High-current balance BMS module based on GaN HEMT and control method

Abstract

The invention discloses a large-current balance BMS module based on a GaN HEMT and a control method. The BMS module comprises a power supply unit, an analog front end, a micro-control unit, an active balance unit, a passive balance unit, a GaN driving unit, a switch array, a current sampling unit, a temperature acquisition unit and a first communication unit. Wherein the switch array comprises a plurality of bidirectional conduction GaN HEMT which are arranged in parallel and have the same specification, the charging, discharging and protection states of the battery pack are switched in response to a driving signal, gate pole driving ends of the GaN HEMT are connected with the driving signal of the GaN driving unit, one end of a symmetrical conduction end is connected with a load or a charger, and the other end of the symmetrical conduction end is connected with a negative electrode of the battery pack; the active equalization unit takes 2n multi-winding transformers which have the same number of turns and are wound on the same magnetic core as a core, and is matched with 2n MOSFETs and driving circuits thereof to form a multi-path parallel synchronous active equalization module. According to the invention, the voltage difference precision can be ensured while large-current equalization is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery management, and particularly relates to a high-current equalization BMS module based on GaN HEMT and a control method thereof. Background Art

[0002] For two-wheeled electric bicycles with a battery replacement (hereinafter referred to as "battery swapping") mode to meet the needs of the takeaway and express delivery services, the performance stability and service life of lithium batteries as their core power sources have received wide attention. The battery operates in a high-current charge and discharge mode, generally charging at 0.3C and discharging at 1C. The battery equalization technology in the Battery Management System (BMS) is a key technology to ensure the health of the battery pack and extend its life. At present, in the field of battery-swapping two-wheeled electric vehicles, the research on the battery management system mainly focuses on improving the management accuracy of single cells and extending the battery life. The lithium battery packs used are closely related to the endurance and safety of the vehicle. Currently, the battery-swapping batteries are mainly composed of multiple single cells connected in series and parallel to form a 16-20 series battery pack with a capacity between 20 and 60 Ah, and generally only passive equalization is adopted. The basic theoretical cycle life of a single battery cell is more than 2000 times. However, in actual operation, for battery packs that have been cycled 300-1000 times, situations such as the battery voltage difference increasing to more than 300 mV, the discharge capacity decreasing, and the State of Health (SOH) decreasing to less than 80% occur, which causes some batteries to withdraw from operation prematurely, resulting in huge resource waste.

[0003] Although the existing BMS adopts the passive equalization method with the advantage of low cost, the passive equalization current is generally in the range of 50-100 mA, which is significantly insufficient in terms of equalization speed and the effect is like scratching an itch through boots, unable to meet the requirements of battery-swapping batteries. Active equalization methods include adjacent inductor equalization, switched capacitor equalization, or taking the total charge of a single group based on BUCK-BOOST technology. Due to hardware topology limitations, the equalization current of traditional single-channel active equalization circuits is usually less than 1A, making it difficult to meet the demand for high-current and fast equalization in high-frequency battery-swapping scenarios. In the existing BMS, a pair of back-to-back MOS transistors are used to switch the current for controlling the charging and discharging of the battery pack. As the current increases, the number of MOS increases, resulting in an increase in the loss and size of the BMS board and a rapid increase in cost. In addition, when the existing BMS adopts active equalization of 1-2A, when the battery is in the 1-2A equalization state, due to the resistance RL on the acquisition line, the equalization current will generate a voltage difference δU = I*RL on the acquisition line. Usually, RL is in the range of 100-200 mΩ. Therefore, when the equalization current is 2A, the maximum voltage error will reach 0.4V.

[0004] The Chinese invention patent application with the publication number CN117595471A discloses a lithium battery BMS active equalization circuit, including a battery pack. The battery pack includes N series-connected single cells. Among them, there are N + 1 connection nodes for the N series-connected single cells. At each connection node, a switch control module is connected in series. The N + 1 switch control modules are divided into switch control modules with odd numbers and switch control modules with even numbers according to the connection node order. Among them, the switch control modules with odd numbers are all connected to the first bus switching balance positive and negative module, and the switch control modules with even numbers are all connected to the second bus switching balance positive and negative module. Both the first bus switching balance positive and negative module and the second bus switching balance positive and negative module are connected to the supercapacitor bidirectional energy exchange module.

[0005] The above solution and the prior art cannot solve the contradiction between equalization efficiency and equalization accuracy; and during equalization, it will cause battery voltage acquisition errors, thus affecting SOC measurement, resulting in covering up the risk of battery anomalies, possibly accelerating the deterioration of abnormal batteries, and causing safety problems; also, due to the large number of MOS used, the cost is high, the heat generation is large, and the size of the BMS is relatively large. Summary of the Invention

[0006] The present invention provides a high-current equalization BMS module based on GaN HEMT, aiming to solve the problems in the prior art that equalization efficiency and equalization accuracy cannot be both achieved, there are acquisition errors in battery voltage, and the size of the BMS is relatively large.

