A method for reducing the temperature of power devices in a direct current brushless controller

Abstract

This invention relates to the field of brushless DC motor control technology, and discloses a method for reducing the temperature of power devices in a brushless DC controller. The method includes: real-time acquisition of the power device temperature; when the temperature is within a first preset range, maintaining the torque current component setpoint and switching to a discontinuous pulse width modulation (PWM) mode; when the temperature enters a second preset range, predicting the turn-off phase using a square wave mode based on a Hall signal, and forcibly adjusting the clamping strategy of the PWM mode to ensure the inactive phase aligns with the turn-off phase; switching to a square wave control mode when the Hall signal changes, and calculating the bus current setpoint using a torque balance principle to maintain constant torque. This invention can significantly reduce switching losses by progressively changing the switching modulation strategy without reducing the output current, thereby effectively reducing the temperature of the power devices and ensuring the high-temperature power performance of the vehicle.

Description

Technical Field

[0001] This invention relates to the field of brushless DC motor control technology, specifically a method for reducing the temperature of power devices in a brushless DC controller. Background Technology

[0002] Brushless DC motor controllers are widely used in electric vehicle drive systems. Their core component, the three-phase inverter bridge, consists of multiple power devices. Under high-load conditions such as long-distance uphill climbing or heavy-load operation, the continuous large phase current will cause significant conduction and switching losses in the power devices, leading to a sharp increase in the internal temperature of the controller. If the heat cannot be dissipated in time, it will directly affect the reliability and service life of the controller.

[0003] Existing mainstream controllers typically employ Space Vector Pulse Width Modulation (SVPWM) technology to control a three-phase inverter bridge to perform high-frequency switching operations with three phases conducting simultaneously, thereby outputting a sinusoidal current to drive the motor for smooth operation. To prevent power devices from being damaged by overheating, traditional thermal management solutions often employ a current derating strategy. That is, when the temperature of a power device is detected to exceed a safe threshold, the controller proportionally and forcibly reduces the output current limit, thereby suppressing temperature rise by reducing the current flowing through the device.

[0004] However, this derating method, which sacrifices output performance, has significant shortcomings. In scenarios requiring sustained high torque, such as climbing hills, reducing the current directly leads to a decrease in the motor's output torque, resulting in insufficient vehicle power or even inability to move. Although the square wave control mode can reduce switching losses by utilizing a two-to-two conduction logic, existing technologies struggle to solve the torque balance and phase alignment issues during the switch from continuous modulation mode to square wave mode without reducing the current command. Direct switching often causes current surges or torque drops, making it difficult to simultaneously meet the requirements of efficient cooling and constant power output.

[0005] Therefore, this invention proposes a method for reducing the temperature of power devices using a brushless DC controller to address the shortcomings of existing technologies. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for reducing the temperature of power devices in a brushless DC controller. This method solves the problem of reducing power device losses and temperature by adjusting the switching modulation strategy and mode switching in stages without reducing the output current, thereby ensuring the continuous heavy-load operation performance of the vehicle.

[0007] To achieve the above objectives, the present invention provides a method for reducing the temperature of power devices using a brushless DC controller, comprising the following steps:

[0008] S10, real-time acquisition of the temperature of the power devices in the controller;

[0009] S20, when the temperature of the power device is in the first preset temperature range, the controller keeps the given value of the torque current component from decreasing and switches the control mode from space vector pulse width modulation mode to discontinuous pulse width modulation mode.

[0010] S30, when the temperature of the power device is higher than the first preset temperature range and enters the second preset temperature range, it enters the transition control state, predicts the turn-off phase corresponding to the square wave control mode at the next moment according to the Hall sensor signal, and adjusts the clamping strategy of the discontinuous pulse width modulation mode to force the inactive phase in the discontinuous pulse width modulation mode to be consistent with the turn-off phase.

[0011] S40, when the Hall sensor signal is detected to have an edge transition, the control mode is switched from the discontinuous pulse width modulation mode to the square wave control mode, and the torque current component setpoint is kept constant in the square wave control mode. The bus current setpoint in the square wave control mode is calculated by the torque balance principle to keep the electromagnetic torque constant while reducing switching losses.

[0012] Preferably, in step S10, the step of real-time acquisition of the power device temperature of the controller includes:

[0013] The microcontroller unit periodically reads the voltage signal output by the temperature detection circuit through the analog-to-digital conversion interface;

[0014] The current resistance value of the thermistor is calculated based on the voltage signal, the known pull-up resistor value in the temperature detection circuit, and the reference voltage source voltage.

[0015] Based on the material constant and nominal temperature parameters of the thermistor, the current resistance value of the thermistor is converted into the current temperature of the power device.

