Series-connected power electronic battery unit, energy storage system and control method thereof

Abstract

This invention discloses a series-type power electronic battery cell, comprising: a battery module; and a series-type interface converter, including an input port and an output port. The input port includes a positive input terminal and a negative input terminal, and the output port includes a positive output terminal and a negative output terminal. The positive terminal of the battery module is connected to the negative output terminal of the series-type interface converter, and the positive output terminal of the series-type interface converter and the negative terminal of the battery module serve as the positive and negative terminals for the power output of the series-type power electronic battery cell.

Description

Technical Field

[0001] This invention relates to the field of battery energy storage technology. Specifically, this invention relates to a series-type power electronic battery cell, an energy storage system based on the series-type power electronic battery cell, and a control method thereof. Background Technology

[0002] With the continuous increase in installed capacity of new energy power generation and the continuous development of smart grids, increasingly higher requirements are being placed on the capacity and functions of energy storage systems. Among them, battery energy storage systems have the advantages of no moving parts, no special site requirements, easy expansion, and good dynamic characteristics, and are increasingly widely used in grid-side frequency regulation and peak shaving, user-side load emergency protection, and smoothing of renewable energy power fluctuations.

[0003] Because a battery is a complex electrochemical system, deviations introduced during its manufacturing process will ultimately be reflected in its external characteristics, such as capacity and internal resistance. Furthermore, the operation of the battery affects the electrochemical system, some of which are irreversible, leading to battery aging. This further impacts the battery's capacity and internal resistance, potentially causing bottlenecks and circulating currents during series and parallel connections. Both phenomena result in energy waste within the battery, thus affecting the economics of the battery energy storage system.

[0004] Therefore, those skilled in the art are dedicated to managing batteries through power electronics and other means to suppress the state-of-charge deviation caused by differences in battery capacity, internal resistance, etc., thereby improving the economics of energy storage systems.

[0005] Chinese invention patent CN113193615A discloses an energy storage system, which includes multiple energy storage branches, at least one switching unit, and a control circuit. Each energy storage branch includes a first bus, a cluster-level conversion circuit, and a battery cluster connected in series, as well as multiple equalization conversion circuits and an equalization bus. The battery cluster includes multiple battery modules connected in series, and each battery module includes a battery pack. The battery pack is connected to the input side of a corresponding equalization conversion circuit, and the output sides of the multiple equalization conversion circuits are respectively connected to the equalization bus. The positive terminal of the battery cluster is connected to the cluster-level conversion circuit, and the negative terminal of the battery cluster is connected to ground. A switching unit is provided between two adjacent energy storage branches. If the switching unit is in the first state, the equalization buses in the two energy storage branches are connected. In this patent, the input side of the cluster-level conversion circuit and the output of the battery cluster are connected in parallel. The cluster-level conversion circuit, as an intermediate conversion circuit between the battery cluster and the external bus voltage, needs to bear the full power of charging and discharging the battery cluster. Summary of the Invention

[0006] In view of the aforementioned problems in the prior art, the technical problem to be solved by the present invention is how to solve the problem of state of charge deviation between and within battery clusters through system architecture innovation; at the same time, it is also necessary to minimize the losses introduced after the control converter is connected. Therefore, the present invention completely divides the system into grids, abandoning the traditional concept of energy storage system clusters, and transforming it into individual power electronic battery units, which are then connected in series and parallel to form a complete battery energy storage system.

[0007] According to one aspect of the present invention, a series-connected power electronic smart battery cell is provided, comprising:

[0008] Battery module; and

[0009] A series interface converter includes an input port and an output port. The input port includes a positive input terminal and a negative input terminal, and the output port includes a positive output terminal and a negative output terminal.

[0010] The positive terminal of the battery module is connected to the negative output terminal of the series interface converter. The positive output terminal of the series interface converter and the negative terminal of the battery module serve as the positive and negative terminals for the power output of the series power electronic battery unit.

[0011] In one embodiment of the present invention, the positive input terminal and the negative input terminal are respectively connected to the positive and negative terminals of the battery module or the positive and negative terminals of the common DC bus capacitor.

