Method for suppressing motor back electromotive force, motor control system and electric vehicle

Abstract

This application discloses a method for suppressing back electromotive force (EMF) in a motor, a motor control system, and an electric vehicle, applied in the field of electric vehicle technology, to solve the problem of poor reliability in the suppression of back EMF in existing technologies. Specifically, it involves: acquiring the current phase current and current speed of the motor; determining the current operating mode of the motor based on the current phase current and current speed; when the current operating mode is power generation mode, acquiring the current temperature of the power devices, and determining the current delay time based on the current temperature and current speed; after the current delay time, controlling at least one phase winding of the motor to be short-circuited to ground. By utilizing the winding's own impedance to dissipate the generated energy, effective suppression of back EMF is achieved without relying on external protection devices such as TVS diodes, significantly improving system reliability. It achieves a dynamic balance between the back EMF suppression effect and the safety protection of the power devices, effectively improving the system's reliability and service life.

Description

Technical Field

[0001] This application relates to the field of electric vehicle technology, and in particular to a method for suppressing back electromotive force of a motor, a motor control system, and an electric vehicle. Background Technology

[0002] With the widespread application of motor control technology, three-phase motors are increasingly used in industrial automation, automotive electronics, and home appliances. During actual operation, when a three-phase motor is decelerating, braking, under reverse load, or in specific conditions, it enters generator mode. In this mode, the motor operates as a generator, generating an induced electromotive force (EMF), or back EMF, in its windings. In generator mode, the motor speed is directly proportional to the induced EMF; the higher the speed, the greater the amplitude of the back EMF. This back EMF, when superimposed on the supply voltage, generates a momentary high voltage in the motor drive circuit. This momentary high voltage often exceeds the rated withstand voltage of the control chip and power switching devices inside the electronic control unit (ECU), easily causing breakdown damage to semiconductor devices and severely affecting the system's reliability and lifespan.

[0003] To suppress the back electromotive force in generator mode, existing technologies typically employ a transient voltage suppressor diode (TVS diode) connected in parallel at the motor power supply terminal. The TVS diode's avalanche breakdown characteristic clamps overvoltage within a safe range, thus protecting the internal circuitry of the ECU. However, to meet the significant energy discharge requirements of generator mode, high-power TVS diodes are required. High-power TVS diodes usually have large package sizes, occupying excessive PCB area in space-constrained applications such as automotive ECUs, thus hindering miniaturization. As passive protection devices, TVS diodes exhibit power dissipation characteristics that degrade after repeated high-energy transient shocks. Their clamping voltage and discharge capability decrease with increasing usage cycles, leading to a significantly higher failure rate, making it difficult to meet the demands of long-life, high-reliability applications. Furthermore, TVS diodes dissipate generated energy as heat, resulting in energy waste and exacerbating the system's thermal management burden.

[0004] Therefore, there is an urgent need for a method to suppress the back electromotive force of a motor that does not rely on a TVS diode, in order to overcome the problem of poor reliability of the existing technology in suppressing the back electromotive force of a motor. Summary of the Invention

[0005] This application provides a method for suppressing back electromotive force of a motor, a motor control system, and an electric vehicle, in order to solve the problem of poor reliability in suppressing back electromotive force of a motor in the prior art.

[0006] The technical solutions provided in this application are as follows: On one hand, embodiments of this application provide a method for suppressing the back electromotive force of a motor, including: Obtain the current phase current and current speed of the motor; The current operating mode of the motor is determined based on the current phase current and the current speed; When the current operating mode is power generation mode, the current temperature of the power device is obtained, and the current delay time is determined based on the current temperature and the current speed. After the current delay time, at least one phase winding of the control motor is shorted to ground.

[0007] Optionally, the current operating mode of the motor can be determined based on the current phase current and the current speed, including: Obtain the historical phase current in the first time period, and determine the current change rate based on the current phase current and the historical phase current; The current output torque of the motor is determined based on the current phase current and the preset current-torque mapping table. The dynamic judgment threshold is determined based on the absolute value of the current speed and the absolute value of the current output torque. The current operating mode of the motor is determined by weighting the current speed, current output torque, current change rate, and dynamic judgment threshold.

[0008] Optionally, the current operating mode of the motor is determined by a weighted judgment based on the current speed, current output torque, current change rate, and dynamic judgment threshold, including: Based on the current speed, current output torque, and preset mode determination criteria, a first determination result is generated; A second judgment result is generated based on the rate of change of current and the dynamic judgment threshold. The first and second judgment results are weighted and fused to obtain the current weighted score; When the current weighted score exceeds the preset score threshold, the current working mode is confirmed as power generation mode; when the current weighted score does not exceed the preset score threshold, the current working mode is confirmed as power consumption mode.

[0009] Optionally, the current delay time can be determined based on the current temperature and current rotation speed, including: Based on the current temperature, the preset temperature-delay mapping table is queried to determine the drive transmission delay and the power device turn-on delay; The speed compensation delay is determined based on the absolute value of the current speed. The current delay time is determined based on the drive transmission delay, power device turn-on delay, and speed compensation delay.

[0010] Optionally, at least one phase winding of the control motor is shorted to ground, including: Obtain braking strength requirements; The target short-circuit mode is determined based on the braking intensity requirements; the target short-circuit mode includes single-phase short-circuit mode, two-phase short-circuit mode or three-phase short-circuit mode; The target number of target phases is determined based on the target short-circuit mode and the instantaneous amplitude of the back electromotive force of each phase winding; The winding of the target phase is short-circuited to ground.

