A lithium battery self-heating method and control device for an electric vehicle when stationary

Abstract

This invention provides a method and control device for self-heating a lithium battery in an electric vehicle when stationary. The self-heating method includes the following steps: a motor controller uses a sinusoidal pulse width modulation method combined with a current closed-loop control strategy to control a three-phase inverter; by controlling the alternating switching of a pair of specific spatial switching vectors, the two-phase stator windings of the permanent magnet synchronous motor are connected in parallel and then in series with the third-phase stator winding, effectively reducing the three-phase inverter to a single-phase inverter at the hardware topology physical level; under this equivalent topology, the stator inductance of the permanent magnet synchronous motor is used as an energy storage element to achieve repeated charging and discharging with the lithium battery; simultaneously, the alternating switching of specific spatial switching vectors is controlled to physically fix the spatial direction of the stator's composite magnetomotive force, passively aligning the rotor's magnetomotive force with the stator's composite magnetomotive force, thereby keeping the motor stationary; the corresponding control device consists of the above-mentioned main circuit and the motor controller executing the control program, and the main circuit does not require additional power switching devices, achieving zero additional hardware cost and zero additional space occupation, eliminating dependence on rotor position sensors, reducing system complexity and improving safety during parking heating.

Description

Technical Field

[0001] This invention relates to the intersection of electric drive and battery thermal management in new energy vehicles, and in particular to a method and control device for self-heating of lithium batteries in electric vehicles when stationary. Background Technology

[0002] As the core power source for electric vehicles, lithium-ion batteries exhibit extremely high sensitivity to environmental temperature in their electrochemical characteristics. At low temperatures, the electrolyte viscosity increases, ionic conductivity decreases, and charge transfer impedance significantly increases, leading to a substantial drop in output power and usable energy. More seriously, charging and discharging lithium-ion batteries at low temperatures slows down the lithium-ion intercalation kinetics between the graphite layers of the negative electrode, making lithium deposition on the negative electrode surface highly likely. This phenomenon not only irreversibly consumes active lithium ions, resulting in permanent battery capacity decay, but the deposited metallic lithium can also form lithium dendrites. Long-term dendrite growth can puncture the internal separator of the battery, causing a short circuit between the positive and negative electrodes, and ultimately triggering irreversible catastrophic safety accidents such as thermal runaway.

[0003] To overcome the problems caused by the aforementioned low temperatures, the industry currently adopts battery heating strategies. Existing automotive lithium battery heating strategies are mainly divided into two categories: external heating methods and internal heating methods. External heating methods mainly include air heating, liquid circulation heating, and PCM heating. However, these external heating solutions generally suffer from objective problems such as low temperature rise rate, large temperature difference between the inside of the battery cell and the inside and outside of the battery pack, high energy consumption, and complex and cumbersome system structure. Other internal heating methods mostly rely on hardware, usually requiring an external dedicated AC power supply to generate AC current, or adding additional relays, contactors, switching components, etc., to temporarily switch the topology of the vehicle's high-voltage circuit during heating to achieve battery charging and discharging and thus achieve self-heating.

[0004] In view of the aforementioned objective defects of the prior art, the present invention aims to solve the problems of high hardware cost and large volume due to additional power devices when the battery is self-heating in an electric vehicle in a stationary state, high system complexity due to reliance on complex algorithms and high-precision sensors caused by the electric vehicle not moving unexpectedly during the heating process. Summary of the Invention

[0005] The main objective of this invention is to provide a method and control device for self-heating of lithium batteries in electric vehicles when stationary, solving the problems of high hardware cost, large footprint, reliance on complex algorithms, and high system complexity.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for self-heating a lithium battery in an electric vehicle when stationary. The main circuit of this self-heating method consists of a lithium battery, a three-phase inverter, and a permanent magnet synchronous motor. The method includes the following steps: S1: The motor controller uses sinusoidal pulse width modulation (SPWM) combined with a current closed-loop control strategy to control the three-phase inverter; S2: In the three-phase inverter, the motor controller uses only two specific switching vectors (1,0,0) and (0,1,1) to alternately control and switch the three-phase bridge arms of the three-phase inverter. Among them, the (1,0,0) switching vector is defined as the upper bridge arm of phase A being turned on and the upper bridge arms of phases B and C being turned off; the (0,1,1) switching vector is defined as the upper bridge arm of phase A being turned off and the upper bridge arms of phases B and C being turned on, with the upper and lower bridge arms of each phase maintaining a complementary conduction state. Through the alternating switching of the above two specific switching vectors, the three-phase inverter is equivalently reduced to a single-phase inverter at the hardware topology physical level. S3: By alternating switching of the switching vector, under the equivalent topology of the single-phase inverter, the stator inductance of the permanent magnet synchronous motor is used as an energy storage element to achieve repeated charging and discharging with the lithium battery. S4: By alternating switching of the switching vector, the direction of the stator synthesized magnetomotive force of the permanent magnet synchronous motor is fixed in space. The physical characteristic of the rotor magnetomotive force automatically aligning with the stator synthesized magnetomotive force is utilized to keep the permanent magnet synchronous motor in a stationary state. In this process, there is no need to introduce complex dq axis coordinate transformation and feedback signals from rotor position sensors.

