Powertrain, electric vehicle, and power battery heating method

Abstract

A powertrain (100), comprising a first driving motor (201), a second driving motor (202), and a motor controller (13), wherein the motor controller (13) comprises a first power circuit (2031), a second power circuit (2032), a first capacitor, a second capacitor, and a controller (2033), and the controller (2033) controls a center tap of a three-phase winding of the first driving motor (201) to be connected to a center tap of a three-phase winding of the second driving motor (202). An electric vehicle (10), comprising a power battery (15), wheels, and the powertrain (100). A power battery heating method, applied to the motor controller (13), which comprises the first power circuit (2031), the second power circuit (2032), the first capacitor, the second capacitor, and the controller (2033), and controls the center tap of the three-phase winding of the first driving motor (201) to be connected to the center tap of the three-phase winding of the second driving motor (202). Such a configuration enables the first power circuit and the second power circuit to output pulse current of a wider range, thereby further increasing the rate of pulse heating of the power battery, not only improving the temperature rise speed of the power battery and shortening the charging waiting time and one-key vehicle preparation time, but also enhancing the flexibility and efficiency of heating of the power battery.

Description

A powertrain, electric vehicle, and a method for heating a power battery Technical Field

[0001] This application relates to the field of electric vehicles, and in particular to a powertrain, an electric vehicle, and a method for heating a power battery. Background Technology

[0002] In low-temperature environments, the charging and discharging capacity of electric vehicle batteries drops sharply, necessitating battery heating to ensure normal operation. Common heating methods include positive temperature coefficient (PTC) ceramic heating and active motor heating. However, these methods all heat the battery via water heating, resulting in a low heating rate and negatively impacting user experience.

[0003] In addition, high-frequency pulse heating can be used to heat the power battery. This method mainly uses the powertrain of the electric vehicle to perform AC high-frequency charging and discharging on the power battery, thereby using the heat generated by the battery's internal resistance to heat the battery. This can make the battery heating temperature distribution more uniform and the heating speed faster.

[0004] For vehicles with dual drive motors, the heating effect of the battery is limited by the adjustable range of the pulse current generated by the two motors due to hardware constraints such as motor windings and capacitors. Therefore, it is necessary to increase the amplitude of the pulse current to further improve the rate of pulse heating of the battery. Summary of the Invention

[0005] This application provides a powertrain, an electric vehicle, and a method for heating a power battery. By connecting the center taps of the three-phase windings of a first drive motor and a second drive motor, the first power circuit and the second power circuit can output a wider range of pulse current, thereby further improving the rate of pulse heating of the power battery. This not only improves the temperature rise rate of the power battery and shortens the charging waiting time and one-click vehicle standby time, but also enhances the flexibility and efficiency of the system, making it particularly suitable for electric vehicle usage scenarios in cold weather conditions.

[0006] In a first aspect, this application provides a powertrain, which includes a first drive motor, a second drive motor, and a motor controller. The motor controller includes a first power circuit, a second power circuit, a first capacitor, a second capacitor, and a controller. The midpoints of the three-phase bridge arms of the first power circuit are respectively used to connect to the three-phase windings of the first drive motor. The midpoints of the three-phase bridge arms of the second power circuit are respectively used to connect to the three-phase windings of the second drive motor. The two ends of each phase bridge arm of the first power circuit are respectively connected to the two ends of the first capacitor. The two ends of each phase bridge arm of the second power circuit are respectively connected to the two ends of the second capacitor. The two ends of the first capacitor and the two ends of the second capacitor are respectively used to connect to the positive and negative terminals of a power battery through a DC bus. The controller is used to control the connection between the center tap of the three-phase windings of the first drive motor and the center tap of the three-phase windings of the second drive motor.

[0007] The controller is used to control the connection between the center taps of the three-phase windings of the first drive motor and the center taps of the three-phase windings of the second drive motor. After the center taps of the three-phase windings of the first and second drive motors are connected, the adjustable range of the pulse current output by the first and second power circuits is expanded, thereby adjusting the heating rate of the power battery. By connecting the center taps of the three-phase windings of the first and second drive motors, the first and second power circuits can output a wider range of pulse currents, thereby effectively improving the heating rate of the power battery.

[0008] In one possible implementation, in response to the pulse current amplitude of the power battery being greater than a set current threshold, the controller controls the center tap of the three-phase winding of the first drive motor to connect with the center tap of the three-phase winding of the second drive motor, and controls the first power circuit and the second power circuit to generate a first pulse AC current on the DC bus. In response to the pulse current amplitude of the power battery being less than the set current threshold, the controller controls the center tap of the three-phase winding of the first drive motor to disconnect with the center tap of the three-phase winding of the second drive motor, and controls the first power circuit and the second power circuit to generate a second pulse AC current on the DC bus. The amplitude of the first pulse AC current is greater than the amplitude of the second pulse AC current.

[0009] After obtaining the pulse current amplitude that the power battery can withstand, the controller takes measures to ensure that the pulse current input to the power battery never exceeds the set current threshold, while simultaneously providing a sufficient battery heating rate. Therefore, when the controller detects that the pulse current to the power battery exceeds the set threshold, it takes measures to optimize heating efficiency while ensuring safety. At this time, the center taps of the two drive motors are connected to generate a first pulse AC current with a higher amplitude, which can raise the battery temperature more quickly. When the current is below the threshold, the connection is disconnected and a second pulse AC current with a lower amplitude is used. This helps to avoid exceeding the current withstand capacity of the power battery while maintaining an appropriate heating rate.

[0010] In one possible implementation, the controller responds when the amplitude of the target current exceeds a set current threshold. The target current is a pulse current required to be generated on the DC bus by the vehicle controller. The controller connects the center taps of the three-phase windings of the first drive motor and the center taps of the three-phase windings of the second drive motor, and controls the first power circuit and the second power circuit to generate the target current on the DC bus. When the amplitude of the target current does not exceed the set current threshold, the controller disconnects the center taps of the three-phase windings of the first drive motor and the center taps of the three-phase windings of the second drive motor, and controls the first power circuit and the second power circuit to generate the target current on the DC bus.

[0011] When the target current exceeds the set current threshold, the center taps of the two motors are connected, and the two power circuits work together to generate a larger pulse current, thereby rapidly increasing the battery temperature. When the target current is less than or equal to the set current threshold, the connection between the motors is disconnected, and the two power circuits generate a smaller pulse current, thus saving energy while maintaining heating effectiveness. Furthermore, by dynamically adjusting the connection status and current output, the system can flexibly respond to the actual needs of the vehicle controller, effectively handling both rapid heating and maintaining a lower heating rate.

[0012] In one possible implementation, in response to the power battery temperature being lower than a set temperature threshold, the controller controls the center tap of the three-phase winding of the first drive motor to connect with the center tap of the three-phase winding of the second drive motor, and controls the first power circuit and the second power circuit to generate a first pulse AC current on the DC bus. In response to the power battery temperature being not lower than the set temperature threshold, the controller controls the center tap of the three-phase winding of the first drive motor to connect with the center tap of the three-phase winding of the second drive motor, and controls the first power circuit and the second power circuit to generate a second pulse AC current on the DC bus. The amplitude of the first pulse AC current is greater than the amplitude of the second pulse AC current.

[0013] When the battery temperature is below a set temperature threshold, a high-amplitude first pulse of alternating current is input to the battery to quickly raise its temperature. Therefore, in low-temperature environments, this heating method can significantly shorten the time it takes for the battery to reach its optimal operating temperature. When the battery temperature reaches or exceeds the set temperature threshold, a lower-amplitude second pulse of alternating current is input to maintain the battery within a suitable operating temperature range and prevent overheating. Furthermore, the magnitude of the pulse of alternating current can be adjusted according to actual needs to regulate the heating intensity of the battery, thereby saving energy. Using a lower amplitude current when high-power heating is not required reduces unnecessary energy consumption. This method ensures that high-power heating is only used when necessary, thus improving the energy utilization efficiency of the battery.

[0014] In one possible implementation, when the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor are disconnected, the controller is configured to: during the discharge cycle, control the upper bridge arm switch of one bridge arm of the first power circuit and the lower bridge arm switch of the other two bridge arms to be turned on, and during the charging cycle, control the lower bridge arm switch of one bridge arm of the first power circuit and the upper bridge arm switch of the other two bridge arms to be turned on.

[0015] Through the aforementioned control method, the controller controls the conduction state of specific switching transistors in the first and second power circuits, causing current to flow from the positive terminal of the power battery, through these switching transistors and windings, and finally back to the negative terminal of the power battery. During this process, the current continuously increases, and the three-phase windings of the first and second power circuits store electrical energy. By controlling the conduction state of specific switching transistors, current can be effectively guided into the three-phase windings, allowing the windings to store electrical energy. The stored energy can be released when needed for heating or other purposes.