[0007] To solve the above technical problems, on the one hand, the present invention proposes a high-current equalization BMS module based on GaN HEMT for the protection and equalization management of multi-section series battery packs. The circuit of the module includes:

[0008] A power supply unit for taking power from the battery pack to supply power to other units in the module;

[0009] An analog front end for collecting battery voltage, current, temperature and switch array control information and sending it to the micro control unit, and sending control signals to the GaN drive unit, and also switching the working state of the passive equalization unit according to the signal of the micro control unit;

[0010] A micro control unit for analyzing the battery state based on the acquired data, performing active equalization and passive equalization control on the battery, and communicating with the first communication unit;

[0011] An active equalization unit for performing active equalization on the battery pack according to the control signal of the micro control unit;

[0012] A passive equalization unit for turning on or off the passive equalization of the battery pack according to the switching signal of the analog front end;

[0013] The GaN driving unit converts the switch array control signal sent by the analog front end into a driving signal and sends it to the switch array;

[0014] The switch array includes a number of bidirectional conducting GaN HEMTs connected in parallel with the same specifications, and responds to the driving signal to switch the charging, discharging, and protection states of the battery pack. The gate driving ends of the GaN HEMTs are all connected to the driving signal of the GaN driving unit. One end of the symmetric conducting end is connected to the load or charger, and the other end is connected to the negative pole of the battery pack;

[0015] The current sampling unit is connected in series between one end of the switch array and the battery pack, and sends the differential signal on the sampling resistor into the analog front end through the differential sampling circuit;

[0016] The temperature acquisition unit collects the battery temperature to the analog front end through a thermistor;

[0017] The first communication unit includes RS485 and / or CAN communication circuits for wired communication interaction with an external system.

[0018] Preferably, the power supply unit includes a first power supply unit and a second power supply unit. The first power supply unit takes power from the battery pack, generates a 12V power supply through BUCK step-down, and provides it to the second power supply unit; the second power supply unit outputs a 3.3V power supply to the micro-control unit and the first communication unit.

[0019] Preferably, the BMS module further includes a TVS protection unit. The TVS protection unit includes a number of transient voltage suppressor TVS tubes connected in parallel on both sides of the switch array.

[0020] Preferably, the BMS module further includes a second communication unit. The second communication unit receives power from the first power supply unit or the second power supply unit and communicates with the micro-control unit; it includes one or more combinations of cellular network communication, Bluetooth communication, Beidou communication, Beidou positioning, and GPS positioning for information interaction and control with an external system.

[0021] Preferably, the active equalization unit includes a multi-winding transformer, MOSFET switches, and a PWM driving circuit;

[0022] The multi-winding transformer further includes 2n windings with a turns ratio of 1:1, where n is the number of battery cells. Each battery cell corresponds to two windings, and one end of the two windings is connected to the positive pole of the corresponding battery;

[0023] The MOSFET switches correspond to the windings one by one and are used to control the conduction and cut-off of the windings. The drain of the MOSFET switch is connected to the other end of the corresponding winding, the source is connected to the negative pole of the corresponding battery, and the gate is connected to the PWM driving circuit;

[0024] The PWM driving circuit receives two complementary PWM signals from the microcontroller unit. One path drives the MOSFETs connected in series with the first winding corresponding to each battery cell, and the other path drives the MOSFETs connected in series with the second winding.

[0025] Preferably, the driving signal includes the following modes:

[0026] The voltage of the driving signal is 5V higher than the voltage at the load end of the GaN HEMT, and the GaN HEMT is turned on, which is used for the battery pack to connect to the load and provide a discharge current for the load.

[0027] The voltage of the driving signal is equal to the voltage at the load end of the GaN HEMT, and the GaN HEMT is turned off, which is used for the battery pack to connect to the load and stop discharging to the load.

[0028] The voltage of the driving signal is 5V higher than the potential at the negative terminal of the battery pack corresponding to the GaN HEMT, and the GaN HEMT is turned on, which is used for the battery pack to be connected to the charger and the charger to charge the battery.

[0029] The voltage of the driving signal is equal to the potential at the negative terminal of the battery pack corresponding to the GaN HEMT, and the GaN HEMT is turned off, which is used for the battery pack to be connected to the charger and stop charging.

[0030] On the other hand, the present invention also proposes a battery equalization control method. The battery equalization control method uses the above-mentioned BMS module, and includes the following steps:

[0031] The analog front end collects the voltage, working current, temperature, state of charge, state of health and historical cycle data of the battery, calculates and judges the battery state according to the collected data, and monitors the voltage difference between the batteries.

[0032] If the voltage difference is greater than or equal to the passive equalization threshold, the analog front end controls the passive equalization unit to start the passive equalization function.

[0033] The analog front end communicates with the microcontroller unit. When the voltage difference meets the preset conditions, the microcontroller unit controls the active equalization unit to perform active equalization through periodic switching control until the active equalization stop condition is met.