[0007] In the preferred embodiment, before executing step S1, the self-heating method for the lithium battery of the electric vehicle when stationary further includes a pre-trigger condition judgment step S0 for initiating self-heating, specifically: S0: The motor controller or battery management system obtains the real-time temperature of the lithium battery and determines that the real-time temperature is lower than the preset low temperature safety threshold; at the same time, it obtains the current operating status signal of the vehicle and determines that the vehicle is in a stationary parking state; when the above conditions are met at the same time, the control steps of the lithium battery self-heating method of the electric vehicle when stationary are triggered and started.

[0008] In the preferred embodiment, in step S2: After converting the three-phase inverter into a single-phase inverter, the mutual inductance between the stator inductors of the permanent magnet synchronous motor is ignored, and the three-phase impedance of the main circuit is converted into a single-phase impedance. definition These are the impedances of the three phases A, B, and C of the motor, respectively. These are three-phase inductors; These are the three-phase stator resistors.

[0009] Under the alternating control of this specific vector (1,0,0) and (0,1,1), phase B and phase C are in parallel in the physical circuit, and then connected in series with phase A; Therefore, the equivalent constant in the equivalent single-phase inverter is: the combined impedance. Composite inductor Synthetic resistance The results are calculated using the following formulas: (1); (2); (3); in, The equivalent combined impedance in a single-phase inverter is used to evaluate the AC response characteristics of the overall circuit. The equivalent composite inductance is used for calculating energy storage and current change rate; This is the equivalent combined resistance, used for calculating energy consumption and voltage drop.

[0010] In the preferred embodiment, the charging and discharging process in step S3 is specifically as follows: By controlling the duty cycles of two specific switching vectors (1,0,0) and (0,1,1), the rising and falling slopes of the current within a specific carrier cycle are controlled, generating an AC trapezoidal wave current on the lithium battery side, consisting of the rising edge, falling edge, and flat top. The AC trapezoidal wave current generates Joule heat on the internal equivalent ohmic resistance and polarization resistance of the lithium battery, achieving self-heating.

[0011] In the preferred scheme, the calculation for generating the AC trapezoidal wave in step S3 is as follows: After obtaining the equivalent constants of the circuit, the motor controller proceeds to step S3 to calculate the AC trapezoidal wave based on the current closed-loop control; defining... This is the DC bus voltage, i.e., the lithium battery terminal voltage; The carrier frequency is preset and calibrated by the MCU. Provide a target set current to maintain the current closed loop; This is the real-time sampled DC-side current feedback value; When the MCU uses SPWM modulation and a (1,0,0) switching vector, the battery discharges to the motor, and the motor inductor acts as an energy storage element to absorb energy. At this time, the circuit generates positive voltage excitation, and the absolute value of the current increases. When a (0,1,1) switching vector is used, the motor inductor charges the battery and releases energy, generating reverse excitation, and the absolute value of the current decreases. Therefore, the current rise amplitude within one carrier cycle and the magnitude of the decline The slope boundary of the trapezoidal wave is planned using the following formula: (4); (5); (6); (7); in, The duration of the (1,0,0) switching vector within one carrier cycle; The duration of the (0,1,1) switching vector within one carrier cycle; The current rise amplitude represents the slope limit of the rising edge of the trapezoidal wave. The current drop amplitude characterizes the slope limit of the falling edge of the trapezoidal wave; Current variation and It is strictly limited within a pre-defined lithium plating boundary as a constraint to protect battery health.

