SOC (State of Charge) balanced hierarchical control method for cascaded H-bridge energy storage converter

Abstract

The invention discloses a cascaded H-bridge energy storage converter SOC equalization hierarchical control method, and the method comprises the steps: determining the inter-phase imbalance degree corresponding to each phase in a cascaded H-bridge energy storage converter, and determining the intra-phase imbalance degree corresponding to each sub-battery module in a single phase; determining a value range of an in-phase equalization coefficient corresponding to each sub-battery module according to the in-phase imbalance degree, generating a modulation wave adjustment amount corresponding to each sub-battery module through the in-phase equalization coefficient, and generating a first modulation wave signal corresponding to each battery sub-module; performing coordinate transformation and coordinate synthesis on the inter-phase imbalance degree to obtain a zero-sequence voltage, and outputting a second modulation wave signal corresponding to each phase by injecting the zero-sequence voltage according to the modulation wave signal corresponding to each phase; and generating a driving signal. And in the interphase equalization layer, interphase power redistribution is realized by injecting a zero-sequence voltage component. According to the in-phase equalization layer, the in-phase equalization speed is increased and the safety and stability margin is ensured through selection of an in-phase equalization coefficient.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of SOC control, in particular to a cascaded H-bridge energy storage converter SOC equalization hierarchical control method, device and medium. BACKGROUND

[0002] The cascaded H-bridge energy storage converter topology has been widely used in large-capacity and high-voltage energy storage systems due to its high degree of modularity and good output harmonic characteristics. The cascaded H-bridge energy storage converter is composed of multiple module units with battery clusters. With the continuous progress of battery cell manufacturing technology, the initial capacity difference of the battery system is usually small.

[0003] However, in actual use, the inconsistency between battery cells gradually appears over time and with the accumulation of charge and discharge cycles. This inconsistency may manifest in capacity degradation, internal resistance changes, and State of Charge (SOC) inconsistency. If this problem is not addressed in a timely manner, it not only leads to waste of the overall capacity of the battery, reduces the energy utilization and operating efficiency of the energy storage system, and increases the investment and operation and maintenance costs of the system, but also may cause local overheating during the operation of the energy storage system, thereby causing serious safety hazards, such as fires or explosions. SUMMARY

[0004] To solve the above problems, the present application proposes a cascaded H-bridge energy storage converter SOC equalization hierarchical control method, comprising: For the cascaded H-bridge energy storage converter, obtain the corresponding operating state parameters; Based on the State of Charge parameter contained in the operating state parameters, determine the inter-phase imbalance degree corresponding to each phase in the cascaded H-bridge energy storage converter, and determine the intra-phase imbalance degree corresponding to each sub-battery module in a single phase; According to the number of cascaded sub-battery modules, the intra-phase imbalance degree corresponding to each sub-battery module, determine the value range of the intra-phase balancing coefficient corresponding to each sub-battery module; Based on the value range, select the corresponding intra-phase balancing coefficient to generate the modulation wave adjustment amount corresponding to each sub-battery module through the intra-phase balancing coefficient, and generate the first modulation wave signal corresponding to each battery sub-module according to the modulation wave adjustment amount; For the inter-phase imbalance degree, perform coordinate transformation and coordinate synthesis to obtain a zero sequence voltage, and for the modulation wave signal corresponding to each phase, output the second modulation wave signal corresponding to each phase by injecting the zero sequence voltage; According to the first modulation wave signal and the second modulation wave signal, perform signal synthesis to generate a driving signal, and drive the cascaded H-bridge energy storage converter.

[0005] In another aspect, the application also provides a cascade H-bridge energy storage converter SOC equalization hierarchical control device, comprising: at least one processor; and a memory in communication connection with the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform the cascade H-bridge energy storage converter SOC equalization hierarchical control method as described in the above examples.

[0006] In another aspect, the application also provides a non-volatile computer storage medium, which stores computer executable instructions, and the computer executable instructions are configured to implement the cascade H-bridge energy storage converter SOC equalization hierarchical control method as described in the above examples.

[0007] The cascade H-bridge energy storage converter SOC equalization hierarchical control method provided by the application can bring the following beneficial effects: In view of the problem of inconsistent SOC of battery side energy storage batteries of the cascade H-bridge energy storage converter caused by long-time operation or parameter difference and other factors, a hierarchical equalization control strategy is proposed.

[0008] At the inter-phase equalization level, the inter-phase power redistribution is realized by injecting zero sequence voltage component, so that the discharging strength of the phase with high SOC is improved, the discharging strength of the phase with low SOC is reduced, and the three-phase SOC is driven to converge to the inter-phase SOC average value.