[0034] Preferably, the active equalization through periodic switching control is specifically as follows:

[0035] Enter the active equalization working stage, and last for a set first time period. During the active equalization working stage, drive the multi-winding transformer to conduct to perform the equalization operation.

[0036] When the first time period ends, enter the active equalization stop stage, and last for a set second time period. During the active equalization stop stage, turn off the driving circuit to stop the equalization operation.

[0037] The active balancing working stage and the active balancing stop stage alternate cyclically to form a periodic switching control mode.

[0038] Preferably, the analog front end also collects the first battery voltage of each battery during the active balancing working stage and the second battery voltage of each battery during the active balancing stop stage; calibrates the state of charge of the battery through the first battery voltage and the second battery voltage, and makes an early judgment on battery aging or faults according to the first battery voltage, the second battery voltage, the voltage difference and the BMS historical data.

[0039] Preferably, the first time period is between 500 milliseconds and 10 minutes, and the second time period is between 1 second and 60 minutes.

[0040] Compared with the prior art, the present invention has the following technical effects:

[0041] 1. The balanced BMS module proposed by the present invention combines a multi-channel parallel synchronous active balancing unit with a passive balancing unit, which can not only achieve rapid battery balancing but also give play to the high-precision advantage of passive balancing; this solution has a large balancing current, synchronous balancing of each battery, fast balancing speed, extremely low energy loss, and meets the accuracy requirement of restoring the battery voltage difference to 1 mV.

[0042] 2. The balanced BMS module proposed by the present invention combines a bidirectional conducting GaN HEMT device and its driving IC, uses 1 GaN HEMT to replace 2 back-to-back MOS transistors in the traditional technology, and uses 1 GaN driving IC to complete overcharge and over-discharge protection of the GaN HEMT device in the BMS circuit. It greatly reduces the number of components, simplifies the circuit, reduces the volume, lowers the system cost, realizes the reduction of power loss, and improves the balancing efficiency. Description of the Drawings

[0043] Figure 1 is the circuit schematic diagram of the BMS module described in the embodiment of the present invention;

[0044] Figure 2 is the schematic diagram of the active balancing unit described in the embodiment of the present invention;

[0045] Figure 3 is the schematic diagram of the GaN driving unit and the switch array described in the embodiment of the present invention;

[0046] Figure 4 is the schematic diagram of the periodic switching control active balancing described in the embodiment of the present invention. Detailed Embodiments

[0047] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will, in conjunction with specific embodiments of the present application and with reference to the accompanying drawings, clearly and completely describe the technical solutions of the present invention.

[0048] Embodiment 1

[0049] This embodiment is a large-current balancing BMS module based on GaN HEMT (Gallium Nitride High Electron Mobility Transistor), which is used for the protection and balancing management of a multi-section series battery pack. As Figure 1 shown, the circuit of the BMS module includes a power supply unit, an analog front end, a microcontroller unit, an active balancing unit, a passive balancing unit, a GaN driving unit, a switch array, a current sampling unit, a temperature acquisition unit, and a first communication unit.

[0050] Specifically, the power supply unit is used to draw power from the battery pack and supply power to other units in the module. In this embodiment, as Figure 1 shown, the power supply unit includes a first power supply unit and a second power supply unit. The first power supply unit draws power from the battery pack and generates a 12V power supply through BUCK step-down to provide it to the second power supply unit; the second power supply unit outputs a 3.3V power supply to the microcontroller unit and the first communication unit.

[0051] The analog front end (AFE) collects battery voltage, current, temperature, and switch array control information and sends it to the microcontroller unit, and also sends control signals to the GaN driving unit, and switches the working state of the passive balancing unit according to the signals of the microcontroller unit. Specifically, the AFE completes the acquisition and monitoring of battery voltage, current, and temperature, completes the control of turning on and off the GaN HEMT, completes protections such as battery overcharging, over-discharging, over-current charging, over-current discharging, and short circuit, communicates and interacts with the MCU, and is controlled by the MCU to turn on and off the passive balance.

[0052] The microcontroller unit (MCU) analyzes the battery state based on the acquired data, performs active and passive balancing control on the battery, and communicates with the first communication unit. The MCU communicates with the AFE to obtain the battery voltage, current, temperature, and GaN HEMT control information collected by the AFE, completes calculations such as battery SOC (State of Charge), SOH, etc., performs active and passive balancing control on the battery, analyzes and processes various battery data, and performs backup safety control on the GaN HEMT and the BMS.

[0053] The AFE collects battery voltage, current, and temperature signals in real time, and communicates the collected signals with the MCU through the I2C interface. In this way, the MCU can know the battery status and perform relevant control on the AFE. The AFE can be programmed to set first-level protection for battery overcharge, over-discharge, over-current, over-temperature, etc.; the MCU can also be programmed. In this embodiment, the protection threshold of the MCU is higher than that of the AFE. The MCU and the AFE cooperate to form a second-level protection for battery overcharge, over-discharge, over-current, over-temperature, etc.

