Balancing test simulation system and method based on BMS

Abstract

The invention discloses an equalization test simulation system and method based on a BMS, and relates to the technical field of battery management system testing, the system comprises at least two simulation units used for testing the equalization function of the BMS, and the simulation units are connected in parallel; when the voltage of the single battery is higher than the target balanced voltage of the BMS, the unit controller controls the bidirectional buck-boost transformer to execute an energy output mode, and the output voltage of the voltage of the single battery is reduced; and when the voltage of the single battery is lower than the target balanced voltage of the BMS, the unit controller controls the bidirectional buck-boost transformer to execute an energy absorption mode, and the output voltage of the voltage of the single battery is increased. The simulator can simulate the voltage of each node of a plurality of batteries which are connected in series, and a chip controls the output of a plurality of half-bridges and the voltage of a plurality of half-bridge output nodes which are connected in parallel on a power bus. The current of each node can flow bidirectionally on the bus, and flows in and out to counteract each other, so that the energy consumption is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery management system testing, in particular to a BMS-based equalization test simulation system and method. BACKGROUND

[0002] The equalization function of a battery management system (BMS) is crucial for ensuring the consistency of a battery pack and prolonging the service life. During the research and development and testing phases, reliable simulated batteries are needed to simulate various states of a real battery pack, especially to verify the active / passive equalization function of a BMS.

[0003] Currently, there are two types of simulated batteries for BMS testing. The first type is a plurality of independent single-cell simulators connected in series by hardwires. This method has many devices, complex wiring, poor synchronization between units, easy introduction of contact resistance and interference, and most of them can only provide a fixed output voltage, and cannot simulate the "high voltage to low voltage" energy bidirectional interaction process required by the active equalization of a BMS. The second type is to use a single DC-DC converter to directly output the total voltage of a battery pack, simulating the overall power supply capability of the battery pack, and can only be used to test the basic functions of a BMS such as total voltage detection and charge / discharge protection. This method has a simple structure, but it cannot simulate the voltage state of a single cell, so it cannot be used to trigger and test any BMS equalization function related to the voltage difference between cells.

[0004] The core defects of the prior art are: complex structure, fragmented function, inability to truly simulate the internal energy flow of a battery pack, and limited test scenarios. This results in incomplete testing of the BMS equalization function, distorted data, and difficulty in accurately evaluating the equalization strategy and effect of a BMS. SUMMARY

[0005] The present application provides a BMS-based equalization test simulation system and method to solve the problems of complex structure, inability to simulate bidirectional energy flow, non-adjustable equivalent internal resistance, lack of central coordination control, etc. in the prior art, and to realize full-process, high-precision, and high-adaptability testing of the equalization function of a BMS.

[0006] The present application provides a BMS-based equalization test simulation system, which includes at least two simulation units for testing the equalization function of a BMS, and the simulation units are connected in parallel.

[0007] The simulation unit includes a unit controller, a bidirectional buck-boost converter, and a voltage sampling module, and the bidirectional buck-boost converter simulates the output of a single-cell voltage to the power input interface of a BMS.

[0008] When the voltage of a single cell is higher than the target equalization voltage of a BMS, the unit controller controls the bidirectional buck-boost converter to execute an energy output mode to reduce the output voltage of the single-cell voltage.

[0009] When the single battery voltage is lower than the BMS target equalization voltage, the unit controller controls the bidirectional buck-boost converter to execute the energy absorption mode to increase the output voltage of the single battery voltage.

[0010] The system realizes the modularization and parallel architecture of the multi-battery simulation unit, supports independent work of each unit, avoids the poor synchronization and complex wiring problem of the traditional series simulation battery. Each unit can independently simulate the voltage state of the single battery, provide the real inter-cell voltage difference detection condition for the BMS, and thus completely support the triggering and testing of the BMS equalization function.