[0012] In one embodiment of the present invention, the series interface converter includes a bidirectional DC-DC converter, a first switching element, and a second switching element.

[0013] The input side of the bidirectional DC-DC converter is directly connected to the input port. The positive terminal of the output side of the bidirectional DC-DC converter is connected to one end of the first switching element. The negative terminal of the output side of the bidirectional DC-DC converter is connected to one end of the second switching element and the negative output terminal. The other ends of the first and second switching elements are connected to each other and connected to the positive output terminal.

[0014] In one embodiment of the present invention, the first switching element and / or the second switching element include a mechanical switch and a bidirectional switch connected in parallel.

[0015] In one embodiment of the present invention, the series-connected power electronic battery cell further includes a battery management unit connected to the battery module.

[0016] The battery management unit includes:

[0017] Sensors that measure the voltage, current, pressure and / or temperature of the battery cells within the corresponding battery module, used for reading information on the voltage, current, pressure and / or temperature of the battery cells within the battery module and storing historical information;

[0018] The external communication port is used for exchanging status and control information.

[0019] According to one aspect of the present invention, an energy storage system is provided, comprising:

[0020] Multiple series-connected power electronic battery cells,

[0021] Multiple series-connected power electronic battery cells are connected in parallel to form a group, and multiple groups are connected in series to form an energy storage system.

[0022] In one embodiment of the present invention, each group of series-connected power electronic battery cells includes a common DC bus capacitor, and the positive and negative terminals of the input port of the series-connected interface converter are connected to the positive and negative terminals of the common DC bus capacitor.

[0023] In one embodiment of the present invention, in each group of series-connected power electronic battery cells, the positive and negative terminals of the input port of the series-connected interface converter are connected to the positive and negative terminals of the corresponding battery module.

[0024] In one embodiment of the present invention, the positive and negative buses of each group of power electronic battery cells are connected to the input terminal of a corresponding isolated bidirectional DC-DC converter, and the output terminal of each group of power electronic battery cells is connected to a common bus.

[0025] In one embodiment of the present invention, the positive and negative buses of each set of series-connected power electronic battery cells are connected to the input terminal of a corresponding non-isolated bidirectional DC-DC converter. Different non-isolated bidirectional DC-DC converters transfer energy from one set of series-connected power electronic battery cells to another set of series-connected power electronic battery cells through energy storage elements.

[0026] In one embodiment of the present invention, each non-isolated bidirectional DC-DC converter includes a first switch, a second switch, and a third switch. The first and second switches are connected in series between the positive and negative buses of a corresponding set of series-connected power electronic battery cells. One end of the third switch is connected to the connection terminal between the first and second switches, and the other end of the third switch is connected to the other end of the third switch of an adjacent non-isolated bidirectional DC-DC converter through a series-connected inductor and capacitor.

[0027] The process involves controlling the switching transistors of a non-isolated bidirectional DC-DC converter to achieve resonance between the inductor and capacitor. Energy is then transferred through the entire inductor-capacitor series branch. Finally, the energy is transferred to the power electronic battery cell array that requires energy through the switching transistors.

[0028] In one embodiment of the present invention, the energy storage system further includes:

[0029] Battery management system, DC-AC converter, energy management system, and grid-side transformer.

[0030] The battery management system is connected to the battery management unit and the energy management system, and the energy management system is also connected to the DC-AC converter at the output port.

[0031] According to another aspect of the present invention, a control method for an energy storage system based on a series-connected power electronic battery cell is provided, comprising: controlling a series-connected interface converter to operate in one of the following operating modes:

[0032] Direct bypass: When the battery management system informs the series-type power electronic battery cell that the battery modules in the same group are in basically the same state, no operation is required. The second switching element is directly closed to bypass the bidirectional DC-DC converter, and the current flows directly through the mechanical switch in the second switching element.

[0033] Voltage regulation: When the battery management system informs the series-connected power electronic battery cell that the state of the battery module within the control unit differs from that of other battery modules in the same group, the series-connected interface converter within the series-connected power electronic battery cell performs voltage regulation control, including:

[0034] Close the mechanical switch in the first switching element and the power electronic switch in the second switching element;

[0035] Disconnect the mechanical switch within the second switching element;

[0036] Disconnect the power electronic switch in the second switching element. At this time, the output side of the bidirectional DC-DC converter body is connected to the power circuit.