[0054] The active equalization unit performs active equalization on the battery pack according to the control signal of the MCU. In this embodiment, the active equalization unit consists of a multi-winding transformer with 2n windings of equal number of turns wound on the same magnetic core and a multi-path parallel synchronous active equalization module composed of 2n MOSs and their drive circuits. Its function is to complete synchronous parallel active equalization of the battery, and the start and stop of the equalization are directly controlled by the MCU; where n is the number of battery cells in the battery pack.

[0055] Specifically, as Figure 2 shown, the active equalization unit includes a multi-winding transformer, MOSFET switches, and a PWM drive circuit;

[0056] The multi-winding transformer further includes 2n windings with a turn ratio of 1:1, where n is the number of battery cells, and each battery cell corresponds to two windings. One end of the two windings is connected to the positive electrode of the corresponding battery;

[0057] The MOSFET switches correspond to the windings one by one, and are used to control the conduction and cut-off of the windings. The drain of the MOSFET switch is connected to the other end of the corresponding winding, the source is connected to the negative electrode of the corresponding battery, and the gate is connected to the PWM drive circuit;

[0058] The PWM drive circuit receives two complementary PWM signals from the microcontroller unit. One drives the MOSFET connected in series with the first winding corresponding to each battery cell, and the other drives the MOSFET connected in series with the second winding. In a preferred embodiment of the present invention, the frequency of the two complementary PWM signals is between 30 kHz and 300 kHz.

[0059] In Figure 2In the circuit shown, taking the first battery from the left as an example to illustrate the structure of the active equalization unit of this embodiment, which includes one battery, two groups of equalization circuits and two groups of PWM drive circuits. Among them, the two groups of equalization circuits are called the odd-group equalization circuit and the even-group equalization circuit in the order from the left. The gate electrodes of the MOSFET switches of all odd-group equalization circuits are connected to the same PWM drive circuit through RC circuits, and the gate electrodes of the MOSFET switches of all even-group equalization circuits are connected to the other PWM drive circuit through RC circuits. The positive electrode of this battery is connected to the negative electrode of the adjacent battery. One end of the winding of the odd-group equalization circuit is also connected to the positive electrode of this battery, and the other end of the winding is connected to the drain of the MOSFET switch. The source of the MOSFET switch is connected to the negative electrode of this battery; correspondingly, the connection method of the even-group equalization circuit is the same as that of the odd-group equalization circuit. The connection methods of the corresponding active equalization circuits of other batteries are also the same as those of this battery.

[0060] In this embodiment, a preferred parameter of the transformer winding is that the primary inductance of the transformer winding ranges from 2 to 10 mH, and the leakage inductance is less than or equal to 5 μH.

[0061] The above active equalization unit can generate an equalization current of 2.5 A, which can drive each battery of a multi-cell series battery pack to perform equalization simultaneously. The electric quantity of the battery with a high voltage is synchronously transferred to the battery with a low voltage through the active equalization unit. The equalization module uses a multi-winding transformer as the core device. For an n-cell series battery pack, the multi-winding transformer has 2n windings with a turns ratio of 1:1 wound on a non-gapped nanocrystalline alloy magnetic ring. The inductance of the primary winding is about 5 mH. Each battery corresponds to 2 groups of windings. The two groups of windings work alternately under a PWM driver with a duty cycle of 50% and a frequency of 30 to 100 KHz, so as to form an induced voltage at each winding port. The value of this induced voltage is equal to the voltage Umax of the battery with the highest voltage in the battery pack. Thus, this active equalization circuit will automatically distribute the energy of the battery with the highest voltage to other batteries with lower voltages according to the battery voltage difference, that is, the battery with the highest voltage is in the discharging state, and the other batteries with lower voltages are in the charging state. The equalization current Ib of a certain battery i is determined by the voltage difference Udi between the voltage Umax of the battery with the highest voltage and the voltage Ui of this battery and the total resistance Rz of the equalization loop of this battery:

[0062]

[0063] In the formula, Rbi is the internal resistance of a single battery, Rl is the total resistance of the connecting wires, RMOS is the internal resistance of the driving MOS, RTdc is the internal resistance of the transformer winding, and RJC is the contact resistance of the loop connector.

[0064] Normally, the driving MOS uses a low-voltage specification of 30V to 50V, with an internal resistance of 10 to 50 mΩ. The smaller the internal resistance, the lower the loss. The length of the transmission wire is in the range of 400 mm to 1200 mm, and the wire resistance is 100 to 200 mΩ. Therefore, Rz is about 200 to 300 mΩ. Generally, the BMS system controls the maximum voltage difference of the battery pack not to exceed 500 mV as an acceptable range. When this value is exceeded, it is considered that the battery pack is abnormal. Thus, the maximum value of the balancing current can reach 2.5 A. The outstanding advantages of multi-path parallel active balancing are large balancing current, synchronous balancing of each battery cell, fast balancing speed, and extremely low energy loss. Balancing can be carried out in various states such as battery charging, discharging, and standing still.

