Cell equalization circuit, energy storage system and equalization method
By combining the cell balancing circuit and the battery management system, energy redistribution between batteries is achieved, solving the inconsistency problem after batteries are connected in series, and improving the balancing efficiency and energy utilization of the energy storage system.
Patent Information
- Application Number
- CN202410638694.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-05-22
- Publication Date
- 2025-11-25
AI Technical Summary
In large-scale energy storage systems, the inconsistency of batteries connected in series leads to limited overall performance, and existing equalization methods suffer from problems such as large energy loss or low efficiency.
A cell balancing circuit is adopted, which uses a voltage conversion module with parallel input and series output, combined with a voltage stabilizing capacitor and a battery management system to achieve energy redistribution and balancing among batteries.
It improves balancing efficiency, reduces energy loss, avoids energy waste, supports discharging, charging and offline balancing, and enhances the overall performance of the battery pack.
Smart Images
Figure CN121012140A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of energy storage, and particularly relates to a battery cell equalization circuit and an energy storage system equalization method. BACKGROUND
[0002] At present, the capacity demand of large-scale energy storage systems on energy storage stacks is increasing, and a large number of batteries in series in the stack becomes the main means for capacity expansion of the energy storage system. However, the inconsistency of each battery after being connected in series becomes a restricting factor for the overall performance of the stack. When a single battery in the stack reaches the charge / discharge cutoff voltage, the entire stack has to stop charging / discharging, otherwise it will cause battery failure and even cause fire accidents. That is, when one of the hundreds of batteries has a problem, the entire system has to be shut down.
[0003] The current equalization methods mainly include passive equalization and active equalization. The passive equalization dissipates the energy of the battery with higher energy through the heating of a resistor, which has the disadvantages of large energy loss and high risk of thermal runaway. The active equalization transfers the energy of the battery with higher energy to the battery with lower energy through a capacitor or an inductor, which causes large energy loss in the transfer process, and it is difficult to directly transfer energy between two non-adjacent batteries, so the equalization efficiency is low. SUMMARY
[0004] The application aims to solve the problems in the prior art, and provides a battery cell equalization circuit, which can improve the equalization efficiency and reduce energy loss.
[0005] The application is achieved by the following technical scheme: a battery cell equalization circuit, comprising a battery string formed by battery cells connected in series, each battery cell being provided with a corresponding voltage conversion module, the input end of the voltage conversion module being connected in parallel with the battery cell, the output ends of the voltage conversion modules being connected in series to form an equalization branch, and each voltage conversion module being connected in parallel with a voltage stabilizing capacitor; the positive end of the battery string serving as a first charge / discharge end, the positive end of the equalization branch serving as a second charge / discharge end, the equalization branch being connected in parallel with the battery string, and the equalization branch being charged or discharged through the first charge / discharge end or the second charge / discharge end.
[0006] Further, the voltage conversion module is an isolated switching power supply module.
[0007] Further, the voltage conversion module is a flyback switching power supply module or a forward switching power supply module.
[0008] The application further provides an energy storage system comprising the battery cell equalization circuit.
[0009] Furthermore, it also includes a battery management system, which monitors the operating status parameters of each cell and controls the voltage conversion module to balance the cells according to the operating status of the cells.
[0010] Furthermore, each voltage conversion module is equipped with a corresponding equalization controller and a cell monitoring module. The cell monitoring module is used to monitor the operating status of the corresponding cell in real time, and the equalization controller is used to control the voltage conversion module to equalize the cell according to the operating status parameters of the cell.
[0011] Furthermore, the operating status parameters of the battery cell include voltage.
[0012] Compared with the prior art, the beneficial effects of the present invention include:
[0013] 1. This invention utilizes a balancing branch composed of voltage conversion modules to perform parallel current sharing of the battery string, thereby outputting a portion of the energy from the battery string through the balancing branch. Since the voltage conversion modules in the balancing branch are connected in series, the output current of each module is equal. However, because the voltage conversion modules can adjust the output voltage, the output power can be adjusted, which means adjusting the power output from the corresponding battery cell through the balancing branch.
[0014] 2. The cell balancing circuit of the present invention can support discharge balancing, charging balancing and offline balancing.
[0015] 3. During discharge, increase the output power of cells with higher charge or voltage, and decrease the output power of cells with lower charge or voltage to achieve discharge balance.
[0016] 4. During charging or offline operation, the battery cells with higher charge or voltage are released through the voltage conversion module to charge the voltage regulator capacitor, and then released back to the battery string through the voltage regulator capacitor to redistribute the excess charge, thereby achieving a balancing effect.
