A method for pulse heating power batteries of an electric vehicle and the electric vehicle

Abstract

The application provides a method for pulse heating a power battery of an electric vehicle and the electric vehicle. The electric vehicle comprises a plurality of motors and a plurality of three-phase bridge arms. A bridge arm midpoint of each three-phase bridge arm is used for connecting three-phase windings of one motor. Each three-phase bridge arm is used for connecting the power battery through a direct current bus. The control method comprises: controlling each three-phase bridge arm to generate a pulse current on the direct current bus; and adjusting a switching frequency of a switching tube of at least one three-phase bridge arm of the plurality of three-phase bridge arms to reduce a phase difference of the pulse currents generated by the plurality of inverter circuits. The phase value of the pulse current output by the at least one three-phase bridge arm is adjusted, so that the phase difference of the pulse currents generated by the plurality of three-phase bridge arms is reduced, and the heating efficiency of the power battery is improved.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202310956800.X, filed on July 31, 2023, with the State Intellectual Property Office of the People's Republic of China, entitled "A Dual-Motor Controller and a Control Method for the Motor Controller", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of electric vehicles, and in particular to a method for pulse heating of a power battery for an electric vehicle and the electric vehicle itself. Background Technology

[0004] 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.

[0005] In addition, high-frequency pulse heating can be used to heat the power battery. This method mainly involves the powertrain performing AC high-frequency charging and discharging on the power battery, thereby utilizing the heat generated by the battery's internal resistance to heat the battery. Using a single powertrain for heating is limited by hardware constraints such as motor windings and bus capacitors, which restrict the adjustable range of the generated pulse current, thus limiting the heating rate of the power battery. Using multiple powertrains for heating results in a large phase difference between the pulse currents flowing into the battery, causing the pulse currents to cancel each other out and affecting the heating rate. Summary of the Invention

[0006] This application provides a control method for electric vehicles and an electric vehicle that improves the heating efficiency of the power battery by reducing the phase difference of the pulse current generated by multiple three-phase bridge arms.

[0007] In a first aspect, this application provides a method for pulse heating of a power battery in an electric vehicle. The electric vehicle includes multiple motors and multiple three-phase bridge arms. The midpoint of each three-phase bridge arm is used to connect a three-phase winding of a motor. Each three-phase bridge arm is used to connect to the power battery via a DC bus. The control method includes controlling each three-phase bridge arm to generate a pulse current on the DC bus, the pulse current being used to heat the power battery; and adjusting the switching frequency of the switching transistor of at least one of the multiple three-phase bridge arms to reduce the phase difference of the pulse current generated by the multiple three-phase bridge arms.

[0008] When the phase difference of the pulse currents flowing into the power battery is large, the direction and intensity of the pulse currents may affect each other, and even if the two pulse currents have opposite directions or amplitudes, the two pulse currents will cancel each other out, thereby seriously affecting the heating efficiency of the power battery. Therefore, by adjusting the phase of the pulse current output by at least one of the plurality of three-phase bridge arms, the phase difference of the pulse currents generated by the plurality of three-phase bridge arms is reduced, thereby improving the heating efficiency of the power battery.

[0009] Since the phase difference of the pulse currents output by each three-phase bridge arm is too small to be measured and has limited impact on the heating efficiency, as a possible implementation, the method comprises adjusting the switching frequency of the switching tube of at least one of the two three-phase bridge arms when the phase difference of the pulse currents generated by any two three-phase bridge arms is greater than a preset value, so as to reduce the phase difference of the pulse currents output by the two three-phase bridge arms.

[0010] When the phase difference of the pulse currents generated by the three-phase bridge arms is small, the direction and intensity of the pulse currents flowing into the power battery will not have a great impact, and when the phase difference of the pulse currents generated by any two three-phase bridge arms is greater than a preset value, there will be a certain cancellation. Therefore, at this time, by adjusting the switching frequency of the switching tube of at least one of the two three-phase bridge arms, the phase difference of the pulse currents generated by the plurality of three-phase bridge arms is reduced, thereby improving the heating efficiency of the power battery.

[0011] As a possible implementation, the method comprises: controlling at least one of the plurality of three-phase bridge arms to generate the pulse current first, controlling the other three-phase bridge arms to generate the pulse current later, or controlling the other three-phase bridge arms to generate the pulse current first, and controlling at least one of the plurality of three-phase bridge arms to generate the pulse current later. In this way, the phase difference of the pulse currents generated by the plurality of three-phase bridge arms can be reduced, thereby improving the heating efficiency of the power battery.

[0012] As a possible implementation, the method comprises: controlling the switching frequency of the switching tube of the other three-phase bridge arms to reduce the phase difference of the pulse current generated by the other three-phase bridge arms and the pulse current generated by at least one of the three-phase bridge arms.

[0013] As a possible implementation, the method comprises: when the phase difference of the pulse current generated by the other three-phase bridge arms and the pulse current generated by at least one of the three-phase bridge arms is greater than a preset value, controlling the switching frequency of the switching tube of the other three-phase bridge arms to reduce the phase difference of the pulse current generated by the other three-phase bridge arms and the pulse current generated by at least one of the three-phase bridge arms. By controlling the switching frequency of the switching tube of the other three-phase bridge arms, the phase difference of the pulse currents generated by the plurality of three-phase bridge arms can be reduced, thereby improving the heating efficiency of the power battery.

[0014] As a possible implementation, the at least one three-phase bridge arm is a three-phase bridge arm corresponding to a drive motor, and the drive motor is used to drive a wheel of an electric vehicle; and the other three-phase bridge arms are three-phase bridge arms corresponding to motors other than the drive motor.

[0015] As a possible implementation, the bridge arm midpoint of each three-phase bridge arm is used to output a three-phase current, and the three-phase current includes a U-phase current, a V-phase current, and a W-phase current. The method includes: in response to a phase difference between the U-phase currents output by any two three-phase bridge arms of the plurality of three-phase bridge arms, or a phase difference between the V-phase currents, or a phase difference between the W-phase currents being greater than a preset value, adjusting a switching frequency of a switching tube of at least one three-phase bridge arm of the any two three-phase bridge arms to reduce the phase difference between the U-phase current, the V-phase current, and the W-phase current output by the any two three-phase bridge arms. Since the three-phase current and the pulse current have the same frequency, by detecting the phase difference between the same-phase currents corresponding to the any two three-phase bridge arms, it can also be determined whether the phase difference between the pulse currents generated by the two three-phase bridge arms is greater than the preset value. When the phase difference between the certain-phase currents output by the any two three-phase bridge arms is greater than the preset value, the switching frequency of the switching tube of at least one three-phase bridge arm of the any two three-phase bridge arms can be adjusted to reduce the phase difference between the certain-phase currents output by the any two three-phase bridge arms, so as to improve the heating efficiency of the power battery.

