Lithium battery equalization control circuit with charging and replenishing function and control method thereof

Abstract

The present invention discloses a lithium battery balancing control circuit with charging and replenishing function and a control method thereof. The circuit comprises an MCU main control unit, a charging and discharging control unit and a battery cell group formed by connecting a plurality of battery cells in series. The first end of the MCU main control unit is electrically connected to each battery cell through a collection and balancing circuit unit. The charging and discharging control unit comprises a MOS driving circuit, a charging MOS tube Q c And discharge MOS tube Q d The second end of the MCU main control unit is connected to the input end of the charge and discharge control unit, and the output end of the charge and discharge control unit is connected to the charging MOS tube Q c The gate and discharge MOS tube Q d The gate of the charging MOS tube Q c A charging and power replenishment circuit is connected in parallel at both ends of the device; and a corresponding control method is disclosed. The present invention significantly prolongs the start time of passive balancing by adding a charging and power replenishment circuit, significantly improves the balancing efficiency, reduces the probability of misbalancing and error balancing of lithium batteries, and has high cost performance.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a lithium battery equalization control circuit with charging and supplementing functions and a control method thereof. Background Art

[0002] With the continuous progress of society, lithium batteries have grown suddenly as a new energy source, and their application has gradually become popular in various fields, especially in electric vehicles, such as electric cars, electric buses, electric vans, electric trucks, electric taxis, etc., and have gradually been put on the market.

[0003] A lithium battery pack is composed of N strings of cells. According to the chemical characteristics, if the voltage difference between two strings of cells is too large, it will cause an imbalance in power. For example, the voltage of one string of cells is 3.6V, and the voltage of the other string of cells is 2.5V. The large difference can easily cause the battery to be scrapped. If the difference between the maximum cell voltage and the minimum cell voltage reaches a certain limit, the probability of failure is very high, so neither discharge nor charging should continue. In order to avoid this situation as much as possible, the BMS battery management system equipped with the lithium battery will be designed with a voltage balancing function. The BMS battery management system, the full name of which is Battery Management System, is a module specifically used for lithium battery operation management.

[0004] Voltage balancing is divided into two types: active and passive. Passive balancing is to design hardware voltage and use voltage comparators. When the voltage of a battery string is too high compared to the voltage of other batteries (for example, the difference reaches 50ms), other components are used to consume the power of the high-voltage battery, or the power of the high-voltage battery is transferred to the low-voltage battery. Active balancing is the same in principle, but more details of the balancing can be controlled by the program, and a serial-to-parallel decoder is used to make a switching circuit. The control system only balances during the charging process, and the voltage threshold for balancing can be set more flexibly.

[0005] Lithium batteries have their own special voltage platform characteristics, especially lithium iron phosphate batteries. In the platform stage, more than 85% of the capacity is concentrated in the voltage range of tens of millivolts, and the cell voltage-SOC correlation curve is very flat. At the end of charge and discharge, as the internal resistance of the cell increases, the cell voltage-SOC correlation curve becomes slightly steeper, but the capacity of these two stages of charge and discharge often only accounts for about 10% of the total capacity.

[0006] Based on this characteristic of lithium batteries, the passive balancing function of the existing multi-string lithium battery BMS battery management system has the following limitations when used:

[0007] 1. The balancing time is short. The passive balancing is started at the charging end of the battery module, but the capacity of the charging end accounts for less than 5% of the battery cell capacity, so the time available for starting the passive balancing is short.

[0008] 2. There are mis-average and erroneous averaging. Some BMSs lower the balancing start voltage to the lithium battery voltage platform to extend the balancing time. However, due to the accuracy of the existing cell voltage acquisition circuit, there is a deviation in the accuracy of identifying the true cell voltage, which results in the cells with higher SOC not being balanced, while the cells with lower SOC are mistakenly balanced, which further worsens the SOC inhomogeneity of the module cells. Summary of the invention

[0009] The present invention provides a lithium battery equalization control circuit with charging and replenishing function and a control method thereof to solve the above technical problems.