[0016] In one possible implementation, when the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor are connected, the controller is used to: control the upper bridge arm switch of each bridge arm of the first power circuit to be turned on and the lower bridge arm switch of each bridge arm of the second power circuit to be turned on during the discharge cycle; and control the lower bridge arm switch of each bridge arm of the first power circuit to be turned on and the upper bridge arm switch of each bridge arm of the second power circuit to be turned on during the charging cycle.

[0017] The controller controls the three-phase bridge arm switching transistors in the first and second power circuits to enable the flow of current between the two power circuits. By connecting the center taps of the three-phase windings of the first drive motor and the second drive motor, the first and second power circuits can output pulse currents over a wider range.

[0018] In one possible implementation, in response to the temperature of the power battery exceeding a set temperature threshold, the controller controls the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor to disconnect, and controls the first power circuit or the second power circuit to generate pulsed AC current on the DC bus.

[0019] When the battery temperature exceeds a set threshold, disconnecting the connection between the two drive motors and using either the first or second power circuit to generate pulsed AC power effectively reduces heating intensity and prevents battery overheating. This helps protect the battery from high-temperature damage and extends its lifespan. By reducing current output, heat generation inside the battery is reduced, keeping it within a safe operating temperature range. High-intensity heating is unnecessary when the battery temperature is high. Using only one power circuit reduces unnecessary energy consumption and improves overall energy efficiency. This method ensures that high-power heating is only used when necessary, thus saving energy and reducing operating costs.

[0020] In one possible implementation, when the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor are disconnected, in response to the phase difference of the pulsed AC current generated by the first power circuit and the second power circuit on the DC bus being greater than a preset value, the switching frequency of the switching transistors of the first power circuit and / or the switching frequency of the switching transistors of the second power circuit is controlled to reduce the phase difference of the pulsed AC current generated by the first power circuit and the second power circuit.

[0021] By adjusting the switching frequencies of the first and second power circuits to reduce the phase difference, it can be ensured that the two pulse currents are synchronized as much as possible in time, thereby maximizing the amplitude of the superimposed pulse current. This can improve the heating power of the power battery and accelerate the temperature rise of the power battery.

[0022] In one possible implementation, the powertrain includes a control switch. The center tap of the three-phase winding of the first drive motor is connected to the center tap of the three-phase winding of the second drive motor via the control switch. The controller connects the center taps of the three-phase windings of the first drive motor and the second drive motor by turning the control switch on, and disconnects the center taps of the three-phase windings of the first drive motor and the second drive motor by turning the control switch off.

[0023] By closing the control switch, the center taps of the two motors are connected. This allows both power circuits to jointly generate a larger pulse current, thereby accelerating the rate at which the battery temperature rises. When high-power heating is not required, the controller can disconnect the control switch, disconnecting the center taps of the two motors and using only one power circuit for heating. This dynamic adjustment optimizes the heating process according to actual needs.

[0024] Secondly, this application provides an electric vehicle, which includes a power battery, wheels, and a powertrain as described in the first aspect. A first power circuit and a second power circuit are used to receive power from the power battery to drive a corresponding motor to drive the wheels, or to generate pulsed alternating current on a DC bus to heat the power battery.

[0025] Thirdly, this application provides a power battery heating method applied to a motor controller. The motor controller includes a first power circuit, a second power circuit, a first capacitor, a second capacitor, and a controller. The midpoints of the three-phase bridge arms of the first power circuit are respectively used to connect to the three-phase windings of a first drive motor, and the midpoints of the three-phase bridge arms of the second power circuit are respectively used to connect to the three-phase windings of a second drive motor.

[0026] The two ends of each phase arm of the first power circuit are respectively connected to the two ends of the first capacitor, and the two ends of each phase arm of the second power circuit are respectively connected to the two ends of the second capacitor. The two ends of the first capacitor and the two ends of the second capacitor are respectively used to connect to the positive and negative terminals of the power battery through the DC bus. The method includes: controlling the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor.

[0027] As one possible implementation, the method further includes: acquiring the amplitude of the pulse current borne by the power battery; when it is determined that the amplitude of the pulse current borne by the power battery is greater than a set current threshold, controlling the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor to connect, and controlling the first power circuit and the second power circuit to generate a first pulse AC current on the DC bus; when it is determined that the amplitude of the pulse current borne by the power battery is not greater than the set current threshold, the controller controls the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor to disconnect, and controlling the first power circuit and the second power circuit to generate a second pulse AC current on the DC bus, wherein the amplitude of the first pulse AC current is greater than the amplitude of the second pulse AC current.

[0028] As one possible implementation, the method further includes: acquiring a target current, which is a pulse current required to be generated on the DC bus by the vehicle controller; when the amplitude of the target current is greater than a set current threshold, controlling the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor to connect, and controlling the first power circuit and the second power circuit to generate the target current on the DC bus; when the amplitude of the target current is not greater than the set current threshold, controlling the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor to disconnect, and controlling the first power circuit and the second power circuit to generate the target current on the DC bus.

[0029] As one possible implementation, the method further includes: acquiring the temperature of the power battery; when the temperature of the power battery is less than a set temperature threshold, controlling the center tap of the three-phase winding of the first drive motor to connect with the center tap of the three-phase winding of the second drive motor, and controlling the first power circuit and the second power circuit to generate a first pulse AC current on the DC bus; when the temperature of the power battery is not less than the set temperature threshold, controlling the center tap of the three-phase winding of the first drive motor to connect with the center tap of the three-phase winding of the second drive motor, and controlling the first power circuit and the second power circuit to generate a second pulse AC current on the DC bus, wherein the amplitude of the first pulse AC current is greater than the amplitude of the second pulse AC current.

[0030] In one possible implementation, when the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor are disconnected, the method further includes: during the discharge cycle, controlling the upper bridge arm switch of one bridge arm of the first power circuit and / or the second power circuit to be turned on, and the lower bridge arm switch of the other two bridge arms to be turned on; during the charging cycle, controlling the lower bridge arm switch of one bridge arm of the first power circuit and / or the second power circuit to be turned on, and the upper bridge arm switch of the other two bridge arms to be turned on.

[0031] As one possible implementation, when the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor are connected, the method further includes: during the discharge cycle, controlling the upper bridge arm switch of each bridge arm of the first power circuit to be turned on and the lower bridge arm switch of each bridge arm of the second power circuit to be turned on; during the charging cycle, controlling the lower bridge arm switch of each bridge arm of the first power circuit to be turned on and the upper bridge arm switch of each bridge arm of the second power circuit to be turned on. Attached Figure Description

[0032] Figure 1 is a schematic diagram of the structure of a distributed drive system;

[0033] Figure 2 is a schematic diagram of the powertrain provided in an embodiment of this application;

[0034] Figure 3A is a schematic diagram of a first power circuit;

[0035] Figure 3B is a schematic diagram of a second power circuit;

[0036] Figure 4A is a discharge diagram of the discharge cycle when the center tap is disconnected;

[0037] Figure 4B is a schematic diagram of the charging cycle when the center tap is disconnected;

[0038] Figure 4C shows the current waveforms on each phase winding when the center tap is disconnected.

[0039] Figure 4D shows the pulse current waveform on the power battery when the center tap is disconnected.

[0040] Figure 5A is a discharge diagram of the discharge cycle when the center tap is connected;

[0041] Figure 5B is a schematic diagram of the charging cycle when the center tap is connected;

[0042] Figure 5C shows the current waveforms on each phase winding when connected with the center tap.

[0043] Figure 5D shows the pulse current waveform on the power battery when the center tap is connected.

[0044] Figure 6 is a schematic diagram of the cross-axis current feedback control circuit of the first drive motor;

[0045] Figure 7 is a schematic diagram of the direct-axis current feedback control circuit of the first drive motor.

[0046] Figure 8 is a schematic diagram of the feedback control circuit;

[0047] Figures 9A to 9D are schematic diagrams of the superimposed pulse currents of one pulse current and another pulse current input to the power battery;

[0048] Figure 10 is a schematic diagram of another powertrain structure provided in an embodiment of this application;

[0049] Figure 11 is a schematic diagram of another powertrain structure provided in an embodiment of this application;

[0050] Figure 12 is a schematic diagram of another powertrain structure provided in an embodiment of this application;

[0051] Figure 13 is a flowchart illustrating the steps of a power battery heating method also provided in this application. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this application clearer, a further detailed description of this application will be provided below in conjunction with the accompanying drawings. However, the exemplary embodiments can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. On the contrary, these embodiments are provided to make this application more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore repeated descriptions of them will be omitted. Terms describing position and direction described in this application are illustrative based on the accompanying drawings, but changes can be made as needed, and all such changes are included within the scope of protection of this application. The accompanying drawings of this application are for illustrating relative positional relationships only and do not represent actual scale.

[0053] It should be noted that in the embodiments of this application, "connection" refers to electrical connection. The connection between two electrical components can be a direct or indirect connection between the two electrical components. For example, the connection between A and B can be a direct connection between A and B, or an indirect connection between A and B through one or more other electrical components, such as the connection between A and B. Alternatively, it can be a direct connection between A and C, a direct connection between C and B, with A and B connected through C.