[0016] Preferably, in step S20, the control process after switching the control mode from space vector pulse width modulation mode to discontinuous pulse width modulation mode includes:

[0017] Obtain the three-phase voltage command value output by the current loop, and compare the absolute values ​​of the three-phase voltage command values;

[0018] The phase voltage command value with the largest absolute value is selected, and the power device bridge arm corresponding to the phase voltage command value with the largest absolute value is determined as the current clamping object.

[0019] The zero-sequence voltage component is calculated based on the polarity of the phase voltage command value with the largest absolute value. The zero-sequence voltage component is then superimposed onto the original three-phase voltage command value, so that the duty cycle of the clamping object reaches the boundary value of the modulation wave.

[0020] Preferably, in step S30, the step of predicting the turn-off phase corresponding to the square wave control mode at the next moment based on the Hall sensor signal includes:

[0021] Read the current status value of the Hall sensor signal;

[0022] Based on the current rotor rotation direction of the motor and the preset Hall state jump sequence table, calculate the Hall sensor signal state value corresponding to the next Hall sector when the rotor rotates to the next Hall sector;

[0023] Query the pre-stored conduction logic mapping table, retrieve the phase that is in a fully off state in the square wave control logic of the next Hall sector, and define the phase in a fully off state as the off phase.

[0024] Preferably, in step S30, the step of forcibly adjusting the inactive phase in the discontinuous pulse width modulation mode to be consistent with the shutdown phase includes:

[0025] The strategy of selecting clamping objects based on the absolute value of three-phase voltage command values ​​is disabled;

[0026] Obtain the voltage command value at the moment before the turn-off, and calculate the forced zero-sequence voltage component, so that the duty cycle of the turn-off phase after superimposing the forced zero-sequence voltage component reaches the boundary value of the modulation waveform.

[0027] The forced zero-sequence voltage component is superimposed on the three-phase voltage command value, so that the off phase stops switching and maintains a constant level during the current pulse width modulation cycle, while the other two phases maintain chopper control.

[0028] Preferably, in step S40, the step of calculating the bus current setpoint under square wave control mode using the torque balance principle includes:

[0029] Read the given value of the torque current component that was held at the moment before switching to square wave control mode;

[0030] Obtain a preset torque equivalence coefficient, which is used to compensate for the difference in current utilization between the space vector pulse width modulation mode and the square wave control mode.

[0031] Multiplying the torque current component setpoint by the torque equivalence coefficient yields the bus current setpoint under the square wave control mode.

[0032] Preferably, in step S40, the specific control process of the square wave control mode includes:

[0033] The three-phase inverter bridge is controlled to maintain a 2-to-2 conduction state according to the preset conduction logic mapping table. The 2-to-2 conduction state means that only two power devices are conducting at any given time.

[0034] Based on the deviation between the real-time collected bus current feedback value and the given bus current value, chopping control is performed on the power device in the conducting state.

[0035] Preferably, in step S40, the step of switching the control mode to square wave control mode when an edge transition of the Hall sensor signal is detected further includes:

[0036] Call the pre-stored Hall effect installation error compensation angle;

[0037] The Hall installation error compensation angle in the angular dimension is converted into a compensation value in the time dimension by combining the real-time speed of the motor.

[0038] The operating timing of the power devices is corrected using the compensation value to ensure that the stator magnetic field and the rotor magnetic field remain orthogonal.

[0039] Preferably, the Hall effect installation error compensation angle is obtained as follows:

[0040] During the operation of the space vector pulse width modulation mode by the controller, the rotor position observer is used to calculate the estimated rotor angle;

[0041] When an edge transition is detected in the Hall sensor signal, the estimated rotor angle at the current moment is recorded, and the theoretical Hall angle corresponding to the current state value of the Hall sensor signal is found.

[0042] The difference between the estimated rotor angle and the theoretical Hall angle is calculated, and the Hall installation error compensation angle is updated using a low-pass filtering algorithm.

[0043] Preferably, the first preset temperature range is defined by a first temperature threshold and a second temperature threshold, and the second preset temperature range is defined by a range that is higher than or equal to the second temperature threshold.

[0044] This invention provides a method for reducing the temperature of power devices using a brushless DC controller. It offers the following advantages:

[0045] 1. This invention monitors the temperature of power devices in real time. When the temperature rises into a first preset range, the control mode is switched from space vector pulse width modulation to discontinuous pulse width modulation mode. This method uses the zero-sequence voltage component to clamp the phase with the largest voltage amplitude, stopping its high-frequency switching operation. While significantly reducing inverter bridge switching losses, it keeps the torque current component setpoint constant, thereby effectively suppressing the temperature rise rate of power devices without reducing motor output torque or sacrificing overall vehicle power performance.