[0010] In order to achieve the above object, the technical solution adopted by the present invention is:

[0011] According to a first aspect of an embodiment of the present invention, a lithium battery balancing control circuit is provided, including an MCU main control unit, a charge and discharge control unit, and a battery cell group formed by connecting a plurality of battery cells in series, wherein a first end of the MCU main control unit is electrically connected to each battery cell through a collection and balancing circuit unit, and the charge and discharge control unit includes a MOS drive circuit, a charging MOS tube Q c And discharge MOS tube Q d The second end of the MCU main control unit is connected to the input end of the charge and discharge control unit, and the output end of the charge and discharge control unit is connected to the charging MOS tube Q c The gate and discharge MOS tube Q d The gate of the charging MOS tube Q c The drain and discharge MOS tube Q d The drain of the discharge MOS tube Q d The source electrode is connected to the negative electrode of the battery pack, and the charging MOS tube Q c A charging circuit is connected in parallel at both ends.

[0012] Preferably, the charging and power replenishment circuit includes a power replenishment MOS tube Q b And the compensation resistor R p , the power-supply MOS tube Q b The drain and charging MOS tube Q c The drain is connected to the compensation resistor R p The two ends of the MOS tube Q b The source of the charging MOS tube Q c The source.

[0013] Preferably, the acquisition and balancing circuit unit comprises a sampling circuit and a plurality of battery cell balancing circuits connected in parallel at both ends of the battery cell, and the battery cell balancing circuit is electrically connected to the sampling circuit.

[0014] As a further preference, the cell balancing circuit includes a balancing resistor and a balancing MOS tube connected in series, the drain of the balancing MOS tube is connected to the positive electrode of the cell, the two ends of the balancing resistor are respectively connected to the negative electrode of the cell and the source of the balancing MOS tube, and the gate of the balancing MOS tube is electrically connected to the sampling circuit.

[0015] Preferably, if the voltage value of one of the battery cells is greater than the balancing start-up voltage, and the difference between the battery cell voltage value and the lowest battery cell voltage value is greater than the first difference, the passive balancing of the battery cell is turned on; if the voltage value of one of the battery cells after passive balancing is turned on is less than the balancing start-up voltage, or the voltage value of the battery cell after passive balancing is turned on is greater than the balancing start-up voltage and the difference between the battery cell voltage value and the lowest battery cell voltage value is less than the second difference, the passive balancing of the battery cell is turned off.

[0016] As a further preference, the battery cell group is a lithium iron phosphate battery, the balanced start-up voltage of each battery cell is 3.45V, the first difference is 50mV, and the second difference is 20mV.

[0017] Preferably, the battery cell group is a lithium iron phosphate battery. When the battery cell is overvoltage protected and the highest battery cell voltage value is less than 3.55V or the lowest battery cell voltage value is greater than the battery cell overvoltage protection recovery voltage value, the charging and replenishing circuit is turned on; if the difference between the highest battery cell voltage value and the lowest battery cell voltage value is less than the second difference and the highest battery cell voltage value is greater than the equalization start-up voltage, or the highest battery cell voltage value is greater than the battery cell overcharge protection voltage, the charging and replenishing circuit is turned off.

[0018] As a further preference, the balanced start-up voltage of each battery cell is 3.45V, the battery cell overvoltage protection recovery voltage value is 3.34V, the battery cell overcharge protection voltage is 3.65V, and the second difference is 20mV.