[0016] As a possible implementation, the frequency of the three-phase current is the same as the frequency of the pulse current.

[0017] As a possible implementation, the method includes: in response to a phase difference between the pulse currents generated by any two three-phase bridge arms of the plurality of three-phase bridge arms being greater than a preset value, or a phase difference between the U-phase current, the V-phase current, or the W-phase current output by the any two three-phase bridge arms being greater than a preset value, adjusting a frequency of a direct-axis current component of the three-phase current output by at least one three-phase bridge arm of the any two three-phase bridge arms. By increasing / decreasing the frequency of the voltage indicated by the voltage given signal corresponding to one of the three-phase bridge arms, the frequency of the direct-axis current component of the pulse current generated by the one three-phase bridge arm can be increased / decreased, and thus the phase difference between the pulse currents generated by the two three-phase bridge arms is reduced, so as to improve the heating efficiency of the power battery.

[0018] As a possible implementation, the method comprises: when the phase difference between the pulse currents generated by any two of the plurality of three-phase bridge arms is greater than a preset value or the phase difference between the U-phase current, V-phase current or W-phase current output by any two of the plurality of three-phase bridge arms is greater than a preset value, adjusting the frequency of the direct-axis current component of the three-phase current output by at least one of the two three-phase bridge arms until the phase difference between the pulse currents generated by any two of the plurality of three-phase bridge arms is less than or equal to the preset value and the phase difference between the U-phase current, V-phase current and W-phase current output by any two of the plurality of three-phase bridge arms is less than or equal to the preset value.

[0019] By increasing / decreasing the frequency of the voltage indicated by the voltage given signal corresponding to one of the three-phase bridge arms, the frequency of the direct-axis current component of the pulse current generated by the three-phase bridge arm can be increased / decreased, so that the phase difference between the pulse currents generated by any two of the plurality of three-phase bridge arms is less than or equal to the preset value and the phase difference between the U-phase current, V-phase current and W-phase current output by any two of the plurality of three-phase bridge arms is less than or equal to the preset value, thereby improving the heating efficiency of the power battery.

[0020] As a possible implementation, the method comprises: when the phase difference between the pulse currents generated by any two of the plurality of three-phase bridge arms is less than or equal to the preset value and the phase difference between the U-phase current, V-phase current or W-phase current output by any two of the plurality of three-phase bridge arms is less than or equal to the preset value, controlling the frequency of the direct-axis current component of the three-phase current output by each three-phase bridge arm to be a preset frequency. After increasing / decreasing the frequency of the voltage indicated by the voltage given signal corresponding to one of the three-phase bridge arms, if the phase difference between the pulse currents generated by the two three-phase bridge arms is again less than or equal to the preset value, the frequency of the direct-axis current component of the three-phase current output by each three-phase bridge arm can be controlled to be the preset frequency, thereby avoiding the phase difference between the plurality of three-phase bridge arms again.

[0021] To avoid the problem of transmission delay caused by different transmission path lengths, as a possible implementation, the method comprises: first outputting a first control signal to control the three-phase bridge arm corresponding to the driving motor to output three-phase current, and then outputting a second control signal to control the three-phase bridge arm corresponding to the other motor to output three-phase current, wherein the frequency of the direct-axis current component of the three-phase current indicated by the first control signal and the second control signal is the same. Using this method can reduce the problem caused by transmission delay, and by adjusting the order of the control signals, the phase difference between the three-phase bridge arms is reduced, thereby improving the heating efficiency of the power battery.

[0022] As a possible implementation, the method comprises: controlling the quadrature-axis current component of the three-phase current output by each three-phase bridge arm to be less than a preset value; or, controlling the torque value output by each motor to be less than a preset torque value. The quadrature-axis current component of the pulse current generated by the three-phase bridge arm of the application is less than a preset value, or the torque value output by the motor is less than a preset torque value, thereby avoiding unintended torque conduction to the wheels to generate vibration and noise, affecting the ride experience of the electric vehicle.

[0023] As a possible implementation, the method comprises: controlling the frequencies of the pulse currents output by the plurality of three-phase bridge arms to be the same.

[0024] As a possible implementation, adjusting the frequency of the direct-axis current component of the three-phase current output by the three-phase bridge arm comprises: increasing the frequency of the direct-axis current component of the three-phase current output by the three-phase bridge arm; or, decreasing the frequency of the direct-axis current component of the three-phase current output by the three-phase bridge arm.

[0025] In a second aspect, the application provides an electric vehicle, comprising a control device, a plurality of motors, and a plurality of three-phase bridge arms corresponding to the plurality of motors one-to-one, each three-phase bridge arm comprising a three-phase bridge arm, the bridge arm midpoint of each three-phase bridge arm being used to connect the three-phase winding of one motor, each three-phase bridge arm being used to connect a power battery through a DC bus, the control device being used to control at least two three-phase bridge arms to generate pulse currents on the DC bus, the frequencies of the pulse currents generated by the at least two three-phase bridge arms on the DC bus being the same and the phase difference value being less than a preset value. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 A connection diagram of an electric vehicle provided by an embodiment of the application Figure 1 ;

[0027] Figure 2 A structure diagram of an electric vehicle provided by an embodiment of the application Figure 2 ;

[0028] Figure 3 A connection diagram of a three-phase bridge arm and a motor provided by an embodiment of the application Figure 1 ;

[0029] Figure 4 A connection diagram of a three-phase bridge arm and a motor provided by an embodiment of the application Figure 2 ;

[0030] Figure 5(a) to Figure 5(d) A diagram of a pulse current inputting a power battery Figure 1 ;

[0031] Figure 6(a) to Figure 6(b) A diagram of a pulse current inputting a power battery Figure 2 ;

[0032] Figure 7 is a schematic view of phase current;

[0033] Figure 8 is a waveform chart of the voltage indicated by the voltage command signal (a) to (c) in

[0034] Figure 9 is a schematic view of the control circuit;

[0035] Figure 10(a) to Figure 10(b) is a schematic view of the voltage command signal and the pulse current Figure 1 ;

[0036] Figure 11(a) to Figure 11(b) is a schematic view of the voltage command signal and the pulse current Figure 2 ;

[0037] Figure 12 is a schematic view of an electric vehicle provided by an embodiment of the present application Figure 3 ;

[0038] Figure 13 is a schematic view of an electric vehicle provided by an embodiment of the present application Figure 4 . DETAILED DESCRIPTION

[0039] The technical solutions involved in the specific embodiments of the present application will be described below in conjunction with the drawings in the embodiments. Before the specific content of the technical solutions is described, the terms used in the present application will be briefly explained.