[0011] Optionally, the target number of target phases is determined based on the target short-circuit mode and the instantaneous amplitude of the back electromotive force of each phase winding, including: When the target short-circuit mode is a single-phase short-circuit mode, the instantaneous amplitude of the back electromotive force of each phase winding is compared, and the phase with the largest instantaneous amplitude of the back electromotive force is determined as the target phase. When the target short-circuit mode is a two-phase short-circuit mode, the instantaneous amplitude of the back electromotive force of each phase winding is compared, and the other two phases, except for the phase with the smallest instantaneous amplitude of the back electromotive force, are determined as the target phases. When the target short-circuit mode is a three-phase short-circuit mode, the three phases are determined as the target phases.

[0012] On the other hand, embodiments of this application provide a motor control system, including: a data acquisition module, a control module, a discharge control module, and a motor drive module; the control module is connected to the data acquisition module, the discharge control module, and the motor drive module respectively; the discharge control module is connected to the motor windings; and the motor drive module is connected to the motor windings. The data acquisition module is used to obtain the current phase current, current speed, and current temperature of the power devices of the motor; The control module is used to acquire the current phase current and current speed of the motor; determine the current operating mode of the motor based on the current phase current and current speed; when the current operating mode is the power generation mode, acquire the current temperature of the power device, and determine the current delay time based on the current temperature and current speed; after the current delay time has elapsed, control the discharge control module to short-circuit at least one phase winding of the motor to ground. A discharge control module is used to connect or disconnect at least one phase winding of the motor from ground. The motor drive module is used to drive the motor to run when the current working mode is power consumption mode, and to stop driving the motor when the current working mode is power generation mode, under the control of the control module.

[0013] Optionally, the discharge control module includes: three low-side power switching devices; The first terminal of each low-side power switch is connected to the corresponding phase winding, the second terminal of each low-side power switch is connected to ground, and the control terminal of each low-side power switch is connected to the control module. The low-side power switch is used to connect or disconnect the connection between the corresponding phase winding and ground under the control of the control module.

[0014] Optionally, the data acquisition module includes: a current sensor, a speed sensor, and a temperature sensor; A current sensor is installed in the motor phase circuit to obtain the current phase current; The speed sensor is mounted on the motor shaft to obtain the current speed; A temperature sensor is placed on the heat dissipation surface of the power device in the motor drive module to obtain the current temperature of the power device.

[0015] On the other hand, embodiments of this application provide an electric vehicle, including: a motor and the aforementioned motor control system; The motor is connected to the motor control system.

[0016] The beneficial effects of the embodiments of this application are as follows: In this embodiment, the current phase current and speed of the motor are acquired in real time to accurately identify the current operating mode of the motor. When the motor is determined to be in power generation mode, the current temperature of the power devices is further acquired, and the current delay time is dynamically determined by combining the temperature parameter with the current speed. After the delay time, at least one phase winding of the motor is short-circuited to ground, thereby utilizing the winding's own impedance to consume the generated energy and effectively suppress the back electromotive force. This eliminates the need for external protection devices such as TVS diodes, significantly reducing the circuit area occupied and fundamentally eliminating the power consumption decay and increased failure rate of TVS diodes due to long-term use, thus greatly improving system reliability. Simultaneously, by introducing power device temperature and speed parameters for adaptive adjustment of the delay time, the optimal short-circuit timing can be intelligently selected based on the device's thermal state and induced electromotive force level. This avoids overcurrent surges caused by direct short-circuiting under high temperature or overspeed conditions and prevents back electromotive force suppression failure due to excessively long delays, achieving a dynamic balance between back electromotive force suppression and power device safety protection, effectively improving system reliability and lifespan.

[0017] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic flowchart illustrating the method for suppressing the back electromotive force of a motor in an embodiment of this application. Figure 2This is a schematic diagram illustrating the specific process of determining the current working mode in the embodiments of this application; Figure 3 This is a schematic diagram illustrating the specific process of determining the current delay time in the embodiments of this application; Figure 4 This is a schematic diagram illustrating the specific process of the control method for short-circuiting the winding to ground in the embodiments of this application; Figure 5 This is a schematic diagram of the system framework of the motor control system in an embodiment of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and beneficial effects of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] This application provides a method for suppressing the back electromotive force of a motor, see below. Figure 1 As shown, the general flow of the motor back electromotive force suppression method provided in this application embodiment is as follows: Step 101: Obtain the current phase current and current speed of the motor.

[0021] In practical applications, the current phase current can be acquired in real time by a current detection unit deployed in the motor phase line circuit, and the current speed can be acquired in real time by a speed detection unit installed at the corresponding position on the motor shaft or rotor. The current phase current includes the instantaneous current value in each phase winding of the motor, specifically the first, second, and third phase currents of the three-phase current, or the equivalent current components obtained after coordinate transformation of the three-phase current. The current phase current reflects the instantaneous electromagnetic load level inside the motor windings. The current speed includes the instantaneous angular velocity value of the motor rotor, and the speed direction information derived from the instantaneous angular velocity. The speed direction information is used to characterize the forward or reverse rotation state of the motor rotor. The current detection unit can use a Hall effect sensor or a shunt resistor sampling circuit to convert the current signal flowing through each phase winding into a voltage signal or digital signal recognizable by the control module; the speed detection unit can use a photoelectric encoder, a magnetoelectric speed sensor, or a rotary transformer to convert the angular displacement or angular velocity information of the motor rotor into a pulse sequence or analog electrical signal.

[0022] Step 102: Determine the current operating mode of the motor based on the current phase current and the current speed.