[0046] 2. This invention switches to square wave control mode under extreme high-temperature conditions, controlling the three-phase inverter bridge to execute a two-by-two conduction logic, thereby minimizing the number of power devices involved in high-frequency operation and reducing system heat generation. Simultaneously, based on the torque balance principle, the bus current setpoint is reconstructed, establishing an equivalent current relationship between the square wave mode and the original modulation mode. This ensures that the electromagnetic torque output remains constant after switching, enabling the reduction of device temperature without current derating under extreme conditions such as hill climbing, thus guaranteeing continuous high-load vehicle operation.

[0047] 3. This invention introduces a transitional control state based on Hall signal prediction to identify the turn-off phase corresponding to the square wave control at the next moment in advance, and forcibly adjusts the clamping strategy of the discontinuous pulse width modulation mode to logically pre-align the inactive phase with the predicted turn-off phase. This strategy eliminates the risk of topological abrupt changes during mode switching, avoids current surges or torque drops caused by control logic switching, and ensures that the control system can smoothly and safely transition from pulse width modulation mode to square wave control mode under full torque output conditions. Attached Figure Description

[0048] Figure 1 This is a flowchart of a method for reducing the temperature of power devices using a DC brushless controller according to the present invention;

[0049] Figure 2 This is a logic diagram for generating clamping signals for the discontinuous pulse width modulation mode of the present invention.

[0050] Figure 3 This is a logic diagram for phase prediction and forced alignment under the transition control state of the present invention. Detailed Implementation

[0051] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] Please see the appendix Figure 1 This invention provides a method for reducing the temperature of power devices using a brushless DC controller, comprising the following steps:

[0053] S10, real-time acquisition of the temperature of the power devices in the controller;

[0054] S20, when the temperature of the power device is in the first preset temperature range, the controller keeps the torque current component setpoint from decreasing and switches the control mode from space vector pulse width modulation mode to discontinuous pulse width modulation mode.

[0055] S30, when the temperature of the power device is higher than the first preset temperature range and enters the second preset temperature range, it enters the transition control state, predicts the turn-off phase corresponding to the square wave control mode at the next moment according to the Hall sensor signal, and adjusts the clamping strategy of the discontinuous pulse width modulation mode to force the inactive phase in the discontinuous pulse width modulation mode to be consistent with the turn-off phase.

[0056] S40, when an edge transition of the Hall sensor signal is detected, switches the control mode from discontinuous pulse width modulation mode to square wave control mode, and keeps the torque current component setpoint from decreasing in square wave control mode. The bus current setpoint in square wave control mode is calculated by the torque balance principle to keep the electromagnetic torque constant while reducing switching losses.

[0057] This embodiment also provides a brushless DC motor drive control system, which mainly includes a DC power supply, a three-phase inverter bridge, a brushless DC motor, Hall sensors, a temperature detection circuit, and a microcontroller unit. The three-phase inverter bridge consists of six power devices (such as MOSFETs), divided into upper and lower arms, used to convert the electrical energy from the DC power supply into three-phase AC power to drive the brushless DC motor. The Hall sensors are installed on the stator side of the brushless DC motor to output Hall signals characterizing the rotor position.

[0058] The temperature detection circuit includes a thermistor, which is physically mounted on the heat sink of the power module of the three-phase inverter bridge to sense the thermal state of the power devices in real time. The microcontroller unit is electrically connected to the gate drive terminal of the three-phase inverter bridge, the signal output terminal of the Hall sensor, and the signal output terminal of the temperature detection circuit.

[0059] See attached document Figure 1 The specific implementation method for real-time acquisition of the power device temperature of the controller in step S10 is as follows: The microcontroller periodically reads the voltage signal output by the temperature detection circuit through the analog-to-digital converter (ADC). The microcontroller has a pre-set calculation formula based on the physical characteristics of the thermistor, which is used to convert the acquired analog voltage into an accurate temperature value.

[0060] Specifically, the temperature detection circuit adopts a pull-up resistor voltage divider structure. The microcontroller first determines the temperature based on the acquired ADC voltage value. Calculate the current resistance value of the thermistor The calculation formula is as follows:

[0061] ;

[0062] In the formula, The pull-up resistor value is known in the temperature detection circuit; This is the reference voltage source voltage.

[0063] The microcontroller then calculates the resistance value based on the thermistor's B-value formula. Converted to current power device temperature (Unit: degrees Celsius), the calculation formula is as follows:

[0064] ;

[0065] In the formula, This refers to the nominal temperature (usually 25 degrees Celsius). This is the rated resistance of the thermistor at the nominal temperature; It is the zero-point conversion constant between the absolute temperature scale (Kelvin) and the Celsius temperature scale; This is the material constant of the thermistor, characterizing the sensitivity of the thermistor's resistance to temperature changes; typical values ​​are, for example, 3435K or 3950K. The microcontroller will calculate the power device temperature. Stored in an internal register.

