Energy storage system and control method thereof

Abstract

The application provides an energy storage system and a control method thereof. The control method comprises: obtaining an expected AC side voltage of each single-phase bridge arm and a preset voltage value of each energy storage unit on each single-phase bridge arm, the expected AC side voltage being used to indicate an expected voltage of an AC side of the single-phase bridge arm in an AC cycle, and the preset voltage value being used to indicate an AC side voltage value of all connected energy storage units on the single-phase bridge arm where the energy storage unit is located when the energy storage unit is connected to the energy storage system; for each energy storage unit, determining an adjustment strategy for adjusting an AC side voltage state of the energy storage unit in an AC cycle according to a comparison result of the expected AC side voltage corresponding to the energy storage unit and the preset voltage value; and for each energy storage unit, executing the adjustment strategy corresponding to the energy storage unit in the AC cycle, so that the AC side voltage of the single-phase bridge arm where the energy storage unit is located conforms to the expected AC side voltage.

Description

Technical Field

[0001] This application relates to the field of energy storage system technology, and in particular to an energy storage system and its control method. Background Technology

[0002] In three-phase cascaded energy storage systems, phase-shifted carrier control is typically used to output three-phase AC power. The energy storage system analyzes the AC power from the grid and determines the sinusoidal target voltage for each single-phase bridge arm based on the connection method between the three-phase bridge arms. Each single-phase bridge arm includes multiple energy storage units and an inverter composed of bridge circuits connecting each energy storage unit. Each bridge circuit uses a phase-shifted carrier modulation method, modulating multiple triangular carriers with the same frequency and amplitude but different phases. This results in the voltage pulses provided by each energy storage unit through the bridge circuit being staggered by a certain angle. After the voltage pulses corresponding to multiple energy storage units are superimposed, the inverter ultimately outputs a stepped voltage waveform that approximates a sine wave. Consequently, each energy storage unit frequently switches the inverter's control switch based on the triangular carrier control signal, increasing switching losses and thus increasing costs.

[0003] Therefore, to reduce switching losses, the nearest level approximation is chosen to control the sinusoidal voltage output of a single-phase bridge arm. However, since it's impossible to send the voltage value at every time point of the sinusoidal target voltage corresponding to each single-phase bridge arm to the battery side, only the amplitude and frequency of the sinusoidal target voltage can be sent to the battery side. The battery side then generates its own sinusoidal analytical voltage based on the amplitude and frequency. This results in the sinusoidal target voltage needing to be decomposed into amplitude and frequency before being reconstructed into a sinusoidal analytical voltage, impacting system control efficiency.

[0004] Furthermore, the battery side needs to compare the voltage of the energy storage unit on the bridge arm with the voltage and value of the sinusoidal analytical voltage as it changes over time. Only after determining that a new energy storage unit needs to be connected will a control signal be sent to the bridge circuit of the energy storage unit. The comparison process and signal transmission will cause an error between the actual AC side voltage of the single-phase bridge arm and the sinusoidal analytical voltage, affecting the AC side voltage quality. Summary of the Invention

[0005] In view of this, the purpose of this application is to provide at least one energy storage system and its control method. By pre-acquiring the desired AC side voltage of each single-phase bridge arm and the preset voltage value corresponding to each energy storage unit when connected to the system, the preset voltage value reflects the AC side voltage and value of all connected energy storage units on the single-phase bridge arm. By comparing the desired AC side voltage and the preset voltage value corresponding to each energy storage unit, the adjustment method for the AC side voltage state of each energy storage unit in one AC cycle is determined. The control of the AC side voltage state of each energy storage unit in the AC cycle is realized according to the adjustment method. This solves the technical problem of repetitive operation of parsing and recombining the desired AC side voltage in the prior art, and achieves the technical effect of improving control efficiency and increasing the power quality of the energy storage system.

[0006] This application mainly includes the following aspects:

[0007] In a first aspect, embodiments of this application provide a control method for an energy storage system. The energy storage system includes three-phase bridge arms, and each single-phase bridge arm includes multiple energy storage units connected in series. The control method includes: acquiring the desired AC-side voltage of each single-phase bridge arm and a preset voltage value for each energy storage unit on each single-phase bridge arm. The desired AC-side voltage is used to indicate the desired voltage of the AC side of the single-phase bridge arm in one AC cycle, and the preset voltage value is used to indicate the sum of the AC-side voltages of all connected energy storage units on the single-phase bridge arm where an energy storage unit is connected to the energy storage system; for each energy storage unit, determining an adjustment strategy for adjusting the AC-side voltage state of the energy storage unit within one AC cycle based on a comparison result between the desired AC-side voltage and the preset voltage value corresponding to the energy storage unit; and for each energy storage unit, executing the adjustment strategy corresponding to the energy storage unit within the AC cycle to make the AC-side voltage of the single-phase bridge arm where the energy storage unit is located conform to the desired AC-side voltage.

[0008] Optionally, the preset voltage value of each energy storage unit on each single-phase bridge arm is obtained by: determining the AC side voltage and value of each energy storage unit and its preceding energy storage unit in each single-phase bridge arm according to the target sorting order of the multiple energy storage units corresponding to each single-phase bridge arm, and using the AC side voltage and value as the preset voltage value.

[0009] Optionally, the target sorting order includes: the default order of multiple series-connected energy storage units, or the state order obtained by sorting multiple series-connected energy storage units according to their state of charge based on the direction of power transmission of the energy storage system.

[0010] Optionally, the AC side voltage state includes an access state and a bypass state. For each energy storage unit in a single-phase bridge arm, the adjustment strategy includes: determining the AC side voltage state of the energy storage unit as an access state when the absolute value of the desired AC side voltage corresponding to the energy storage unit in one AC cycle is greater than the absolute value of the preset voltage value; and determining the AC side voltage state of the energy storage unit as a bypass state when the absolute value of the desired AC side voltage corresponding to the energy storage unit in one AC cycle is not greater than the absolute value of the preset voltage value.

