A bidirectional active balanced BMS circuit and control method thereof

Abstract

The present invention discloses a bidirectional active balanced BMS circuit, including a battery pack with n single cells, n identical secondary circuits, a transformer T1, a primary circuit and a control chip U10, wherein the transformer T1 includes a primary winding with a first tap, a second tap and a third tap and n secondary windings with a first tap, a second tap and a third tap, wherein the primary winding is connected to the primary circuit, and the n secondary windings are respectively connected to one side of the n identical secondary circuits, and the other side of the n secondary circuits are respectively connected to the n single cells in parallel, where n≥2. A control method for a bidirectional active balanced BMS circuit is also disclosed. The present invention transfers the energy of a single cell with slightly higher energy to a battery with slightly lower energy through an energy storage link in the form of bidirectional charging and discharging, thereby realizing active balancing and effectively reducing energy loss.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply, and in particular to a bidirectional active balanced BMS circuit and a control method thereof. Background Art

[0002] With the vigorous development of the new energy automobile industry and the widespread application of lithium-ion batteries, lithium-ion battery packs play an increasingly important role. In order to ensure the consistency of the balanced capacity of cells between battery packs and avoid shortening the service life of the battery pack due to the imbalance of energy between cells between groups, the balance of the capacity of cells between battery packs has become an indispensable and important function in many product designs. Traditional battery pack balancing circuits balance the capacity of cells between battery packs in a passive energy consumption mode, using the large power consumption of the circuit itself. Although the structure is simple and the cost is low, the resistance energy consumption generates heat, which reduces the efficiency of the entire system. Therefore, a BMS circuit with less energy loss is needed. Summary of the invention

[0003] 1. Technical issues to be resolved

[0004] Based on the above problems, the present invention provides a bidirectional active balancing BMS circuit and a control method thereof, which transfers the energy of a single cell with slightly higher energy to a battery with slightly lower energy through an energy storage link in the form of bidirectional charging and discharging, thereby achieving active balancing and effectively reducing energy loss.

[0005] (II) Technical solution

[0006] Based on the above technical problems, the present invention provides a bidirectional active balanced BMS circuit, including a battery pack with n single cells, n identical secondary circuits, a transformer T1, a primary circuit and a control chip U10, wherein the transformer T1 includes a primary winding with a first tap, a second tap and a third tap and n secondary windings with a first tap, a second tap and a third tap, wherein the primary winding is connected to the primary circuit, the n secondary windings are respectively connected to one side of the n identical secondary circuits, and the other sides of the n secondary circuits are respectively connected in parallel with the n single cells, where n≥2;

[0007] Each of the secondary circuits includes an LC filter circuit connected to the single cell and the second tap of the secondary winding, a secondary push-pull circuit and a current limiting rectifier circuit connected to the first tap and the third tap of the secondary winding, and a self-excitation drive circuit connected to the current limiting rectifier circuit; the primary circuit includes a boost amplifier circuit and a charging drive circuit connected to the second tap of the primary winding and an external power supply, a primary push-pull circuit connected to the first tap and the third tap of the primary winding, and a PWM charge and discharge power supply control chip U8 connected to the primary push-pull circuit and the boost amplifier circuit; the charging drive circuit and the self-excitation drive circuit are both connected to the I / O port of the control chip U10;

[0008] Each of the secondary circuits has the same components and structures as the first secondary circuit. In the first secondary circuit, the current limiting rectifier circuit includes a diode D10, and the secondary push-pull circuit includes switch tubes Q2B and Q2A, and corresponding gate resistors R37 and R39. The G poles of Q2A and Q2B are connected to one end of R39 and R37 respectively. The first tap of the first secondary winding is connected to the D pole of Q2B, an anode of D10 and the other end of R39. The third tap of the first secondary winding is connected to the D pole of Q2A, another anode of D10 and the other end of R37. The self-excited driving circuit includes an optocoupler U1, switch tubes Q1A, Q1B and a resistor R40. The anode of the light-emitting diode of the optocoupler U1 is connected to the power supply, the cathode of the light-emitting diode is connected to the I / O port c1 of U10, the emitter of the phototransistor is connected to the G poles of Q1B and Q1A and one end of R40, the collector of the phototransistor is connected to the cathode of D10, the S poles of Q1B and Q1A are connected to the other end of R40, and the D pole of Q1B is connected to the S poles of Q2A and Q2B; the charging driving circuit includes an optocoupler U7, and the cathode of the light-emitting diode of U7 is connected to the I / O port c0 of U10.

[0009] Furthermore, the charging drive circuit also includes a switch tube Q16, a pull-up resistor R1 and a voltage divider resistor R7, the S pole of Q16 and one end of the pull-up resistor R1 are connected to an external power supply, the other end of R1 is connected to the G pole of Q16 and one end of R7, the D pole of Q16 is connected to the second tap of the primary winding, the anode of the light-emitting diode, the collector of the phototransistor, and the emitter of the phototransistor of U7 are respectively connected to the power supply, the other end of R7, and ground; the primary push-pull circuit includes an upper switch tube Q14 and a lower switch tube Q13, corresponding gate resistors R20 and R21, and a charging sampling resistor R15, the first tap and the third tap of the primary winding are respectively connected to the D poles of Q13 and Q14 of the primary push-pull circuit , the S poles of Q13 and Q14 are connected to one end of the charging sampling resistor R15 and then grounded, the G poles of Q13 and Q14 are connected to the charging drive terminal L and the charging drive terminal H of U8 through gate resistors R21 and R20 respectively, and one end of R15 is also connected to the charging protection terminal of U8; the boost amplifier circuit includes a discharge switch tube Q15, a diode D2 and an inductor L7, the S pole of Q15 is connected to one end of the discharge sampling resistor R13 and then grounded, the G pole of Q15 and one end of R13 are respectively connected to the discharge drive terminal and the discharge protection terminal of U8, the D pole of Q15 is connected to the anode of the diode D2 and one end of L7, the cathode of D2 is connected to the external power supply, and the other end of the inductor L7 is connected to the second tap of the primary winding.