[0023] In practical applications, the current phase current and current speed are used as input variables for calculation or table lookup comparison to determine the motor's current operating mode. The current operating mode is at least divided into two basic states: power consumption mode and power generation mode. In power consumption mode, the motor absorbs electrical energy from the power source and converts it into mechanical energy to output driving torque. In power generation mode, the motor is driven to rotate by external mechanical force, inducing a back electromotive force in the windings, exhibiting a tendency to feed energy back to the power source. The mode determination logic can be based on the relative relationship between the speed direction and the electromagnetic torque direction, or on a threshold combination of current amplitude and speed amplitude. When the speed direction is opposite to the electromagnetic torque direction derived from the phase current, or the numerical combination of current and speed meets the power generation mode determination condition, the identification result is power generation mode; when the speed direction is the same as the electromagnetic torque direction derived from the phase current, or the numerical combination of current and speed meets the power consumption mode determination condition, the identification result is power consumption mode.

[0024] Step 103: When the current working mode is power generation mode, obtain the current temperature of the power device, and determine the current delay time based on the current temperature and the current rotation speed.

[0025] In practical applications, the current temperature of a power device can be obtained through a temperature sensing device mounted on the heat dissipation surface of the power device. The current temperature characterizes the actual thermal state of the power device due to the accumulation of conduction and switching losses. The switching characteristics of the power device are temperature sensitive; its turn-on delay and drive transmission delay change with the increase of junction temperature or case temperature. Simultaneously, the current rotational speed directly affects the rate of change and amplitude of the back electromotive force (EMF) in the windings; the higher the rotational speed, the larger the amplitude and the shorter the period of the back EMF. Using the current temperature and current rotational speed as dual-variable inputs for delay tuning, the current delay time is calculated through a preset mapping relationship or compensation algorithm. The current delay time is used to compensate for timing deviations caused by differences in the thermal state of the power device and differences in motor speed, ensuring that the timing of subsequent short-circuit actions precisely matches the actual development process of the back EMF.

[0026] In addition, when the current operating mode is the power consumption mode, the control maintains the normal driving state of the motor and does not perform winding short-circuiting operation.

[0027] Step 104: After the current delay time has elapsed, at least one phase winding of the control motor is short-circuited to ground.

[0028] In practical applications, after the current delay time has elapsed, a conduction command is sent to the power switching device connected between the motor windings and ground, controlling at least one phase winding of the motor to be short-circuited to ground through a low-impedance path. This short-circuit action creates a closed loop within the winding, and the induced back electromotive force is released as heat dissipation through the winding resistance and loop impedance, preventing back electromotive force energy from flowing back to the DC bus or power supply side and causing overvoltage faults. The short-circuit to ground path can be achieved through a low-side power switching device. The first terminal of this low-side power switching device is electrically connected to the corresponding phase winding, and the second terminal is electrically connected to the system ground potential. Upon receiving a valid conduction signal, it enters a low-impedance conduction state, forming a controllable short-circuit loop between the corresponding phase winding and ground. Depending on the braking intensity requirements or back electromotive force discharge requirements, single-phase winding short-circuiting, two-phase winding short-circuiting, or simultaneous short-circuiting of three-phase windings can be controlled to achieve differentiated braking torque output and energy discharge capabilities.

[0029] In one possible implementation, see [reference] Figure 2 As shown, the current operating mode of the motor is determined based on the current phase current and the current speed, including: Step 201: Obtain the historical phase current within the first time period, and determine the current change rate based on the current phase current and the historical phase current.

[0030] In practical applications, a preset first time interval is used as the sampling window to continuously collect historical phase current data in the motor's phase circuits within that time interval. The historical phase current data includes multiple instantaneous phase current values ​​recorded at a fixed sampling period within the sampling window. Differential operations or slope calculations are performed on the first phase current and the historical first phase current, the second phase current and the historical second phase current, and the third phase current and the historical third phase current to obtain the rate of change of the first phase current, the rate of change of the second phase current, and the rate of change of the third phase current. The arithmetic mean of these rates of change is then used to determine the current change rate. The current change rate reflects the transient trend of the motor's load or operating state, providing a dynamic basis for identifying operating mode switching.

[0031] Step 202: Determine the current output torque of the motor based on the current phase current and the preset current-torque mapping table.

[0032] In practical applications, a current-torque mapping table, pre-calibrated through bench testing or electromagnetic simulation, is invoked. This table, determined by the motor's pole pair number, flux linkage parameters, and winding design parameters, establishes a correspondence between the effective value of the phase current and the electromagnetic output torque. Using the first, second, and third phase currents as inputs, the first, second, and third phase output torques are obtained through table lookup matching or linear interpolation. The arithmetic mean of these three output torques is then calculated to determine the current output torque.

[0033] Step 203: Determine the dynamic judgment threshold based on the absolute value of the current rotational speed and the absolute value of the current output torque.

[0034] In practical applications, the absolute value of the current speed is used to obtain the speed amplitude, and the absolute value of the current output torque is used to obtain the torque amplitude. Using the speed amplitude and torque amplitude as input variables, a preset threshold generation rule is invoked to determine the dynamic judgment threshold. This threshold generation rule includes a two-dimensional mapping table lookup mechanism. In this mechanism, the mapping table is pre-calibrated through mode-switching tests at different speed and torque levels on a motor test bench. The table stores optimized threshold data corresponding to each operating condition coordinate. Threshold values ​​matching the current speed amplitude and torque amplitude are obtained through table lookup or bilinear interpolation, and these values ​​are used as the dynamic judgment threshold.

[0035] Step 204: Perform a weighted judgment based on the current speed, current output torque, current change rate, and dynamic judgment threshold to obtain the current working mode of the motor.

[0036] Specifically, the current operating mode of the motor is determined by weighting the current speed, current output torque, current change rate, and dynamic judgment threshold. This can be achieved using, but is not limited to, the following methods: First, based on the current speed, current output torque, and preset mode determination criteria, a first judgment result is generated.

