Cascaded energy storage system and inter-phase SOC equalization method thereof under condition of unbalanced power grid voltage

Abstract

The invention relates to the technical field of cascading energy storage systems, and discloses a cascading energy storage system and an inter-phase SOC balancing method under the condition of unbalanced power grid voltage thereof, and the cascading energy storage system comprises power supply and distribution equipment and three power conversion units. The power supply and distribution equipment is connected with the three power conversion units; each power conversion unit comprises an energy storage device, a cascade type energy storage converter and a power consumption unit; the power consumption unit comprises a switch and an active load; the power consumption unit is connected to the alternating current side of the cascaded energy storage converter; the control unit is used for calculating an unbalanced power given value output by the cascaded energy storage converter of each power conversion unit according to the charge state quantity, and controlling the duty ratio of a switch in the power consumption unit, so that the power consumed by the active load is equal to the unbalanced power given value; according to the invention, the target power is consumed by controlling the power consumption unit, so that the inter-phase equalization of the charge state quantity is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of cascaded energy storage systems, and particularly to a cascaded energy storage system and an inter-phase SOC balancing method under unbalanced grid voltage conditions. Background Art

[0002] A cascaded energy storage PCS (Power Conversion System, converter) is a power electronic device used in an energy storage system, mainly for realizing energy conversion and control between an energy storage battery and a power grid or other power systems. The cascaded energy storage PCS can be applied to a three-phase energy storage system that needs to handle high power and large capacity. The primary task of the cascaded energy storage PCS is power control. However, under unbalanced grid voltage conditions, there may be a problem of uneven power injected into the grid by the cascaded energy storage PCS, and it is necessary to control each phase of the PCS to inject equal power into the grid. At the same time, due to inconsistent device parameters, initial states, electrical losses, and aging effects of each phase, there may be a problem of inconsistent battery SOC (State of Charge) between phases in the three-phase energy storage system. When the inter-phase SOC imbalance is relatively serious, it is necessary to control the uneven power output of each phase of the PCS to make the SOC return to balance.

[0003] In related technologies, to solve the above two problems, by controlling the appropriate positive-sequence voltage and negative-sequence voltage output on the AC side of the cascaded energy storage PCS, the power injected into the grid by the cascaded energy storage PCS is balanced. At the same time, by controlling the appropriate zero-sequence voltage output on the AC side of the cascaded energy storage PCS, the power corresponding to the zero-sequence voltage is transmitted to the cascaded energy storage PCS of different phases to change the magnitude of the output power of each phase and achieve inter-phase balance of the SOC.

[0004] However, on the premise of controlling the balanced power injected into the grid by the cascaded energy storage PCS, controlling the appropriate zero-sequence voltage output by the cascaded energy storage PCS requires calculating the zero-sequence voltage value, resulting in a complex control process. The zero-sequence voltage output by the PCS will also cause the neutral point voltage of the cascaded energy storage PCS to shift, leading to systematic risks such as increased harmonic pollution, damage to the insulation system, and failure of the control strategy. Summary of the Invention

[0005] In view of this, the present invention provides a cascaded energy storage system and an inter-phase SOC balancing method under unbalanced grid voltage conditions to solve the problem of inter-phase SOC imbalance without inputting zero-sequence voltage.

[0006] In a first aspect, the present invention provides a cascaded energy storage system, comprising: a power supply and distribution device and three power conversion units; the power supply and distribution device is connected to the three power conversion units; the three power conversion units are respectively an A-phase power conversion unit, a B-phase power conversion unit, and a C-phase power conversion unit; the power supply and distribution device is configured to receive electric energy transmitted by the three power conversion units; wherein, each power conversion unit includes an energy storage device, a cascaded energy storage converter, and a power consumption unit; the power consumption unit includes a switch and an active load, two ends of the energy storage device are respectively connected to a first end point and a second end point of the DC side of the cascaded energy storage converter, and two ends of the power consumption unit are respectively connected to a third end point and a fourth end point of the AC side of the cascaded energy storage converter; the energy storage device is configured to supply power to the cascaded energy storage converter; the control unit is configured to calculate an unbalanced power set value output by the cascaded energy storage converter of each power conversion unit according to the state of charge quantities of the three power conversion units obtained, and control the duty cycle of the switch of the power consumption unit, so that the power consumed by the active load is equal to the unbalanced power set value output by the cascaded energy storage converter of each power conversion unit.