[0010] Furthermore, the current limiting rectifier circuit also includes a current limiting resistor R35 and a filter capacitor C20, the cathode of D10 is connected to the phototransistor collector of U1 through R35, the phototransistor collector of U1 is also connected to one end of C20, the other end of C20 is connected to the D pole of Q1B, and the cathode of the light-emitting diode of U1 is connected to the I / O port c1 of U10 through a resistor R38; the LC filter circuit includes a filter capacitor C1 and an inductor L1, the D pole of Q1A and one end of the inductor L1 are respectively connected to the two ends of the filter capacitor C1, the other end of the inductor L1 is connected to the second tap of the first secondary winding, and the filter capacitor C1 is connected in parallel to the two ends of the single cell cell1.

[0011] Furthermore, the second tap of the primary winding is also connected to a filter circuit, which includes capacitors C10 and C11 connected in parallel to the ground. One end of the filter capacitors C10 and C11 is grounded, and the other end is connected to the second tap of the primary winding.

[0012] Furthermore, the BMS circuit also includes a voltage acquisition circuit, which includes an AFE analog front-end chip U9 for collecting n+1 voltages at both ends of n single cells. The AFE analog front-end chip U9 is connected to the control chip U10 via an SPI bus.

[0013] Furthermore, the upper switch tube Q14, the lower switch tube Q13, the discharge switch tube Q15, the switch tube Q1A, the switch tube Q1B, the switch tube Q2A, and the switch tube Q2B are N-channel enhancement MOSFETs, the switch tube Q16 is a P-channel enhancement MOSFET, and the body diode of Q1A points from the S pole to the D pole.

[0014] Furthermore, when n=6, the I / O ports c1, c2, c3, c4, c5, and c6 output by the control chip U10 correspond to the cathodes of the light-emitting diodes connected to the optical couplers U1, U2, U3, U4, U5, and U6, respectively.

[0015] Furthermore, the control chip U10 is an MCU single-chip computer, an ARM processor or a DSP controller, the optocouplers are all EL357, the PWM charge and discharge power supply control chip U8 includes a charging driver chip SG2525 and a discharging driver chip UC2843, the charging driver terminal H is the output terminal A of SG2525, the charging driver terminal L is the output terminal B of SG2525, and the discharging driver terminal is the output terminal of UC2843.

[0016] The present invention also discloses a control method for a bidirectional active balanced BMS circuit, the control method comprising:

[0017] When the voltage of a single cell is low, c0 of U10 and the I / O port corresponding to the low single cell both output a low level, the optocoupler U7 and the optocoupler corresponding to the low single cell are both turned on, the external power flows into the second tap of the primary winding through the charging drive circuit, and the PWM pulse generated by U8 drives the upper and lower switch tubes of the primary push-pull circuit to be turned on or off, so that the primary winding generates an induced voltage, which is coupled to the secondary winding through the transformer T1, and the driving current flows out of the first / third tap of the secondary winding in two ways, the first way flows through the body of D10, U1, R40, Q1A, and the second way flows out. The first path flows through the pole tube, the low single battery, and L1 back to the second tap of the secondary winding to drive Q1A and Q1B; the second path flows through R39 / R37, the G pole and S pole of Q2A / Q2B, Q1B, Q1A, the low single battery, and L1 back to the second tap of the secondary winding to drive Q2A / Q2B; when Q1A, Q1B, and Q2A / Q2B are all driven on, the charging current is rectified from the second tap of the secondary winding through L1, the low single battery, Q1A, Q1B, and Q2A / Q2B back to the third / first tap of the secondary winding to complete the charging of the low single battery;

[0018] When the voltage of a single cell is too high, c0 of U10 outputs a high level, the I / O port corresponding to the single cell with a high voltage outputs a low level, the optocoupler U7 is cut off, and the optocoupler corresponding to the single cell with a high voltage is turned on. The driving current of the single cell with a high voltage flows out from the positive electrode, passes through L1 and the second tap of the secondary winding to the first / third tap, and then is divided into two paths. The first driving current flows through the body diode of D10, U1, R40, and Q1A, returns to the negative electrode of the single cell with a high voltage, and drives Q1A and Q1B; the second driving current flows through R39 / R37, the G pole and S pole, Q1B, Q1A, and return to the negative pole of the higher single battery to drive Q2A / Q2B; when Q1A, Q1B, Q2A / Q2B are all driven to be turned on, the discharge current flows out from the positive pole of the higher single battery, passes through L1 and the second tap of the secondary winding to the third / first tap, and is rectified by Q2A / Q2B and returns to the negative pole of the higher single battery, completing the discharge of the higher single battery, and is coupled to the primary winding by the secondary winding, and then drives the discharge switch tube Q15 through the PWM pulse generated by U8, and the boost amplifier circuit stores energy and charges the external power supply.

