Control method and circuit for suppressing starting impact current

Abstract

The invention belongs to the technical field of current suppression, and particularly relates to a control method and circuit for suppressing starting impact current. The method comprises the steps of determining a PWM pulse signal frequency according to a charge-discharge time constant of a capacitive load, a driving switch short-circuit current threshold and a current rise rate of a power supply loop, and determining a duty ratio according to the charge-discharge time constant or the charge-discharge time constant and the frequency, so that a current pulse peak value is always smaller than the short-circuit current threshold during a driving switch turn-on period; according to the current value of a power supply loop and the voltage of a power supply when the PWM pulse signal is switched to the 100% duty ratio, the pre-charging voltage value which the capacitive load needs to reach when the PWM pulse signal is stopped from being output is determined, and according to the pre-charging voltage value and the PWM duty ratio and frequency, the number of pulses is calculated. And the current value of the power supply loop is smaller than the short-circuit current threshold value, so that the starting impact current is accurately suppressed on the premise that the cost is not increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of current suppression, and particularly relates to a control method and circuit for suppressing starting inrush current. Background Art

[0002] With the improvement of the electrification and intelligence levels of vehicle powertrains, more and more vehicle models use drive switches (high-side switches or gate drivers) for intelligent power distribution. The drive switches are arranged in the power supply loop for supplying power to vehicle loads. However, due to the presence of large electrolytic capacitors in vehicle loads, especially fans, water pumps, and steering oil pumps, when the intelligent power distribution system powers on the capacitive load at the moment of power-on for the vehicle load, a large inrush current will be generated during the charging of the capacitive load. This inrush current usually exceeds the short-circuit current threshold set by the high-side switch or gate driver, triggering the short-circuit protection of the high-side switch or gate driver, resulting in the high-side switch or gate driver being turned off, thus disconnecting the power supply loop of the load and preventing the load from starting normally. To solve this problem, the commonly used methods are as follows: 1) increasing the short-circuit current threshold of the high-side switch or gate driver; 2) adding a resistor pre-charge loop. However, increasing the short-circuit current threshold of the high-side switch or gate driver requires using a larger specification high-side switch or increasing the number of MOS transistors driven by the gate driver, and adding a resistor pre-charge loop requires using a pre-charge resistor with a larger power. Both of the above two schemes will cause an increase in cost and an increase in the size of the power distribution product. Moreover, due to the large correlation between the actual current suppression effect and the capacitive load, the flexibility of the above two schemes in suppressing the starting inrush current is poor. Although the concept of suppressing the starting inrush current through PWM (Pulse Width Modulation) technology has been proposed, no specific control method has been given, and the control parameters and control effects are not clear. Summary of the Invention

[0003] The purpose of the present invention is to provide a control method and circuit for suppressing starting inrush current, which can more accurately suppress the starting inrush current without increasing costs.

[0004] The present invention provides a control method for suppressing starting inrush current. When the load of the vehicle needs to start and be powered on, a PWM pulse signal with a set duty cycle and a set frequency is output to the drive switch in the load power supply loop. When the PWM pulse signal reaches the set number, the output of this PWM pulse signal is stopped;

[0005] Among them, the set duty cycle is determined based on the minimum duty cycle or the maximum duty cycle. The minimum duty cycle is the ratio of the charging time constant of the capacitive load to the sum of the charging time constant and the discharging time constant. The maximum duty cycle is determined based on the maximum value of the current rise time and the set frequency. The maximum value of the current rise time is the ratio of the short-circuit current threshold of the driving switch to the current rise rate of the power supply circuit. The set frequency is determined based on the minimum duty cycle and the maximum value of the current rise time. The set number is determined based on the pre-charging voltage value that the capacitive load needs to reach when the PWM pulse signal stops outputting, the set duty cycle, and the set frequency. The pre-charging voltage value is determined based on the power supply voltage and the target current value. Among them, the target current value refers to the current value of the power supply circuit when the PWM pulse signal switches to a 100% duty cycle, and the target current value is less than the short-circuit current threshold of the driving switch.

[0006] Further, the set frequency is the ratio of the minimum duty cycle of the set multiple to the maximum value of the current rise time.

[0007] Further, the determination process of the set frequency is as follows: calculate the ratio of the minimum duty cycle of the set multiple to the maximum value of the current rise time, round up the calculated ratio of the minimum duty cycle of the set multiple to the maximum value of the current rise time to the nearest hundred to obtain the set frequency of the PWM pulse signal, and the unit of the set frequency is Hz.