[0009] At the intra-phase equalization level, on the basis of the traditional power distribution intra-phase SOC equalization strategy, the mathematical relationship between the module modulation voltage and the equalization coefficient is established through theoretical derivation, and the dynamic optimization mechanism is designed, so that the maximum value in the allowable range is preferentially selected to accelerate equalization, and the minimum value of the equalization coefficient of the same-phase module is used to avoid over-modulation risk, thereby improving the intra-phase equalization speed while ensuring the safety and stability margin, and realizing the intra-phase SOC equalization. BRIEF DESCRIPTION OF DRAWINGS

[0010] The accompanying drawings described herein are used to provide further understanding of the application, and form a part of the application. The schematic embodiments of the application and the description thereof are used to explain the application, and do not constitute an improper limitation on the application. In the drawings: Figure 1 It is a flowchart of the cascade H-bridge energy storage converter SOC equalization hierarchical control method in the embodiments of the application; Figure 2 It is a topology structure diagram of the A-phase of the cascade H-bridge energy storage converter in one case in the embodiments of the application; Figure 3 It is an intra-phase SOC equalization control block diagram of the i th module unit in one case in the embodiments of the application; Figure 4 For one case in the embodiment of the application, the phase-in SOC adaptive equalization control strategy block diagram of phase A; Figure 5 For one case in the embodiment of the application, the phase-in SOC adaptive equalization control strategy flow chart; Figure 6 For one case in the embodiment of the application, the zero sequence voltage injection principle diagram; Figure 7 For one case in the embodiment of the application, the three-phase unbalance degree conversion principle diagram; Figure 8 For one case in the embodiment of the application, the inter-phase SOC equalization control strategy block diagram of cascade H-bridge energy storage converter; Figure 9 For one case in the embodiment of the application, the overall SOC equalization control strategy block diagram; Figure 10 For one case in the embodiment of the application, the three-phase SOC change curve when the inter-phase SOC adaptive equalization control strategy is not used; Figure 11 For one case in the embodiment of the application, the three-phase SOC change curve when the inter-phase SOC adaptive equalization control strategy is used; Figure 12 For one case in the embodiment of the application, the inter-phase SOC unbalance degree change curve when the inter-phase SOC adaptive equalization control strategy is used; Figure 13 For one case in the embodiment of the application, the three-phase current waveform when the inter-phase SOC adaptive equalization control strategy is used; Figure 14 For one case in the embodiment of the application, the phase-in SOC change curve of phase A before the phase-in SOC adaptive equalization control strategy is added; Figure 15 For one case in the embodiment of the application, the phase-in SOC change curve of three phases after the phase-in SOC adaptive equalization control strategy is added; Figure 16 For one case in the embodiment of the application, the phase-in SOC unbalance degree change curve when the phase-in SOC adaptive equalization control strategy is used; Figure 17 For one case in the embodiment of the application, the SOC change curve of phase A when the phase-in SOC adaptive equalization control strategy is used; Figure 18 For one case in the embodiment of the application, the output current waveform after the phase-in SOC adaptive equalization control strategy is added; Figure 19For the case in the embodiment of the present application, the SOC change curve after adding the in-phase SOC adaptive equalization control strategy and the inter-phase SOC adaptive equalization control strategy is shown in the following figure: Figure 20 For the schematic diagram of the SOC equalization hierarchical control device of the cascaded H-bridge energy storage converter in the embodiment of the present application. DETAILED DESCRIPTION

[0011] In order to make the objectives, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described below in conjunction with the specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0012] The technical solutions provided by the embodiments of the present application will be described in detail below in conjunction with the drawings.

[0013] Based on the above technical problems, power redistribution can be achieved at two levels of inter-phase and in-phase through inter-phase equalization strategy and in-phase equalization strategy, thereby solving the problems of capacity attenuation, internal resistance change and state of charge inconsistency.

[0014] Specifically, for the inter-phase equalization strategy (also referred to as inter-phase SOC adaptive equalization strategy), a zero sequence voltage injection strategy can be used. Injecting a zero sequence voltage into the energy storage converter can adjust the amplitude and phase angle of the zero sequence component, change the three-phase alternating current side output voltage vector distribution, thereby achieving system power redistribution among the three phases to achieve the equalization goal of inter-phase SOC. This strategy has low control complexity and is easy to implement in engineering.

[0015] Similar to the zero sequence voltage injection strategy, the negative sequence voltage injection strategy achieves three-phase power redistribution by introducing a negative sequence voltage with a specific amplitude and phase into the cascaded H-bridge energy storage converter. This strategy has strong equalization capability and is more suitable for high imbalance degree energy storage systems compared to the zero sequence voltage injection strategy.

[0016] However, the introduction of negative sequence voltage usually generates negative sequence current, which has a certain impact on the power quality of the energy storage system.

[0017] Based on this, an inter-phase SOC adaptive equalization strategy based on joint regulation of zero sequence and negative sequence voltage is proposed, which dynamically selects the type of injected voltage according to the size of the inter-phase battery SOC imbalance. However, this strategy achieves better equalization effect, but its control process is more complex. And there is still negative sequence current in the system, which is not conducive to the long-term operation of the system.

[0018] Therefore, a self-adaptive proportional hierarchical control strategy is proposed, which obtains the corresponding adjustment coefficient by taking the inverse of the obtained SOC information, so as to realize the balance of the inter-phase SOC. However, the addition of the DC / DC bidirectional converter between the battery and the H-bridge not only increases the cost, but also occupies more internal space of the energy storage system in actual application, which is not conducive to popularization and application.

[0019] For the inter-phase balance strategy (also referred to as the intra-phase SOC self-adaptive balance strategy), the energy of the high-energy battery is transferred to the low-energy battery through the power conversion circuit, or the excess energy of the high-energy battery is consumed through the power device, so as to realize the balance. However, both of the above strategies need to add additional hardware, and increase the control difficulty and potential safety hazards.

[0020] Therefore, a software control intra-phase SOC balance strategy is provided, which realizes the SOC balance adjustment through three links of sampling, sorting and comparison. The core idea is to increase the discharge of the SOC higher module, and at the same time reduce the discharge of the SOC lower module. However, with the increase of the number of modules of the energy storage system, the calculation complexity of the method is also significantly improved, which affects the real-time control performance of the system.