[0066] At power device temperature When the first preset temperature range is not reached, the controller defaults to operating in space vector pulse width modulation (SVM) mode. In this mode, based on the field-oriented control principle, the controller acquires the motor phase current and performs coordinate transformation, outputting a continuously changing pulse width modulation waveform to drive the three-phase inverter bridge. The six power devices of the three-phase inverter bridge then perform high-frequency switching operations following a three-by-three conduction logic. The coordinate transformation and sector vector synthesis algorithm in the SVM mode can be implemented using existing vector control technology by those skilled in the art; these are well-known techniques and will not be elaborated upon here.

[0067] To ensure accurate commutation when switching to square wave control mode under high-temperature conditions, the controller executes phase self-calibration logic in the background task of running space vector pulse width modulation mode. The microcontroller internally operates a rotor position observer, which uses the motor phase current and voltage equations to calculate a smooth and continuous estimated rotor angle in real time. Due to mechanical tolerances during the manufacturing and installation of Hall sensors, there is a phase deviation between the physical transition edge of the Hall signal and the ideal zero-crossing point of the motor's back electromotive force.

[0068] The controller monitors the Hall signal level in real time. When an edge transition of the Hall signal is detected (a rising or falling edge interruption is captured), the controller immediately reads the estimated rotor angle output by the rotor position observer at the current moment. Simultaneously, the corresponding theoretical Hall angle is found based on the current Hall signal state value. The controller calculates the difference between the two and updates the Hall installation error compensation angle using a first-order low-pass filtering algorithm. The calculation formula is as follows:

[0069] ;

[0070] In the formula, The Hall installation error compensation angle is updated for the current calculation cycle; This is the Hall installation error compensation angle for the previous calculation cycle; These are the filter coefficients (with values ​​ranging from 0.01 to 0.1). The estimated rotor angle is recorded at the Hall transition moment; This is the theoretical geometric angle corresponding to this Hall state. The Hall installation error compensation angle. It is stored in the controller's non-volatile memory area.

[0071] See attached document Figure 1 and Figure 2 Step S20 mainly involves the control strategy switching logic executed by the controller in the initial stage of detecting abnormal temperature rise. When the power device temperature is collected in real time in step S10... When the temperature rises and enters the first preset temperature range, the controller triggers the primary thermal management logic. The first preset temperature range is determined by a first temperature threshold pre-stored in the controller. Second temperature threshold Limited (i.e.) In this state, the controller switches the drive motor's control mode from space vector pulse width modulation (SVM) to discontinuous pulse width modulation (DMCM). Note that during this switching process and subsequent operation in discontinuous DMCM mode, the controller maintains the torque current component setpoint (denoted as ) within the field-oriented control algorithm. The current derating algorithm is not applied. Instead, the controller maintains the original torque request command and suppresses temperature rise by changing the topology logic of the power device switching operation rather than sacrificing the motor output torque.

[0072] In discontinuous pulse width modulation mode, the controller achieves clamping control of specific power device arms by injecting zero-sequence voltage components into the three-phase voltage command. The specific implementation process is as follows:

[0073] The controller acquires the three-phase voltage command value output from the current loop within each pulse width modulation carrier cycle. , , The controller compares the absolute values ​​of the three voltage command values, selects the phase voltage command value with the largest absolute value, and identifies the corresponding power device bridge arm as the current clamping target.

[0074] The controller calculates the zero-sequence voltage component based on the voltage polarity of the phase with the largest absolute value. The calculation logic follows the maximum amplitude clamping principle, aiming to correct the duty cycle of the phase with the largest absolute value to the boundary value of the modulated wave (i.e., the fully on or fully off state).

[0075] If the voltage command value of phase A is The absolute value is the largest, and The controller determines that the upper arm of phase A must remain constantly on and the lower arm must remain constantly off. At this time, the zero-sequence voltage component... The calculation formula is:

[0076] ;

[0077] If the voltage command value of phase A is The absolute value is the largest, and The controller determines that the lower arm of phase A must remain constantly on, while the upper arm must remain constantly off. At this time, the zero-sequence voltage component... The calculation formula is:

[0078] ;

[0079] Similarly, if phase B or phase C is the phase with the largest absolute value, the controller calculates the corresponding zero-sequence voltage component based on the same logic described above. .