[0037] In practical applications, the first judgment result is the steady-state power generation tendency score. The mode determination criteria include the direction comparison sub-criteria and the interval division sub-criteria. The direction comparison sub-criteria outputs the direction deviation score, which is obtained by normalizing and linearly scaling the dot product of the direction vector of the current rotational speed and the electromagnetic torque direction vector derived from the current phase current. The value ranges from 0 to 50 points. When the two directions are completely opposite, the direction deviation score approaches 50 points, and when the two directions are exactly the same, it approaches 0 points. The interval division sub-criteria outputs the power generation interval. The membership score for the power generation interval is obtained by bilinear interpolation of the absolute value of the current rotational speed and the absolute value of the current output torque in a preset two-dimensional mapping table of power generation conditions, and then scaling it to a percentage. The score ranges from 0 to 50. When the operating point falls completely into the center of the power generation condition, it approaches 50 points, and when it deviates completely from the power generation condition, it approaches 0 points. The steady-state power generation tendency score is determined by arithmetic summation of the directional deviation score and the membership score for the power generation interval, so that the steady-state power generation tendency score is a continuous value between 0 and 100 points.

[0038] Then, based on the rate of change of current and the dynamic judgment threshold, a second judgment result is generated.

[0039] In practical applications, the second judgment result is the dynamic switching urgency score. The dynamic switching urgency score is determined by the ratio of the absolute value of the current change rate to the dynamic judgment threshold through a segmented continuous percentage system. The ratio λ of the absolute value of the current change rate to the dynamic judgment threshold is calculated. When the ratio λ is less than or equal to 1, the dynamic switching urgency score is calculated according to the formula S1=50λ, with a value range of 0 to 50. When the ratio λ is greater than 1, the dynamic switching urgency score is calculated according to the formula S2=50+50[1-e^{-(λ-1)}], where e is a natural constant. This allows the dynamic switching urgency score to asymptotically saturate to 100 as the disturbance intensity increases after the ratio λ is greater than 1.

[0040] Next, the first judgment result and the second judgment result are weighted and fused to obtain the current weighted score; Finally, if the current weighted score exceeds the preset score threshold, the current working mode is confirmed as the power generation mode; if the current weighted score does not exceed the preset score threshold, the current working mode is confirmed as the power consumption mode.

[0041] In practical applications, steady-state and dynamic discrimination branches are constructed in parallel to extract steady-state and dynamic features of the motor's operating state, respectively. These features are then fused to reliably confirm the operating mode. In the weighted fusion stage, a continuous percentage weighted summation model is used. The steady-state power generation tendency score is multiplied by a first weighting coefficient, and the dynamic switching urgency score is multiplied by a second weighting coefficient. The two products are summed to obtain the current weighted score; the sum of the first and second weighting coefficients is always equal to 1. The current weighted score comprehensively reflects the combined contribution of steady-state operating features and dynamic change features to mode discrimination, allowing misjudgments or noise interference from a single branch to be suppressed through complementary information from the other branch. The current weighted score is numerically compared with a preset score threshold, determined through offline calibration experiments or online adaptive algorithms, and used to ultimately arbitrate the discrimination opinions of the two branches. If the current weighted score exceeds the threshold, the motor's current operating mode is confirmed as a power generation mode; if the current weighted score does not exceed the threshold, the motor's current operating mode is confirmed as a power consumption mode. This threshold comparison mechanism maps continuous weighted scores to discrete mode states, enabling the final determination and locking of the working mode.

[0042] In one possible implementation, see [reference] Figure 3 As shown, the current delay time is determined based on the current temperature and current rotation speed, including: Step 301: Query the preset temperature-delay mapping table based on the current temperature to determine the drive transmission delay and power device turn-on delay.

[0043] In practical applications, a preset temperature-delay mapping table is consulted based on the current temperature. This table is calibrated offline by testing the switching characteristics of the drive circuit and power devices under different ambient temperatures. The table records the mapping relationships between multiple temperature ranges and their corresponding delay parameters. The query operation can employ direct table lookup matching or piecewise linear interpolation to determine the corresponding drive transmission delay and power device turn-on delay based on the current temperature range. Specifically, the drive transmission delay refers to the time interval required for a logic level signal to be transmitted from the drive amplifier circuit to the control electrode of the power device. This time interval is influenced by the combined effects of the internal logic delay of the drive chip, the transmission delay of isolation components, and the trace delay of the printed circuit board. The power device turn-on delay refers to the time interval required for the power device to form its rated on-resistance between the control electrode and the main circuit electrode after receiving a valid drive signal. This time interval is influenced by the combined effects of carrier migration rate, gate charge charging and discharging rate, and junction temperature. As the current temperature rises, the carrier migration rate decreases and the gate charge characteristics drift, resulting in a corresponding increase in the turn-on delay of power devices. Changes in the transistor parameters inside the driver chip with temperature also cause a drift in the drive transmission delay. The temperature-delay mapping table quantifies the above temperature-sensitive characteristics into a queryable delay value.

[0044] Step 302: Determine the speed compensation delay based on the absolute value of the current speed.

[0045] In practical applications, the absolute value of the current speed is calculated to obtain the speed amplitude. Based on this speed amplitude, a preset speed-compensation delay mapping relationship is queried or a preset speed compensation function is called to determine the speed compensation delay. This speed compensation delay is used to compensate for the timing deviation caused by the difference in the rate of change of back EMF due to different speeds. When the speed amplitude is high, the amplitude of the back EMF induced in the motor winding is large and the electrical period is short. The time interval required for the back EMF to grow from zero to its peak value is correspondingly shortened. At this time, the value of the speed compensation delay is correspondingly reduced, so that the short-circuit action is triggered earlier to match the rapid establishment process of the back EMF. When the speed amplitude is low, the amplitude of the back EMF is small and the electrical period is long. The time interval required for the back EMF to grow from zero to its peak value is correspondingly extended. At this time, the value of the speed compensation delay is correspondingly increased to avoid the short-circuit action being triggered too early, which would cause a phase mismatch between the peak short-circuit current and the back EMF. The speed-compensation delay mapping relationship is calibrated offline by sampling and analyzing the back EMF waveform at different speed levels, establishing a monotonically decreasing or piecewise linear correspondence between the speed amplitude and the optimal compensation delay.