[0037] Starting from 0 output, the output voltage of the bidirectional DC-DC converter is gradually increased to raise the power output port voltage of the series-connected power electronic battery cell, so that the series-connected power electronic battery cell can output power to other series-connected power electronic battery cells in the same group. The bidirectional DC-DC converter operates in current-limiting mode. By monitoring the output current on the output side, the output current is limited to not exceed the maximum output current of the battery module, thereby determining the output voltage of the converter at this time.

[0038] When the SOC of the battery module of the series-type power electronic battery cell is basically consistent with the SOC of other battery modules in the same group, the output voltage of the bidirectional DC-DC converter is reduced to 0, the power electronic switch in the first switching element and the mechanical switch in the second switching element are closed, the mechanical switch in the first switching element is opened, and the power electronic switch in the first switching element is opened. At this time, the output side of the bidirectional DC-DC converter body has been bypassed from the power circuit.

[0039] Fault clearance: When the battery management system informs the series-connected power electronic battery cell that there is an internal fault in the battery module within the control unit, the power electronic switch in the second switching element is closed to enable the freewheeling function, the mechanical switch in the second switching element is disconnected, and finally the power electronic switch in the second switching element is disconnected. At this time, since neither the first nor the second switching element is connected to the circuit, the series-connected power electronic battery cell has been disconnected from the energy storage system.

[0040] Compared with the prior art, the embodiments of the present invention have at least one of the following beneficial effects:

[0041] This invention realizes full-grid management and control of energy storage systems, in which each battery module can exit after a failure, and the system can still operate stably after exiting.

[0042] This invention achieves partial processing of battery power. By using the idea of ​​connecting battery modules in series with a converter, it is possible to perform state of charge balancing within the battery module group without processing the full power of the battery. Only the converter output port current multiplied by the converter output port voltage needs to be processed, which reduces the power level of the converter and facilitates converter miniaturization.

[0043] This invention utilizes a mechanical switch to achieve the effect of minimizing losses in the bypass state. Since the conduction loss of the mechanical switch is negligible, the energy storage system can be regarded as the battery modules being directly connected in series and parallel during normal operation. This method can minimize the total loss of the battery energy storage system.

[0044] This invention achieves mismatch suppression in energy storage systems. By using a series interface converter to access voltage regulation function, the output voltage of the power electronic battery cells can be adjusted, thereby suppressing circulating current within the group. Through control algorithms or equalization circuits, state balance between groups can be achieved. Attached Figure Description

[0045] To further illustrate the above and other advantages and features of the various embodiments of the present invention, a more specific description of the embodiments of the invention will be presented with reference to the accompanying drawings. It is to be understood that these drawings depict only typical embodiments of the invention and are therefore not intended to limit its scope. In the drawings, identical or corresponding parts will be indicated by identical or similar reference numerals for clarity.

[0046] Figure 1 This is a schematic diagram of an energy storage system based on a series-connected power electronic battery cell according to an embodiment of the present invention.

[0047] Figure 2 This is a schematic diagram of the connection relationship of a series interface converter according to an embodiment of the present invention.

[0048] Figure 3A A schematic diagram illustrating a switching element implementation according to an embodiment of the present invention is shown.

[0049] Figure 3B A schematic diagram illustrating a switching element implementation according to another embodiment of the present invention is shown.

[0050] Figure 4 This is a feasible embodiment of a series-type power electronic battery cell pack according to one embodiment of the present invention.

[0051] Figure 5 This is another feasible embodiment of a series-type power electronic battery cell pack according to one embodiment of the present invention.

[0052] Figure 6 This is a connection diagram of a feasible common bus equalization circuit according to an embodiment of the present invention.

[0053] Figure 7A This is a schematic diagram of a feasible non-common bus equalization circuit according to an embodiment of the present invention.

[0054] Figure 7B Show Figure 7A The circuit diagram shown is a schematic of the equalization circuit.