[0080] The controller then superimposes the calculated zero-sequence voltage component onto the original three-phase voltage command value to generate the final modulation wave duty cycle command used for comparison in generating the PWM waveform. , , The calculation formula is as follows:

[0081] ;

[0082] Through the above calculations, the value of one phase in the three-phase duty cycle command will be forcibly corrected to +1 or -1. The power device arm corresponding to this phase will stop high-frequency switching during the current carrier cycle and will be in a constant conduction or constant freewheeling state; while the duty cycle command values ​​of the remaining two phases are in the range of (-1, 1), and the corresponding power device arms will continue to perform high-frequency chopping. Compared to the space vector pulse width modulation mode in which all three phase arms participate in switching, this discontinuous pulse width modulation mode theoretically reduces the overall switching loss of the system by about one-third, thereby slowing down the rate of temperature rise of the power devices while keeping the torque current component setpoint unchanged.

[0083] See attached document Figure 1 and Figure 3 Step S30 illustrates the implementation flow of the transition control strategy when the power device temperature further increases. The power device temperature is collected in real-time during step S10. As the temperature continues to rise and exceeds the first preset temperature range, entering the second preset temperature range, the controller switches the operating state of the DC brushless motor drive control system to a transition control state. The second preset temperature range is determined by a second temperature threshold pre-stored in the controller. Define (i.e.) This upper temperature threshold represents the critical point at which the brushless DC motor drive control system is about to enter the extreme thermal management mode. In this transitional control state, the controller no longer follows the control logic in step S20 with the sole objective of minimizing switching losses, but instead executes a pre-alignment strategy based on topology prediction, which aims to bridge the space vector pulse width modulation mode and the square wave control mode.

[0084] The controller executes phase prediction logic based on the Hall sensor signal to determine the control topology for the next moment. The controller first reads the current Hall sensor signal state value, denoted as... Based on the current rotor rotation direction of the motor (determined by the Hall signal change sequence or speed observer) and the preset Hall state jump sequence table, the controller calculates the Hall sensor signal state value corresponding to the next Hall sector when the rotor rotates, denoted as... The controller then queries the conduction logic mapping table in square wave control mode.

[0085] The conduction logic mapping table is a data array pre-stored in the controller's non-volatile memory. It defines the specific switching state logic of the six power devices in the three-phase inverter bridge for each Hall sector state in six-step square wave control (120-degree conduction mode). Specifically, for each specific Hall signal value, the conduction logic mapping table specifies that the upper arm of one phase is on, the lower arm of another phase is on, while the upper and lower arms of the remaining third phase are both off (i.e., floating or high-impedance). The controller then determines the switching state based on the predicted values. The phase that is in a completely off state in the square wave control mode corresponding to the next Hall sector is retrieved from the conduction logic mapping table and defined as the off phase.

[0086] After identifying the off-phase, the controller adjusts the clamping strategy of the discontinuous pulse width modulation (PWM) mode. The clamping strategy, in PWM, refers to the selection rule used to determine which phase arm of the three-phase inverter bridge stops high-frequency switching and maintains a constant voltage level. In the transition control state, the controller disables the conventional clamping strategy in step S20, which selects the clamping object based on the absolute value of the three-phase voltage command, and forcibly executes clamping logic based on the prediction result. This means forcibly adjusting the inactive phase in the PWM mode (i.e., the phase with a constant duty cycle and no high-frequency switching) to match the predicted off-phase. This process achieves pre-locking of the controlled object at the logic level.

[0087] Specifically, assuming the predicted turn-off phase is phase A, the controller obtains the voltage command value of phase A at the current moment. In order to force phase A to be set as a non-operating phase, the controller calculates the forced zero-sequence voltage component. This causes the duty cycle of phase A after superimposing the forced zero-sequence voltage component to reach the boundary value of the modulation waveform.

[0088] If the voltage command value of phase A is The controller calculates the forced zero-sequence voltage component as follows:

[0089] ;

[0090] At this point, the final duty cycle corresponding to phase A will be fixed at 1 (or 100%), and the upper arm of phase A will remain constantly conducting.

[0091] If the voltage command value of phase A is The controller calculates the forced zero-sequence voltage component as follows:

[0092] ;

[0093] At this point, the final duty cycle corresponding to phase A will be fixed at -1 (or 0%), and the lower arm of phase A will remain constantly conducting.

[0094] Similarly, if the predicted shutdown phase is phase B or phase C, the controller performs the same logic calculation. The controller adds the forced zero-sequence voltage component to the original three-phase voltage command value. , , Above, generate the final duty cycle instruction in the transition state. , , :

[0095] ;

[0096] Through the above steps, during the transition control state, the phase predicted to be about to turn off is forcibly converted to a non-operating phase (clamping state) within the current PWM cycle, while the other two phases continue to maintain chopper control. This strategy ensures that at the instant the Hall signal changes and the brushless DC motor drive control system officially switches to square wave control mode, the power devices of a specific phase are already in a defined level state, thereby reducing the risk of current surges caused by abrupt changes in topology during mode switching.