[0007] The cascaded energy storage system of the present invention includes a power supply and distribution device and three power conversion units. Each power conversion unit includes an energy storage device, a cascaded energy storage converter, and a power consumption unit. The power consumption unit includes a switch and an active load. Two ends of the energy storage device are respectively connected to a first end point and a second end point of the DC side of the cascaded energy storage converter, and two ends of the power consumption unit are respectively connected to a third end point and a fourth end point of the AC side of the cascaded energy storage converter. The control unit of the present invention is configured to calculate an unbalanced power set value output by the cascaded energy storage converter of each power conversion unit according to the state of charge quantities of the three power conversion units obtained, and control the duty cycle of the switch of the power consumption unit, so that the power consumed by the active load is equal to the unbalanced power set value output by the cascaded energy storage converter of each power conversion unit. By using the active load to consume the unbalanced power set value, the power distribution of each power conversion unit can be effectively adjusted, so that the state of charge is balanced among the three phases. Compared with the related art, the present invention directly consumes the unbalanced power set value by controlling the power consumption unit without injecting a zero-sequence voltage. The control process is simple, avoiding the problem of neutral point voltage offset caused by injecting the zero-sequence voltage, and improving the safety of the cascaded energy storage system.

[0008] In an optional embodiment, the power supply and distribution device includes a power grid and a circuit breaker; the power grid is connected to the circuit breaker; wherein, the power grid is configured to receive electric energy transmitted by the three power conversion units; the circuit breaker is configured to control the start and stop of the power grid receiving electric energy transmitted by the three power conversion units.

[0009] In an alternative embodiment, each power conversion unit further includes a reactance; one end of the reactance is connected to the power supply and distribution equipment, and the other end of the reactance is connected to the cascaded energy storage converter; wherein, the reactance is used to provide impedance for the power conversion unit.

[0010] Each power conversion unit of the present invention further includes a reactance. One end of the reactance is connected to the power supply and distribution equipment, and the other end of the reactance is connected to the cascaded energy storage converter. The reactance is used to provide impedance for the power conversion unit. The impedance can limit the magnitude of the current in the power conversion unit and prevent components such as energy storage devices and converters from being damaged due to excessive current. During normal operation, the impedance can keep the current in the power conversion unit relatively stable, improving the stability of the cascaded energy storage system.

[0011] In a second aspect, the present invention provides a method for balancing the inter-phase SOC of a cascaded energy storage system under voltage imbalance, which is applied to the control unit of the cascaded energy storage system according to the first aspect or any corresponding embodiment thereof. The method for balancing the inter-phase SOC of the cascaded energy storage system under voltage imbalance includes: calculating the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit according to the obtained state of charge quantities of the three power conversion units; controlling the duty cycle of the switch of the power consumption unit so that the power consumed by the active load is equal to the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit.

[0012] The present invention calculates the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit according to the obtained state of charge quantities of the three power conversion units, and controls the duty cycle of the switch of the power consumption unit so that the power consumed by the active load is equal to the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit. By using the active load to consume the unbalanced power given value, the power distribution of each power conversion unit can be effectively adjusted, making the state of charge balanced among the three phases. Compared with the related art, the present invention directly consumes the unbalanced power given value by controlling the power consumption unit without injecting zero-sequence voltage. The control process is simple, avoiding the problem of neutral point voltage offset caused by injecting zero-sequence voltage and improving the safety of the cascaded energy storage system.

[0013] In an alternative embodiment, calculating the unbalanced power setpoint output by the cascaded energy storage converter of each power conversion unit according to the obtained state of charge (SOC) values of three power conversion units includes: obtaining the SOC values of the three power conversion units, and selecting the minimum value of the SOC values of the three power conversion units as the target SOC value; determining the SOC deviation of each power conversion unit according to the difference between the SOC value of each power conversion unit and the target SOC value; selecting at least one target power conversion unit from the three power conversion units according to the SOC deviation; the target power conversion unit is the power conversion unit with a non-zero SOC deviation; multiplying the equalization speed adjustment coefficient by the SOC deviation of at least one target power conversion unit to obtain the unbalanced power setpoint of at least one target power conversion unit.

[0014] In an alternative embodiment, controlling the duty cycle of the switch in the power consumption unit so that the power consumed by the active load is equal to the unbalanced power setpoint output by the cascaded energy storage converter of each power conversion unit includes: substituting the unbalanced power setpoint into the voltage-power relationship formula to obtain the target voltage of at least one target power conversion unit; the voltage-power relationship formula is used to characterize the relationship between the voltage and power of the power consumption unit; obtaining the target duty cycle of at least one target power conversion unit according to the quotient of the target voltage and the instantaneous voltage, where the instantaneous voltage is the voltage on the AC side of the cascaded energy storage converter; adjusting the duty cycle of the switch of at least one target power conversion unit to the target duty cycle so that the power consumed by the active load is equal to the unbalanced power setpoint output by the cascaded energy storage converter of each power conversion unit.

