Battery Equalization Circuit Based on Bidirectional Flyback Converter and Battery Equalization Control Method

Abstract

The present application discloses a battery equalization circuit and a battery equalization control method based on a bidirectional flyback converter, belonging to the field of circuit technology. In the battery equalization circuit, the control module controls the primary switch tube to conduct and the secondary switch tube to disconnect, and the battery pack bus transmits electrical energy to the primary winding; the control module controls the primary switch tube to disconnect and the secondary switch tube to conduct, the primary winding transmits electrical energy to the secondary winding, and the secondary winding transmits electrical energy to the battery to achieve charging the battery from the battery pack bus; the control module controls the secondary switch tube to conduct and the primary switch tube to disconnect, and the battery transmits electrical energy to the secondary winding; the control module controls the secondary switch tube to disconnect and the primary switch tube to conduct, the secondary winding transmits electrical energy to the primary winding, and the primary winding transmits electrical energy to the battery pack bus to achieve discharging the battery to the battery pack bus. The present application can simplify the circuit structure, simplify the control process of the bidirectional flyback converter, improve the system efficiency, and simplify the voltage detection process.

Description

Technical Field

[0001] This application relates to the field of circuit technologies, and particularly to a battery equalization circuit and a battery equalization control method based on a bidirectional flyback converter. Background Art

[0002] In fields such as electric vehicles and energy storage systems, there are extremely high requirements for the performance, lifespan, and safety of battery systems. In a battery system, due to differences in parameters such as voltage, capacity, and internal resistance among battery cells, as the charge-discharge cycles progress, this inconsistency gradually intensifies, resulting in a decline in the overall performance of the battery system. To address the issue of battery inconsistency and improve the overall performance of the battery system, battery equalization technology has emerged. Battery equalization technology can analyze various characteristic data of the battery in real time and perform equalization charge and discharge as needed to quickly improve the consistency among battery cells.

[0003] As Figure 1 shown, the existing battery equalization circuit based on a bidirectional flyback converter mainly includes a voltage detection module for battery cells, an isolation transmission module, a control module, a switch matrix module, and a bidirectional flyback converter. To ensure safety, isolation is required for the input and output of the bidirectional flyback converter.

[0004] As Figure 2 shown, the battery cells are in series form, and the ground of each battery cell is independent. Therefore, a voltage detection module is required at each battery cell, and the signals between the voltage detection module and the control module need to be isolated for transmission. Since a voltage detection module is required for each battery cell and it needs to be transmitted to the control module in an isolated manner, the voltage detection and transmission system is relatively complex.

[0005] As Figure 3 shown, the control module calculates the output voltage, connects a specific battery cell to the bidirectional flyback converter through the switch matrix of the battery cell, and simultaneously outputs a control signal to the bidirectional flyback converter to determine whether the battery cell is charging or discharging. The signals between the switch matrix and the control module also need to be isolated for transmission. Since a complex switch matrix is required to control the battery cells and the signal transmission between the control module and the switch matrix also needs isolation, the switch control and transmission system is complex.

[0006] In addition, after the Metal-Oxide-Semiconductor Field-Effect Transistor (MOS) on one side of the bidirectional flyback converter conducts, the MOS transistor on the other side will turn off, and a parallel diode is required for freewheeling. However, the loss of the diode is relatively large, resulting in low system efficiency, and adding a diode will increase the circuit cost. Summary of the Invention

[0007] The present application provides a battery equalization circuit and a battery equalization control method based on a bidirectional flyback converter, which are used to solve the problems of complex voltage detection, switch control and circuit of the battery equalization circuit, low system efficiency and high circuit cost. The technical solutions are as follows:

[0008] According to the first aspect of the present application, a battery equalization circuit based on a bidirectional flyback converter is provided. The battery equalization circuit based on the bidirectional flyback converter includes a plurality of battery packs, a battery pack bus, a step-down converter and a control module. The battery pack bus is a bus commonly connected after a plurality of battery packs are connected in parallel. Each battery pack is composed of a plurality of series-connected battery equalization units;

[0009] Each battery equalization unit includes a battery, a bidirectional flyback converter, a first filter capacitor and a second filter capacitor. The bidirectional flyback converter includes a transformer, a primary switch tube and a secondary switch tube. The first end of the first filter capacitor is respectively connected to the battery pack bus, the first end of the primary winding in the transformer and the first end of the first filter capacitor in the adjacent battery equalization unit. The second end of the first filter capacitor is respectively connected to the battery pack bus, the source electrode of the primary switch tube and the ground. The first end of the second filter capacitor is respectively connected to the first end of the secondary winding in the transformer and the positive electrode of the battery. The second end of the second filter capacitor is respectively connected to the source electrode of the secondary switch tube and the negative electrode of the battery. The negative electrode of the battery is connected to the positive electrode of the battery in the adjacent battery equalization unit;