[0055] Figure 8 This is a flowchart of the operation mode of a serial interface converter according to an embodiment of the present invention. Detailed Implementation

[0056] In the following description, the invention is described with reference to various embodiments. However, those skilled in the art will recognize that the embodiments may be practiced without one or more specific details or with other alternatives and / or additional methods, materials, or components. In other instances, well-known structures, materials, or operations are not shown or described in detail so as not to obscure aspects of the embodiments of the invention. Similarly, for purposes of explanation, specific quantities, materials, and configurations are set forth to provide a comprehensive understanding of the embodiments of the invention. However, the invention may be practiced without specific details. Furthermore, it should be understood that the embodiments shown in the drawings are illustrative representations and are not necessarily drawn to scale.

[0057] In this specification, references to "an embodiment" or "this embodiment" mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. The phrase "in one embodiment" appearing throughout this specification does not necessarily refer to the same embodiment in all instances.

[0058] Figure 1 This is a schematic diagram of an energy storage system based on a series-connected power electronic battery cell, according to an embodiment of the present invention. Figure 1 As shown, the energy storage system 100 based on series-connected power electronic battery cells includes multiple series-connected power electronic battery cells 110. Each series-connected power electronic battery cell consists of a battery management unit (BMU), a series interface converter (DC / DC), and a battery module.

[0059] The battery management unit is connected to the battery module, the battery management system (BMS), and the series interface converter. The battery management system (BMS) is also connected to the energy management system (EMS). The energy management system (EMS) is also connected to the DC-AC converter (also known as the energy storage inverter PCS) at the output port.

[0060] A battery module can be composed of several battery cells connected in series, and has energy storage function. The positive terminal of the battery module is connected to the negative terminal of the output side of the series-type interface converter. The positive terminal of the output side of the series-type interface converter and the negative terminal of the battery module serve as the positive and negative terminals for the power output of the series-type power electronic battery unit.

[0061] Multiple series-connected power electronic battery cells are connected in parallel to form a group, and multiple groups are connected in series to form an energy storage system.

[0062] In one embodiment of the present invention, the equalization circuit can be connected to the positive and negative buses of each group and connected to the battery management system via a communication line.

[0063] The energy storage system 100 is connected to the grid via a DC-AC converter and a grid-side transformer.

[0064] The energy management system is connected to the DC-AC converter and the battery management system.

[0065] The series-type interface converters within the energy storage system 100 are usually not in operation. They only start working when there is a large capacity difference or failure between the battery module they control and other series-type power electronic battery cells in the same group, in order to achieve circulating current suppression and fault reconfiguration.

[0066] The energy storage system 100 comprises three levels: the most basic level consists of a series-connected power electronic battery unit composed of a battery module, a battery management unit, and a series-connected interface converter; the intermediate level consists of a group of multiple series-connected power electronic battery units connected in parallel; and the highest level consists of an energy storage system formed by multiple groups connected in series.

[0067] In some embodiments of the present invention, the battery management unit (BMU) may have the following functions:

[0068] Includes sensors that measure the voltage, current, pressure and / or temperature of the battery cells within the corresponding managed battery module, for reading information on the voltage, current, pressure and / or temperature of the battery cells within the battery module and storing historical information.

[0069] It includes an external communication port, which can connect to the series interface converter in the same series-type power electronic battery cell and the battery management system of the entire energy storage system for the exchange of status information and control information.

[0070] Figure 2 This is a schematic diagram of the connection relationship of a series interface converter according to an embodiment of the present invention. Figure 2 As shown, the series interface converter 200 includes input / output ports, a bidirectional DC-DC converter 201, and two switching elements S1 and S2.

[0071] The input / output ports have four terminals: the input port includes a positive input terminal 202 and a negative input terminal 203; the output port includes a positive output terminal 204 and a negative output terminal 205. The positive terminal of the battery module is connected to the negative output terminal 205. The positive output terminal 204 of the series-type interface converter and the negative terminal of the battery module serve as the positive and negative terminals for the power output of the series-type power electronic battery unit. Positive input terminal 202 and negative input terminal 203

[0072] The bidirectional DC-DC converter 201 can adopt a non-isolated topology, such as a non-isolated bidirectional DC-DC converter. Alternatively, it can adopt an isolated topology, such as an isolated bidirectional DC-DC converter. A non-isolated bidirectional DC-DC converter can be a Buck-Boost circuit. An isolated bidirectional DC-DC converter can be a flyback circuit, a forward circuit, an LLC circuit, a dual active bridge circuit, etc.