[0015] Before calculating the unbalanced power setpoint output by the cascaded energy storage converter of each power conversion unit according to the obtained SOC values of three power conversion units, the method for inter-phase SOC equalization of the cascaded energy storage system under voltage imbalance further includes: obtaining the grid voltage on the DC side of the power supply and distribution equipment, and decomposing the grid voltage to obtain the grid negative-sequence voltage; injecting a target negative-sequence voltage with the same amplitude and phase as the grid negative-sequence voltage on the AC side of the cascaded energy storage converter to remove the grid negative-sequence current; the obtained SOC values of the three power conversion units are the SOC values after removing the grid negative-sequence current.

[0016] In the present invention, the grid negative-sequence voltage in the grid will cause voltage imbalance in the three-phase voltage injected into the grid, resulting in problems such as overheating, increased vibration, and reduced efficiency of electrical equipment. By decomposing to obtain the grid negative-sequence voltage and injecting a target negative-sequence voltage with the same amplitude and phase, the present invention can effectively cancel the grid negative-sequence current, improve the power quality, ensure the normal operation of electrical equipment, and extend the service life of electrical equipment.

[0017] In a third aspect, the present invention provides an electronic device, including: a memory and a processor, which are communicatively connected to each other. The memory stores computer instructions, and the processor executes the computer instructions to perform the method for inter-phase SOC balancing of a cascaded energy storage system under voltage imbalance according to the second aspect or any corresponding embodiment thereof.

[0018] In a fourth aspect, the present invention provides a computer-readable storage medium, on which computer instructions are stored, and the computer instructions are used to cause a computer to execute the method for inter-phase SOC balancing of a cascaded energy storage system under voltage imbalance according to the second aspect or any corresponding embodiment thereof.

[0019] In a fifth aspect, the present invention provides a computer program product, including computer instructions, and the computer instructions are used to cause a computer to execute the method for inter-phase SOC balancing of a cascaded energy storage system under voltage imbalance according to the second aspect or any corresponding embodiment thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the related art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the related art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0021] Figure 1 FIG. is a schematic structural diagram of a cascaded energy storage system according to an embodiment of the present invention.

[0022] Figure 2 FIG. is a schematic flow diagram of a method for inter-phase SOC balancing of a cascaded energy storage system under voltage imbalance according to an embodiment of the present invention.

[0023] Figure 3 FIG. is a schematic flow diagram of another method for inter-phase SOC balancing of a cascaded energy storage system under voltage imbalance according to an embodiment of the present invention.

[0024] Figure 4 FIG. is a schematic hardware structure diagram of an electronic device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0026] The cascaded energy storage PCS is applied to a cascaded energy storage system that needs to handle high power and large capacity. The primary task of the cascaded energy storage PCS is power control. In the cascaded energy storage system, due to factors such as unstable load, the problem of interphase imbalance may occur in the power grid. Due to inconsistent device parameters, initial states, electrical losses, and aging effects of each phase, the problem of uneven SOC among phases may occur. To ensure the safety of the cascaded energy storage system, it is necessary to make the three-phase power injected into the power grid the same and perform balanced control on the interphase SOC.

[0027] In the related art, by controlling the appropriate positive and negative sequence voltages output by the PCS on the AC side and injecting the appropriate positive and negative sequence voltages into the power grid, the three-phase power injected into the power grid is made the same. And according to the measured values of the SOC of each phase, the PCS is controlled to output an appropriate zero-sequence voltage, so that the zero-sequence voltage is exchanged among the PCSs of each phase, thereby realizing power exchange among the PCSs of each phase without affecting the power injected into the power grid by each phase, and achieving interphase balance of the SOC.

[0028] However, when controlling the PCS to output an appropriate zero-sequence voltage, it is necessary to generate a zero-sequence voltage expression based on the interphase unbalance degree and balance coefficient of each phase. Calculate the balance coefficient when the cascaded energy storage system reaches the balanced state according to the fixed modulation ratio and the interphase unbalance degree of each phase of the cascaded energy storage system, and fit to generate a functional relationship between the interphase unbalance degree and the balance coefficient of each phase. Furthermore, generate a zero-sequence voltage expression with a variable balance coefficient to obtain the zero-sequence voltage that the PCS needs to output. The calculation process is complex, resulting in a complex control process. Controlling the cascaded energy storage PCS to output an appropriate zero-sequence voltage will cause the neutral point voltage of the cascaded energy storage PCS to shift, leading to systematic risks such as increased harmonic pollution, damage to the insulation system, and failure of the control strategy.