[0021] For example, the phase difference pulse width modulation (PD-PWM) strategy is used to realize the SOC balance of the intra-phase battery module, but when the number of sub-modules is large, this method occupies a large amount of software and hardware resources.

[0022] For another example, the reference voltage regulation control strategy is used, which calculates the balance error and injects a proper proportion of reference voltage to adjust the voltage distribution of each module in the phase, so as to realize the power balance. This strategy does not change the total power in the phase, and the balance effect is better. However, when the balance error is large, the amplitude of the superimposed reference voltage increases, which may cause over-modulation of some modules, thereby affecting the system stability.

[0023] At this time, the reference voltage superposition strategy with dynamic adjustment coefficient is used, which sets the distribution coefficient by calculating the initial SOC value in each phase, so as to speed up the balance speed, but there is still the risk of over-modulation.

[0024] At the same time, based on the model predictive control strategy, the modulation signal and the current reference in the rotating synchronous d-q coordinate system are taken as the control input, and the optimal charge and discharge current of each unit module is obtained by solving the maximum rated current. However, with the increase of the number of module units, the calculation amount increases exponentially, which is not conducive to the application in practice.

[0025] In summary, the above-mentioned various intra-phase SOC adaptive equalization strategies can achieve certain effects, but their safety will still decrease when facing excessive intra-phase SOC imbalance. Specifically, the above-mentioned strategies often lead to excessive modulation voltage of a certain module and enter the over-modulation range during equalization, and long-term over-modulation will endanger the safety of the cascaded H-bridge energy storage converter, accompanied by potential problems such as output power quality decline, overheating, electromagnetic interference, etc.

[0026] Therefore, it is of important practical application value to study an SOC equalization strategy that can adapt to the constraints of the modulation voltage of each module for the promotion and application of the cascaded H-bridge energy storage converter.

[0027] Based on this, as shown in Figure 1 , the embodiment of the present application provides a cascaded H-bridge energy storage converter SOC equalization hierarchical control method, which comprises: S101: For the cascaded H-bridge energy storage converter, the running state parameters corresponding to itself are obtained.

[0028] The cascaded H-bridge energy storage converter (CHB-ESC) is a core power electronic device based on the cascaded H-bridge (CHB) topology for bidirectional energy conversion between the battery energy storage system and the grid / load. It connects multiple independent H-bridge power modules in series, combines with energy storage battery units, realizes high-voltage, large-capacity, and high-power quality energy scheduling, and is the key equipment for large-scale energy storage power stations, distributed energy storage, and grid auxiliary services.

[0029] In the cascaded H-bridge energy storage converter, there is a three-phase main circuit corresponding to phase A, phase B, and phase C, respectively, and each phase main circuit is basically the same. For convenience of description, the A phase is taken as an example for explanation and description in the embodiment of the present application.

[0030] As shown in Figure 2 , the topology structure of the A phase is provided, and each battery cluster corresponds to a single sub-battery module. In Figure 2 , the cascaded number is taken as 3 (including 3 sub-battery modules) as an example for explanation and description.

[0031] The running state parameters can include the cascaded number, voltage value, charging and discharging state, etc.

[0032] S102: Based on the state of charge parameter contained in the running state parameter, the inter-phase imbalance degree corresponding to each phase in the cascaded H-bridge energy storage converter is determined, and the intra-phase imbalance degree corresponding to each sub-battery module in a single phase is determined.

[0033] Interphase imbalance mainly reflects the difference in state of charge parameters between different phases, while intraphase imbalance mainly reflects the difference in state of charge parameters between sub-cell modules within a single phase.

[0034] Specifically, the phases included in the cascaded H-bridge energy storage converter and the sub-battery modules included in a single phase are determined. In this embodiment, phase A is used as an example for explanation, and phase A contains 3 sub-battery modules.

[0035] Based on the operating status parameters, the state of charge parameters corresponding to each sub-battery module are determined. Here, the state of charge parameters are simply referred to as SOC values.

[0036] For a single sub-cell module, the intra-phase imbalance corresponding to that sub-cell module is determined based on its corresponding state of charge parameters and the first average state of charge parameters of each sub-cell module in the same phase.

[0037] like Figure 3 The diagram shows the intra-phase SOC balancing control block diagram for the i-th module unit in phase A. In phase A of the cascaded H-bridge energy storage converter, the SOC value of the i-th sub-battery module is compared with the average SOC value of all battery modules in phase A (the first average state of charge parameter). The difference between the values ​​can be used as the intra-phase imbalance ΔSOC corresponding to the sub-battery module.

[0038] For a single phase, the phase imbalance is determined based on its corresponding first average state of charge parameter and the corresponding second average state of charge parameters in the cascaded H-bridge energy storage converter.

[0039] Corresponding to the intra-phase imbalance, the inter-phase imbalance refers to the difference in the state of charge parameters between different phases. By averaging the corresponding first average state of charge parameters, the corresponding second average state of charge parameters in the cascaded H-bridge energy storage converter are obtained. Then, by calculating the difference between the first average state of charge parameters and the second average state of charge parameters, the inter-phase imbalance corresponding to each phase is obtained.

[0040] S103: Determine the range of values ​​for the phase balance coefficient corresponding to each sub-battery module based on the number of cascaded sub-battery modules and the phase imbalance degree corresponding to each sub-battery module.

