Battery balancing circuit and battery balancing control method based on bidirectional flyback converter

Abstract

The present application discloses a battery balancing circuit and a battery balancing control method based on a bidirectional flyback converter, and belongs to the field of circuit technology. In the battery balancing circuit, the control module controls the primary switch tube to be turned on and the secondary switch tube to be turned off, and the battery pack bus transmits electric energy to the primary winding; the control module controls the primary switch tube to be turned off and the secondary switch tube to be turned on, and the primary winding transmits electric energy to the secondary winding, and the secondary winding transmits electric energy to the battery, so as to realize charging from the battery pack bus to the battery; the control module controls the secondary switch tube to be turned on and the primary switch tube to be turned off, and the battery transmits electric energy to the secondary winding; the control module controls the secondary switch tube to be turned off and the primary switch tube to be turned on, and the secondary winding transmits electric energy to the primary winding, and the primary winding transmits electric energy to the battery pack bus, so as to realize discharging from 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] The present application relates to the field of circuit technology, and in particular to a battery balancing circuit and a battery balancing control method based on a bidirectional flyback converter. Background Art

[0002] In the fields of electric vehicles and energy storage systems, there are extremely high requirements for the performance, life and safety of battery systems. In the battery system, due to the differences in parameters such as voltage, capacity, internal resistance, etc. between battery cells, this inconsistency will gradually increase as the charge and discharge cycle proceeds, resulting in a decrease in the overall performance of the battery system. In order to solve the problem of battery inconsistency and improve the overall performance of the battery system, battery balancing technology came into being. Battery balancing technology can analyze the characteristic data of the battery in real time, balance the charge and discharge as needed, and quickly improve the consistency between battery cells.

[0003] like Figure 1 As shown, the existing battery balancing circuit based on the bidirectional flyback converter mainly includes a battery cell voltage detection module, an isolation transmission module, a control module, a switch matrix module and a bidirectional flyback converter. In order to ensure safety, the input and output of the bidirectional flyback converter need to be isolated.

[0004] like Figure 2 As shown, the battery cells are connected in series, and the ground of each battery cell is independent. Therefore, a voltage detection module is required at each battery cell, and the signal between the voltage detection module and the control module needs to be isolated and transmitted. Since each battery requires a voltage detection module and needs to be transmitted to the control module in an isolated manner, the voltage detection and transmission system is relatively complicated.

[0005] like Figure 3 As shown, the control module calculates the output voltage, connects a specific battery cell to the bidirectional flyback converter by controlling the switch matrix of the battery cell, and outputs a control signal to the bidirectional flyback converter to determine whether the battery cell is charged or discharged. The signal between the switch matrix and the control module also needs to be isolated and transmitted. Since a complex switch matrix is ​​required to control the battery cell, and the signal transmission between the control module and the switch matrix also needs to be isolated, 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 is turned on, the MOS tube on the other side will be turned off and needs to be connected to a parallel diode for freewheeling. However, the diode has a large loss, 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 balancing circuit and a battery balancing 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 balancing circuit, low system efficiency and high circuit cost. The technical solution is as follows: According to a first aspect of the present application, a battery balancing circuit based on a bidirectional flyback converter is provided, wherein the battery balancing circuit based on a bidirectional flyback converter comprises a plurality of battery packs, a battery pack bus, a buck and a control module, wherein the battery pack bus is a bus connected to a plurality of battery packs in parallel, and 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.

[0008] In a possible implementation, 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.

[0009] In a possible implementation, the battery balancing circuit further 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.

[0010] According to a second aspect of the present application, a battery balancing control method of a battery balancing circuit based on a bidirectional flyback converter is provided, which is used in the battery balancing circuit based on a bidirectional flyback converter as described above, and the method includes: 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.

[0011] In a possible implementation, 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.

[0012] In a possible implementation, 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.

[0013] In a possible implementation, 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.

[0014] In a possible implementation, the control module realizes discharge from the target battery to the battery pack bus through a 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.

[0015] In a possible implementation, 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.

[0016] In a possible implementation, the method further includes: When charging or discharging the target battery, the control module periodically updates the current voltage of the target battery.

[0017] The beneficial effects of the technical solution provided by this application include at least: By controlling the primary side switch tube, charging from the battery pack bus to the battery can be realized; by controlling the secondary side switch tube, discharging from the battery to the battery pack bus can be realized, thereby achieving battery balancing, which can save switch matrices and isolation transmission devices to simplify the structure of the battery balancing circuit and also simplify the control process of the bidirectional flyback converter.

[0018] When the primary switch tube changes from on to off, the secondary body diode is turned on to make the secondary switch tube turned on; when the secondary switch tube changes from on to off, the primary body diode is turned on to make the primary switch tube turned on, which can make the opposite end enter the synchronous rectification state during the freewheeling period, thereby saving parallel diodes and improving system efficiency.