[0046] Step 303: Determine the current delay time based on the drive transmission delay, power device turn-on delay, and speed compensation delay.

[0047] In practical applications, the drive transmission delay, power device turn-on delay, and speed compensation delay are algebraically summed or weighted according to preset rules to determine the current delay time. In the algebraic summation mechanism, the current delay time equals the arithmetic sum of the drive transmission delay, power device turn-on delay, and speed compensation delay, advancing the initiation time of the short-circuit command by the sum of the three delay components to offset the accumulated delay in the signal transmission link. In the weighted accumulation mechanism, a first weighting coefficient is assigned to the drive transmission delay, a second weighting coefficient to the power device turn-on delay, and a third weighting coefficient to the speed compensation delay. The current delay time is generated through weighted summation. Each weighting coefficient is offline tuned based on actual circuit parameters and motor electromagnetic characteristics to adapt to the differentiated timing characteristics of different hardware platforms and motor models. The current delay time serves as the actual waiting time for subsequent short-circuit actions, ensuring that after the short-circuit command is issued, the power device turns on precisely when the back EMF reaches the target discharge phase, achieving precise control of the back EMF suppression timing.

[0048] In one possible implementation, see [reference] Figure 4 As shown, controlling at least one phase winding of the motor to be shorted to ground includes: Step 401: Obtain braking intensity requirements.

[0049] In practical applications, braking intensity requirements are received through the vehicle controller or brake pedal sensors. These requirements are characterized as a braking deceleration request or a percentage of braking torque. Alternatively, they can be obtained by converting raw physical quantities collected by brake pedal travel sensors, pedal force sensors, or brake master cylinder pressure sensors through a preset mapping relationship. The magnitude of the braking intensity requirement directly reflects the driver's or vehicle's energy recovery system's desired level of motor braking torque, providing a target input for subsequent short-circuit mode selection.

[0050] Step 402: Determine the target short-circuit mode based on the braking intensity requirement; wherein, the target short-circuit mode includes single-phase short-circuit mode, two-phase short-circuit mode or three-phase short-circuit mode.

[0051] In practical applications, the target short-circuit mode is determined from a pre-defined short-circuit mode library based on the required braking intensity. The target short-circuit modes include single-phase, two-phase, or three-phase short-circuit modes. The single-phase short-circuit mode is suitable for low-level braking intensity requirements, shorting only one phase winding to ground to provide basic braking torque and energy dissipation capacity. The current capacity and heat dissipation power in the short-circuit circuit are at a relatively low level. The two-phase short-circuit mode is suitable for medium-level braking intensity requirements, shorting both phase windings to ground simultaneously to provide medium-level braking torque and a larger short-circuit current capacity. The resultant magnetomotive force and energy dissipation rate in the short-circuit circuit are higher than in the single-phase short-circuit mode. The three-phase short-circuit mode is suitable for high-level braking intensity requirements, shorting all three phase windings to ground to provide maximum braking torque and full energy dissipation capacity. The resultant magnetomotive force in the short-circuit circuit reaches its maximum, and the three-phase current is symmetrically distributed. The numerical range of braking intensity requirements is compared with the preset threshold boundaries. Braking intensity requirements falling into the first range correspond to a single-phase short circuit mode, braking intensity requirements falling into the second range correspond to a two-phase short circuit mode, and braking intensity requirements falling into the third range correspond to a three-phase short circuit mode.

[0052] Step 403: Determine the target number of target phases based on the target short-circuit mode and the instantaneous amplitude of the back electromotive force of each phase winding.

[0053] In practical applications, based on the number of short-circuit phases required by the target short-circuit mode and the relative magnitudes of the instantaneous back EMF amplitudes of each phase winding, the target number of target phases is determined according to a preset selection logic. In single-phase short-circuit mode, the instantaneous back EMF amplitudes of each phase are compared, and the phase with the largest amplitude is selected as the target phase to maximize the induced EMF in the single-phase short-circuit loop, thereby obtaining the optimal short-circuit current and braking torque. In two-phase short-circuit mode, the instantaneous back EMF amplitudes of each phase are compared and sorted, and the two phases with higher amplitudes are selected as target phases to maximize the combined back EMF in the two-phase short-circuit loop and achieve balanced current distribution between the two phases. In three-phase short-circuit mode, all three phase windings are directly selected as target phases, enabling synchronous short-circuiting of the three phase windings. This selection logic based on instantaneous amplitude ensures that the short-circuit operation is performed at the most favorable phase and phase sequence for the back EMF.

[0054] Step 404: Short-circuit the winding of the target phase to ground.

[0055] In practical applications, a turn-on command is issued to the power switching device connected between the target phase winding and ground. This power switching device is a low-side power switching device, with its first terminal directly electrically connected to the output terminal of the corresponding phase winding and its second terminal electrically connected to the system ground potential. After an effective turn-on signal is output to the control terminal of the corresponding low-side power switching device, the device enters a low-resistance conduction state, forming a low-resistance short-circuit loop between the target phase winding and ground. The induced back electromotive force forms a circulating current in this short-circuit loop. The circulating current flows through the winding resistance and the conduction resistance of the power switching device, converting electromagnetic energy into heat energy for dissipation, thus preventing back EMF energy from flowing back to the DC bus or power supply side and causing overvoltage faults. Based on changes in braking intensity requirements or feedback from the back EMF discharge process, the number of phases participating in the short circuit or the target phase is continuously adjusted to achieve continuous adjustment of braking torque and directional discharge of back EMF energy.