[0019] Furthermore, the charging driving terminal H, the charging driving terminal L and the discharging driving terminal of the U8 all output PWM pulses, and the phase difference between the PWM pulses output by the charging driving terminal H and the charging driving terminal L is 180 degrees.

[0020] (III) Beneficial effects

[0021] The above technical solution of the present invention has the following advantages:

[0022] (1) The present invention is a bidirectional charging and discharging topology circuit. When there is a difference in the capacity of each single cell between the battery packs, the switch of the single cell with the lowest capacity is turned on to charge it, and the switch of the single cell with the highest capacity is turned on to discharge it, so as to achieve a balanced and consistent capacity of the single cells in the battery pack, and to transfer energy through the energy storage link to achieve active balancing, effectively reduce energy loss, and improve energy utilization. In addition, no resistance energy consumption is used, and the switch tubes in the push-pull circuit are all connected to the gate resistor to reduce heat generation;

[0023] (2) In the present invention, energy can be transferred in two directions. Compared with the existing unidirectional balancing, the bidirectional balancing improves the conversion efficiency and shortens the balancing time.

[0024] (3) The secondary circuits of the present invention all adopt MOS tube synchronous rectification. The on-state resistance of the MOS tube is extremely low, which greatly improves the efficiency of the BMS circuit and reduces the power consumption. Compared with the diode rectification, it has obvious advantages. Therefore, under the same power loss, the power of the BMS circuit can be greater, and the balancing current increases proportionally with the power increase. In practical applications, the charging and discharging current can reach 5-10A;

[0025] (4) The secondary circuit of the present invention is a self-excited circuit, which is enabled by an optocoupler. Each MOS tube of the secondary push-pull circuit and the self-excited drive circuit is turned on by self-excited oscillation of the winding, and no external PWM drive control chip is required to turn it on, thereby improving the efficiency of the BMS circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the present invention in any way. In the accompanying drawings:

[0027] Figure 1 A schematic diagram of the topological structure of a bidirectional active balanced BMS circuit according to an embodiment of the present invention;

[0028] Figure 2 A schematic diagram of the topological structure of a primary circuit according to an embodiment of the present invention;

[0029] Figure 3 is a schematic diagram of the topological structure of a first secondary circuit according to an embodiment of the present invention;

[0030] Figure 4 A schematic diagram of the topological structure of a voltage acquisition circuit according to an embodiment of the present invention;

[0031] Figure 5 FIG. 1 is a schematic diagram of the topological structure of the control chip U10 according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0033] A bidirectional active balanced BMS circuit, such as Figure 1 As shown, it includes a battery pack with n single cells, n identical secondary circuits, a transformer T1, a primary circuit, a control chip U10 and a voltage acquisition circuit, wherein the transformer T1 includes a primary winding with a first tap, a second tap and a third tap and n secondary windings with a first tap, a second tap and a third tap, wherein the second tap is a center tap, the primary winding is connected to the primary circuit, the n secondary windings are respectively connected to one side of the n identical secondary circuits, and the other sides of the n secondary circuits are respectively connected in parallel with the n single cells;

[0034] Each of the secondary circuits includes an LC filter circuit connected to the single cell and the second tap of the secondary winding, a secondary push-pull circuit and a current limiting rectifier circuit connected to the first tap and the third tap of the secondary winding, and a self-excited drive circuit connected to the current limiting rectifier circuit; the primary circuit includes a filter circuit, a boost amplifier circuit, and a charging drive circuit connected to the second tap of the primary winding, a primary push-pull circuit connected to the first tap and the third tap of the primary winding, and a PWM charge and discharge power supply control chip U8 connected to the primary push-pull circuit and the boost amplifier circuit, and the boost amplifier circuit and the charging drive circuit are connected to an external power supply; the control chip U10 is connected to the charging drive circuit, the self-excited drive circuit, and the voltage acquisition circuit, and the voltage acquisition circuit is connected to both ends of the n single cells;

[0035] like Figure 2As shown, the primary push-pull circuit includes an upper switch tube Q14 and a lower switch tube Q13, corresponding gate resistors R20 and R21, and a charging sampling resistor R15. The first tap and the third tap of the primary winding are respectively connected to the D poles of Q13 and Q14 of the primary push-pull circuit, and the S poles of Q13 and Q14 are connected to one end of the charging sampling resistor R15 and then grounded. The G poles of Q13 and Q14 are respectively connected to the charging drive terminal L and the charging drive terminal H of U8 through the gate resistors R21 and R20. One end of R15 is also connected to the charging protection terminal of U8. The gate resistor is used to quickly attenuate the oscillation generated under pulse excitation to prevent the driving power from being consumed on the switch tube and the temperature from rising. The sampling resistor is used to extract the signal and feed it back to the charging protection terminal or the discharge protection terminal of U8; the boost amplifier circuit includes a discharge switch tube Q15, a diode D2 and an inductor L7. The S pole of Q15 is connected to one end of the discharge sampling resistor R13 and then grounded. The G pole of Q15 and one end of R13 are respectively connected to the discharge driving end and the discharge protection end of U8, the D pole of Q15 is connected to the anode of the diode D2 and one end of L7, and the other end of the inductor L7 is connected to the second tap of the primary winding; the charging drive circuit includes an optocoupler U7, a switch tube Q16, a pull-up resistor R1 and a voltage-dividing resistor R7, the cathode of D2, the S pole of Q16, and one end of the pull-up resistor R1 are connected to an external power supply +24V, the other end of R1 is connected to the G pole of Q16 and one end of the voltage-dividing resistor R7, the D pole of Q16 is connected to the second tap of the primary winding, the light-emitting diode anode, the light-emitting diode cathode, the phototransistor collector, and the phototransistor emitter of the optocoupler U7 are respectively connected to the +5V power supply, the I / O port c0 of the control chip U10, the other end of R7, and grounding; the filtering circuit includes capacitors C10 and C11 connected to the ground in parallel, one end of the filter capacitors C10 and C11 is grounded, and the other end is connected to the second tap of the primary winding;