[0097] See attached document Figure 1When the transition control state in step S30 continues and the controller detects an edge transition in the Hall sensor signal, the controller immediately terminates the discontinuous pulse width modulation mode and switches the control mode to square wave control mode. At this moment, the controller uses the physical transition edge of the Hall signal as the absolute position reference to initiate the six-step commutation logic. To compensate for the installation error of the Hall sensor, the controller calls the Hall installation error compensation angle stored in step S10 when performing square wave commutation. The controller calculates the electrical angular velocity based on the current real-time speed of the motor, and then converts the angular dimension... The delay or advance compensation value is converted into a time dimension, and the power device is controlled to operate at the corrected time to ensure that the stator magnetic field and the rotor magnetic field remain orthogonal.

[0098] After switching to square wave control mode, the controller performs current command reconstruction based on the torque balance principle to reduce switching losses while maintaining constant electromagnetic torque. It's important to note that although the power device temperature is now within the higher second preset temperature range, the controller still maintains the torque current component setpoint generated in the field-oriented control algorithm. No reduction means that the software derating strategy for the current amplitude is not implemented, thereby ensuring that the output power of the motor does not decrease under extreme operating conditions.

[0099] Since the controlled object in square wave control mode changes from the phase current in the rotating coordinate system to the bus current on the DC side, the controller calculates the bus current setpoint in square wave control mode based on the torque balance principle. The torque balance principle means that, with the motor parameters unchanged, by establishing an equivalent proportional relationship between the torque current in space vector pulse width modulation mode and the bus current in square wave control mode, the two control modes produce electromagnetic torques of equal magnitude under the same current command input.

[0100] The controller reads the torque current component setpoint held at the moment before the switch. The bus current setpoint in square wave control mode is calculated using the following formula. :

[0101] ;

[0102] In the formula, The converted bus current setpoint is used to set the current target of the square wave control loop; The given value for the undated torque current component; This is a preset torque equivalent coefficient. Depending on the back EMF waveform coefficient and winding structure of the motor, for typical surface-mount permanent magnet synchronous motors or brushless DC motors, this coefficient is usually between 0.75 and 0.866 (e.g., taking...). This is to compensate for the physical difference in current utilization between the two modulation methods.

[0103] Obtain bus current setpoint Then, the controller assigns the value to the current comparator or current regulator of the square wave control loop. During square wave control mode operation, the controller controls the three-phase inverter bridge to maintain a "two-two conduction" state (i.e., only two power devices are on at any given time, and the other four are off) according to the preset conduction logic mapping table, and based on the real-time acquired bus current feedback value and the bus current setpoint. To mitigate the deviation, PWM chopping control is applied to the upper or lower bridge arm of the conducting phase.

[0104] Through the aforementioned control strategy, the system further reduces switching losses and heat generation in square wave control mode by reducing the number of power devices in operation (from three-phase to two-phase operation). Simultaneously, through current command conversion based on torque balance principles, it ensures that the electromagnetic torque output by the motor remains consistent with the SVPWM mode before switching, achieving the ultimate thermal management goal of "cooling without torque reduction." The controller will maintain this square wave control mode until it detects that the power device temperature has fallen below the safe threshold.

[0105] The following describes in detail the method for reducing the temperature of power devices using a DC brushless controller provided in this embodiment of the invention, using a specific ramp-up and heavy-load application scenario. This scenario demonstrates how the controller, when faced with a temperature rise caused by a sustained high load, achieves graded thermal management according to the logic of steps S10 to S40 without performing current derating.

[0106] Application scenario description:

[0107] Suppose an electric vehicle equipped with this brushless DC motor drive control system is climbing a long hill. The driver keeps the throttle lever at its maximum opening, the system is operating under high load, and the motor phase current is large, causing the temperature of the three-phase inverter bridge power devices inside the controller to rise continuously. The controller's preset first temperature threshold... Set to 85 degrees Celsius, second temperature threshold Set to 95 degrees Celsius.

[0108] Step S10:

[0109] During the initial ramp-up phase, the controller operates in space vector pulse width modulation mode, and the three-phase inverter bridge performs a three-by-three high-frequency switching action to output a sinusoidal current, driving the motor to run smoothly. The microcontroller unit periodically reads the voltage signal from the temperature detection circuit through the analog-to-digital converter interface and calculates the temperature of the power devices in real time using the B-value formula of the thermistor. At this point, although the load is large, the controller maintains the standard control strategy due to the low initial temperature (e.g., 60 degrees Celsius).