[0011] Further, the bidirectional buck-boost converter comprises a first MOS tube, a second MOS tube, an inductor L and a capacitor C, the drain electrode of the first MOS tube is connected to a power supply VUBS, the source electrode of the first MOS tube, the drain electrode of the second MOS tube and one end of the inductor L are connected at the same point, the other end of the inductor L is an output interface of the single battery voltage, and the output interface is connected to the ground through the capacitor C in series, the gate electrode of the first MOS tube and the gate electrode of the second MOS tube are respectively connected to the high voltage output port and the low voltage output port of the unit controller;

[0012] When the first MOS tube is turned on and the second MOS tube is turned off, the circuit works in the energy output mode;

[0013] When the second MOS tube is turned on and the first MOS tube is turned off, the circuit works in the energy absorption mode.

[0014] Further, the unit controller is a PIC24, the high voltage output port HO of the chip PIC24 is connected to the gate electrode of the first MOS tube, the low voltage output port LO of the chip PIC24 is connected to the gate electrode of the second MOS tube, and one end of the inductor L is connected to the Vs port of the chip PIC24.

[0015] Further, the corresponding demand resistance is matched according to the equalization current demand of the BMS;

[0016] In the energy output mode, the chip PIC24 outputs the corresponding voltage through the high voltage output port HO to adjust the equivalent resistance of the first MOS tube to be consistent with the demand resistance;

[0017] In the energy absorption mode, the chip PIC24 outputs the corresponding voltage through the low voltage output port LO to adjust the equivalent resistance of the first MOS tube to be consistent with the demand resistance.

[0018] Further, the chip PIC24 controls the number of turned-on MOS tubes and the size of the gate voltage of each MOS tube by adjusting the output voltage, so as to realize the continuous adjustment of the equivalent resistance in the range of 0.05Ω~10Ω.

[0019] Furthermore, the single-cell battery voltage output of each analog unit has an adjustment range of 2.5V to 4.5V, with an adjustment accuracy of no less than ±0.001V.

[0020] Furthermore, the system also includes a copper busbar for connecting the analog units in series to form a total voltage output.

[0021] Furthermore, the system also includes a voltage sampling unit and a central controller. The voltage sampling unit is used to collect the voltage of a single battery cell, and the central controller receives the voltage of the single battery cell and compares it with the target equalization voltage of the BMS.

[0022] When the voltage of a single battery cell is higher than the target equalization voltage of the BMS, the central controller sends an energy output mode command to the unit controller.

[0023] When the voltage of a single battery cell is lower than the target equalization voltage of the BMS, the central controller sends an energy absorption mode command to the unit controller.

[0024] Furthermore, the voltage sampling module includes a first resistor and a second resistor connected in series. One end of the first resistor is connected to the output terminal of the bidirectional buck-boost converter, and one end of the second resistor is grounded.

[0025] This invention also provides a BMS-based balanced load testing simulation method, comprising:

[0026] S1, set the initial test parameters, including the target voltage and equivalent internal resistance of each simulation unit;

[0027] S2, the central controller controls each analog unit to output a single-cell battery voltage with its own equivalent internal resistance and a preset voltage difference between each analog unit;

[0028] S3, connect the output ports of each analog unit to the power input interface of the BMS accordingly;

[0029] S4, the central controller monitors the balancing status of the BMS. When the BMS starts balancing due to the detection of a voltage difference, it enters S5.

[0030] S5, for simulation units where the voltage of a single cell is higher than the target equalization voltage of the BMS, the central controller controls the simulation unit to enter the energy output mode; for simulation units where the voltage of a single cell is lower than the target equalization voltage of the BMS, the central controller controls the simulation unit to enter the energy absorption mode.

[0031] S6, the central controller dynamically adjusts the energy transfer power of each analog unit according to the real-time sampled voltage and current values ​​of each analog unit, so that the voltage of each unit converges towards the equilibrium target value, and maintains this process until the preset equilibrium termination condition is reached.

[0032] S7 records and outputs key data throughout the testing process.

