Vehicle-mounted DC-DC conversion device and electric vehicle

Abstract

The application provides a vehicle-mounted DC-DC converter and an electric vehicle, and relates to the field of power supplies.The vehicle-mounted DC-DC converter comprises a first bridge unit, a transformer, a synchronous rectification unit and a clamping absorption circuit; a controller is used for outputting a driving signal for driving a switch tube in the first bridge unit, the synchronous rectification unit and the clamping absorption circuit, and in the starting stage of the vehicle-mounted DC-DC converter used for working in the reverse mode of converting from a second voltage to a first voltage, sequentially working in the discharge stage of the clamping capacitor, the pre-charging stage of the clamping capacitor and the starting stage of gradually increasing the duty cycle. The reliability of the starting of the vehicle-mounted DC-DC converter can be improved.

Description

Technical Field

[0001] This invention relates to the field of power supply, and in particular to vehicle-mounted DC-DC converters and electric vehicles. Background Technology

[0002] With the development of science and technology and society, new energy vehicles have been widely used and their proportion is increasing.

[0003] Electric vehicles typically include a high-voltage battery that draws electrical energy from the power grid and stores it to power the vehicle's internal loads. An onboard DC-DC converter is used to convert the energy from the high-voltage battery into, for example, 12V low-voltage battery energy to power the loads within the electric vehicle.

[0004] Commonly used vehicle-mounted DC-DC converters are bidirectional DC-DC converters, which can convert high voltage (e.g., 400V) from high-voltage batteries to low voltage (e.g., 12V) from low-voltage batteries, and vice versa.

[0005] When starting an onboard DC-DC converter, it may require the converter to operate in a forward starting mode, converting the high voltage (e.g., 400V) on the high-voltage battery to the low voltage (e.g., 12V) on the low-voltage battery. Alternatively, it may require the converter to operate in a reverse starting mode, converting the low voltage (e.g., 12V) on the low-voltage battery to the high voltage (e.g., 400V) on the high-voltage battery.

[0006] Whether starting in the forward or reverse direction, it may cause interference such as inrush current and inrush voltage, and may also cause some components to malfunction, such as switching transistor losses, driver chip damage, or transformer magnetic saturation, thus affecting the reliability of the vehicle DC-DC converter. Summary of the Invention

[0007] This invention proposes an on-board DC-DC converter, comprising:

[0008] An on-board DC-DC converter includes: a first bridge unit for receiving or outputting a first voltage; a secondary winding center-tapped transformer, the first bridge unit being connected to the primary winding; a synchronous rectifier unit, wherein a first synchronous rectifier diode and a second synchronous rectifier diode are respectively connected between the two ends of the secondary winding and the ground terminal, wherein an inductor is connected between the center tap and the first end of a second capacitor, the second end of the second capacitor being grounded, and the second capacitor being used to output or receive a second voltage; and a clamping snubber circuit, wherein a first clamping switch and a second clamping switch are respectively connected between the two ends of the secondary winding and the first end of the clamping capacitor, the second end of the clamping capacitor being grounded.

[0009] The controller is used to control the on-board DC-DC converter to operate sequentially during the startup phase when the on-board DC-DC converter is operating in the reverse mode of converting from the second voltage to the first voltage, and to control the on-board DC-DC converter to operate in the following phases: the discharge phase of the clamping capacitor, the pre-charge phase of the clamping capacitor, and the startup phase with a gradually increasing duty cycle.

[0010] Furthermore, during the discharge phase of the clamping capacitor, the drive signal output by the controller first controls the switching transistors in the first bridge unit to be inactive, while the first synchronous rectifier and the second synchronous rectifier are active to store energy in the inductor in the forward direction; then, it controls the first clamping switching transistors and the second clamping switching transistors to be active, and the switching transistors in the first bridge unit to be active, so as to discharge the voltage on the clamping capacitor to the first capacitor.

[0011] Furthermore, during the discharge phase of the clamping capacitor, the drive signal output by the controller controls the first clamping switch and the second clamping switch to operate in the amplification region, and also controls the first synchronous rectifier and the second synchronous rectifier to operate in the amplification region.