[0029] The embodiments of the present invention provide a cascaded energy storage system, which consumes the target power by controlling the power consumption unit to achieve the effect of interphase balance of the SOC.

[0030] In this embodiment, a cascaded energy storage system is provided. Figure 1 It is a schematic structural diagram of the cascaded energy storage system according to the embodiment of the present invention, as Figure 1As shown in the figure, the system includes: a power supply and distribution device 11 and three power conversion units; the power supply and distribution device 11 is connected to the three power conversion units; the three power conversion units are respectively a phase-A power conversion unit 12, a phase-B power conversion unit 13, and a phase-C power conversion unit 14; the power supply and distribution device 11 is used to receive the electric energy delivered by the three power conversion units; among them, each power conversion unit (such as the phase-C power conversion unit 14) includes an energy storage device 141, a cascaded energy storage inverter 142, and a power consumption unit 143; the power consumption unit 143 includes a switch 1431 and an active load 1432, both ends of the energy storage device 141 are respectively connected to the first end point and the second end point of the DC side of the cascaded energy storage inverter 142, and both ends of the power consumption unit 143 are respectively connected to the third end point and the fourth end point of the AC side of the cascaded energy storage inverter 142; the energy storage device 141 is used to supply power to the cascaded energy storage inverter 142; a control unit 15 is used to calculate the unbalanced power given value output by the cascaded energy storage inverter 142 of each power conversion unit according to the obtained state of charge of the three power conversion units, and control the duty cycle of the switch 1431 in the power consumption unit 143, so that the power consumed by the active load 1432 is equal to the unbalanced power given value output by the cascaded energy storage inverter 142 of each power conversion unit.

[0031] Among them, in the switch 1431, E represents the emitter, B represents the base, and C represents the collector.

[0032] In some optional embodiments, the control unit 15 is used to control the cascaded energy storage inverter 142 to output a desired power to the power supply and distribution device 11.

[0033] In some optional embodiments, the active load 1432 refers to a load that is used to consume electric energy and convert the electric energy into other forms of useful energy (such as mechanical energy, thermal energy, light energy, etc.). In the embodiments of the present invention, the active load 1432 may be a resistor.

[0034] In some optional embodiments, the control unit 15 is respectively communicatively connected to the switch 1431 and the cascaded energy storage inverter 142 in each power conversion unit. The control unit 15 may be a control device such as a microcontroller unit (MCU) or a programmable logic controller (PLC). The control unit 15 controls the switch 1431 and the cascaded energy storage inverter 142 by sending instructions to the switch 1431 and the cascaded energy storage inverter 142.

[0035] In some alternative embodiments, the power supply and distribution device 11 includes a power grid 111 and a circuit breaker 112; the power grid 111 is connected to the circuit breaker 112; wherein, the power grid 111 is configured to receive electrical energy delivered by three power conversion units; the circuit breaker 112 is configured to control the start and stop of the power grid 111 receiving the electrical energy delivered by the three power conversion units.

[0036] Wherein, Figure 1 the power grid 111 in [description] includes three phases of three-phase electricity, namely phase A, phase B, and phase C. The circuit breaker 112 includes three phases (phase A, phase B, and phase C) corresponding to the three phases of the power grid 111, phase lines (phase a, phase b, and phase c) of another set of three-phase electricity corresponding to the three phases, and a common terminal (com). The three-phase electricity of the power supply and distribution device 11 is respectively connected to the phase A power conversion unit 12, the phase B power conversion unit 13, and the phase C power conversion unit 14.

[0037] In some alternative embodiments, each power conversion unit further includes a reactance 144; one end of the reactance 144 is connected to the power supply and distribution device 11, and the other end of the reactance 144 is connected to the cascaded energy storage converter 142; wherein, the reactance 144 is configured to provide impedance for the power conversion unit.

[0038] Each power conversion unit in the embodiment of the present invention further includes a reactance 144. The reactance 144 is configured to provide impedance for the power conversion unit. The impedance can limit the magnitude of the current in the power conversion unit and prevent components such as energy storage devices and converters from being damaged due to excessive current. During normal operation, the impedance can keep the current in the power conversion unit relatively stable, improving the stability of the cascaded energy storage system.

