Fast SOC balancing control method for cascaded H-bridge converter energy storage grid-connected system

Abstract

The present invention discloses a fast SOC balancing control method for a cascaded H-bridge converter energy storage grid-connected system, which realizes inter-phase SOC balancing control by zero-sequence voltage injection. After the zero-sequence voltage is injected, the amplitude of the modulation wave corresponding to the maximum amplitude in the three-phase modulation wave is 1, so as to realize fast inter-phase SOC balancing control; the present invention also realizes intra-phase SOC balancing control by superimposing fundamental wave components. After superimposing fundamental wave components, the maximum amplitude in the modulation wave of each H-bridge unit is 1, so as to realize fast intra-phase SOC balancing control. The present invention realizes fast SOC balancing control of the cascaded energy storage grid-connected system through a control strategy, does not require additional hardware equipment, reduces system cost, and improves SOC balancing speed.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronic control, and in particular relates to the design of a fast SOC balancing control method for a cascaded H-bridge converter energy storage grid-connected system. Background Art

[0002] There is inconsistency in the battery modules in the energy storage grid-connected system, and their capacities may be different. The state of charge (SOC) is an important parameter value that describes the remaining capacity of the battery. During the operation of the energy storage grid-connected system, due to differences in the electrolyte density, temperature and ventilation conditions, self-discharge degree, discharge depth and charging and discharging process of each battery, the decay rate of each battery is different, and the differences generated during use are cumulative, which will further aggravate the inconsistency of the battery. An important factor affecting the service life of the battery is the overcharge and over-discharge phenomenon caused by the imbalance of SOC between battery modules during the battery charging and discharging process. When the battery stores electrical energy, if the SOC of a battery is too high, the entire energy storage system cannot continue to charge; and when the battery releases electrical energy, if the SOC of a battery is too low, the entire energy storage system cannot continue to discharge. This short board effect will limit the availability of the energy storage grid-connected system. Therefore, the energy storage grid-connected system should have the ability to balance the SOC of the battery modules to increase and extend the service life of the system.

[0003] The battery SOC balancing control strategy is to adjust the charging and discharging power of the energy storage grid-connected system according to the current battery SOC value. When the battery module is discharging, the battery with a smaller SOC is controlled to release less energy, and the battery with a larger SOC is controlled to output more energy; conversely, when the battery module is charging, the battery with a smaller SOC is controlled to store more energy, and the battery with a larger SOC is controlled to absorb less energy, so that the SOC value of the battery module in the entire system tends to be balanced.

[0004] At present, the commonly used battery SOC balancing control method is to adjust the power between the three phases by injecting zero-sequence voltage, that is, to generate an additional power in each phase by injecting zero-sequence voltage, and to achieve the system inter-phase SOC balancing through this additional power. At the same time, a corresponding fundamental voltage component is superimposed on the output voltage of the AC side of each H-bridge unit to distribute the power within the phase, so as to achieve the SOC balancing within the phase. However, in the traditional SOC balancing control strategy, the proportional coefficient determines the balancing speed. The larger the coefficient, the larger the amplitude of the zero-sequence voltage and the fundamental voltage component, the larger the additional power generated, and the shorter the time to reach the equilibrium state; on the contrary, if the coefficient is too small, the regulation efficiency is too low and the dynamic performance deteriorates. However, if the coefficient is too large, the system will be over-modulated, resulting in a large distortion of the system output voltage, affecting the safety of the grid-connected system. In actual engineering, it is necessary to select a suitable proportional coefficient according to the initial imbalance of the battery module, and the imbalance of each battery module will become smaller and smaller with the effect of the balancing control. If the coefficient remains unchanged, the amplitude of the injected zero-sequence voltage and the fundamental voltage component will become smaller and smaller, and the balancing control effect will weaken over time. Summary of the invention

[0005] The purpose of the present invention is to solve the shortcomings of the battery SOC balancing control method, and proposes a fast SOC balancing control method for a cascaded H-bridge converter energy storage grid-connected system. While using a cascaded H-bridge converter to realize the grid-connected control of the energy storage system, it ensures that fast phase-to-phase SOC balancing control and intra-phase SOC balancing control can be achieved without overmodulation.