[0019] When the battery voltage needs to be detected, the battery can be charged a little bit and then the battery voltage can be calculated based on the measured parameters during charging, thereby simplifying the battery voltage detection process. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0021] Figure 1 It is a structural schematic diagram of a battery balancing circuit based on a bidirectional flyback converter according to the related art; Figure 2It is a structural schematic diagram of a battery voltage detection circuit according to the related art; Figure 3 is a structural schematic diagram of a switch array according to the related art; Figure 4 It is a structural schematic diagram of a battery balancing circuit based on a bidirectional flyback converter provided by an embodiment of the present application; Figure 5 It is a structural schematic diagram of a battery balancing circuit based on a bidirectional flyback converter provided by an embodiment of the present application; Figure 6 It is a flow chart of a battery balancing control method provided by an embodiment of the present application. DETAILED DESCRIPTION

[0022] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the implementation methods of the present application will be further described in detail below in conjunction with the accompanying drawings.

[0023] like Figure 4 As shown, an embodiment of the present application provides a battery balancing circuit based on a bidirectional flyback converter, and the battery balancing circuit based on a bidirectional flyback converter includes: a plurality of battery packs 410, a battery pack bus 420, a buck ( Figure 4 The battery pack bus 420 is a bus bar to which multiple battery packs 410 are connected in parallel and are connected together. The battery pack is composed of multiple battery balancing units connected in series.

[0024] Figure 5 The schematic diagram of a battery pack formed by a plurality of battery balancing units connected in series is shown, wherein each battery balancing unit includes a battery, a bidirectional flyback converter, a first filter capacitor C1 and a second filter capacitor C2, and the bidirectional flyback converter includes a transformer, a primary switch tube M1 and a secondary switch tube M2; the first end of the first filter capacitor C1 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 C1 in the adjacent battery balancing unit, and the second end of the first filter capacitor C1 is respectively connected to the battery pack bus 420, the source of the primary switch tube M1 and the ground; the first end of the second filter capacitor C2 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 C2 is respectively connected to the source of the secondary switch tube M2 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 filter capacitor C1 and the second filter capacitor C2 are used for circuit filtering.

[0025] For a battery balancing unit, its adjacent battery balancing units include a battery balancing unit that is arranged before the battery balancing unit and a battery balancing unit that is arranged after the battery balancing unit in the battery pack. Figure 5In the example, each battery balancing unit is numbered from top to bottom, and the adjacent battery balancing unit of the battery balancing unit numbered 1 is numbered 2; the adjacent battery balancing units of the battery balancing unit numbered 2 are numbered 1 and 3; the adjacent battery balancing units of the battery balancing unit numbered 3 are numbered 2 and 4, ..., and the adjacent battery balancing unit of the battery balancing unit numbered a is numbered a-1.

[0026] For the first battery balancing unit in a battery pack, since there is no battery balancing unit arranged before it, in the first battery balancing unit, the first end of the first filter capacitor C1 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 C1 in the second battery balancing unit, the positive electrode of the battery is respectively connected to the first end of the second filter capacitor C2 and the first end of the secondary winding in the transformer, and the negative electrode of the battery is respectively connected to the second end of the second filter capacitor C2, the source electrode of the secondary switch tube M2, and the positive electrode of the battery in the second battery balancing unit.

[0027] For the last battery balancing unit in the battery pack, since there is no battery balancing unit arranged after it, in the last battery balancing unit, the first end of the first filter capacitor C1 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 C1 in the penultimate battery balancing unit, the positive electrode of the battery is respectively connected to the first end of the second filter capacitor C2, the first end of the secondary winding in the transformer, and the negative electrode of the battery in the penultimate battery balancing unit, and the negative electrode of the battery is respectively connected to the second end of the second filter capacitor C2 and the source electrode of the secondary switch tube M2.

[0028] For the middle (except the first and last) battery balancing units in the battery pack, the first end of the first filter capacitor C1 is respectively connected to the battery pack bus 420, the first end of the primary winding in the transformer, the first end of the first filter capacitor C1 in the previous battery balancing unit, and the first end of the first filter capacitor C1 in the next battery balancing unit, the positive electrode of the battery is respectively connected to the first end of the second filter capacitor C2, the first end of the secondary winding in the transformer, and the negative electrode of the battery in the previous battery balancing unit, and the negative electrode of the battery is respectively connected to the second end of the second filter capacitor C2, the source electrode of the secondary switch tube M2, and the positive electrode of the battery in the next battery balancing unit.