[0039] The cascaded energy storage system according to the embodiment of the present invention includes a power supply and distribution device 11 and three power conversion units. Each power conversion unit includes an energy storage device 141, a cascaded energy storage converter 142, and a power consumption unit 143. The power consumption unit 143 includes a switch 1431 and an active load 1432. The two ends of the energy storage device 141 are respectively connected to the first end point and the second end point of the DC side of the cascaded energy storage converter 142, and the two ends of the power consumption unit 143 are respectively connected to the third end point and the fourth end point of the AC side of the cascaded energy storage converter 142. The control unit 15 of the present invention is configured to calculate the unbalanced power given value output by the cascaded energy storage converter 142 of each power conversion unit according to the obtained state of charge of the three power conversion units, and control the duty ratio of the switch 1431 of the power consumption unit 143, so that the power consumed by the active load 1432 is equal to the unbalanced power given value output by the cascaded energy storage converter 142 of each power conversion unit. By using the active load 1432 to consume the unbalanced power given value, the power distribution of each power conversion unit can be effectively adjusted, so that the state of charge is balanced among the three phases. Compared with the related art, the embodiment of the present invention directly consumes the unbalanced power given value by controlling the power consumption unit 143, without injecting a zero-sequence voltage. The control process is simple, avoiding the problem of neutral point voltage offset caused by injecting a zero-sequence voltage, and improving the safety of the cascaded energy storage system.

[0040] In this embodiment, a method for balancing the phase SOC of a cascaded energy storage system under voltage imbalance is provided, which can be used for the control unit of the above cascaded energy storage system. Figure 2 It is a flowchart of another method for balancing the phase SOC of a cascaded energy storage system under voltage imbalance according to the embodiment of the present invention, as Figure 2 shown. The process includes the following steps:

[0041] Step S201, calculate the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit according to the obtained state of charge of the three power conversion units.

[0042] Among them, the cascaded energy storage converter is a power conversion device used in a cascaded energy storage system. During the charging process, the cascaded energy storage converter converts the alternating current of the power grid or other power sources into direct current suitable for the energy storage device to realize the storage of electric energy. During the discharging process, the cascaded energy storage converter converts the direct current of the energy storage device into alternating current and transmits it to the power grid or load to provide power for the electrical equipment. The cascaded energy storage converter adopts control algorithms such as pulse width modulation algorithm and space vector modulation algorithm to accurately control the switching actions of the power sub-modules to achieve accurate regulation of the output voltage, current and power. In the embodiment of the present invention, the cascaded energy storage converter is controlled to output a target power equal to the unbalanced power given value to the power consumption unit.

[0043] In some alternative embodiments, when the power grid is supplying power under normal conditions, the cascaded energy storage converter is controlled to output the power required by the power grid.

[0044] In some alternative embodiments, the unbalanced power setpoint output by the cascaded energy storage converter for each power conversion unit is calculated based on the obtained state-of-charge values of the three power conversion units, including: obtaining the state-of-charge values of the three power conversion units, and selecting the minimum value of the state-of-charge values of the three power conversion units as the target state-of-charge value; determining the state-of-charge deviation of each power conversion unit according to the difference between the state-of-charge value of each power conversion unit and the target state-of-charge value; selecting at least one target power conversion unit from the three power conversion units according to the state-of-charge deviation; the target power conversion unit is the power conversion unit with a non-zero state-of-charge deviation; multiplying the balance speed adjustment coefficient by the state-of-charge deviation of at least one target power conversion unit to obtain the unbalanced power setpoint of at least one target power conversion unit.

[0045] Wherein, the state-of-charge value refers to the ratio of the remaining power to the rated capacity in the cascaded energy storage system. In the embodiments of the present invention, the charging and discharging current is calculated by measuring the current during the charging and discharging process of each power conversion unit and integrating over time, and the ratio is obtained according to the quotient of the charging and discharging current and the rated capacity of each power conversion unit. The state-of-charge values of the three power conversion units are obtained according to the difference between the initial state-of-charge value and the ratio. Exemplarily, the state-of-charge value of each power conversion unit can be represented as SOC i , where i = 1, 2, 3, respectively representing the state-of-charge values of the A-phase power conversion unit, B-phase power conversion unit, and C-phase power conversion unit.

[0046] In some alternative embodiments, the target state-of-charge value is the minimum value of the state-of-charge values of the three-phase power conversion units. Exemplarily, the target state-of-charge value can be represented as min{SOC i}.

[0047] In some alternative embodiments, the calculation formula for the state-of-charge deviation of each power conversion unit is:

[0048] ΔSOC i = SOC i - min{SOC i}

[0049] Wherein, ΔSOC i represents the state-of-charge deviation of the i-th phase power conversion unit, SOC i represents the state-of-charge value of the i-th phase power conversion unit, min{SOC i} represents the target state of charge.

