Vehicle-mounted DCDC active RCD absorption control method

Abstract

The invention discloses a vehicle-mounted DCDC active RCD absorption control method, which comprises the following steps: by additionally arranging a device for detecting the temperatures of resistors R1 and R2 in real time and two voltage detection circuits for monitoring the VDS stress of a tube SR1 and a tube SR2, reading the temperatures TR1 and TR2 of the resistors R1 and R2 by utilizing a single chip microcomputer, and reducing the duty ratio of a PWPMOS1 when the temperatures exceed an allowable value, so as to realize the absorption control of the vehicle-mounted DCDC active RCD. And the conduction time of the R1 and the R2 is reduced, so that the temperature of the R1 and the R2 is reduced to be within an allowable value TPASS. According to the technical scheme, the heating problem of the active absorption resistors R1 and R2 and the heating and VDS stress problem caused by the difference between the active absorption resistors and power tube devices can be effectively solved on the basis of not increasing extra heat dissipation scheme cost and occupying the PCB area, and adaptive control and real-time detection and real-time independent control adjustment can be achieved.

Description

Technical Field

[0001] This invention relates to the field of switching power supplies, and in particular to a method for controlling the active RCD absorption of an on-board DC-DC converter. Background Technology

[0002] Currently, the function of onboard DC-DC modules in electric vehicles is to convert the voltage of the high-voltage battery pack (380V-560V for 400V systems, 400V-900V for 800V systems) into a low-voltage (9V-16V) output to charge the low-voltage battery and power 12V low-voltage loads. The mainstream circuit topology for DC-DC modules is PSFB (Phase-Shifted Full-Bridge), such as... Figure 1 As shown.

[0003] Because the high-voltage input HV_BAT has a relatively large voltage range (400V-900V), especially at 900V input, the VDS stress of the low-voltage side Sd1 and Sd2 transistors is particularly high. The mainstream technical solution to reduce VDS stress is to add a passive RC snubber circuit or an active RCD snubber circuit between the DS and voltage sources.

[0004] A more effective method is using an active RCD absorption circuit, such as... Figure 2 As shown. The mainstream technical solution is to send a PWM wave with a fixed duty cycle to PMOS1 and PMOS2 to reduce VDS stress. The drawback of this solution is that it cannot solve the heat generation problem of R1 and R2. It usually requires additional heat dissipation solutions and increased power ratings of R1 and R2. Heat dissipation solutions increase costs, and high-power resistors occupy a larger package and take up more space on the already limited PCB. Summary of the Invention

[0005] This invention aims to solve the following technical problems existing in current active RCD absorption circuits:

[0006] (1) Existing technologies cannot solve the heat generation problem of R1 and R2;

[0007] (2) Existing technologies usually require additional heat dissipation solutions and increased power of resistors R1 and R2. Heat dissipation solutions increase costs, and high-power resistors occupy a larger area of ​​the already limited PCB.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: a vehicle-mounted DC-DC active RCD absorption control method, characterized in that it includes: real-time monitoring of the temperatures T_R1 and T_R2 of resistors R1 and R2 and the VDS stress of their respective power transistors SR1 and SR2; when the temperatures T_R1 and T_R2 exceed the design allowable value T_PASS, controlling the duty cycle to decrease; if the duty cycle has decreased to the minimum adjustable allowable value, but the temperatures T_R1 and / or T_R2 of resistors R1 and / or R2 have not yet decreased to within the allowable value T_PASS, initiating the power derating of the DC-DC module to reduce the operating power of the DC-DC module until the temperatures of R1 and R2 decrease to within the allowable value T_PASS.

[0009] Preferably, the temperatures T_R1 of resistor R1 and T_R2 of resistor R2 are obtained by temperature sensors located next to the positions of resistors R1 and R2, respectively.

[0010] Preferably, the VDS stress of the power transistor devices of resistors R1 and R2 is monitored by two additional voltage detection circuits.

[0011] Preferably, the full power allowable range of the resistors R1 and R2 is 0W-3kW.

[0012] Preferably, the temperatures T_R1 and T_R2 are read and determined by a microcontroller.

[0013] Preferably, the voltages of VDS_SR1 and VDS_SR2 are monitored simultaneously during the reduction of the duty cycle to ensure that the voltages of VDS_SR1 and VDS_SR2 do not exceed the design allowable value V_PASS.

[0014] Preferably, the reduction of the duty cycle is achieved through software.

