Cell equalization circuit and energy storage system

Abstract

The utility model belongs to the technical field of energy storage, and particularly relates to a battery cell equalization circuit and an energy storage system, comprising a battery string formed by serially connecting battery cells, each battery cell is provided with a voltage conversion module in one-to-one correspondence, the input ends of the voltage conversion modules are connected in parallel with the battery cells, and the output ends of the voltage conversion modules are serially connected to form an equalization branch. And the equalization branch is connected with the battery series and parallel. According to the utility model, the battery string can be shunted in parallel through the equalization branch circuit formed by the voltage conversion modules, so that part of energy of the battery string is output through the equalization branch circuit. When the electric quantity or the voltage of the battery cell is unbalanced, the output power of the battery cell is adjusted through the voltage conversion module for equalization, and discharging equalization, charging equalization and off-line equalization are supported.

Description

Technical Field

[0001] The utility model belongs to the technical field of energy storage, and specifically relates to a battery cell balancing circuit and an energy storage system. Background Art

[0002] At present, large-scale energy storage systems have an increasing demand for the capacity of energy storage stacks. The series connection of a large number of batteries in the stack has become the main means of expanding the capacity of the energy storage system. However, the inconsistency of each battery after the series connection has become a limiting factor in the overall performance of the stack. When a single battery in the stack reaches the charge and discharge cut-off voltage, the entire stack has to stop charging and discharging, otherwise it will cause battery failure and even cause accidents such as fire. In other words, if there is a problem with one of the hundreds of batteries, the entire system must fail and shut down.

[0003] The current balancing methods are mainly divided into passive balancing and active balancing: Passive balancing is to dissipate the energy of the battery with higher energy through resistance heating, which has the disadvantages of large energy loss and high risk of thermal runaway; active balancing is to transfer the energy of the battery with higher energy to the battery with lower energy through capacitors or inductors. The transfer process causes large energy loss. For two non-adjacent batteries, it is difficult to directly transfer energy, and the balancing efficiency is low. Utility Model Content

[0004] The purpose of the utility model is to solve the above-mentioned problems existing in the prior art and provide a cell balancing circuit that can improve balancing efficiency and reduce energy loss.

[0005] The utility model is realized through the following technical scheme: a battery cell balancing circuit, comprising a battery string formed by connecting battery cells in series, each battery cell is provided with a one-to-one corresponding voltage conversion module, the input end of the voltage conversion module is connected in parallel with the battery cell, the output ends of each voltage conversion module are connected in series to form a balancing branch, and the balancing branch is connected in parallel with the battery string; the positive end of the battery string serves as a first charge / discharge end, and the positive end of the balancing branch serves as a second charge / discharge end.

[0006] Furthermore, the voltage conversion module is an isolated switching power supply module.

[0007] Furthermore, the voltage conversion module is a flyback switching power supply module or a forward switching power supply module.

[0008] Furthermore, a voltage stabilizing module is connected in parallel to the output end of each voltage conversion module, and the voltage stabilizing module is a voltage stabilizing capacitor.

[0009] Furthermore, it also includes a battery management system, which is used to monitor the operating status parameters of each battery cell and control the voltage conversion module according to the operating status of the battery cell to balance the battery cells.

[0010] Furthermore, a corresponding balancing controller and a battery cell monitoring module are provided corresponding to each voltage conversion module. The battery cell monitoring module is used to monitor the operating status of the corresponding battery cell in real time, and the balancing controller is used to control the voltage conversion module according to the operating status parameters of the battery cell to balance the battery cell.

[0011] Furthermore, the operating state parameter of the battery cell includes voltage.

[0012] Compared with the prior art, the beneficial effects of the utility model include:

[0013] 1. The utility model can shunt the battery string in parallel through the balancing branch composed of voltage conversion modules, so that part of the energy of the battery string is output through the balancing branch. The voltage conversion modules in the balancing branch are connected in series, so the output current of each voltage conversion module is equal, but because the voltage conversion module can adjust the output voltage, the output power can be adjusted, that is, the power output of the corresponding battery cell from the balancing branch can be adjusted.

[0014] 2. The cell balancing circuit of the utility model can support discharge balancing, charge balancing and offline balancing.

[0015] 3. During discharge, the output power of cells with higher power or voltage is increased, and the output power of cells with lower power or voltage is reduced, so as to achieve balanced discharge.

[0016] 4. During the charging process or in the offline state, the power of the battery cell with higher power or voltage is released through the voltage conversion module to charge the voltage stabilizing capacitor, and then released back to the battery string through the voltage stabilizing capacitor to redistribute the excess power to achieve a balancing effect.