[0040] The terms "first", "second", "third" or "module A", "module B", "module C" and the like similar terms in the specification and claims are only used to distinguish similar objects, and do not represent a specific order or sequence of the objects. It can be understood that the specific order or sequence can be interchanged as allowed, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.

[0041] The term "comprising" used in the specification and claims should not be interpreted as limited to the listed elements; it does not exclude other elements or steps. Therefore, it should be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. Therefore, the expression "a device comprising means A and B" should not be limited to a device consisting only of components A and B.

[0042] Reference in this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. The appearances of the phrase "in one embodiment" or "in an embodiments" in various places in the specification are not necessarily all referring to the same embodiment, but can refer to different embodiments. Furthermore, the particular features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the specification is for describing particular embodiments only and is not intended to be limiting of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the specification is for describing particular embodiments only and is not intended to be limiting of the application.

[0044] The motor of an electric vehicle is generally an alternating current motor, and the power battery is a direct current source. Therefore, the direct current output by the power battery is converted into three-phase alternating current of the motor through an inverter circuit. The coordinate axes of the three-phase alternating current are U-axis, V-axis and W-axis, respectively. The three phases of the alternating current can also be referred to as U-phase, V-phase and W-phase, respectively. In order to simplify the analysis of the motor, the stationary three-phase coordinate is usually transformed into a rotating d-q coordinate. This transformation is called park transformation. In the d-q coordinate system, the three coordinate axes are called direct axis, quadrature axis and zero axis, respectively.

[0045] The direct axis, also referred to as D-axis or d-axis, is a time-varying direct current coordinate axis obtained by park transformation of the stationary U / V / W three-phase coordinate axis.

[0046] The quadrature axis, also referred to as Q-axis or q-axis, is a time-varying alternating current coordinate axis obtained by park transformation of the stationary U / V / W three-phase coordinate axis.

[0047] The zero axis, also referred to as 0-axis or 0-axis, is a coordinate axis perpendicular to the d-q plane in which the direct axis and the quadrature axis are located.

[0048] Specifically, the formula of the park transformation can be as follows:

[0049]

[0050] where θ is the included angle between the d-axis and the U-axis; I_d is referred to as the direct axis current, which is mainly used for adjusting the magnetic field; I_q is referred to as the quadrature axis current, which is mainly used for adjusting the torque; I_0 is referred to as the zero sequence current; I_u, I_v and I_w are the currents on the U-axis, V-axis and W-axis, respectively, i.e. the three-phase currents.

[0051] The above matrix is an expression of three-phase current transformation to I_d, I_q, I_0. Inverse transformation of the matrix can obtain an expression of transformation from I_d, I_q, I_0 to three-phase current, which is not described herein.

[0052] The electric vehicle includes a motor, a motor controller, and a power battery. The motor controller receives power from the power battery and supplies power to the motor. The motor drives the wheels of the electric vehicle to move the electric vehicle.

[0053] Temperature has a great impact on the power battery. The power battery may have lithium precipitation phenomenon when charging and discharging at low temperature, which leads to capacity attenuation of the power battery and even safety hazards of the power battery. Therefore, the power battery needs to be heated to a certain temperature before the electric vehicle is allowed to run.

[0054] Currently, there are three main heating methods for power batteries, including:

[0055] One way to heat the power battery is to use an external heating system to heat the power battery. For example, a power battery thermal loop is arranged outside the power battery, and a heat-carrying thermal fluid is arranged in the power battery thermal loop. A positive temperature coefficient resistor (PTC) heats the thermal fluid in the power battery thermal loop, and the thermal fluid in the power battery thermal loop conducts heat to the power battery to heat the power battery. The above method needs to heat the thermal fluid in the power battery thermal loop first, and then heat the power battery through the thermal fluid in the power battery thermal loop. The heat transfer path is long, and the heating efficiency is low.

[0056] One way to heat the power battery is electric drive active heating. The electric drive active heating method uses the excitation current of the motor to generate heat on the motor to heat the power battery. The motor controller outputs three-phase alternating current to the motor, and the three-phase alternating current makes the torque of the motor zero. The excitation current generates heat on the motor winding, and the heat generated on the motor is conducted to the power battery through a heat conduction device between the motor and the power battery to heat the power battery. The above method has the disadvantages of long heat transfer path, low power battery heating rate, and low heating efficiency because the heat of the motor needs to be conducted to the power battery through the heat conduction device.

[0057] One way to heat the power battery is high-frequency pulse heating. The high-frequency pulse heating method uses the high-frequency pulse current generated by the motor controller to heat the power battery. The motor controller bridge arm circuit generates high-frequency pulse current, and the high-frequency pulse current generates heat on the internal resistance of the power battery when passing through the power battery to heat the power battery. The high-frequency heating method has the advantage of fast heating rate and is widely valued.

[0058] In the high-frequency pulse heating method, the use of a single motor controller in the powertrain for heating is limited by the hardware limitations of the motor windings, bus capacitance, etc. The range of high-frequency pulse current generated is limited, and thus the heating rate of the power battery is limited. If multiple motor controllers are used to output multiple high-frequency pulse currents to simultaneously heat the power battery, the heating rate can be improved, but due to the large phase difference between the pulse currents flowing into the battery, the pulse currents will cancel each other out and affect the heating rate. When multiple pulse currents appear alternately, their direction and intensity can affect each other. If two pulse currents have opposite directions or amplitudes, they will cancel each other out to some extent, resulting in a weakened superimposed current effect. Therefore, the present application provides a method for pulse heating of a power battery of an electric vehicle and an electric vehicle, which reduces the phase difference of the pulse currents generated by multiple three-phase bridge arms to improve the heating efficiency of the power battery.