[0012] In the preferred embodiment, the physical self-locking mechanism in step S4 is specifically as follows: The above control steps cause the A-phase current to... With phase B and C current An absolute coupling relationship is established, as can be seen from the equivalent circuit. ,definition This represents the amplitude of the three-phase combined current. The stator magnetomotive force generated by the three-phase combined current, due to Always equal and phase with Forming an angle of 120°, The spatial vector direction is physically fixed and aligned on the A-phase axis of the stator, resulting in this fixed position. It will serve as the sole stationary target for rotor magnetomotive force tracking; The rotor magnetomotive force generated by the rotor permanent magnet represents the inherent magnetic field strength of the rotor.

[0013] When the stator generates magnetomotive force When fixed on axis A, electromagnetic torque The essence is rotor magnetomotive force Attempting to interact with the stator magnetomotive force Alignment, so that electromagnetic torque The generation of torque follows the physical law that magnetic fields always tend to follow the path of least magnetic reluctance. The formula for calculating the torque generated by the interaction of two magnetomotive forces is as follows: (8); in, Rotor magnetomotive force and stator magnetomotive force The spatial electrical angle between them; This represents the number of pole pairs on the motor rotor. From this formula, we can see that the torque The magnitude is directly determined by the upstream input variable, the stator magnetomotive force. Rotor magnetomotive force and the angle between the two Co-coupling determines; In the initial heating stage, if the rotor is not aligned (i.e. ), and The interaction will produce transient torque This causes the rotor to rotate; as the rotor approaches the path of minimum magnetic reluctance under torque drive, Gradual alignment included angle Automatically approaches 0; when hour, This results in output torque By resetting to zero, the motor enters and remains in a state of absolute stillness. Throughout the entire process, the electrical angle of the motor rotation is physically limited to an extremely small range of no more than 180°, the process is extremely fast and has no significant impact on the overall vehicle mechanics.

[0014] In a preferred embodiment, the present invention provides a lithium battery self-heating control device for an electric vehicle when stationary, which performs the above-described self-heating method. The control device includes a main circuit section and a control logic execution section, wherein: The main circuit consists of a lithium battery, a three-phase inverter, and a permanent magnet synchronous motor. The DC end of the lithium battery is connected to the DC side of the three-phase inverter, and the AC side of the three-phase inverter is connected to the three-phase stator windings of the permanent magnet synchronous motor. The control logic execution section uses the existing motor controller for electric vehicles; The motor controller is internally equipped with an SPWM modulation module and a current closed-loop control module. The motor controller is programmed and configured to take over the gate drive signal of the three-phase inverter after receiving the self-heating command, and output only two specific switching vector control signals (1,0,0) and (0,1,1) to be alternately applied to the power switching transistors of the three-phase inverter. The control device reduces the physical hardware of the three-phase inverter to a single-phase inverter by reconstructing the motor controller at the software control level. This allows the permanent magnet synchronous motor to generate AC current for heating on the lithium battery side without adding any additional power devices, using the stator inductance of the permanent magnet synchronous motor as an energy storage element. At the same time, the motor is kept stationary by utilizing the physical law that the stator's synthesized magnetomotive force is spatially fixed and the rotor's magnetomotive force automatically tends to align with the stator's magnetomotive force.

[0015] This invention provides a method and control device for self-heating of a lithium battery in an electric vehicle when stationary. In terms of circuit topology, it completely reuses the original three-phase inverter and stator winding hardware of the drive motor, eliminating the need for any additional relays, contactors, power switches, or large-capacity energy storage and filtering capacitors between the battery and the inverter, or between the inverter and the motor neutral point. This achieves zero additional hardware cost and zero additional space occupation, reducing manufacturing and BOM costs, eliminating electrical fault points caused by the introduction of additional hardware, and improving the overall reliability of the electric vehicle system. Regarding the safety mechanism for maintaining vehicle stationary operation, an innovative physical self-locking mechanism is proposed, utilizing only the single-phase dimensionality reduction caused by the alternating switching of two specific vectors to generate the stator's synthesized magnetomotive force. Physically locked to the A-axis, the rotor automatically aligns using the principle of minimum magnetic reluctance, fundamentally eliminating the need for complex dq-axis coordinate transformations and freeing the system from dependence on rotor position sensors. This ensures the system's static safety during vehicle parking heating even under harsh conditions such as sensor failure or strong electromagnetic interference. Furthermore, a heating method with a customized waveform slope is proposed. Compared to uncontrollable high-frequency spikes or simple sine waves, AC trapezoidal waves have controllable flat tops and slopes. This allows the motor controller to control the amplitude and frequency of the trapezoidal wave within the lithium plating physical boundaries of a specific lithium battery model, based on pre-calibrated safe operating parameters. This balances rapid heating with prevention of polarization lithium plating damage, maximizing the protection of the battery pack's health and cycle life while achieving self-heating. Attached Figure Description