[0073] The input side of the bidirectional DC-DC converter 201 is directly connected to the input port. The positive terminal of the output side of the bidirectional DC-DC converter 201 is connected to one end of the first switching element S1. The negative terminal of the output side of the bidirectional DC-DC converter 201 is connected to one end of the second switching element S2 and the negative output terminal 205. The other ends of the first and second switching elements S1 and S2 are directly connected and connected to the positive output terminal 204.

[0074] The first and second switching elements S1 and S2 can have similar structures. For example, both the first and second switching elements S1 and S2 consist of a mechanical switch and a power electronic bidirectional switch. Figure 3A and Figure 3B Schematic diagrams illustrating two implementations of a switching element according to an embodiment of the present invention are shown. For example... Figure 3A As shown, the switching element 310 includes a mechanical switch 311 and a power electronic bidirectional switch. The power electronic bidirectional switch includes two insulated-gate bipolar transistors 312 and 313 connected in series. The mechanical switch 311 and the power electronic bidirectional switch are connected in parallel between the two terminals A and B of the switching element 310. Figure 3B As shown, the switching element 320 includes a mechanical switch 321 and a power electronic bidirectional switch. The power electronic bidirectional switch includes two MOS transistors 322 and 323 connected in series. The mechanical switch 321 and the power electronic bidirectional switch are connected in parallel between the two terminals A and B of the switching element 320.

[0075] Figure 4 An embodiment of a feasible series-connected power electronic battery cell pack according to one embodiment of the present invention is shown. Figure 4 The diagram shows the connection of m groups of series-connected power electronic battery cells, each group consisting of n cells. Each group of series-connected power electronic battery cells includes a common DC bus capacitor. Figure 4 The numbers are C1, C2, ..., Cm. In each control unit within a group, the positive and negative terminals of the input port of the series-type interface converter are connected to the positive and negative terminals of the common DC bus capacitor, and the negative terminal of its output port is connected to the positive terminal of the controlled battery module. The positive terminal of the output port and the negative terminal of the controlled battery module serve as the positive and negative terminals of the power output of the series-type power electronic battery unit.

[0076] Figure 5 This illustrates another feasible embodiment of a series-connected power electronic battery cell pack according to one embodiment of the present invention. Figure 5 The diagram shows the connection of m groups, each containing n series-connected power electronic battery cells. In each group of series-connected power electronic battery cells, the positive and negative terminals of the input port of the series interface converter in each control unit are connected to the positive and negative terminals of the controlled battery module, and the negative terminal of the output port is connected to the positive terminal of the controlled battery module. The positive output terminal and the negative terminal of the controlled battery module serve as the positive and negative power output terminals of the series-connected power electronic battery cell.

[0077] Figure 6 A connection diagram of a feasible common-bus equalization circuit according to an embodiment of the present invention is shown. Figure 6As shown, in m groups of series-connected power electronic battery cells, the positive and negative buses of each group of power electronic battery cells are connected to the input terminals of a corresponding isolated bidirectional DC-DC converter, and the output terminals of each group of power electronic battery cells are connected to a common bus. Figure 6 The diagram shows a direct connection to the main DC bus of the battery system, but it can also be connected to any individual DC bus.