[0012] Furthermore, during the discharge phase of the clamping capacitor, the drive signal output by the controller causes the first synchronous rectifier and the second synchronous rectifier to conduct alternately.

[0013] Furthermore, during the discharge phase of the clamping capacitor, the drive signal output by the controller causes the first clamping switch and the second clamping switch to conduct alternately, and the switch corresponding to the first bridge unit to operate.

[0014] Furthermore, during the discharge phase of the clamping capacitor, the drive signals output by the controller to control the first and second synchronous rectifiers are a cluster of narrow pulses with a phase shift angle of 180°, and the drive signals to control the first and second clamping switches are also a cluster of narrow pulses with a phase shift angle of 180°.

[0015] Furthermore, a cluster of narrow pulses alternately emitted by the first synchronous rectifier and the first clamping switch, and a cluster of narrow pulses alternately emitted by the second synchronous rectifier and the second clamping switch.

[0016] Furthermore, the duration of the high level of one pulse cycle of the narrow pulse is 150ns to 200ns.

[0017] Furthermore, during the pre-charging phase of the clamping capacitor, the controller performs:

[0018] S1: The controller outputs a drive signal with a fixed duty cycle for one cycle to the switching transistor working in the vehicle DC-DC converter, and increments the count value Cnt by 1;

[0019] S2: Determine whether the count value Cnt is less than the maximum count value Cntr. If yes, proceed to step S3; otherwise, proceed to step S4.

[0020] S3: Determine whether the voltage Vclamp on the clamping capacitor is greater than the voltage setting value Vr. If yes, proceed to step S5; otherwise, proceed to step S1.

[0021] S4: Reporting pre-charging failure, ending the startup phase of the on-board DC-DC converter;

[0022] S5: Entering the startup phase where the duty cycle of the on-board DC-DC converter gradually increases.

[0023] Furthermore, during the pre-charging phase of the clamping capacitor, the on-board DC-DC converter operates in open-loop mode.

[0024] Furthermore, during the pre-charging phase of the clamping capacitor, the controller outputs a drive signal with a fixed duty cycle.

[0025] Furthermore, during the pre-charging phase of the clamping capacitor, the clamping switch tube operating in the clamping absorption circuit turns on after the corresponding switch tube operating in the first bridge unit turns on, and turns off before the corresponding switch tube operating in the first bridge unit turns off; the synchronous rectifier tube operating in the synchronous rectifier unit turns on and off synchronously with the corresponding switch tube operating in the first bridge unit.

[0026] Furthermore, during the startup phase where the duty cycle gradually increases, when the duty cycle of the drive signal of the switching transistor in the low-voltage side synchronous rectification unit is less than 50%, the switching transistor in the synchronous rectification unit works synchronously with the corresponding switching transistor in the first bridge unit, and the duty cycle gradually increases synchronously.

[0027] Furthermore, during the startup phase where the duty cycle gradually increases, when the duty cycle of the drive signal of the switching transistor in the low-voltage side synchronous rectification unit increases to more than 50%, the switching transistor in the synchronous rectification unit and the corresponding switching transistor in the first bridge unit work in a complementary manner.

[0028] This application also provides an electric vehicle, including: the above-described on-board DC-DC converter. Attached Figure Description

[0029] Figure 1 This is a circuit diagram of an on-board DC-DC converter.

[0030] Figure 2 This is a schematic diagram of an on-board DC-DC converter according to an embodiment of the present invention.

[0031] Figure 3 for Figure 2 A schematic diagram of the vehicle-mounted DC-DC converter operating in the first mode of the startup phase.

[0032] Figure 4 for Figure 2 A schematic diagram of the vehicle-mounted DC-DC converter operating in the second mode during the startup phase.

[0033] Figure 5 for Figure 2 A schematic diagram of the vehicle-mounted DC-DC converter operating in the third mode during the startup phase.

[0034] Figure 6 for Figure 2 A schematic diagram of the vehicle-mounted DC-DC converter operating in the fourth mode during the startup phase.