[0011] Optionally, an AC cycle includes a positive half-cycle and a negative half-cycle, and the access state includes a positive access state and a negative access state. The adjustment strategy includes: during the positive half-cycle, when the absolute value of the desired AC side voltage corresponding to the energy storage unit is greater than the absolute value of the preset voltage value, determining the AC side voltage state of the energy storage unit as the positive access state; and when the absolute value of the desired AC side voltage corresponding to the energy storage unit is not greater than the absolute value of the preset voltage value, determining the AC side voltage state of the energy storage unit as the bypass state. During the negative half-cycle, when the absolute value of the desired AC side voltage corresponding to the energy storage unit is greater than the absolute value of the preset voltage value, determining the AC side voltage state of the energy storage unit as the negative access state; and when the absolute value of the desired AC side voltage corresponding to the energy storage unit is not greater than the absolute value of the preset voltage value, determining the AC side voltage state of the energy storage unit as the bypass state.

[0012] Optionally, the AC side voltage state includes an access state and a bypass state. An AC cycle includes a positive half-cycle and a negative half-cycle distinguished by the midpoint of the AC side cycle. The access state includes a positive access state corresponding to the positive half-cycle and a negative access state corresponding to the negative half-cycle. For each energy storage unit of a single-phase bridge arm, the adjustment strategy includes: within the target half-cycle, when the absolute value of the desired AC side voltage corresponding to the energy storage unit is greater than the absolute value of the preset voltage value, determining the AC side voltage state of the energy storage unit as the access state corresponding to the target half-cycle; when the absolute value of the desired AC side voltage corresponding to the energy storage unit is not greater than the absolute value of the preset voltage value, the AC side voltage state of the energy storage unit is determined to be the access state corresponding to the target half-cycle. When the absolute value of the preset voltage value is determined, the AC side voltage state of the energy storage unit is determined to be the bypass state, and the target half-cycle is one of the positive half-cycle and the negative half-cycle; within the preset half-cycle, the time period during which the AC side voltage state of the energy storage unit is determined to be the access state corresponding to the preset half-cycle is symmetrical to the time period during which the access state corresponding to the target half-cycle is determined to be the bypass state, and the time period during which the AC side voltage state of the energy storage unit is determined to be the bypass state is symmetrical to the time period during which the bypass state corresponding to the target half-cycle is determined to be the other of the positive half-cycle and the negative half-cycle.

[0013] Optionally, the adjustment strategy is executed during the AC cycle in the following manner: at the beginning of the positive access state during the positive half-cycle, the AC side voltage state of the energy storage unit is adjusted to the positive access state; at the end of the positive access state during the positive half-cycle, the AC side voltage state of the energy storage unit is adjusted to the bypass state; at the beginning of the negative access state during the negative half-cycle, the AC side voltage state of the energy storage unit is adjusted to the negative access state; at the end of the negative access state during the negative half-cycle, the AC side voltage state of the energy storage unit is adjusted to the bypass state.

[0014] Secondly, embodiments of this application provide an energy storage system, the energy storage system including a three-phase bridge arm and a control unit, each single-phase bridge arm including multiple energy storage units connected in series, the control unit being connected to the multiple energy storage units corresponding to each single-phase bridge arm respectively, wherein the control unit is configured to: acquire the desired AC side voltage of each single-phase bridge arm and a preset voltage value of each energy storage unit on each single-phase bridge arm, the desired AC side voltage being used to indicate the desired voltage of the AC side of the single-phase bridge arm in one AC cycle, the preset voltage value being used to indicate the sum of the AC side voltages of all connected energy storage units on the single-phase bridge arm where an energy storage unit is connected to the energy storage system; for each energy storage unit, based on the comparison result between the desired AC side voltage and the preset voltage value corresponding to the energy storage unit, determine an adjustment strategy for adjusting the AC side voltage state of the energy storage unit within one AC cycle; for each energy storage unit, execute the adjustment strategy corresponding to the energy storage unit within the AC cycle so that the AC side voltage of the single-phase bridge arm where the energy storage unit is located conforms to the desired AC side voltage.

[0015] Optionally, each energy storage unit includes at least one battery cell and a bridge circuit. The at least one battery cell is connected to one end of the bridge circuit, and the other end of the bridge circuit serves as the AC side of the energy storage unit. The bridge circuit is used to regulate the AC side voltage state. The control unit is connected to the control terminal of the bridge circuit corresponding to each energy storage unit to regulate the AC side voltage state by sending a control signal to the control terminal of the bridge circuit.

[0016] Optionally, the bridge circuit includes a first control switch, a second control switch, a third control switch, and a fourth control switch. One end of the first control switch is connected to one end of the second control switch, and the other end of the first control switch is connected to one end of the third control switch. The other end of the second control switch is connected to one end of the fourth control switch, and the other end of the third control switch is connected to the other end of the fourth control switch. The connection points between the first and second control switches and between the third and fourth control switches serve as one end of the bridge circuit for connecting at least one battery cell. The connection points between the first and third control switches and between the second and fourth control switches serve as the other end of the bridge circuit. The control terminals of the first, second, third, and fourth control switches serve as the control terminals of the bridge circuit for receiving control signals from the control unit for adjusting the AC side voltage state.