[0059] Figure 1 A schematic diagram of an electric vehicle provided by an embodiment of the present application Figure 1 . Referring to Figure 2 , the electric vehicle 10 includes a plurality of motors 11, a plurality of three-phase bridge arms 12, a power battery 13, and wheels 14. The plurality of motors 11 correspond one-to-one to the plurality of three-phase bridge arms 12. The motors 11 can be drive motors, generators, compressors, etc. The three-phase bridge arms 12 corresponding to the drive motors are used to receive power from the power battery 13 to drive the wheels 14 or to heat the power battery 13. The three-phase bridge arms 12 corresponding to the generators are used to convert the kinetic energy of the electric vehicle 10 into electrical energy, thereby powering the drive motors to drive the wheels 14, charging the power battery 13, or heating the power battery 13. The three-phase bridge arms 12 corresponding to the compressors are used to receive power from the power battery 13 to drive the refrigeration system in the vehicle or to heat the power battery 13. It should be noted that the present application does not specifically limit the specific type of motor 11.

[0060] Figure 2 A schematic diagram of an electric vehicle provided by an embodiment of the present application Figure 2 . Referring to Figure 3 , the three-phase bridge arms 12 receive direct current from the power battery 13 and convert the direct current into three-phase alternating current to power the motors 11. The motors 11 and the wheels 14 are connected through a reducer or a transmission. During the driving of the electric vehicle 10, the torque of the motors 11 is transmitted to the wheels 14 to provide power for the electric vehicle 10.

[0061] Figure 1 A schematic diagram of a three-phase bridge arm and a motor connection provided by an embodiment of the present application Figure 3 . Referring to Figure 3As shown in the figure, one end of each bus capacitor C is used to connect the positive pole of the power battery 13, and the other end of each bus capacitor C is used to connect the negative pole of the power battery 13. Each three-phase bridge arm 12 includes three switch tube bridge arms, and the two ends of each switch tube bridge arm are connected to the two ends of the corresponding bus capacitor C. The bridge arm midpoint of each switch tube bridge arm is used to connect a phase winding of the corresponding motor 11. The two ends of the three-phase bridge arm 12 are connected to the positive pole and the negative pole of the power battery 13, respectively, to form a power battery 13 pulse heating loop.

[0062] Continuing to refer to Figure 4 As shown in the figure, the three bridge arms included in the three-phase bridge arm 12 can be respectively denoted as a U-phase bridge arm, a V-phase bridge arm, and a W-phase bridge arm. The upper bridge switch tube in the U-phase bridge arm is the switch tube Q1, and the lower bridge switch tube is the switch tube Q2. The upper bridge switch tube in the V-phase bridge arm is the switch tube Q3, and the lower bridge switch tube is the switch tube Q4. The upper bridge switch tube in the W-phase bridge arm is the switch tube Q5, and the lower bridge switch tube is the switch tube Q6. One end of each bridge arm is used to be connected to one end of the power battery 13, i.e., the collector of the switch tube Q1, the collector of the switch tube Q3, and the collector of the switch tube Q5 are connected to one end of the power battery 13. The other end of each bridge arm is connected to the other end of the power battery 13, i.e., the emitter of the switch tube Q2, the emitter of the switch tube Q4, and the emitter of the switch tube Q6 are connected to the other end of the power battery 13. Optionally, one end of the power battery 13 can be the positive pole of the power battery 13, and the other end of the power battery 13 can be the negative pole of the power battery 13. Alternatively, one end of the power battery 13 can be the negative pole of the power battery 13, and the other end of the power battery 13 can be the positive pole of the power battery 13.

[0063] Optionally, the upper bridge switch tube can be an insulated gate bipolar transistor (IGBT) and an anti-parallel diode thereof, or a metal oxide semiconductor field effect transistor (MOSFET), etc. The present application does not make too many limitations on the specific structure inside the upper bridge switch tube. Optionally, the lower bridge switch tube can be an IGBT and an anti-parallel diode thereof or a MOSFET. The present application does not make too many limitations on the specific structure inside the lower bridge switch tube.

[0064] The upper bridge switch tube of one of the three bridge arms and the lower bridge switch tubes of the other two bridge arms are periodically turned on by the control signal, so that the power battery 13, the turned-on one of the upper bridge switch tubes, the two-phase winding of the motor 11, and the turned-on two of the lower bridge switch tubes form a discharge circuit. The internal resistance of the power battery 13 generates heat under the action of the pulse current in the discharge circuit, and the power battery 13 can be heated. Alternatively, the lower bridge switch tube of one of the three bridge arms and the upper bridge switch tubes of the other two bridge arms are periodically turned on by the control signal, so that the power battery 13, the turned-on one of the lower bridge switch tubes, the two-phase winding of the motor 11, and the turned-on two of the upper bridge switch tubes form a discharge circuit. The internal resistance of the power battery 13 generates heat under the action of the pulse current in the discharge circuit, and the power battery 13 can be heated.

[0065] Figure 2 Three-phase bridge arm and motor connection schematic provided for the embodiments of the application Figure 5(a) to Figure 5(c) The electric vehicle 10 further includes a control circuit 121. The control circuit 121 is configured to control the upper bridge switch tube of one of the three bridge arms and the lower bridge switch tubes of the other two bridge arms to be periodically turned on by a control signal, so that the power battery 13, the turned-on one of the upper bridge switch tubes, the two-phase winding of the motor, and the turned-on two of the lower bridge switch tubes form a discharge circuit. The internal resistance of the power battery 13 generates heat under the action of the current in the discharge circuit, and the power battery 13 can be heated. Alternatively, the lower bridge switch tube of one of the three bridge arms and the upper bridge switch tubes of the other two bridge arms are periodically turned on by the control signal, so that the power battery 13, the turned-on one of the lower bridge switch tubes, the two-phase winding of the motor, and the turned-on two of the upper bridge switch tubes form a discharge circuit. The internal resistance of the power battery 13 generates heat under the action of the current in the discharge circuit, and the power battery 13 can be heated. The control signal is used to indicate the direct-axis current component and the quadrature-axis current component of the three-phase current. The direct-axis current component is used to control the direction and size of the magnetic field generated by the motor 11, and the quadrature-axis current component is used to control the torque output by the motor 11.