[0019] According to a second aspect of an embodiment of the present invention, a lithium battery balancing control method is provided, which is applied to the lithium battery balancing control circuit as described above, wherein the battery cell group includes n battery cells CELL i , i and n are positive integers and 1≤i≤n, the battery pack is a lithium iron phosphate battery, comprising the following steps:

[0020] Step 101, the MCU main control unit charges the MOS tube Q c Charging the battery pack and collecting the voltage value of each battery cell through the collection and balancing circuit unit;

[0021] Step 102: When the voltage value U of the i-th battery cell is CELLiAfter exceeding the balanced opening voltage, if the difference between the voltage value of the ith cell and the lowest cell voltage value is greater than the first difference, the cell CELL is turned on. i Balanced switch Q i , turn on the cell CELL i Passive equilibrium;

[0022] Step 103, through the charging MOS tube Q c Continue to charge the battery pack until the maximum battery voltage value U CELLmax When the voltage is greater than 3.65V, the overcharge protection is triggered and the charging MOS tube Q is turned off. c ;

[0023] Step 104: During the charging process, when the highest cell voltage value U CELLmax <3.55V and the minimum cell voltage value U CELLmin Higher than the cell overvoltage protection recovery voltage, turn on the power-up MOS tube Q b The battery is continuously replenished through the replenishment circuit. When the highest cell voltage value U CELLmax When the voltage is higher than the overcharge protection voltage of the battery cell, the MOS tube Q is turned off. b ;

[0024] Step 105: the highest cell voltage value U CELLmax During the fallback process, when the highest cell voltage value U CELLmax <3.55V and the minimum cell voltage value U CELLmin Higher than the cell overvoltage protection recovery voltage value, re-enable the power MOS tube Q b , repeat step 104 so that the voltage of each battery cell that has started balancing is always kept above the balancing start voltage;

[0025] Step 106, when the balanced cell CELL is turned on i The voltage value U CELLi With the lowest single cell voltage value U CELLmin The difference is less than the second difference, and the cell CELL i The voltage value U CELLi When it is greater than the balanced start voltage or the cell CELL i The voltage value U CELLi Lower than the balanced start voltage, turn off the cell i Balance switch CELL i , turn off the cell CELL i Passive equilibrium;

[0026] Step 107: When the difference U between the highest cell voltage value and the lowest cell voltage value is CELLmax -U CELLmin Less than the second difference and the highest cell voltage value U CELLmaxWhen the voltage is greater than the balanced start-up voltage, the MOS tube Q is turned off. b , turn off passive balancing for all cells that have passive balancing turned on.

[0027] Preferably, the balanced start-up voltage of each battery cell is 3.45V, the battery cell overvoltage protection recovery voltage value is 3.34V, the battery cell overcharge protection voltage is 3.65V, the first difference is 50mV, and the second difference is 20mV.

[0028] Compared with the prior art, the present invention adds a charging and replenishing circuit to the charging control loop of the BMS battery management system, which greatly prolongs the start-up time of passive balancing, significantly improves the balancing efficiency, reduces the probability of misbalancing and incorrect balancing of lithium batteries, and has high cost performance. Through the charging and replenishing circuit, under certain conditions, the voltage of all series-connected cells can be controlled within a smaller range (such as 20mV) without triggering single-cell charging protection, reducing the risk of voltage breakdown when the charging switch cuts off a large current during single-cell overcharging protection, and increasing the reliability of BMS operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a circuit diagram of a lithium battery balancing control circuit with charging and supplementing function.

[0030] In the figure, 1-MCU main control unit, 2-charge and discharge control unit, 3-collection and balancing circuit unit, 4-charging and replenishing circuit, 5-MOS driving circuit, 6-sampling circuit. DETAILED DESCRIPTION

[0031] The present invention will be described in detail below in conjunction with the specific embodiments shown in the accompanying drawings. However, these embodiments do not limit the present invention, and any structural, methodological, or functional changes made by a person skilled in the art based on these embodiments are all within the scope of protection of the present invention.