[0078] Figure 7A This is a schematic diagram of a feasible non-common bus equalization circuit according to an embodiment of the present invention. Figure 7B Show Figure 7A The circuit diagram of the equalization circuit shown is as follows. Figure 7A As shown, in the structure of m sets of series-connected power electronic battery cells, the positive and negative buses of each set of power electronic battery cells are connected to the input terminals of a corresponding non-isolated bidirectional DC-DC converter. The non-isolated bidirectional DC-DC converter transfers energy from one set of battery cells to another through energy storage elements, such as inductors and capacitors, utilizing resonant characteristics. Figure 7B As shown, the first non-isolated bidirectional DC-DC converter includes three switching transistors Q. 1a Q 1b and Q 1c The first switching transistor Q 1a Second switch Q 1b It is connected in series between the positive and negative buses of the first group of series-connected power electronic battery cells. The third switch Q... 1c One end is connected to the first switching transistor Q 1a Second switch Q 1b One end is connected to the terminal block of the capacitor L1, and the other end is connected to one end of the inductor L1. The other end of the inductor L1 is connected to one end of the capacitor C1. The other end of the capacitor C1 is connected to the inductor L2 of the second non-isolated bidirectional DC-DC converter and the third switch Q. 2c Connected. That is, inductor L1 and capacitor C1 are connected in series to the third switch Q of the first non-isolated bidirectional DC-DC converter. 1c The source and the third switch Q of the second non-isolated bidirectional DC-DC converter 2c Between the source and the source. And so on, for inductor L... m-1 and capacitor C m-1 The third switch Q, connected in series in the (m-1)th non-isolated bidirectional DC-DC converter m-1c The source and the third switch Q of the m-th non-isolated bidirectional DC-DC converter mc Between the source and the source. The resonance of the inductor and capacitor can be achieved by controlling the switching transistor of the non-isolated bidirectional DC-DC converter, and the energy can be transferred by using the entire inductor-capacitor series branch. Finally, the energy is transferred to the power electronic battery cell pack that needs energy through the switching transistor.

[0079] In the energy storage system based on series-connected power electronic battery cells of the present invention, the battery management system connects each battery management unit and the energy management system through a communication network, and includes the following functions:

[0080] Hierarchical positioning function: Based on the information reported by each battery management unit, locate the position of each managed battery module in the energy storage system;

[0081] Status identification function: Based on the information reported by each battery module, identify the state of charge (SOC), state of health (SOH), and fault status of the cells in each battery module;

[0082] Control guidance function: Based on the status information of each battery module identified by the status identification function, the function guides the corresponding series-type power electronic battery unit to perform voltage compensation or fault isolation for the corresponding series-type interface converter. Based on the battery system's state of charge (SOC) and fault status, the function informs the energy management system: when the SOC is too high, it instructs the energy management system to reduce energy input to avoid overcharging; when the SOC is too low or some batteries are faulty, it instructs the energy management system to reduce energy output to avoid over-discharging. When there is a large SOC deviation between groups, the function controls the group with the highest total SOC, selecting some units as hot standby. These are generally not added to the energy storage system, but only used to replace faulty units within the group. Simultaneously, the function instructs the energy management system to reduce input and output power levels to match the input and output capabilities of the remaining power electronic battery units. Once the average SOC of the group with the highest total SOC reaches a level close to that of other groups after reducing the number of modules, the hot standby modules are restored, and the converters within the group are notified to achieve SOC balancing within the group. When the inter-group equalization circuit is selected, the inter-group equalization converter can be directly controlled to achieve the corresponding inter-group equalization.

[0083] In the energy storage system based on series-type power electronic battery cells of the present invention, the DC-AC converter, energy management system, and grid-side transformer shall include the following functions:

[0084] Grid connection control function: The energy management system can control the DC-AC converter to track the grid voltage phase and control the output waveform of the DC-AC converter so that the output can be connected to the grid through the grid-side transformer;

[0085] Special auxiliary functions: The energy management system can control the amplitude and phase of the DC-AC converter output waveform according to the application needs of the energy storage system, so as to realize the functions of reactive power compensation, peak shaving and frequency regulation, inertia support, etc. on the grid side.

[0086] Figure 8 This is a flowchart illustrating the operation mode of an energy storage system based on a series-connected power electronic battery cell, according to an embodiment of the present invention. (Refer to...) Figure 8The control methods of the series interface converter include the following categories:

[0087] Direct bypass: When the battery management system informs the series-connected power electronic battery cell that the battery modules in the same group are in almost the same state, no operation is required. At this time, the second switching element can be directly closed to bypass the bidirectional DC-DC converter body, and the current flows directly through the mechanical switch in the second switching element.