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a schematic diagram of the main circuit topology of a lithium battery self-heating control device for an electric vehicle when stationary, according to the present invention. Figure 2 This is a schematic diagram of the equivalent single-phase inverter topology of the main circuit of the lithium battery self-heating control device for an electric vehicle when stationary, under a specific vector alternation switching. Figure 3 This invention relates to a current flow diagram of the equivalent single-phase inverter of a lithium battery self-heating control device for an electric vehicle when stationary, under specific switching vectors (1,0,0) and (0,1,1). Figure 4 This is a schematic diagram of the three-phase combined current and its magnetomotive force and rotor magnetomotive force in a self-heating method for lithium batteries of an electric vehicle when stationary, according to the present invention. Figure 5 This invention relates to a method for self-heating a lithium battery in an electric vehicle when it is stationary. Simulation results for phase A not aligned; Figure 6This invention relates to a method for self-heating a lithium battery in an electric vehicle when it is stationary. Simulation results when aligning phase A; Figure 7 This is a waveform response diagram of the charging and discharging current in a self-heating method for a lithium battery of an electric vehicle when stationary, according to the present invention. Figure 8 This is a flowchart of a method for self-heating a lithium battery in an electric vehicle when stationary, according to the present invention. Detailed Implementation

[0017] Example 1 To further demonstrate the reliability of this invention in practical applications, the following Simulink simulation implementation example is provided, which illustrates in detail the entire process of specific switch vector switching and AC trapezoidal wave generation.

[0018] like Figure 1-8 As shown, a method and control device for self-heating of lithium battery in an electric vehicle when stationary is disclosed. This embodiment fully reuses the existing power drive system architecture of electric vehicles in its control device. The main circuit of this control device is strictly limited to only three parts, wherein: Lithium batteries provide and absorb heating energy; three-phase inverters serve as the physical carrier for power conversion; permanent magnet synchronous motors utilize their stator three-phase windings as energy storage and smoothing inductors. The core control logic of this system is executed by the motor controller (MCU) that comes with the electric vehicle. The MCU has a software reconfiguration instruction set. After entering the self-heating mode, the MCU will take over the gate drive signals of the six power switching transistors in the three-phase inverter. Under this architecture, this invention does not require any additional physical contactors, relays, fourth bridge arms or large-capacity high-frequency filter capacitors between the lithium battery and the three-phase inverter, or between the three-phase inverter and the permanent magnet synchronous motor, thus achieving zero cost and zero modification at the hardware level.

[0019] In the preferred embodiment, in step S1: the motor controller or battery management system obtains the real-time temperature of the current lithium battery and determines that the real-time temperature is lower than the preset low temperature safety threshold; at the same time, it obtains the current operating status signal of the vehicle and determines that the vehicle is in a stationary parking state; when the above conditions are met simultaneously, the control steps of the lithium battery self-heating method of the electric vehicle when stationary are triggered and started. The MCU performs the pre-action, enables the internal SPWM modulation module, and constructs a current closed-loop control framework with the A-phase current as feedback. The MCU completely abandons the space vector pulse width modulation and complex dq axis decoupling algorithm used in traditional motor drives, and only uses two specific switching vectors (1,0,0) and (0,1,1) for alternating control switching; In this implementation example, it is assumed that the preset hardware operating environment and battery status input parameters of the electric vehicle power system are: the current terminal voltage of the lithium battery, i.e., the DC power supply voltage. The motor controller, based on the current extremely cold temperature and the maximum allowable charge / discharge limits provided by the BMS, uses a lookup table to send a pre-calibrated carrier frequency to the SPWM modulation module. The target setpoint current given by the current closed loop. The three-phase hardware attributes of the motor are: three-phase inductance. Three-phase stator resistance .