[0035] Figure 7 for Figure 2 The waveform of the drive signal output by the controller in one embodiment is shown when the vehicle-mounted DC-DC converter is operating in the discharge phase of the clamping capacitor during the startup phase.

[0036] Figure 8 for Figure 2 A schematic diagram of the vehicle-mounted DC-DC converter operating in the fifth mode during the startup phase.

[0037] Figure 9 for Figure 2 A schematic diagram of the vehicle-mounted DC-DC converter operating in the sixth mode of the startup phase.

[0038] Figure 10 for Figure 2 A schematic diagram of the vehicle-mounted DC-DC converter operating in the seventh mode during the startup phase.

[0039] Figure 11 for Figure 2 A schematic diagram of the vehicle-mounted DC-DC converter operating in the eighth mode during the startup phase.

[0040] Figure 12 This is a flowchart illustrating the control process for the pre-charging stage of the clamping capacitor according to an embodiment of the present invention. Detailed Implementation

[0041] The technical solutions of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0042] Please see Figure 1 The circuit diagram shown is a typical embodiment of an on-board DC-DC converter, which is a commonly used on-board DC-DC converter.

[0043] Specifically, such as Figure 1 As shown, the vehicle-mounted DC-DC converter 100 includes a first bridge unit 110 for receiving or outputting a first voltage V1. Specifically, the first bridge unit 110 includes at least a first switching bridge arm formed by a first switching transistor S1 and a second switching transistor S2 connected in series, and the first terminal of the first bridge unit 110 is used to receive or output the first voltage V1. In actual implementation, the first bridge unit 110 can be implemented as a full-bridge unit, such as... Figure 1 As shown, the first bridge unit 110 also includes a second switch bridge arm formed by a third switch S3 and a fourth switch S4 connected in series. The first switch bridge arm and the second switch bridge arm are connected in parallel, and the two ends of the parallel branch are used to receive the first voltage V1. Of course, the first bridge unit 110 can be implemented as other bridge units, such as a half-bridge unit. This application does not limit its specific structure, as long as it includes at least one switch bridge arm.

[0044] Please refer to the following: Figure 1 The on-board DC-DC converter 100 also includes: a secondary winding center-tapped transformer 120, which includes a primary winding LP1 and a secondary winding, the secondary winding including a first secondary winding LS2 and a second secondary winding LS3. For example... Figure 1 As shown, the second end of the first secondary winding LS2 is connected to the second end of the second secondary winding LS3 to form the center tap N of the transformer 120. The first end of the first secondary winding LS2 and the first end of the second secondary winding LS3 form the two ends of the secondary winding. The second end of the first bridge unit 110 is connected to the primary winding LP1. Figure 1As shown, when the first bridge unit 110 is implemented as a full-bridge unit, the two ends of the primary winding LP1 are respectively connected to the common node of the first switch bridge arm and the common node of the second switch bridge arm, that is, connected to the second end of the first bridge unit 110.

[0045] Please refer to the following: Figure 1 The vehicle-mounted DC-DC converter 100 further includes a synchronous rectification unit 130, which includes a first synchronous rectifier SR1, a second synchronous rectifier SR2, and an inductor L. The first synchronous rectifier SR1 is connected between the first end of the secondary winding and the ground terminal GND. The second synchronous rectifier SR2 is connected between the second end of the secondary winding LS3 and the ground terminal GND. The inductor L is connected between the center tap N and the first end of the second capacitor C2. The second end of the second capacitor C2 is grounded (i.e., connected to the ground terminal GND). The second capacitor C2 is used to output or receive the second voltage V2.

[0046] Please refer to the following: Figure 1 The vehicle-mounted DC-DC converter 100 also includes a clamping snubber circuit 140, which includes a first clamping switch AC1, a second clamping switch AC2, and a clamping capacitor Clamp. The first clamping switch AC1 is connected between the first end of the secondary winding and the first end of the clamping capacitor Clamp, and the second clamping switch AC2 is connected between the second end of the secondary winding and the first end of the clamping capacitor Clamp. The second end of the clamping capacitor Clamp is grounded (i.e. connected to the ground terminal GND).