[0017] 5. The utility model performs balancing during the discharge process and can directly output the unbalanced energy to the load, which will not cause energy waste, reduces energy loss, and improves balancing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the energy storage system in Example 1;

[0019] Figure 2 This is a simulation test diagram of using a flyback switching power supply module as a voltage conversion module in Example 1. DETAILED DESCRIPTION

[0020] In the prior art, passive balancing has the disadvantage of large energy loss, and active balancing has the disadvantage of low balancing efficiency. In addition, considering the circuit complexity and cost issues, active balancing is difficult to achieve balance between battery cells, and in practical applications it can often only achieve balance between battery packs.

[0021] In order to improve the balancing efficiency and reduce energy loss, refer to Figure 1 As shown, the utility model provides a battery cell balancing circuit, including a battery string formed by battery cells BAT1, BAT2...BATn connected in series, each battery cell is provided with a one-to-one corresponding voltage conversion module U1, U2...Un, the input end of the voltage conversion module is connected in parallel with the battery cell, and the output end of each voltage conversion module is connected in series to form a balancing branch, and the balancing branch is connected in parallel with the battery string. The output end of each voltage conversion module is connected in parallel with a voltage stabilizing module, and the voltage stabilizing module is a voltage stabilizing capacitor.

[0022] In this specific implementation, the voltage conversion module is an isolated switching power supply module, such as a flyback switching power supply module, a forward switching power supply module, and the like.

[0023] Both the forward switching power supply module and the flyback switching power supply module belong to the isolated switching power supply module. The difference between the isolated switching power supply module and the non-isolated switching power supply module is that the input and output circuits of the isolated switching circuit module are isolated by a transformer, and there is no direct electrical connection. The isolated switching power supply module has higher safety. The cost of the flyback switching power supply module is lower than that of the forward switching power supply module, which is conducive to promotion and application.

[0024] The positive terminal of the battery string is used as the first charge / discharge terminal VCC_MAIN, and the positive terminal of the balancing branch is used as the second charge / discharge terminal OUT1. The first charge / discharge terminal is used to output a large current, and the second charge / discharge terminal is used to output a small current.

[0025] In this specific implementation, the first charging / discharging end is connected to the energy storage converter PCS to achieve grid-connected energy storage power generation.

[0026] The utility model can parallel shunt the battery string through the balancing branch composed of voltage conversion modules, so that part of the energy of the battery string is output through the balancing branch. The voltage conversion modules in the balancing branch are connected in series, so the output current of each voltage conversion module is equal, but because the voltage conversion module can adjust the output voltage, the output power can be adjusted, that is, the output power output from the balancing branch of the corresponding battery cell can be adjusted.

[0027] During the discharge process, the battery string and the balancing branch discharge outward at the same time and merge to the first charge / discharge terminal VCC_MAIN for external output. If the voltage or power of the battery cells is unbalanced during the charging process, the output power of the battery cells with higher power or voltage is increased, and the output power of the battery cells with lower power or voltage is reduced, so that the balancing effect can be achieved quickly.

[0028] During the charging process, the external current is input from the first charge / discharge terminal VCC_MAIN and flows to the battery string and the balancing branch respectively. The current flowing into the balancing branch will charge the voltage stabilizing capacitor. If the voltage or power of the battery cell is uneven during the charging process, the power of the battery cell with higher power or voltage will be output to the corresponding voltage stabilizing capacitor through the switching power supply module, thereby extending the charging time of the battery cell and preventing the battery cell from being fully charged before other batteries, forcing the entire battery string to stop charging.

[0029] In the offline state, that is, the battery string neither inputs current through the first charge / discharge terminal VCC_MAIN nor outputs current through the first charge / discharge terminal VCC_MAIN, if the cells in the battery string are unbalanced, the power of the cell with higher power or voltage is output to the corresponding voltage stabilizing capacitor through the switching power supply module. After the voltage stabilizing capacitor is fully charged, it is discharged to the battery string through the balancing circuit, which is equivalent to redistributing the excess power of the cell to the cells in the battery string to achieve a balancing effect.

[0030] Since the output power of each battery cell can be adjusted simultaneously during the discharge process, the balancing efficiency during the discharge process is higher than that during the charging and offline processes, when only the battery cells with higher power or battery cells are adjusted.

[0031] The utility model is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0032] Example 1

[0033] This embodiment provides an energy storage system, including the battery cell balancing circuit of the utility model, and also includes a battery management system (Battery Management System, BMS), the battery management system is used to monitor the operating state parameters of each battery cell and control the voltage conversion module according to the operating state of the battery cell to balance the battery cell. The battery management system monitors the operating state parameters of each battery such as voltage, SOC, temperature, etc. in real time.