[0010] The first end of the control module is connected to the battery pack bus through the step-down converter, and the second end of the control module is connected to the ground in each battery equalization unit;

[0011] When the control module controls the primary switch tube in a battery equalization unit to conduct and the secondary switch tube to disconnect, the battery pack bus is used to transmit electric energy to the primary winding. When the control module controls the primary switch tube in the battery equalization unit to disconnect and the secondary switch tube to conduct, the primary winding is used to transmit the electric energy to the secondary winding, and the secondary winding is used to transmit the electric energy to the battery to realize charging the battery from the battery pack bus;

[0012] When the control module controls the secondary switch tube in a battery equalization unit to conduct and the primary switch tube to disconnect, the battery is used to transmit electric energy to the secondary winding. When the control module controls the secondary switch tube in the battery equalization unit to disconnect and the primary switch tube to conduct, the secondary winding is used to transmit the electric energy to the primary winding, and the primary winding is used to transmit the electric energy to the battery pack bus to realize discharging the battery to the battery pack bus.

[0013] In a possible implementation, the primary side switching transistor includes a primary side body diode, and the secondary side switching transistor includes a secondary side body diode;

[0014] When the primary side switching transistor changes from conduction to disconnection, the secondary side body diode conducts to make the secondary side switching transistor conduct;

[0015] When the secondary side switching transistor changes from conduction to disconnection, the primary side body diode conducts to make the primary side switching transistor conduct.

[0016] In a possible implementation, the battery equalization circuit further includes a primary side power management chip and a secondary side power management chip;

[0017] The second end of the primary side winding is connected to the drain of the primary side switching transistor, and the gate of the primary side switching transistor is connected to the primary side power management chip;

[0018] The second end of the secondary side winding is connected to the drain of the secondary side switching transistor, and the gate of the secondary side switching transistor is connected to the secondary side power management chip.

[0019] According to a second aspect of the present application, there is provided a battery equalization control method for a battery equalization circuit based on a bidirectional flyback converter, which is used in the battery equalization circuit based on a bidirectional flyback converter as described above. The method includes:

[0020] When it is necessary to detect the voltage of the target battery, the control module charges the target battery from the battery pack bus through the bidirectional flyback converter corresponding to the target battery, and calculates the current voltage of the target battery according to the measurement parameters during charging;

[0021] If it is determined according to the current voltage that the target battery needs to be charged, the control module charges the target battery from the battery pack bus through the bidirectional flyback converter corresponding to the target battery until the charging stops after the current voltage reaches the first voltage threshold;

[0022] If it is determined according to the current voltage that the target battery needs to be discharged, the control module discharges the target battery to the battery pack bus through the bidirectional flyback converter corresponding to the target battery until the discharging stops after the current voltage reaches the second voltage threshold.

[0023] In a possible implementation, when the battery equalization circuit further includes a primary side power management chip and a secondary side power management chip, the control module charges the target battery from the battery pack bus through the bidirectional flyback converter corresponding to the target battery, including:

[0024] The control module sends a detection signal to the primary power management chip corresponding to the target battery;

[0025] The primary power management chip controls the conduction of the primary switching tube according to the detection signal, and the bus of the battery pack transmits electric energy to the primary winding through the conducted primary switching tube;

[0026] The primary power management chip controls the disconnection of the primary switching tube to enable the conduction of the secondary switching tube. The primary winding transmits the electric energy to the target battery through the conducted secondary switching tube and the secondary winding, so as to realize charging the target battery from the bus of the battery pack.

[0027] In a possible implementation manner, calculating the current voltage of the target battery according to the measurement parameters during charging includes:

[0028] The primary power management chip obtains a first measurement parameter during charging, and the first measurement parameter includes the input voltage of the bus of the battery pack and the drain-ground voltage of the primary switching tube;

[0029] The primary power management chip divides the difference obtained by subtracting the input voltage from the drain-ground voltage by the turn ratio of the primary side to the secondary side to obtain the current voltage of the target battery;

[0030] The control module obtains the current voltage calculated by the primary power management chip.

[0031] In a possible implementation manner, calculating the current voltage of the target battery according to the measurement parameters during charging includes:

[0032] The primary power management chip obtains a second measurement parameter during charging, and the second measurement parameter includes the duty ratio of the conduction time of the primary switching tube and the input voltage of the bus of the battery pack;

[0033] The primary power management chip divides the input voltage by the turn ratio of the primary side to the secondary side and then multiplies it by a predetermined ratio to obtain the current voltage of the target battery, and the predetermined ratio is the ratio of the duty ratio to the difference between 1 and the duty ratio;

[0034] The control module obtains the current voltage calculated by the primary power management chip.