[0033] This method forms a complete, systematic, and reproducible BMS load balancing test process. The method is clear and the operation is standardized. It supports the entire process of testing from condition setting to result analysis, which significantly improves testing efficiency and result reliability. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the principle of the BMS-based equalization test simulation system of the present invention;

[0035] Figure 2 This is a schematic diagram of the BMS-based balanced test simulation method of the present invention. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0038] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0039] like Figure 1As shown, this invention proposes a BMS-based equalization test simulation system, including at least two simulation units for testing the equalization function of the BMS, with each simulation unit connected in parallel. The system is composed of multiple completely independent simulation units connected in parallel, each powered uniformly. The total voltage of each simulation unit can be superimposed via series wires. The output terminals correspond to the total positive and negative terminals of the BMS and the positive and negative terminals of each individual battery cell. A fixed output voltage is set for each simulation unit manually or via independent commands. The output terminals of each simulation unit are connected in series via copper busbars to form the total voltage of a multi-cell battery pack, simulating the power supply characteristics of the battery pack. A MOSFET simulates the internal resistance of the battery, and the current output capability is determined by the power module of each individual simulation unit. By simplifying the structural design of the multi-cell simulated battery pack, an integrated system is achieved, eliminating the need for independent wiring and power supply for multiple devices, thus improving test stability and operational convenience.

[0040] The simulation unit includes a unit controller, a bidirectional buck-boost converter, and a voltage sampling module. The bidirectional buck-boost converter simulates the output voltage of a single battery cell to the power input interface of the BMS. When the voltage of a single battery cell is higher than the target equalization voltage of the BMS, the unit controller controls the bidirectional buck-boost converter to execute the energy output mode, reducing the output voltage of the single battery cell. When the voltage of a single battery cell is lower than the target equalization voltage of the BMS, the unit controller controls the bidirectional buck-boost converter to execute the energy absorption mode, increasing the output voltage of the single battery cell. Each single-cell simulation unit is equipped with an independent bidirectional DC-DC converter and a programmable equivalent internal resistance module, realizing independent adjustment of single-cell voltage, bidirectional energy flow, and on-demand setting of internal resistance. It also retains the independent node interface of each single battery cell, fully simulating the single-cell voltage state and total voltage characteristics of multiple battery packs, adapting to the full-process testing of BMS active / passive equalization functions. It achieves bidirectional energy transfer of the single-cell simulation unit, accurately matching the energy interaction requirements of BMS active equalization, and fully verifying the triggering, transfer, and effect of active equalization. Ultimately, a multi-string battery with equalization function was achieved, which is characterized by "simplified structure, comprehensive functions, strong adaptability, and accurate testing", thus meeting the comprehensive testing requirements of the BMS equalization function.

[0041] A further proposed solution is a bidirectional buck-boost converter comprising a first MOSFET, a second MOSFET, an inductor L, and a capacitor C. The drain of the first MOSFET is connected to the power supply VUBS. The source of the first MOSFET, the drain of the second MOSFET, and one end of the inductor L are common to each other. The other end of the inductor L is the single-cell battery voltage output interface and is grounded after being connected in series with the capacitor C. The gates of the first MOSFET and the second MOSFET are respectively connected to the high-voltage output port and the low-voltage output port of the unit controller.

[0042] When the first MOSFET is turned on and the second MOSFET is turned off, the circuit operates in energy output mode;

[0043] When the second MOSFET is turned on and the first MOSFET is turned off, the circuit operates in energy absorption mode.

[0044] The bidirectional Buck-Boost converter of the single-section analog unit supports two operating modes, which are switched by the unit control chip according to central instructions:

[0045] (1) Energy output mode (power supply unit): When the voltage of a single section is higher than the target equalization voltage, Q1 is turned on and Q2 is turned off. The converter operates in buck mode and transfers excess energy to other units through the series bus.

[0046] (2) Energy absorption mode (energy receiving unit): When the voltage of a single section is lower than the target equalization voltage, Q2 is turned on and Q1 is turned off. The converter operates in boost mode, absorbing energy from the series bus to supplement its own voltage.