[0066] The control circuit 121 may, for example, include but is not limited to a central processing unit (CPU), other general purpose processors, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, etc. The control circuit 121 may control the switching on or off of the switches in each of the three-phase bridge arms 12 by outputting control signals to each of the three-phase bridge arms 12. The control signals may be pulse width modulation (PWM) signals, for example. The control circuit 121 may be connected to the gates of each of the switches in the three bridge arms of the three-phase bridge 12 and control the switching on or off of each of the switches in the three-phase bridge 12, for example. In some application scenarios, the control circuit 121 may generate the control signals for each of the switches in the three bridge arms in combination with a space vector pulse width modulation (SVPWM) technique.

[0067] Referring to Figure 5(a) to Figure 5(c) illustrated, Figure 5(a) to Figure 5(c) is a schematic diagram of the superimposed pulse current input to the power battery 13. Referring to FIG. 5(a), when the two pulse currents have no phase difference when input to the power battery 13, the superimposed pulse current input to the power battery 13 is the first superimposed pulse current. Referring to FIG. 5(b), when the two pulse currents have a first phase difference when input to the power battery 13, the superimposed pulse current input to the power battery 13 is the second superimposed pulse current. Referring to FIG. 5(c), when the two pulse currents have a second phase difference when input to the power battery 13, the superimposed pulse current input to the power battery 13 is the third superimposed pulse current. Referring to FIG. 5(d), it is a comparison schematic diagram of the superimposed pulse currents described above. When there is a large phase difference between the pulse currents flowing into the power battery 13, the direction and intensity may affect each other. Since the heating power of the power battery 13 is positively correlated with the amplitude of the pulse current, if the two pulse currents have opposite directions or amplitudes (for example, the case of the third superimposed pulse current), the two pulse currents may even cancel each other out, thereby seriously affecting the heating efficiency of the power battery 13. Figure 6(a) to Figure 6(b)

[0068] ​As can be seen from Fig. 5(a), the phase difference of the pulse current needs to be solved so as to make the power battery 13 obtain higher heating efficiency. In order to make the pulse current have as small phase difference as possible, the frequencies of the pulse currents generated by the plurality of three-phase bridge arms 12 are usually the same. Even so, there are many reasons for the phase difference of the pulse currents generated by the plurality of three-phase bridge arms 12. For example, due to the phase delay caused by hardware when each three-phase bridge arm 12 inputs the pulse current to the power battery 12, and due to the difference in phase delay, the phase difference of each pulse current exists. For another example, when the control signal is issued to each three-phase bridge arm 12, the pulse currents generated by each three-phase bridge arm 12 also have phase difference due to the difference in time of issuing the control signal.

[0069] Therefore, the phase of the pulse current generated by each three-phase bridge arm 12 needs to be monitored, and when it is detected that the pulse currents generated by each three-phase bridge arm 12 have phase difference, the phase difference of the pulse currents generated by the plurality of three-phase bridge arms 12 is reduced by adjusting the pulse current output by at least one three-phase bridge arm 12 of the plurality of three-phase bridge arms 12.

[0070] In particular, the phase difference of the pulse currents generated by the plurality of three-phase bridge arms 12 is reduced by adjusting the switching frequency of the switching tube of at least one three-phase bridge arm 12 of the plurality of three-phase bridge arms 12, specifically, by adjusting the periodically on frequency of the upper bridge switching tube of one bridge arm and the lower bridge switching tube of the other two bridge arms of at least one three-phase bridge arm 12 of the plurality of three-phase bridge arms 12, or by adjusting the periodically on frequency of the lower bridge switching tube of one bridge arm and the upper bridge switching tube of the other two bridge arms of at least one three-phase bridge arm 12 of the plurality of three-phase bridge arms 12, so as to improve the heating efficiency of the power battery 13.

[0071] In addition, when the phase difference between the pulse current generated by the other three-phase bridge arm 12 and the pulse current generated by the at least one three-phase bridge arm 12 is greater than a preset value, the phase difference between the pulse current generated by the other three-phase bridge arm 12 and the pulse current generated by the at least one three-phase bridge arm 12 can also be reduced by controlling the switching frequency of the switching tube of the other three-phase bridge arm 12, so as to achieve the effect of reducing the phase difference of the pulse current.

[0072] Since the phase difference of each three-phase bridge arm 12 is difficult to be measured when it is too small, as a possible implementation, the control method comprises adjusting the switching frequency of the switching tube of at least one three-phase bridge arm 12 of any two three-phase bridge arms 12 of the plurality of three-phase bridge arms 12 to reduce the phase difference of the pulse currents output by the two three-phase bridge arms 12 when the phase difference of the pulse currents generated by the two three-phase bridge arms 12 is greater than a preset value.

[0073] When the phase difference of the pulse current generated by any two of the three-phase bridge arms 12 is less than a preset value, the direction and intensity of the pulse current flowing into the power battery 13 will not change greatly, and when the phase difference of the pulse current generated by any two of the three-phase bridge arms 12 is greater than the preset value, there will be a certain offset. Therefore, at this time, the switching frequency of the switching tube of at least one of the two three-phase bridge arms 12 is adjusted to reduce the phase difference of the pulse currents output by the two three-phase bridge arms 12. For example, the preset value corresponding to the phase difference of the pulse current can be 10°, and the preset value of the phase difference can be freely set by the person skilled in the art according to the measurement accuracy and heating efficiency, which will not be limited here.

[0074] Since the phase of the current is difficult to detect, in response to the current difference of the pulse currents generated by any two of the three-phase bridge arms 12 at the same time being greater than a preset value, the switching frequency of the switching tube of at least one of the two three-phase bridge arms 12 is adjusted to reduce the phase difference of the pulse currents output by the two three-phase bridge arms 12.

[0075] Wherein, if the amplitude of the pulse current output by each three-phase bridge arm 12 is the same, the preset values corresponding to the two three-phase bridge arms 12 can be the same, and if the amplitude of the pulse current output by each three-phase bridge arm 12 is not completely the same, different preset values can be set respectively. The person skilled in the art can set different preset values according to different current differences corresponding to different phase differences, which will not be described here.

[0076] In addition, when the phase difference of the pulse currents generated by any two of the three-phase bridge arms 12 is greater than a preset value, the order of generating the pulse currents by the three-phase bridge arms 12 can also be adjusted to reduce the phase difference of the pulse currents output by the two three-phase bridge arms 12. Referring to Figure 7 As a possible implementation, at least one of the three-phase bridge arms 12 in the plurality of three-phase bridge arms 12 is controlled to generate a pulse current first, and the other three-phase bridge arms 12 except the at least one three-phase bridge arm 12 are controlled to generate a pulse current later, or the other three-phase bridge arms 12 except the at least one three-phase bridge arm 12 are controlled to generate a pulse current first, and at least one of the three-phase bridge arms 12 in the plurality of three-phase bridge arms 12 is controlled to generate a pulse current later. In this way, the phase difference of the pulse currents output by the plurality of three-phase bridge arms 12 can also be reduced.