[0056] In one possible implementation, determining the target number of target phases based on the target short-circuit mode and the instantaneous amplitude of the back electromotive force of each phase winding includes: When the target short-circuit mode is a single-phase short-circuit mode, the instantaneous amplitude of the back electromotive force of each phase winding is compared, and the phase with the largest instantaneous amplitude of the back electromotive force is determined as the target phase. When the target short-circuit mode is a two-phase short-circuit mode, the instantaneous amplitude of the back electromotive force of each phase winding is compared, and the other two phases, except for the phase with the smallest instantaneous amplitude of the back electromotive force, are determined as the target phases. When the target short-circuit mode is a three-phase short-circuit mode, the three phases are determined as the target phases.

[0057] In practical applications, when the target short-circuit mode is a single-phase short-circuit mode, the instantaneous amplitude of the back electromotive force (EMF) of each phase winding is compared in real time, and the phase with the largest instantaneous amplitude of the back EMF is determined as the target phase. This phase winding can generate the largest short-circuit current at the moment of short-circuit, thus achieving optimal braking torque output and energy dissipation efficiency under the condition that only one phase is involved in the short circuit. When the target short-circuit mode is a two-phase short-circuit mode, the instantaneous amplitude of the back EMF of each phase winding is compared in real time and sorted, and the phase with the smallest instantaneous amplitude of the back EMF is excluded, with the remaining two phases determined as the target phases. This selection method maximizes the combined back EMF in the two-phase short-circuit loop, while avoiding including the phase with excessively low back EMF in the short-circuit loop, which would lead to uneven current distribution and unbalanced braking torque output between the two phases. When the target short-circuit mode is a three-phase short-circuit mode, all three phase windings are directly determined as the target phases, so that the three phase windings are simultaneously short-circuited to ground, forming a three-phase full short-circuit loop, realizing the full-phase synchronous discharge of back electromotive force energy and the output of the maximum synthetic braking torque.

[0058] Based on the above embodiments, this application provides a motor control system, see below. Figure 5 As shown, the motor control system 100 provided in this embodiment includes at least: a data acquisition module 110, a control module 120, a discharge control module 130, and a motor drive module 140; the control module 120 is connected to the data acquisition module 110, the discharge control module 130, and the motor drive module 140 respectively; the discharge control module 130 is connected to the motor windings; and the motor drive module 140 is connected to the motor windings. The data acquisition module 110 is used to acquire the current phase current, current speed and current temperature of the power devices of the motor; The control module 120 is used to acquire the current phase current and current speed of the motor; determine the current operating mode of the motor based on the current phase current and current speed; when the current operating mode is the power generation mode, acquire the current temperature of the power device, and determine the current delay time based on the current temperature and current speed; after the current delay time has elapsed, control the discharge control module 130 to short-circuit at least one phase winding of the motor to ground. The discharge control module 130 is used to connect or disconnect at least one phase winding of the motor from the ground; The motor drive module 140 is used to drive the motor to run when the current working mode is power consumption mode, and to stop driving the motor when the current working mode is power generation mode, under the control of the control module 120.

[0059] In practical applications, the control module 120 establishes communication connections with the data acquisition module 110, the discharge control module 130, and the motor drive module 140 via a signal bus or dedicated control line. The discharge control module 130 is electrically connected to each phase winding of the motor via a power line, used to control the discharge control module 130 to short-circuit the corresponding winding to ground under specific operating conditions. The motor drive module 140 is electrically connected to each phase winding of the motor via a power line, used to output drive power to the windings under normal operating conditions. These connections enable the control module 120 to synchronously receive sensing information from the data acquisition module 110 and send mutually exclusive or coordinated power control commands to the discharge control module 130 and the motor drive module 140.

[0060] The data acquisition module 110 is used to acquire the current phase current, current speed, and current temperature of the power devices of the motor in real time. The current phase current includes the instantaneous current values ​​in each phase winding of the motor, covering the first, second, and third phase currents of the three-phase current, or the equivalent current components obtained after coordinate transformation. The current speed includes the instantaneous angular velocity value of the motor rotor and its direction of rotation. The current temperature of the power devices includes the casing temperature or junction temperature of the power devices.

[0061] The control module 120 executes the logic flow of the motor back electromotive force suppression method. First, the control module 120 receives the current phase current and current speed of the motor from the data acquisition module 110, and calls a preset mode determination algorithm to determine the current operating mode of the motor based on the current phase current and current speed. This mode determination algorithm determines whether the motor is in power consumption mode or power generation mode based on the relative relationship between the speed direction and the electromagnetic torque direction, or based on a combined threshold of current amplitude and speed amplitude. When the determination result is power generation mode, the control module 120 obtains the current temperature of the power devices from the data acquisition module 110, uses the current temperature and current speed as dual-variable inputs, and calls a preset temperature-delay mapping relationship and speed compensation rule to determine the current delay time. This current delay time is used to compensate for timing deviations caused by differences in the thermal state of the power devices and differences in motor speed. At the moment the current delay time is determined, the control module 120 starts an internal timer or delay counter. After the duration corresponding to the current delay time has elapsed, it outputs a short-circuit control command to the discharge control module 130.

[0062] The discharge control module 130 performs power execution and loop switching functions, and is used to connect or disconnect the electrical connection between at least one phase winding of the motor and ground under the command of the control module 120. The discharge control module 130 integrates a low-side power switching device array. The first terminal of each low-side power switching device is connected to the output terminal of the corresponding phase winding, the second terminal is connected to the system ground potential, and the control terminal is connected to the corresponding output port of the control module 120. When the discharge control module 130 receives a valid turn-on command from the control module 120, the corresponding low-side power switching device enters a low-impedance turn-on state, forming a short-circuit loop between the target phase winding and ground through a low-impedance path. When it receives a turn-off command or a short-circuit discharge completion signal, the corresponding low-side power switching device enters a high-impedance cut-off state, disconnecting the electrical connection between the winding and ground. This module can independently control the on / off state of each phase power switching device, realizing flexible short-circuiting of single-phase, two-phase, or three-phase windings.