[0036] Said n≥2, each of said secondary circuits has the same components and structure as the first secondary circuit, such as Figure 3As shown, in the first secondary circuit, the secondary push-pull circuit includes switch tubes Q2B and Q2A, and corresponding gate resistors R37 and R39, the G poles of Q2A and Q2B are connected to one end of R39 and R37 respectively, the first tap of the first secondary winding is connected to the D pole of Q2B, an anode of a diode D10 and the other end of R39, and the third tap of the first secondary winding is connected to the D pole of Q2A, the other anode of the diode D10 and the other end of R37; the current limiting rectifier circuit includes a diode D10, a current limiting resistor R35 and a filter capacitor C20, the cathode of D10 is connected to one end of the current limiting resistor R35, the other end of R35 and one end of the filter capacitor C20 are connected to the collector of the phototransistor of the optocoupler U1; the self-excited drive The circuit includes an optocoupler U1, switch tubes Q1A, Q1B and a resistor R40, the anode of the light-emitting diode of the optocoupler U1 is connected to a +5V power supply, the cathode of the light-emitting diode is connected to an I / O port c1 of a control chip U10 through R38, the emitter of the phototransistor is connected to the G poles of Q1B and Q1A and one end of R40, the S poles of Q1B and Q1A are connected to the other end of R40, and the D pole of Q1B is connected to the other end of a filter capacitor C20 and the S poles of Q2A and Q2B; the LC filter circuit includes a filter capacitor C1 and an inductor L1, the D pole of Q1A and one end of the inductor L1 are respectively connected to the two ends of the filter capacitor C1, the other end of the inductor L1 is connected to the second tap of the first secondary winding, and the filter capacitor C1 is connected in parallel to the two ends of a single cell cell1.

[0037] like Figure 4 As shown, the voltage acquisition circuit includes an AFE analog front-end chip U9, Schottky diodes D6, D8, D9, D11, D12, D13, sampling resistors R27, R29, R34, R36, R41, R42, capacitors C21, C22, C23, C24, C25, C26. When n=6, the two ends of each single battery, that is, n+1=7 sampling points B0-B6, B0 is the negative electrode of the battery pack, and U9 is used to collect voltage at the two ends B0-B6 of each battery in the group; the six input ends of U9 are respectively connected to a sampling resistor and then connected to the six sampling points B1, B2, B3, B4, B5, B6, and the remaining input end of U9 is connected to B0, and the remaining input end is connected to the six input ends through a capacitor respectively, and each adjacent two input ends are connected through a Schottky diode, from the input end connected to B0 to the input end connected to B1, and so on.

[0038] like Figure 5As shown, the control chip U10 includes an MCU microcontroller, an ARM processor or a DSP controller, etc., which communicates with the AFE analog front-end chip U9 through the SPI bus, and is used to read the voltage of each battery, and control the output of the I / O ports c0-c6 according to the stored balancing and control strategies. The I / O ports c0, c1, c2, c3, c4, c5, and c6 correspondingly control the optical couplers U7, U1, U2, U3, U4, U5, and U6.

[0039] The upper switch tube Q14, the lower switch tube Q13, the discharge switch tube Q15, the switch tube Q1A, the switch tube Q1B, the switch tube Q2A, and the switch tube Q2B are N-channel enhancement MOSFETs, and the switch tube Q16 is a P-channel enhancement MOSFET. The MOSFET has a body diode. The body diode of the N-channel MOSFET points from the S pole to the D pole, and the body diode of the P-channel MOSFET points from the D pole to the S pole; the optical couplers U1-U7 are all EL357; the PWM charge and discharge power supply control chip U8 includes a charge drive chip SG2525 and a discharge drive chip UC2843, the charge drive terminal H is the output terminal A of SG2525, the charge drive terminal L is the output terminal B of SG2525, and the discharge drive terminal is the output terminal of UC2843; or the PWM charge and discharge power supply control chip U8 is a DSP28035 chip, or the PWM charge and discharge power supply control chip U8 and the control chip U10 are implemented by a DSP28035 chip.

[0040] The working process of this embodiment and its circuit topology is as follows:

[0041] Taking single cell cell1 as an example, when the AFE analog front-end chip U9 collects voltage through B0 and B1, the control chip U10 reads that the voltage of single cell cell1 is low, and the I / O ports c0 and c1 output low levels, respectively turning on the optocouplers U7 and U1, enabling the PWM charge and discharge power supply control chip U8, so that the phase difference of the PWM pulses output by the charging drive terminal H and the charging drive terminal L of U8 is 180 degrees; since the optocoupler U7 is turned on, Q16 is turned on, and the +24V external power flows into the second tap of the primary winding through Q16; since the charging drive terminal H and the charging drive terminal L of U8 are respectively the high-level charging drive terminal and the low-level charging drive terminal, the phase difference of the output PWM pulses is 180 degrees, there are two situations:

[0042] When it is the positive half cycle, that is, Q14 is turned on and Q13 is turned off, the primary power supply VCC1 passes through the second tap of the primary winding to the first tap, then passes through the D pole to the S pole of Q14, and then passes through the resistor R15 to the ground. At this time, an induced voltage is generated between the second tap and the first tap of the primary winding, with the second tap being positive and the first tap being negative. Due to the magnetic coupling of the transformer, an induced voltage with positive upper and negative lower is generated between the first secondary winding of the transformer T1, that is, the first tap of the first secondary winding is positive and the second tap is negative; the second tap is positive and the third tap is negative; the drive current flows out from the first tap of the first secondary winding in two ways, the first way flows through an anode and cathode of the diode D10, the current limiting resistor R35, the turned-on optocoupler U1, R40, and the S pole of Q1A. The first path flows through the body diode of the D pole, and then returns to the second tap of the first secondary winding through the inside of cell1 and L1. This loop constitutes the driving loop of Q1A and Q1B; the second path flows through R39, the G pole and S pole of Q2A, the D pole and S pole of the turned-on Q1B, the S pole and D pole of the turned-on Q1A, and then returns to the second tap of the first secondary winding through the inside of the single battery cell1 and L1. This loop constitutes the driving loop of Q2A; when Q1A, Q1B, and Q2A are all driven to conduct, the charging current is rectified from the second tap of the first secondary winding through the inductor L1, the single battery cell1, Q1A, Q1B, and Q2A and returns to the third tap of the first secondary winding. At this time, the charging of the cell1 battery in the positive half cycle is completed.

[0043] When it is the negative half cycle, that is, Q13 is turned on and Q14 is turned off, the primary power supply VCC1 passes through the second tap of the primary winding to the third tap, then passes through the D pole to the S pole of Q13, and then passes through the resistor R15 to the ground. At this time, an induced voltage is generated between the second tap and the third tap of the primary winding, with the second tap being positive and the third tap being negative. Due to the magnetic coupling of the transformer, an induced voltage with a negative top and a positive bottom is generated between the first secondary winding of the transformer T1, that is, the first tap of the first secondary winding is negative and the second tap is positive; the second tap is negative and the third tap is positive; the drive current flows out from the third tap of the first secondary winding in two ways, the first way flows through the other anode and cathode of the diode D10, the current limiting resistor R35, the turned-on optocoupler U1, R40, and the source of Q1A. The first path flows through the body diode with the first pole pointing to the drain pole, and then returns to the second tap of the first secondary winding through the inside of cell1 and L1. This loop constitutes the driving loop of Q1A and Q1B; the second path flows through R37, the G pole and S pole of Q2B, the D pole and S pole of the turned-on Q1B, the S pole and D pole of the turned-on Q1A, and then returns to the second tap of the first secondary winding through the inside of the single cell cell1 and L1. This loop constitutes the driving loop of Q2B; when Q1A, Q1B, and Q2B are all turned on, the charging current is rectified from the second tap of the first secondary winding through the inductor L1, the single cell cell1, Q1A, Q1B, and Q2B to the first tap of the first secondary winding, and the charging of the cell1 battery in the negative half cycle is completed. The positive and negative half cycles are circulated in this way until the microcontroller sends a stop command, and the charging is completed.

[0044] When the AFE analog front-end chip U9 collects voltage through B0 and B1, the control chip U10 reads that the voltage of the single battery cell1 is too high, and the I / O ports c0 and c1 output high and low levels respectively, which respectively cut off the optocoupler U7 and turn on U1, enabling the PWM charge and discharge power supply control chip U8, so that the discharge drive end of U8 outputs PWM pulses; the secondary circuit connected to the secondary winding is also described in two half-cycles:

[0045] The driving current of the single cell cell1 flows out from the positive electrode, passes through L1, the second tap of the first secondary winding to the first tap, and then is divided into two paths. The first driving current flows through an anode and cathode of the diode D10, the current limiting resistor R35, the conductive optocoupler U1, R40, and the body diode of Q1A pointing from the S pole to the D pole, and returns to the negative pole of the single cell cell1. This loop constitutes the driving loop of Q1A and Q1B; the second driving current flows through R39, the G pole and S pole of Q2A, the D pole and S pole of the conductive Q1B, and the S pole and D pole of the conductive Q1A, and returns to the single cell. The negative electrode of battery cell1, this circuit constitutes the driving circuit of Q2A; after Q1A, Q1B, and Q2A are driven to turn on, the discharge circuit of cell1 is opened, and the discharge current flows out from the positive electrode of cell1, passes through L1, the second tap to the third tap of the first secondary winding, and then rectifies back to the negative electrode of cell1 through the D and S poles of Q2A, the D and S poles of the turned-on Q1B, and the S and D poles of the turned-on Q1A; the first secondary winding converts the electrical energy to the primary winding through coupling, and cell1 completes the discharge of half a cycle of the secondary push-pull circuit.

[0046] The driving current of the single cell cell1 flows out from the positive electrode, passes through L1, the second tap of the first secondary winding to the third tap, and then is divided into two paths. The first driving current flows through the other anode and cathode of the diode D10, the current limiting resistor R35, the conductive optocoupler U1, R40, and the body diode of Q1A pointing from the S pole to the D pole, and returns to the negative electrode of the single cell cell1. This loop constitutes the driving loop of Q1A and Q1B; the second driving current flows through R37, the G pole and S pole of Q2B, the D pole and S pole of the conductive Q1B, and the S pole and D pole of the conductive Q1A, and returns to the negative pole of the single cell cell1. To the negative electrode of battery cell1, this circuit constitutes the driving circuit of Q2B; after Q1A, Q1B, and Q2B are driven to turn on, the discharge circuit of cell1 is opened, and the discharge current flows out from the positive electrode of cell1, passes through L1, the second tap of the first secondary winding to the first tap, and then returns to the negative electrode of cell1 through the D and S poles of Q2B, the D and S poles of the turned-on Q1B, and the S and D poles of the turned-on Q1A; the first secondary winding converts the electrical energy to the primary winding through coupling, and cell1 completes the discharge of the other half cycle of the secondary push-pull circuit.