[0047] During reverse start-up, i.e., when starting up in a mode that converts a low-voltage second voltage V2 (e.g., 12V) to a high-voltage first voltage V1 (e.g., 400V), this application provides an on-board DC-DC converter device to ensure reliable reverse start-up of the vehicle-mounted DC-DC converter 100. Please refer to [link to relevant documentation]. Figure 2 The schematic diagram shown is of an embodiment of the vehicle-mounted DC-DC converter of this application, which includes... Figure 1 The vehicle-mounted DC-DC converter 100 and controller 200 shown are used to control the operation of the vehicle-mounted DC-DC converter 100, such as controlling the vehicle-mounted DC-DC converter 100 to operate in the normal operation phase or in the reverse start-up phase.

[0048] Under normal circumstances, the on-board DC-DC converter needs to go through a reverse start-up phase to transition from a non-operational state to a state where it converts a low-voltage second voltage V2 (e.g., 12V) to a high-voltage first voltage V1 (e.g., 400V). After a safe and reliable reverse start-up phase, it enters the normal operation phase. In the normal operation phase, the controller 200 receives a sampling signal from the on-board DC-DC converter 100 and outputs a drive signal to control the switching transistors inside the on-board DC-DC converter 100 based on the sampling signal, thereby boosting the second voltage V2 to the desired first voltage V1.

[0049] Please refer to the following for specific implementation details. Figure 1 The vehicle-mounted DC-DC converter 100 also includes a first capacitor C1, which is connected to the first terminal of the first bridge unit 110. Specifically, when the first bridge unit 110 is implemented as a full-bridge unit, the first capacitor C1 is connected in parallel with the first switch bridge arm and the second switch bridge arm.

[0050] The first bridge unit 110 is located on the primary winding side of the transformer, and its received or output voltage is high voltage. The primary winding side of the transformer can be referred to as the high-voltage side. Conversely, the synchronous rectification unit 130 and the clamping absorption circuit 140 are located on the secondary winding side of the transformer, and their corresponding output or received voltage is low voltage. The secondary winding side of the transformer can be referred to as the low-voltage side.

[0051] In this application, during the reverse startup phase, the controller 200 outputs drive signals to drive the switching transistors in the first bridge unit 110, the synchronous rectification unit 130, and the clamping absorption circuit 140, so as to control the on-board DC-DC converter 100 to operate sequentially in the following phases: the discharge phase of the clamping capacitor Clamp, the pre-charge phase of the clamping capacitor Clamp, and the startup phase with a gradually increasing duty cycle.

[0052] Research has revealed that after the DC-DC converter completes its reverse operation, a residual voltage remains on the clamping capacitor (Clamp), which can affect the startup safety of the DC-DC converter to some extent. Specifically, during the second startup, if the clamping capacitor (Clamp) is not fully discharged, it will rapidly discharge to the high-voltage side when the first clamping switch (AC1) or the second clamping switch (AC2) is turned on. This hard-turn-on and hard-turn-off of the first clamping switch (AC1) or the second clamping switch (AC2) causes significant interference, potentially damaging the driver chip of the first clamping switch (AC1) or the second clamping switch (AC2), and further damaging the first clamping switch (AC1) or the second clamping switch (AC2). Therefore, it is necessary to discharge the clamping capacitor (Clamp) to a safe voltage level before startup.

[0053] After the clamping capacitor Clamp has discharged, the voltage across it is very low. When the first clamping switch AC1 and the second clamping switch AC2 are turned on, the second capacitor C2 is directly connected to both the clamping capacitor Clamp and the first capacitor C1. To prevent instantaneous discharge of the capacitors and potential safety issues, the clamping capacitor Clamp must be pre-charged to the desired value. Preferably, the first capacitor C1 can also be pre-charged simultaneously to improve startup reliability.

[0054] The controller 200 of this application controls the on-board DC-DC converter 100 to operate sequentially in three phases: a discharge phase of the clamping capacitor Clamp, a pre-charge phase of the clamping capacitor Clamp, and a start-up phase with a gradually increasing duty cycle. The discharge phase discharges the clamping capacitor Clamp to below a safe voltage, and the pre-charge phase pre-charges the clamping capacitor Clamp to the desired value. Then, the start-up phase with a gradually increasing duty cycle improves the start-up speed and reliability. These three start-up phases ensure reliable reverse start-up of the on-board DC-DC converter 100.