[0017] This application provides an energy storage system and its control method. The energy storage system includes a three-phase bridge arm, and each single-phase bridge arm includes multiple energy storage units connected in series. The control method includes: acquiring the desired AC side voltage of each single-phase bridge arm and a preset voltage value for each energy storage unit on each single-phase bridge arm. The desired AC side voltage is used to indicate the desired AC side voltage of the single-phase bridge arm in one AC cycle, and the preset voltage value is used to indicate the sum of the AC side voltages of all connected energy storage units on the single-phase bridge arm where an energy storage unit is connected to the energy storage system; for each energy storage unit, determining an adjustment strategy for adjusting the AC side voltage state of the energy storage unit within one AC cycle based on the comparison result between the desired AC side voltage and the preset voltage value corresponding to the energy storage unit; and for each energy storage unit, executing the adjustment strategy corresponding to the energy storage unit within the AC cycle to make the AC side voltage of the single-phase bridge arm where the energy storage unit is located conform to the desired AC side voltage. By pre-acquiring the desired AC side voltage of each single-phase bridge arm and the preset voltage value corresponding to each energy storage unit when connected to the system, the preset voltage value reflects the AC side voltage and value of all connected energy storage units on the single-phase bridge arm. Therefore, by comparing the desired AC side voltage and the preset voltage value corresponding to each energy storage unit, the adjustment method for the AC side voltage state of each energy storage unit within one AC cycle is determined. The AC side voltage state of each energy storage unit is controlled according to the adjustment method within the AC cycle. This solves the technical problem of repetitive operation of parsing and recombining the desired AC side voltage in the prior art, and achieves the technical effect of improving control efficiency and increasing the power quality of the energy storage system.

[0018] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic diagram of an energy storage system provided in an embodiment of this application is shown.

[0021] Figure 2 A schematic diagram of another energy storage system provided in an embodiment of this application is shown.

[0022] Figure 3 A flowchart of a control method for an energy storage system provided in an embodiment of this application is shown.

[0023] Figure 4 This diagram illustrates the desired AC side voltage of a single-phase bridge arm provided in an embodiment of this application over one AC cycle. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the drawings in this application are for illustrative and descriptive purposes only and are not intended to limit the scope of protection of this application. Furthermore, it should be understood that the schematic drawings are not drawn to scale. The flowcharts used in this application illustrate operations implemented according to some embodiments of this application. It should be understood that the operations in the flowcharts may not be implemented in sequence, and steps without logical contextual relationships may be reversed or implemented simultaneously. In addition, those skilled in the art, guided by the content of this application, may add one or more other operations to the flowcharts, or remove one or more operations from the flowcharts.

[0025] Furthermore, the described embodiments are merely some, not all, of the embodiments of this application. The components of the embodiments of this application described and illustrated herein can typically be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0026] In existing technologies, each single-phase bridge arm of a three-phase energy storage system includes multiple cascaded energy storage units. The inverter of the energy storage system needs to frequently switch on and off using triangular carrier waves to achieve a sinusoidal voltage output on the AC side, which increases switching losses and thus increases costs. Furthermore, replacing the phase-shifted carrier modulation method with a nearest-level approximation method requires resolving the sinusoidal voltage of each single-phase bridge arm by referencing the grid voltage to the connection method of the three-phase bridge arms. The amplitude and frequency of the sinusoidal voltage are then sent to the battery side so that the battery side can reconstruct the sinusoidal voltage based on the amplitude and frequency. This requires resolving and reconstructing the same data, affecting the system's control efficiency. The battery side compares the target sinusoidal voltage with the voltage and value of each energy storage unit based on the time-varying reconstructed sinusoidal voltage. Each time a new energy storage unit needs to be connected, a control signal is sent to the bridge circuit corresponding to that unit. This results in a time lag between the comparison result, the actual issuance of the control signal, and the switching action of the bridge circuit, leading to poor voltage quality in the final output.

[0027] Based on this, this application provides an energy storage system and its control method. By pre-acquiring the desired AC side voltage of each single-phase bridge arm and the preset voltage value corresponding to each energy storage unit when connected to the system, the preset voltage value reflects the sum of the AC side voltages of all connected energy storage units on the single-phase bridge arm. Therefore, by comparing the desired AC side voltage with the preset voltage value corresponding to each energy storage unit, the adjustment method for the AC side voltage state of each energy storage unit within one AC cycle is determined. Control of the AC side voltage state of each energy storage unit within the AC cycle is achieved according to the adjustment method. This solves the technical problem of repetitive operations in the analysis and recombination of the desired AC side voltage in the prior art, achieving the technical effect of improving control efficiency and increasing the power quality of the energy storage system, as detailed below:

[0028] Please see Figure 1 , Figure 1 This is a schematic diagram of an energy storage system provided in an embodiment of this application. Figure 1As shown, the energy storage system provided in this application embodiment includes a three-phase bridge arm and a control unit U1. Each single-phase bridge arm includes multiple energy storage units connected in series. The control unit is connected to the multiple energy storage units corresponding to each single-phase bridge arm.

[0029] like Figure 1 As shown, each energy storage unit of phase A bridge arm is connected to the control unit, each energy storage unit of phase B bridge arm is connected to the control unit, and each energy storage unit of phase C bridge arm is connected to the control unit.

[0030] Please see Figure 2 , Figure 2 This is a schematic diagram of another energy storage system provided in an embodiment of this application. Figure 2 As shown, each energy storage unit 101 includes at least one battery cell BAT and a bridge circuit 1011. The at least one battery cell is connected to one end of the bridge circuit, and the other end of the bridge circuit serves as the AC side of the energy storage unit. The bridge circuit is used to regulate the AC side voltage state. The control unit U1 is connected to the control terminal of the bridge circuit corresponding to each energy storage unit to regulate the AC side voltage state by sending a control signal to the control terminal of the bridge circuit.