[0047] By simulating the energy flow of a real battery pack during active balancing by the BMS, the energy transfer efficiency and balancing effect of the BMS are fully verified.

[0048] In addition, the bidirectional Buck-Boost converter can be replaced with a bidirectional Cuk converter. The advantages are lower output voltage ripple and higher energy transfer efficiency (≥98%); the disadvantages are a more complex circuit structure and slightly higher cost, making it suitable for BMS testing scenarios with extremely high voltage stability requirements.

[0049] The unit controller is a PIC24, with its high-voltage output port HO, low-voltage output port LO, and Vs port connected to the MOSFET gate and inductor node, respectively. Utilizing a high-performance MCU like the PIC24, precise control of the MOSFET drive signals is achieved, supporting high-frequency PWM modulation to improve voltage regulation response speed and stability, ensuring high accuracy and low ripple in the analog voltage output, meeting the BMS's requirements for voltage sampling accuracy. Independent node interfaces are provided for each individual cell, supporting precise adjustment of individual cell voltage and creating controllable inter-cell voltage differences to meet the simulation requirements of BMS equalization triggering conditions. Independent setting of individual cell voltage is supported, allowing for flexible creation of inter-cell voltage differences of varying amplitudes to fully simulate battery pack imbalance scenarios and verify voltage consistency after BMS equalization.

[0050] The V+ and V- terminals of each individual simulation unit are connected in series via a series bus to form the total voltage output terminal (total positive and total negative). The power supply module is connected to the central controller and each individual simulation unit via power lines. The B- to B4+ interfaces of each simulation unit of the simulation battery are connected to the individual battery detection interfaces of the BMS (such as B-, B1+, B2+, B3+, and B4+ of the BMS), and the total positive / total negative interfaces of the simulation battery are connected to the power input interface of the BMS. The communication interface of the BMS is connected to the auxiliary communication port of the central controller for reading the BMS balance status (such as balance enable bit and balance current feedback).

[0051] Each individual analog unit's controller receives voltage commands from the central controller and drives the MOSFETs Q1 / Q2 of the bidirectional Buck-Boost converter via PWM signals to adjust the output voltage. The voltage sampling module collects the output voltage in real time and feeds it back to the control chip to form a closed-loop regulation (regulation bandwidth ≥1kHz). The single-cell voltage adjustment range is 2.5V~4.5V (covering the entire operating range of lithium batteries), with an adjustment accuracy of ±0.001V, and supports setting any inter-cell voltage difference (adjustable from 0V to 1V). For example, when testing the BMS equalization threshold (0.1V), setting unit 1=4.0V, units 2~4=3.9V, and the inter-cell difference of 0.1V precisely triggers BMS equalization.

[0052] A further approach is to match the required internal resistance based on the BMS's balanced current requirements.

[0053] In the output mode, the PIC24 chip outputs a corresponding voltage through the high voltage output port HO to adjust the equivalent internal resistance of the first MOS transistor to match the required internal resistance.

[0054] In energy absorption mode, the PIC24 chip outputs a corresponding voltage through the low-voltage output port LO to adjust the equivalent internal resistance of the first MOS transistor to match the required internal resistance.

[0055] Based on the BMS balancing current requirements, the corresponding internal resistance is matched by adjusting the gate voltage of the MOSFET to make its equivalent internal resistance consistent with the requirements. This achieves programmable matching of the equivalent internal resistance, simulating the internal resistance characteristics of different batteries, making the balancing current test closer to the behavior of real battery packs, and improving the accuracy of test data and BMS adaptability.

[0056] Furthermore, the equivalent internal resistance module adopts a "MOS transistor array + sampling feedback" design. The unit control chip changes the equivalent internal resistance (adjustable from 0.05Ω to 10Ω in 0.01Ω steps) by adjusting the number of MOS transistors on and their gate voltage. Combined with Ohm's law (I=ΔV / R), it matches the balancing current requirements of different BMSs. For example, when testing an active balancing BMS (designed balancing current 1A), with a junction difference of 0.2V and an equivalent internal resistance of 0.2Ω, the simulated battery energy transfer current stabilizes at 1A, matching the BMS design value.

