Battery pack equalizing charging system based on series-parallel connection switching and working method thereof

Abstract

The invention discloses a battery pack equalizing charging system based on series-parallel connection switching and a working method thereof, and belongs to the technical field of battery management. The system comprises a battery pack, a voltage detection module for measuring the voltage of each single battery and transmitting a measured voltage signal to an MCU, a series-parallel connection switching module for realizing the switching between the series connection topology and the parallel connection topology of the battery pack, and a bypass equalization module for switching the single batteries reaching an equalization voltage threshold out of a charging loop, the MCU is used for receiving the voltage information of each single battery transmitted by the voltage detection module, executing a preset control algorithm and outputting a control signal; and the charger is used for providing a constant-current charging mode and a constant-voltage charging mode. According to the invention, the voltage difference between monomers is eliminated, and basic conditions of zero-circulation risk are provided for the parallel connection stage; the charging efficiency is improved, and the charging safety is guaranteed; the overall available capacity of the battery pack is improved, the cycle life is prolonged, and safe and reliable system operation is ensured.

Description

Technical Field

[0001] This invention relates to a battery pack equalization charging system based on series-parallel switching and its working method, belonging to the field of battery management technology. Background Technology

[0002] Lithium-ion battery packs, especially lithium iron phosphate battery packs, play a crucial role in the large-scale application of electric vehicles and energy storage systems due to their high safety characteristics and long cycle life. These battery packs typically consist of multiple individual cells connected in series or parallel. In series configurations, due to the inherent slight differences in electrochemical parameters such as capacity and internal resistance between individual cells, the voltage states of each cell will gradually become inconsistent after multiple charge-discharge cycles, resulting in battery pack imbalance.

[0003] The aforementioned imbalance can lead to multiple technical problems: First, the actual usable capacity of the battery pack is significantly reduced; second, high-voltage cells are prone to overcharging during charging and low-voltage cells are prone to over-discharging during discharging, both of which accelerate battery aging and cause safety risks, ultimately leading to performance degradation, shortened cycle life, and reduced safety of the battery pack.

[0004] Existing equalization solutions are mainly divided into two categories: passive equalization and active equalization. Passive equalization technology dissipates excess energy from high-voltage cells as heat through passive devices such as resistors, achieving voltage equalization. However, this process has inherent drawbacks such as low energy utilization and high heat generation. While active equalization technology can achieve higher energy transfer efficiency, it requires complex power conversion circuits, leading to a significant increase in system cost. Furthermore, in the later stages of charging, due to limitations in control strategies or circuit topology, the equalization current is usually small, and the equalization speed is slow, making it difficult to meet the demands of fast charging.

[0005] In addition, to improve charging efficiency, the industry has proposed a technical solution of connecting battery packs in parallel and then charging them with high current. However, when there are differences in the initial voltage of the parallel battery packs, direct parallel connection will cause severe circulating current between the batteries, causing mechanical impact and electrochemical stress on the battery body, posing serious safety hazards and limiting the engineering application of this solution. Summary of the Invention

[0006] To address the problems existing in the background technology, the present invention provides a battery pack equalization charging system based on series-parallel switching and its working method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a battery pack equalization charging system based on series-parallel switching, comprising: The battery pack consists of multiple individual cells BAT1, BAT2, ..., BAT n ; The voltage detection module, integrated in the AFE of the BMS, is connected to the positive and negative terminals of each individual cell to measure the voltage of each individual cell and transmit the measured voltage signal to the MCU. The series-parallel switching module includes multiple relays K1, K2, ..., K n The on / off state of the relay is controlled by the control signal output by the MCU, realizing the switching between series and parallel topologies of the battery pack; The bypass balancing module, which is individually equipped for each individual cell, includes a power MOSFET and a current-limiting resistor, and is used to disconnect individual cells that have reached the balancing voltage threshold from the charging circuit. The MCU, as the core control unit of the entire system, receives the voltage information of each individual battery from the voltage detection module, executes the preset control algorithm, and outputs control signals to control the relay on / off of the series-parallel switching module, the MOSFET on / off of the bypass equalization module, and the start / stop and charging mode switching of the charger. The charger, controlled by the MCU, provides constant current charging mode and constant voltage charging mode to provide stable charging power to the battery pack.