[0041] Based on the positive and negative values ​​of the intra-phase imbalance degree corresponding to the sub-cell module, the intra-phase balance coefficient is segmented and valued. For example, when the intra-phase imbalance degree is positive and negative, corresponding expressions are set to calculate the value range of the corresponding intra-phase balance coefficient.

[0042] For each range of values, according to the number of cascades of the sub-battery module, the in-phase imbalance degree corresponding to each sub-battery module, the upper limit value and the lower limit value corresponding to the range of values are determined.

[0043] Specifically, it can be seen from Figure 3 that through a proportional adjustment link, the difference of the SOC value can be converted into the corresponding difference, and on this basis, multiplied by the modulation voltage of phase A, each module unit will obtain the corresponding modulation voltage. It is not difficult to see that the power distribution ratio of each sub-battery module of phase A can be determined by the corresponding power distribution coefficient , and accordingly the modulation voltage of each sub-battery module is adjusted.

[0044] After combining the constants in the calculation link, the expression of the modulation wave of each sub-module unit is as shown in Formula One: Formula One; Among them, is the adjusted modulation wave reference signal of the i th sub-battery module of phase A, is the power distribution coefficient, is the total modulation wave reference signal of phase A, is the in-phase balancing coefficient, the sign of which is determined by the state of the cascaded H-bridge energy storage converter, and takes a positive value in the charging state and a negative value in the discharging state, is the first average state of charge parameter of phase A, is the SOC value of the i th sub-battery module of phase A, is the in-phase imbalance degree of the i th sub-battery module of phase A, and N is the number of cascades.

[0045] As can be seen from Formula One, the power distribution coefficient is only affected by τ and the imbalance degree of each module, and when the SOC in phase A is balanced, the imbalance degree difference of each sub-module tends to zero, at this time . Therefore, the in-phase SOC overall control block diagram of each sub-battery module of phase A can be as shown in Figure 4 .

[0046] It is worth noting that the selection of the in-phase balancing coefficient τ will directly affect the control dynamic performance. In some in-phase balancing strategies, when the absolute value of τ is too large, it will often lead to problems such as increased harmonic distortion of the cascaded H-bridge energy storage converter system, overheating, increased electromagnetic interference (EMI), decreased output power quality, increased stress of switching devices, etc. Therefore, the embodiments of the present application consider the balancing efficiency and the reliability of the system by optimizing the power distribution coefficient in real time, which provides a guarantee for the safe and stable operation of the cascaded H-bridge energy storage converter.

[0047] Taking the cascade number N=3 as an example, formula one is further analyzed, and formula two is obtained by expansion: Formula two; wherein, wherein, α is a power factor angle, ψ is a charge and discharge angle, ψ=0 when charging, ψ=π when discharging, ω is an angular frequency, and t is time.

[0048] At this time, formula two is further expanded to obtain formula three: Formula three.

[0049] Since the value of ψ is only 0 or π, sin(ψ)=0. Therefore, formula three can be further simplified to formula four: Formula four.

[0050] At this time, in order to prevent the modulation wave corresponding to the sub battery module from entering the over-modulation region, it can be obtained that The value range of | is as formula five: Formula five.

[0051] Combining formula four and formula five, the inequality as formula six can be obtained: Formula six.

[0052] It can be known from formula six that the value range of the phase internal balancing coefficient τ is not only related to the cascade number N, but also related to the charge and discharge state of the cascade H-bridge energy storage converter system and the phase internal unbalance degree of the sub battery module.

[0053] Since the value range of the balancing coefficient τ is relatively complex to obtain, the segmented value of the balancing coefficient can be represented as formula seven: Formula seven.

[0054] At this time, the phase internal balancing coefficient τ value can be dynamically calculated through the unbalance degree and the cascade number N (3 is taken as an example in the embodiment of the application).

[0055] It should be noted that a in the parameters such as formula one to formula seven in the application can refer to the A phase, or refer to any single phase of the A phase, the B phase and the C phase. In the embodiment of the application, the A phase is taken as an example for explanation and description. Taking formula seven as an example, , the phase internal unbalance degree of the i th sub battery module of a single phase can be , and the first average state of charge parameter corresponding to a single phase is . Of course, based on the demand, it can be changed to when corresponding to the B phase and the C phase. 、 、 、 and so on.

[0056] S104: Based on the value range, the corresponding intra-phase balancing coefficient is selected to generate the modulation wave adjustment amount corresponding to each battery sub-module through the intra-phase balancing coefficient, and the first modulation wave signal corresponding to each battery sub-module is generated according to the modulation wave adjustment amount.

[0057] Specifically, in order to achieve the balance between fast intra-phase SOC balancing and safe operation, a double constraint mechanism can be adopted.

[0058] For a single sub-battery module, the maximum value of the value range is taken as the first intra-phase balancing coefficient corresponding to the sub-battery module according to the value range corresponding thereto. The maximum value is selected in the value range of the intra-phase balancing coefficient allowed by each sub-battery module, which preferentially accelerates the convergence of the deviation of the SOC value.

[0059] According to the first intra-phase balancing coefficient corresponding to all sub-battery modules, the minimum value is selected as the second intra-phase balancing coefficient corresponding to the single phase. The minimum value is selected from all first intra-phase balancing coefficients of the sub-battery modules in the same phase (such as each sub-battery module in phase A), which avoids voltage out-of-limit caused by local over-modulation while maintaining the coordination of intra-phase power distribution.