[0050] In some alternative embodiments, the balancing speed adjustment coefficient is used to adjust the SOC balancing speed. The larger its value, the faster the SOC balancing speed, and an appropriate balancing speed adjustment coefficient can be selected according to engineering requirements.

[0051] In some alternative embodiments, the calculation formula for the unbalanced power given value is:

[0052] ΔP i =λΔSOC i

[0053] where, ΔP i is the unbalanced power given value of the i-th phase power conversion unit, λ is the balancing speed adjustment coefficient, and ΔSOC i is the state of charge deviation of the i-th phase power conversion unit.

[0054] Step S202, control the duty cycle of the switch of the power consumption unit so that the power consumed by the active load is equal to the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit.

[0055] In some alternative embodiments, controlling the duty cycle of the switch of the power consumption unit so that the power consumed by the active load is equal to the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit includes: substituting the unbalanced power given value into the voltage-power relationship formula to obtain the target voltage of at least one target power conversion unit; the voltage-power relationship formula is used to characterize the relationship between the voltage and power of the power consumption unit; obtaining the target duty cycle of at least one target power conversion unit according to the quotient of the target voltage and the instantaneous voltage, and the instantaneous voltage is the voltage on the AC side of the cascaded energy storage converter; adjusting the duty cycle of the switch of at least one target power conversion unit to the target duty cycle so that the power consumed by the active load is equal to the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit.

[0056] where, the voltage-power relationship formula is used to characterize the relationship between the voltage and power of the power consumption unit. Exemplarily, the voltage-power relationship formula can be expressed as u = f(P). Substituting the unbalanced power given value ΔP i into the voltage-power relationship formula, the target voltage u ref =f(ΔP i ).

[0057] In some alternative embodiments, the formula for the target duty cycle of the target power conversion unit is:

[0058] m=u ref / u0

[0059] where m is the target duty cycle, u ref is the target voltage, and u0 is the instantaneous voltage.

[0060] In some alternative embodiments, adjusting the duty cycle of the switch of at least one target power conversion unit to the target duty cycle includes: converting the target duty cycle into a digital signal, generating a pulse width modulation signal according to the digital signal; driving the switch by amplifying and processing the pulse width modulation signal through a driving circuit.

[0061] In the embodiment of the present invention, the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit is calculated according to the obtained state of charge quantities of the three power conversion units, and the duty cycle of the switch of the power consumption unit is controlled so that the power consumed by the active load is equal to the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit. By using the active load to consume the unbalanced power given value, the power distribution of each power conversion unit can be effectively adjusted, so that the state of charge is balanced among the three phases. Compared with the related art, the present invention directly consumes the unbalanced power given value by controlling the power consumption unit, without injecting a zero-sequence voltage. The control process is simple, avoiding the problem of neutral point voltage deviation caused by injecting the zero-sequence voltage, and improving the safety of the cascaded energy storage system.

[0062] In this embodiment, a method for balancing the inter-phase SOC of a cascaded energy storage system under voltage imbalance is provided, which can be used for the control unit of the above-mentioned cascaded energy storage system. Figure 3 is a flowchart of another method for balancing the inter-phase SOC of a cascaded energy storage system under voltage imbalance according to the embodiment of the present invention, as Figure 3 shown. The process includes the following steps:

[0063] Step S301, obtaining the grid voltage on the DC side of the power supply and distribution equipment, and decomposing the grid voltage to obtain the grid negative-sequence voltage.

[0064] Among them, the grid voltage is decomposed by using the symmetrical component method to obtain the grid negative-sequence voltage. The symmetrical component method is a method of decomposing a set of unbalanced three-phase voltages into three sets of symmetrical components, namely the positive-sequence component, the negative-sequence component, and the zero-sequence component. The negative-sequence component is obtained to obtain the grid negative-sequence voltage.

[0065] Step S302, injecting a target negative-sequence voltage with the same amplitude and phase as the grid negative-sequence voltage on the AC side of the cascaded energy storage converter to remove the grid negative-sequence current; the obtained state of charge quantities of the three power conversion units are the state of charge quantities after removing the grid negative-sequence current.

[0066] Step S303: Calculate the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit according to the state of charge of the three obtained power conversion units. For details, please refer to Figure 2 Step S201 of the embodiment shown, which will not be elaborated here.

[0067] Step S304: Control the duty cycle of the switch of the power consumption unit so that the power consumed by the active load is equal to the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit. For details, please refer to Figure 2 Step S203 of the embodiment shown, which will not be elaborated here.