[0031] If there is only one battery cell, the positive and negative terminals of the battery cell are led out to connect to the DC side of the bridge circuit, and the AC side of the bridge circuit serves as the AC side of the energy storage unit. If there are multiple battery cells, they can be connected in series or in parallel according to the power requirements of the energy storage unit. The positive and negative terminals of the multiple battery cells after being connected in series or in parallel are led out to connect to the DC side of the bridge circuit.

[0032] like Figure 2As shown, the bridge circuit includes a first control switch Q1, a second control switch Q2, a third control switch Q3, and a fourth control switch Q4. One end of the first control switch is connected to one end of the second control switch, and the other end of the first control switch is connected to one end of the third control switch. The other end of the second control switch is connected to one end of the fourth control switch, and the other end of the third control switch is connected to the other end of the fourth control switch. The connection points between the first and second control switches and between the third and fourth control switches serve as one end of the bridge circuit, used to connect at least one battery cell. The connection points between the first and third control switches and between the second and fourth control switches serve as the other end of the bridge circuit. The control terminals of the first, second, third, and fourth control switches serve as the control terminals of the bridge circuit, used to receive control signals from the control unit for adjusting the AC side voltage state.

[0033] In other words, the AC voltage state of the energy storage unit is changed by adjusting the on / off state of each control switch in the bridge circuit.

[0034] For example, for each energy storage unit, the connection between the first control switch and the third control switch of the bridge circuit corresponding to the energy storage unit is connected to the connection between the second control switch and the fourth control switch of the bridge circuit corresponding to the previous energy storage unit, so as to connect the various energy storage units in series.

[0035] The conduction states of the bridge circuit include forward connection, reverse connection, and bypass. Specifically, when the first and fourth control switches are closed and the second and third control switches are open, the bridge circuit is in the forward connection state, meaning the energy storage unit is positively connected to the energy storage system, and the AC side voltage of the energy storage unit is equal to the positive voltage of at least one cell of the energy storage unit. When the second and third control switches are closed and the first and fourth control switches are open, the bridge circuit is in the reverse connection state, meaning the energy storage unit is negatively connected to the energy storage system, and the AC side voltage of the energy storage unit is equal to the negative voltage of at least one cell of the energy storage unit. When the first and second control switches are closed and the third and fourth control switches are open, or when the first and second control switches are open and the third and fourth control switches are closed, the bridge circuit is in the bypass state, meaning the energy storage unit is disconnected from the energy storage system, and the AC side voltage of the energy storage unit is 0.

[0036] For example, the first control switch Q1, the second control switch Q2, the third control switch Q3 and the fourth control switch Q4 can all be configured as field-effect transistors (FETs), with the gate of the FET serving as the control terminal of the control switch, the source of the FET serving as one end of the control switch, and the drain of the FET serving as the other end of the control switch.

[0037] Furthermore, the control terminals of the control switches are used to control the on / off states of the various control switches in the bridge circuit, thereby controlling the AC side voltage state of the energy storage unit.

[0038] Please see Figure 3 , Figure 3 A flowchart illustrating a control method for an energy storage system provided in an embodiment of this application. Figure 3 As shown in the embodiments of this application, the control method for an energy storage system is applied in the control unit of the energy storage system and includes the following steps:

[0039] S101: Obtain the desired AC side voltage of each single-phase bridge arm and the preset voltage value of each energy storage unit on each single-phase bridge arm.

[0040] The desired AC side voltage is used to indicate the desired voltage of the AC side of a single-phase bridge arm in one AC cycle, and the preset voltage value is used to indicate the AC side voltage and value of all connected energy storage units on the single-phase bridge arm where an energy storage unit is connected to the energy storage system.

[0041] Furthermore, the expected voltage for different AC cycles can be the same or different. For example, the AC cycle corresponding to the expected AC side voltage in this application can be understood as the next AC cycle relative to the current AC cycle, so as to know in advance the time periods corresponding to the connection and disconnection of each energy storage unit in the next AC cycle. Here, the expected AC side voltage is equivalent to the sinusoidal target voltage of each single-phase bridge arm obtained by the energy storage system in the prior art by analyzing the AC power of the grid.

[0042] The control unit determines the AC side voltage of the energy storage system based on the external devices connected to the AC side of the energy storage system. Then, according to the connection method of the three-phase bridge arms (star or delta connection), it determines the expected AC side voltage of each single-phase bridge arm in one AC side cycle. In other words, if the external device connected to the AC side of the energy storage system is the power grid, the grid voltage is then analyzed according to the connection method of the three-phase bridge arms to determine the expected AC side voltage of each single-phase bridge arm in one AC side cycle.

[0043] For each energy storage unit, the preset voltage value corresponding to the energy storage unit can be understood as the voltage on the single-phase bridge arm where the energy storage unit is connected to the energy storage system. At this time, the preset voltage value is the sum of the AC side voltages of all energy storage units connected to the energy storage system on the single-phase bridge arm where the energy storage unit is located.

[0044] Specifically, the preset voltage value of each energy storage unit on each single-phase bridge arm is obtained in the following way: based on the target sorting order of multiple energy storage units corresponding to each single-phase bridge arm, the AC side voltage and value of each energy storage unit and its preceding energy storage unit in each single-phase bridge arm are determined, and the AC side voltage and value are used as the preset voltage value.

[0045] The target sorting order includes: the default order of multiple series-connected energy storage units, or the state order obtained by sorting multiple series-connected energy storage units according to their state of charge based on the direction of power transmission of the energy storage system.

[0046] In other words, for each energy storage unit, the sum of the AC side voltage corresponding to the energy storage unit when it is connected to the energy storage system and the AC side voltage values ​​of at least one preceding energy storage unit in the target sorting order when it is connected to the energy storage system is used as the preset voltage value for that energy storage unit. That is, the preset voltage value for each energy storage unit is different, and the first energy storage unit in the preset sorting order has no preceding energy storage unit.