[0055] Furthermore, in specific implementation, during the discharge phase of the clamping capacitor Clamp, the drive signal output by the controller 200 first controls the switching transistors in the first bridge unit 110 to be inactive, while the first synchronous rectifier SR1 and the second synchronous rectifier SR2 are active, and the inductor L stores energy in the forward direction. Then, it controls the first clamping switch AC1 and the second clamping switch AC2 to be active, and the switching transistors in the first bridge unit 110 are active, so as to discharge the voltage on the clamping capacitor Clamp to the first capacitor C1. During the discharge of the voltage on the clamping capacitor Clamp to the first capacitor C1, the inductor L is reverse-energized to prevent inductor saturation due to magnetic bias.

[0056] Furthermore, in specific implementation, during the discharge phase of the clamp capacitor, the drive signal output by the controller 200 controls the first clamp switch AC1 and the second clamp switch AC2 to operate in the amplification region, preventing the overcurrent protection on the high-voltage side from being triggered and causing startup failure. It also controls the first synchronous rectifier SR1 and the second synchronous rectifier SR2 to operate in the amplification region, which prevents backflow of current on the low-voltage side.

[0057] Furthermore, in practical implementation, during the discharge phase of the clamp capacitor, the drive signal output by the controller 200 controls the first synchronous rectifier SR1 and the second synchronous rectifier SR2 to conduct alternately. For details, please refer to [link to relevant documentation]. Figure 3 shown Figure 2A schematic diagram of the vehicle-mounted DC-DC converter operating in the first mode of the startup phase. (See diagram below.) Figure 3 As shown, when the first synchronous rectifier SR1 is turned on and all other switches in the vehicle-mounted DC-DC converter 100 are turned off, an energy storage circuit is formed from the first terminal of the second capacitor C2, the first secondary winding LS2, the first synchronous rectifier SR1, to the second terminal of the second capacitor C2, thus the inductor L stores energy in the forward direction. For details, please refer to [reference needed]. Figure 4 shown Figure 2 A schematic diagram showing the vehicle-mounted DC-DC converter operating in the second mode during the startup phase. (See diagram for example.) Figure 4 As shown, when the second synchronous rectifier SR2 is turned on and all other switches in the vehicle DC-DC converter 100 are turned off, an energy storage circuit is formed from the first end of the second capacitor C2, the second secondary winding LS3, the second synchronous rectifier SR2, to the second end of the second capacitor C2, and the inductor L stores energy in the forward direction.

[0058] Furthermore, in specific implementation, during the discharge phase of the clamping capacitor Clamp, the drive signal output by the controller 200 also controls the alternating conduction of the first clamping switch AC1 and the second clamping switch AC2, as well as the operation of the corresponding switch in the first bridge unit 110. For details, please refer to [link to relevant documentation]. Figure 5 shown Figure 2 A schematic diagram showing the vehicle-mounted DC-DC converter operating in the third mode during the startup phase. (See diagram for example.) Figure 5 As shown, when the first clamping switch AC1 is turned on, the first switch S1 and the fourth switch S4 corresponding to the first bridge unit 110 operate, and all other switches in the on-board DC-DC converter 100 are turned off. This forms a loop from the first terminal of the clamping capacitor Clamp, the first clamping switch AC1, the first secondary winding LS2, the inductor L, the second capacitor C2, to the second terminal of the clamping capacitor Clamp. Simultaneously, a loop is formed from the primary winding LP1, the first switch S1, the first capacitor C1, the fourth switch S4, to the primary winding LP1, thus discharging the voltage on the clamping capacitor Clamp to the first capacitor C1. For details, please refer to [reference needed]. Figure 6 shown Figure 2 A schematic diagram showing the vehicle-mounted DC-DC converter operating in the fourth mode during the startup phase. (See diagram for example.) Figure 6As shown, when the second clamping switch AC2 is turned on, the third switch S3 and the second switch S2 corresponding to the first bridge unit 110 are activated, and all other switches in the vehicle DC-DC converter 100 are turned off. This forms a loop from the first terminal of the clamping capacitor Clamp, the second clamping switch AC2, the second secondary winding LS3, the inductor L, the second capacitor C2, to the second terminal of the clamping capacitor Clamp. Simultaneously, a loop is formed from the primary winding LP1, the third switch S3, the first capacitor C1, the second switch S2, to the primary winding LP1, thus discharging the voltage on the clamping capacitor Clamp to the first capacitor C1. The drive signal output by the controller 200 controls the vehicle DC-DC converter 100 to initially operate in... Figure 3 and Figure 4 Switching between the two modes, inductor L stores energy in the forward direction; then it operates in... Figure 5 and Figure 6 Switching between the two modes allows the voltage on the clamp capacitor Clamp to be discharged to the first capacitor C1.