[0065] Since there is always leakage inductance Lk in each winding of the multi-winding transformer, the voltage error ΔV caused by the leakage inductance results in relatively low precision of multi-path parallel active balancing. The measured leakage inductance is between 1.5 and 5 μH. When the experimentally measured leakage inductance Lk = 5 μH, the ΔV error is controlled within 20 mV. In a 16- to 20-series battery pack system, it can only reach the level of 10 to 20 mV, which cannot meet the high balancing precision requirement of 1 to 5 mV in the industry. Therefore, in this embodiment, a passive balancing module is introduced. Cooperating with the active balancing, the passive balancing is started when the battery is close to full charge, which can accelerate the completion of balancing and control the battery voltage difference to a high-precision range of 1 to 5 mV.

[0066] The passive balancing unit turns on or off the passive balancing of the battery pack according to the switching signal of the analog front end. In this embodiment, the passive balancing unit is composed of a discharge resistor, an NPN triode, and a drive circuit, which is connected in parallel across each battery cell and is controlled by the AFE to turn on or off the passive balancing of n battery cells.

[0067] Among them, the switching between the active balancing unit and the passive balancing unit is as follows: The active balancing is controlled by the MCU to start and stop. The MCU controls the active balancing module to perform balancing work and stop balancing in a low-frequency PWM mode according to the battery state and algorithm. The passive balancing is controlled and stopped by the AFE unit, and the MCU can control the start and stop of the passive balancing of the AFE through I2C communication. The switching conditions are the battery voltage, capacity, charge and discharge state, which are generated by the MCU through the control algorithm. For example, when the battery is in a normal state, if the battery is in the charging mode and the voltage difference is greater than 100 mV, the active balancing is started. When the battery voltage is close to the overcharge protection voltage threshold, the passive balancing is started simultaneously to increase the balancing current of the highest battery cell. When the battery voltage difference is close to being consistent and less than 20 mV, the active balancing can be stopped. When the battery voltage difference is less than 2 mV or the value required by the program, the passive balancing can be stopped. The control strategies of active balancing and passive balancing are complex. Based on the basic requirements of battery historical data and safety, combined with the current battery charge and discharge state, SOC value, voltage, and voltage difference of each cell, the balancing scheme is determined through the algorithm to achieve the purpose of eliminating the battery voltage difference and maintaining the battery consistency.

[0068] Please refer to Figure 1 and 3 , the GaN drive unit converts the switch array control signal sent by the analog front end into a drive signal and sends it to the switch array. The GaN drive unit converts the CHG (charge control) and DSG (discharge control) signals sent by the AFE into drive signals for the GaN HEMT.

[0069] Please refer to Figure 1 and 3 , the switch array includes a number of bidirectional conducting GaN HEMTs connected in parallel with the same specifications, and responds to the drive signal to switch the charging, discharging and protection states of the battery pack. The GaN HEMT is a bidirectional symmetric conducting structure switch element with three terminals, where D1 and D2 are symmetric conducting terminals, and G is the gate drive terminal. The gate drive ends of the GaN HEMTs are all connected to the drive signals of the GaN drive unit. One end D2 of the symmetric conducting end is connected to the load or charger, and the other end D1 is connected to the negative pole of the battery pack. In some embodiments of the present invention, for example, 5 GaN HEMTs with an internal resistance of 100V and 1.2mΩ are connected in parallel to meet the battery protection requirements of a rated charge and discharge current of 50A, an overcurrent of 100A, and a short circuit of 1500A. The two signals DSG and CHG connected between the AFE and the GaN drive unit are respectively the drive signals when the AFE is connected to the traditional MOS. DSG is the drive signal of the discharge MOS, and CHG is the drive signal of the charging MOS.

[0070] The GaN drive unit and switch array of this embodiment are as shown in Figure 3 . In Figure 3 , the U2 chip is the GaN drive unit, which receives the control signal of the AFE through the CHG and DSG pins, and sends the drive signal to the gate drive end of the GaN HEMT of the switch array through the GRV pin according to the control signal.

[0071] For a battery pack of 36 - 72V, the voltage of the GaN HEMT set according to this embodiment is 100V, and the internal resistance is usually between 1 - 3mΩ. A single transistor can continuously conduct a current of about 10A. As shown in Figure 3 , Q1, Q2, and Qm are the 1st, 2nd, and mth GaN HEMT devices respectively. Usually, a single GaN HEMT can allow a continuous discharge / charge current of about 10A. If the charge and discharge current is large, multiple GaN HEMTs need to be connected in parallel to expand the current conduction capacity of the switch array. If the circuit needs to ensure a long-term charge or discharge current of 50A, usually 50A / 10A = 5 GaN HEMTs need to be connected in parallel. Generally, the parallel number m = rated charge and discharge current / 10A.