[0054] Distributed powertrains are used to support distributed drive systems, which are widely applicable to various types of electric vehicles. Such powertrains contain at least two drive motors, each responsible for driving the two front wheels or two rear wheels of the vehicle to move forward.

[0055] [Correction based on Rule 91, April 2026] Referring to Figure 1, a schematic diagram of the distributed drive system illustrates an example of a distributed powertrain 100, consisting of a first drive motor 201 and a second drive motor 202. In this system, the motor controller 13 controls the first drive motor 201 to drive the two front wheels, and simultaneously controls the second drive motor 202 to drive the two rear wheels. Furthermore, the distributed drive system can also be used in distributed rear-wheel-drive vehicles, where the first drive motor 201 drives the left rear wheel and the second drive motor 202 drives the right rear wheel (this layout is not shown in Figure 1).

[0056] Regarding power batteries, their performance is significantly affected by temperature. In particular, under low-temperature conditions, lithium plating may occur during the charging and discharging process of power batteries, which not only leads to a decrease in battery capacity but may also cause safety issues. Therefore, it is usually necessary to preheat the power battery to a suitable temperature range before starting an electric vehicle.

[0057] There are currently three main methods for heating power batteries:

[0058] The first method is to use an external heating system. For example, a thermal circuit can be set up for the power battery, in which a heat transfer fluid circulates. This heat transfer fluid is then heated using a positive temperature coefficient (PTC) heater, and subsequently, the heat transfer fluid transfers heat to the power battery. However, this method has relatively low heating efficiency due to the relatively long heat transfer process.

[0059] The second method is electric drive active heating technology. This method outputs specific three-phase AC power to the drive motor through the motor controller, causing the motor windings to generate heat without producing torque. The generated heat is then transferred to the power battery through a heat conduction device, achieving the heating purpose. However, this method also faces the problems of long heat transfer paths, slow heating speed, and low efficiency.

[0060] The third method is high-frequency pulse heating, which uses high-frequency pulsed AC power generated by the motor controller to heat the power battery. The high-frequency pulsed AC power is generated by the motor controller's bridge arm circuit. When this power voltage passes through the power battery, it generates heat on the battery's internal resistance, thus heating the battery. High-frequency heating has gained widespread attention due to its fast heating rate; however, it currently suffers from problems such as poor control system robustness, low control precision, and a tendency to generate unexpected torque.

[0061] Electric vehicle motors are generally AC motors, while the power battery is a DC source. Therefore, the DC power output from the power battery is converted into three-phase AC power for the motor via a three-phase bridge arm. The coordinate axes of the three-phase AC power are the U-axis, V-axis, and W-axis. The three phases of the AC power can also be referred to as the U-phase, V-phase, and W-phase. To simplify motor analysis, the stationary three-phase coordinates are usually transformed into rotating dq coordinates; this transformation is called the Park transformation. In the dq coordinate system, the three coordinate axes are called the direct axis, quadrature axis, and zero axis.

[0062] The direct axis, also known as the D-axis or d-axis, is a time-varying DC coordinate axis obtained by Parker transformation from the stationary U / V / W three-phase coordinate axes.

[0063] The quadrature axis, also known as the Q-axis or q-axis, is a time-varying AC coordinate axis obtained by Parker transformation from the stationary U / V / W three-phase coordinate axes.

[0064] The zero axis, also known as the 0-axis, is a coordinate axis perpendicular to the dq plane containing the direct axis and the intersection axis.

[0065] Specifically, the formula for the Parker transform can be shown below:

[0066] Where θ is the angle between the d-axis and the U-axis, I_d is called the direct-axis current, which is mainly used to adjust the magnetic field, I_q is called the quadrature-axis current, which is mainly used to adjust the torque, I_0 is called the zero-sequence current, and I_u, I_v, and I_w are the currents on the U-axis, V-axis, and W-axis, respectively, which are the three-phase currents.

[0067] The above matrix is ​​an expression for transforming three-phase currents to I_d, I_q, and I_0. By performing the inverse transformation of this matrix, we can obtain the expression for transforming I_d, I_q, and I_0 back to three-phase currents, which will not be elaborated here.

[0068] Since the three-phase current corresponds to the actual winding current in the motor, when outputting current to the direct axis of the motor, the motor controller needs to convert I_d into three-phase currents I_u, I_v, and I_w through the inverse transformation of the Parker transformation, and then pass I_u, I_v, and I_w into the motor windings. When outputting current to the zero axis of the motor, the motor controller 13 needs to convert I_0 into three-phase currents I_u, I_v, and I_w through the inverse transformation of the Parker transformation, and then pass I_u, I_v, and I_w into the motor windings.

[0069] The quadrature-axis voltage / current is used to control the torque output by the motor, while the direct-axis voltage / current is used to control the direction and magnitude of the magnetic field generated by the motor.

[0070] In the high-frequency pulse heating method, the heating using the two power circuits of the motor controller 13 is limited by hardware limitations such as the motor windings and bus capacitors, which restrict the adjustable range of the high-frequency pulse AC power generated, thus limiting the heating rate of the power battery.

[0071] In view of this, this application provides a powertrain, an electric vehicle, and a method for heating a power battery. By adjusting the connection relationship of the power circuit, the amplitude of the pulse current is increased, thereby further adjusting the pulse heating rate according to the battery capacity.

[0072] Referring to Figure 2, which is a schematic diagram of the powertrain provided in an embodiment of this application, the distributed powertrain 200 shown in Figure 2 includes a first drive motor 201, a second drive motor 202, and a motor controller. The motor controller includes a first power circuit 2031, a second power circuit 2032, and a controller 2033.

[0073] The midpoint of the three-phase bridge arm of the first power circuit 2031 is used to connect the three-phase windings of the first drive motor 201, and the midpoint of the three-phase bridge arm of the second power circuit 2032 is used to connect the three-phase windings of the second drive motor 202. Each phase bridge arm of the first power circuit 2031 is connected to both ends of the first bus capacitor 2041, and each phase bridge arm of the second power circuit 2032 is connected to both ends of the second bus capacitor 2042. The first bus capacitor 2041 and the second bus capacitor 2042 are connected to the positive and negative terminals of the power battery 15 via a DC bus.

[0074] It should be noted that, in this embodiment of the application, the first bus capacitor 2041 and the second bus capacitor 2042 may each include a single capacitor (as shown in Figure 2). In some possible implementations, the first bus capacitor 2041 and the second bus capacitor 2042 may also include at least two capacitors connected in series or in parallel. That is, this embodiment of the application does not limit the number of capacitors in the first bus capacitor 2041 and the second bus capacitor 2042, or the connection method between the capacitors.

[0075] Figure 3A is a schematic diagram of a first power circuit. The first power circuit 2031 includes three bridge arms connected in parallel, which can be referred to as the U-phase bridge arm, V-phase bridge arm, and W-phase bridge arm, respectively. The first drive motor 201 includes three first drive motor 201 windings corresponding to the three bridge arms (e.g., first drive motor 201 winding GU, first drive motor 201 winding GV, and first drive motor 201 winding GW). In the U-phase bridge arm, the upper bridge switch is switch GQ1, and the lower bridge switch is switch GQ2. In the V-phase bridge arm, the upper bridge switch is switch GQ3, and the lower bridge switch is switch GQ4. In the W-phase bridge arm, the upper bridge switch is switch GQ5, and the lower bridge switch is switch GQ6. The collectors of switching transistors GQ1, GQ3, and GQ5 are connected to one end of the bus capacitor 204, and the emitters of switching transistors GQ2, GQ4, and GQ6 are connected to the other end of the first bus capacitor 2041. The emitter of switching transistor GQ1 and the collector of switching transistor GQ2 are connected to one end of the winding GU of the first drive motor 201, the emitter of switching transistor GQ3 and the collector of switching transistor GQ4 are connected to one end of the winding Gv of the first drive motor 201, and the emitter of switching transistor GQ5 and the collector of switching transistor GQ6 are connected to one end of the winding Gw of the first drive motor 201. The other ends of the windings GU, GV, and GW of the first drive motor 201 can be referred to as the center tap point of the first drive motor 201.

[0076] Figure 3B is a schematic diagram of a second power circuit. The second power circuit 2032 includes three bridge arms connected in parallel, which can be referred to as the U-phase bridge arm, V-phase bridge arm, and W-phase bridge arm, respectively. The second drive motor 202 includes three second drive motor 202 windings corresponding to the three bridge arms (e.g., second drive motor 202 winding gU, first drive motor 204 winding gV, and first drive motor 204 winding gW). In the U-phase bridge arm, the upper bridge switch is switch gQ1, and the lower bridge switch is switch gQ2. In the V-phase bridge arm, the upper bridge switch is switch gQ3, and the lower bridge switch is switch gg. In the W-phase bridge arm, the upper bridge switch is switch gQ5, and the lower bridge switch is switch gQ6. The collectors of switching transistors gQ1, gQ3, and gQ5 are connected to one end of the second bus capacitor 2042, and the emitters of switching transistors gQ2, gQ4, and gQ6 are connected to the other end of the second bus capacitor 2042. The emitter of switching transistor gQ1 and the collector of switching transistor gQ2 are connected to one end of the winding gU of the first drive motor 201, the emitter of switching transistor gQ3 and the collector of switching transistor gQ4 are connected to one end of the winding gv of the second drive motor 202, and the emitter of switching transistor gQ5 and the collector of switching transistor gQ6 are connected to one end of the winding GW of the second drive motor 202. The other end of the windings gU, gV, and GW of the second drive motor 202 can be referred to as the center tap point of the second drive motor 202.