[0006] The technical solution of the present invention is: a fast SOC balancing control method for a cascaded H-bridge converter energy storage grid-connected system, comprising the following steps:

[0007] S1, inject zero-sequence voltage into the cascaded H-bridge converter energy storage grid-connected system, so that the amplitude of the modulation wave with the largest amplitude in the three-phase modulation wave is 1, realizing fast phase-to-phase SOC balancing control.

[0008] S2, outputting a superimposed fundamental voltage component to the AC side of each H-bridge unit in the cascaded H-bridge converter energy storage grid-connected system, so that the maximum amplitude of the modulation wave of each H-bridge unit is 1, thereby realizing fast intra-phase SOC balancing control.

[0009] Furthermore, the zero-sequence voltage injected in step S1 is expressed as:

[0010] u0=U0cos(ωt-θ)

[0011] Where u0 represents the zero-sequence voltage, U0, ω, θ represent the amplitude, angular frequency and phase angle of the zero-sequence voltage respectively, and t represents time.

[0012] Furthermore, if the maximum amplitude of the a-phase modulation wave after the zero-sequence voltage injection is 1, the calculation formula of the amplitude U0 of the zero-sequence voltage is:

[0013]

[0014] where U′ a is the original amplitude of the a-phase modulation wave, A, B, and C are all intermediate coefficients, and:

[0015] B=2U′ a cos(γ)cos(θ)-2U′ a sin(γ)sin(θ)

[0016] Where γ represents the phase angle of the modulation wave leading the grid voltage.

[0017] Furthermore, if the maximum amplitude of the b-phase modulation wave after the zero-sequence voltage injection is 1, the calculation formula of the amplitude U0 of the zero-sequence voltage is:

[0018]

[0019] where U′ b is the original amplitude of the b-phase modulation wave, A, B, and C are all intermediate coefficients, and:

[0020]

[0021] Where γ represents the phase angle of the modulation wave leading the grid voltage.

[0022] Furthermore, if the maximum amplitude of the c-phase modulation wave after the zero-sequence voltage injection is 1, the calculation formula of the amplitude U0 of the zero-sequence voltage is:

[0023]

[0024] where U′ c is the original amplitude of the c-phase modulation wave, A, B, and C are all intermediate coefficients, and:

[0025]

[0026] Where γ represents the phase angle of the modulation wave leading the grid voltage.

[0027] Furthermore, the calculation formula of the phase angle θ of the zero-sequence voltage is:

[0028] θ=arctan(ΔSOC α / ΔSOC β )

[0029] Where ΔSOC α , ΔSOC β They respectively represent the components of the three-phase SOC difference in the α and β coordinate systems after the PARK coordinate transformation.

[0030] Furthermore, in step S2, the superimposed fundamental voltage component output to the AC side of each H-bridge unit is:

[0031]

[0032] where v 1an 、v 1bn 、v 1cn They represent the superimposed fundamental voltage components output to the AC side of the nth H-bridge unit of phases a, b, and c, respectively. 1a , K 1b , K 1c Respectively represent the proportional coefficients of phases a, b, and c, ΔSOC an , ΔSOC bn , ΔSOC cn They represent the unbalance degree of the nth H-bridge unit of phases a, b, and c respectively, ω represents the angular frequency of the zero-sequence voltage, t represents time, and N represents the total number of H-bridge units in each phase.

[0033] Furthermore, the proportionality coefficient K of phases a, b, and c is 1a , K 1b , K 1c The calculation formula is:

[0034]

[0035] Among them U o-maxa , U o-maxb , U o-maxc Respectively represent the amplitude of the fundamental voltage component superimposed on phases a, b, and c, ΔSOC maxa , ΔSOC maxb , ΔSOC maxc Represent the maximum imbalance of phases a, b, and c respectively.

[0036] Furthermore, the amplitude U of the fundamental voltage component superimposed on phases a, b, and c is o-maxa , U o-maxb , U o-maxc The calculation formula is:

[0037]

[0038] Among them U a , U b , U c It represents the amplitude of the three-phase modulation wave after injecting zero-sequence voltage.