[0068] In the embodiment of the present invention, the negative sequence voltage in the power grid will cause the voltage imbalance of the three-phase injection into the power grid, resulting in problems such as overheating, increased vibration, and reduced efficiency of electrical equipment. By decomposing and obtaining the negative sequence voltage of the power grid and injecting the target negative sequence voltage with the same amplitude and phase, the present invention can effectively cancel the negative sequence current of the power grid, improve the power quality, ensure the normal operation of electrical equipment, and extend the service life of electrical equipment.

[0069] The embodiment of the present invention also provides an electronic device for executing the above Figure 2 Inter-phase SOC balancing method of cascaded energy storage system under voltage imbalance shown.

[0070] Please refer to Figure 4 , Figure 4 is a schematic structural diagram of an electronic device provided by an optional embodiment of the present invention. As shown in Figure 4 , the electronic device includes: one or more processors 10, a memory 20, and interfaces for connecting various components, including a high-speed interface and a low-speed interface. Each component communicates with each other using different buses and can be installed on a common main board or installed in other ways as needed. The processor can process instructions executed within the electronic device, including instructions stored in the memory or on the memory to display graphical information of the GUI on an external input / output device (such as a display device coupled to the interface). In some optional embodiments, if necessary, multiple processors and / or multiple buses can be used together with multiple memories and multiple memories. Similarly, multiple electronic devices can be connected, and each device provides some necessary operations (such as an array of servers, a set of blade servers, or a multi-processor system). Figure 4 One processor 10 is taken as an example in

[0071] The processor 10 may be a central processing unit, a network processor, or a combination thereof. Among them, the processor 10 may further include a hardware chip. The above-mentioned hardware chip may be an application-specific integrated circuit, a programmable logic device, or a combination thereof. The above-mentioned programmable logic device may be a complex programmable logic device, a field-programmable gate array, a generic array logic, or any combination thereof.

[0072] Among them, the memory 20 stores instructions executable by at least one processor 10, so that the at least one processor 10 executes the method shown in the above embodiments.

[0073] The memory 20 may include a program storage area and a data storage area. Among them, the program storage area may store an operating system and application programs required for at least one function; the data storage area may store data created according to the use of the electronic device, etc. In addition, the memory 20 may include a high-speed random access memory, and may further include a non-transitory memory, such as at least one magnetic disk storage device, a flash memory device, or other non-transitory solid-state storage devices. In some alternative embodiments, the memory 20 may optionally include a memory remotely provided with respect to the processor 10, and these remote memories may be connected to the electronic device through a network. Examples of the above-mentioned network include but are not limited to the Internet, an enterprise intranet, a local area network, a mobile communication network, and combinations thereof.

[0074] The memory 20 may include a volatile memory, such as a random access memory; the memory may also include a non-volatile memory, such as a flash memory, a hard disk, or a solid-state drive; the memory 20 may further include a combination of the above types of memories.

[0075] The electronic device further includes a communication interface 30 for the electronic device to communicate with other devices or communication networks.

[0076] The embodiment of the present invention also provides a computer-readable storage medium. The method according to the embodiment of the present invention may be implemented in hardware, firmware, or may be implemented as computer code recorded on a storage medium, or may be implemented as computer code originally stored in a remote storage medium or a non-temporary machine-readable storage medium and downloaded through a network and to be stored in a local storage medium, so that the method described herein may be stored in such software processing on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. Among them, the storage medium may be a magnetic disk, an optical disc, a read-only memory, a random access memory, a flash memory, a hard disk, or a solid-state drive, etc.; further, the storage medium may further include a combination of the above types of memories. It can be understood that a computer, a processor, a microprocessor controller, or programmable hardware includes a storage component that can store or receive software or computer code, and when the software or computer code is accessed and executed by the computer, the processor, or the hardware, the method shown in the above embodiments is implemented.

[0077] A part of the present invention can be applied as a computer program product, such as computer program instructions. When executed by a computer, through the operation of the computer, the methods and / or technical solutions according to the present invention can be invoked or provided. Those skilled in the art should understand that the forms of existence of computer program instructions in a computer-readable medium include, but are not limited to, source files, executable files, installation package files, etc. Correspondingly, the ways for a computer to execute computer program instructions include, but are not limited to: the computer directly executes the instruction, or the computer compiles the instruction and then executes the corresponding compiled program, or the computer reads and executes the instruction, or the computer reads and installs the instruction and then executes the corresponding installed program. Herein, the computer-readable medium can be any available computer-readable storage medium or communication medium accessible by the computer.