[0017] 5. This invention performs balancing during the discharge process, and can directly output the unbalanced energy to the load, without wasting energy, reducing energy loss and improving balancing efficiency.
[0018] 6. This invention does not require point-to-point balancing between battery cells during the charging process. Instead, it achieves overall balancing through power redistribution, thereby improving balancing efficiency. Attached Figure Description
[0019] Figure 1 This is a schematic diagram of the energy storage system in Example 1;
[0020] Figure 2 The above is a simulation test diagram of the flyback switching power supply module used as the voltage conversion module in Example 1. Detailed Implementation
[0021] In existing technologies, passive balancing suffers from high energy loss, while active balancing suffers from low balancing efficiency. Furthermore, considering circuit complexity and cost issues, active balancing is difficult to achieve balancing between individual cells and can often only achieve balancing between battery packs in practical applications.
[0022] To improve equilibrium efficiency and reduce energy loss, refer to Figure 1 As shown, the present invention provides a cell balancing circuit, including a battery string composed of cells BAT1, BAT2...BATn connected in series. Each cell is provided with a corresponding voltage conversion module U1, U2...Un. The input terminal of the voltage conversion module is connected in parallel with the cell, and the output terminals of each voltage conversion module are connected in series to form a balancing branch. The balancing branch is connected in parallel with the battery string.
[0023] The positive terminal of the battery string is used as the first charge / discharge terminal VCC_MAIN, and the positive terminal of the equalization 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.
[0024] In this specific embodiment, grid-connected energy storage power generation is achieved by connecting the first charging / discharging terminal to the energy storage converter PCS.
[0025] This invention utilizes a balancing branch composed of voltage conversion modules to perform parallel current sharing of the battery string, thereby outputting a portion of the battery string's energy through the balancing branch. Since the voltage conversion modules in the balancing branch are connected in series, the output current of each module is equal. However, because the voltage conversion modules can adjust their output voltage, the output power can be adjusted, thus regulating the power output from the corresponding battery cell through the balancing branch.
[0026] During discharge, the battery string and the balancing branch discharge simultaneously and converge at the first charge / discharge terminal VCC_MAIN for output. If voltage or charge imbalance occurs during charging, the output power of the cell with higher charge or voltage is increased, while the output power of the cell with lower charge or voltage is decreased, thus quickly achieving a balancing effect.
[0027] During charging, 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 charges the voltage regulator capacitor. If the voltage or charge of the cells is unbalanced during charging, the charge of the cell with higher charge or voltage is output to the corresponding voltage regulator capacitor through the switching power supply module, thereby extending the charging time of that cell and preventing it from being fully charged before the other cells, which would force the entire battery string to stop charging.
[0028] In offline mode, meaning the battery string neither receives current through the first charging / discharging terminal VCC_MAIN nor outputs current through the first charging / discharging terminal VCC_MAIN, if the cells in the battery string are unbalanced, the charge of the cell with higher charge or voltage is output to the corresponding voltage regulator capacitor through the switching power supply module. After the voltage regulator capacitor is fully charged, it discharges to the battery string through the balancing circuit, which is equivalent to redistributing the excess charge of the cells to the cells in the battery string to achieve a balancing effect.
[0029] Because the output power of each cell can be adjusted simultaneously during the discharge process, compared to the charging and offline processes which only adjust the cells with higher charge or higher cell capacity, the balancing efficiency during the discharge process is higher.
[0030] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.
[0031] Example 1
[0032] This embodiment provides an energy storage system, including the cell balancing circuit of the present invention, and a battery management system (BMS). The battery management system monitors the operating status parameters of each cell and controls the voltage conversion module to balance the cells according to the operating status of the cells. The battery management system monitors the operating status parameters of each cell in real time, such as voltage, SOC, and temperature.
[0033] This embodiment uses a switching power supply module as the voltage conversion module. The types of switching power supply modules that can be used include, but are not limited to, flyback switching power supply modules or forward switching power supply modules. The main difference between flyback and forward switching power supply modules is that the output voltage of a flyback switching power supply module decreases as the duty cycle increases, while the output voltage of a forward switching power supply module increases as the duty cycle increases. Duty cycle control can be achieved through PWM pulse width modulation.
[0034] The following explanation uses a flyback switching power supply module as an example.
[0035] refer to Figure 2 As shown, the flyback switching power supply module includes a MOSFET M1, a transformer T2, a diode D1, and a capacitor C1. The flyback switching power supply module receives the battery voltage through its VCC and GND terminals. By controlling the duty cycle of the MOSFET M1, the output voltage of the flyback switching power supply module can be adjusted. Figure 2 As shown, the input voltage is 3V, the duty cycle is 70%, and the output voltage is 2.5V.