[0032] The terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "the" and "the" used in the present invention and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0033] like Figure 1As shown, a lithium battery balancing control circuit with charging and replenishing function includes an MCU main control unit 1, a charging and discharging control unit 2, and a battery cell group formed by connecting a plurality of battery cells in series. The first end of the MCU main control unit 1 is electrically connected to each battery cell through a collection and balancing circuit unit 3. The charging and discharging control unit 1 includes a MOS driving circuit 5, a charging MOS tube Q c And discharge MOS tube Q d The second end of the MCU main control unit 1 is connected to the input end of the charge and discharge control unit 2, and the output end of the charge and discharge control unit 2 is connected to the charging MOS tube Q c The gate and discharge MOS tube Q d The gate of the charging MOS tube Q c The drain and discharge MOS tube Q d The drain of the discharge MOS tube Q d The source electrode is connected to the negative electrode of the battery pack, and the charging MOS tube Q c A charging and replenishing circuit 4 is connected in parallel at both ends.

[0034] The battery cell group used in the present invention generally consists of n battery cells CELL i The MCU main control unit 1 is the main control chip and peripheral circuit of the BMS battery management system, which is used for collecting battery cell data and driving the charge and discharge control unit 2 to achieve balanced control of the lithium battery.

[0035] In one embodiment of the present invention, the charging and power replenishment circuit 4 may include a power replenishment MOS tube Q b And the compensation resistor R p , where the power supply MOS tube Q b The drain and charging MOS tube Q c The drain is connected to the compensation resistor R p The two ends of the MOS tube Q b The source of the charging MOS tube Q c The source.

[0036] The collection and equalization circuit unit 3 includes a sampling circuit 6 for collecting the voltage value of each battery cell and a plurality of battery cell equalization circuits connected in parallel at both ends of the battery cell for equalizing the battery cell voltages. The battery cell equalization circuit is electrically connected to the sampling circuit 6 .

[0037] Specifically, each cell balancing circuit includes a balancing resistor and a balancing MOS tube connected in series, the drain of the balancing MOS tube is connected to the positive electrode of the cell, and the two ends of the balancing resistor are respectively connected to the negative electrode of the cell and the source of the balancing MOS tube. Figure 1 Connect in parallel with the battery cell CELL n The balancing resistor R n And balanced MOS tube Q n, the gate of each balancing MOS tube is connected to the sampling circuit 6. The structure of the sampling circuit 6 and the connection method between the gate of the balancing MOS tube and the sampling circuit 6 are conventional circuits, which will not be described in detail here.

[0038] Here, the passive balancing logic of each battery cell is as follows: if the voltage value of one of the battery cells is greater than the balancing start-up voltage, and the difference between the battery cell voltage value and the lowest battery cell voltage value is greater than the first difference, then the passive balancing of the battery cell is turned on; if the voltage value of one of the battery cells after passive balancing is turned on is less than the balancing start-up voltage, or the voltage value of the battery cell after passive balancing is turned on is greater than the balancing start-up voltage and the difference between the battery cell voltage value and the lowest battery cell voltage value is less than the second difference, then the passive balancing of the battery cell is turned off.

[0039] Here, the battery pack generally uses lithium iron phosphate batteries, which are generally equipped with overvoltage protection. The conditions for opening and closing the charging and recharging circuit 4 are as follows: when the battery cell is in overvoltage protection, and the highest battery cell voltage value is less than 3.55V or the lowest battery cell voltage value is greater than the battery cell overvoltage protection recovery voltage value, the charging and recharging circuit is turned on, that is, the recharging MOS tube Q is turned on. b If the difference between the highest cell voltage and the lowest cell voltage is less than the second difference and the highest cell voltage is greater than the equalization start voltage, or the highest cell voltage is greater than the cell overcharge protection voltage, the charging and replenishing circuit is turned off, that is, the replenishing MOS tube Q is turned off. b .

[0040] Among them, the balanced start voltage of each battery cell is 3.45V, the battery cell overvoltage protection recovery voltage value is 3.34V, the battery cell overcharge protection voltage is 3.65V, and the second difference is 20mV. These values ​​are selected based on multiple tests and experience.