[0072] The current sampling unit is connected in series between one end of the switch array and the battery pack, and sends the differential signal on the sampling resistor into the analog front end through the differential sampling circuit. As Figure 1 shown, the current sampling unit in this embodiment is composed of several resistors with low resistance in parallel, which are connected in series between one end of the GaN HEMT and the negative terminal B- of the battery, and send the differential signals CS1 and CS2 on the sampling resistor into the AFE unit through the differential sampling circuits RS1 and RS2.

[0073] The temperature acquisition unit acquires the battery temperature to the analog front end through a thermistor.

[0074] The first communication unit includes RS485 and / or CAN communication circuits, and is used for wired communication interaction with an external system.

[0075] In the circuit as Figure 1 shown, the battery terminal is connected to the n-section series lithium battery pack through the acquisition line, and the voltage of each battery can be acquired and the battery can be balanced. The temperature acquisition unit externally arranges an NTC (Negative Temperature Coefficient thermistor) sensor to be connected to the battery surface to acquire the battery temperature. The negative terminal B- of the battery pack is connected to the B- terminal of the BMS module, and the positive terminal of the battery pack is connected to the B+ terminal of the BMS module to provide auxiliary power supply. It is also connected to the positive terminal of the external load, and the negative terminal of the load is connected to the P- terminal of the BMS. The load current flows through the GaN HEMT switch array and the current detection unit in the module to complete the power supply to the load, battery charging control, current detection and related protection functions.

[0076] In some other embodiments of the present invention, the BMS module further includes a TVS protection unit, and the TVS protection unit includes several transient voltage suppressors TVS (Transient Voltage Suppressor), which are connected in parallel to the two-side switch ends of the switch array. The TVS is used to absorb the overvoltage generated when the GaN HEMT is turned off, and protect the GaN HEMT from being damaged by the high-voltage voltage spike exceeding the rated withstand voltage.

[0077] In some other embodiments of the present invention, the BMS module further includes a second communication unit, and the second communication unit receives power supply from the first power supply unit or the second power supply unit and communicates with the micro control unit; it includes one or more combinations of cellular network communication, Bluetooth communication, Beidou communication, Beidou positioning, and GPS positioning, and is used for information interaction and control with an external system.

[0078] The drive signal includes the following modes:

[0079] The driving signal voltage is 5V higher than the voltage at the load end of the GaN HEMT, that is, the driving signal voltage is 5V higher than the potential at the D2 terminal of the GaN HEMT. The GaN HEMT is turned on, used for the battery pack to connect to the load and provide a discharge current for the load; the current flows out from the positive electrode B+ of the battery, flows into the positive end of the load, passes through the load to the negative end P- of the load, and then returns to the negative electrode B- of the battery through multiple parallel current sampling resistors Rs1 to RSm.

[0080] The driving signal voltage is equal to the voltage at the load end of the GaN HEMT, that is, the driving signal voltage is equal to the potential at the D2 terminal of the GaN HEMT. The GaN HEMT is turned off, and the current cannot flow between the D1 and D2 terminals, used for the battery pack to connect to the load and stop discharging to the load.

[0081] The driving signal voltage is 5V higher than the potential corresponding to the negative terminal of the battery pack of the GaN HEMT, that is, the driving signal voltage is 5V higher than the potential at the D1 terminal of the GaN HEMT. The GaN HEMT is turned on, used for the battery pack to connect to the charger and the charger to charge the battery; at this time, the charger can charge the battery, and the charging current flows out from the positive electrode of the charger, flows into the positive electrode B+ of the battery, flows out from the negative electrode B- of the battery, and then flows through the current sampling resistors RS1 to RSm to the D2 terminal of the GaN HEMT, and returns to the negative electrode of the charger through the D1 terminal of the GaN HEMT to complete the charging of the battery.

[0082] The driving signal voltage is equal to the potential corresponding to the negative terminal of the battery pack of the GaN HEMT, that is, the driving signal voltage is equal to the potential at the D1 terminal of the GaN HEMT. The GaN HEMT is turned off, and the charging current is cut off, used for the battery pack to connect to the charger and stop charging.

[0083] Embodiment 2

[0084] This embodiment is a battery equalization control method. The battery equalization control method uses the BMS module as described in Embodiment 1, and includes the following steps:

[0085] The analog front end collects the voltage, working current, temperature, state of charge, health state, and historical cycle data of the battery, calculates and judges the battery state according to the collected data, and monitors the voltage difference between the batteries;

[0086] If the voltage difference is greater than or equal to the passive equalization threshold, the analog front end controls the passive equalization unit to start the passive equalization function;

[0087] The analog front end communicates with the micro control unit. When the voltage difference meets the preset conditions, the micro control unit controls the active equalization unit to perform active equalization through periodic switching control until the active equalization stop condition is met.