[0020] In the preferred embodiment, step S2 of the present invention involves the alternating switching of a specific switching vector: When the MCU sends a (1,0,0) switching vector, it forces the upper bridge arm of phase A of the three-phase inverter to turn on, while its complementary lower bridge arm of phase A turns off; it forces the upper bridge arms of phases B and C to turn off, while their complementary lower bridge arms of phases B and C turn on; at this time, the positive terminal of the lithium battery is connected to the stator winding of phase A of the motor through the phase A bridge arm, and the negative terminal of the lithium battery is connected to the stator winding of phases B and C of the motor through the lower bridge arms of phases B and C. When the MCU sends a (0,1,1) switching vector, the state undergoes a complementary flip: the upper bridge arm of phase A is turned off and the lower bridge arm is turned on; the upper bridge arms of phases B and C are turned on and the lower bridge arms are turned off. Through the complementary switching of the two specific states at high frequency, the three-phase inverter is equivalently reduced to a single-phase inverter in the electrical circuit. In the equivalent topology, the B-phase winding and C-phase winding of the motor are connected in parallel in the physical circuit, and then the B and C parallel body is connected in series with the A-phase winding. According to the established formulas (1) to (3) for the equivalent combined impedance variable flow, the parameters of the equivalent circuit of the single-phase inverter are: Equivalent composite inductance: ; Equivalent combined resistance: .

[0021] In the preferred embodiment, during the repeated charging and discharging of the lithium battery in step S3 of the present invention: Regarding current waveform control, after entering single-phase equivalent control, the equivalent combined inductance is utilized. As an energy storage element, it works with lithium batteries to perform high-frequency charge throughput, thereby generating Joule heat on the equivalent ohmic internal resistance and polarization internal resistance inside the battery. The MCU uses a pre-calibrated SPWM modulation wave within one complete PWM carrier cycle: exist During the time period, the MCU continuously outputs a specific switching vector of (1,0,0). At this time, the lithium battery discharges to the stator inductor of the motor after it has been converted to a single phase. The inductor is in a state of magnetic energy storage, and the discharge current on the battery side shows a controlled upward slope. exist During the time period, the MCU switches and continuously outputs a specific switching vector (0,1,1). At this time, the motor stator inductor generates a back electromotive force to recharge the lithium battery. The inductor is in a demagnetized release state, and the charging current on the battery side shows a controlled downward slope.

[0022] With the high-frequency SPWM cycle, an AC trapezoidal current is formed on the battery side, consisting of rising edge, falling edge, and a flat top constrained by the current closed loop. In this embodiment, when the system stabilizes and enters current closed-loop control, the given current is maintained. hour; The equivalent hardware variables calculated above , ,as well as Substitute into formulas (4) to (7) to calculate the current rise range boundary; steady-state duty cycle (Right now If the value is approximately 0.5, then the duration of action of (1,0,0) is... According to formula (6), substituting the variables, we can obtain: ; Simulation measurements showed that the final waveform generated on the battery side was a standard AC trapezoidal wave with a frequency of 10kHz. The measured duty cycle under current closed-loop operation remained stable at 0.506. The measured current rise and fall amplitudes were equal to 33A, consistent with the theoretically derived value. The variable flow calculation results are highly consistent; since the trapezoidal wave pulsation amplitude of the 33A is much lower than the limit boundary that the battery of this model may trigger lithium plating at the current temperature, the occurrence of lithium plating is eliminated from the physical root at the micro level, which fully proves that the present invention achieves precise waveform engraving and battery safety protection through simple specific dual vector control.

[0023] In the preferred embodiment, the physical self-locking mechanism in step S4 of the invention includes: When the MCU forcibly takes over and alternately applies the (1,0,0) and (0,1,1) vectors, the current ratio in the same phase direction will change. The absolute constancy of the stator magnetomotive force It is instantly fixed in the A-axis direction of the stator's physical space; Assuming the initial state of rotor magnetomotive force Located in misaligned or Position, included angle Not zero; according to the electromagnetic torque flow formula (8), the non-zero value at this time is... Transient torque that leads to nonzero The transient torque The drive rotor rotates by less than 180° in a very short time. With this slight deflection of the mechanical angle, the included angle... It is rapidly compressed to zero, once the rotor magnetomotive force Fully aligned to stator magnetomotive force The direction of the output torque It immediately decays and locks to 0; due to the disappearance of rotational power, the motor stops instantly by relying on the slight resistance of the vehicle's transmission system and enters a state of absolute physical stillness. This process is extremely fast, and the electrical angle corresponding to the mechanical displacement of the rotor will not exceed 180 degrees. The actual physical displacement reflected on the wheel is almost zero. In the simulation, the system briefly outputs torque and a small speed in the early stage of operation. Once the A phase is aligned, the speed and torque are locked to 0, which verifies the feasibility of the physical self-locking mechanism without position sensors. If the rotor is exactly in the initial aligned position, then It does not generate any torque from beginning to end.