[0008] Further, the set duty cycle is the minimum duty cycle of the set multiple, and the set multiple is greater than 1.

[0009] Further, the set duty cycle is the value obtained by rounding down the maximum duty cycle, and the maximum duty cycle is the product of the set frequency and the maximum value of the current rise time.

[0010] Further, the determination process of the set number is as follows: determine the charging time and discharging time of the capacitive load in one PWM cycle according to the set frequency and the set duty cycle, calculate the voltage of the capacitive load after each charging and discharging according to the charging time, discharging time, charging time constant, and discharging time constant of the capacitive load in one PWM cycle. When the voltage of the capacitive load after the (N - 1)th charging and discharging is less than the pre-charging voltage value but the voltage of the capacitive load after the Nth charging and discharging is greater than or equal to the pre-charging voltage value, N is used as the set number of the PWM pulse signal.

[0011] Further, the method further includes: calculating the surge current parameter of the freewheeling diode according to the actual turn-on time of the drive switch within a PWM period, the derating factor of the freewheeling diode, and the current rise rate of the power supply loop; wherein, the actual turn-on time of the drive switch within the PWM period is calculated according to the set duty cycle and set frequency of the PWM pulse signal; the freewheeling diode is used to conduct current through the freewheeling diode at the moment when the drive switch is turned off, the anode of the freewheeling diode is connected to the load ground wire, and the cathode is connected between the drive switch and the load.

[0012] The beneficial effects of the above technical solutions are as follows: The present invention is an exploratory invention and provides a specific control method for suppressing the inrush current when powering on a capacitive load through PWM, including the determination of parameters such as the frequency, duty cycle, and number of pulses of the PWM pulse signal. The frequency of the PWM pulse signal is determined according to the charge and discharge time constant of the capacitive load, the short-circuit current threshold of the drive switch, and the current rise rate of the power supply loop. The duty cycle is determined according to the charge and discharge time constant or the charge and discharge time constant and the frequency, so that the peak value of the current pulse is always less than the short-circuit current threshold during the turn-on period of the drive switch. At the same time, the capacitive load is charged during the turn-on period of the switch, and the target current value is calculated based on the target that the current value is always limited below the short-circuit current threshold when the PWM pulse signal is switched to 100% duty cycle (that is, the drive switch is always in the on state). The pre-charge capacitance value that the capacitive load needs to reach is calculated, and the number of pulses of the PWM pulse signal to be output is determined based on the pre-charge capacitance value and the parameters of the PWM pulse signal, so that when the PWM control ends and switches to the normal turn-on of the drive switch, the capacitance of the capacitive load has a certain initial voltage, and the current value of the power supply loop at this voltage is the target current value. Since the target current value is less than the short-circuit current threshold, the drive switch will not trigger short-circuit protection after the PWM control ends, thus realizing the normal start of the load, being able to more accurately suppress the starting inrush current without increasing costs, and the PWM control parameters can be configured according to different vehicles and loads, with higher flexibility.

[0013] To solve the above technical problems, the present invention also provides a control circuit for suppressing the starting inrush current, including a drive switch, the drive switch is arranged between the power supply of the load power supply loop and the load, and further includes a controller, the controller is connected to the drive switch in a controlling manner, and is used to send a PWM pulse signal to the drive switch according to the control method for suppressing the starting inrush current introduced above to realize the suppression of the inrush current when the load needs to be started and powered on.

[0014] Further, the drive switch is a high-side switch or a power MOS transistor.

[0015] Further, the control circuit further includes a freewheeling diode. The anode of the freewheeling diode is connected to the load ground wire, and the cathode is connected between the driving switch and the load, and is used for freewheeling through the freewheeling diode at the moment when the driving switch is turned off. The surge current parameter of the freewheeling diode is determined according to the actual on-time of the driving switch within a PWM period, the derating factor of the freewheeling diode, and the current rising rate of the power supply circuit. Among them, the actual on-time of the driving switch within a PWM period is calculated according to the set duty cycle and set frequency of the PWM pulse signal.