[0060] According to the second intra-phase balancing coefficient, the modulation wave adjustment amount corresponding to each sub-battery module in a single phase is generated, and at this time, the adjusted modulation wave reference signal of each sub-battery module can be obtained through Formula One.

[0061] As shown in Figure 5 , when the intra-phase SOC adaptive balancing strategy is executed, the inter-phase SOC adaptive balancing strategy is performed to obtain the zero sequence voltage and the second modulation wave signal corresponding to each phase. At the same time, the SOC value of each sub-battery module is calculated, and the value range of the intra-phase balancing coefficient is obtained, so as to select the second intra-phase balancing coefficient, thereby obtaining the adjusted first modulation wave signal. At this time, if the intra-phase balancing coefficient is 0, it is considered that the intra-phase SOC is balanced, and if the intra-phase balancing coefficient is not 0, the intra-phase SOC adaptive balancing strategy is iteratively executed.

[0062] S105: For the inter-phase imbalance degree, coordinate transformation and coordinate synthesis are performed to obtain the zero sequence voltage, and for the modulation wave signal corresponding to each phase, the second modulation wave signal corresponding to each phase is output by injecting the zero sequence voltage.

[0063] Before the zero-sequence voltage determination, the proportional relationship between the inter-phase imbalance degree and the power adjustment amount corresponding to each phase can be determined based on the characteristics of the zero-sequence voltage injection. At this time, the injection of the zero-sequence voltage can achieve independent adjustment of the power of each phase without changing the total power.

[0064] Specifically, in the actual operation of the system, not only the SOC within the phase is different, but also the SOC between the phases is inconsistent. Therefore, in order to further improve the overall performance of the system, it is necessary to realize the balance control of the SOC between the phases.

[0065] Each chain of the cascaded H-bridge energy storage converter can independently adjust the DC side and the AC side power difference, so as to realize the SOC balance through power distribution. Still taking the A phase as an example, the relationship between the SOC and the energy consumption is represented as shown in formula eight: Formula eight wherein, is the rated energy of the battery side of the cascaded H-bridge energy storage converter, t is time, is the AC side power.

[0066] As can be seen from formula eight, by adjusting the power change amount, the control of the inter-phase SOC imbalance can be realized, and the adjustment of the power change amount directly affects the energy change of each phase battery, thereby realizing the control of the three-phase SOC. In the ideal case of ignoring the power conversion loss of the energy storage converter A phase, the DC side power change amount of the system is equal to the AC side power change amount, so the control of each phase SOC can be realized by adjusting the DC side power change.

[0067] As Figure 6 shown, in the three-phase three-wire cascaded H-bridge energy storage converter, due to the lack of zero-sequence current path, the adjustment of the zero-sequence voltage will not affect the total output power of the system.

[0068] At this time, the three-phase symmetrical current and the three-phase symmetrical voltage of the cascaded H-bridge energy storage converter can be represented as shown in formula nine and formula ten: Formula nine Formula ten wherein, I is the effective value of the three-phase current of the cascaded H-bridge energy storage converter, U is the effective value of the three-phase voltage of the cascaded H-bridge energy storage converter, ω is the grid angular frequency, δ is the initial phase angle of the system three-phase current, , , are the currents of the A phase, the B phase and the C phase respectively, , , The voltages of the A-phase, the B-phase and the C-phase respectively.

[0069] The injected zero-sequence voltage is set as , and its expression is shown in Equation 11: Equation 11; wherein, is the effective value of the zero-sequence voltage of the cascaded H-bridge energy storage converter, and θ is the initial phase angle of the zero-sequence voltage.

[0070] The output voltage expressions of the A-phase, the B-phase and the C-phase after the injection of the zero-sequence voltage are shown in Equation 12: Equation 12; wherein, , , The voltages of the A-phase, the B-phase and the C-phase respectively after the injection of the zero-sequence voltage.

[0071] By combining Equation 9 and Equation 12, the active power expressions of the three phases after the injection of the zero-sequence voltage can be obtained, as shown in Equation 13: Equation 13; wherein, , , is the active power of the A-phase, the B-phase and the C-phase after the injection of the zero-sequence voltage, is the active power before the injection, , , is the zero-sequence active power change of each phase after the injection of the zero-sequence voltage of the A-phase, the B-phase and the C-phase.

[0072] At this time, the changes are added to obtain Equation 14: Equation 14.

[0073] As can be seen from Equation 14, after the injection of the zero-sequence voltage, the sum of the three-phase powers of the cascaded H-bridge energy storage converter remains constant. Therefore, by adjusting the effective value and the phase angle θ of the injected zero-sequence voltage, the output power of each phase can be adjusted, so as to realize accurate control of the three-phase output power.

[0074] Based on this, it can be known that the additional power adjustment amount is proportional to the SOC imbalance degree of each phase, at this time, the proportional coefficient of the two is η. The specific expression is shown in Equation 15: Equation 15.

[0075] At this time, when the zero sequence voltage is generated, it is determined that the cascaded H-bridge energy storage converter contains a three-phase main circuit, and for the inter-phase imbalance degree, coordinate conversion is carried out through the Clark transformation to obtain component data in the two-phase stationary coordinate system.