[0077] In this way, the phase difference of the pulse currents generated by the two three-phase bridge arms 12 can also be reduced to improve the heating efficiency of the power battery 13.

[0078] In this system, the midpoint of each three-phase bridge arm 12 is used to output three-phase current, which includes U-phase current, V-phase current, and W-phase current. The U-phase current, V-phase current, and W-phase current together constitute a pulse current. Since the three-phase current and the pulse current have the same frequency, the phase difference between the in-phase currents corresponding to any two three-phase bridge arms 12 can be detected to determine whether the phase difference between the pulse currents generated by the two three-phase bridge arms 12 is greater than a preset value.

[0079] As one possible implementation, in response to the phase difference between the U-phase current, V-phase current, and W-phase current output by any two three-phase bridge arms 12 exceeding a preset value, the switching frequency of the switching transistor of at least one of the three-phase bridge arms 12 is adjusted to reduce the phase difference between the U-phase current, V-phase current, and W-phase current output by any two three-phase bridge arms 12. The waveform of each phase current can be a single-sided triangular wave.

[0080] See Figure 7 As shown, Figure 8 This is a schematic diagram of the phase current. Taking the comparison of the phase of the U-phase current output by any two three-phase bridge arms 12 as an example, when the phase difference of the U-phase current output by any two three-phase bridge arms 12 is greater than a preset value, the switching frequency of the switching transistor of at least one of the three-phase bridge arms 12 can be adjusted to reduce the phase difference of the U-phase current output by any two three-phase bridge arms 12.

[0081] Since the three-phase current corresponds to the current in the windings of motor 11, when outputting current to the direct axis of motor 11, the motor controller needs to convert the direct axis current into three-phase currents U-phase current, V-phase current and W-phase current through the inverse transformation of the Parker transformation, and then pass the U-phase current, V-phase current and W-phase current into the motor windings.

[0082] Since the phase of the current is difficult to detect, if the current difference between the U-phase current, V-phase current and W-phase current generated by any two three-phase bridge arms 12 at the same time is greater than the preset value, the switching frequency of the switching transistor of at least one of the three-phase bridge arms 12 can be adjusted to reduce the phase difference between the U-phase current, V-phase current and W-phase current output by any two three-phase bridge arms 12.

[0083] If the amplitudes of the U-phase current, V-phase current, and W-phase current output by each three-phase bridge arm 12 are the same, then the preset values ​​corresponding to the two three-phase bridge arms 12 can be the same. If the amplitudes of the U-phase current, V-phase current, and W-phase current output by each three-phase bridge arm 12 are not completely the same, then different preset values ​​can be set for each. Those skilled in the art can also set different preset values ​​based on the different current differences corresponding to different phase differences, which will not be elaborated on here.

[0084] The direct-axis current component is used to control the direction and size of the magnetic field generated by the motor 11, and by controlling the direction and size of the magnetic field generated by the motor 11, the size and direction of the pulse current can be adjusted. Specifically, the direct-axis current component can be determined according to the power battery 13 heating power indicated by the heating instruction. The direct-axis current component includes two parameters, one is the frequency and amplitude of the direct-axis current, and the other is the bias of the direct-axis current. Optionally, the direct-axis current component can be composed of a voltage given signal and a direct-axis bias signal, the voltage given signal is used to indicate the frequency and amplitude of the voltage, and the direct-axis bias signal is used to generate a direct current bias for the voltage. That is, the direct-axis current signal with a direct current bias is input to the control circuit 121, so that the control circuit 121 generates a control signal according to the direct-axis current signal, and then drives the motor 11 using the control signal. The direct-axis current signal with a direct current bias can improve the effective value of the three-phase current of the motor 11, thereby improving the heating efficiency of the power battery 13. It should be noted that the direct-axis current signal with a direct current bias can be a positive direct current bias or a negative direct current bias, which can be set separately according to the demand for heating power by those skilled in the art.

[0085] The quadrature-axis current component is used to control the torque output by the motor 11. During the high-frequency pulse heating process of the power battery 13, if the quadrature-axis current component of the motor 11 is not less than a preset value, the motor 11 will generate an unexpected torque output. The unexpected torque of the motor 11 conducted to the wheels 12 will cause the electric vehicle 10 to vibrate and generate noise, affecting the ride experience of the electric vehicle 10. Therefore, the quadrature-axis current component of the pulse current of the three-phase current output by the three-phase bridge arm 12 is less than a preset value, or the quadrature-axis current component is zero, thereby avoiding the unexpected torque from being conducted to the wheels to generate vibration and noise, affecting the ride experience of the electric vehicle 10.

[0086] Figure 8 (a) in FIG. 4 is a waveform diagram of the voltage indicated by the voltage given signal, taking the waveform of the voltage given signal as an example. Figure 8 (b) in FIG. 4 is a waveform diagram of the bias voltage indicated by the direct-axis bias signal, Figure 8 (c) in FIG. 4 is a waveform diagram of the voltage given signal with a direct current bias, that is, Figure 8 The waveform diagram of (c) in FIG. 4 is Figure 8 The voltage signal of (a) in FIG. 4 and Figure 9 (b) in FIG. 4 are superimposed to form.

[0087] As shown in Figure 10(a) to Figure 10(b)As shown, the control circuit 121 includes a quadrature axis current controller 901, a direct axis current controller 902, and a drive circuit 903. In the embodiment of the present application, the control circuit 121 is configured to receive a heating instruction, and determine the quadrature axis current component by the quadrature axis current controller 901 and the direct axis current component by the direct axis current controller 902 according to the heating power of the power battery 13 indicated by the heating instruction. The drive circuit 903 can include a park's transmission module and a clark's transmission module, the park's transmission module is configured to convert two components in an αβ coordinate system into a dq orthogonal rotating coordinate system, and the clark's transmission module is configured to convert time domain components of a three-phase system (in an abc coordinate system) into two components in an αβ stationary coordinate system. In the embodiment of the present application, the park's transmission module receives a quadrature axis current signal Uq and a direct axis current signal Ud, and performs park's inverse transformation on the Uq and Ud signals in a direct-quadrature (d-q) coordinate system to obtain voltage signals Uα and Uβ in an αβ coordinate system, and generates a PWM control signal according to the Uα and Uβ signals, the control signal is configured to control the conduction frequency and duty cycle of the switching tubes of the three-phase bridge arm 12.