[0008] The present invention discloses a method for operating a battery pack equalization charging system based on series-parallel switching, the method comprising the following steps: S1: After the battery pack has finished discharging and is in a static state, the voltage of all individual cells is detected by the voltage detection module to obtain the initial voltage of each individual cell. S2: The system closes the series circuit relay, opens the parallel circuit relay, configures the battery pack as a series connection, starts the charger to perform series constant current charging of the battery pack, and the voltage detection module continuously monitors the voltage of each individual battery in real time. S3: When the voltage of any single cell reaches the preset equalization voltage threshold, the MCU controls the bypass equalization module corresponding to that single cell to turn on, cutting that single cell out of the series charging circuit. The charging current continues to charge the remaining single cells that have not reached the equalization voltage threshold until the voltage of all single cells reaches the equalization voltage threshold, and the series equalization charging stage ends. S4: The MCU controls the series-parallel switching module to disconnect all series circuit relays and close all parallel circuit relays to switch the battery pack to the parallel connection state; it starts the charger to charge the parallel battery pack with a constant current that is larger than that of series equalization charging, and monitors the total voltage of the battery pack and the temperature of each individual cell during the charging process. S5: When the total voltage of the battery pack reaches the preset full charge voltage threshold and the charging current drops to the cutoff current, charging is complete. S6: The MCU disconnects the charger, disconnects the parallel circuit relay, switches the battery pack back to series mode, and prepares for the next discharge.

[0009] Furthermore, in S5, if the total voltage does not reach the full charge voltage threshold or the current does not drop to the cutoff current after a preset time during parallel charging, the MCU will switch the battery pack back to the series balancing mode and perform individual cell balancing based on the voltage status of each individual battery cell.

[0010] Furthermore, the series balancing mode of S3 and the parallel charging mode of S4 can be repeated a maximum of three times. If the full charge condition is still not met after three cycles, the system will stop charging and record the abnormal individual battery, prompting the user to replace it.

[0011] Compared with the prior art, the beneficial effects of the present invention are: This invention employs a sequential active balancing mechanism during the series charging stage. By using a bypass module, cells that reach the threshold are disconnected from the charging circuit, effectively eliminating voltage differences between cells and providing a foundation for zero circulating current risk in the parallel stage. During the parallel stage, the high-current constant-current fast charging characteristics significantly improve charging efficiency, while real-time monitoring of total voltage and temperature ensures charging safety. The MCU dynamically controls the timing of series-parallel switching and charging mode conversion, combined with a three-cycle protection mechanism and abnormal cell marking function. This improves the overall usable capacity of the battery pack, extends cycle life, and ensures safe and reliable system operation. It resolves the technical contradictions of low energy efficiency in passive balancing, high cost in active balancing, and high circulating current risk in fast charging, achieving a unified improvement in charging speed, balancing efficiency, and safety. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the system structure of the present invention; Figure 2 This is a flowchart of the method of the present invention. Detailed Implementation

[0013] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0014] A battery pack equalization charging system based on series-parallel switching includes: The battery pack consists of multiple individual cells BAT1, BAT2, ..., BAT n It is an energy storage carrier in the charging process and is suitable for lithium-ion batteries (especially lithium iron phosphate batteries). The voltage detection module, integrated into the AFE (Analog Front End) of the BMS (Battery Management System), is connected to the positive and negative terminals of each individual cell. Its core function is to accurately measure the voltage of each individual cell and transmit the measured voltage signal to the MCU (Main Controller) to provide data support for equalization control and charging status judgment. The series-parallel switching module includes multiple relays K1, K2, ..., K n The on / off state of the relay is controlled by the control signal output by the MCU. By combining different on / off states of the relays, the switching between series and parallel topologies of the battery pack can be achieved, meeting the different connection requirements of series equalization charging and parallel fast charging. The bypass equalization module is individually equipped for each individual cell, including power MOSFETs (Q1, Q2, ..., Q...). n ) and current-limiting resistors (R1, R2, ..., R n ), used to cut off individual cells that have reached the equalization voltage threshold from the charging circuit; When the MCU determines that the voltage of a certain single cell has reached the equalization voltage threshold, it outputs a control signal to turn on the corresponding MOSFET. The single cell is then bypassed through the current-limiting resistor, disconnected from the series charging circuit, and overcharged, while ensuring that the charging current continues to charge other single cells.

[0015] The MCU, as the core control unit of the entire system, receives the voltage information of each individual battery from the voltage detection module, executes the preset control algorithm, and outputs control signals to control the relay on / off of the series-parallel switching module, the MOSFET on / off of the bypass equalization module, and the start / stop and charging mode switching of the charger, coordinating the orderly operation of each module to achieve full-process control of equalization charging. The charger, controlled by the MCU, provides constant current charging mode and constant voltage charging mode to provide stable charging power to the battery pack. It provides an appropriate constant current charging current during the series equalization charging stage and a larger constant current charging current during the parallel fast charging stage to meet the fast charging requirements.

[0016] The present invention discloses a method for operating a battery pack equalization charging system based on series-parallel switching, the method comprising the following steps: S1: After the battery pack has finished discharging and is in a static state, the voltage of all individual cells is detected by the voltage detection module to obtain the initial voltage of each individual cell; assuming that the voltage is distributed between 2.5V and 2.9V at this time.