[0077] The switching transistors in the aforementioned bridge arms can be insulated-gate bipolar transistors (IGBTs) and their anti-parallel diodes, or metal-oxide-semiconductor field-effect transistors (MOSFETs), etc. This application does not impose excessive restrictions on the specific internal structure of the switching transistors.

[0078] It should be noted that Figure 2 uses the example of the first drive motor 201 being a three-phase AC motor and the second drive motor 202 being a three-phase AC motor. In some possible implementations, the first drive motor 201 may also be a two-phase AC motor, a four-phase AC motor, or a multi-phase AC motor. In this case, the first power circuit 2031 can adaptively change the number of bridge arms according to the number of first drive motor windings in different types of first drive motors 201. For example, when the first drive motor 201 is a two-phase AC motor, the first power circuit 2031 includes two-phase bridge arms; when the first drive motor 201 is a four-phase AC motor, the first power circuit 2031 includes four-phase bridge arms.

[0079] Similarly, the first drive motor 201 and the second drive motor 202 can also be two-phase AC motors, four-phase AC motors, or five-phase AC motors, etc. In this case, the power circuit adapts to the number of bridge arms according to the number of windings of different types of motors. For example, when the drive motor is a two-phase AC motor, the power circuit includes two-phase bridge arms, and when the drive motor is a four-phase AC motor, the power circuit includes four-phase bridge arms.

[0080] It should be noted that the controller 2033 can individually control at least one bridge arm of the first power circuit 2031 and the second power circuit 2032 to enable the power battery 15 and the first bus capacitor 2041 / second bus capacitor 2042 to charge and discharge at a preset cycle. The controller 2033 can also individually control at least one bridge arm of the first power circuit 2031 to enable the power battery 15 to charge and discharge at a preset cycle. Alternatively, the controller 2033 can simultaneously control at least one bridge arm of the first power circuit 2031 and at least one bridge arm of the second power circuit 2032 to enable the power battery 15 to charge and discharge at a preset cycle.

[0081] Furthermore, the controller 2033 may also include multiple sub-control circuits, which respectively control the first power circuit 2031 and the second power circuit 2032. One of the sub-control circuits controls at least one bridge arm of the first power circuit 2031, and the other controls at least one bridge arm of the second power circuit 2032. The controller 2033 may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0082] Upon receiving a heating command, at least one arm of the first power circuit 2031 and the second power circuit 2032 enables the power battery 15 and the bus capacitor 204 to charge and discharge at a preset cycle. The heating command can be issued by the vehicle controller or other in-vehicle control devices, and the required heating power is calculated based on the current temperature of the power battery 15. The heating command carries the heating power, and the control circuit 2033, based on at least one arm of the first power circuit 2031 and the second power circuit 2032, enables the power battery 15 to utilize the heat generated by its own AC resistance to heat the battery, thereby improving the charging and discharging capability of the power battery 15 in low-temperature environments.

[0083] Figures 4A and 4B below illustrate the control logic of the first power circuit 2031 and the second power circuit 2032 when the center tap of the three-phase winding of the first drive motor 201 and the center tap of the three-phase winding of the second drive motor 202 are disconnected.

[0084] The power battery 15 charge and discharge cycle includes a discharge cycle and a charging cycle. During the discharge cycle, the control circuit 2033 controls the upper bridge arm switch of at least one bridge arm of the first power circuit 2031 and the second power circuit 2032 to be turned on with a preset duty cycle, and the upper bridge arm switches of the other two bridge arms are turned on with a preset duty cycle. During the charging cycle, the control circuit 2033 controls the lower bridge arm switch of at least one bridge arm to be turned on with a preset duty cycle, and the upper bridge arm switches of the other two bridge arms are turned on with a preset duty cycle.

[0085] The duty cycle refers to the percentage of time during which at least one bridge arm switch (either the lower or upper arm switch) outputs a high-level signal within the entire discharge / charge cycle. Controlling the duty cycle can be understood as controlling the on-time of the bridge arm switch. The charging cycle can be equal to or different from the discharging cycle.

[0086] Example of controller 2033 controlling one of the bridge arms of the first power circuit 2031 and one of the bridge arms of the second power circuit 2032 to be U-phase bridge arms, as shown in Figure 4A. Figure 4A is a discharge diagram of the discharge cycle when the center tap is disconnected.

[0087] During the discharge cycle:

[0088] The controller 2033 controls the upper bridge arm switch of the U-phase bridge arm, the lower bridge arm switch of the W-phase bridge arm, and the lower bridge arm switch of the V-phase bridge arm in the first power circuit 2031 to be turned on. The current flows out from the positive terminal of the power battery 15, passes through the upper bridge arm switch of the U-phase bridge arm, the U-phase winding, the V-phase winding, the W-phase winding, the lower bridge arm switch of the V-phase bridge arm, and the lower bridge arm switch of the W-phase bridge arm in the first power circuit 2031, and flows back to the negative terminal of the power battery 15. The current flowing through it continuously increases, and the U-phase winding, V-phase winding, and W-phase winding of the first power circuit 2031 store electrical energy.

[0089] The controller 2033 controls the upper bridge arm switch of the U-phase bridge arm, the lower bridge arm switch of the W-phase bridge arm, and the lower bridge arm switch of the V-phase bridge arm in the second power circuit 2032 to be turned on. The current flows out from the positive terminal of the power battery 15, passes through the upper bridge arm switch of the U-phase bridge arm, the U-phase winding, the V-phase winding, the W-phase winding, the lower bridge arm switch of the V-phase bridge arm, and the lower bridge arm switch of the W-phase bridge arm in the first power circuit 2031, and flows back to the negative terminal of the power battery 15. The current flowing through it continuously increases. The U-phase winding, V-phase winding, and W-phase winding of the second power circuit 2032 store electrical energy.

[0090] As shown in Figure 4B, Figure 4B is a charging schematic diagram of the charging cycle when the center tap is disconnected.

[0091] During a charging cycle:

[0092] The controller 2033 controls the lower bridge arm switch of the U-phase bridge arm, the upper bridge arm switch of the W-phase bridge arm, and the upper bridge arm switch of the V-phase bridge arm in the first power circuit 2031 to be turned on. The current flows out from the V-phase winding and the W-phase winding, passes through the upper bridge arm switch of the V-phase bridge arm and the upper bridge arm switch of the W-phase bridge arm respectively, and flows into the positive terminal of the power battery 15. The current flows out from the positive terminal of the power battery 15 and through the lower bridge arm switch of the U-phase bridge arm, and flows back to the U-phase winding.

[0093] The controller 2033 controls the lower bridge arm switch of the U-phase bridge arm, the upper bridge arm switch of the W-phase bridge arm, and the upper bridge arm switch of the V-phase bridge arm in the second power circuit 2031 to be turned on. The current flows out from the V-phase winding and the W-phase winding, passes through the upper bridge arm switch of the V-phase bridge arm and the upper bridge arm switch of the W-phase bridge arm respectively, flows into the negative terminal of the power battery 15, flows out from the positive terminal of the power battery 15, passes through the lower bridge arm switch of the U-phase bridge arm, and flows back to the U-phase winding.

[0094] The alternating discharge and charging cycles generate a high-frequency alternating current in the power battery 15, thereby heating the power battery 15.

[0095] Referring to Figure 4C, which shows the current waveforms on each phase winding when the center tap is disconnected, and referring to Figure 4D, which shows the pulse current waveforms on the power battery when the center tap is disconnected.

[0096] The controller 2033 is used to control the connection of the center tap of the three-phase winding of the first drive motor 201 and the center tap of the three-phase winding of the second drive motor 202. After the center tap of the three-phase winding of the first drive motor 201 and the center tap of the three-phase winding of the second drive motor 202 are connected, the adjustable range of the pulse current output by the first power circuit 2031 and the second power circuit 2032 is expanded, thereby adjusting the heating rate of the power battery.

[0097] Figures 5A and 5B below illustrate the control logic of the first power circuit 2031 and the second power circuit 2032 when the center tap of the three-phase winding of the first drive motor 201 and the center tap of the three-phase winding of the second drive motor 202 are connected.

[0098] As shown in Figure 5A, Figure 5A is a discharge diagram of the discharge cycle when the center tap is connected.