[0016] The beneficial effects of the above technical solution are as follows: The present invention is an exploratory invention, and a specific control method for suppressing the inrush current when powering on a capacitive load through PWM is given, including the determination of parameters such as the frequency, duty cycle, and number of pulses of the PWM pulse signal. The frequency of the PWM pulse signal is determined according to the charge-discharge time constant of the capacitive load, the short-circuit current threshold of the driving switch, and the current rising rate of the power supply circuit. The duty cycle is determined according to the charge-discharge time constant or the charge-discharge time constant and the frequency, so that the peak value of the current pulse is always less than the short-circuit current threshold during the on period of the driving switch. At the same time, the capacitive load is charged during the on period of the switch, and the target current value is calculated based on the target that the current value is always limited below the short-circuit current threshold when the PWM pulse signal is switched to 100% duty cycle (that is, the driving switch is always in the on state). The pre-charge capacitance value that the capacitive load needs to reach is calculated, and the number of pulses of the PWM pulse signal to be output is determined based on the pre-charge capacitance value and the parameters of the PWM pulse signal, so that when the PWM control ends and switches to the normal on state of the driving switch, the capacitance of the capacitive load has a certain initial voltage, and the current value of the power supply circuit at this voltage is the target current value. Since the target current value is less than the short-circuit current threshold, the driving switch will not trigger short-circuit protection after the PWM control ends, thus realizing the normal start of the load, being able to more accurately suppress the starting inrush current without increasing costs, and the PWM control parameters can be configured according to different vehicles and loads, with higher flexibility. Description of the Drawings

[0017] Figure 1 is a schematic diagram of the principle of suppressing the starting inrush current in the method embodiment of the present invention;

[0018] Figure 2 is a control flowchart of a method for suppressing the starting inrush current in the method embodiment of the present invention. Detailed Embodiments

[0019] In order to make the purpose, technical solution and advantages of the present invention clearer, the following further describes the detailed embodiments of the present invention with reference to the drawings.

[0020] The present invention provides a method for determining PWM parameters required to more precisely suppress the starting inrush current using PWM without increasing costs, based on the capacitive load configured in the vehicle, the drive switch configured in the load power supply circuit, the power supply, and the measured current rise rate of the power supply circuit.

[0021] Method embodiment

[0022] As Figure 1 shown, vehicles generally use drive switches to perform intelligent power distribution for loads. The loads of the vehicle include resistive loads and capacitive loads. The drive switch is arranged between the power supply and the load in the load power supply circuit. By sending a PWM pulse signal to the control end of the drive switch, the turn-on time of the drive switch is controlled, so that the peak value of the current pulse in the power supply circuit during the turn-on period is less than the short-circuit current threshold set by the determining switch. At the same time, the capacitive load is pre-charged using the current during the turn-on period. When the PWM drive ends and the capacitive load has a certain initial voltage, when switching to normal turn-on of the drive switch, the peak value of the current pulse in the power supply circuit is reduced below the short-circuit current threshold, thereby achieving the suppression of the inrush current during startup and enabling the load to start normally.

[0023] The drive switch can be a high-side switch or a power MOS transistor. The power MOS transistor can be a single MOS transistor or an assembly of multiple MOS transistors. When the drive switch is a high-side switch, the input end of the drive switch is connected to the power supply, the output end is connected to the load, and the input end also serves as the control end to receive the PWM pulse signal. When the drive switch is a power MOS transistor, the drain of the drive switch is connected to the power supply, the source is connected to the load, and the gate serves as the control end to receive the PWM pulse signal.

[0024] Based on the above circuit configuration, the present invention provides a control method for suppressing the starting inrush current. When the load of the vehicle needs to be started and powered on, a PWM pulse signal with a set duty cycle and a set frequency is output to the drive switch in the load power supply circuit. When the PWM pulse signal reaches the set number, the output of the PWM pulse signal is stopped. The set duty cycle of the PWM pulse signal is determined based on the minimum duty cycle or the maximum duty cycle. The minimum duty cycle is the ratio of the charging time constant of the capacitive load to the sum of the charging time constant and the discharging time constant. The maximum duty cycle is determined based on the maximum value of the current rise time and the set frequency. The maximum value of the current rise time is the ratio of the short-circuit current threshold of the drive switch to the current rise rate of the power supply circuit. The set frequency is determined based on the minimum duty cycle and the maximum value of the current rise time. The set number is determined based on the pre-charge voltage value that the capacitive load needs to reach when the output of the PWM pulse signal is stopped, the set duty cycle, and the set frequency. The pre-charge voltage value is determined based on the power supply voltage and the target current value. As Figure 2 shown, the determination of each parameter is described in detail below.