[0017] S2: The system closes the series circuit relay, opens the parallel circuit relay, configures the battery pack as a series connection, starts the charger to perform series constant current charging of the battery pack, and the voltage detection module continuously monitors the voltage of each individual battery in real time. S3: When the voltage of any single cell reaches the preset equalization voltage threshold (e.g., 2.9V), the MCU controls the bypass equalization module corresponding to that single cell to turn on, cutting that single cell out of the series charging circuit. The charging current continues to charge the remaining single cells that have not reached the equalization voltage threshold until the voltage of all single cells reaches the equalization voltage threshold, and the series equalization charging stage ends. S4: The MCU controls the series-parallel switching module to disconnect all series circuit relays and close all parallel circuit relays, switching the battery pack to a parallel connection state. Since all individual cells have reached a consistent voltage through series equalization charging, there is no risk of circulating current in parallel connection. The charger is started to charge the parallel battery pack with a constant current that is larger than that of series equalization charging. During the charging process, the total voltage of the battery pack and the temperature of each individual cell are monitored simultaneously. S5: When the total voltage of the battery pack reaches the preset full charge voltage threshold (e.g., 3.65V) and the charging current drops to the cutoff current, charging is complete; If, during parallel charging, the total voltage fails to reach the full charge voltage threshold or the current fails to drop to the cutoff current after a preset time, the MCU will switch the battery pack back to series balancing mode to perform individual cell balancing based on the voltage state of each cell. The series balancing mode (S3) and parallel charging mode (S4) will cycle a maximum of three times. If the full charge condition is still not met after three cycles, the system will stop charging, record the abnormal individual cell, and prompt the user to replace it.

[0018] S6: The MCU disconnects the charger, disconnects the parallel circuit relay, switches the battery pack back to series mode, and prepares for the next discharge.

[0019] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0020] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A battery pack equalization charging system based on series-parallel switching, characterized in that: include: The battery pack consists of multiple individual cells BAT1, BAT2, ..., BAT n ; The voltage detection module, integrated in the AFE of the BMS, is connected to the positive and negative terminals of each individual cell to measure the voltage of each individual cell and transmit the measured voltage signal to the MCU. The series-parallel switching module includes multiple relays K1, K2, ..., K n The on / off state of the relay is controlled by the control signal output by the MCU, realizing the switching between series and parallel topologies of the battery pack; The bypass balancing module, which is individually equipped for each individual cell, includes a power MOSFET and a current-limiting resistor, and is used to disconnect individual cells that have reached the balancing voltage threshold from the charging circuit. The MCU, as the core control unit of the entire system, receives the voltage information of each individual battery from the voltage detection module, executes the preset control algorithm, and outputs control signals to control the relay on / off of the series-parallel switching module, the MOSFET on / off of the bypass equalization module, and the start / stop and charging mode switching of the charger. The charger, controlled by the MCU, provides constant current charging mode and constant voltage charging mode to provide stable charging power to the battery pack.

2. A method for operating a battery pack equalization charging system based on series-parallel switching according to claim 1, characterized in that: The method includes the following steps: S1: After the battery pack has finished discharging and is in a static state, the voltage of all individual cells is detected by the voltage detection module to obtain the initial voltage of each individual cell. S2: The system closes the series circuit relay, opens the parallel circuit relay, configures the battery pack as a series connection, starts the charger to perform series constant current charging of the battery pack, and the voltage detection module continuously monitors the voltage of each individual battery in real time. S3: When the voltage of any single cell reaches the preset equalization voltage threshold, the MCU controls the bypass equalization module corresponding to that single cell to turn on, cutting that single cell out of the series charging circuit. The charging current continues to charge the remaining single cells that have not reached the equalization voltage threshold until the voltage of all single cells reaches the equalization voltage threshold, and the series equalization charging stage ends. S4: The MCU controls the series-parallel switching module to disconnect all series circuit relays and close all parallel circuit relays to switch the battery pack to the parallel connection state; it starts the charger to charge the parallel battery pack with a constant current that is larger than that of series equalization charging, and monitors the total voltage of the battery pack and the temperature of each individual cell during the charging process. S5: When the total voltage of the battery pack reaches the preset full charge voltage threshold and the charging current drops to the cutoff current, charging is complete. S6: The MCU disconnects the charger, disconnects the parallel circuit relay, switches the battery pack back to series mode, and prepares for the next discharge.

3. The method according to claim 2, characterized in that: In S5, if the total voltage does not reach the full charge voltage threshold or the current does not drop to the cutoff current after a preset time during parallel charging, the MCU will switch the battery pack back to the series balancing mode and perform individual cell balancing based on the voltage status of each individual cell.

4. The method according to claim 3, characterized in that: The series balancing mode of S3 and the parallel charging mode of S4 can repeat the cycle a maximum of three times. If the full charge condition is still not met after three cycles, the system will stop charging and record the abnormal individual battery, prompting the user to replace it.

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