[0024] The simulation results are in high agreement with the theory. In summary, the present invention, with its extremely simple hardware reuse approach and physical rule-based alignment mechanism, fundamentally overturns the traditional design experience of stacking hardware and relying on complex algorithms in high-frequency AC heating systems. The AC trapezoidal wave it generates not only ensures the high efficiency of heat generation, but also guarantees the absolute safety of the battery pack at the electrochemical level, which has extremely high industrial application value and patent protection significance.

[0025] In the description of this invention, it should be noted that the terms "first," "second," "phase A," "phase B," and "phase C," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The terms "connection" and "linked" should be interpreted broadly; for example, they can refer to a direct connection or an indirect connection through an electrical intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0026] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for self-heating a lithium battery in an electric vehicle when stationary, characterized in that, The method includes the following steps: S1. The motor controller uses sinusoidal pulse width modulation combined with current closed-loop control strategy to control the three-phase inverter. S2. Control the alternating switching of a pair of specific space switch vectors to connect the two-phase stator windings of the permanent magnet synchronous motor in parallel and then connect them in series with the third-phase stator winding, thus reducing the three-phase inverter to a single-phase inverter. S3. Under the equivalent topology of a single-phase inverter, the stator inductance of a permanent magnet synchronous motor is used as an energy storage element to achieve repeated charging and discharging with a lithium battery. S4. Control the alternating switching of specific spatial switching vectors to physically fix the spatial direction of the stator composite magnetomotive force, so that the rotor magnetomotive force is passively aligned with the stator composite magnetomotive force, and the motor remains stationary.

2. The method for self-heating of a lithium battery in an electric vehicle when stationary, as described in claim 1, is characterized in that... Before step S1, there is also a pre-trigger condition judgment step for starting self-heating: S0, the motor controller or battery management system obtains the real-time temperature of the current lithium battery and determines that the real-time temperature is lower than the preset low temperature safety threshold; at the same time, it obtains the current operating status signal of the vehicle and determines that the vehicle is in a stationary parking state. When the above temperature threshold condition and the stationary parking condition are met simultaneously, the subsequent control steps of the lithium battery self-heating method for the electric vehicle when stationary are triggered and started.

3. The method for self-heating of a lithium battery in an electric vehicle when stationary, as described in claim 1, is characterized in that... After converting the three-phase inverter to a single-phase inverter in step S2, the process also includes converting the three-phase impedance of the main circuit to single-phase impedance. A specific pair of space switch vectors includes: When one phase is conducting and the other two phases are disconnected, it is defined as the first phase upper arm being conducting and the second and third phase upper arms being disconnected. When one phase is disconnected and the other two phases are conducting, it is defined as the upper arm of the first phase being off and the upper arms of the second and third phases being conducting, with the upper and lower arms of each phase maintaining a complementary conducting state. Based on the topological relationship of the two-phase stator windings connected in parallel and the third-phase stator winding connected in series, and considering the three-phase impedance, three-phase inductance, and three-phase stator resistance of the motor, the equivalent constant of the entire circuit in the equivalent single-phase inverter is calculated. This equivalent constant includes the combined impedance. Composite inductor and combined resistance .

4. The method for self-heating of a lithium battery in an electric vehicle when stationary, as described in claim 1, is characterized in that... The repeated charge-discharge process described in step S3 specifically includes the following steps: By controlling the duty cycle of the aforementioned pair of specific switching vectors, the rising and falling slopes of the charging and discharging current within a specific carrier cycle are controlled, thereby generating an AC trapezoidal wave current on the lithium battery side, consisting of the rising edge, falling edge, and flat top. Joule heating is generated inside a lithium battery using an alternating trapezoidal wave current.