[0063] The motor drive module 140 executes a corresponding power output strategy according to the current operating mode under the control of the control module 120. The motor drive module 140 integrates an inverter bridge arm, whose DC input terminal is connected to the vehicle's high-voltage DC bus or power battery, and whose AC output terminal is connected to each phase winding of the motor. When the current operating mode is power consumption mode, the motor drive module 140 receives the pulse-width modulation drive signal output by the control module 120, converts DC power into three-phase AC power through the inverter bridge arm, and drives the motor to output electromagnetic torque and operate. When the current operating mode is power generation mode, the motor drive module 140 receives the drive blocking command output by the control module 120, stops outputting drive power to the motor windings, and puts the power switching devices of the upper and lower bridge arms of the inverter bridge arm in the off state. The energy feedback path between the motor windings and the DC bus is cut off, creating conditions for the discharge control module 130 to perform a winding short-circuit operation.

[0064] In one possible implementation, see [reference] Figure 5 As shown, the discharge control module 130 includes: three low-side power switching devices; The first terminal of each low-side power switch is connected to the corresponding phase winding, the second terminal of each low-side power switch is connected to ground, and the control terminal of each low-side power switch is connected to the control module 120. The low-side power switch is used to connect or disconnect the connection between the corresponding phase winding and ground under the control of the control module 120.

[0065] In practical applications, the discharge control module 130 consists of three low-side power switching devices, each corresponding to one of the three phase windings of the motor. The high-side of the main circuit of each device is connected to the output terminal of the corresponding phase winding, and the low-side of the main circuit is connected to the system ground. The control terminals are independently connected to the three switching signal output lines of the control module 120. The devices use N-channel power MOSFETs or IGBTs, with the anode of the body diode or anti-parallel freewheeling diode grounded and the cathode connected to the winding, allowing the back electromotive force to be clamped by the diode to prevent overvoltage damage to the devices. The logic level output by the control module 120 is amplified into a voltage drive signal by the gate drive circuit and applied to the control terminals of each device. The on / off states of the three devices are independently controlled by the control module 120 and do not affect each other. When the single-phase short-circuit mode is selected, the control module 120 only outputs a high-level drive signal to the control terminal of the corresponding phase device, which turns on. The corresponding phase winding is grounded through its on-resistance, and the back electromotive force forms a single-loop short-circuit current across the phase winding resistance and the device's on-resistance. When a two-phase or three-phase short-circuit mode is selected, the control module 120 simultaneously outputs drive signals to two or three devices, forming a multi-phase parallel short-circuit loop. The back electromotive force in each phase winding is released to ground through its respective conducting device, synthesizing the total braking torque and total discharge power. When the control module 120 outputs a low-level or negative-voltage turn-off signal, the devices return to the high-resistance cut-off state, the electrical connection between the winding and ground is cut off, and the motor returns to the driveable state.

[0066] In one possible implementation, the data acquisition module includes: a current sensor, a speed sensor, and a temperature sensor; A current sensor is installed in the motor phase circuit to obtain the current phase current; The speed sensor is mounted on the motor shaft to obtain the current speed; A temperature sensor is placed on the heat dissipation surface of the power device in the motor drive module to obtain the current temperature of the power device.

[0067] In practical applications, current sensors are connected in series or coupled in the motor phase circuit to acquire the current phase current. This current phase current includes the instantaneous current values ​​in each phase winding of the motor, specifically covering the first, second, and third phase currents of the three-phase current, or the equivalent current components obtained after coordinate transformation. The current sensor uses a Hall effect sensor or a shunt resistor sampling circuit to convert the current signal flowing through each phase winding into a voltage signal or digital signal proportional to the current value, which is transmitted to the analog-to-digital converter interface of the control module via shielded cables or printed circuit board traces. A speed sensor is installed at the end of the motor shaft or at a corresponding position on the rotor core to acquire the current speed. This current speed includes the instantaneous angular velocity value of the motor rotor, and the speed direction information derived from the instantaneous angular velocity, which characterizes whether the motor rotor is rotating forward or backward. The speed sensor uses a photoelectric encoder, a magnetoelectric speed sensor, or a rotary transformer to convert the angular displacement or angular velocity information of the motor rotor into a pulse frequency signal or analog voltage signal, which is transmitted to the digital input interface or capture unit of the control module via signal cables. Temperature sensors are mounted or disposed adjacent to the metal heat sink or ceramic substrate of the power devices in the motor drive module to acquire the current temperature of the power devices. This current temperature characterizes the actual thermal state of the power devices due to the accumulation of conduction and switching losses, specifically including the case temperature or junction temperature of the power devices. The temperature sensor employs a thermistor, thermocouple, or integrated temperature sensing chip to convert the temperature signal into a resistance or voltage signal, which is then transmitted to the analog-to-digital converter interface of the control module via a sampling circuit.

[0068] It should be noted that the principle of the motor control system provided in this application embodiment to solve the technical problem is similar to the motor back electromotive force suppression method provided in this application embodiment. Therefore, the implementation of the motor control system provided in this application embodiment can refer to the implementation of the motor back electromotive force suppression method provided in this application embodiment, and the repeated parts will not be described again.

[0069] Based on the above embodiments, this application proposes an electric vehicle, which includes: a motor and the above-described motor control system; The motor is connected to the motor control system.

[0070] It should be noted that although several units or sub-units of the device have been mentioned in the detailed description above, this division is merely exemplary and not mandatory. In fact, according to embodiments of this application, the features and functions of two or more units described above can be embodied in one unit. Conversely, the features and functions of one unit described above can be further divided and embodied by multiple units.