[0047] Furthermore, the control unit obtains the identifier ID and state of charge (SOC) of each energy storage unit on each single-phase bridge arm. Therefore, the control unit can use the default order of the identifiers of each energy storage unit as the target sorting order. For example, if multiple energy storage units in a single-phase bridge arm are sorted by their default identifiers as energy storage unit A1, energy storage unit A2, ..., energy storage unit A... n Furthermore, the preset voltage value of energy storage unit A1 is the AC side voltage when energy storage unit A1 is connected to the energy storage system, and the preset voltage value of energy storage unit A2 is the sum of the AC side voltages of energy storage unit A1 and energy storage unit A2 when they are connected to the energy storage system, and so on. The control unit calculates the preset voltage value corresponding to each energy storage unit according to the default order.

[0048] The power transmission direction includes the charging direction of external equipment transmitting power to each energy storage unit of the energy storage system or the discharging direction of each energy storage unit of the energy storage system transmitting power to external equipment. The state sequence corresponding to the charging direction is sorted according to the order of the state of charge from small to large, and the state sequence corresponding to the discharging direction is sorted according to the order of the state of charge from large to small. In this way, during the charging process, the energy storage unit with the smaller state of charge is charged first, and during the discharging process, the energy storage unit with the larger state of charge is controlled to discharge first, so as to maintain the consistency of the state of charge of each energy storage unit in the energy storage system.

[0049] For example, if the power transmission direction of the energy storage system is the charging direction, and the target sorting order of multiple energy storage units in a single-phase bridge arm according to their State of Charge (SOC) from smallest to largest is energy storage unit A. i Energy storage unit A i+1 ..., Energy Storage Unit A i+m Therefore, energy storage unit A i The preset voltage value is for energy storage unit A. i AC side voltage when connected to the energy storage system, energy storage unit A i+1 The preset voltage value is for energy storage unit A. i and energy storage unit A i+1 The sum of the AC side voltages when connected to the energy storage system, ..., energy storage unit A i+m The preset voltage value is for energy storage unit A. i Energy storage unit A i+1 ..., Energy Storage Unit A i+m The sum of the AC side voltages when connected to the energy storage system is used to calculate the preset voltage value for each energy storage unit based on the target sorting order.

[0050] Furthermore, the control unit determines the expected AC side voltage of phase A bridge arm, the expected AC side voltage of phase B bridge arm, and the expected AC side voltage of phase C bridge arm, and obtains the preset voltage value of each energy storage unit on phase A bridge arm, the preset voltage value of each energy storage unit on phase B bridge arm, and the preset voltage value of each energy storage unit on phase C bridge arm.

[0051] S102: For each energy storage unit, based on the comparison result between the expected AC side voltage and the preset voltage value corresponding to the energy storage unit, determine the adjustment strategy for adjusting the AC side voltage state of the energy storage unit within one AC cycle.

[0052] The AC side voltage state includes an access state and a bypass state. For each energy storage unit in a single-phase bridge arm, the adjustment strategy includes: when the absolute value of the expected AC side voltage corresponding to the energy storage unit in one AC cycle is greater than the absolute value of the preset voltage value, the AC side voltage state of the energy storage unit is determined to be an access state; when the absolute value of the expected AC side voltage corresponding to the energy storage unit in one AC cycle is not greater than the absolute value of the preset voltage value, the AC side voltage state of the energy storage unit is determined to be a bypass state.

[0053] For example, please refer to Figure 4 , Figure 4 This is a schematic diagram illustrating the desired AC side voltage of a single-phase bridge arm in one AC cycle, as provided in an embodiment of this application. Figure 4 As shown in the embodiment of this application, the desired AC side voltage of a single-phase bridge arm changes with time t within one AC cycle T. If the target order is energy storage unit 1 and energy storage unit 2, and the absolute value of the AC side voltage of energy storage unit 1 and energy storage unit 2 connected to the energy storage system is U0, then when the absolute value of the desired AC side voltage is greater than the absolute value U0 of the AC side voltage of energy storage unit 1 connected to the energy storage system, that is, at time t... 1,1 up to time t 1,2 and time t 1,3 up to time t 1,4 When the AC side voltage state of energy storage unit 1 is determined to be in the connected state; when the absolute value of the desired AC side voltage is not greater than the absolute value U0 of the AC side voltage of energy storage unit 1 connected to the energy storage system, that is, from time 0 to time t 1,1 Time t 1,2 up to time t 1,3 and time t 1,4 At time T, the AC side voltage state of energy storage unit 1 is determined to be in bypass state. When the absolute value of the desired AC side voltage is greater than the absolute value 2U0 of the AC side voltage when both energy storage unit 1 and energy storage unit 2 are connected to the energy storage system, i.e., at time t... 2,1 up to time t 2,2 and time t 2,3 up to time t 2,4 When the AC side voltage state of energy storage unit 2 is determined to be in the connected state; when the absolute value of the desired AC side voltage is not greater than the absolute value 2U0 of the AC side voltage of both energy storage unit 1 and energy storage unit 2 connected to the energy storage system, that is, from time 0 to time t 2,1 Time t 2,2 up to time t 2,3 and time t 2,4 At time T, the AC side voltage state of energy storage unit 2 is determined to be in bypass state.

[0054] One AC cycle includes a positive half-cycle and a negative half-cycle, and the connection state includes a positive connection state and a negative connection state. That is, the positive connection state of the AC side voltage state corresponds to the forward connection state of the bridge circuit, the negative connection state of the AC side voltage state corresponds to the reverse connection state of the bridge circuit, and the bypass state of the AC side voltage state corresponds to the bypass state of the bridge circuit.