[0088] The battery operating state is combined with multi-channel parallel synchronous active balancing and passive balancing. On the one hand, it ensures the efficiency and effect of battery balancing. On the other hand, it ensures the elimination of battery voltage acquisition and SOC capacity errors caused by active balancing to ensure safety. The AFE samples the battery voltage, judges the state of the battery through internal calculation, and then controls the bidirectional GaN HEMT according to the battery state to realize the charging, discharging and protection functions of the battery; the AFE internally judges the voltage difference between each section of the battery pack at the same time. When the voltage difference between the batteries is greater than the preset passive balancing threshold, the passive balancing function is started; the AFE communicates with the MCU. When the battery voltage difference meets the preset conditions, the MCU controls the start of active balancing. The active balancing working mode of this embodiment is the low-frequency PWM mode, that is, the active balancing will stop balancing briefly every time it works for a period of time. The AFE samples the battery voltage without balancing conditions, and then starts the active balancing again after the AFE finishes sampling the battery voltage. It can not only ensure that the voltages of all series-connected batteries are always kept consistent, inhibit the attenuation of battery capacity, and extend the battery life; but also ensure that the aging and abnormal fault batteries can be detected early to ensure battery safety.

[0089] Specifically, the preset condition for starting active balancing is that the voltage difference is greater than or equal to the preset active balancing start voltage difference. In some other embodiments of the present invention, it should also meet that the battery voltage is within the preset safe range. The active balancing stop conditions include: the voltage difference is less than or equal to the preset stop voltage difference, and / or the battery voltage is within the preset safe range, and / or the voltage difference is greater than the preset safe voltage difference.

[0090] As Figure 4 shown, the horizontal axis of the coordinates in the figure represents time, and the vertical axis represents the voltage difference ΔU. The three marking lines on the vertical axis from small to large are the preset stop voltage difference ΔU_stop, the active balancing start voltage difference ΔU_start and the preset safe voltage difference ΔU_error in sequence; the voltage difference between ΔU_stop and ΔU_error is the active balancing interval. The active balancing is controlled by periodic switching, specifically:

[0091] Enter the active balancing working stage (ON), and last for the set first time period (Ton). In the active balancing working stage (ON), drive the multi-winding transformer to conduct to perform the balancing operation;

[0092] When the first time period (Ton) ends, enter the active balancing stop (OFF) stage, and last for the set second time period (Toff). In the active balancing stop stage (OFF), drive the circuit to turn off to stop the balancing operation;

[0093] The active balancing working stage (ON) and the active balancing stop stage (OFF) alternate cyclically to form a periodic switching control mode.

[0094] Specifically, please refer toFigure 4 For the PWM waveform corresponding to the active balancing operation, as the battery pack charges and discharges, the voltage difference between individual batteries gradually increases. Before the voltage difference reaches ΔU_start, the active balancing is not initiated. When the voltage difference reaches ΔU_start, the level of the low-frequency PWM waveform switches, for example, switches to a high level as shown in the figure, and the active balancing unit starts to perform active balancing on the battery pack. After the high level is maintained for a period of time (Ton), the low-frequency PWM waveform switches to a low level, and the active balancing unit stops balancing. After the low level is maintained for a period of time (Toff), it is determined again whether to switch to a high level based on the voltage difference. Figure 4 Since the voltage difference does not drop to ΔU_stop, the active balancing is continued; this cycle continues until the voltage difference ΔU drops to the preset stop voltage difference ΔU_stop, and the active balancing ends.

[0095] The analog front end also acquires the first battery voltage of each battery during the active balancing operation stage and the second battery voltage of each battery during the active balancing stop stage; calibrates the state of charge of the battery based on the first battery voltage and the second battery voltage, and makes an early judgment on battery aging or faults based on the first battery voltage, the second battery voltage, the voltage difference, and the BMS historical data.

[0096] In this embodiment, the first time period (Ton) is between 500 milliseconds and 10 minutes, and the second time period (Toff) is between 1 second and 60 minutes. In other embodiments of the present invention, the first time period (Ton) and the second time period (Toff) can be adjusted as needed. For example, when the battery is in a safe state, the first time period (Ton) can be increased and the second time period (Toff) can be decreased; when the battery may be aging or abnormal, the second time period (Toff) can be gradually increased.

[0097] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A large-current equalization BMS module based on GaN HEMT, used for the protection and equalization management of multi-section series battery packs, characterized in that, The circuit of the module includes: A power supply unit for taking power from the battery pack to supply power to other units in the module; An analog front end for collecting battery voltage, current, temperature and switch array control information and sending it to the micro control unit, sending control signals to the GaN driver unit, and switching the working state of the passive equalization unit according to the signals of the micro control unit; A micro control unit for analyzing the battery state based on the acquired data, performing active equalization and passive equalization control on the battery, and communicating with the first communication unit; An active equalization unit for performing active equalization on the battery pack according to the control signal of the micro control unit; A passive equalization unit for turning on or off the passive equalization of the battery pack according to the switching signal of the analog front end; A GaN driver unit for converting the switch array control signal sent by the analog front end into a drive signal and sending it to the switch array; The switch array includes a number of bidirectional conducting GaN HEMTs connected in parallel with the same specifications, which respond to the drive signal to switch the charging, discharging and protection states of the battery pack. The gate drive ends of the GaN HEMTs are all connected to the drive signal of the GaN driver unit, one end of the symmetric conduction end is connected to the load or charger, and the other end is connected to the negative pole of the battery pack; A current sampling unit is connected in series between one end of the switch array and the battery pack, and the differential signal on the sampling resistor is sent into the analog front end through a differential sampling circuit; A temperature acquisition unit for collecting the battery temperature to the analog front end through a thermistor; The first communication unit includes RS485 and / or CAN communication circuits for wired communication interaction with an external system.