[0076] The coordinate transformation does not change the actual power of the cascaded H-bridge energy storage converter system, and Figure 7 as shown, the imbalance degree 、 、 between the three phases is transformed by equal power. Through the transformation, it is mapped from the ABC three-phase to the αβ two-phase stationary coordinate system, so that its expression in the αβ coordinate system is as shown in formula sixteen: Formula sixteen; wherein, 、 are 、 、 mapping quantities in the αβ two-phase stationary coordinate system.

[0077] The component data in the two-phase stationary coordinate system is vector synthesized to obtain amplitude data and phase angle data of the synthesized vector.

[0078] The amplitude of the synthesized vector and the included angle ζ (phase angle) with the α axis in the αβ stationary coordinate system can be expressed as formula seventeen and formula eighteen: Formula seventeen; Formula eighteen; wherein, is the amplitude of the synthesized vector , and ζ is the phase angle.

[0079] According to the amplitude data and the phase angle data, the zero sequence voltage is obtained.

[0080] Based on the above analysis, the control block diagram of the inter-phase balance strategy is as shown in Figure 8 , wherein, is a variable coefficient for changing the size of the injected zero sequence voltage. The larger the variable coefficient k is, the larger the injected zero sequence voltage is.

[0081] In addition, it should be noted that in the embodiments of the present application, the sequence S103-S104 is mainly for intra-phase balancing control, and S105 is mainly for inter-phase balancing control. There is no strict sequence between the two, and S103-S104 can be executed first, then S105, or S105 can be executed first, then S103-S104, or S103-S104 and S105 can be executed synchronously.

[0082] S106: generating a driving signal according to the first modulation wave signal and the second modulation wave signal, and driving the cascaded H-bridge energy storage converter.

[0083] The first modulation wave signal obtained by the intra-phase SOC adaptive balancing strategy is combined with the second modulation wave signal obtained by the inter-phase SOC adaptive balancing strategy to construct an SOC balancing hierarchical control framework of the cascaded H-bridge energy storage converter as shown in Figure 9 The SOC balancing hierarchical control framework realizes inter-phase and intra-phase SOC balancing, thereby ensuring safe and stable operation of the cascaded H-bridge energy storage converter.

[0084] A hierarchical balancing control strategy is proposed to solve the problem of inconsistent SOC of the battery side energy storage battery of the cascaded H-bridge energy storage converter due to long-time operation or parameter differences.

[0085] At the inter-phase balancing level, the inter-phase power redistribution is realized by injecting a zero sequence voltage component, so that the discharging strength of the phase with high SOC is increased, and the discharging strength of the phase with low SOC is decreased, thereby driving the three-phase SOC to converge to the inter-phase SOC average value.

[0086] At the intra-phase balancing level, on the basis of the traditional power distribution intra-phase SOC balancing strategy, the mathematical relationship between the module modulation voltage and the balancing coefficient is established through theoretical derivation, and a dynamic optimization mechanism is designed to preferentially select the maximum value within the allowable range to accelerate balancing, and the minimum value of the balancing coefficient of the same phase module is used to avoid over-modulation risk, thereby improving the intra-phase balancing speed while ensuring safe and stable margin, and realizing intra-phase SOC balancing.

[0087] In one embodiment, to verify the effectiveness of the inter-phase SOC balancing control strategy of the cascaded H-bridge energy storage converter in the embodiments of the present application, based on the simulation parameters listed in Table 1 (including the initial SOC value of each sub-battery module and the key circuit parameters), the inter-phase SOC variation of each phase is observed by comparing two scenarios without inter-phase SOC balancing control strategy under discharge working conditions.

[0088] Table 1: Inter-phase SOC balancing control simulation parameters

[0089] Embodiment 1: The inter-phase SOC balancing control of the embodiments of the present application is not used.

[0090] As shown in Figure 10 , when the inter-phase SOC adaptive equalization strategy is not adopted, the inter-phase difference cannot be eliminated by itself during the three-phase discharging process due to the initial SOC value difference of each module. Simulation data shows that even after a long time of operation, the three-phase SOC still shows a divergence trend, verifying the inherent defect that natural discharging cannot achieve inter-phase equalization.

[0091] Embodiment 2: Adopting the inter-phase SOC adaptive equalization strategy proposed in the embodiment of the present application.

[0092] As shown in Figure 11 , at t = 0.25s, the inter-phase SOC equalization control strategy proposed in the embodiment of the present application is adopted, and the energy storage converter realizes fast convergence through dynamic power distribution. In order to achieve the equalization of the SOC of each phase, the phase with high SOC (C phase) needs to output more power, while the phase with low SOC (A phase) outputs less power. Therefore, the SOC of the ABC three-phase shows a decreasing trend, and the decay rate of each phase is different. As shown in the above analysis, at t = 6s, the SOC values of the three phases will be consistent and remain consistent, and the sub-modules will discharge at the same speed.

[0093] In order to more clearly show the change trend of the SOC of the three phases, the change trends of the unbalance degrees of the three phases are recorded , and , as shown in Figure 12 . From the figure, it can be more intuitively seen that when the inter-phase SOC adaptive equalization strategy is not adopted, the unbalance degrees of each phase are greatly different, at 0.25s, the inter-phase SOC unbalance degrees of each phase become smaller and smaller, and eventually the inter-phase SOC unbalance degrees tend to 0 and no longer change. In addition, as shown in Figure 13 , the three-phase current of the cascaded H-bridge energy storage converter does not change after the injection of the zero sequence voltage.