[0055] Specifically, the adjustment strategy includes: during the positive half-cycle, when the absolute value of the desired AC side voltage corresponding to the energy storage unit is greater than the absolute value of the preset voltage value, determining the AC side voltage state of the energy storage unit as the positive access state; when the absolute value of the desired AC side voltage corresponding to the energy storage unit is not greater than the absolute value of the preset voltage value, determining the AC side voltage state of the energy storage unit as the bypass state; during the negative half-cycle, when the absolute value of the desired AC side voltage corresponding to the energy storage unit is greater than the absolute value of the preset voltage value, determining the AC side voltage state of the energy storage unit as the negative access state; when the absolute value of the desired AC side voltage corresponding to the energy storage unit is not greater than the absolute value of the preset voltage value, determining the AC side voltage state of the energy storage unit as the bypass state.

[0056] Furthermore, during the positive half-cycle of an AC cycle, it is desirable for the AC side voltage to be positive. Therefore, the control unit controls the bridge circuit of the energy storage unit to be in a forward connection state during the positive half-cycle so that the AC side voltage of the energy storage unit is in a positive connection state. During the negative half-cycle of an AC cycle, it is desirable for the AC side voltage to be negative. Therefore, the control unit controls the bridge circuit of the energy storage unit to be in a reverse connection state during the negative half-cycle so that the AC side voltage of the energy storage unit is in a negative connection state.

[0057] The preset voltage value can be the AC side voltage of the single-phase bridge arm where the energy storage unit is located when it is in a positive connection state, or it can be the AC side voltage of the single-phase bridge arm where the energy storage unit is located when it is in a negative connection state. Furthermore, the preset voltage value can be a positive voltage or a negative voltage. Therefore, during the positive half-cycle, the absolute value of the desired AC side voltage is compared with the absolute value of the preset voltage value, and during the negative half-cycle, the absolute value of the desired AC side voltage is compared with the absolute value of the preset voltage value.

[0058] In other words, for each energy storage unit, during the positive half-cycle of the AC cycle, a first time period is determined where the absolute value of the desired AC side voltage is greater than the absolute value of the preset voltage corresponding to the energy storage unit, and a second time period is determined where the desired AC side voltage is not greater than the absolute value of the preset voltage corresponding to the energy storage unit. During the negative half-cycle of the AC cycle, a third time period is determined where the absolute value of the desired AC side voltage is greater than the absolute value of the preset voltage corresponding to the energy storage unit, and a fourth time period is determined where the desired AC side voltage is not greater than the absolute value of the preset voltage corresponding to the energy storage unit. Furthermore, the energy storage unit is controlled to connect to the energy storage system during the first and third time periods, and its bridge circuit is controlled to bypass during the second and fourth time periods.

[0059] The AC side voltage state includes an access state and a bypass state. An AC cycle includes a positive half-cycle and a negative half-cycle, distinguished by the midpoint of the AC side cycle. The access state includes a positive access state corresponding to the positive half-cycle and a negative access state corresponding to the negative half-cycle. For each energy storage unit in a single-phase bridge arm, the adjustment strategy includes: within the target half-cycle, when the absolute value of the desired AC side voltage corresponding to the energy storage unit is greater than the absolute value of the preset voltage value, determining the AC side voltage state of the energy storage unit as the access state corresponding to the target half-cycle; and when the absolute value of the desired AC side voltage corresponding to the energy storage unit is not greater than the absolute value of the preset voltage value. When the absolute value of the voltage is set, the AC side voltage state of the energy storage unit is determined to be the bypass state, and the target half-cycle is one of the positive half-cycle and the negative half-cycle; within a preset half-cycle, the time period during which the AC side voltage state of the energy storage unit is in the access state corresponding to the preset half-cycle is symmetrical to the time period during which the access state corresponding to the target half-cycle is relative to the midpoint, and the time period during which the AC side voltage state of the energy storage unit is in the bypass state is symmetrical to the time period during which the bypass state corresponding to the target half-cycle is relative to the midpoint, and the preset half-cycle is the other of the positive half-cycle and the negative half-cycle.

[0060] In other words, if the energy storage unit is in the access state and bypass state respectively in one half-cycle or the negative half-cycle, then the time periods corresponding to the access state and bypass state in the other half-cycle can be determined by distinguishing the midpoint between the two half-cycles.

[0061] like Figure 4 As shown, if the target half-cycle is a positive half-cycle, that is, from time 0 to time 0.5T, at time t 1,1 up to time t 1,2 At that time, the AC side voltage state of energy storage unit 1 is determined to be in the connected state, from time 0 to time t. 1,1 Time t1,2 At time 0.5T, the AC side voltage state of energy storage unit 1 is determined to be in bypass state. Furthermore, the times of the positive and negative half-cycles are symmetrical about the midpoint of one AC cycle, 0.5T. Therefore, in the negative half-cycle, i.e., from time 0.5T to time T, at time 0.5T+t... 1,1 up to time 0.5T+t 1,2 At that time, the AC side voltage state of energy storage unit 1 is determined to be in the connected state, from time 0.5T to time 0.5T+t. 1,1 Time 0.5T+t 1,2 At time T, the AC side voltage state of energy storage unit 1 is determined to be in bypass state.

[0062] S103: For each energy storage unit, execute the regulation strategy corresponding to that energy storage unit during the AC cycle to make the AC side voltage of the single-phase bridge arm where the energy storage unit is located conform to the desired AC side voltage.

[0063] The regulation strategy is executed within the AC cycle in the following manner: at the beginning of the positive access state during the positive half-cycle, the energy storage unit regulates the AC side voltage state to the positive access state; at the end of the positive access state during the positive half-cycle, the energy storage unit regulates the AC side voltage state to the bypass state; at the beginning of the negative access state during the negative half-cycle, the energy storage unit regulates the AC side voltage state to the negative access state; at the end of the negative access state during the negative half-cycle, the energy storage unit regulates the AC side voltage state to the bypass state.