[0099] The controller 2033 controls the upper bridge arm switch of the three-phase bridge arm in the first power circuit 2031 to turn on, and controls the lower bridge arm switch of the three-phase bridge arm in the second power circuit 2032 to turn on. The current flows out from the positive terminal of the power battery 15, passes through the upper bridge arm switch of the three-phase bridge arm in the first power circuit 2031, then through the U-phase winding, V-phase winding and W-phase winding of the first power circuit 2031, and flows out from the center tap of the three-phase winding to the U-phase winding, V-phase winding and W-phase winding of the second power circuit 2032. After passing through the lower bridge arm switch of the three-phase bridge arm in the second power circuit 2032, the current flows back to the negative terminal of the power battery 15.

[0100] As shown in Figure 5B, Figure 5B is a charging diagram of the charging cycle when the center tap is connected.

[0101] The controller 2033 controls the lower bridge arm switch of the three-phase bridge arm in the first power circuit 2031 to turn on, and controls the upper bridge arm switch of the three-phase bridge arm in the second power circuit 2032 to turn on. Current flows out from the U-phase winding, V-phase winding and W-phase winding of the first power circuit 2031 and the U-phase winding, V-phase winding and W-phase winding of the second power circuit 2032. The current flows into the negative terminal of the power battery 15 through the lower bridge arm switch of the three-phase bridge arm of the first power circuit 2031 and flows out from the positive terminal of the power battery 15. Then, the current flows back to the U-phase winding, V-phase winding and W-phase winding of the first power circuit 2031 and the U-phase winding, V-phase winding and W-phase winding of the second power circuit 2032 through the upper bridge arm switch of the three-phase bridge arm of the second power circuit 2031.

[0102] Referring to Figure 5C, which shows the current waveforms on each phase winding when the center tap is connected, and referring to Figure 5D, which shows the pulse current waveforms on the power battery when the center tap is connected.

[0103] Comparing Figures 4D and 5D, it can be seen that by connecting the center taps of the three-phase windings of the first drive motor 201 and the second drive motor 202, the first power circuit 2031 and the second power circuit 2032 can output a wider range of pulse current, thereby effectively improving the heating rate of the power battery. This not only improves the battery temperature rise rate and shortens the charging waiting time and one-click standby time, but is also particularly suitable for electric vehicle usage scenarios in cold weather conditions.

[0104] The following embodiment uses the controller 2033 controlling the first power circuit 2031 as an example. The controller 2033 is used to perform closed-loop control of the direct-axis current and quadrature-axis current of the drive motor during pulse heating. As shown in Figure 6, Figure 6 is a schematic diagram of the first drive motor quadrature-axis current feedback control circuit. The first drive motor control circuit includes a first drive motor direct-axis current feedback control circuit and a first drive motor quadrature-axis current feedback control circuit.

[0105] The first drive motor quadrature-axis current feedback control circuit generates a quadrature-axis voltage based on the quadrature-axis current indicated by the quadrature-axis current given signal and inputs it to the first drive motor 201. At the same time, the first drive motor quadrature-axis current feedback control circuit adjusts the magnitude of the quadrature-axis current given signal based on the quadrature-axis current of the first drive motor 201 indicated by the quadrature-axis current feedback signal collected from the first drive motor 201 to achieve closed-loop control of the quadrature-axis current.

[0106] In one possible implementation, the controller includes a first drive motor Parker inverse converter circuit, a second drive motor Parker inverse converter circuit, a first drive motor drive circuit, and a second drive motor drive circuit. The first drive motor drive circuit is used to output three sets of first drive motor drive signals. Each set of first drive motor drive signals is used to control the switching frequency and duty cycle of the upper and lower bridge arm switches of the switching transistor bridge arm of the first power circuit. The second drive motor drive circuit is used to output three sets of second drive motor drive signals. Each set of second drive motor drive signals is used to control the switching frequency and duty cycle of the upper and lower bridge arm switches of the switching transistor bridge arm of the second power circuit.

[0107] The first drive motor Parker inverse converter circuit is used to receive the first drive motor voltage setpoint signal, the first drive motor feedback control signal, and the first drive motor rotor position signal sent by the vehicle controller, and to control the phase difference of the three sets of first drive motor drive signals and the frequency and duty cycle of each set of first drive motor drive signals. The second drive motor Parker inverse converter circuit is used to receive the second drive motor voltage setpoint signal, the second drive motor feedback control signal, and the second drive motor rotor position signal, and to control the phase difference of the three sets of second drive motor drive signals and the frequency and duty cycle of each set of second drive motor drive signals.

[0108] Continuing as shown in Figure 6, taking the first drive motor as an example, iq is the quadrature-axis current value indicated by the quadrature-axis current command signal, and iq' is the quadrature-axis current of the first drive motor indicated by the quadrature-axis current feedback signal. The quadrature-axis current feedback controller of the first drive motor compares the difference between iq and iq'. The PI regulator outputs an adjustment value based on the difference between iq and iq' to adjust the quadrature-axis current command signal sent to the drive power in a timely manner. The drive circuit outputs a PWM control signal based on the adjusted quadrature-axis current command signal to control the first power circuit 2031 to output three-phase current. The quadrature-axis current component of the three-phase current is the quadrature-axis current indicated by the quadrature-axis current command signal.

[0109] In one possible implementation, the controller includes a first drive motor voltage signal generator and a second drive motor signal generator. The first drive motor voltage signal generator is used to output a first drive motor voltage setpoint signal based on a first drive motor voltage frequency signal and a first drive motor voltage amplitude signal. The second drive motor voltage signal generator is used to output a second drive motor voltage setpoint signal based on a second drive motor voltage frequency signal and a second drive motor voltage amplitude signal.

[0110] As one possible implementation, the quadrature axis components of the three-phase current of the first drive motor and the three-phase current of the second drive motor are zero, or the torque values ​​of the three-phase current of the first drive motor and the second drive motor are less than a preset torque value.

[0111] In this embodiment, the quadrature-axis current indicated by the quadrature-axis current given signal is 0. As previously stated, the quadrature-axis current of the first drive motor 201 is used to control the torque output of the drive motor. During the pulse heating process of the power battery 15, if the quadrature-axis current of the first drive motor 201 is not zero, the first drive motor 201 will have unexpected torque output. The unexpected torque of the first drive motor 201 transmitted to the wheels will cause vibration and noise in the electric vehicle 10, affecting the riding experience of the electric vehicle 10. However, if the quadrature-axis current of the first drive motor 201 is controlled in an open-loop manner, it is difficult to accurately control the quadrature-axis current of the first drive motor 201 to zero, thus making the first drive motor 201 prone to generating unexpected torque. Therefore, this embodiment provides a method to accurately control the quadrature-axis current of the first drive motor 201 to zero by performing closed-loop control, thereby avoiding unexpected torque output from the first drive motor 201 and improving the vehicle's heating performance and driving comfort.

[0112] In one possible implementation, the direct-axis current setting signal of the first drive motor is a DC bias signal, the quadrature-axis current setting signal of the first drive motor is 0, the direct-axis current setting signal of the second drive motor is a DC bias signal, the quadrature-axis current setting signal of the second drive motor is 0, and the DC bias is either a positive DC bias or a negative DC bias.

[0113] In this embodiment, the motor controller receives a heating command and determines a direct-axis current reference signal and a direct-axis current reference signal based on the heating power of the power battery 15 indicated by the heating command. The direct-axis current reference signal indicates the frequency and amplitude of the square wave voltage, and is used to generate a DC bias on the square wave voltage. In other words, the final direct-axis voltage input by the motor controller to the drive motor is a direct-axis voltage with a DC bias. This DC bias can improve the effective value of the three-phase current of the drive motor, thereby improving the heating efficiency of the power battery 15.

[0114] Figure 7 is a schematic diagram of the direct-axis current feedback control circuit of the first drive motor. As shown in Figure 7, id is the direct-axis current given signal, id' is the direct-axis current feedback signal, and Ud is the direct-axis current given signal. As previously mentioned, during the pulse heating process of the power battery 15, the quadrature-axis current of the first drive motor 201 is zero to ensure that the drive motor does not output unexpected torque. Therefore, during the high-frequency pulse heating process of the power battery 15, the controller 2033 inputs the direct-axis current to the first drive motor 201, thereby generating high-frequency pulsed AC current on the bus capacitor. Optionally, the control circuit 2033 also includes a low-pass filter, which is used to filter the direct-axis current feedback signal of the three-phase current of the first drive motor and the high-frequency components in the direct-axis current feedback signal of the three-phase current of the first drive motor.

[0115] In one embodiment, the direct-axis current injected by the motor controller into the first drive motor is a sinusoidal current. However, when the direct-axis voltage of the first drive motor 201 is a sinusoidal voltage, the ripple current of the high-frequency pulsed AC current generated on the bus capacitor is relatively large, resulting in low heating efficiency of the power battery 15. In this embodiment, the direct-axis voltage input by the motor controller to the drive motor is a square-wave voltage Ud. The square-wave direct-axis voltage of the first drive motor 201 can effectively reduce the ripple of the bus current in the bus capacitor, thereby improving the heating efficiency of the power battery 15.