[0094] Based on the simulation, it can be known that the inter-phase SOC adaptive equalization strategy proposed in the embodiment of the present application can adjust the distribution of the three-phase active power of the cascaded H-bridge energy storage converter, change the SOC equalization rate of each phase unit module, and make the inter-phase SOC gradually consistent, verifying the effectiveness of the adopted inter-phase SOC equalization control strategy. In addition, the zero sequence injection method does not interfere with the output current of the energy storage converter.

[0095] In one embodiment, similar to the inter-phase SOC adaptive equalization strategy, in order to verify the effectiveness of the intra-phase SOC equalization control strategy of the cascaded H-bridge energy storage converter, each phase module unit is numbered in Table 2, and it is assumed that the initial SOC of the module unit batteries in each phase is not equal.

[0096] Table 2 Simulation parameters of the intra-phase SOC adaptive equalization control strategy

[0097] Example 1: The intra-phase SOC equalization control in this application embodiment was not used.

[0098] like Figure 14 As shown, when the intra-phase SOC adaptive equalization strategy is not adopted, the modules of phase A of the cascaded H-bridge energy storage converter have difficulty converging during the discharge process due to the initial SOC differences. Simulation waveforms show that the SOC differences between modules do not change over time, verifying that natural discharge cannot eliminate the inherent defect of intra-phase inconsistency.

[0099] Example 2: The intra-phase SOC adaptive equalization control strategy in the embodiments of this application is adopted.

[0100] like Figure 15 As shown, when the proposed intra-phase SOC adaptive equalization control strategy is adopted at t=0.25s, the submodule with a high SOC will obtain a larger modulation voltage coefficient and output more power; conversely, the submodule with a low SOC will obtain a smaller modulation voltage coefficient and output less power. Eventually, the SOC of each submodule within the phase will be equalized, and this phenomenon will continue. Afterward, each submodule unit will discharge at the same rate. As shown in the above analysis, at t=6s, the SOC values ​​of each module unit within the three-phase phase will reach a uniform value.

[0101] To more clearly demonstrate the changing trend of inter-phase SOC when using the intra-phase SOC adaptive equalization strategy proposed in the embodiments of this application, taking phase A as an example, the intra-phase SOC imbalance degree of phase A is recorded. Δ and The change curve, such as Figure 16 As shown in the figure, without the intra-phase SOC adaptive equalization strategy, the imbalance degree of each module in phase A varies greatly. When the proposed intra-phase equalization method is applied at 0.25s, the difference in SOC imbalance degree among the modules in phase A gradually decreases. Finally, intra-phase SOC equalization is completed, and the intra-phase SOC imbalance degree of phase A approaches 0 and no longer changes.

[0102] Furthermore, to verify the effectiveness of the proposed intra-phase SOC adaptive equalization control strategy, the proposed method is compared with traditional intra-phase SOC equalization control methods. Figure 17 As shown, the traditional in-phase SOC equalization control method based on power ratio is compared with the in-phase SOC adaptive equalization control method proposed in this application during the discharge process. Under the same initial SOC value and the same strategy switching time, the traditional in-phase SOC equalization control method (Figure 17 The SOC values of the module units in phase A reach the balanced state at 6s, and the SOCs of the modules remain consistent. When the SOC adaptive equalization control method in the phase is used Figure 17 The SOC values of the module units in phase A reach the balanced state at 4.3s, and the SOCs of the modules remain consistent, and the discharge continues at the same rate. Therefore, compared with the original control method, the adaptive control method proposed in the application improves the speed by about 25%.

[0103] In addition, as shown in Figure 18 When the adaptive equalization control method in the phase is used, the three-phase output currents remain obviously symmetrical, which shows that the adaptive equalization control strategy in the phase does not affect the three-phase current output.

[0104] As shown in Figure 19 When the hierarchical SOC equalization control strategy based on inter-phase and intra-phase equalization in the application is used, the SOC change curves of the module units of the cascaded H-bridge energy storage converter show the synchronous convergence characteristics, and all the model SOCs reach consistency at 10s, and the inter-phase and intra-phase double equalization goals are achieved. The simulation results show that the inter-phase SOC equalization control strategy and the intra-phase SOC adaptive control strategy have high compatibility, and the regulation processes of the two strategies do not conflict, and do not affect the stable output of the energy storage converter current. Through the hierarchical equalization control mechanism, the adaptive control of the battery side SOC equalization of the cascaded H-bridge energy storage converter is achieved, and good performance and equalization effect are obtained.

[0105] The simulation model of the cascaded H-bridge energy storage converter built by MATLAB and Simulink sets the initial SOC values of the module batteries to be unequal. The simulation results show that the inter-phase SOC equalization control strategy can effectively achieve three-phase SOC equalization; the intra-phase SOC adaptive equalization control strategy proposed achieves intra-phase SOC equalization while obtaining a faster equalization rate, which proves the effectiveness of the SOC equalization hierarchical control method proposed in the application, improves the energy utilization efficiency, battery service life and operation reliability of the system, and provides theoretical support for engineering application.

[0106] As shown in Figure 20 The application further provides a cascaded H-bridge energy storage converter SOC equalization hierarchical control device, which comprises: at least one processor; and a memory in communication connection with the at least one processor; wherein The memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform the cascade H-bridge energy storage converter SOC equalization hierarchical control method according to any one of the above examples.