[0088] As a possible implementation, in response to a phase difference between pulse currents generated by any two of the plurality of three-phase bridge arms 12 being greater than a preset value, or a phase difference between U-phase currents, V-phase currents, or W-phase currents output by any two of the plurality of three-phase bridge arms 12 being greater than a preset value, the frequency of the direct axis current component of the three-phase current output by at least one of the any two of the plurality of three-phase bridge arms 12 is adjusted.

[0089] wherein the direct axis current component of the three-phase current output by the three-phase bridge arm 12 is determined by a voltage given signal and a direct axis bias signal, refer to Figure 10(a) to Figure 10(b) As shown, Figure 10(a) to Figure 10(b) is a schematic diagram of the voltage given signal. Since the voltage given signal is used to indicate the frequency and amplitude of the voltage, by adjusting the frequency of the voltage given signal, the frequency of the direct axis current component of the pulse current can be adjusted. As can be seen from Figure 12 , when in response to a phase difference between pulse currents generated by any two of the plurality of three-phase bridge arms 12 being greater than a preset value, or a phase difference between U-phase currents, V-phase currents, or W-phase currents output by any two of the plurality of three-phase bridge arms 12 being greater than a preset value, by adjusting the frequency of the voltage given signal, the phase adjustment of the U, V, and W phase currents and the pulse current can be achieved, and thus the phase difference between the U-phase currents output by any two of the plurality of three-phase bridge arms 12 can be reduced, and the heating efficiency of the power battery 13 can be improved.

[0090] Referring to FIG. 10(a), when there is a phase difference between the two pulse currents (or U, V, W phase currents) input to the power battery 13, by increasing the frequency of the voltage indicated by the voltage given signal corresponding to one of the three-phase bridge arms 12 (the frequency of the direct-axis current component of the three-phase current), the frequency of the direct-axis current component of the pulse current generated by the one of the three-phase bridge arms 12 can be increased, and the phase difference between the pulse currents generated by the two three-phase bridge arms 12 can be reduced, thereby improving the heating efficiency of the power battery 13. Referring to FIG. 10(b), when there is a phase difference between the two pulse currents (or U, V, W phase currents) input to the power battery 13, by decreasing the frequency of the voltage indicated by the voltage given signal corresponding to one of the three-phase bridge arms 12 (the frequency of the direct-axis current component of the three-phase current), the frequency of the direct-axis current component of the pulse current generated by the one of the three-phase bridge arms 12 can be decreased, and the phase difference between the pulse currents generated by the two three-phase bridge arms 12 can be reduced, thereby improving the heating efficiency of the power battery 13. Similarly, by increasing / decreasing the frequency of the voltage indicated by the voltage given signal corresponding to the other of the three-phase bridge arms 12, the phase difference between the pulse currents generated by the two three-phase bridge arms 12 can also be reduced, thereby improving the heating efficiency of the power battery 13, which will not be described in detail here.

[0091] After increasing / decreasing the frequency of the voltage indicated by the voltage given signal corresponding to one / other of the three-phase bridge arms 12, in order to ensure that the subsequent pulse currents generated by the two three-phase bridge arms 12 do not generate a phase difference, as a possible implementation, the control method comprises: when the phase difference between the pulse currents generated by any two of the three-phase bridge arms 12 is less than or equal to a preset value, and the phase difference between the U phase current, the V phase current or the W phase current output by any two of the three-phase bridge arms 12 is less than or equal to a preset value, controlling the frequency of the direct-axis current component of the three-phase current output by each of the three-phase bridge arms 12 to be a preset frequency.

[0092] If the frequency of the two pulse currents is different, even if the phase difference of the pulse currents generated by the two three-phase bridge arms 12 is less than or equal to the preset value in the period, the phase difference of the pulse currents generated by the two three-phase bridge arms 12 will not be less than or equal to the preset value in the next period. Thus, once the phase difference of the pulse currents generated by any two three-phase bridge arms 12 of the plurality of three-phase bridge arms 12 is less than or equal to the preset value and the phase difference of the U-phase current, the V-phase current or the W-phase current output by any two three-phase bridge arms 12 is less than or equal to the preset value, the frequency of the direct-axis current component of the three-phase current output by each three-phase bridge arm 12 can be controlled to be a preset frequency, which can be the frequency of the direct-axis current component before adjustment or other preset frequency. In other words, after the phase difference of the pulse currents generated by any two three-phase bridge arms 12 of the plurality of three-phase bridge arms 12 is less than or equal to the preset value and the phase difference of the U-phase current, the V-phase current or the W-phase current output by any two three-phase bridge arms 12 is less than or equal to the preset value, it is only required to ensure that the frequency of the direct-axis current component of the three-phase current output by each three-phase bridge arm 12 is the same.

[0093] Referring to FIG. 11(a), when the two pulse currents (or the U-phase current, the V-phase current and the W-phase current) have a phase difference at the input power battery 13, by increasing the frequency of the voltage indicated by the voltage given signal corresponding to one of the three-phase bridge arms 12 (the frequency of the direct-axis current component of the three-phase current), the frequency of the direct-axis current component of the pulse current generated by the three-phase bridge arm 12 can be increased, and thus the phase difference of the pulse currents generated by the two three-phase bridge arms 12 can be reduced.

[0094] When the phase difference of the two pulse currents at the input power battery 13 is less than or equal to the preset value (the preset value is 0° in FIG. 11(a)), by adjusting the frequency of the voltage indicated by the voltage given signal corresponding to one of the three-phase bridge arms 12, the frequency of the direct-axis current component of the three-phase current output by each three-phase bridge arm 12 can be controlled to be a preset frequency, so that the subsequent generated pulse currents do not generate phase difference again.