[0039] Furthermore, the unbalanced degree ΔSOC of the nth H-bridge unit of phases a, b, and c is an , ΔSOC bn , ΔSOC cn The calculation formula is:

[0040]

[0041] Among them, SOC an , SOC bn , SOC cn Respectively represent the SOC value of the nth H-bridge unit of phase a, b, and c, SOC a , SOC b , SOC c Represent the average SOC values ​​of phases a, b, and c respectively.

[0042] The beneficial effects of the present invention are:

[0043] (1) The present invention realizes inter-phase SOC balancing control by zero-sequence voltage injection. After zero-sequence voltage injection, the amplitude of the modulation wave with the largest amplitude in the three-phase modulation wave corresponds to 1, so as to realize fast inter-phase SOC balancing control.

[0044] (2) The present invention realizes intra-phase SOC balancing control by superimposing fundamental wave components. After superimposing fundamental wave components, the maximum amplitude of the modulation wave of each H-bridge unit is 1, so as to realize fast intra-phase SOC balancing control.

[0045] (3) The present invention realizes fast SOC balancing control of the cascaded energy storage grid-connected system through a control strategy, which does not require additional hardware equipment, reduces system costs, and improves the SOC balancing speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Shown is a flow chart of a fast SOC balancing control method for a cascaded H-bridge converter energy storage grid-connected system provided by an embodiment of the present invention.

[0047] Figure 2 Shown is a topological structure diagram of a cascaded H-bridge converter energy storage grid-connected system provided by an embodiment of the present invention.

[0048] Figure 3 The figure shows the grid-connected current and voltage waveform of phase A provided by an embodiment of the present invention.

[0049] Figure 4 Shown is a comparison diagram of zero-sequence voltage injected into three phases provided by an embodiment of the present invention.

[0050] Figure 5 Shown is a three-phase output power comparison diagram of the cascaded H-bridge converter provided by an embodiment of the present invention.

[0051] Figure 6 Shown is a comparison diagram of three-phase modulation waves provided by an embodiment of the present invention.

[0052] Figure 7 The figure shows the phase imbalance ΔSOC provided by the embodiment of the present invention. mComparison chart.

[0053] Figure 8 Shown is a three-phase SOC value comparison diagram provided by an embodiment of the present invention.

[0054] Fig. 9 The figure shows a comparison diagram of the fundamental voltage of the three H-bridge units superimposed on the a-phase provided by the embodiment of the present invention.

[0055] Fig.10 The figure shows a comparison diagram of modulation waves of three H-bridge units of phase a provided by an embodiment of the present invention.

[0056] Fig.11 The maximum unbalance degree ΔSOC of phase a provided by the embodiment of the present invention is shown as follows: maxa Comparison chart

[0057] Fig.12 The figure shows a comparison diagram of SOC values ​​of three modules of phase a provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0058] Now, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood that the embodiments shown and described in the accompanying drawings are only exemplary and are intended to explain the principles and spirit of the present invention, rather than to limit the scope of the present invention.

[0059] The embodiment of the present invention provides a fast SOC balancing control method for a cascaded H-bridge converter energy storage grid-connected system, such as Figure 1 As shown, the following steps S1 to S2 are included:

[0060] S1, inject zero-sequence voltage into the cascaded H-bridge converter energy storage grid-connected system, so that the amplitude of the modulation wave with the largest amplitude in the three-phase modulation wave is 1, realizing fast phase-to-phase SOC balancing control.

[0061] In the embodiment of the present invention, the topological structure of the cascaded H-bridge converter energy storage grid-connected system is as follows: Figure 2 As shown. The rated power of the system is 5.6kW, with 3 H-bridge units in each phase and 9 H-bridge units in total for three phases. The grid voltage is 380V. To meet the grid voltage level requirements, the DC voltage is set at 600V, and the DC bus voltage corresponding to each H-bridge unit is 200V. According to the battery supply market research, the operating voltage range of lithium batteries is about 1.9-2.7V. Usually 21 battery cells are connected in series to form a 48V battery module. Considering that the battery voltage will drop slightly during discharge, each H-bridge unit requires 5 battery modules in series. The simulation parameters are set as follows: DC bus capacitor C1=C2=470μF, switching frequency f=10kHz, sampling time T=0.1ms, cascaded H-bridge converter output voltage frequency f=50Hz, and filter inductor L=10mH.