[0035] In a possible implementation manner, the control module realizes discharging from the target battery to the bus of the battery pack through the bidirectional flyback converter corresponding to the target battery, including:

[0036] The control module sends a discharge signal to the primary power management chip corresponding to the target battery;

[0037] The primary-side power management chip notifies the secondary-side power management chip to discharge the target battery according to the discharge signal;

[0038] The secondary-side power management chip controls the secondary-side switch tube to conduct, and the target battery transmits electrical energy to the secondary-side winding through the conducted secondary-side switch tube;

[0039] The secondary-side power management chip controls the secondary-side switch tube to disconnect, so that the primary-side switch tube conducts. The secondary-side winding transmits the electrical energy to the battery pack bus through the conducted primary-side switch tube and the primary-side winding, so as to realize discharging from the target battery to the battery pack bus.

[0040] In a possible implementation manner, the primary-side power management chip notifies the secondary-side power management chip to discharge the target battery according to the discharge signal, including:

[0041] The primary-side power management chip controls the primary-side switch tube to switch the working mode according to the discharge signal, so that the secondary-side power management chip determines to discharge the target battery according to the working mode; or,

[0042] The primary-side power management chip controls the primary-side switch tube to conduct and disconnect according to a predetermined rule according to the discharge signal, so that the secondary-side power management chip determines to discharge the target battery according to the predetermined rule.

[0043] In a possible implementation manner, the method further includes:

[0044] When charging or discharging the target battery, the control module periodically updates the current voltage of the target battery.

[0045] The beneficial effects of the technical solution provided by this application at least include:

[0046] By controlling the primary-side switch tube, charging the battery from the battery pack bus can be realized; by controlling the secondary-side switch tube, discharging the battery to the battery pack bus can be realized, so as to realize the balance of the battery, which can save the switch matrix and isolation transmission devices to simplify the structure of the battery balancing circuit, and can also simplify the control process of the bidirectional flyback converter.

[0047] When the primary-side switch tube changes from conducting to disconnecting, the secondary-side body diode conducts to make the secondary-side switch tube conduct; when the secondary-side switch tube changes from conducting to disconnecting, the primary-side body diode conducts to make the primary-side switch tube conduct, which can make the opposite end enter the synchronous rectification state during the freewheeling period, so as to save the parallel-connected diodes and improve the system efficiency.

[0048] When voltage detection of the battery is required, the battery can be charged a little bit, and then the voltage of the battery can be calculated according to the measurement parameters during charging, which simplifies the voltage detection process of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0050] Figure 1 FIG. 1 is a schematic structural diagram of a battery equalization circuit based on a bidirectional flyback converter shown according to the related art;

[0051] Figure 2 FIG. 2 is a schematic structural diagram of a voltage detection circuit of a battery shown according to the related art;

[0052] Figure 3 FIG. 3 is a schematic structural diagram of a switch array shown according to the related art;

[0053] Figure 4 FIG. 4 is a schematic structural diagram of a battery equalization circuit based on a bidirectional flyback converter provided by an embodiment of the present application;

[0054] Figure 5 FIG. 5 is a schematic structural diagram of a battery equalization circuit based on a bidirectional flyback converter provided by an embodiment of the present application;

[0055] Figure 6 FIG. 6 is a flowchart of a battery equalization control method provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0056] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will further describe the embodiments of the present application in detail with reference to the drawings.

[0057] As Figure 4 shown, an embodiment of the present application provides a battery equalization circuit based on a bidirectional flyback converter. The battery equalization circuit based on the bidirectional flyback converter includes: a plurality of battery packs 410, a battery pack bus 420, a step-down converter ( Figure 4 not shown in FIG. 4) and a control module 430. The battery pack bus 420 is a bus commonly connected after a plurality of battery packs 410 are connected in parallel. Each battery pack is composed of a plurality of serially connected battery equalization units.

[0058] Figure 5Shown is a schematic diagram of a battery pack formed by connecting multiple battery equalization units in series. Each battery equalization unit includes a battery, a bi-directional flyback converter, and a first filter capacitor C 1 and a second filter capacitor C 2 . The bi-directional flyback converter includes a transformer, a primary switch tube M 1 and a secondary switch tube M 2 ; The first end of the first filter capacitor C 1 is respectively connected to the battery pack bus 420, the first end of the primary winding in the transformer, and the first end of the first filter capacitor C in the adjacent battery equalization unit 1 . The second end of the first filter capacitor C 1 is respectively connected to the battery pack bus 420, the source electrode of the primary switch tube M 1 and the ground; The first end of the second filter capacitor C 2 is respectively connected to the first end of the secondary winding in the transformer and the positive electrode of the battery. The second end of the second filter capacitor C 2 is respectively connected to the source electrode of the secondary switch tube M 2 and the negative electrode of the battery; The negative electrode of the battery is connected to the positive electrode of the battery in the adjacent battery equalization unit. Among them, the first filter capacitor C 1 and the second filter capacitor C 2 are used for circuit filtering.

