components of the zero-sequence current; the second module is configured to obtain the active and reactive components of the zero-sequence current in each phase based on the zero-sequence current; acquiring the current command values of the active and reactive power of the system externally in real time; the third module is configured to judge in real time whether the first condition is satisfied; when the first condition is satisfied, entering the second mode, otherwise operating in the first mode; the first condition includes that the absolute value of the maximum value of the inter-phase SOC deviation is less than or equal to a preset threshold; the first mode includes: continuously obtaining the zero-sequence current adjustment factors for each phase according to the preset maximum converter phase current threshold, the current command value, and the active and reactive components of the zero-sequence current in each phase, and selecting the real-time minimum value among the zero-sequence current adjustment factors for each phase as the real-time adjustment factor; multiplying the real-time adjustment factor by the zero-sequence current and injecting it into the PCS; The second mode includes: multiplying the real-time adjustment factor at the moment of entering the second mode by the zero-sequence current and injecting the result into the PCS; when the current command value changes, entering the first mode.

Images