[0059] When the first synchronous rectifier diode SR1 and the second synchronous rectifier diode SR2 work alternately, the inductor L stores energy in the forward direction. When the first clamping switch AC1 and the second clamping switch AC2 work alternately, the inductor L is energized in the reverse direction. This prevents inductor saturation due to magnetic bias and improves the startup reliability of the vehicle-mounted DC-DC converter 100. Discharging the voltage on the clamping capacitor Clamp to the first capacitor C1 improves the utilization rate of electrical energy.

[0060] Furthermore, the controller 200 controls the first synchronous rectifier tube SR1 and the second synchronous rectifier tube SR2 to operate in the amplification region, thereby preventing backflow of current on the low-voltage side; the first clamping switch tube AC1 and the second clamping switch tube AC2 operate in the amplification region, thereby preventing the triggering of the overcurrent protection on the high-voltage side, which would lead to startup failure.

[0061] Furthermore, in specific implementation, during the discharge phase of the clamp capacitor Clamp, the drive signals output by the controller 200 to control the first synchronous rectifier SR1 and the second synchronous rectifier SR2 are a cluster of narrow pulses with a phase shift angle of 180°, and the drive signals to control the first clamp switch AC1 and the second clamp switch AC2 are also a cluster of narrow pulses with a phase shift angle of 180°. For details, please refer to... Figure 7The diagram shows the drive signal waveform output by the controller in one embodiment when the clamping capacitor is discharging during the startup phase of the on-board DC-DC converter. It can be seen that the phase shift angle of the drive signals for the first synchronous rectifier SR1 and the second synchronous rectifier SR2 is 180°, and they are a cluster of narrow pulses. The phase shift angle of the drive signals for the first clamping switch AC1 and the second clamping switch AC2 is also 180°, and they are a cluster of narrow pulses; moreover, the cluster of narrow pulses from the first synchronous rectifier SR1 and the first clamping switch AC1 alternates, as do the clusters of narrow pulses from the second synchronous rectifier SR2 and the second clamping switch AC2. This prevents inductor L from becoming magnetically saturated during the discharge phase of the clamping capacitor, thus avoiding damage to the drive chip of the first clamping switch AC1 or the second clamping switch AC2, further damaging the first clamping switch AC1 or the second clamping switch AC2, and preventing low-voltage side current backflow, ensuring reliable startup of the on-board DC-DC converter 100.

[0062] Furthermore, in specific implementations, the duration of the high level in one pulse cycle of the narrow pulse is 150ns to 200ns. The specific duration can be set according to actual product requirements.

[0063] When the first clamping switch AC1 is working, the first switch S1 and the fourth switch S4 work synchronously; when the second clamping switch AC2 is working, the third switch S3 and the second switch S2 work synchronously. That is, the first switch S1 and the fourth switch S4 also work in the amplification region, and the third switch S3 and the second switch S2 also work in the amplification region.