[0071] Furthermore, although the operations of the method of this application are described in a specific order in the accompanying drawings, this does not require or imply that these operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.

[0072] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0073] Obviously, those skilled in the art can make various modifications and variations to the embodiments of this application without departing from the spirit and scope of the embodiments of this application. Therefore, if these modifications and variations to the embodiments of this application fall within the scope of the claims of this application and their equivalents, this application also intends to include these modifications and variations.

Claims

1. A method for suppressing back electromotive force of a motor, characterized in that, include: Obtain the current phase current and current speed of the motor; The current operating mode of the motor is determined based on the current phase current and the current speed; When the current operating mode is power generation mode, the current temperature of the power device is obtained, and the current delay time is determined based on the current temperature and the current rotation speed; After the current delay time has elapsed, at least one phase winding of the motor is shorted to ground.

2. The method for suppressing back electromotive force of a motor as described in claim 1, characterized in that, Determining the current operating mode of the motor based on the current phase current and the current speed includes: Obtain the historical phase current within a first time period, and determine the current change rate based on the current phase current and the historical phase current; The current output torque of the motor is determined based on the current phase current and the preset current-torque mapping table. The dynamic judgment threshold is determined based on the absolute value of the current rotational speed and the absolute value of the current output torque; The current operating mode of the motor is obtained by weighting the current speed, the current output torque, the current change rate, and the dynamic determination threshold.

3. The method for suppressing the back electromotive force of a motor as described in claim 2, characterized in that, The step of weighting the current speed, the current output torque, the current change rate, and the dynamic determination threshold to obtain the current operating mode of the motor includes: Based on the current rotational speed, the current output torque, and the preset mode determination criteria, a first determination result is generated; Based on the current change rate and the dynamic judgment threshold, a second judgment result is generated; The first judgment result and the second judgment result are weighted and fused to obtain the current weighted score; When the current weighted score exceeds a preset score threshold, the current working mode is confirmed as the power generation mode; when the current weighted score does not exceed the preset score threshold, the current working mode is confirmed as the power consumption mode.

4. The method for suppressing the back electromotive force of a motor as described in claim 1, characterized in that, Determining the current delay time based on the current temperature and the current rotation speed includes: Based on the current temperature, a preset temperature-delay mapping table is queried to determine the drive transmission delay and the power device turn-on delay; The speed compensation delay is determined based on the absolute value of the current speed. The current delay time is determined based on the drive transmission delay, the power device turn-on delay, and the speed compensation delay.

5. The method for suppressing back electromotive force of a motor as described in claim 1, characterized in that, The control of shorting at least one phase winding of the motor to ground includes: Obtain braking strength requirements; The target short-circuit mode is determined based on the braking intensity requirement; wherein, the target short-circuit mode includes a single-phase short-circuit mode, a two-phase short-circuit mode, or a three-phase short-circuit mode; The target number of target phases is determined based on the target short-circuit mode and the instantaneous amplitude of the back electromotive force of each phase winding; The winding of the target phase is short-circuited to ground.

6. The method for suppressing back electromotive force of a motor as described in claim 5, characterized in that, The target phases for determining the target number based on the target short-circuit mode and the instantaneous amplitude of the back electromotive force of each phase winding include: When the target short-circuit mode is the single-phase short-circuit mode, the instantaneous amplitude of the back electromotive force of each phase winding is compared, and the phase with the largest instantaneous amplitude of the back electromotive force is determined as the target phase; When the target short-circuit mode is the two-phase short-circuit mode, the instantaneous amplitude of the back electromotive force of each phase winding is compared, and the other two phases, except for the phase with the smallest instantaneous amplitude of the back electromotive force, are determined as the target phases; When the target short-circuit mode is the three-phase short-circuit mode, the three phases are determined to be the target phases.

7. A motor control system, characterized in that, include: The system includes a data acquisition module, a control module, a discharge control module, and a motor drive module; the control module is connected to the data acquisition module, the discharge control module, and the motor drive module; the discharge control module is connected to the motor windings; and the motor drive module is connected to the motor windings. The data acquisition module is used to acquire the current phase current, current speed, and current temperature of the power devices of the motor. The control module is used to acquire the current phase current and current speed of the motor; The current operating mode of the motor is determined based on the current phase current and the current speed; when the current operating mode is the power generation mode, the current temperature of the power device is obtained, and the current delay time is determined based on the current temperature and the current speed; after the current delay time has elapsed, the discharge control module is controlled to short-circuit at least one phase winding of the motor to ground. The discharge control module is used to connect or disconnect at least one phase winding of the motor from the ground; The motor drive module is used to drive the motor to operate when the current working mode is power consumption mode, and to stop driving the motor when the current working mode is power generation mode, under the control of the control module.

8. The motor control system as described in claim 7, characterized in that, The discharge control module includes: three low-side power switching devices; The first terminal of each low-side power switch is connected to the corresponding phase winding, the second terminal of each low-side power switch is connected to ground, and the control terminal of each low-side power switch is connected to the control module; the low-side power switch is used to connect or disconnect the connection between the corresponding phase winding and ground under the control of the control module.

9. The motor control system as described in claim 7, characterized in that, The data acquisition module includes: a current sensor, a speed sensor, and a temperature sensor; The current sensor is installed in the motor phase line circuit to obtain the current phase current; The speed sensor is mounted on the motor shaft and is used to acquire the current speed. The temperature sensor is disposed on the heat dissipation surface of the power device in the motor drive module and is used to obtain the current temperature of the power device.

10. An electric vehicle, characterized in that, include: The electric motor and the electric motor control system as described in any one of claims 7-9; The motor is connected to the motor control system.

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