5. A method for self-heating a lithium battery in an electric vehicle when stationary, as described in claim 4, characterized in that, The generated AC trapezoidal current includes the following control steps: After obtaining the equivalent constants of the circuit, the motor controller enters the calculation of generating an AC trapezoidal wave based on the current closed-loop control; the lithium battery terminal voltage is defined and obtained. carrier frequency Target current and DC side current feedback value ; When sinusoidal pulse width modulation is used and a switching vector with one phase on and the other two phases off is used, the lithium battery discharges to the motor, the motor inductor absorbs energy as an energy storage element, the circuit generates positive voltage excitation, and the absolute value of the current increases. When sinusoidal pulse width modulation is used and a switching vector is used where one phase is disconnected and the other two phases are connected, the motor inductor charges the lithium battery and releases energy, generating reverse excitation, and the absolute value of the current decreases. Calculate the rise in current within one carrier cycle. and the magnitude of the decline To plan the slope boundary of the trapezoidal wave; Among them, the increase Used to characterize the slope limit of the rising edge of a trapezoidal wave; the falling edge Used to characterize the slope limit of the falling edge of a trapezoidal wave; Control the rise of the generated current With the magnitude of current drop It is confined within a pre-defined lithium plating boundary.

6. The method for self-heating of a lithium battery in an electric vehicle when stationary, as described in claim 1, is characterized in that... The physical self-locking mechanism in step S4 includes the following steps: By alternating the switching of the space switch vector, the currents of the two-phase stator windings are coupled with the current of the third-phase stator winding. Since the currents of the two-phase stator windings in parallel are always equal and their phases form a 120-degree angle with the current of the third-phase stator winding, the stator composite magnetomotive force generated by the three-phase composite current is thus achieved. The spatial vector direction is physically fixed and aligned on the axis of the third phase, and the stator synthesized magnetomotive force As rotor magnetomotive force The only stationary target being tracked.

7. A method for self-heating a lithium battery in an electric vehicle when stationary, as described in claim 6, is characterized in that... Step S4, which involves keeping the permanent magnet synchronous motor stationary, specifically includes the following steps: In the initial heating stage, the stator synthesized magnetomotive force is based on the stator fixed on the third phase axis. If the rotors are not aligned, the rotor magnetomotive force... Combined magnetomotive force with stator The interaction generates transient electromagnetic torque. ; As the rotor is subjected to electromagnetic torque Driven by the path of minimum magnetic reluctance, the rotor magnetomotive force tends to move towards the path of minimum magnetic reluctance. Gradually align the stator's combined magnetomotive force To make the rotor magnetomotive force Combined magnetomotive force with stator The electrical angle between the spaces automatically approaches zero; When the rotor magnetomotive force When fully aligned and with the spatial electrical angle at zero, the electromagnetic torque output by the motor Then it returns to zero, and the motor enters and remains in a physically stationary state.

8. A self-heating control device for a lithium battery of an electric vehicle when stationary, performing the self-heating method as described in any one of claims 1 to 7, characterized in that, The control device includes a main circuit and a control logic execution section: The main circuit includes a lithium battery, a three-phase inverter, and a permanent magnet synchronous motor; the DC end of the lithium battery is connected to the DC side of the three-phase inverter, and the AC side of the three-phase inverter is connected to the three-phase stator windings of the permanent magnet synchronous motor; the main circuit does not require additional power switching devices for the self-heating circuit. The control logic execution part is the existing motor controller of electric vehicles. The motor controller stores a computer control program. When the motor controller executes the program, it is used to implement the self-heating method according to any one of claims 1 to 7.

9. A self-heating control device for a lithium battery in an electric vehicle when stationary, as described in claim 8, is characterized in that... The motor controller is equipped with a sinusoidal pulse width modulation module and a current closed-loop control module, and is programmed to: Upon receiving the self-heating command, it takes over the gate drive signal of the three-phase inverter, outputs and alternately applies a pair of specific space switch vectors to the power switch transistors of the three-phase inverter, effectively reducing the three-phase inverter to a single-phase inverter.

10. A self-heating control device for a lithium battery in an electric vehicle when stationary, as described in claim 8, is characterized in that... The sinusoidal pulse width modulation module and the current closed-loop control module within the motor controller are further configured in a coordinated manner as follows: The duty cycle of a specific switching vector is adjusted and controlled in real time to control the rising and falling slopes of the charging and discharging current within the carrier cycle; an AC trapezoidal wave current composed of the rising edge, falling edge, and flat top of the controlled slope is stably generated on the lithium battery side, and the AC trapezoidal wave is used to continuously generate Joule heat on the internal impedance of the lithium battery. At the same time, the static state of the motor is maintained by utilizing the physical law that the stator's synthesized magnetomotive force is spatially fixed and the rotor's magnetomotive force automatically tends to align with the stator's magnetomotive force.

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