[0034] This embodiment uses a switching power supply module as a voltage conversion module, and the types of switching power supply modules that can be used include but are not limited to a flyback switching power supply module or a forward switching power supply module. The main difference between a flyback switching power supply module and a forward switching power supply module is that the output voltage of the flyback switching power supply module decreases as the duty cycle increases, while the output voltage of the forward switching power supply module increases as the duty cycle increases. Duty cycle control can be achieved through PWM pulse width modulation.

[0035] The following is an explanation using discharge balancing based on a flyback switching power supply module as an example.

[0036] refer to Figure 2As shown, the flyback switching power supply module includes a MOS tube M1, a transformer T2, a diode D1 and a capacitor C1. The flyback switching power supply module inputs the voltage of the battery cell through the VCC terminal and the GND terminal. By controlling the duty cycle of the MOS tube M1 in the flyback switching power supply module, the output voltage of the flyback switching power supply module can be adjusted, such as Figure 2 As shown, the input voltage is 3V, the duty cycle is 70%, and the output voltage is 2.5V.

[0037] During the discharge process, the battery management system collects the voltage of each battery cell in the battery string and calculates the average voltage of the battery cell. For the battery cells with voltage higher than the average voltage, the output power needs to be increased, that is, the duty cycle of the flyback switching power supply module is reduced. For the battery cells with voltage lower than the average voltage, the output power needs to be reduced, that is, the duty cycle of the flyback switching power supply module is increased.

[0038] Example 2

[0039] The present embodiment provides an energy storage system, including the battery cell balancing circuit of the present invention, wherein a corresponding balancing controller and a battery cell monitoring module are provided corresponding to each voltage conversion module, wherein the battery cell monitoring module is used to monitor the operating status of the corresponding battery cell in real time, and the balancing controller is used to control the voltage conversion module according to the operating status parameters of the battery cell to balance the battery cell.

[0040] This embodiment adopts a forward switching power supply module as a voltage conversion module.

[0041] During the discharge process, the battery cell monitoring module collects the voltage of each battery cell in the battery string, and the balancing controller compares the voltage of each battery cell with the voltage threshold. For batteries with voltage higher than the voltage threshold, it is necessary to increase the output power, that is, increase the duty cycle of the forward switching power supply module; for batteries with voltage lower than the voltage threshold, it is necessary to reduce the output power, that is, reduce the duty cycle of the forward switching power supply module.

[0042] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] In the description of the present invention, unless otherwise specified, the terms "upper", "lower", "left", "right", "inside", "outside", etc. indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0044] The above technical solution is only one implementation method of the utility model. For technicians in this field, it is easy to make various types of improvements or modifications based on the principles disclosed in the utility model, and it is not limited to the technical solution described in the above specific embodiments of the utility model. Therefore, the above description is only preferred and does not have a restrictive meaning.

Claims

1. A cell balancing circuit, characterized in that: It comprises a battery string formed by connecting battery cells in series, each battery cell is provided with a one-to-one corresponding voltage conversion module, the input end of the voltage conversion module is connected in parallel with the battery cell, the output ends of each voltage conversion module are connected in series to form a balancing branch, and the balancing branch is connected in parallel with the battery string.

2. The cell balancing circuit according to claim 1, characterized in that: The voltage conversion module is an isolated switching power supply module.

3. The cell balancing circuit according to claim 2, characterized in that: The voltage conversion module is a flyback switching power supply module or a forward switching power supply module.

4. The cell balancing circuit according to claim 1, characterized in that: The output end of each voltage conversion module is connected in parallel with a voltage stabilization module.

5. The cell balancing circuit according to claim 4, characterized in that: The voltage stabilizing module is a voltage stabilizing capacitor.

6. An energy storage system, characterized in that: The invention comprises a cell balancing circuit as claimed in any one of claims 1 to 5.

7. The energy storage system according to claim 6, characterized in that: It also includes a battery management system, which is used to monitor the operating status parameters of each battery cell and control the output voltage of the voltage conversion module according to the operating status of the battery cell to balance the battery cells.

8. The energy storage system according to claim 6, characterized in that: Corresponding to each voltage conversion module, a corresponding balancing controller and a battery cell monitoring module are provided. The battery cell monitoring module is used to monitor the operating status of the corresponding battery cell in real time, and the balancing controller is used to control the output voltage of the voltage conversion module according to the operating status parameters of the battery cell to balance the battery cell.

9. The energy storage system according to claim 7 or 8, characterized in that: The operating state parameters of the battery cell include voltage or power.

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