[0116] To achieve closed-loop control of the direct-axis current, this application embodiment provides a low-pass filter 211. The low-pass filter is used to filter the high-frequency components of the direct-axis current collected from the first drive motor 201, thereby obtaining the DC bias in the direct-axis current of the first drive motor 201. After the high-frequency components of the direct-axis current signal collected from the first drive motor 201 are filtered out by the low-pass filter, a direct-axis current feedback signal is obtained. The direct-axis current control loop compares the direct-axis current feedback signal and the direct-axis current setpoint signal and adjusts the direct-axis current bias value. The direct-axis current setpoint signal is superimposed with a square wave voltage signal to generate a square wave voltage signal.

[0117] In this embodiment of the application, the control circuit includes a first drive motor voltage signal generator, which is used to output a direct-axis current given signal based on the square wave voltage frequency signal and the square wave voltage amplitude signal.

[0118] As shown in Figure 8, the direct-axis current feedback control circuit of the first drive motor further includes a Parker transformation module, an inverse Parker transformation module, and a Clarke transformation module. The Parker transformation module converts the two components in the αβ coordinate system into an orthogonal rotating coordinate system (dq). The Clarke transformation module converts the time-domain components of the three-phase system (in the abc coordinate system) into two components in an orthogonal stationary coordinate system (αβ). Specifically, in this embodiment, the Parker transformation module receives the quadrature-axis voltage signal Uq and the direct-axis voltage signal Ud, and performs an inverse Parker transformation on Uq and Ud in the direct-axis-quadrature-axis coordinate system to obtain voltage signals Uα and Uβ in the αβ coordinate system. The drive circuit generates a PWM control signal based on the Uα and Uβ signals. The PWM control signal is used to control the conduction frequency and duty cycle of the switching transistors in the three-phase bridge arms. On the other hand, the current sensor collects the three-phase current signals ia, ib, and ic of the first drive motor 201. The Clarke transform module is used to convert the current signals ia, ib, and ic in the three-phase coordinate system into current signals iα and iβ in the αβ coordinate system. Then, the Park transform module performs Park transform on the current signals iα and iβ in the αβ coordinate system to convert the current signals iα and iβ in the αβ coordinate system into current signals id and iq in the direct-axis-quadrature-axis coordinate system. iq is output as the quadrature-axis current feedback signal, while id is output as the direct-axis current feedback signal after the high-frequency signal components are filtered out by the low-pass filter.

[0119] In one possible implementation, in response to the pulse current amplitude received by the power battery 15 exceeding a set current threshold, the controller 2033 controls the connection of the center tap of the three-phase winding of the first drive motor 201 and the center tap of the three-phase winding of the second drive motor 202, and controls the first power circuit 2031 and the second power circuit 2032 to generate a first pulse AC current on the DC bus.

[0120] In response to the fact that the amplitude of the pulse current received by the power battery 15 is not greater than the set current threshold, the controller 2033 controls the center tap of the three-phase winding of the first drive motor 201 and the center tap of the three-phase winding of the second drive motor 202 to disconnect, and controls the first power circuit 2031 and the second power circuit 2032 to generate a second pulse AC current on the DC bus. The amplitude of the first pulse AC current is greater than the amplitude of the second pulse AC current.

[0121] The battery manufacturer will provide detailed datasheets, which include the battery's performance parameters under various operating conditions. For example, the datasheet may specify the maximum permissible pulse current amplitude for the battery at different temperatures. Alternatively, laboratory tests can be conducted to determine the maximum pulse current the battery can withstand at different temperatures.

[0122] After obtaining the pulse current amplitude that the power battery 15 can withstand, in order to ensure that the pulse current input to the power battery 15 does not exceed the set current threshold at any time, and at the same time provide a sufficient battery heating rate, the controller 2033 will take measures to ensure safety and optimize heating efficiency when it detects that the pulse current that the power battery 15 can withstand exceeds the set threshold. At this time, the center taps of the two drive motors are connected to generate a first pulse AC current with a higher amplitude, which can raise the battery temperature more quickly. When the current is lower than the threshold, the connection is disconnected and a second pulse AC current with a lower amplitude is used. This helps to avoid exceeding the current carrying capacity of the power battery while maintaining an appropriate heating rate.

[0123] In one possible implementation, the controller 2033 responds to a target current amplitude exceeding a set current threshold. The target current is a pulse current required to be generated on the DC bus by the vehicle controller. The controller 2033 controls the connection of the center taps of the three-phase windings of the first drive motor 201 and the center taps of the three-phase windings of the second drive motor 202, and controls the first power circuit 2031 and the second power circuit 2032 to generate the target current on the DC bus.

[0124] In response to the target current amplitude not exceeding the set current threshold, the controller 2033 controls the center tap of the three-phase winding of the first drive motor 201 and the center tap of the three-phase winding of the second drive motor 202 to disconnect, and controls the first power circuit 2031 and the second power circuit 2032 to generate the target current on the DC bus.

[0125] When the target current exceeds the set current threshold, the center taps of the two motors are connected, and the two power circuits work together to generate a larger pulse current, thereby rapidly increasing the battery temperature. When the target current is less than or equal to the set current threshold, the connection between the motors is disconnected, and the two power circuits generate a smaller pulse current, thus saving energy while maintaining heating effectiveness. Furthermore, by dynamically adjusting the connection status and current output, the system can flexibly respond to the actual needs of the vehicle controller, effectively handling both rapid heating and maintaining a lower heating rate.

[0126] In one possible implementation, in response to the temperature of the power battery 15 being lower than a set temperature threshold, the controller 2033 controls the connection of the center tap of the three-phase winding of the first drive motor 201 and the center tap of the three-phase winding of the second drive motor 202, and controls the first power circuit 2031 and the second power circuit 2032 to generate a first pulse AC current on the DC bus.

[0127] In response to the temperature of the power battery 15 not being lower than a set temperature threshold, the controller 2033 controls the connection of the center tap of the three-phase winding of the first drive motor 201 and the center tap of the three-phase winding of the second drive motor 202, and controls the first power circuit 2031 and the second power circuit 2032 to generate a second pulse AC current on the DC bus. The amplitude of the first pulse AC current is greater than the amplitude of the second pulse AC current.

[0128] When the temperature of the power battery 15 is lower than the set temperature threshold, a first pulse of AC power with a higher amplitude is input to the power battery 15, which helps to quickly raise the battery temperature. Therefore, in low-temperature environments, this heating method can significantly shorten the time it takes for the battery to reach its optimal operating temperature. When the battery temperature reaches or exceeds the set temperature threshold, a second pulse of AC power with a lower amplitude is input to the power battery to maintain the power battery 15 within a suitable operating temperature range and avoid overheating.

[0129] Furthermore, the intensity of heating the power battery can be adjusted by changing the magnitude of the pulsed AC current according to actual needs, thereby saving energy. Using a lower amplitude current when high-power heating is not required reduces unnecessary energy consumption. This method ensures that high-power heating is only used when necessary, thus improving the energy utilization efficiency of the power battery 15.

[0130] In one possible implementation, in response to the temperature of the power battery 15 being greater than a set temperature threshold, the controller 2033 controls the center tap of the three-phase winding of the first drive motor 201 and the center tap of the three-phase winding of the second drive motor 202 to disconnect, and controls the first power circuit 2031 or the second power circuit 2032 to generate pulsed AC current on the DC bus.

[0131] Since the center taps of the three-phase windings of the first drive motor 201 and the second drive motor 202 are connected, the adjustable range of the pulse current output by the first power circuit 2031 and the second power circuit 2032 is expanded, thereby adjusting the heating rate of the power battery 15. Therefore, when the power battery temperature exceeds a set threshold, disconnecting the connection between the two drive motors and using either the first power circuit 2031 or the second power circuit 2032 to generate pulsed AC current can effectively reduce the heating intensity and prevent the battery from overheating. This helps protect the battery from high-temperature damage and extends its service life. By reducing the current output, the heat generation inside the battery can be reduced, thereby keeping the battery within a safe operating temperature range. High-intensity heating is not required when the battery temperature is high. By using only one power circuit, unnecessary energy consumption can be reduced, improving overall energy efficiency. This method ensures that high-power heating is only used when necessary, thereby saving energy and reducing operating costs.

[0132] In one possible implementation, when the center tap of the three-phase winding of the first drive motor 201 and the center tap of the three-phase winding of the second drive motor 201 are disconnected, in response to the phase difference of the pulsed AC current generated on the DC bus by the first power circuit 2031 and the second power circuit 2032 being greater than a preset value, the switching frequency of the switching transistors of the first power circuit 2031 and the second power circuit 2032 and / or the switching frequency of the switching transistors of the second power circuit 2032 are controlled to reduce the phase difference of the pulsed AC current generated by the first power circuit 2031 and the second power circuit 2032.