[0110] Step S20:

[0111] As the ramp-up process continues, the temperature of the power devices... Rise and reach 85 degrees Celsius (i.e., enter) (Range). Upon detecting this state, the controller immediately switches the control mode to discontinuous pulse width modulation mode. During this process, the controller reads the torque current component setpoint output by the field-oriented control algorithm. The controller maintains this value unchanged and does not send derating commands to the speed loop or current loop. Based on the magnitude of the three-phase voltage commands, the controller identifies the phase with the largest absolute value of the current amplitude (e.g., phase A voltage command). (At maximum positive value). The controller adjusts the zero-sequence voltage component, clamping the upper arm of phase A to a constant conducting state while turning off the lower arm, performing high-frequency chopping only on phases B and C. In this way, one-third of the switching losses in the three-phase inverter bridge are eliminated. Although the temperature is still rising, the rate of temperature rise is slower than before the switch, and the motor output torque is unaffected, maintaining a constant vehicle climbing speed.

[0112] Step S30:

[0113] Due to the steep slope and limited heat dissipation, the temperature of the power devices... Continue to rise to 95 degrees Celsius (i.e. The controller determines that the system is in a transitional control state before entering extreme thermal management. At this time, the controller reads the current Hall sensor signal state (assuming it is state 101) and predicts the state of the next Hall sector as 100 based on the rotation direction.

[0114] The controller queries the conduction logic mapping table of the square wave control mode to confirm that in the square wave control logic corresponding to Hall state 100, both the upper and lower bridge arms of phase B should be in the off state.

[0115] The controller then adjusts the clamping strategy of the discontinuous pulse width modulation mode, no longer selecting the clamping target based on the voltage amplitude, but instead forcibly setting phase B as the non-operating phase. The controller calculates the forced zero-sequence voltage component. This causes the duty cycle command of phase B after superposition to reach a boundary value (e.g., locked to a constant low level based on voltage polarity), thereby stopping the switching action of phase B within the current PWM cycle. This operation logically aligns the controller's switching topology with the upcoming square wave mode in advance.

[0116] Step S40:

[0117] After running for several milliseconds in the transition control state, the controller detects an edge transition in the Hall sensor signal (from 101 to 100). In response to this interrupt signal, the controller immediately terminates the discontinuous pulse width modulation mode and formally switches to the square wave control mode.

[0118] To prevent a torque drop during switching that could cause the vehicle to decelerate on a slope, the controller calculates the current command based on the torque balance principle. The controller reads the torque and current component setpoints from the moment before the switch (e.g., ...). ), and utilize preset torque equivalence coefficients (e.g. Calculate the bus current setpoint under square wave control mode:

[0119] ;

[0120] The controller will The target value for the bus current loop is set, and the three-phase inverter bridge is controlled to execute a two-by-two conduction logic (at this time, only phases A and C are turned on, while phase B remains off). In square wave control mode, the number of power devices involved in high-frequency switching is further reduced, and the controller always maintains the original... With the equivalent electromagnetic torque output, the temperature of the power device gradually decreases or approaches thermal equilibrium, while the vehicle maintains its original driving force and continues to climb the hill, thus achieving effective cooling of the power device without reducing power performance.

[0121] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for reducing the temperature of power devices using a brushless DC controller, characterized in that, Includes the following steps: S10, real-time acquisition of the temperature of the power devices in the controller; S20, when the temperature of the power device is in the first preset temperature range, the controller keeps the given value of the torque current component from decreasing and switches the control mode from space vector pulse width modulation mode to discontinuous pulse width modulation mode. S30, when the temperature of the power device is higher than the first preset temperature range and enters the second preset temperature range, it enters the transition control state, predicts the turn-off phase corresponding to the square wave control mode at the next moment according to the Hall sensor signal, and adjusts the clamping strategy of the discontinuous pulse width modulation mode to force the inactive phase in the discontinuous pulse width modulation mode to be consistent with the turn-off phase. S40, when the Hall sensor signal is detected to have an edge transition, the control mode is switched from the discontinuous pulse width modulation mode to the square wave control mode, and the torque current component setpoint is kept constant in the square wave control mode. The bus current setpoint in the square wave control mode is calculated by the torque balance principle to keep the electromagnetic torque constant while reducing switching losses.

2. The method for reducing the temperature of power devices using a brushless DC controller according to claim 1, characterized in that, In step S10, the step of real-time acquisition of the power device temperature of the controller includes: The microcontroller unit periodically reads the voltage signal output by the temperature detection circuit through the analog-to-digital conversion interface; The current resistance value of the thermistor is calculated based on the voltage signal, the known pull-up resistor value in the temperature detection circuit, and the reference voltage source voltage. Based on the material constant and nominal temperature parameters of the thermistor, the current resistance value of the thermistor is converted into the current temperature of the power device.