[0041] The present invention connects a charging and recharging circuit 4 consisting of an electronic switch and a power resistor in series in parallel to the lithium battery BMS charging circuit control switch, thereby constructing a new BMS battery management system connected to the battery cell group. After the lithium battery is fully charged and meets certain voltage conditions, by turning on the charging and recharging circuit 4, the battery can be charged with a small current, the balancing time can be extended, and the risk of mis-balancing and mis-balancing can be reduced. Under certain conditions, the voltage of all series-connected cells in the module can be controlled within a small range (such as 20mV) to avoid triggering the single-cell charging protection, reduce the probability of turning off the charging protection switch under high current conditions, and increase the reliability of the system.

[0042] Based on the above lithium battery balancing control circuit, the present invention provides a lithium battery balancing control method, comprising the following steps:

[0043] Step 101, the MCU main control unit charges the MOS tube Q cCharging the battery pack and collecting the voltage value of each battery cell through the collection and balancing circuit unit;

[0044] Step 102: When the voltage value U of the i-th battery cell is CELLi After exceeding the balanced opening voltage, if the difference between the voltage value of the ith cell and the lowest cell voltage value is greater than the first difference, the cell CELL is turned on. i Balanced switch Q i , turn on the cell CELL i Passive equilibrium;

[0045] Step 103, through the charging MOS tube Q c Continue to charge the battery pack until the maximum battery voltage value U CELLmax When the voltage is greater than 3.65V, the overcharge protection is triggered and the charging MOS tube Q is turned off. c ;

[0046] Step 104: During the charging process, when the highest cell voltage value U CELLmax <3.55V and the minimum cell voltage value U CELLmin Higher than the cell overvoltage protection recovery voltage, turn on the power-up MOS tube Q b The battery is continuously replenished through the replenishment circuit. When the highest cell voltage value U CELLmax When the voltage is higher than the overcharge protection voltage of the battery cell, the MOS tube Q is turned off. b At this time, the battery is at the end of charging, the cell voltage-SOC curve is steep, and a relatively small supplementary current can maintain the cell voltage above the equilibrium start voltage. n The passive equilibrium can continue;

[0047] Step 105: the highest cell voltage value U CELLmax During the fallback process, when the highest cell voltage value U CELLmax <3.55V and the minimum cell voltage value U CELLmin Higher than the cell overvoltage protection recovery voltage value, re-enable the power MOS tube Q b , repeat step 104 so that the voltage of each battery cell that has started balancing is always kept above the balancing start voltage;

[0048] Step 106, when the balanced cell CELL is turned on i The voltage value U CELLi With the lowest single cell voltage value U CELLmin The difference is less than the second difference, and the cell CELL i The voltage value U CELLi When it is greater than the balanced start voltage or the cell CELL i The voltage value U CELLi Lower than the balanced start voltage, turn off the cell iBalance switch CELL i , turn off the cell CELL i Passive equilibrium;

[0049] Step 107: When the difference between the highest cell voltage value and the lowest cell voltage value is U CELLmax -U CELLmin Less than the second difference and the highest cell voltage value U CELLmax When the voltage is greater than the balanced start-up voltage, the MOS tube Q is turned off. b , turn off passive balancing for all cells that have passive balancing turned on.

[0050] In this way, the balance of the lithium battery module is completed, and the voltage difference of all the battery cells connected in series is controlled to be smaller than the second difference.

[0051] Among them, the balanced start-up voltage of each battery cell is 3.45V, the battery cell overvoltage protection recovery voltage value is 3.34V, the battery cell overcharge protection voltage is 3.65V, the first difference is 50mV, and the second difference is 20mV.

[0052] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the present invention, which follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and examples are intended to be exemplary only, and the true scope and spirit of the present invention are indicated by the claims of the present application.