[0064] For example, during the positive half-cycle, the energy storage unit is in a bypass state by default. The control unit controls the bridge circuit to be in a positive connection state at the start of the time period when the absolute value of the desired AC side voltage is greater than the preset voltage value, so as to achieve a positive connection state for the AC side voltage of the energy storage unit. The control unit controls the bridge circuit to be in a bypass state at the end of the time period when the absolute value of the desired AC side voltage is greater than the preset voltage value, so as to achieve a bypass state for the AC side voltage of the energy storage unit. During the negative half-cycle, the control unit controls the bridge circuit to be in a reverse connection state at the start of the time period when the absolute value of the desired AC side voltage is greater than the preset voltage value, so as to achieve a negative connection state for the AC side voltage of the energy storage unit. The control unit controls the bridge circuit to be in a bypass state at the end of the time period when the absolute value of the desired AC side voltage is greater than the preset voltage value, so as to achieve a bypass state for the AC side voltage of the energy storage unit.

[0065] In other words, the control unit does not need to resolve the desired AC side voltage into amplitude and frequency and send it to the energy storage unit. Instead of comparing the desired AC side voltage that changes over time within an AC cycle with the sum of the AC side voltages of each energy storage unit, it controls the bridge circuit based on the predetermined time periods corresponding to the access state and bypass state within an AC cycle. Specifically, for each energy storage unit, when the time reaches the start time of the time period corresponding to the access state of the energy storage unit, a control signal is directly sent to the bridge circuit of the energy storage unit to access the energy storage unit. When the time reaches the start time of the time period corresponding to the bypass state of the energy storage unit, a control signal is directly sent to the bridge circuit of the energy storage unit to disconnect the energy storage unit. This reduces the error between the AC side voltage and the desired AC side voltage of the energy storage system caused by the time difference between obtaining the comparison conclusion and actually sending the control signal in the prior art.

[0066] In other words, the control unit controls the conduction state of the bridge circuit according to the different AC side voltage states in an AC cycle. Thus, the control unit directly controls the bridge circuit and does not need to constantly compare the desired AC side voltage with the preset voltage value as time changes. Instead, it determines the adjustment strategy for an AC cycle in advance so that the energy storage unit is controlled according to the adjustment strategy in each AC cycle.

[0067] Based on the same application concept, this application also provides a control device for an energy storage system corresponding to the control method of the energy storage system provided in the above embodiments. Since the principle of the device in this application is similar to the control method of the energy storage system in the above embodiments of this application, the implementation of the device can refer to the implementation of the method, and the repeated parts will not be described again.

[0068] Based on the same concept, this application also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, performs the steps of the control method for the energy storage system provided in the above embodiments.

[0069] Specifically, the storage medium can be a general-purpose storage medium, such as a portable disk or hard disk. When the computer program on the storage medium is run, it can execute the control method of the energy storage system described above. By pre-acquiring the desired AC side voltage of each single-phase bridge arm and the preset voltage value corresponding to each energy storage unit when connected to the system, the preset voltage value reflects the AC side voltage and value of all connected energy storage units on the single-phase bridge arm. Thus, by comparing the desired AC side voltage and the preset voltage value corresponding to each energy storage unit, the adjustment method for the AC side voltage state of each energy storage unit within one AC cycle is determined. The control of the AC side voltage state of each energy storage unit within the AC cycle is achieved according to the adjustment method. This solves the technical problem of repetitive operation of parsing and recombining the desired AC side voltage in the prior art, and achieves the technical effect of improving control efficiency and increasing the power quality of the energy storage system.

[0070] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems and devices described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. In the several embodiments provided in this application, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of units is only a logical functional division; in actual implementation, there may be other division methods. Furthermore, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Another point is that the displayed or discussed mutual coupling or direct coupling or communication connection may be through some communication interfaces; the indirect coupling or communication connection of devices or units may be electrical, mechanical, or other forms.

[0071] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0072] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0073] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a processor-executable, non-volatile, computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0074] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A control method for an energy storage system, characterized in that, The energy storage system includes three-phase bridge arms, and each single-phase bridge arm includes multiple energy storage units connected in series. The control method includes: The desired AC side voltage of each single-phase bridge arm and the preset voltage value of each energy storage unit on each single-phase bridge arm are obtained. The desired AC side voltage is used to indicate the desired voltage of the AC side of the single-phase bridge arm in one AC cycle. The preset voltage value is used to indicate the AC side voltage and value of all connected energy storage units on the single-phase bridge arm where an energy storage unit is connected to the energy storage system. For each energy storage unit, based on the comparison result between the expected AC side voltage and the preset voltage value corresponding to the energy storage unit, a regulation strategy for regulating the AC side voltage state of the energy storage unit within one AC cycle is determined. For each energy storage unit, the corresponding adjustment strategy is executed during the AC cycle to make the AC side voltage of the single-phase bridge arm where the energy storage unit is located conform to the desired AC side voltage.

2. The control method according to claim 1, characterized in that, The preset voltage value of each energy storage unit on each single-phase bridge arm is obtained in the following way: Based on the target sorting order of multiple energy storage units corresponding to each single-phase bridge arm, the AC side voltage and value of each energy storage unit and its preceding energy storage unit in each single-phase bridge arm are determined, and the AC side voltage and value are used as the preset voltage value.

3. The control method according to claim 2, characterized in that, The target sorting order includes: the default order of multiple series-connected energy storage units, or the state order obtained by sorting multiple series-connected energy storage units according to their state of charge based on the direction of power transmission of the energy storage system.