[0059] For a battery equalization unit, its adjacent battery equalization units include a battery equalization unit arranged before this battery equalization unit and a battery equalization unit arranged after this battery equalization unit in the battery pack. Assume Figure 5 each battery equalization unit is numbered in the order from top to bottom, then the numbers of the adjacent battery equalization units of the battery equalization unit numbered 1 are 2; the numbers of the adjacent battery equalization units of the battery equalization unit numbered 2 are 1 and 3; the numbers of the adjacent battery equalization units of the battery equalization unit numbered 3 are 2 and 4,..., the numbers of the adjacent battery equalization units of the battery equalization unit numbered a are a - 1.

[0060] For the first battery equalization unit in a battery pack, since there is no battery equalization unit arranged before it, therefore, in the first battery equalization unit, the first end of the first filter capacitor C 1 is respectively connected to the battery pack bus 420, the first end of the primary winding in the transformer, and the first end of the first filter capacitor C in the second battery equalization unit 1 . The positive electrode of the battery is respectively connected to the first end of the second filter capacitor C 2 and the first end of the secondary winding in the transformer. The negative electrode of the battery is respectively connected to the second end of the second filter capacitor C 2 , the source electrode of the secondary switch tube M 2The source electrode is connected to the positive electrode of the battery in the second battery equalization unit.

[0061] For the last battery equalization unit in the battery pack, since there is no battery equalization unit arranged after it, in the last battery equalization unit, the first terminal of the first filter capacitor C 1 is respectively connected to the battery pack bus 420, the first terminal of the primary winding in the transformer, and the first terminal of the first filter capacitor C in the penultimate battery equalization unit 1 The positive electrode of the battery is respectively connected to the first terminal of the second filter capacitor C 2 the first terminal of the secondary winding in the transformer, and the negative electrode of the battery in the penultimate battery equalization unit. The negative electrode of the battery is respectively connected to the second terminal of the second filter capacitor C 2 and the source electrode of the secondary switch tube M 2 is connected.

[0062] For the middle (except the first and the last) battery equalization unit in the battery pack, the first terminal of the first filter capacitor C 1 is respectively connected to the battery pack bus 420, the first terminal of the primary winding in the transformer, the first terminal of the first filter capacitor C in the previous battery equalization unit 1 and the first terminal of the first filter capacitor C in the subsequent battery equalization unit 1 The positive electrode of the battery is respectively connected to the first terminal of the second filter capacitor C 2 the first terminal of the secondary winding in the transformer, and the negative electrode of the battery in the previous battery equalization unit. The negative electrode of the battery is respectively connected to the second terminal of the second filter capacitor C 2 the source electrode of the secondary switch tube M 2 and the positive electrode of the battery in the subsequent battery equalization unit.

[0063] The first terminal of the control module 430 is connected to the battery pack bus 420 through a step-down voltage regulator. The second terminal of the control module 430 is connected to the ground in each battery equalization unit. Among them, the step-down voltage regulator is used to step down the voltage input from the battery pack bus 420 to the control module 430 to protect the control module 430. The control module 430 is used to detect the voltage of the battery, control the charging of the battery from the battery pack bus 420, and control the discharging of the battery to the battery pack bus 420.

[0064] In this embodiment, the battery equalization circuit further includes a primary power management chip and a secondary power management chip; the second terminal of the primary winding is connected to the drain electrode of the primary switch tube M 1 The gate electrode of the primary switch tube M 1 is connected to the primary power management chip; the second terminal of the secondary winding is connected to the drain electrode of the secondary switch tube M 2 The gate electrode of the secondary switch tube M 2The gate is connected to the secondary-side power management chip. In this way, the primary-side power management chip is used to control the conduction and disconnection of the primary-side switching transistor M 1 The secondary-side power management chip is used to control the conduction and disconnection of the secondary-side switching transistor M 2 The conduction and disconnection.

[0065] In this embodiment, the primary-side switching transistor M 1 Includes a primary-side body diode inside, and the secondary-side switching transistor M 2 Includes a secondary-side body diode inside; when the primary-side switching transistor M 1 Changes from conduction to disconnection, the secondary-side body diode conducts, so that the secondary-side switching transistor M 2 Conducts; when the secondary-side switching transistor M 2 Changes from conduction to disconnection, the primary-side body diode conducts, so that the primary-side switching transistor M 1 Conducts.