[0047] Since the optocoupler U7 is cut off, Q16 is cut off, and Q15 is periodically turned on and off, when Q15 is turned on, the electric energy coupled from the secondary winding to the primary winding charges L7 through the second tap of the primary winding to store energy; when Q15 is cut off, L7 discharges and charges the external battery through the diode D2.

[0048] That is, the control method of the bidirectional active balanced BMS circuit is:

[0049] When the voltage of a single cell is low, c0 of U10 and the I / O port corresponding to the low single cell both output a low level, the optocoupler U7 and the optocoupler corresponding to the low single cell are both turned on, the external power flows into the second tap of the primary winding through the charging drive circuit, and the PWM pulse generated by U8 drives the upper and lower switch tubes of the primary push-pull circuit to be turned on or off, so that the primary winding generates an induced voltage, which is coupled to the secondary winding through the transformer T1, and the driving current flows out of the first / third tap of the secondary winding in two ways, the first way flows through the body of D10, U1, R40, Q1A, and the second way flows out. The first path flows through the pole tube, the low single battery, and L1 back to the second tap of the secondary winding to drive Q1A and Q1B; the second path flows through R39 / R37, the G pole and S pole of Q2A / Q2B, Q1B, Q1A, the low single battery, and L1 back to the second tap of the secondary winding to drive Q2A / Q2B; when Q1A, Q1B, and Q2A / Q2B are all driven on, the charging current is rectified from the second tap of the secondary winding through L1, the low single battery, Q1A, Q1B, and Q2A / Q2B back to the third / first tap of the secondary winding to complete the charging of the low single battery;

[0050] When the voltage of a single cell is too high, c0 of U10 outputs a high level, the I / O port corresponding to the single cell with a high voltage outputs a low level, the optocoupler U7 is cut off, and the optocoupler corresponding to the single cell with a high voltage is turned on. The driving current of the single cell with a high voltage flows out from the positive electrode, passes through L1 and the second tap of the secondary winding to the first / third tap, and then is divided into two paths. The first driving current flows through the body diode of D10, U1, R40, and Q1A, returns to the negative electrode of the single cell with a high voltage, and drives Q1A and Q1B; the second driving current flows through R39 / R37, the G pole and S pole, Q1B, Q1A, and return to the negative pole of the higher single battery to drive Q2A / Q2B; when Q1A, Q1B, Q2A / Q2B are all driven to be turned on, the discharge current flows out from the positive pole of the higher single battery, passes through L1 and the second tap of the secondary winding to the third / first tap, and is rectified by Q2A / Q2B and returns to the negative pole of the higher single battery, completing the discharge of the higher single battery, and is coupled to the primary winding by the secondary winding, and then drives the discharge switch tube Q15 through the PWM pulse generated by U8, and the boost amplifier circuit stores energy and charges the external power supply.

[0051] The cathodes of the light-emitting diodes of the optocouplers U1-U6 are respectively connected to the I / O ports c1-c6 of the control chip U10 through a gate resistor. When a low level is input, the corresponding optocouplers U1-U6 are turned on, and the corresponding single cells cell1-cell6 enter a balanced state. When a high level is input, the corresponding optocouplers U1-U6 are turned off, and the corresponding single cells cell1-cell6 exit the balanced state. The cathode of the light-emitting diode of the optocoupler U7 is connected to the I / O port c0 of the control chip U10. When a low level is input, U7 is turned on, and the BMS circuit enters a charging mode. When a high level is input, U7 is turned off, and the BMS circuit enters a discharging mode.

[0052] In summary, the above-mentioned bidirectional active balancing BMS circuit and control method thereof have the following advantages:

[0053] (1) The present invention is a bidirectional charging and discharging topology circuit. When there is a difference in the capacity of each single cell between the battery packs, the switch of the single cell with the lowest capacity is turned on to charge it, and the switch of the single cell with the highest capacity is turned on to discharge it, so as to achieve a balanced and consistent capacity of the single cells in the battery pack, and to transfer energy through the energy storage link to achieve active balancing, effectively reduce energy loss, and improve energy utilization. In addition, no resistance energy consumption is used, and the switch tubes in the push-pull circuit are all connected to the gate resistor to reduce heat generation;

[0054] (2) In the present invention, energy can be transferred in two directions. Compared with the existing unidirectional balancing, the bidirectional balancing improves the conversion efficiency and shortens the balancing time.

[0055] (3) The secondary circuits of the present invention all adopt MOS tube synchronous rectification. The on-state resistance of the MOS tube is extremely low, which greatly improves the efficiency of the BMS circuit and reduces the power consumption. Compared with the diode rectification, it has obvious advantages. Therefore, under the same power loss, the power of the BMS circuit can be greater, and the balancing current increases proportionally with the power increase. In practical applications, the charging and discharging current can reach 5-10A;

[0056] (4) The secondary circuit of the present invention is a self-excited circuit, which is enabled by an optocoupler. Each MOS tube of the secondary push-pull circuit and the self-excited drive circuit is turned on by self-excited oscillation of the winding, and no external PWM drive control chip is required to turn it on, thereby improving the efficiency of the BMS circuit.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the embodiments of the present invention are described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations shall fall within the scope defined by the appended claims.