[0025] 1. Determine the minimum duty cycle of the PWM pulse signal.

[0026] Calculate the charging time constant of the capacitive load according to the following formula:

[0027] τ1 = R ESR ·CL·10 -6

[0028] where τ1 is the charging time constant of the capacitive load; R ESR is the parasitic series resistance of the capacitive load, in units of Ω; CL is the capacitance of the capacitive load, in units of μF.

[0029] Calculate the discharging time constant of the capacitive load according to the following formula:

[0030] τ2 = RL·CL·10 -6

[0031] where τ2 is the discharging time constant of the capacitive load; RL is the equivalent resistance of the resistive load, in units of Ω.

[0032] Take the ratio of the charging time constant of the capacitive load to the sum of the charging time constant and the discharging time constant of the capacitive load as the minimum duty cycle:

[0033]

[0034] 2. Determine the set frequency and set duty cycle of the PWM pulse signal.

[0035] In practical applications, the duty cycle of the PWM pulse signal should be greater than the minimum duty cycle. The larger the duty cycle, the better the pre-charging effect on the capacitor and the smaller the inrush current at startup. In one implementation, take the set multiple of the minimum duty cycle as the set duty cycle of the PWM pulse signal; the set multiple is greater than 1, for example, set to 5. To ensure a better pre-charging effect, in engineering practice, the set multiple can be set to a value greater than 6, such as set to 6, 7, or 8, etc., which can be set according to specific requirements. That is:

[0036] Duty = K duty ·Duty min

[0037] where Duty is the set duty cycle of the PWM pulse signal, and K duty is the set multiple.

[0038] Determine the set frequency of the PWM pulse signal based on the minimum duty cycle and the maximum value of the current rise time. Specifically, calculate the maximum value of the current rise time according to the short-circuit current threshold of the driving switch and the current rise rate of the power supply circuit, and then take the ratio of the set duty cycle to the maximum value of the current rise time as the set frequency of the PWM pulse signal.

[0039] Calculate the maximum value of the current rise time according to the following formula:

[0040]

[0041] where t rise is the maximum value of the current rise time, in μS; I sc is the short-circuit current threshold of the drive switch, in A; K I_Slope is the current rise rate of the power supply circuit, in A / μS. The current rise rate of the power supply circuit refers to the current rise rate of the main circuit where the drive switch is located when the drive switch is turned on. K I_Slope is obtained according to actual tests. When the on-vehicle load and the wire diameter of the cable are different, K I_Slope varies slightly.

[0042] Calculate the set frequency of the PWM pulse signal according to the following formula:

[0043]

[0044] As a preferred implementation, for the convenience of the processor to control, both the set duty cycle and the set frequency are integers. After the minimum duty cycle is increased by a set multiple, calculate the ratio of the duty cycle of the set multiple to the maximum value of the current rise time, and then round up the calculated ratio to the nearest hundred. Take the value after rounding up to the nearest hundred as the set frequency of the PWM pulse signal. At this time, calculate the set frequency of the PWM pulse signal according to the following formula:

[0045]

[0046] where round represents rounding. The unit of the set frequency is Hz.

[0047] When the set frequency of the PWM pulse signal is a value rounded to the nearest hundred, determine the set duty cycle based on the maximum duty cycle. Specifically, multiply the set frequency by the maximum value of the current rise time as the maximum duty cycle, round down the maximum duty cycle, and take the value after rounding down as the set duty cycle of the PWM pulse signal. The calculation process is as follows:

[0048] Duty max = t rise · 10 -6 · f PWM

[0049] Duty = round(Duty max · 100)

[0050] where Duty max is the maximum duty cycle.

[0051] 3. Determine the set number of PWM pulse signals.

[0052] It includes the following steps:

[0053] 1) Determine the charging time and discharging time of the capacitive load within one PWM cycle according to the set frequency and set duty ratio of the PWM pulse signal:

[0054]

[0055] Among them, T1 is the charging time of the capacitive load within 1 PWM cycle, and T2 is the discharging time of the capacitive load within 1 PWM cycle.