[0088] Voltage regulation: When the battery management system informs the series-connected power electronic battery cell that there is a significant difference in the state of the battery module within the control unit compared to other battery modules in the same group, such as if the state of charge (SOC) of the module is more than 1% higher than the average SOC of other battery modules in the group, the series-connected interface converter within the series-connected power electronic battery cell can perform voltage regulation control based on this SOC difference. The specific adjustment steps are as follows:

[0089] Step 1: Close the mechanical switch in the first switching element and the power electronic switch in the second switching element;

[0090] Step 2: Disconnect the mechanical switch inside the second switching element;

[0091] Step 3: Disconnect the power electronic switch inside the second switching element. At this point, the power circuit is connected to the output side of the series interface converter.

[0092] Step 4: Starting from zero output, gradually increase the output voltage of the series interface converter to raise the power output port voltage of the series-connected power electronic battery cell, enabling this cell to output power to other series-connected power electronic battery cells in the same group. The series interface converter operates in current-limiting mode, monitoring the output current to limit it from exceeding the maximum output current of the battery module, thereby determining the converter's output voltage at this point.

[0093] Step 5: When the SOC of the battery module in the series-connected power electronic battery cell is almost the same as that of the other battery modules in the group, reduce the output voltage of the series-connected interface converter to 0, close the power electronic switch in the first switching element and the mechanical switch in the second switching element, open the mechanical switch in the first switching element, and open the power electronic switch in the first switching element. At this time, the output side of the bidirectional DC-DC converter body has been bypassed from the power circuit.

[0094] Fault Clearance: When the battery management system informs the series-connected power electronic battery cell that there is an internal fault in the battery module within the control unit, the series interface converter within the series-connected power electronic battery cell needs to perform fault clearance. The specific fault clearance steps are as follows: close the power electronic switch within the second switching element to enable freewheeling, disconnect the mechanical switch within the second switching element, and finally disconnect the power electronic switch within the second switching element. At this point, since neither the first nor the second switching element is connected to the circuit, the series-connected power electronic battery cell has been disconnected from the energy storage system.

[0095] Although various embodiments of the invention have been described above, it should be understood that they are presented by way of example only and not as limitations. It will be apparent to those skilled in the art that various combinations, modifications, and alterations can be made without departing from the spirit and scope of the invention. Therefore, the breadth and scope of the invention disclosed herein should not be limited by the exemplary embodiments disclosed above, but should be defined solely by the appended claims and their equivalents.

Claims

1. A series-connected power electronic battery cell, comprising: Battery module; as well as A series interface converter includes an input port and an output port. The input port includes a positive input terminal and a negative input terminal, and the output port includes a positive output terminal and a negative output terminal. The positive terminal of the battery module is connected to the negative output terminal of the series interface converter. The positive output terminal of the series interface converter and the negative terminal of the battery module serve as the positive and negative terminals for the power output of the series-type power electronic battery unit. The series-type interface converter includes a bidirectional DC-DC converter, a first switching element, and a second switching element. The input side of the bidirectional DC-DC converter is directly connected to the input port. The positive terminal of the output side of the bidirectional DC-DC converter is connected to one end of the first switching element, and the negative terminal of the output side of the bidirectional DC-DC converter is connected to one end of the second switching element and the negative output terminal. The other ends of the first and second switching elements are connected to each other and connected to the positive output terminal. The first and second switching elements include a mechanical switch and a bidirectional switch connected in parallel. The serial interface converter operates in the following modes: Direct bypass: When the battery management system informs the series-connected power electronic battery cell that the battery modules in the same group are in basically the same state, no operation is required. The mechanical switch of the second switching element is directly closed to bypass the bidirectional DC-DC converter, and the current flows directly through the mechanical switch in the second switching element. Voltage regulation: When the battery management system informs the series-connected power electronic battery cell that the state of the battery modules within the cell differs from that of other battery modules in the same group, the series-connected interface converter within the cell performs voltage regulation control, including: Close the mechanical switch in the first switching element and the bidirectional switch in the second switching element; Disconnect the mechanical switch within the second switching element; Disconnect the bidirectional power electronic switch in the second switching element. At this time, the output side of the bidirectional DC-DC converter body is connected to the power circuit. Starting from 0 output, the output voltage of the bidirectional DC-DC converter is gradually increased to raise the power output port voltage of the series-connected power electronic battery cell, so that the series-connected power electronic battery cell can output power to other series-connected power electronic battery cells in the same group. The bidirectional DC-DC converter operates in current-limiting mode. By monitoring the output current on the output side, the output current is limited to not exceed the maximum output current of the battery module, thereby determining the output voltage of the converter at this time. When the SOC of the battery module of the series-type power electronic battery cell is basically consistent with the SOC of other battery modules in the same group, reduce the output voltage of the bidirectional DC-DC converter to 0, close the bidirectional switch in the first switching element and the mechanical switch in the second switching element, open the mechanical switch in the first switching element, and open the bidirectional switch in the first switching element. At this time, the output side of the bidirectional DC-DC converter body has been bypassed from the power circuit. Fault clearance: When the battery management system informs the series-connected power electronic battery cell that there is an internal fault in the battery module within the series-connected power electronic battery cell, the bidirectional switch in the second switching element is closed to enable the freewheeling function, the mechanical switch in the second switching element is disconnected, and finally the bidirectional switch in the second switching element is disconnected. At this time, since neither the first nor the second switching element is connected to the circuit, the series-connected power electronic battery cell has been disconnected from the energy storage system.