[0062] Based on the above topological structure, the zero-sequence voltage injected in the embodiment of the present invention is expressed as:

[0063] u0=U0cos(ωt-θ)

[0064] Where u0 represents the zero-sequence voltage, U0, ω, θ represent the amplitude, angular frequency and phase angle of the zero-sequence voltage respectively, and t represents time.

[0065] The following describes in detail the method for obtaining the amplitude U0 and phase angle θ of the zero-sequence voltage.

[0066] (1) The amplitude of zero-sequence voltage U0.

[0067] The grid voltage phase a is selected as the reference voltage to achieve unity power factor grid-connected control. The modulation wave leads the grid voltage phase angle γ according to the filter inductance value calculation or simulation. The three-phase modulation wave is:

[0068]

[0069] Among them, u′ a , u′ b , u′ c Represents a three-phase modulation wave, U′ a , U′ b , U′ c is the original amplitude of the three-phase modulation wave, and γ is the phase angle of the modulation wave leading the grid voltage.

[0070] Three-phase modulation wave u after zero-sequence voltage injection a 、u b 、u c for:

[0071]

[0072] Using the phasor method to calculate, the phasor form of the three-phase modulation wave is:

[0073]

[0074] in It is in the form of three-phase modulation wave phase.

[0075] Taking phase a as an example, we have:

[0076]

[0077] Where j is the imaginary unit, and then:

[0078]

[0079] Assume that the maximum amplitude of the a-phase modulation wave after zero-sequence voltage injection is 1, that is, U 2 a-max=1, then:

[0080]

[0081] Then U0 can be obtained using the universal formula:

[0082]

[0083] where U′ a is the original amplitude of the a-phase modulation wave, A, B, and C are all intermediate coefficients of the quadratic equation, and:

[0084] B=2U′ a cos(γ)cos(θ)-2U′ a sin(γ)sin(θ)

[0085] Similarly, the maximum amplitude of the zero-sequence voltage can be calculated when the amplitude of the modulation wave of phase b or phase c is 1 after the zero-sequence voltage is injected, and the phase difference of the three-phase modulation wave is Then, when the amplitude of the b-phase modulation wave is 1 at most after the zero-sequence voltage is injected, the calculation formula for the amplitude U0 of the zero-sequence voltage is:

[0086]

[0087] where U′ b is the original amplitude of the b-phase modulation wave, A, B, C are the intermediate coefficients of the quadratic equation, and:

[0088]

[0089] When the amplitude of the c-phase modulation wave is 1 at most after the zero-sequence voltage is injected, the calculation formula for the amplitude U0 of the zero-sequence voltage is:

[0090]

[0091] where U′ c is the original amplitude of the c-phase modulation wave, A, B, and C are the intermediate coefficients of the quadratic equation, and:

[0092]

[0093] (2) The phase angle θ of the zero-sequence voltage.

[0094] The average value of the three-phase SOC is:

[0095]

[0096] Among them, SOC is the average value of the three-phase SOC, SOC a , SOC b , SOC cRepresent the average SOC values ​​of phases a, b, and c respectively.

[0097] Then we have:

[0098]

[0099] Where ΔSOC a , ΔSOC b , ΔSOC c They are the SOC differences (phase imbalance) of phases a, b, and c respectively.

[0100] After PARK coordinate transformation, it can be calculated:

[0101] θ=arctan(ΔSOC α / ΔSOC β )

[0102] Where ΔSOC α , ΔSOC β Represents the SOC difference ΔSOC of the three phases respectively a , ΔSOC b , ΔSOC c The components in the α and β coordinate systems after PARK coordinate transformation are:

[0103]

[0104] In order to achieve fast phase-to-phase SOC balancing, the amplitude of the injected zero-sequence voltage needs to be as large as possible, but it cannot be over-modulated at the same time. Therefore, after the zero-sequence voltage is injected, the maximum amplitude of the three-phase modulation wave is always kept at 1 to obtain a fast balancing speed. Taking discharge as an example for analysis, the SOC value higher than the average value needs to be discharged more. Therefore, the amplitude of the modulation wave of the phase with the largest SOC value is kept at 1 after the zero-sequence voltage is injected.