[0066] Specifically, when the primary-side switching transistor M 1 Changes from conduction to disconnection, it enters the freewheeling state, and the secondary-side body diode in the secondary-side switching transistor M 2 Conducts. At this time, the drain-ground voltage V 2 Of the secondary-side switching transistor M MOS Is negative, and the secondary-side switching transistor M 2 Can be conducted at a very fast speed, and the current flows through the conductive channel of the secondary-side switching transistor M 2 . When the secondary-side switching transistor M 2 Changes from conduction to disconnection, it enters the freewheeling state, and the primary-side body diode in the primary-side switching transistor M 1 Conducts. At this time, the drain-ground voltage V 1 Of the primary-side switching transistor M MOS Is negative, and the primary-side switching transistor M 1 Can be conducted at a very fast speed, and the current flows through the conductive channel of the primary-side switching transistor M 1 . This method of first conducting the body diode and then quickly conducting the switching transistor can avoid paralleling a diode for conducting the switching transistor outside the switching transistor, reduce losses, and improve system efficiency.

[0067] When charging the battery from the battery pack bus 420, the control module 430 controls the primary-side switching transistor M in a battery equalization unit 1 To conduct and the secondary-side switching transistor M 2 To disconnect. The battery pack bus 420 is used to transmit electrical energy to the primary winding; the control module 430 controls the primary-side switching transistor M in the battery equalization unit 1 To disconnect and the secondary-side switching transistor M 2 To conduct. The primary winding is used to transmit electrical energy to the secondary winding, and the secondary winding is used to transmit electrical energy to the battery to realize charging the battery from the battery pack bus 420. Among them, only the primary-side switching transistor M needs to be controlled 1Just turn on and off the primary side switch tube M 1 When the primary side switch tube M 2 is turned off, the secondary side switch tube M

[0068] will automatically turn on without control. When discharging from the battery to the battery pack bus 420, the control module 430 controls the secondary side switch tube M 2 in a battery equalization unit to turn on, and the primary side switch tube M 1 to turn off the battery for transmitting electrical energy to the secondary winding; when the control module 430 controls the secondary side switch tube M 2 in the battery equalization unit to turn off and the primary side switch tube M 1 to turn on, the secondary winding is used to transmit electrical energy to the primary winding, and the primary winding is used to transmit electrical energy to the battery pack bus 420 to achieve discharging from the battery to the battery pack bus 420. Among them, only the on and off of the secondary side switch tube M 2 need to be controlled. When the secondary side switch tube M 2 is turned off, the primary side switch tube M 1 will automatically turn on without control.

[0069] In summary, the battery equalization circuit based on the bidirectional flyback converter provided by the embodiment of the present application can charge the battery from the battery pack bus by controlling the primary side switch tube, and can discharge from the battery to the battery pack bus by controlling the secondary side switch tube, so as to achieve battery equalization. It can save the switching matrix and isolation transmission devices to simplify the structure of the battery equalization circuit, and can also simplify the control process of the bidirectional flyback converter.

[0070] When the primary side switch tube changes from on to off, the secondary side body diode conducts to turn on the secondary side switch tube; when the secondary side switch tube changes from on to off, the primary side body diode conducts to turn on the primary side switch tube, which can make the opposite end enter the synchronous rectification state during the freewheeling period, thereby saving the parallel diodes and improving the system efficiency.

[0071] As Figure 6 shown, this embodiment provides a battery equalization control method applied to the above battery equalization circuit based on the bidirectional flyback converter. The battery equalization control method includes:

[0072] Step 601, when it is necessary to detect the voltage of the target battery, the control module charges the target battery from the battery pack bus through the bidirectional flyback converter corresponding to the target battery, and calculates the current voltage of the target battery according to the measurement parameters during charging.

[0073] The target battery is the battery in the battery pack that requires battery balancing. Among them, battery balancing refers to controlling the charging of the battery with a lower power level so that its power level after charging is balanced with that of other batteries, or controlling the discharging of the battery with a higher power level so that its power level after discharging is balanced with that of other batteries.

[0074] When detecting the current voltage of the target battery, a little charge needs to be applied to the target battery. Specifically, when the battery balancing circuit further includes a primary power management chip and a secondary power management chip, the control module can charge the target battery from the battery pack bus through the bidirectional flyback converter corresponding to the target battery, which may include: the control module sends a detection signal to the primary power management chip corresponding to the target battery; the primary power management chip controls the primary switch tube to conduct according to the detection signal, and the battery pack bus transmits electrical energy to the primary winding through the conducted primary switch tube; the primary power management chip controls the primary switch tube to disconnect so that the secondary switch tube conducts, and the primary winding transmits electrical energy to the target battery through the conducted secondary switch tube and the secondary winding, so as to realize charging the target battery from the battery pack bus.