Claims

1. A bidirectional active balanced BMS circuit, characterized in that: A battery pack including n single cells, n identical secondary circuits, a transformer T1, a primary circuit and a control chip U10, wherein the transformer T1 includes a primary winding having a first tap, a second tap and a third tap and n secondary windings having a first tap, a second tap and a third tap, wherein the primary winding is connected to the primary circuit, the n secondary windings are respectively connected to one side of the n identical secondary circuits, and the other sides of the n secondary circuits are respectively connected in parallel to the n single cells, where n≥2; Each of the secondary circuits includes an LC filter circuit connected to the single cell and the second tap of the secondary winding, a secondary push-pull circuit and a current limiting rectifier circuit connected to the first tap and the third tap of the secondary winding, and a self-excitation drive circuit connected to the current limiting rectifier circuit; the primary circuit includes a boost amplifier circuit and a charging drive circuit connected to the second tap of the primary winding and an external power supply, a primary push-pull circuit connected to the first tap and the third tap of the primary winding, and a PWM charge and discharge power supply control chip U8 connected to the primary push-pull circuit and the boost amplifier circuit; the charging drive circuit and the self-excitation drive circuit are both connected to the I / O port of the control chip U10; Each of the secondary circuits has the same components and structures as the first secondary circuit. In the first secondary circuit, the current limiting rectifier circuit includes a diode D10, and the secondary push-pull circuit includes a switch tube Q2B, a switch tube Q2A, and corresponding gate resistors R37 and R39. The G poles of the switch tubes Q2A and Q2B are connected to one end of the gate resistors R39 and R37, respectively. The first tap of the first secondary winding is connected to the D pole of the switch tube Q2B, an anode of the diode D10, and the other end of the gate resistor R39. The third tap of the first secondary winding is connected to the switch tube Q2A. The D pole of the diode D10, the other anode of the diode D10 and the other end of the gate resistor R37; the self-excited driving circuit includes an optocoupler U1, a switch tube Q1A, a switch tube Q1B and a resistor R40, the anode of the light-emitting diode of the optocoupler U1 is connected to the power supply, the cathode of the light-emitting diode is connected to the I / O port c1 of the control chip U10, the emitter of the phototransistor is connected to the G pole of the switch tube Q1B, the switch tube Q1A and one end of the resistor R40, the collector of the phototransistor is connected to the cathode of the diode D10, the S pole of the switch tube Q1B, the switch tube Q1A is connected to the other end of the resistor R40, and the D pole of the switch tube Q1B is connected to the S pole of the switch tube Q2A, the switch tube Q2B; the charging driving circuit includes an optocoupler U7, and the cathode of the light-emitting diode of the optocoupler U7 is connected to the I / O port c0 of the control chip U10; The charging drive circuit also includes a switch tube Q16, a pull-up resistor R1 and a voltage-dividing resistor R7. The S pole of the switch tube Q16 and one end of the pull-up resistor R1 are connected to an external power supply, the other end of the pull-up resistor R1 is connected to the G pole of the switch tube Q16 and one end of the voltage-dividing resistor R7, the D pole of the switch tube Q16 is connected to the second tap of the primary winding, and the anode of the light-emitting diode, the collector of the phototransistor, and the emitter of the phototransistor of the optocoupler U7 are respectively connected to the power supply, the other end of the voltage-dividing resistor R7, and ground; the primary push-pull circuit includes an upper switch tube Q14 and a lower switch tube Q13, corresponding gate resistors R20 and R21, and a charging sampling resistor R15, the first tap and the third tap of the primary winding are respectively connected to the D poles of the lower switch tube Q13 and the upper switch tube Q14 of the primary push-pull circuit, and the S poles of the lower switch tube Q13 and the upper switch tube Q14 are connected to the charging sampling resistor R1 5 is connected to ground, the G poles of the lower switch tube Q13 and the upper switch tube Q14 are connected to the charging drive end L and the charging drive end H of the PWM charging and discharging power supply control chip U8 through the gate resistor R21 and the gate resistor R20 respectively, and one end of the charging sampling resistor R15 is also connected to the charging protection end of the PWM charging and discharging power supply control chip U8; the boost amplifier circuit includes a discharge switch tube Q15, a diode D2 and an inductor L7, the S pole of the discharge switch tube Q15 is connected to one end of the discharge sampling resistor R13 and then grounded, the G pole of the discharge switch tube Q15 and one end of the discharge sampling resistor R13 are respectively connected to the discharge driving end and the discharge protection end of the PWM charging and discharging power supply control chip U8, the D pole of the discharge switch tube Q15 is connected to the anode of the diode D2 and one end of the inductor L7, the cathode of the diode D2 is connected to the external power supply, and the other end of the inductor L7 is connected to the second tap of the primary winding; The current limiting rectifier circuit also includes a current limiting resistor R35 and a filter capacitor C20. The cathode of the diode D10 is connected to the collector of the phototransistor of the optocoupler U1 through the current limiting resistor R35. The collector of the phototransistor of the optocoupler U1 is also connected to one end of the filter capacitor C20. The other end of the filter capacitor C20 is connected to the D pole of the switch tube Q1B. The cathode of the light-emitting diode of the optocoupler U1 is connected to the I / O port c1 of the control chip U10 through a resistor R38. The LC filter circuit includes a filter capacitor C1 and an inductor L1. The D pole of the switch tube Q1A and one end of the inductor L1 are respectively connected to the two ends of the filter capacitor C1. The other end of the inductor L1 is connected to the second tap of the first secondary winding. The filter capacitor C1 is connected in parallel to the two ends of the single battery cell1.