[0015] Preferably, R1 and R2 are controlled separately and independently.

[0016] The beneficial effect of this invention is that, based on the temperature and stress feedback of R1 and R2, the duty cycle of the PWM of the active MOS is adjusted in real time, so that the temperature of the resistor is controlled within the allowable range. Furthermore, the independent control of R1 and R2 can solve the problems of heat generation and different VDS stress caused by the differences in the resistor and power transistor devices themselves. Attached Figure Description

[0017] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings required in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can obtain these drawings without any additional creative effort.

[0018] Figure 1 It is currently the mainstream circuit topology solution for automotive power supply DC-DC modules;

[0019] Figure 2 It is currently the best performing active RCD absorption circuit;

[0020] Figure 3 This is a flowchart of an active RCD absorption control method for vehicle-mounted DC-DC converters according to the present invention;

[0021] Figure 4 This is a circuit diagram of an embodiment of the active RCD absorption control method for vehicle-mounted DC-DC converters according to the present invention. Detailed Implementation

[0022] The technical solutions will now be clearly and completely described with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the examples described are only a part of the embodiments of the present invention and do not cover all possible implementations. Based on the embodiments of the present invention, all other embodiments that can be obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0023] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. In the description of the present invention, the terms "upper," "lower," "top," "bottom," etc., refer to the orientation or positional relationship based on the orientation or position shown in the accompanying drawings, and are used only for the convenience of describing the present invention and simplifying expression, and do not imply that the device or element must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0024] like Figure 3 As shown, an active RCD absorption control method for an on-board DC-DC converter includes: real-time monitoring of the temperature T_R1 of resistor R1 and the VDS stress of its self-power transistor SR1; when the temperature T_R1 exceeds the design allowable value T_PASS, controlling the duty cycle to decrease; if the duty cycle has already decreased to the minimum adjustable allowable value, but the temperature T_R1 of resistor R1 has not yet decreased to within the allowable value T_PASS, then initiating the power derating of the DC-DC module to reduce the operating power of the DC-DC module until the temperature of R1 decreases to within the allowable value T_PASS.

[0025] like Figure 4As shown, the NTC temperature sensing resistor R4 (or other temperature sensor) is placed close to R1 in the PCB layout. When the temperature of R1 changes, the resistance of R4 will change. The voltage divider formula V_T_R1=R4 / (R4+R2) means that when the resistance of R4 changes, the value of V_T_R1 will also change in real time. The voltage value of V_T_R1 is sent to the microcontroller for processing. The voltage value of V_T_R1 provides real-time feedback on the temperature of the active absorption resistor R1. The voltage value of V_T_R1 and the temperature of the active absorption resistor R1 are proportional.

[0026] The voltage stress VDS across MOSFET SR1 is sent to the voltage stress detection circuit, which uses an operational amplifier proportional circuit (any other sampling circuit can be used as long as it can sample the VDS voltage). In the voltage stress detection circuit, R6=R8, R9=R5, and the voltage stress detection circuit calculation formula is VDS_SR1=VDS*R5 / R6;

[0027] The value of VDS_SR1 provides real-time feedback on the voltage stress VDS across SR1. The active clamp RCD circuit is used to absorb the peak voltage stress VDS across SR1. A peak voltage stress VDS is generated when SR1 is turned off. This peak voltage stress VDS charges capacitor C1, transferring the peak voltage stress to C1 and preventing excessive VDS stress from damaging the MOSFET SR1. During the SR1 turn-off period...

[0028] refer to Figure 2 The peak voltage stress across C1 is released through the R1, Pmos1, SR2, Lk circuit, converting the energy of the voltage change across the capacitor, C*∆U*∆U / 2, into heat energy in resistor R1. The heat energy of resistor R1 is calculated using the formula W_R1=I*I*R1*Ton. When the on-time Ton of Pmos1 is long, the heating of R1 is more severe, and the temperature of R1 is higher; when the on-time Ton of Pmos1 is short, the heating of R1 is reduced, and the temperature of R1 is lower. Ton is determined by the duty cycle D of the PWM_PMOS1 driving signal of Pmos1, Ton=D*Tsw, where Tsw is the switching period of the PWM_PMOS1 driving signal of Pmos1.