3. The method for reducing the temperature of power devices using a brushless DC controller according to claim 1, characterized in that, In step S20, the control process after switching the control mode from space vector pulse width modulation mode to discontinuous pulse width modulation mode includes: Obtain the three-phase voltage command value output by the current loop, and compare the absolute values ​​of the three-phase voltage command values; The phase voltage command value with the largest absolute value is selected, and the power device bridge arm corresponding to the phase voltage command value with the largest absolute value is determined as the current clamping object. The zero-sequence voltage component is calculated based on the polarity of the phase voltage command value with the largest absolute value. The zero-sequence voltage component is then superimposed onto the original three-phase voltage command value, so that the duty cycle of the clamping object reaches the boundary value of the modulation wave.

4. The method for reducing the temperature of power devices using a brushless DC controller according to claim 1, characterized in that, In step S30, the step of predicting the turn-off phase corresponding to the square wave control mode at the next moment based on the Hall sensor signal includes: Read the current status value of the Hall sensor signal; Based on the current rotor rotation direction of the motor and the preset Hall state jump sequence table, calculate the Hall sensor signal state value corresponding to the next Hall sector when the rotor rotates to the next Hall sector; Query the pre-stored conduction logic mapping table, retrieve the phase that is in a fully off state in the square wave control logic of the next Hall sector, and define the phase in a fully off state as the off phase.

5. The method for reducing the temperature of power devices using a brushless DC controller according to claim 1, characterized in that, In step S30, the step of forcibly adjusting the inactive phase in the discontinuous pulse width modulation mode to be consistent with the shutdown phase includes: The strategy of selecting clamping objects based on the absolute value of three-phase voltage command values ​​is disabled; Obtain the voltage command value at the moment before the turn-off, and calculate the forced zero-sequence voltage component, so that the duty cycle of the turn-off phase after superimposing the forced zero-sequence voltage component reaches the boundary value of the modulation waveform. The forced zero-sequence voltage component is superimposed on the three-phase voltage command value, so that the off phase stops switching and maintains a constant level during the current pulse width modulation cycle, while the other two phases maintain chopper control.

6. The method for reducing the temperature of power devices using a brushless DC controller according to claim 1, characterized in that, In step S40, the step of calculating the bus current setpoint under square wave control mode using the torque balance principle includes: Read the given value of the torque current component that was held at the moment before switching to square wave control mode; Obtain a preset torque equivalence coefficient, which is used to compensate for the difference in current utilization between the space vector pulse width modulation mode and the square wave control mode; Multiplying the torque current component setpoint by the torque equivalence coefficient yields the bus current setpoint under the square wave control mode.

7. The method for reducing the temperature of power devices using a brushless DC controller according to claim 1, characterized in that, In step S40, the specific control process of the square wave control mode includes: The three-phase inverter bridge is controlled to maintain a 2-to-2 conduction state according to the preset conduction logic mapping table. The 2-to-2 conduction state means that only two power devices are conducting at any given time. Based on the deviation between the real-time collected bus current feedback value and the given bus current value, chopping control is performed on the power device in the conducting state.

8. A method for reducing the temperature of power devices using a brushless DC controller according to claim 1, characterized in that, In step S40, the step of switching the control mode to square wave control mode when an edge transition of the Hall sensor signal is detected further includes: Call the pre-stored Hall effect installation error compensation angle; The Hall installation error compensation angle in the angular dimension is converted into a compensation value in the time dimension by combining the real-time speed of the motor. The operating timing of the power devices is corrected using the compensation value to ensure that the stator magnetic field and the rotor magnetic field remain orthogonal.

9. A method for reducing the temperature of power devices using a brushless DC controller according to claim 8, characterized in that, The method for obtaining the Hall effect installation error compensation angle is as follows: During the operation of the space vector pulse width modulation mode by the controller, the rotor position observer is used to calculate the estimated rotor angle; When an edge transition is detected in the Hall sensor signal, the estimated rotor angle at the current moment is recorded, and the theoretical Hall angle corresponding to the current state value of the Hall sensor signal is found. The difference between the estimated rotor angle and the theoretical Hall angle is calculated, and the Hall installation error compensation angle is updated using a low-pass filtering algorithm.

10. A method for reducing the temperature of power devices using a brushless DC controller according to claim 1, characterized in that, The first preset temperature range is defined by a first temperature threshold and a second temperature threshold, and the second preset temperature range is defined by a range that is higher than or equal to the second temperature threshold.

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