[0105] S2, outputting a superimposed fundamental voltage component to the AC side of each H-bridge unit in the cascaded H-bridge converter energy storage grid-connected system, so that the maximum amplitude of the modulation wave of each H-bridge unit is 1, thereby realizing fast intra-phase SOC balancing control.

[0106] The superimposed fundamental voltage component output to the AC side of each H-bridge unit is:

[0107]

[0108] where v 1an 、v 1bn 、v 1cn They represent the superimposed fundamental voltage components output to the AC side of the nth H-bridge unit of phases a, b, and c, respectively. 1a , K 1b , K 1c Respectively represent the proportional coefficients of phases a, b, and c, ΔSOCan , ΔSOC bn , ΔSOC cn They represent the unbalance degree of the nth H-bridge unit of phases a, b, and c respectively, ω represents the angular frequency of the zero-sequence voltage, t represents time, and N represents the total number of H-bridge units in each phase.

[0109] The proportional coefficient K of phases a, b, and c 1a , K 1b , K 1c The calculation formula is:

[0110]

[0111] Among them U o-maxa , U o-maxb , U o-maxc Respectively represent the amplitude of the fundamental voltage component superimposed on phases a, b, and c, ΔSOC maxa , ΔSOC maxb , ΔSOC maxc Represent the maximum imbalance of phases a, b, and c respectively.

[0112] When the SOC value is higher than the phase average, more discharge is required, and the same-direction fundamental component is superimposed, which will increase the amplitude; while when the SOC value is lower than the phase average, less discharge is required, and the opposite-direction fundamental component should be superimposed to reduce the amplitude. To avoid over-modulation, the maximum amplitude of the corresponding modulation wave after superimposing the same-direction fundamental component is 1, and the amplitude of the fundamental voltage component superimposed on phases a, b, and c can be obtained as U o-maxa , U o-maxb , U o-maxc The calculation formula is:

[0113]

[0114] Among them U a , U b , U c It represents the amplitude of the three-phase modulation wave after injecting zero-sequence voltage.

[0115] Unbalanced degree ΔSOC of the nth H-bridge unit of phases a, b, and c an , ΔSOC bn , ΔSOC cn The calculation formula is:

[0116]

[0117] Among them, SOC an , SOC bn , SOC cn Respectively represent the SOC value of the nth H-bridge unit of phase a, b, and c, SOC a , SOC b, SOC c Represent the average SOC values ​​of phases a, b, and c respectively.

[0118] like Figure 3 The waveform of the current and voltage of phase A is shown in Figure 1. Figure 3 It can be seen that the current and voltage of phase a of the battery module discharge are in phase, and the cascaded H-bridge converter energy storage grid-connected system achieves unity power factor grid connection.

[0119] like Figure 4 The following is a comparison diagram of the zero-sequence voltage injected into the three phases. Figure 4 (a) is the zero-sequence voltage injected into the three phases by the traditional SOC balancing control strategy. Figure 4 (b) is the zero-sequence voltage injected into the three phases of the present invention. It can be seen that as the phase-to-phase imbalance decreases when the balancing control takes effect, the amplitude of the zero-sequence voltage of the traditional SOC balancing control strategy becomes smaller and smaller, and the effect of the balancing control becomes weaker and weaker; while the amplitude of the zero-sequence voltage of the fast SOC balancing control method provided by the present invention remains unchanged, and the amplitude remains unchanged as the phase-to-phase imbalance decreases until the phase-to-phase balance is achieved and the amplitude is reduced to zero.

[0120] Figure 5 This is a comparison chart of the three-phase output power of the cascaded H-bridge converter. Figure 5 (a) is the three-phase output power of the cascaded H-bridge converter with the traditional SOC balancing control strategy. Figure 5 (b) is the three-phase output power of the cascaded H-bridge converter of the present invention. It can be seen that the SOC value of phase c is the largest and the most energy P needs to be released. c >P b >P a , traditional SOC balance control strategy P c However, when the fast SOC balancing control method provided by the present invention is working, P c A constant value provides maximum adjustability.