[0107] The embodiment of the present application further provides a nonvolatile computer storage medium, which stores computer executable instructions configured to implement the cascade H-bridge energy storage converter SOC equalization hierarchical control method according to any one of the above examples.

[0108] The above merely illustrates the embodiments of the present application, but is not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the scope of the claims of the present application.

Claims

1. A SOC equalization hierarchical control method for a cascaded H-bridge energy storage converter, characterized in that, The method comprises the following steps: For a cascade H-bridge energy storage converter, obtain the corresponding operating state parameters of itself; Based on the state of charge parameter contained in the operating state parameter, determine the inter-phase imbalance degree of each phase in the cascade H-bridge energy storage converter, and determine the intra-phase imbalance degree of each sub-cell module in a single phase; According to the cascade number of the sub-cell module and the intra-phase imbalance degree of each sub-cell module, determine the value range of the intra-phase balancing coefficient corresponding to each sub-cell module; Based on the value range, select the corresponding intra-phase balancing coefficient to generate the modulation wave adjustment amount of each sub-cell module through the intra-phase balancing coefficient, and generate the first modulation wave signal of each sub-cell module according to the modulation wave adjustment amount; For the inter-phase imbalance degree, coordinate transformation and coordinate synthesis are performed to obtain a zero sequence voltage, and for the modulation wave signal corresponding to each phase, the second modulation wave signal corresponding to each phase is output by injecting the zero sequence voltage; According to the first modulation wave signal and the second modulation wave signal, signal synthesis is performed to generate a driving signal to drive the cascade H-bridge energy storage converter.

2. The method of claim 1, wherein, Based on the state of charge parameter contained in the operating state parameter, determine the inter-phase imbalance degree of each phase in the cascade H-bridge energy storage converter, and determine the intra-phase imbalance degree of each sub-cell module in a single phase, specifically comprising: Determine each phase in the cascade H-bridge energy storage converter and each sub-cell module in a single phase; Based on the operating state parameter, determine the state of charge parameter corresponding to each sub-cell module; For a single sub-cell module, based on the state of charge parameter corresponding to it and the first average state of charge parameter corresponding to each sub-cell module in the single phase where it is located, determine the intra-phase imbalance degree corresponding to the sub-cell module; For a single phase, based on the first average state of charge parameter corresponding to it and the second average state of charge parameter corresponding to each phase in the cascade H-bridge energy storage converter where it is located, determine the inter-phase imbalance degree corresponding to the phase.

3. The method of claim 1, wherein, According to the cascade number of the sub-cell module and the intra-phase imbalance degree of each sub-cell module, determine the value range of the intra-phase balancing coefficient, specifically comprising: Based on the positive and negative values of the intra-phase imbalance degree corresponding to the sub-cell module, the intra-phase balancing coefficient is segmented and valued; For each value range, according to the cascade number of the sub-cell module and the intra-phase imbalance degree of each sub-cell module, determine the upper limit value and the lower limit value corresponding to the value range.

4. The method of claim 3, wherein, The cascade number is 3, and the phases of the cascade H-bridge energy storage converter include A phase, B phase and C phase; The expression corresponding to the value range of the intra-phase balancing coefficient comprises: ; wherein, is a phase-wise imbalance degree of the i-th sub-cell module of the single phase, is a phase-wise balancing coefficient, is a first average state-of-charge parameter corresponding to the single phase.

5. The method of claim 1, wherein, Based on the value range, select the corresponding intra-phase balancing coefficient to generate the modulation wave adjustment amount of each sub-cell module through the intra-phase balancing coefficient, specifically comprising: For a single sub-cell module, according to the value range corresponding to it, the maximum value of the value range is taken as the first intra-phase balancing coefficient corresponding to the sub-cell module; According to the first intra-phase balancing coefficients corresponding to all sub-cell modules, the minimum value is selected as the second intra-phase balancing coefficient corresponding to the single phase; According to the second intra-phase balancing coefficient, the modulation wave adjustment amount corresponding to each sub-cell module in the single phase is generated.

6. The method of claim 1, wherein, Before the coordinate transformation and coordinate synthesis of the inter-phase imbalance degree to obtain the zero sequence voltage, the method further comprises: Based on the characteristics of zero sequence voltage injection, it is determined that the inter-phase imbalance degree is proportional to the power adjustment amount corresponding to each phase.

7. The method of claim 1, wherein, The coordinate transformation and coordinate synthesis of the inter-phase imbalance degree to obtain the zero sequence voltage, specifically comprising: Determine that the cascaded H-bridge energy storage converter contains a three-phase main circuit, and for the inter-phase imbalance degree, the Clark transformation is used for coordinate conversion to obtain component data in a two-phase stationary coordinate system; The vector synthesis is performed on the component data in the two-phase stationary coordinate system to obtain amplitude data and phase angle data of the synthesized vector; According to the amplitude data and the phase angle data, the zero sequence voltage is obtained.

8. The method of claim 7, wherein, The cascaded number is 3, and the phase of the cascaded H-bridge energy storage converter includes A phase, B phase and C phase; The expression of the coordinate conversion includes: ; wherein, , , respectively are the first average state-of-charge parameters of the A phase, the B phase and the C phase, , are , , mapping quantities under the αβ two-phase stationary coordinate system; The expression of the vector synthesis includes: and ; wherein, is the magnitude of the resultant vector and ζ is the phase angle data.

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