[0133] When the center taps of the three-phase windings of the first drive motor 201 and the second drive motor 201 are disconnected, the pulse currents input to the power battery 15 by the first power circuit 2031 and the second power circuit 2032 are independent. Therefore, when the two pulse currents are input to the power battery 15, the different phase difference between them will affect the heating efficiency. Specifically, this application reduces the phase difference between the pulsed AC currents generated by the first power circuit 2031 and the second power circuit 2032 by adjusting their switching frequencies, thereby improving the heating efficiency of the power battery 15.

[0134] Figures 9A to 9D are schematic diagrams of the superimposed pulse currents of one pulse current and another pulse current input to the power battery 15. Referring to Figure 9A, when the two pulse currents have no phase difference when input to the power battery 15, the superimposed pulse current is the first superimposed pulse current. Referring to Figure 9B, when the two pulse currents have a first phase difference when input to the power battery 15, the superimposed pulse current is the second superimposed pulse current. Referring to Figure 9C, when the two pulse currents have a second phase difference when input to the power battery 15, the superimposed pulse current is the third superimposed pulse current. Figure 9D is a schematic diagram comparing the superimposed pulse currents. When there is a large phase difference between the pulse currents flowing into the power battery 15, their direction and intensity may affect each other. Since the heating power of the power battery 15 is positively correlated with the amplitude of the pulse current, if the two pulse currents have opposite directions or amplitudes (e.g., in the case of the third superimposed pulse current), the two pulse currents may even cancel each other out, thus severely affecting the heating efficiency of the power battery 15.

[0135] Therefore, by adjusting the switching frequencies of the first power circuit 2031 and the second power circuit 2032 to reduce the phase difference, it can be ensured that the two pulse currents are synchronized as much as possible in time, thereby maximizing the amplitude of the superimposed pulse current. This can improve the heating power of the power battery 15 and accelerate the temperature rise rate of the power battery 15.

[0136] Referring to Figure 10, which is a schematic diagram of another powertrain structure provided in the embodiment of this application, as a possible implementation, the powertrain includes a control switch 1001, and the center tap of the three-phase winding of the first drive motor 201 is connected to the center tap of the three-phase winding of the second drive motor 202 through the control switch 1001.

[0137] The controller 2033 connects the center tap of the three-phase winding of the first drive motor 201 and the center tap of the three-phase winding of the second drive motor 202 by controlling the conduction of the control switch 1001.

[0138] The controller 2033 disconnects the center tap of the three-phase winding of the first drive motor 201 and the center tap of the three-phase winding of the second drive motor 202 by turning off the control switch 1001.

[0139] When rapid heating of the power battery is required, the controller 2033 can connect the center taps of the two motors by closing the control switch 1001. This allows the two power circuits to jointly generate a larger pulse current, thereby accelerating the rate at which the battery temperature rises. When high-power heating is not required, the controller 2033 can disconnect the control switch 1001, disconnecting the center taps of the two motors, and using only one power circuit for heating. This dynamic adjustment can optimize the heating process according to actual needs.

[0140] As shown in Figure 11, the electric vehicle 10 provided in this embodiment includes a heat exchange circuit 1100. According to the thermal effect of current, the three-phase currents on the first drive motor 201 and the second drive motor 202 cause the three-phase windings of the first drive motor 201 and the second drive motor 202 to heat up. The heat exchange circuit is used to conduct the heat generated on the windings of the first drive motor 201 and the second drive motor 202 to the power battery 15, thereby improving energy utilization efficiency, saving energy, and increasing the heating efficiency of the power battery 15.

[0141] In one embodiment, as shown in FIG12, the heat exchange circuit includes a heat transfer medium 1200, a heat transfer medium flow circuit 1201, a liquid pump 1202, and a heat exchanger 1203. The heat transfer medium is used to absorb the heat generated on the windings of the first drive motor 201 and the second drive motor 202. The heat transfer medium flows in the heat transfer medium flow circuit. The liquid pump 1202 is used to provide power for the flow of the heat transfer medium. The heat exchanger 1203 is used to absorb the heat in the heat transfer medium and conduct the absorbed heat in the heat transfer medium to the power battery 15 to heat the power battery 15.

[0142] Based on the same concept, this application also provides a power battery heating method applied to a motor controller. The motor controller includes a first power circuit, a second power circuit, a first capacitor, a second capacitor, and a controller. The midpoints of the three-phase bridge arms of the first power circuit are respectively used to connect to the three-phase windings of a first drive motor. The midpoints of the three-phase bridge arms of the second power circuit are respectively used to connect to the three-phase windings of a second drive motor. The two ends of each phase bridge arm of the first power circuit are respectively connected to the two ends of the first capacitor. The two ends of each phase bridge arm of the second power circuit are respectively connected to the two ends of the second capacitor. The two ends of the first capacitor and the two ends of the second capacitor are respectively used to connect to the positive and negative terminals of the power battery through a DC bus. The method includes: controlling the center tap of the three-phase windings of the first drive motor to connect to the center tap of the three-phase windings of the second drive motor.

[0143] Referring to Figure 13, which is a step diagram of a power battery heating method also provided in this application.

[0144] Step S1301: Determine whether to enable pulse heating and send a pulse heating command to the controller in the motor controller.

[0145] Step S1302: Obtain the pulse current amplitude that the power battery can withstand, determine the relationship between the pulse current amplitude that the power battery can withstand and the set current threshold. If the pulse current amplitude that the power battery can withstand is greater than the set current threshold, execute step S1305. If the pulse current amplitude that the power battery can withstand is greater than the set current threshold, execute step S1306.

[0146] Step S1303: Obtain the target current and determine the relationship between the target current and the set current threshold. The target current is the pulse current that needs to be generated on the DC bus issued by the vehicle controller. Execute step S1305: When the amplitude of the target current is greater than the set current threshold, execute step S1306.

[0147] Step S1304: Obtain the temperature of the power battery, determine the relationship between the temperature of the power battery and the set temperature threshold, and execute step S1305 when the temperature of the power battery is lower than the set temperature threshold, and execute step S1306 when the temperature of the power battery is not lower than the set temperature threshold.

[0148] Step S1305: Control the connection of the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor.

[0149] In step S1306, the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor are disconnected.

[0150] In step S1307, during the discharge cycle, the upper bridge arm switch of at least one bridge arm of the first power circuit and the second power circuit is controlled to be turned on with a preset duty cycle, and the upper bridge arm switches of the other two bridge arms are turned on with a preset duty cycle. During the charging cycle, the control circuit is used to control the lower bridge arm switch of at least one bridge arm to be turned on with a preset duty cycle, and the upper bridge arm switches of the other two bridge arms are turned on with a preset duty cycle.

[0151] In step S1308, during the discharge cycle, the upper bridge arm switch of the three-phase bridge arm of the first power circuit is turned on, and the lower bridge arm switch of the three-phase bridge arm of the second power circuit is turned on. During the charging cycle, the lower bridge arm switch of the three-phase bridge arm of the first power circuit is turned on, and the upper bridge arm switch of the three-phase bridge arm of the second power circuit is turned on.

[0152] Step S1309: Determine whether the temperature of the power battery has reached the preset target temperature. When the temperature of the power battery reaches the preset target temperature, proceed to step S1310.

[0153] In step S1310, the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor are disconnected.

[0154] In one possible implementation, embodiments of this application provide a computer-readable storage medium storing program code that, when run on a computer, causes the computer to perform the above-described method.

[0155] In one possible implementation, embodiments of this application provide a computer program product that, when run on a computer, causes the computer to perform the above-described method.

[0156] Based on the same concept, this application also provides an electric vehicle, which includes a power battery, wheels and a powertrain as described in the above embodiments. A first power circuit and a second power circuit are used to receive power from the power battery to drive the corresponding motor to drive the wheels, or to generate pulsed AC current on the DC bus to heat the power battery.

[0157] This application also relates to a chip system including a processor for calling a computer program or computer instructions stored in a memory to cause the processor to execute the methods of any of the above embodiments.

[0158] In one possible implementation, the processor can be coupled to the memory via an interface.

[0159] In one possible implementation, the chip system may also directly include a memory in which computer programs or computer instructions are stored.

[0160] For example, the memory can be volatile memory or non-volatile memory, or may include both. The non-volatile memory can be read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or flash memory. The volatile memory can be random access memory (RAM), which serves as an external cache. By way of example, but not limitation, many forms of RAM are available, such as static random access memory (SRAM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), double data rate synchronous dynamic random access memory (DDR SDRAM), enhanced synchronous dynamic random access memory (ESDRAM), synchronous linked dynamic random access memory (SLDRAM), and direct rambus RAM (DR RAM).

[0161] This application also relates to a processor for calling a computer program or computer instructions stored in a memory to cause the processor to perform the methods of any of the above embodiments.