[0036] When an imbalance is detected between battery cells based on their operating parameters, a balancing mode is selected according to the operating status of the energy storage system.
[0037] In this embodiment, when the deviation of the average voltage of the cells exceeds the allowable range, an imbalance is considered to have occurred.
[0038] When the energy storage system is in a discharging state, the first equalization mode is adopted: each voltage conversion module is turned on, and the output voltage of the corresponding voltage conversion module is adjusted according to the operating status parameters of each cell. The higher the voltage of the cell, the greater the output voltage of the corresponding voltage conversion module.
[0039] The first equalization mode follows the principle of "more output from cells with more capacity and less output from cells with less capacity," which avoids the situation where cells with more capacity and cells with less capacity output the same amount of power at the same time, resulting in cells with less capacity discharging before cells with more capacity.
[0040] When the energy storage system is in charging or offline state, the second equalization mode is adopted: the voltage conversion module corresponding to the target cell is turned on. The target cell refers to the cell whose operating state parameters are higher than the average value. The output voltage of the corresponding voltage conversion module is adjusted according to the operating state parameters of the target cell, and the output voltage of the voltage conversion module corresponding to the cell with higher voltage is greater.
[0041] The second balancing mode practices the principle of "reducing excess capacity and supplementing deficiency capacity". It transfers the power of cells with more power to the voltage regulator capacitor, and then the voltage regulator capacitor charges the battery string, redistributing the excess power so that the excess power of cells with more power is transferred to cells with less power.
[0042] Both the first and second equalization modes use the voltage gradient descent method to adjust the output voltage of the voltage conversion module.
[0043] The cells are sorted in descending order of voltage. In the first balancing mode, all cells in the battery string are sorted, while in the second balancing mode, only the target cells are sorted.
[0044] Calculate the output voltage of the corresponding voltage conversion module based on the cell order:
[0045] V o,i =V max -Δv(i-1)
[0046] In the formula, i represents the cell sequence number, i≥1; V o,i This represents the output voltage of the voltage conversion module corresponding to the i-th cell in the sequence; V max Δv represents the maximum output voltage of the voltage conversion module; Δv represents the voltage descent gradient.
[0047] In the voltage gradient descent method, the higher the voltage of the battery cell, the greater the output voltage of the corresponding voltage converter, and thus the greater the output power. Conversely, the lower the voltage of the battery cell, the lower the output voltage of the corresponding voltage converter, and thus the lower the output power.
[0048] Example 2
[0049] This embodiment provides an energy storage system, including the cell balancing circuit of the present invention. Each voltage conversion module is provided with a corresponding balancing controller and a cell monitoring module. The cell monitoring module is used to monitor the operating status of the corresponding cell in real time, and the balancing controller is used to control the voltage conversion module to balance the cell according to the operating status parameters of the cell.
[0050] This embodiment uses a forward converter switching power supply module as the voltage conversion module. Both forward and flyback switching power supply modules are isolated switching power supply modules. The difference between isolated and non-isolated switching power supply modules is that in isolated switching power supply modules, the input and output circuits are isolated via a transformer, with no direct electrical connection. Isolated switching power supply modules offer higher safety.
[0051] During the discharge process, the cell monitoring module collects the voltage of each cell in the battery string. The equalization controller compares the voltage of each cell with the voltage threshold. For cells with voltages higher than the voltage threshold, the output power needs to be increased, that is, the duty cycle of the forward switching power supply module needs to be increased. For cells with voltages lower than the voltage threshold, the output power needs to be reduced, that is, the duty cycle of the forward switching power supply module needs to be reduced.
[0052] When an imbalance is detected between battery cells based on their operating parameters, a balancing mode is selected according to the operating status of the energy storage system.
[0053] In this embodiment, when the deviation of the voltage threshold between battery cells exceeds the allowable range, an imbalance is considered to have occurred.
[0054] When the energy storage system is in a discharging state, the first equalization mode is adopted: each voltage conversion module is turned on, and the output voltage of the corresponding voltage conversion module is adjusted according to the operating status parameters of each cell. The higher the voltage of the cell, the greater the output voltage of the corresponding voltage conversion module.
[0055] The first equalization mode follows the principle of "more output from cells with more capacity and less output from cells with less capacity," which avoids the situation where cells with more capacity and cells with less capacity output the same amount of power at the same time, resulting in cells with less capacity discharging before cells with more capacity.