4. The control method according to claim 1, characterized in that, The AC side voltage state includes an access state and a bypass state. For each energy storage unit of a single-phase bridge arm, the regulation strategy includes: When the absolute value of the desired AC side voltage of the energy storage unit within one AC cycle is greater than the absolute value of the preset voltage value, the AC side voltage state of the energy storage unit is determined to be in the connected state. When the absolute value of the desired AC side voltage of the energy storage unit within one AC cycle is not greater than the absolute value of the preset voltage value, the AC side voltage state of the energy storage unit is determined to be a bypass state.

5. The control method according to claim 4, characterized in that, An alternating current cycle includes a positive half-cycle and a negative half-cycle, the connection state includes a positive connection state and a negative connection state, and the adjustment strategy includes: During the positive half-cycle, when the expected AC side voltage corresponding to the energy storage unit is greater than the absolute value of the preset voltage value, the AC side voltage state of the energy storage unit is determined to be the positive access state; when the expected AC side voltage corresponding to the energy storage unit is not greater than the absolute value of the preset voltage value, the AC side voltage state of the energy storage unit is determined to be the bypass state. During the negative half-cycle, if the absolute value of the desired AC side voltage corresponding to the energy storage unit is greater than the absolute value of the preset voltage value, the AC side voltage state of the energy storage unit is determined to be the negative access state; if the absolute value of the desired AC side voltage corresponding to the energy storage unit is not greater than the absolute value of the preset voltage value, the AC side voltage state of the energy storage unit is determined to be the bypass state.

6. The control method according to claim 4, characterized in that, The AC side voltage state includes an access state and a bypass state. An AC cycle includes a positive half-cycle and a negative half-cycle, distinguished by the midpoint of the AC side cycle. The access state includes a positive access state corresponding to the positive half-cycle and a negative access state corresponding to the negative half-cycle. For each energy storage unit of a single-phase bridge arm, the regulation strategy includes: Within the target half-cycle, if the absolute value of the desired AC side voltage corresponding to the energy storage unit is greater than the absolute value of the preset voltage value, the AC side voltage state of the energy storage unit is determined to be the access state corresponding to the target half-cycle; if the absolute value of the desired AC side voltage corresponding to the energy storage unit is not greater than the absolute value of the preset voltage value, the AC side voltage state of the energy storage unit is determined to be the bypass state. The target half-cycle is one of the positive half-cycle and the negative half-cycle. Within a preset half-cycle, the time period during which the AC side voltage state of the energy storage unit is in the access state corresponding to the preset half-cycle is symmetrical to the time period during which the access state corresponding to the target half-cycle is relative to the intermediate moment. The time period during which the AC side voltage state of the energy storage unit is in the bypass state is symmetrical to the time period during which the bypass state corresponding to the target half-cycle is relative to the intermediate moment. The preset half-cycle is the other of the positive half-cycle and the negative half-cycle.

7. The control method according to claim 5 or 6, characterized in that, The regulation strategy corresponding to this energy storage unit is executed during the alternating current cycle in the following manner: At the beginning of the positive access state during the positive half-cycle, the AC side voltage state of the energy storage unit is adjusted to the positive access state, and at the end of the positive access state during the positive half-cycle, the AC side voltage state of the energy storage unit is adjusted to the bypass state. At the beginning of the negative access state during the negative half-cycle, the AC side voltage state of the energy storage unit is adjusted to the negative access state; at the end of the negative access state during the negative half-cycle, the AC side voltage state of the energy storage unit is adjusted to the bypass state.

8. An energy storage system, characterized in that, The energy storage system includes three-phase bridge arms and a control unit. Each single-phase bridge arm includes multiple energy storage units connected in series. The control unit is connected to the multiple energy storage units corresponding to each single-phase bridge arm. The control unit is configured as follows: The desired AC side voltage of each single-phase bridge arm and the preset voltage value of each energy storage unit on each single-phase bridge arm are obtained. The desired AC side voltage is used to indicate the desired voltage of the AC side of the single-phase bridge arm in one AC cycle. The preset voltage value is used to indicate the AC side voltage and value of all connected energy storage units on the single-phase bridge arm where an energy storage unit is connected to the energy storage system. For each energy storage unit, based on the comparison result between the expected AC side voltage and the preset voltage value corresponding to the energy storage unit, a regulation strategy for regulating the AC side voltage state of the energy storage unit within one AC cycle is determined. For each energy storage unit, the corresponding adjustment strategy is executed during the AC cycle to make the AC side voltage of the single-phase bridge arm where the energy storage unit is located conform to the desired AC side voltage.

9. The system according to claim 8, characterized in that, Each energy storage unit includes at least one battery cell and a bridge circuit. The at least one battery cell is connected to one end of the bridge circuit, and the other end of the bridge circuit serves as the AC side of the energy storage unit. The bridge circuit is used to regulate the voltage state of the AC side. The control unit is connected to the control terminal of the bridge circuit corresponding to each energy storage unit, so as to adjust the AC side voltage state by sending control signals to the control terminal of the bridge circuit.

10. The system according to claim 9, characterized in that, The bridge circuit includes a first control switch, a second control switch, a third control switch, and a fourth control switch. Wherein, one end of the first control switch is connected to one end of the second control switch, the other end of the first control switch is connected to one end of the third control switch, the other end of the second control switch is connected to one end of the fourth control switch, and the other end of the third control switch is connected to the other end of the fourth control switch. The connection between the first control switch and the second control switch, and the connection between the third control switch and the fourth control switch, serve as one end of the bridge circuit for connecting at least one battery cell. The connection between the first control switch and the third control switch, and the connection between the second control switch and the fourth control switch, serve as the other end of the bridge circuit. The control terminals of the first control switch, the second control switch, the third control switch, and the fourth control switch serve as the control terminals of the bridge circuit, used to receive control signals from the control unit for adjusting the AC side voltage state.

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