[0075] During the charging process, measurement parameters can be obtained, and the current voltage can be calculated according to the measurement parameters. Two calculation methods for the current voltage are provided in this embodiment, which are specifically as follows:

[0076] (1) The first calculation method

[0077] When electrical energy is transmitted from the primary side to the secondary side and the secondary side is in freewheeling, the drain-to-ground voltage on the primary switch tube is: V MOS =V in +n×V b (1)

[0078] Among them, V MOS is the drain-to-ground voltage of the primary switch tube, V in is the input voltage of the battery pack bus, V b is the current voltage of the target battery, and n is the turns ratio of the primary and secondary sides, which is a fixed value.

[0079] By transforming formula (1), the voltage of the target battery can be obtained:

[0080] (2)

[0081] That is, calculating the current voltage of the target battery according to the measurement parameters during charging may include: the primary power management chip obtains the first measurement parameter during charging, and the first measurement parameter includes the input voltage of the battery pack bus and the drain-to-ground voltage of the primary switching transistor; the primary power management chip divides the difference obtained by subtracting the input voltage from the drain-to-ground voltage by the turns ratio of the primary and secondary sides to obtain the current voltage of the target battery; the control module obtains the current voltage calculated by the primary power management chip.

[0082] (2) The second calculation method

[0083] When electric energy is transmitted from the primary side to the secondary side and the primary switching transistor is turned on, there is the following formula:

[0084] V in ×T on =L p ×I pk (3)

[0085] Among them, V in is the input voltage of the battery pack bus, T on is the on-time of the primary switching transistor, L p is the inductance of the primary side, and I pk is the peak current of the primary side.

[0086] When the primary switching transistor is turned off and the secondary side conducts freewheeling, there is the following formula:

[0087] (4)

[0088] Among them, T off is the off-time of the primary switching transistor, and n is the turns ratio of the primary and secondary sides.

[0089] It is known that

[0090] T on +T off =T (5)

[0091] (6)

[0092] Therefore, it can be deduced that:

[0093] (7)

[0094] That is, calculating the current voltage of the target battery based on the measurement parameters during charging may include: the primary power management chip obtains the second measurement parameters during charging, and the second measurement parameters include the duty ratio of the conduction time of the primary switching tube and the input voltage of the battery pack bus; the primary power management chip divides the input voltage by the turn ratio of the primary and secondary sides and then multiplies it by a predetermined ratio to obtain the current voltage of the target battery, and the predetermined ratio is the ratio of the duty ratio to the difference between 1 and the duty ratio; the control module obtains the current voltage calculated by the primary power management chip.

[0095] When it is necessary to detect the current voltage of each battery one by one, the control module outputs a scan signal, and controls the bidirectional flyback converter through the primary power management chip to charge each battery in turn in a very short time, scans the current voltage of the battery, and the current voltages of all batteries can be obtained by this method.

[0096] Step 602, if it is determined according to the current voltage that the target battery needs to be charged, the control module realizes charging from the battery pack bus to the target battery through the bidirectional flyback converter corresponding to the target battery, and stops charging until the current voltage reaches the first voltage threshold.

[0097] Among them, the charging process of the target battery is the same as the charging process during voltage detection, which will not be elaborated here.

[0098] In this embodiment, when charging the target battery, the control module periodically updates the current voltage of the target battery, and the detection process is as described in step 601 in detail. Then, the control module compares the current voltage updated each time with the first voltage threshold. If the current voltage reaches the first voltage threshold, charging stops; if the current voltage does not reach the first voltage threshold, charging continues.

[0099] Step 603, if it is determined according to the current voltage that the target battery needs to be discharged, the control module realizes discharging from the target battery to the battery pack bus through the bidirectional flyback converter corresponding to the target battery, and stops discharging until the current voltage reaches the second voltage threshold.

[0100] Specifically, the control module realizes discharging from the target battery to the battery pack bus through the bidirectional flyback converter corresponding to the target battery, which may include: the control module sends a discharge signal to the primary power management chip corresponding to the target battery; the primary power management chip notifies the secondary power management chip to discharge the target battery according to the discharge signal; the secondary power management chip controls the secondary switching tube to conduct, and the target battery transmits electrical energy to the secondary winding through the conducted secondary switching tube; the secondary power management chip controls the secondary switching tube to disconnect, so that the primary switching tube conducts, and the secondary winding transmits electrical energy to the battery pack bus through the conducted primary switching tube and the primary winding to realize discharging from the target battery to the battery pack bus.

[0101] Among them, the primary-side power management chip needs to make the primary-side switch tube work in a special mode to notify the secondary-side power management chip to discharge the target battery in this way. Specifically, the primary-side power management chip notifies the secondary-side power management chip to discharge the target battery according to the discharge signal, which may include: the primary-side power management chip controls the primary-side switch tube to switch the working mode according to the discharge signal, so that the secondary-side power management chip determines to discharge the target battery according to the working mode; or, the primary-side power management chip controls the primary-side switch tube to conduct and disconnect according to a predetermined rule according to the discharge signal, so that the secondary-side power management chip determines to discharge the target battery according to the predetermined rule.