[0095] Referring to Figure 11(b), when there is a phase difference between the two pulse currents input to the power battery 13, by reducing the frequency of the voltage indicated by the voltage setpoint signal corresponding to one of the three-phase bridge arms 12 (the frequency of the direct-axis current component of the three-phase current), the frequency of the direct-axis current component of the pulse current generated by one of the three-phase bridge arms 12 can be reduced, thereby reducing the phase difference between the pulse currents generated by the two three-phase bridge arms 12. Furthermore, when the phase difference between the two pulse currents input to the power battery 13 is less than or equal to a preset value, by adjusting the frequency of the voltage indicated by the voltage setpoint signal corresponding to one of the three-phase bridge arms 12, the frequency of the direct-axis current component of the three-phase current output by each three-phase bridge arm 12 can be controlled to be the preset frequency. Similarly, by increasing / decreasing the frequency of the voltage indicated by the voltage setpoint signal corresponding to the other three-phase bridge arm 12, if the phase difference between the pulse currents generated by the two three-phase bridge arms 12 is again less than or equal to the preset value, the frequency of the direct-axis current component of the three-phase current output by each three-phase bridge arm 12 can be controlled to be the preset frequency, thereby preventing subsequent pulse currents from generating a phase difference again.

[0096] As one possible implementation, the control method for reducing phase difference includes first outputting a first control signal to control the three-phase bridge arm 12 corresponding to motor 11 to output three-phase current, and then outputting a second control signal to control the three-phase bridge arm 12 corresponding to other motors to output three-phase current, wherein the direct-axis current components of the three-phase current indicated by the first control signal and the second control signal have the same frequency.

[0097] Due to the transmission delay caused by different transmission path lengths, even when control signals are sent simultaneously to the three-phase bridge arm 12 corresponding to motor 11 and the three-phase bridge arm 12 corresponding to other motors using a DSP-to-DSP hardware communication channel, the pulse currents generated by the three-phase bridge arm 12 corresponding to motor 11 and the three-phase bridge arm 12 corresponding to other motors may still have a phase difference. Therefore, a first control signal can be output first to control the three-phase current output of the three-phase bridge arm 12 corresponding to motor 11, and then a second control signal can be output to control the three-phase current output of the three-phase bridge arm 12 corresponding to other motors. In this way, the problem caused by transmission delay can be reduced, the phase difference of the output of each three-phase bridge arm 12 can be reduced, thereby improving the heating efficiency of the power battery 13.

[0098] like Figure 13 As shown, the electric vehicle 10 provided in this embodiment includes a heat exchange circuit 15. Due to the thermal effect of current, the three-phase current on the motor 11 causes the three-phase windings of the motor 11 to heat up. The heat exchange circuit 15 is used to conduct the heat generated on the three-phase windings of the motor 11 to the power battery 13, thereby improving energy utilization efficiency, saving energy, and increasing the heating efficiency of the power battery 13.

[0099] In one embodiment, such as ​ As shown, the heat exchange circuit 15 includes a heat transfer medium, a heat transfer medium flow circuit, a liquid pump 1301, and a heat exchanger 1302. The heat transfer medium is used to absorb the heat generated on the windings of the motor 11. The heat transfer medium flows in the heat transfer medium flow circuit. The liquid pump 1301 is used to provide power for the flow of the heat transfer medium. The heat exchanger 1302 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 13 to heat the power battery 13.

[0100] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for pulse heating a power cell of an electric vehicle, characterized in that, The electric vehicle comprises a plurality of motors, a plurality of three-phase bridge arms, three bridge arm midpoints of each three-phase bridge arm are used for connecting three-phase windings of one motor, each three-phase bridge arm is used for connecting the power battery through a DC bus, and the method comprises: controlling the bridge arm midpoints of each three-phase bridge arm to output three-phase current, the three-phase current is used for generating pulse current for heating the power battery on the DC bus, the size of quadrature axis current of the three-phase current is zero, and the frequency of direct axis current of the three-phase current is a preset frequency; in the process of controlling the bridge arm midpoints of each three-phase bridge arm to output the three-phase current, when the phase difference of pulse currents generated by any two three-phase bridge arms in the plurality of three-phase bridge arms is greater than a preset value, adjusting the frequency of the direct axis current component of the three-phase current output by at least one three-phase bridge arm in the any two three-phase bridge arms to be greater than or smaller than the preset frequency until the phase difference of the pulse currents generated by the any two three-phase bridge arms is less than or equal to the preset value; after the phase difference of the pulse currents generated by the any two three-phase bridge arms is less than or equal to the preset value, readjusting the frequency of the direct axis current component of the three-phase current output by each three-phase bridge arm to be the preset frequency.

2. The method of claim 1, wherein, The at least one three-phase bridge arm is a three-phase bridge arm corresponding to a drive motor, and the drive motor is used for driving connection of a wheel of the electric vehicle.

3. The method of claim 1, wherein, The frequency of the three-phase current is the same as that of the pulse current.

4. The method according to any of claims 1 to 3, characterized in that, The method specifically comprises: after the phase difference of the pulse currents generated by the any two three-phase bridge arms is less than or equal to the preset value and the phase difference of U-phase current, V-phase current or W-phase current output by the any two three-phase bridge arms is less than or equal to the preset value, readjusting the frequency of the direct axis current component of the three-phase current output by each three-phase bridge arm to be the preset frequency.

5. The method according to any one of claims 1 to 3, characterized in that, The method comprises: controlling the frequency of the pulse currents output by the plurality of three-phase bridge arms to be the same.

6. An electric vehicle, characterized by The electric vehicle comprises a control device, a plurality of motors and a plurality of three-phase bridge arms corresponding to the plurality of motors one by one, bridge arm midpoints of each three-phase bridge arm are used for connecting three-phase windings of one motor, each three-phase bridge arm is used for connecting a power battery through a DC bus, and the control device is used for: controlling the bridge arm midpoints of each three-phase bridge arm to output three-phase current, the three-phase current is used for generating pulse current for heating the power battery on the DC bus, the size of quadrature axis current of the three-phase current is zero, and the frequency of direct axis current of the three-phase current is a preset frequency; in the process of controlling the bridge arm midpoints of each three-phase bridge arm to output the three-phase current, when the phase difference of pulse currents generated by any two three-phase bridge arms in the plurality of three-phase bridge arms is greater than a preset value, adjusting the frequency of the direct axis current component of the three-phase current output by at least one three-phase bridge arm in the any two three-phase bridge arms to be greater than or smaller than the preset frequency until the phase difference of the pulse currents generated by the any two three-phase bridge arms is less than or equal to the preset value; After the phase difference of the pulse currents generated by the arbitrary two three-phase bridge arms is less than or equal to a preset value, the frequency of the direct-axis current component of the three-phase current output by each three-phase bridge arm is controlled to be a preset frequency.

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