[0078] Although the embodiments of the present invention are described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A cascaded energy storage system, characterized in that, The system includes: a power supply and distribution device and three power conversion units; the power supply and distribution device is connected to the three power conversion units; the three power conversion units are respectively an A-phase power conversion unit, a B-phase power conversion unit, and a C-phase power conversion unit; the power supply and distribution device is used to receive the electric energy transmitted by the three power conversion units; Wherein, each of the power conversion units includes an energy storage device, a cascaded energy storage converter, and a power consumption unit; the power consumption unit includes a switch and an active load, two ends of the energy storage device are respectively connected to a first end point and a second end point of the DC side of the cascaded energy storage converter, and two ends of the power consumption unit are respectively connected to a third end point and a fourth end point of the AC side of the cascaded energy storage converter; The energy storage device is used to supply power to the cascaded energy storage converter; The control unit is used to calculate the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit according to the state of charge of the three power conversion units obtained, and control the duty cycle of the switch in the power consumption unit so that the power consumed by the active load is equal to the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit.

2. The system according to claim 1, wherein The power supply and distribution device includes a power grid and a circuit breaker; the power grid is connected to the circuit breaker; Wherein, the power grid is used to receive the electric energy transmitted by the three power conversion units; The circuit breaker is used to control the start and stop of the power grid receiving the electric energy transmitted by the three power conversion units.

3. The system according to claim 1 or 2, characterized in that, Each of the power conversion units further includes a reactance; one end of the reactance is connected to the power supply and distribution device, and the other end of the reactance is connected to the cascaded energy storage converter; Wherein, the reactance is used to provide impedance for the power conversion unit.

4. A method for inter-phase SOC balancing of a cascaded energy storage system under voltage imbalance, characterized in that, A control unit applied to the cascaded energy storage system according to any one of claims 1 to 3, the method includes: Calculating the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit according to the state of charge of the three power conversion units obtained; Controlling the duty cycle of the switch in the power consumption unit so that the power consumed by the active load is equal to the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit.

5. The method according to claim 4, wherein The calculating the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit according to the state of charge of the three power conversion units obtained includes: Obtaining the state of charge of the three power conversion units, and selecting the minimum value of the state of charge of the three power conversion units as the target state of charge; Determining the state of charge deviation of each power conversion unit according to the difference between the state of charge of each power conversion unit and the target state of charge; Selecting at least one target power conversion unit from the three power conversion units according to the state of charge deviation; the target power conversion unit is the power conversion unit with the state of charge deviation not equal to 0; Multiply the balance speed adjustment coefficient by the state of charge deviation of at least one of the target power conversion units to obtain the unbalanced power given value of at least one of the target power conversion units.

6. The method according to claim 5, wherein Controlling the duty cycle of the switch in the control power consumption unit so that the power consumed by the active load is equal to the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit includes: Substitute the unbalanced power given value into the voltage-power relationship formula to obtain the target voltage of at least one of the target power conversion units; the voltage-power relationship formula is used to characterize the relationship between the voltage and power of the power consumption unit; Obtain the target duty cycle of at least one of the target power conversion units according to the quotient of the target voltage and the instantaneous voltage, where the instantaneous voltage is the voltage on the AC side of the cascaded energy storage converter; Adjust the duty cycle of the switch of at least one of the target power conversion units to the target duty cycle so that the power consumed by the active load is equal to the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit.

7. The method according to claim 5, characterized in that, Before calculating the unbalanced power given value output by the cascaded energy storage converter of each power conversion unit according to the state of charge quantities of the three power conversion units obtained, the method further includes: Obtain the grid voltage on the DC side of the power supply and distribution equipment, and decompose the grid voltage to obtain the grid negative-sequence voltage; Inject a target negative-sequence voltage with the same amplitude and phase as the grid negative-sequence voltage on the AC side of the cascaded energy storage converter to remove the grid negative-sequence current; the state of charge quantities of the three obtained power conversion units are the state of charge quantities after removing the grid negative-sequence current.

8. An electronic device, characterized in that, Includes: A memory and a processor, the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the computer instructions to execute the method for inter-phase SOC balance of the cascaded energy storage system under voltage imbalance according to any one of claims 4 to 7.

9. A computer-readable storage medium, characterized in that Computer instructions are stored on the computer-readable storage medium, and the computer instructions are used to cause a computer to execute the method for inter-phase SOC balance of the cascaded energy storage system under voltage imbalance according to any one of claims 4 to 7.

10. A computer program product, characterized in that, Includes computer instructions, and the computer instructions are used to cause a computer to execute the method for inter-phase SOC balance of the cascaded energy storage system under voltage imbalance according to any one of claims 4 to 7.

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