[0029] The first end of the control module 430 is connected to the battery bus 420 through a voltage reducer, and the second end of the control module 430 is connected to the ground in each battery balancing unit. The voltage reducer is used to reduce the voltage input to the control module 430 from the battery bus 420 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 bus 420, and control the discharge of the battery from the battery to the battery bus 420.

[0030] In this embodiment, the battery balancing circuit further includes a primary power management chip and a secondary power management chip; the second end of the primary winding is connected to the drain of the primary switch tube M1, and the gate of the primary switch tube M1 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 M2, and the gate of the secondary switch tube M2 is connected to the secondary power management chip. In this way, the primary power management chip is used to control the conduction and disconnection of the primary switch tube M1, and the secondary power management chip is used to control the conduction and disconnection of the secondary switch tube M2.

[0031] In this embodiment, the primary switch tube M1 includes a primary body diode, and the secondary switch tube M2 includes a secondary body diode; when the primary switch tube M1 changes from on to off, the secondary body diode is turned on to turn on the secondary switch tube M2; when the secondary switch tube M2 changes from on to off, the primary body diode is turned on to turn on the primary switch tube M1.

[0032] Specifically, when the primary switch tube M1 changes from on to off, it enters the freewheeling state, and the secondary body diode in the secondary switch tube M2 is turned on. At this time, the drain-ground voltage V MOS When the secondary switch tube M2 changes from on to off, it enters the freewheeling state, and the primary body diode in the primary switch tube M1 is turned on. At this time, the drain-to-ground voltage V MOS If the voltage is negative, the primary switch tube M1 can be turned on at a very fast speed, and the current flows through the conductive channel of the primary switch tube M1. This method of first turning on the body diode and then quickly turning on the switch tube can avoid connecting a diode in parallel outside the switch tube for turning on the switch tube, which can reduce losses and improve system efficiency.

[0033] When charging the battery from the battery bus 420, the control module 430 controls the primary switch tube M1 in a battery balancing unit to be turned on and the secondary switch tube M2 to be turned off, and the battery bus 420 is used to transmit electric energy to the primary winding; the control module 430 controls the primary switch tube M1 in the battery balancing unit to be turned off and the secondary switch tube M2 to be turned on, the primary winding is used to transmit electric energy to the secondary winding, and the secondary winding is used to transmit electric energy to the battery, so as to realize charging from the battery bus 420 to the battery. Among them, it is only necessary to control the on and off of the primary switch tube M1. When the primary switch tube M1 is turned off, the secondary switch tube M2 will automatically turn on without control.

[0034] When discharging from the battery to the battery bus 420, the control module 430 controls the secondary switch tube M2 in a battery balancing unit to turn on and the primary switch tube M1 to turn off the battery to transfer electric energy to the secondary winding; when the control module 430 controls the secondary switch tube M2 in the battery balancing unit to turn off and the primary switch tube M1 to turn on, the secondary winding is used to transfer electric energy to the primary winding, and the primary winding is used to transfer electric energy to the battery bus 420, so as to realize discharging from the battery to the battery bus 420. Among them, it is only necessary to control the on and off of the secondary switch tube M2. When the secondary switch tube M2 is turned off, the primary switch tube M1 will automatically turn on without control.

[0035] In summary, the battery balancing circuit based on the bidirectional flyback converter provided in the embodiment of the present application can realize charging from the battery pack bus to the battery by controlling the primary side switch tube; and can realize discharging from the battery to the battery pack bus by controlling the secondary side switch tube, thereby realizing battery balancing, 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.

[0036] When the primary switch tube changes from on to off, the secondary body diode is turned on to make the secondary switch tube turned on; when the secondary switch tube changes from on to off, the primary body diode is turned on to make the primary switch tube turned on, which can make the opposite end enter the synchronous rectification state during the freewheeling period, thereby saving parallel diodes and improving system efficiency.

[0037] like Figure 6 As shown, this embodiment provides a battery balancing control method applied to the battery balancing circuit based on the bidirectional flyback converter, and the battery balancing control method includes: 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.

[0038] The target battery is the battery in the battery pack that needs to be balanced. Battery balancing refers to controlling the charging of the battery with lower power so that its power after charging is balanced with the power of other batteries, or controlling the discharge of the battery with higher power so that its power after discharge is balanced with the power of other batteries.

[0039] When detecting the current voltage of the target battery, it is necessary to charge the target battery a little bit. Specifically, when the battery balancing circuit also includes a primary power management chip and a secondary power management chip, the control module realizes charging from the battery pack bus to the target battery 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 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 turned off to turn on the secondary switch tube, and the primary winding transmits 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.