[0064] Furthermore, in practical implementation, during the pre-charging phase of the clamp capacitor, please refer to... Figure 8 shown Figure 2 A schematic diagram of the vehicle-mounted DC-DC converter operating in the fifth mode during the startup phase, as shown below. Figure 8 As shown, the first switch S1 and the fourth switch S4 in the first bridge unit 110 are turned on, and simultaneously the second synchronous rectifier SR2 is turned on. This forms a circuit on the low-voltage side consisting of the second capacitor C2, the inductor L, the second secondary winding Ls3, the turned-on second synchronous rectifier SR2, and the second capacitor C2. During this period, the body diode of the first clamping switch AC1 is turned on, forming a circuit from the first end of the first secondary winding Ls2, the body diode of the first clamping switch AC1, the first end of the clamping capacitor Clamp, the second capacitor C2, the inductor L, to the second end of the first secondary winding LS2, charging the clamping capacitor Clamp.

[0065] Then, control is applied to turn on the first clamping switch AC1, which can be referred to [reference needed]. Figure 9 shown Figure 2A schematic diagram of the vehicle-mounted DC-DC converter operating in the sixth mode during the startup phase, as shown below. Figure 9 As shown, on the low-voltage side, the first clamping switch AC1 and the second synchronous rectifier SR2 are simultaneously turned on, and on the high-voltage side, the first switch S1 and the fourth switch S4 are simultaneously turned on. Therefore, the clamping capacitor Clamp discharges to the first capacitor C1. This demonstrates that during the pre-charging phase of the clamping capacitor Clamp, the first capacitor C1 is also pre-charged simultaneously.

[0066] See also Figure 10 shown Figure 2 A schematic diagram of the vehicle-mounted DC-DC converter operating in the seventh mode during the startup phase, as shown below. Figure 10 As shown, the second switch S2 and the third switch S3 in the first bridge unit 110 are turned on, and simultaneously the first synchronous rectifier SR1 is turned on. This forms a circuit on the low-voltage side consisting of the second capacitor C2, inductor L, first secondary winding Ls2, the turned-on first synchronous rectifier SR1, and the second capacitor C2, with inductor L being forward-energized. During this period, the body diode of the second clamping switch AC2 is turned on, forming a circuit that charges the clamping capacitor Clamp from the first end of the second secondary winding Ls3, the body diode of the second clamping switch AC2, the first end of the clamping capacitor Clamp, the second capacitor C2, inductor L, and the second end of the second secondary winding Ls3.

[0067] Then, control is applied to turn on the second clamping switch AC2. (See reference...) Figure 11 shown Figure 2 A schematic diagram of the vehicle-mounted DC-DC converter operating in the eighth mode of the startup phase, as shown below. Figure 11 As shown, on the low-voltage side, the second clamping switch AC2 and the first synchronous rectifier SR1 are simultaneously turned on, and on the high-voltage side, the second switch S2 and the third switch S3 are simultaneously turned on. Therefore, the clamping capacitor Clamp discharges to the first capacitor C1. This demonstrates that during the pre-charging phase of the clamping capacitor Clamp, the first capacitor C1 is simultaneously pre-charged.

[0068] Thus, the drive signal output by the controller 200 controls the on-board DC-DC converter 100 to... Figure 8 , Figure 9 and Figure 8 and Figure 10 , Figure 11 and Figure 10 The system switches between two modes to precharge the clamping capacitor Clamp and simultaneously precharge the first capacitor C1.

[0069] In practical implementation, during the pre-charging phase of the clamp capacitor Clamp, the on-board DC-DC converter 100 operates in open-loop mode. That is, the controller 200 does not sample any signals from the on-board DC-DC converter 100, but instead outputs a drive signal with a certain duty cycle or a gradually changing duty cycle.

[0070] In practice, during the pre-charging phase of the clamp capacitor Clamp, the controller 200 outputs a drive signal with a fixed duty cycle, making control simpler.