[0162] For example, in the embodiments of this application, the processor is an integrated circuit chip with signal processing capabilities. For instance, the processor can be a field-programmable gate array (FPGA), a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, a system-on-chip (SoC), a central processing unit (CPU), a network processor (NP), a microcontroller unit (MCU), a programmable logic device (PLD), or other integrated chips. It can implement or execute the methods, steps, and logic block diagrams disclosed in the embodiments of this application. The general-purpose processor can be a microprocessor or any conventional processor. The steps of the methods disclosed in the embodiments of this application can be directly manifested as being executed by a hardware decoding processor, or executed by a combination of hardware and software modules in the decoding processor. The software module can reside in a mature storage medium in the field, such as random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, or registers. This storage medium is located in memory, and the processor reads information from the memory and, in conjunction with its hardware, completes the aforementioned method.

[0163] It should be understood that embodiments of this application may be provided as methods, systems, or computer program products. Therefore, this application may take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0164] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means that implement the functions specified in one or more flowcharts and / or one or more block diagrams.

[0165] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, such that the instructions, which execute on the computer or other programmable apparatus, provide steps for implementing the functions specified in one or more flowcharts and / or one or more block diagrams.

[0166] Obviously, those skilled in the art can make various modifications and variations to the embodiments of this application without departing from the scope of the embodiments of this application. Therefore, if these modifications and variations to the embodiments of this application fall within the scope of the claims of this application and their equivalents, this application also intends to include these modifications and variations.

Claims

1. A powertrain, characterized by, The powertrain includes a first drive motor, a second drive motor, and a motor controller; The motor controller includes a first power circuit, a second power circuit, a first capacitor, a second capacitor, and a controller. The midpoints of the three-phase bridge arms of the first power circuit are respectively used to connect the three-phase windings of the first drive motor, and the midpoints of the three-phase bridge arms of the second power circuit are respectively used to connect the three-phase windings of the second drive motor. The two ends of each phase arm of the first power circuit are respectively connected to the two ends of the first capacitor, and the two ends of each phase arm of the second power circuit are respectively connected to the two ends of the second capacitor. The two ends of the first capacitor and the two ends of the second capacitor are respectively used to connect to the positive and negative terminals of the power battery through the DC bus. The controller is used to control the connection between the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor.

2. The powertrain of claim 1, wherein, In response to the power battery experiencing a pulse current amplitude greater than a set current threshold, the controller controls the connection of the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor, and controls the first power circuit and the second power circuit to generate a first pulse AC current on the DC bus. In response to the fact that the amplitude of the pulse current borne by the power battery is not greater than a set current threshold, the controller controls the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor to disconnect, and controls the first power circuit and the second power circuit to generate a second pulse AC current on the DC bus, wherein the amplitude of the first pulse AC current is greater than the amplitude of the second pulse AC current.

3. The powertrain of any of claims 1-2, wherein, The controller responds when the amplitude of the target current is greater than a set current threshold. The target current is a pulse current that needs to be generated on the DC bus, issued by the vehicle controller. The controller controls the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor to be connected, and controls the first power circuit and the second power circuit to generate the target current on the DC bus. In response to the target current amplitude not exceeding a set current threshold, the controller controls the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor to disconnect, and controls the first power circuit and the second power circuit to generate the target current on the DC bus.

4. The powertrain of any of claims 1-3, wherein, In response to the temperature of the power battery being lower than a set temperature threshold, the controller controls the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor to connect, and controls the first power circuit and the second power circuit to generate a first pulse AC current on the DC bus. In response to the temperature of the power battery not being lower than a set temperature threshold, the controller controls the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor to connect, and controls the first power circuit and the second power circuit to generate a second pulse AC current on the DC bus, wherein the amplitude of the first pulse AC current is greater than the amplitude of the second pulse AC current.

5. The powertrain of any of claims 1-4, wherein, When the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor are disconnected, the controller is used to: During the discharge cycle, the upper bridge arm switch of one bridge arm of the first power circuit and the second power circuit is turned on, and the lower bridge arm switches of the other two bridge arms are turned on. During the charging cycle, the lower bridge arm switch of one bridge arm of the first power circuit and the second power circuit is turned on, and the upper bridge arm switches of the other two bridge arms are turned on.

6. The powertrain of any of claims 1-5, wherein, When the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor are connected, the controller is used to: During the discharge cycle, the upper bridge arm switch of each bridge arm of the first power circuit is turned on, and the lower bridge arm switch of each bridge arm of the second power circuit is turned on. During the charging cycle, the lower bridge arm switch of each bridge arm of the first power circuit is turned on, and the upper bridge arm switch of each bridge arm of the second power circuit is turned on.

7. The powertrain of any of claims 1-6, wherein, In response to the temperature of the power battery exceeding a set temperature threshold, the controller controls the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor to disconnect, and controls the first power circuit or the second power circuit to generate pulsed AC current on the DC bus.

8. The powertrain of claim 1, wherein, When the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor are disconnected; In response to the phase difference of the pulsed AC current generated by the first power circuit and the second power circuit on the DC bus being greater than a preset value, the switching frequency of the switching transistors of the first power circuit and / or the switching frequency of the switching transistors of the second power circuit is controlled to reduce the phase difference of the pulsed AC current generated by the first power circuit and the second power circuit.

9. The powertrain of any of claims 1-8, wherein, The powertrain includes a control switch, and the center tap of the three-phase winding of the first drive motor is connected to the center tap of the three-phase winding of the second drive motor through the control switch. The controller connects the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor by controlling the conduction of the control switch. The controller disconnects the center tap of the three-phase winding of the first drive motor from the center tap of the three-phase winding of the second drive motor by turning off the control switch.

10. An electric vehicle, characterized by The electric vehicle includes a power battery, wheels, and a powertrain as described in any one of claims 1-9. The first power circuit and the second power circuit are used to receive power from the power battery to drive a corresponding motor to drive the wheels, or to generate pulsed alternating current on the DC bus to heat the power battery.

11. A method of heating a power cell, the method comprising: The invention is applied to a motor controller, which includes a first power circuit, a second power circuit, a first capacitor, a second capacitor, and a controller. The midpoints of the three-phase bridge arms of the first power circuit are respectively used to connect the three-phase windings of the first drive motor, and the midpoints of the three-phase bridge arms of the second power circuit are respectively used to connect the three-phase windings of the second drive motor. The two ends of each phase arm of the first power circuit are respectively connected to the two ends of the first capacitor, and the two ends of each phase arm of the second power circuit are respectively connected to the two ends of the second capacitor. The two ends of the first capacitor and the two ends of the second capacitor are respectively used to connect to the positive and negative terminals of the power battery through the DC bus. The method includes: The center tap of the three-phase winding of the first drive motor is connected to the center tap of the three-phase winding of the second drive motor.

12. The method of claim 11, wherein, The method further includes: Obtain the amplitude of the pulse current that the power battery can withstand; When it is determined that the amplitude of the pulse current that the power battery can withstand is greater than the set current threshold, the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor are connected, and the first power circuit and the second power circuit are controlled to generate a first pulse AC current on the DC bus. When it is determined that the amplitude of the pulse current that the power battery can withstand is not greater than the set current threshold, the controller controls the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor to disconnect, and controls the first power circuit and the second power circuit to generate a second pulse AC current on the DC bus, wherein the amplitude of the first pulse AC current is greater than the amplitude of the second pulse AC current.

13. The method according to claim 11 or 12, characterized in that, The method further includes: The target current is obtained, which is the pulse current that needs to be generated on the DC bus issued by the vehicle controller; when the amplitude of the target current is greater than the set current threshold, the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor are connected, and the first power circuit and the second power circuit are controlled to generate the target current on the DC bus. When the amplitude of the target current is not greater than the set current threshold, the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor are disconnected, and the first power circuit and the second power circuit are controlled to generate the target current on the DC bus.

14. The method according to any of claims 11-13, characterized by, The method further includes: Obtain the temperature of the power battery; When the temperature of the power battery is lower than a set temperature threshold, the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor are connected, and the first power circuit and the second power circuit generate a first pulse AC current on the DC bus. When the temperature of the power battery is not lower than a set temperature threshold, the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor are connected, and the first power circuit and the second power circuit are controlled to generate a second pulse AC current on the DC bus, wherein the amplitude of the first pulse AC current is greater than the amplitude of the second pulse AC current.

15. The method according to any one of claims 11-14, characterized in that, When the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor are disconnected, the method further includes: During the discharge cycle, the upper bridge arm switch of one bridge arm of the first power circuit and / or the second power circuit is turned on, and the lower bridge arm switches of the other two bridge arms are turned on. During the charging cycle, the lower bridge arm switch of one bridge arm of the first power circuit and / or the second power circuit is turned on, and the upper bridge arm switches of the other two bridge arms are turned on.

16. The method according to any one of claims 11-15, characterized in that, When the center tap of the three-phase winding of the first drive motor and the center tap of the three-phase winding of the second drive motor are connected, the method further includes: During the discharge cycle, the upper bridge arm switch of each bridge arm of the first power circuit is turned on, and the lower bridge arm switch of each bridge arm of the second power circuit is turned on. During the charging cycle, the lower bridge arm switch of each bridge arm of the first power circuit is turned on, and the upper bridge arm switch of each bridge arm of the second power circuit is turned on.

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