[0121] Figure 6 It is a comparison diagram of three-phase modulation wave. Figure 6 (a) is the three-phase modulation wave of the traditional SOC balance control strategy. Figure 6 (b) is the three-phase modulation wave of the present invention. It can be seen that the SOC value of phase c is the largest, so the amplitude of the modulation wave of phase c is the largest. As the amplitude of the injected zero-sequence voltage decreases, the amplitude of the three-phase modulation wave of the traditional SOC balance control strategy decreases and tends to the steady-state value. The maximum amplitude of the modulation wave after the zero-sequence voltage is injected into the fast SOC balance control method provided by the present invention is 1, and it is maintained at the maximum value until phase balance is achieved.

[0122] Figure 7 is the phase asymmetry ΔSOC m Comparison chart, Figure 7(a) is the interphase asymmetry ΔSOC of the traditional SOC balancing control strategy m , Figure 7 (b) is the phase asymmetry ΔSOC of the present invention m , we can see that the traditional SOC balance control strategy starts with ΔSOC m The fast SOC balancing control method ΔSOC provided by the present invention decreases significantly and decreases slowly in the later stage. m It decreases linearly until phase balance is achieved, and the balancing speed is greatly improved.

[0123] Figure 8 This is a comparison chart of three-phase SOC values. Figure 8 (a) is the three-phase SOC value of the traditional SOC balancing control strategy, Figure 8 (b) is the three-phase SOC value of the present invention. It can be seen that the SOC value of phase C is the largest and the downward trend is the most obvious. The traditional SOC balancing control strategy slows down with the balancing trend; while the fast SOC balancing control method provided by the present invention greatly improves the balancing speed.

[0124] Fig. 9 This is a comparison diagram of the fundamental voltage of the three H-bridge units superimposed on phase a. Fig. 9 (a) is the fundamental voltage of the three H-bridge units superimposed on the a phase of the traditional SOC balancing control strategy. Fig. 9 (b) is the fundamental voltage of the three H-bridge units superimposed on phase a of the present invention. It can be seen that in the traditional SOC balancing control strategy, as the imbalance degree of each module in the phase where the balancing control takes effect decreases, the amplitude of the fundamental voltage becomes smaller and smaller, and the effect of the balancing control becomes weaker and weaker; the amplitude of the fundamental voltage of the fast SOC balancing control method provided by the present invention is kept constant to achieve a fast regulation effect.

[0125] Fig.10 This is the comparison diagram of the modulation waves of the three H-bridge units in phase a. Fig.10 (a) is the modulation wave of three H-bridge units in phase a of the traditional SOC balancing control strategy. Fig.10 (b) is the modulation wave of the three H-bridge units of phase a of the present invention. It can be seen that the SOC value of H2 is the largest, so the modulation wave amplitude of H2 is the largest. The traditional SOC balancing control strategy tends to a steady-state value as the superimposed fundamental voltage amplitude decreases; the modulation wave amplitude of H2 in the fast SOC balancing control method provided by the present invention is maximum 1 until intra-phase balance is achieved.

[0126] Fig.11 is the maximum asymmetry of phase a ΔSOC maxa Comparison chart, Fig.11 (a) is the maximum asymmetry ΔSOC of phase a of the traditional SOC balancing control strategy maxa , Fig.11 (b) is the maximum asymmetry ΔSOC of the a phase of the present inventionmaxa , we can see that the traditional SOC balance control strategy starts with ΔSOC maxa The fast SOC balancing control method ΔSOC provided by the present invention decreases significantly, and decreases slowly in the later stage. maxa It decreases linearly until the phase is balanced.

[0127] Fig.12 This is a comparison chart of the SOC values ​​of the three battery modules in phase a. Fig.12 (a) is the SOC value of the three battery modules in phase a of the traditional SOC balancing control strategy. Fig.12 (b) is the SOC value of the three battery modules of phase a of the present invention. It can be seen that the SOC value of H2 is the largest and the downward trend is the most obvious. The traditional SOC balancing control strategy slows down with the balancing trend; the fast SOC balancing control method provided by the present invention greatly improves the balancing speed.