2. The large current balancing BMS module based on GaN HEMT according to claim 1, wherein The power supply unit includes a first power supply unit and a second power supply unit. The first power supply unit takes power from the battery pack and generates a 12V power supply through BUCK step-down to provide it to the second power supply unit; the second power supply unit outputs a 3.3V power supply to the micro control unit and the first communication unit.

3. The large current balancing BMS module based on GaN HEMT according to claim 1, characterized in that, The BMS module further includes a TVS protection unit, and the TVS protection unit includes a number of transient voltage suppressor TVS tubes connected in parallel to the two side switch ends of the switch array.

4. A large - current equalization BMS module based on GaN HEMT according to claim 1, characterized in that, The BMS module further includes a second communication unit, and the second communication unit receives the power supply from the first power supply unit or the second power supply unit and communicates with the micro control unit; Including one or more combinations of cellular network communication, Bluetooth communication, Beidou communication, Beidou positioning, and GPS positioning for information interaction and control with an external system.

5. A high-current equalizing BMS module based on GaN HEMT according to any one of claims 1-4, characterized in that, The active equalization unit includes a multi-winding transformer, MOSFET switches and a PWM drive circuit; The multi-winding transformer further includes 2n windings with a turn ratio of 1:1, where n is the number of battery cells, and each battery cell corresponds to two windings. One end of the two windings is connected to the positive pole of the corresponding battery; The MOSFET switches correspond to the windings one by one and are used to control the conduction and cutoff of the windings. The drain of the MOSFET switch is connected to the other end of the corresponding winding, the source is connected to the negative pole of the corresponding battery, and the gate is connected to the PWM drive circuit; The PWM drive circuit receives two complementary PWM signals from the microcontroller unit. One path drives the MOSFETs connected in series with the first winding corresponding to each battery, and the other path drives the MOSFETs connected in series with the second winding.

6. A high-current equalization BMS module based on GaN HEMT according to any one of claims 1-4, characterized in that, The drive signals include the following modes: The voltage of the drive signal is 5V higher than the voltage at the load end of the GaN HEMT, and the GaN HEMT is turned on, which is used for the battery pack to connect to the load and provide a discharge current for the load. The voltage of the drive signal is equal to the voltage at the load end of the GaN HEMT, and the GaN HEMT is turned off, which is used for the battery pack to connect to the load and stop discharging the load. The voltage of the drive signal is 5V higher than the potential at the negative terminal of the battery pack corresponding to the GaN HEMT, and the GaN HEMT is turned on, which is used for the battery pack to be connected to the charger and the charger to charge the battery. The voltage of the drive signal is equal to the potential at the negative terminal of the battery pack corresponding to the GaN HEMT, and the GaN HEMT is turned off, which is used for the battery pack to be connected to the charger and stop charging.

7. A battery balancing control method, characterized in that, The control method uses the BMS module as described in any one of claims 1-4, and includes the following steps: The analog front end collects the voltage, working current, temperature, state of charge, health state, and historical cycle data of the battery, calculates and judges the battery state according to the collected data, and monitors the voltage difference between the batteries. When the voltage difference is greater than or equal to the passive equalization threshold, the analog front end controls the passive equalization unit to start the passive equalization function. The analog front end communicates with the microcontroller unit. When the voltage difference meets the preset conditions, the microcontroller unit controls the active equalization unit to perform active equalization through periodic switching until the active equalization stop condition is met.

8. The battery equalization control method according to claim 7, wherein, The active equalization through periodic switching is specifically as follows: Enter the active equalization working stage and last for a set first time period. In the active equalization working stage, drive the multi-winding transformer to conduct to perform the equalization operation. When the first time period ends, enter the active equalization stop stage and last for a set second time period. In the active equalization stop stage, turn off the drive circuit to stop the equalization operation. The active equalization working stage and the active equalization stop stage alternate cyclically to form a periodic switching control mode.

9. The battery equalization control method according to claim 8, wherein The analog front end also collects the first battery voltage of each battery in the active equalization working stage and the second battery voltage of each battery in the active equalization stop stage; calibrate the state of charge of the battery through the first battery voltage and the second battery voltage, and perform an early judgment on battery aging or faults according to the first battery voltage, the second battery voltage, the voltage difference, and the BMS historical data.

10. The battery equalization control method according to claim 8, wherein, The first time period is between 500 milliseconds and 10 minutes, and the second time period is between 1 second and 60 minutes.

Images