[0056] When the energy storage system is in charging or offline state, the second equalization mode is adopted: the voltage conversion module corresponding to the target cell is turned on. The target cell refers to a cell whose operating state parameters are higher than the cell voltage threshold. The output voltage of the corresponding voltage conversion module is adjusted according to the operating state parameters of the target cell, and the output voltage of the voltage conversion module corresponding to the cell with higher voltage is greater.
[0057] The second balancing mode practices the principle of "reducing excess capacity and supplementing deficiency capacity". It transfers the power of cells with more power to the voltage regulator capacitor, and then the voltage regulator capacitor charges the battery string, redistributing the excess power so that the excess power of cells with more power is transferred to cells with less power.
[0058] Both the first and second equalization modes adjust the output voltage of the voltage conversion module based on the voltage deviation, which refers to the deviation between the cell voltage and the cell voltage threshold.
[0059] If the voltage deviation is greater than 0, the output voltage will increase, and the larger the deviation, the larger the output voltage; if the voltage deviation is less than 0, the output voltage will decrease, and the smaller the deviation, the smaller the output voltage.
[0060] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.
[0061] In the description of this invention, unless otherwise stated, the terms "upper," "lower," "left," "right," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.
[0062] The above technical solution is only one embodiment of the present invention. For those skilled in the art, based on the principles disclosed in the present invention, it is easy to make various types of improvements or modifications, and not limited to the technical solutions described in the specific embodiments of the present invention. Therefore, the foregoing description is only a preferred option and is not restrictive.
Claims
1. A cell equalization circuit, comprising: The battery string comprises a plurality of battery cells connected in series, each battery cell is provided with a corresponding voltage conversion module, the input end of the voltage conversion module is connected in parallel with the battery cell, the output ends of the voltage conversion modules are connected in series to form an equalization branch, and each voltage conversion module is connected in parallel with a voltage stabilizing capacitor; the positive end of the battery string is used as a first charging / discharging end, the positive end of the equalization branch is used as a second charging / discharging end, the equalization branch is connected in parallel with the battery string, and the battery string is charged or discharged through the first charging / discharging end or the second charging / discharging end.
2. The cell balancing circuit of claim 1, wherein, The voltage conversion module is an isolated switching power supply module.
3. The cell balancing circuit of claim 2, wherein, The voltage conversion module is a flyback switching power supply module or a forward switching power supply module.
4. An energy storage system characterized by, The battery cell equalization circuit comprises the battery cell equalization circuit according to any one of claims 1 to 3.
5. The energy storage system of claim 4, wherein, The battery management system is further used for monitoring the operating state parameters of the battery cells and controlling the output voltage of the voltage conversion module according to the operating state of the battery cells to equalize the battery cells.
6. The energy storage system of claim 5, wherein, The equalization controller and the battery cell monitoring module are provided for each voltage conversion module, the battery cell monitoring module is used for monitoring the operating state of the corresponding battery cell in real time, and the equalization controller is used for controlling the output voltage of the voltage conversion module according to the operating state parameters of the battery cell to equalize the battery cell.
7. The energy storage system of claim 7 or 8, wherein, The operating state parameters of the battery cell include voltage or power.
8. A method of equalizing an energy storage system as claimed in claim 4, characterized in that, The method comprises the following steps: When it is determined that the battery cells are not balanced according to the operating state parameters of the battery cells, the equalization mode is selected according to the working state of the energy storage system: When the energy storage system is in a discharging state, the first equalization mode is adopted: each voltage conversion module is turned on, the output voltage of the corresponding voltage conversion module is adjusted according to the operating state parameters of each battery cell, and the output voltage of the voltage conversion module corresponding to the battery cell with a higher voltage is greater; When the energy storage system is in a charging state or an offline state, the second equalization mode is adopted: the voltage conversion module corresponding to the target battery cell is turned on, the target battery cell refers to the battery cell with an operating state parameter higher than the average value or the threshold value, the output voltage of the corresponding voltage conversion module is adjusted according to the operating state parameters of the target battery cell, and the output voltage of the voltage conversion module corresponding to the battery cell with a higher voltage is greater.
9. The equalization method of an energy storage system according to claim 8, wherein, The voltage gradient descent method is used to adjust the output voltage of the voltage conversion module: The battery cells are sorted in the order of high to low voltage; The output voltage of the corresponding voltage conversion module is calculated according to the sorting of the battery cells: V o,i = V max - Δv(i-1) In the formula, i represents the sequence position of the battery cell, i≥1; V o,i represents the output voltage of the voltage transformation module corresponding to the battery cell with the i-th sequence position; V max represents the maximum output voltage of the voltage transformation module; and Δv represents the voltage drop gradient.