[0057] A further advanced solution involves the PIC24 chip, which controls the conduction frequency of MOSFETs and the gate voltage of each MOSFET by adjusting the output voltage, achieving continuously adjustable equivalent internal resistance within the range of 0.05Ω to 10Ω. This provides wide-range, high-precision internal resistance adjustment capabilities, supports various BMS equalization current parameter testing requirements, and enhances the system's versatility and test scenario coverage.

[0058] A further improved scheme allows for single-cell battery voltage adjustment ranging from 2.5V to 4.5V output by each simulation unit, with an adjustment accuracy of no less than ±0.001V. This covers the typical operating voltage range of lithium batteries, and the high-precision voltage adjustment capability can simulate minute voltage differences (such as 0.01V) for testing the sensitivity and threshold accuracy of BMS equalization triggering.

[0059] A further refinement of the system includes a copper busbar for connecting the analog units in series to form the total voltage output. This copper busbar enables a low-impedance, high-reliability series connection, ensuring a stable total voltage output and providing a physical channel for energy transfer between units, supporting energy flow during active balancing. Furthermore, all individual analog units, the central controller, and the power supply module are integrated into a single chassis with a modular internal layout. Individual units are connected in series via built-in copper busbars, eliminating the need for external wiring. This reduces the device size by over 60%, and operation requires only parameter setting via a human-machine interface module, eliminating the need for individual unit debugging and improving testing efficiency by 50%.

[0060] In a more preferred embodiment, the system further includes a voltage sampling unit and a central controller. The voltage sampling unit is used to sample the voltage of a single battery cell, and the central controller receives the voltage of the single battery cell and compares it with the target equalization voltage of the BMS.

[0061] When the voltage of a single battery cell is higher than the target equalization voltage of the BMS, the central controller sends an energy output mode command to the unit controller.

[0062] When the voltage of a single battery cell is lower than the target equalization voltage of the BMS, the central controller sends an energy absorption mode command to the unit controller.

[0063] By adding a central controller, synchronous control of each individual analog unit is achieved, maintaining preset voltage differences and energy states in real time to ensure the stability of test conditions. Furthermore, through a communication bus, all individual analog units are coordinated, supporting programmable adjustment of equivalent internal resistance. This allows for precise matching of the balancing current parameters of different BMSs, ensuring accurate control of inter-section voltage differences and synchronization of energy transfer, thus improving test versatility and data accuracy. System-level collaborative control and intelligent decision-making are realized, with the central controller uniformly scheduling the operating modes of each unit to ensure an orderly and rapid testing process, improving the degree of test automation and result consistency.

[0064] The voltage sampling module includes a first resistor and a second resistor connected in series. One end of the first resistor is connected to the output of the bidirectional buck-boost converter, and one end of the second resistor is grounded. This provides a simple, reliable, and low-cost voltage sampling scheme. By using a resistor divider in conjunction with an ADC, high-precision voltage feedback is achieved, providing accurate input for closed-loop control.

[0065] The following is a detailed explanation of the working process using a specific implementation case as an example: "Active Balancing Function Test of 4 Lithium-ion Battery BMS".

[0066] 1. Test parameter settings (input via the human-computer interaction module):

[0067] Initial voltage of a single section: Section 1 = 4.1V (overcharge simulation), Sections 2~4 = 3.7V (undervoltage simulation), inter-section voltage difference 0.4V;

[0068] Equivalent internal resistance: All elements are set to 0.1Ω;

[0069] Equalization target voltage: 3.8V (final voltage of all units is consistent);

[0070] Test duration: 30 minutes.