[0053] It should be understood that the present invention is not limited to the exact construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A lithium battery balancing control method is applied to a lithium battery balancing control circuit with charging and replenishing function. The lithium battery balancing control circuit includes an MCU main control unit, a charge and discharge control unit, and a battery cell group composed of several battery cells connected in series. The battery cell group includes n battery cells CELL i , i and n are positive integers and 1≤i≤n, the battery pack is a lithium iron phosphate battery, characterized in that, The first end of the MCU main control unit is electrically connected to each battery cell through a collection and balancing circuit unit, and the charge and discharge control unit includes a MOS drive circuit, a charging MOS tube Q c And discharge MOS tube Q d The second end of the MCU main control unit is connected to the input end of the charge and discharge control unit, and the output end of the charge and discharge control unit is connected to the charging MOS tube Q c The gate and discharge MOS tube Q d The gate of the charging MOS tube Q c The drain and discharge MOS tube Q d The drain of the discharge MOS tube Q d The source electrode is connected to the negative electrode of the battery pack, and the charging MOS tube Q c A charging and power replenishment circuit is connected in parallel at both ends of the charging and power replenishment circuit; the charging and power replenishment circuit includes a power replenishment MOS tube Q b And the compensation resistor R p , the power-supply MOS tube Q b The drain and charging MOS tube Q c The drain is connected to the compensation resistor R p The two ends of the MOS tube Q b The source of the charging MOS tube Q c The acquisition and balancing circuit unit includes a sampling circuit and a plurality of cell balancing circuits connected in parallel to the two ends of the cell, and the cell balancing circuit is electrically connected to the sampling circuit; the cell balancing circuit includes a balancing resistor and a balancing MOS tube connected in series, the drain of the balancing MOS tube is connected to the positive electrode of the cell, the two ends of the balancing resistor are respectively connected to the negative electrode of the cell and the source of the balancing MOS tube, and the gate of the balancing MOS tube is electrically connected to the sampling circuit; The steps include: Step 101, the MCU main control unit charges the MOS tube Q c Charging the battery pack and collecting the voltage value of each battery cell through the collection and balancing circuit unit; Step 102: When the voltage value U of the i-th battery cell is CELLi After exceeding the balanced opening voltage, if the difference between the voltage value of the ith cell and the lowest cell voltage value is greater than the first difference, the cell CELL is turned on. i Balanced switch Q i , turn on the cell CELL i Passive equilibrium; Step 103, through the charging MOS tube Q c Continue to charge the battery pack until the maximum battery voltage value U CELLmax Greater than 3.65V triggers overcharge protection and shuts down the charging MOS tube Q c ; Step 104: During the charging process, when the highest cell voltage value U CELLmax <3.55V and the minimum cell voltage value U CELLmin Higher than the cell overvoltage protection recovery voltage, turn on the power-up MOS tube Q b The battery is continuously replenished through the replenishment circuit. When the highest cell voltage value U CELLmax When the voltage is higher than the overcharge protection voltage of the battery cell, the MOS tube Q is turned off. b ; Step 105, the highest cell voltage value U CELLmax During the fallback process, when the highest cell voltage value U CELLmax <3.55V and the minimum cell voltage value U CELLmin Higher than the cell overvoltage protection recovery voltage value, re-enable the power MOS tube Q b , repeat step 104 so that the voltage of each battery cell that has started balancing is always kept above the balancing start voltage; Step 106, when the balanced cell CELL is turned on i The voltage value U CELLi With the minimum single cell voltage value U CELLmin The difference is less than the second difference, and the cell CELL i The voltage value U CELLi Greater than the balanced start voltage or cell CELL i The voltage value U CELLi Lower than the balanced start voltage, turn off the cell i Balanced switch Q i , turn off the cell CELL i Passive equilibrium; Step 107: When the difference U between the highest cell voltage value and the lowest cell voltage value is CELLmax -U CELLmin Less than the second difference and the highest cell voltage value U CELLmax When the voltage is greater than the balanced start-up voltage, the MOS tube Q is turned off. b , turn off passive balancing for all cells that have passive balancing turned on.

2. The lithium battery equalization control method according to claim 1, characterized in that: The balanced start-up voltage of each battery cell is 3.45V, the battery cell overvoltage protection recovery voltage value is 3.34V, the battery cell overcharge protection voltage is 3.65V, the first difference is 50mV, and the second difference is 20mV.

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