[0102] The working modes of the primary-side switch tube include Continuous Conduction Mode (CCM), Discontinuous Conduction Mode (DCM), Boundary Conduction Mode (BCM), etc. For example, a switching method of the working mode is to switch from CCM to BCM, then from BCM to DCM, and then from DCM to BCM. When the secondary-side power management chip detects this switching method, it determines that the target battery needs to be discharged.

[0103] In this embodiment, when discharging the target battery, the control module periodically updates the current voltage of the target battery, and the detection process is detailed in the description of step 601. Then, the control module compares the current voltage after each update with the second voltage threshold. If the current voltage reaches the second voltage threshold, the discharge stops; if the current voltage is higher than the second voltage threshold, the discharge continues.

[0104] When it is determined that the discharge needs to be stopped, the synchronous rectification of the primary-side switch tube will be turned off in advance to notify the secondary-side power management chip to stop charging. After receiving the notification, the secondary-side power management chip ends the discharge of the target battery.

[0105] In summary, the battery equalization control method provided by the embodiments of this application can charge the battery from the battery pack bus by controlling the primary-side switch tube; and can discharge the battery to the battery pack bus by controlling the secondary-side switch tube, thereby realizing the equalization of the battery. It can save the switch matrix and isolation transmission devices to simplify the structure of the battery equalization circuit, and can also simplify the control process of the bidirectional flyback converter.

[0106] When the primary side switch transistor changes from conduction to disconnection, the secondary side body diode conducts to enable the secondary side switch transistor to conduct; when the secondary side switch transistor changes from conduction to disconnection, the primary side body diode conducts to enable the primary side switch transistor to conduct, which can make the opposite end enter the synchronous rectification state during the freewheeling period, thereby saving the parallel-connected diodes and improving the system efficiency.

[0107] When the battery voltage needs to be detected, the battery can be charged a little bit, and then the battery voltage can be calculated according to the measurement parameters during charging, which simplifies the battery voltage detection process.

[0108] Those of ordinary skill in the art can understand that all or part of the steps to implement the above embodiments can be completed by hardware, or can be completed by a program instructing relevant hardware. The program can be stored in a computer-readable storage medium. The above-mentioned storage medium can be a read-only memory, a disk or an optical disc, etc.

[0109] The above does not intend to limit the embodiments of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the embodiments of the present application shall be included in the protection scope of the embodiments of the present application.

Claims

1. A battery balancing circuit based on a bidirectional flyback converter, characterized in that: The battery balancing circuit includes a plurality of battery packs, a battery pack bus, a voltage reducer and a control module. The battery pack bus is a bus connected together after the plurality of battery packs are connected in parallel. The battery pack is composed of a plurality of battery balancing units connected in series. Each battery balancing unit includes a battery, a bidirectional flyback converter, a first filter capacitor and a second filter capacitor. The bidirectional flyback converter includes a transformer, a primary switch tube and a secondary switch tube. The first end of the first filter capacitor is respectively connected to the battery pack bus, the first end of the primary winding in the transformer and the first end of the first filter capacitor in the adjacent battery balancing unit, and the second end of the first filter capacitor is respectively connected to the battery pack bus, the source of the primary switch tube and the ground; the first end of the second filter capacitor is respectively connected to the first end of the secondary winding in the transformer and the positive electrode of the battery, and the second end of the second filter capacitor is respectively connected to the source of the secondary switch tube and the negative electrode of the battery; the negative electrode of the battery is connected to the positive electrode of the battery in the adjacent battery balancing unit; The first end of the control module is connected to the battery pack bus through the voltage reducer, and the second end of the control module is connected to the ground in each battery balancing unit; When the control module controls the primary switch tube in a battery balancing unit to be turned on and the secondary switch tube to be turned off, the battery pack bus is used to transmit electric energy to the primary winding; when the control module controls the primary switch tube in the battery balancing unit to be turned off and the secondary switch tube to be turned on, the primary winding is used to transmit the electric energy to the secondary winding, and the secondary winding is used to transmit the electric energy to the battery, so as to realize charging the battery from the battery pack bus; When the control module controls the secondary switch tube in a battery balancing unit to be turned on and the primary switch tube to be turned off, the battery is used to transmit electric energy to the secondary winding; when the control module controls the secondary switch tube in the battery balancing unit to be turned off and the primary switch tube to be turned on, the secondary winding is used to transmit the electric energy to the primary winding, and the primary winding is used to transmit the electric energy to the battery pack bus, so as to realize discharge from the battery to the battery pack bus.