[0056] 2) Calculate the pre-charge voltage value that the capacitive load needs to reach when stopping outputting the PWM pulse signal according to the supply power voltage and the target current value. The target current value refers to the current value of the power supply circuit when the PWM pulse signal switches to a 100% duty ratio, that is, the peak current detected at the driving switch of the power supply circuit when the driving switch is always on. The target current value is less than the short-circuit current threshold of the driving switch.

[0057] V CAP_PreCharge = V BAT - R ESR · I target

[0058] Among them, V CAP_PreCharge is the pre-charge voltage value that the capacitive load needs to reach, with the unit of V; V BAT is the supply power voltage, with the unit of V; I target is the target current value, with the unit of A.

[0059] 3) Calculate the voltage of the capacitive load after each charge and discharge according to the charging time, discharging time, charging time constant and discharging time constant of the capacitive load within one PWM cycle. When the voltage of the capacitive load after the Nth charge and discharge is greater than or equal to the pre-charge voltage value, take N as the set number of PWM pulse signals.

[0060]

[0061] Among them, V CAP (n) is the voltage value of the capacitive load after the nth charge and discharge, V τ1 is the voltage value of the capacitive load after charging, V τ2 is the voltage value of the capacitive load after discharging.

[0062] The V at the initial moment τ2 is set to 0, and the operation formula V CAP(n) Perform iterative operations. When the voltage of the capacitive load is less than the pre-charge voltage value after the (N - 1)-th charge and discharge, but the voltage of the capacitive load is greater than or equal to the pre-charge voltage value after the N-th charge and discharge, take N as the set number of PWM pulse signals. That is, when N satisfies the following formula, take N as the set number of PWM pulse signals: V CAP (N - 1) < V CAP_PreCharge And V CAP (N) ≥ V CAP_PreCharge .

[0063] 4. Determine the surge current of the freewheeling diode.

[0064] Due to the existence of the parasitic inductance of the cable, a freewheeling diode is provided in the load power supply circuit. The anode of the freewheeling diode is connected to the load ground wire, and the cathode is connected between the drive switch and the load. Freewheeling is performed through the freewheeling diode at the moment when the PWM control drive switch is turned off. To avoid the normal operation of the freewheeling diode, the present invention also designs the surge current parameter I FSM of the freewheeling diode. The surge current parameter is determined based on the set duty cycle and set frequency of the PWM pulse signal, the derating factor of the freewheeling diode, and the current rising rate of the power supply circuit. The determination process is as follows:

[0065] Calculate the actual on-time of the drive switch within one PWM period according to the set duty cycle and set frequency of the PWM pulse signal:

[0066]

[0067] Take the product of the actual on-time of the drive switch within one PWM period, the derating factor of the freewheeling diode, and the current rising rate of the power supply circuit as the minimum value of the surge current of the freewheeling diode:

[0068]

[0069] Where, t rise_actual is the actual on-time of the drive switch within one PWM period, with the unit of μS; is the minimum value of the surge current of the freewheeling diode, with the unit of A; K IFSM is the derating factor of the freewheeling diode.

[0070] Circuit embodiment

[0071] A control circuit for suppressing the starting inrush current of the present invention, as Figure 1 shown, includes a drive switch and a controller. The drive switch is arranged between the power supply of the load power supply circuit and the load, and the controller is connected to the drive switch in a control manner. The drive switch is a high-side switch or a power MOS transistor ( Figure 1(in the gate driver). The controller is used to send a PWM pulse signal to the drive switch according to the control method for suppressing the starting inrush current introduced in the above method embodiments to achieve the suppression of the inrush current when the load needs to be started and powered on. Among them, the controller can be a microprocessor MCU, a programmable logic device FPGA, a single-chip microcomputer, etc.

[0072] The control circuit further includes a freewheeling diode. The anode of the freewheeling diode is connected to the load ground wire, and the cathode is connected between the drive switch and the load, and is used for freewheeling through the freewheeling diode at the moment when the drive switch is turned off; the surge current parameter of the freewheeling diode is determined according to the actual on-time of the drive switch within a PWM period, the derating factor of the freewheeling diode, and the current rising rate of the power supply circuit. Among them, the actual on-time of the drive switch within a PWM period is calculated according to the set duty cycle and set frequency of the PWM pulse signal.