[0029] Since Tsw is a fixed value, it can be deduced that the duty cycle D of the PWM_PMOS1 driving signal of Pmos1 is directly proportional to the temperature of the active absorption R1. A larger duty cycle results in a higher temperature of the active absorption R1, and a smaller duty cycle results in a lower temperature of the active absorption R1. The temperature of R1 can be adjusted by adjusting the duty cycle to ensure that the temperature of R1 does not exceed the temperature T_PASS that we designed.

[0030] The purpose of the active clamping RCD circuit is to reduce the peak voltage stress VDS across SR1. As long as the peak voltage stress VDS across SR1 does not exceed the allowable value we designed, the temperature of resistor R1 can be reduced by adjusting the duty cycle D according to the real-time operating conditions, ensuring that the temperature of R1 is within the allowable T_PASS range.

[0031] If the voltage of VDS_SR1 is guaranteed not to exceed the design allowable value V_PASS, the duty cycle has been reduced to the minimum allowable value D_min, and the temperature of R1 has not yet dropped below the allowable value T_PASS, then the power derating of the DC-DC module will be started to reduce the operating power of the DC-DC module until the temperature of R1 drops below the allowable value T_PASS.

[0032] The control method is implemented by first sending the sampled values ​​of T_R1 and VDS_SR1 to the microcontroller (MCU) for processing in real time. After calculation and processing, the MCU outputs an appropriate duty cycle D and an appropriate power to ensure that the stress of VDS_SR1 is within the range of V_PASS and the temperature of R1 is within the range of T_PASS.

[0033] SR1 and SR2 are controlled independently. The control process of SR2 is the same as that of SR1, so it will not be repeated.

[0034] The separate real-time feedback control of the active absorption resistors R1 and R2 effectively solves the parasitic parameter differences between the power MOSFETs SR1 and SR2 caused by PCB layout, including the differences in the parameters of the power MOSFETs and resistors themselves. This eliminates the need for additional heat dissipation solutions to address the heat generation issue of the active absorption resistors R1 and R2. The specific control process of this method is detailed in [link to documentation]. Figure 3 The control method is precise and dynamically adjusted in real time, solving the overheating problem of R1 and R2.

[0035] The above description represents preferred embodiments and implementation methods of the present invention. It should be noted that those skilled in the art can make various improvements and adjustments without departing from the principles of the present invention, and these improvements and adjustments should also be considered within the scope of protection of the present invention.

Claims

1. A method for controlling the absorption of an onboard DC-DC active RCD, characterized in that, include: The system monitors the temperatures T_R1 and T_R2 of resistors R1 and R2 in real time, as well as the VDS stress of their respective power transistors SR1 and SR2. When the temperatures T_R1 and T_R2 exceed the design allowable value T_PASS, the duty cycle is reduced. If the duty cycle has been reduced to the minimum adjustable value, but the temperatures T_R1 and / or T_R2 of resistors R1 and / or R2 have not yet decreased to within the design allowable value T_PASS, the power derating of the DC-DC module is activated to reduce its operating power until the temperatures of R1 and R2 decrease to within the design allowable value T_PASS.

2. The method for controlling the absorption of an on-board DC-DC active RCD according to claim 1, characterized in that, The temperatures T_R1 of resistor R1 and T_R2 of resistor R2 are obtained by temperature sensors located next to the positions of resistors R1 and R2, respectively.

3. The method for controlling the absorption of an on-board DC-DC active RCD according to claim 1, characterized in that, The VDS stress of the power transistor devices of resistors R1 and R2 is monitored by two additional voltage detection circuits.

4. The method for controlling the absorption of an on-board DC-DC active RCD according to claim 1, characterized in that, The full power allowable range of resistors R1 and R2 is 0W-3kW.

5. The method for controlling the absorption of an on-board DC-DC active RCD according to claim 1, characterized in that, The temperatures T_R1 and T_R2 are read and determined by a microcontroller.

6. The method for controlling the absorption of an on-board DC-DC active RCD according to claim 1, characterized in that, During the reduction of the duty cycle, the voltages of VDS_SR1 and VDS_SR2 are monitored simultaneously to ensure that the voltages of VDS_SR1 and VDS_SR2 do not exceed the design allowable value V_PASS.

7. The method for controlling the absorption of an on-board DC-DC active RCD according to claim 1, characterized in that, The reduction in the duty cycle is achieved through software.

8. A method for controlling the absorption of an on-board DC-DC active RCD according to any one of claims 1-7, characterized in that, R1 and R2 are controlled separately and independently.

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