2. A bidirectional active balanced BMS circuit according to claim 1, characterized in that: The second tap of the primary winding is also connected to the filter circuit, which includes a filter capacitor C10 and a filter capacitor C11 connected in parallel to the ground. One end of the filter capacitor C10 and the filter capacitor C11 is grounded, and the other end is connected to the second tap of the primary winding.

3. A bidirectional active balanced BMS circuit according to claim 1, characterized in that: The BMS circuit also includes a voltage acquisition circuit, which includes an AFE analog front-end chip U9 for acquiring n+1 voltages at both ends of n single cells. The AFE analog front-end chip U9 is connected to the control chip U10 via an SPI bus.

4. A bidirectional active balanced BMS circuit according to claim 1, characterized in that: The upper switch tube Q14, the lower switch tube Q13, the discharge switch tube Q15, the switch tube Q1A, the switch tube Q1B, the switch tube Q2A, and the switch tube Q2B are N-channel enhancement MOSFETs, the switch tube Q16 is a P-channel enhancement MOSFET, and the body diode of the switch tube Q1A points from the S pole to the D pole.

5. A bidirectional active balanced BMS circuit according to claim 1, characterized in that: When n=6, the I / O ports c1, c2, c3, c4, c5, and c6 output by the control chip U10 correspond to the cathodes of the light-emitting diodes connected to the optical couplers U1, U2, U3, U4, U5, and U6, respectively.

6. A bidirectional active balanced BMS circuit according to claim 1, characterized in that: The control chip U10 is an MCU single-chip computer, an ARM processor or a DSP controller, the optocouplers are all EL357, the PWM charge and discharge power supply control chip U8 includes a charging driver chip SG2525 and a discharging driver chip UC2843, the charging driver terminal H is the output terminal A of SG2525, the charging driver terminal L is the output terminal B of SG2525, and the discharging driver terminal is the output terminal of UC2843.

7. A control method for a bidirectional active balanced BMS circuit as claimed in claim 6, characterized in that: The control method comprises: When the voltage of a single cell is low, c0 of the control chip U10 and the I / O port corresponding to the low single cell both output a low level, the optocoupler U7 and the optocoupler corresponding to the low single cell are both turned on, the external power flows into the second tap of the primary winding through the charging drive circuit, and the PWM pulse generated by the PWM charge and discharge power supply control chip U8 drives the upper and lower switch tubes of the primary push-pull circuit to be turned on or off, so that the primary winding generates an induced voltage, which is coupled to the secondary winding through the transformer T1, and the drive current flows out from the first or third tap of the secondary winding in two ways, the first way flows through the diode D10, the optocoupler U1, the resistor R40, the body diode of the switch tube Q1A, the low single cell, and ... second way flows through the optocoupler U1. The second path flows through the gate resistor R39 / R37, the G pole and S pole of the switch tube Q2A / Q2B, the switch tube Q1B, the switch tube Q1A, the low single battery, and the inductor L1 to return to the second tap of the secondary winding to drive the switch tube Q2A / Q2B; when the switch tubes Q1A, Q1B, and Q2A / Q2B are all driven to conduct, the charging current is rectified from the second tap of the secondary winding through the inductor L1, the low single battery, the switch tube Q1A, the switch tube Q1B, and the switch tube Q2A / Q2B to return to the third or first tap of the secondary winding to complete the charging of the low single battery; When the voltage of a single cell is too high, c0 of the control chip U10 outputs a high level, the I / O port corresponding to the single cell with a relatively high voltage outputs a low level, the optocoupler U7 is cut off, and the optocoupler corresponding to the single cell with a relatively high voltage is turned on. The driving current of the single cell with a relatively high voltage flows out from the positive electrode, passes through the inductor L1 and the second tap of the secondary winding to the first or third tap, and then is divided into two paths. The first driving current flows through the diode D10, the optocoupler U1, the resistor R40, and the body diode of the switch tube Q1A, and returns to the negative electrode of the single cell with a relatively high voltage to drive the switch tube Q1A and the switch tube Q1B; the second driving current flows through the gate resistor R39 / R37, the G and S poles of the switch tube Q2A / Q2B, The switch tubes Q1B and Q1A return to the negative electrode of the relatively high single battery to drive the switch tubes Q2A / Q2B; when the switch tubes Q1A, Q1B, and Q2A / Q2B are all driven to be turned on, the discharge current flows out from the positive electrode of the relatively high single battery, passes through the inductor L1 and the second tap of the secondary winding to the third or first tap, and is rectified by the switch tubes Q2A / Q2B and returns to the negative electrode of the relatively high single battery, completing the discharge of the relatively high single battery, and is coupled to the primary winding by the secondary winding, and then the PWM pulse generated by the PWM charge and discharge power supply control chip U8 drives the discharge switch tube Q15, and the boost amplifier circuit stores energy and charges the external power supply.

8. The control method of a bidirectional active balanced BMS circuit according to claim 7, characterized in that: The charging drive terminal H, the charging drive terminal L and the discharging drive terminal of the PWM charging and discharging power supply control chip U8 all output PWM pulses, and the phase difference between the PWM pulses output by the charging drive terminal H and the charging drive terminal L is 180 degrees.

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