Claims

1. A control method for suppressing starting inrush current, characterized in that: include: When the vehicle's load needs to be powered on, a PWM pulse signal with a set duty cycle and a set frequency is output to the drive switch in the load power supply circuit. When the PWM pulse signal reaches the set number, the PWM pulse signal is stopped from being output; Among them, the set duty cycle is determined based on the minimum duty cycle or the maximum duty cycle, the minimum duty cycle is the ratio of the charging time constant of the capacitive load to the sum of the charging time constant and the discharging time constant, the maximum duty cycle is determined based on the maximum current rise time and the set frequency, the maximum current rise time is the ratio of the short-circuit current threshold of the drive switch and the current rise rate of the power supply circuit; the set frequency is determined based on the minimum duty cycle and the maximum current rise time; the set number is determined based on the pre-charge voltage value, the set duty cycle and the set frequency that the capacitive load needs to reach when the output of the PWM pulse signal is stopped, the pre-charge voltage value is determined based on the power supply voltage and the target current value; wherein, the target current value refers to the current value of the power supply circuit when the PWM pulse signal is switched to a 100% duty cycle, and the target current value is less than the short-circuit current threshold of the drive switch.

2. The control method for suppressing starting inrush current according to claim 1, characterized in that: The set frequency is the ratio of the minimum duty cycle of the set multiple to the maximum value of the current rise time.

3. The control method for suppressing starting inrush current according to claim 1, characterized in that: The process of determining the set frequency is as follows: calculating the ratio of the minimum duty cycle of the set multiple to the maximum value of the current rise time, and rounding up the calculated ratio of the minimum duty cycle of the set multiple to the maximum value of the current rise time to obtain the set frequency of the PWM pulse signal, and the unit of the set frequency is Hz.

4. The control method for suppressing starting inrush current according to claim 2, characterized in that: The set duty cycle is a minimum duty cycle of the set multiple, and the set multiple is greater than 1.

5. The control method for suppressing starting inrush current according to claim 3, characterized in that: The set duty cycle is a value obtained by rounding down the maximum duty cycle, and the maximum duty cycle is the product of the set frequency and the maximum value of the current rise time.

6. The control method for suppressing starting inrush current according to claim 1, characterized in that: The process of determining the set number is as follows: determining the charging time and discharging time of the capacitive load within a PWM cycle according to the set frequency and the set duty cycle, calculating the voltage of the capacitive load after each charging and discharging according to the charging time, discharging time, charging time constant and discharging time constant of the capacitive load within a PWM cycle, and when the voltage of the capacitive load after the N-1th charging and discharging is less than the pre-charge voltage value but the voltage of the capacitive load after the Nth charging and discharging is greater than or equal to the pre-charge voltage value, taking N as the set number of PWM pulse signals.

7. The control method for suppressing starting inrush current according to claim 1, characterized in that: The method also includes: calculating the surge current parameter of the freewheeling diode according to the actual on-time of the driving switch within a PWM cycle, the derating factor of the freewheeling diode, and the current rise rate of the power supply circuit; wherein the actual on-time of the driving switch within the PWM cycle is calculated according to the set duty cycle and the set frequency of the PWM pulse signal; the freewheeling diode is used for freewheeling through the freewheeling diode at the turn-off moment of the driving switch, the anode of the freewheeling diode is connected to the load ground wire, and the cathode is connected between the driving switch and the load.

8. A control circuit for suppressing startup inrush current, comprising a drive switch, wherein the drive switch is arranged between a power supply of a load power supply circuit and a load, and wherein: It also includes a controller, which controls the connected drive switch and is used to send a PWM pulse signal to the drive switch according to the control method for suppressing startup impact current as described in any one of claims 1-6 to achieve impact current suppression when the load needs to be started and powered on.

9. The control circuit for suppressing starting inrush current according to claim 8, characterized in that: The driving switch is a high-side switch or a power MOS tube.

10. The control circuit for suppressing starting inrush current according to claim 8 or 9, characterized in that: The control circuit also includes a freewheeling diode, an anode of which is connected to a load ground wire, and a cathode of which is connected between a drive switch and a load, for freewheeling current through the freewheeling diode at the moment when the drive switch is turned off; a surge current parameter of the freewheeling diode is determined according to an actual on-time of the drive switch within a PWM cycle, a derating factor of the freewheeling diode, and a current rise rate of a power supply circuit, wherein the actual on-time of the drive switch within a PWM cycle is calculated according to a set duty cycle and a set frequency of a PWM pulse signal.

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