[0040] During the charging process, measurement parameters can be obtained and the current voltage can be calculated based on the measurement parameters. This embodiment provides two methods for calculating the current voltage, as follows: (1) The first calculation method When the primary side transmits electric energy to the secondary side and the secondary side continues to flow, the drain-to-ground voltage on the primary side switch tube is: V MOS =V in +n×V b (1) Among them, V MOS is the drain-to-ground voltage of the primary switch tube, V in is the input voltage of the battery bus, V b is the current voltage of the target battery, and n is the turns ratio of the original secondary side, which is a constant.

[0041] By transforming formula (1), we can get the voltage of the target battery: (2) 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, the first measurement parameter including the input voltage of the battery pack bus and the 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; and the control module obtains the current voltage calculated by the primary power management chip.

[0042] (2) The second calculation method When the primary side transmits electric energy to the secondary side and the primary side switch is turned on, the following formula is used: V in ×T on =L p ×I pk (3) Among them, V in is the input voltage of the battery bus, T on is the conduction time of the primary switch tube, L p is the inductance of the primary side, I pk is the peak current of the primary side.

[0043] When the primary switch is turned off and the secondary is freewheeling, the following formula is used: (4) Among them, T off is the disconnection time of the primary switch tube, and n is the turns ratio of the primary to secondary side.

[0044] Known T on +T off =T (5) (6) Therefore, it can be deduced that: (7) 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 second measurement parameter during charging, the second measurement parameter includes the duty cycle of the conduction time of the primary switch tube and the 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 multiplies it by a predetermined ratio to obtain the current voltage of the target battery, the predetermined ratio is the ratio of the duty cycle to the difference between 1 minus the duty cycle; the control module obtains the current voltage calculated by the primary power management chip.

[0045] When it is necessary to detect the current voltage of the batteries one by one, the control module outputs a scanning signal, and controls the bidirectional flyback converter through the primary power management chip to charge each battery in turn in a very short time, and scans the current voltage of the battery. This method can obtain the current voltage of all batteries.

[0046] Step 602: If it is determined that the target battery needs to be charged according to the current voltage, the control module charges the target battery from the battery pack bus through the bidirectional flyback converter corresponding to the target battery, and stops charging after the current voltage reaches a first voltage threshold.

[0047] The charging process for the target battery is the same as the charging process during voltage detection, which will not be described in detail here.

[0048] 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 described in step 601. Then, the control module compares the current voltage after each update with the first voltage threshold, and stops charging if the current voltage reaches the first voltage threshold; if the current voltage does not reach the first voltage threshold, continues charging.

[0049] Step 603, 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 the second voltage threshold and then stops discharging.

[0050] Specifically, the control module realizes discharge 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 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 turned off to turn on the primary switch tube, and the secondary winding transmits electric energy to the battery pack bus through the turned-on primary switch tube and the primary winding, so as to realize discharge from the target battery to the battery pack bus.

[0051] Among them, the primary power management chip needs to make the primary switch tube work in a special mode, so as to notify the secondary power management chip to discharge the target battery. Specifically, the primary power management chip notifies the secondary power management chip to discharge the target battery according to the discharge signal, which may include: 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 turn 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.

[0052] The working modes of the primary side switch tube include continuous conduction mode (CCM), discontinuous conduction mode (DCM), boundary or boundary line conduction mode (BCM), etc. For example, one way to switch 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 mode, it determines that the target battery needs to be discharged.

[0053] 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 described in step 601. Then, the control module compares the current voltage after each update with the second voltage threshold, and stops discharging if the current voltage reaches the second voltage threshold; if the current voltage is higher than the second voltage threshold, continues discharging.

[0054] When it is determined that discharging needs to be stopped, the synchronous rectification of the primary switch tube will be turned off in advance to notify the secondary power management chip to stop charging. After receiving the notification, the secondary power management chip ends the discharge of the target battery.

[0055] In summary, the battery balancing control method provided in the embodiment of the present application can realize charging from the battery pack bus to the battery by controlling the primary side switch tube; and can realize discharging from the battery to the battery pack bus by controlling the secondary side switch tube, thereby realizing battery balancing, 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.

[0056] When the primary switch tube changes from on to off, the secondary body diode is turned on to make the secondary switch tube turned on; when the secondary switch tube changes from on to off, the primary body diode is turned on to make the primary switch tube turned on, which can make the opposite end enter the synchronous rectification state during the freewheeling period, thereby saving parallel diodes and improving system efficiency.

[0057] When the battery voltage needs to be detected, the battery can be charged a little bit and then the battery voltage can be calculated based on the measured parameters during charging, thereby simplifying the battery voltage detection process.

[0058] A person skilled in the art will understand that all or part of the steps to implement the above embodiments may be accomplished by hardware or by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, and the above-mentioned storage medium may be a read-only memory, a disk or an optical disk, etc.

[0059] The above description is not intended to limit the embodiments of the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present application should 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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