[0128] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A fast SOC balancing control method for a cascaded H-bridge converter energy storage grid-connected system, characterized in that: The following steps are involved: S1, inject zero-sequence voltage into the cascaded H-bridge converter energy storage grid-connected system, so that the amplitude of the modulation wave with the largest amplitude in the three-phase modulation wave corresponds to 1, and realize fast inter-phase SOC balancing control; If the maximum amplitude of the a-phase modulation wave after the zero-sequence voltage is injected is 1, the calculation formula of the amplitude U0 of the zero-sequence voltage is: Among them U a ' is the original amplitude of the a-phase modulation wave, A, B, and C are all intermediate coefficients, and: B=2U a ′cos(γ)cos(θ)-2U a ′sin(γ)sin(θ) Where γ represents the phase angle of the modulation wave leading the grid voltage; S2, outputting a superimposed fundamental voltage component to the AC side of each H-bridge unit in the cascaded H-bridge converter energy storage grid-connected system, so that the maximum amplitude of the modulation wave of each H-bridge unit is 1, and realizing fast intra-phase SOC balancing control; The superimposed fundamental voltage component output to the AC side of each H-bridge unit is: where v 1an 、v 1bn 、v 1cn They represent the superimposed fundamental voltage components output to the AC side of the nth H-bridge unit of phases a, b, and c, respectively. 1a , K 1b , K 1c Respectively represent the proportional coefficients of phases a, b, and c, ΔSOC an , ΔSOC bn , ΔSOC cn represents the unbalance degree of the nth H-bridge unit of phase a, b, and c respectively, ω represents the angular frequency of the zero-sequence voltage, t represents the time, and N represents the total number of H-bridge units in each phase; The proportional coefficient K of phases a, b, and c 1a , K 1b , K 1c The calculation formula is: Among them U o-maxa , U o-maxb , U o-maxc Respectively represent the amplitude of the fundamental voltage component superimposed on phases a, b, and c, ΔSOC maxa , ΔSOC maxb , ΔSOC maxc Represent the maximum imbalance of phases a, b, and c respectively; The amplitude U of the fundamental voltage component superimposed on phases a, b, and c o-maxa , U o-maxb , U o-maxc The calculation formula is: Among them U a , U b , U c It represents the amplitude of the three-phase modulation wave after injecting zero-sequence voltage.

2. The fast SOC balancing control method of the cascaded H-bridge converter energy storage grid-connected system according to claim 1 is characterized in that: The zero-sequence voltage injected in step S1 is expressed as: u0=U0cos(ωt-θ) Where u0 represents the zero-sequence voltage, U0, ω, θ represent the amplitude, angular frequency and phase angle of the zero-sequence voltage respectively, and t represents time.

3. The fast SOC balancing control method of the cascaded H-bridge converter energy storage grid-connected system according to claim 2 is characterized in that: If the maximum amplitude of the b-phase modulation wave after the zero-sequence voltage is injected is 1, the calculation formula of the amplitude U0 of the zero-sequence voltage is: Among them U b ′ is the original amplitude of the b-phase modulation wave, A, B, and C are all intermediate coefficients, and: Where γ represents the phase angle of the modulation wave leading the grid voltage.

4. The fast SOC balancing control method of the cascaded H-bridge converter energy storage grid-connected system according to claim 2, characterized in that: If the maximum amplitude of the c-phase modulation wave after the zero-sequence voltage is injected is 1, the calculation formula of the amplitude U0 of the zero-sequence voltage is: Among them U c ′ is the original amplitude of the c-phase modulation wave, A, B, and C are all intermediate coefficients, and: Where γ represents the phase angle of the modulation wave leading the grid voltage.

5. The fast SOC balancing control method of the cascaded H-bridge converter energy storage grid-connected system according to claim 2, characterized in that: The calculation formula of the zero-sequence voltage phase angle θ is: θ=arctan(ΔSOC α / ΔSOC β ) Where ΔSOC α , ΔSOC β They respectively represent the components of the three-phase SOC difference in the α and β coordinate systems after the PARK coordinate transformation.

6. The fast SOC balancing control method of the cascaded H-bridge converter energy storage grid-connected system according to claim 1, characterized in that: The unbalanced degree ΔSOC of the nth H-bridge unit of phases a, b, and c is an , ΔSOC bn , ΔSOC cn The calculation formula is: Among them, SOC an , SOC bn , SOC cn Respectively represent the SOC value of the nth H-bridge unit of phase a, b, and c, SOC a , SOC b , SOC c Represent the average SOC values ​​of phases a, b, and c respectively.

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