2. The series-connected power electronic battery cell as described in claim 1, characterized in that, The positive input terminal and negative input terminal are respectively connected to the positive and negative terminals of the battery module or the positive and negative terminals of the common DC bus capacitor.

3. The series-connected power electronic battery cell as described in claim 1, characterized in that, It also includes a battery management unit, which is connected to the battery module. The battery management unit includes: Sensors that measure the voltage, current, pressure and / or temperature of the battery cells within the corresponding battery module, used for reading information on the voltage, current, pressure and / or temperature of the battery cells within the battery module and storing historical information; The external communication port is used for exchanging status and control information.

4. An energy storage system, comprising: Multiple series-connected power electronic battery cells as described in any one of claims 1 to 3, Multiple series-connected power electronic battery cells are connected in parallel to form a group, and multiple groups are connected in series to form an energy storage system.

5. The energy storage system as described in claim 4, characterized in that, Each series-connected power electronic battery cell includes a common DC bus capacitor, and the positive and negative terminals of the input port of the series-connected interface converter are connected to the positive and negative terminals of the common DC bus capacitor.

6. The energy storage system as described in claim 4, characterized in that, In each group of series-connected power electronic battery cells, the positive and negative terminals of the input port of the series-connected interface converter are connected to the positive and negative terminals of the corresponding battery module.

7. The energy storage system as described in claim 4, characterized in that, The positive and negative buses of each group of power electronic battery cells are connected to the input of a corresponding isolated bidirectional DC-DC converter, and the output of each group of power electronic battery cells is connected to a common bus.

8. The energy storage system as described in claim 4, characterized in that, The positive and negative buses of each series-connected power electronic battery cell are connected to the input of a corresponding non-isolated bidirectional DC-DC converter. Different non-isolated bidirectional DC-DC converters transfer energy from one series-connected power electronic battery cell to another series-connected power electronic battery cell through energy storage elements.

9. The energy storage system as described in claim 8, characterized in that, Each non-isolated bidirectional DC-DC converter includes a first switch, a second switch, and a third switch. The first and second switches are connected in series between the positive and negative buses of a corresponding set of series-connected power electronic battery cells. One end of the third switch is connected to the connection terminal between the first and second switches, and the other end of the third switch is connected to the other end of the third switch of an adjacent non-isolated bidirectional DC-DC converter through a series-connected inductor and capacitor. The process involves controlling the switching transistors of a non-isolated bidirectional DC-DC converter to achieve resonance between the inductor and capacitor. Energy is then transferred through the entire inductor-capacitor series branch. Finally, the energy is transferred to the power electronic battery cell array that requires energy through the switching transistors.

10. The energy storage system as described in claim 4, characterized in that, Also includes: Battery management system, DC-AC converter, energy management system, and grid-side transformer. The battery management system is connected to the battery management unit and the energy management system, and the energy management system is also connected to the DC-AC converter at the output port.

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