[0071] 2. Equipment startup: The central controller sends parameters to each unit, and each unit stabilizes its output voltage through closed-loop regulation. The total voltage after series connection is 4.1V + 3.7V × 3 = 15.2V.

[0072] 3. Connect to BMS: Connect the single-cell interface and total voltage interface of the simulated battery to the BMS. After the BMS is powered on, it detects an inter-cell voltage difference of 0.4V (exceeding the equalization threshold of 0.1V) and starts active equalization.

[0073] 4. Energy transfer process:

[0074] Unit 1 (Power Supply Unit): The central controller detects that the BMS has started equalization and instructs Unit 1 to switch to buck mode, releasing energy through bidirectional DC-DC, with a current of (4.1V-3.8V) / 0.1Ω=3A;

[0075] Units 2-4 (Energy Receiving Units): The central controller instructs units 2-4 to switch to boost mode and absorb energy from the series bus. The current of each unit is 3A / 3=1A.

[0076] 5. Closed-loop regulation: The central controller collects the voltage of each unit every 10ms. When the voltage of unit 1 drops to 3.9V and the voltage of units 2 to 4 rises to 3.85V, the power output of unit 1 is dynamically reduced to maintain the stability of the inter-unit voltage difference until the voltage of all units approaches 3.8V (error ±0.02V).

[0077] 6. Test completion: The equipment automatically records the test data (equalization trigger time, equalization current curve, final inter-section voltage difference) and displays it through the human-machine interaction module, supporting export to a computer for analysis.

[0078] Based on the same inventive concept, such as Figure 2 As shown, the present invention also provides a BMS-based equilibrium test simulation method, including:

[0079] S1, set the initial test parameters, including the target voltage and equivalent internal resistance of each simulation unit;

[0080] S2, the central controller controls each analog unit to output a single-cell battery voltage with its own equivalent internal resistance and a preset voltage difference between each analog unit;

[0081] S3, connect the output ports of each analog unit to the power input interface of the BMS accordingly;

[0082] S4, the central controller monitors the balancing status of the BMS. When the BMS starts balancing due to the detection of a voltage difference, it enters S5.

[0083] S5, for simulation units where the voltage of a single cell is higher than the target equalization voltage of the BMS, the central controller controls the simulation unit to enter the energy output mode; for simulation units where the voltage of a single cell is lower than the target equalization voltage of the BMS, the central controller controls the simulation unit to enter the energy absorption mode.

[0084] S6, the central controller dynamically adjusts the energy transfer power of each analog unit according to the real-time sampled voltage and current values ​​of each analog unit, so that the voltage of each analog unit converges towards the equilibrium target value, and maintains this process until the preset equilibrium termination condition is reached.

[0085] S7 records and outputs key data throughout the testing process.

[0086] This solution integrates multiple analog units into a single chassis, eliminating the need for external wiring and reducing size by over 60%. It supports active / passive equalization testing, realistically simulating bidirectional energy flow. Individual section voltage (2.5V~4.5V, ±0.001V accuracy) and equivalent internal resistance (0.05Ω~10Ω, 0.01Ω steps) are adjustable, making it compatible with various BMS products. Centralized coordinated control ensures stable inter-section voltage differential, with a closed-loop regulation bandwidth ≥1kHz. Automatic data recording and report generation improve testing efficiency by over 50%.

[0087] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A BMS-based equalization test simulation system, characterized in that, The system comprises at least two simulation units for testing the BMS equalization function, and the simulation units are connected in parallel. The simulation unit comprises a unit controller, a bidirectional buck-boost converter and a voltage sampling module, and the bidirectional buck-boost converter simulates the output of a single battery voltage to the power input interface of the BMS. When the single battery voltage is higher than the target equalization voltage of the BMS, the unit controller controls the bidirectional buck-boost converter to execute the energy output mode to reduce the output voltage of the single battery voltage. When the single battery voltage is lower than the target equalization voltage of the BMS, the unit controller controls the bidirectional buck-boost converter to execute the energy absorption mode to increase the output voltage of the single battery voltage.