2. The battery balancing circuit based on a bidirectional flyback converter according to claim 1, characterized in that: The primary switch tube includes a primary body diode, and the secondary switch tube includes a secondary body diode; When the primary switch tube changes from being on to being off, the secondary body diode is turned on, so that the secondary switch tube is turned on; When the secondary switch tube changes from being on to being off, the primary body diode is turned on to make the primary switch tube turned on.

3. The battery balancing circuit based on a bidirectional flyback converter according to claim 1, characterized in that: The battery balancing circuit also includes a primary side power management chip and a secondary side power management chip; The second end of the primary winding is connected to the drain of the primary switch tube, and the gate of the primary switch tube is connected to the primary power management chip; The second end of the secondary winding is connected to the drain of the secondary switch tube, and the gate of the secondary switch tube is connected to the secondary power management chip.

4. A battery balancing control method based on a battery balancing circuit of a bidirectional flyback converter, characterized in that: Used in a battery balancing circuit based on a bidirectional flyback converter according to any one of claims 1 to 3, the method comprising: When it is necessary to detect the voltage of the target battery, the control module charges the target battery from the battery pack bus through the bidirectional flyback converter corresponding to the target battery, and calculates the current voltage of the target battery according to the measurement parameters during charging; If it is determined according to the current voltage that the target battery needs to be charged, the control module charges the target battery from the battery pack bus through a bidirectional flyback converter corresponding to the target battery, and stops charging after the current voltage reaches a first voltage threshold; If it is determined according to the current voltage that the target battery needs to be discharged, the control module discharges from the target battery to the battery pack bus through the bidirectional flyback converter corresponding to the target battery until the current voltage reaches a second voltage threshold and then stops discharging.

5. The battery balancing control method according to claim 4, characterized in that: When the battery balancing circuit further includes a primary power management chip and a secondary power management chip, the control module realizes charging the target battery from the battery pack bus through a bidirectional flyback converter corresponding to the target battery, including: The control module sends a detection signal to the primary power management chip corresponding to the target battery; The primary power management chip controls the primary switch tube to be turned on according to the detection signal, and the battery pack bus transmits electric energy to the primary winding through the turned-on primary switch tube; The primary power management chip controls the primary switch tube to be disconnected so that the secondary switch tube is turned on, and the primary winding transmits the electric energy to the target battery through the turned-on secondary switch tube and the secondary winding, so as to realize charging from the battery pack bus to the target battery.

6. The battery balancing control method according to claim 5, characterized in that: The calculating the current voltage of the target battery according to the measurement parameters during charging includes: The primary power management chip acquires a first measurement parameter during charging, where the first measurement parameter includes an input voltage of the battery pack bus and a drain-ground voltage of the primary switch tube; The primary power management chip divides the difference obtained by subtracting the input voltage from the drain-ground voltage by the turns ratio of the primary-secondary side to obtain the current voltage of the target battery; The control module obtains the current voltage calculated by the primary power management chip.

7. The battery balancing control method according to claim 5, characterized in that: The calculating the current voltage of the target battery according to the measurement parameters during charging includes: The primary power management chip acquires a second measurement parameter during charging, where the second measurement parameter includes a duty cycle of the on-time of the primary switch tube and an input voltage of the battery pack bus; The primary power management chip divides the input voltage by the turns ratio of the primary secondary side and then multiplies by a predetermined ratio to obtain the current voltage of the target battery, wherein the predetermined ratio is the ratio of the duty cycle to the difference between 1 and the duty cycle; The control module obtains the current voltage calculated by the primary power management chip.

8. The battery balancing control method according to claim 4, characterized in that: The control module realizes discharge from the target battery to the battery pack bus through the bidirectional flyback converter corresponding to the target battery, including: The control module sends a discharge signal to the primary power management chip corresponding to the target battery; The primary power management chip notifies the secondary power management chip to discharge the target battery according to the discharge signal; The secondary power management chip controls the secondary switch tube to be turned on, and the target battery transmits electric energy to the secondary winding through the turned-on secondary switch tube; The secondary power management chip controls the secondary switch tube to be disconnected so that the primary switch tube is turned on, and the secondary winding transmits the electric energy to the battery pack bus through the turned-on primary switch tube and the primary winding to realize discharge from the target battery to the battery pack bus.

9. The battery balancing control method according to claim 8, characterized in that: The primary power management chip notifies the secondary power management chip to discharge the target battery according to the discharge signal, including: The primary power management chip controls the primary switch tube to switch the working mode according to the discharge signal, so that the secondary power management chip determines to discharge the target battery according to the working mode; or The primary power management chip controls the primary switch tube to be turned on and off according to a predetermined rule according to the discharge signal, so that the secondary power management chip determines to discharge the target battery according to the predetermined rule.

10. The battery balancing control method according to any one of claims 4 to 9, characterized in that: The method further comprises: When charging or discharging the target battery, the control module periodically updates the current voltage of the target battery.

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