2. The system of claim 1, wherein, The bidirectional buck-boost converter comprises a first MOS tube, a second MOS tube, an inductor L and a capacitor C, the drain electrode of the first MOS tube is connected to a power supply VUBS, the source electrode of the first MOS tube, the drain electrode of the second MOS tube and one end of the inductor L are connected at the same point, the other end of the inductor L is a single battery voltage output interface, and the capacitor C is connected in series and then grounded, and the gate electrode of the first MOS tube and the gate electrode of the second MOS tube are respectively connected to the high voltage output port and the low voltage output port of the unit controller. When the first MOS tube is turned on and the second MOS tube is turned off, the circuit works in the energy output mode. When the second MOS tube is turned on and the first MOS tube is turned off, the circuit works in the energy absorption mode.

3. The system of claim 2, wherein, The unit controller is a PIC24 chip, the high voltage output port HO of the chip PIC24 is connected to the gate electrode of the first MOS tube, the low voltage output port LO of the chip PIC24 is connected to the gate electrode of the second MOS tube, and the Vs port of the chip PIC24 is connected to one end of the inductor L.

4. The system of claim 3, wherein, The corresponding demand resistance is matched according to the equalization current demand of the BMS. In the energy output mode, the chip PIC24 outputs the corresponding voltage through the high voltage output port HO to adjust the equivalent resistance of the first MOS tube to be consistent with the demand resistance. In the energy absorption mode, the chip PIC24 outputs the corresponding voltage through the low voltage output port LO to adjust the equivalent resistance of the first MOS tube to be consistent with the demand resistance.

5. The system of claim 4, wherein, The chip PIC24 controls the number of turned-on MOS tubes and the size of the gate voltage of each MOS tube by adjusting the output voltage, so as to realize the continuous adjustment of the equivalent resistance in the range of 0.05Ω-10Ω.

6. The system of claim 1, wherein, The adjustment range of the single battery voltage output by each simulation unit is 2.5V-4.5V, and the adjustment accuracy is not less than ±0.001V.

7. The system of claim 1, wherein, The system further comprises a copper bar for connecting the simulation units in series to form a total voltage output.

8. The system of claim 1, wherein, The system further comprises a voltage sampling unit and a central controller, the voltage sampling unit is used to collect the single battery voltage, and the central controller receives the single battery voltage and compares the size of the single battery voltage with the target equalization voltage of the BMS. When the single battery voltage is higher than the target equalization voltage of the BMS, the central controller sends an energy output mode instruction to the unit controller. When the single battery voltage is lower than the target equalization voltage of the BMS, the central controller sends an energy absorption mode instruction to the unit controller.

9. The system of claim 8, wherein, The voltage sampling module comprises a first resistor and a second resistor connected in series, one end of the first resistor being connected to the output end of the bidirectional buck-boost converter, and one end of the second resistor being grounded.

10. A BMS-based equalization test simulation method, characterized in that, The method comprises the following steps: S1, setting initial test parameters, including target voltages and equivalent internal resistances of each simulation unit; S2, the central controller controls each simulation unit to output a single battery voltage with its own equivalent internal resistance and a preset voltage difference between the simulation units; S3, connecting the output ports of each simulation unit with the power input interface of the BMS in correspondence; S4, the central controller monitors the balancing state of the BMS, and when the BMS starts balancing due to the detection of a voltage difference, S5 is entered; S5, for the simulation unit with a single battery voltage higher than the target balancing voltage of the BMS, the central controller controls the simulation unit to enter the energy output mode, and for the simulation unit with a single battery voltage lower than the target balancing voltage of the BMS, the central controller controls the simulation unit to enter the energy absorption mode; S6, the central controller dynamically adjusts the energy transfer power of each simulation unit according to the real-time sampled voltage and current values of each simulation unit, so that the voltage of each simulation unit converges towards the balancing target value, and this process is maintained until the preset balancing end condition is reached; S7, recording and outputting the key data in the entire test process.

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