[0071] In specific implementation, during the pre-charging phase of the clamping capacitor Clamp, the clamping switch operating in the clamping absorption circuit 140 turns on after the corresponding switch operating in the first bridge unit 110 turns on, and turns off before the corresponding switch operating in the first bridge unit 110 turns off; the synchronous rectifier operating in the synchronous rectifier unit 130 turns on and off synchronously with the corresponding switch operating in the first bridge unit 110. The second synchronous rectifier SR2 is the switch corresponding to the first switch S1 and the fourth switch S4, such as... Figure 8 As shown, it operates synchronously with the first switch S1 and the fourth switch S4. The first clamping switch AC1 is the switch corresponding to the first switch S1 and the fourth switch S4, as shown... Figure 9 As shown, the first clamping switch AC1 turns on after the first switch S1 and the fourth switch S4 are turned on, and turns off before they turn off, thus achieving soft turn-on of the first clamping switch AC1. The first synchronous rectifier SR1 is the switch corresponding to the second switch S2 and the third switch S3, as shown... Figure 10 As shown, it operates synchronously with the second switch S2 and the third switch S3. The second clamping switch AC2 is the switch corresponding to the second switch S2 and the third switch S3, as shown... Figure 11 As shown, the second clamping switch AC2 turns on after the second switch S2 and the third switch S3 are turned on, and turns off before they turn off. This enables soft-start of the first clamping switch AC1 and the second clamping switch AC2, improving the startup efficiency of the on-board DC-DC converter 100.

[0072] Alternatively, the first clamping switch AC1 and the second clamping switch AC2 can be left uncontrolled to operate, and their body diodes can be used instead.

[0073] In one specific embodiment, during the pre-charging phase of the clamp capacitor Clamp, see [reference needed]. Figure 12 The diagram shown is a control flowchart for the pre-charge stage of the clamping capacitor according to an embodiment of this application. The controller 200 executes:

[0074] S1: The controller 200 outputs a drive signal with a fixed duty cycle for one cycle to the switching transistor working in the vehicle DC-DC converter 100, and increments the count value Cnt by 1;

[0075] S2: Determine whether the count value Cnt is less than the maximum count value Cntr. If yes, proceed to step S3; otherwise, proceed to step S4.

[0076] S3: Determine whether the voltage Vclamp on the clamping capacitor Clamp is greater than the voltage setting value Vr. If yes, proceed to step S5; otherwise, proceed to step S1.

[0077] S4: Reporting pre-charging failure, ending the startup phase of the on-board DC-DC converter;

[0078] S5: Entering the startup phase where the duty cycle of the on-board DC-DC converter gradually increases.

[0079] Thus, the controller 200 counts once for each cycle of the drive signal output and checks whether the voltage on the clamp capacitor (Clamp) has reached the set voltage value. Once the set voltage value is reached, the controller exits the pre-charging phase of the clamp capacitor (Clamp) and enters the next stage of startup. This avoids overcharging the clamp capacitor (Clamp) and improves the startup speed. Furthermore, if the voltage on the clamp capacitor (Clamp) cannot be charged to the set voltage value after reaching the maximum count value (Cntr, e.g., 300 counts), the pre-charging is considered a failure, i.e., a startup failure. The startup phase of the on-board DC-DC converter can then be terminated, and the cause of the failure can be investigated. This further improves the startup reliability of the on-board DC-DC converter 100.

[0080] Furthermore, the clamping capacitor Clamp is much smaller than the second capacitor C2.

[0081] Furthermore, in specific implementation, after completing the discharge phase and pre-charge phase of the clamping capacitor, the startup phase with a gradually increasing duty cycle begins. Specifically, during the startup phase with a gradually increasing duty cycle, when the duty cycle of the drive signal of the switching transistor in the low-voltage side synchronous rectifier unit 130 is less than 50%, the switching transistor in the synchronous rectifier unit 130 works synchronously with the corresponding switching transistor in the first bridge unit 110, and thus the duty cycle gradually increases synchronously.

[0082] For details, please refer to Figure 8 and Figure 9 and its description, and Figure 10 and Figure 11The description is that, during this process, the duty cycle of the control signal output by the controller 200 is no longer a fixed duty cycle, but the duty cycles of the first synchronous rectifier SR1, the second switch S2 and the third switch S3 gradually increase synchronously, and the duty cycles of the second synchronous rectifier SR2, the first switch S1 and the fourth switch S4 gradually increase synchronously.

[0083] Specifically, when the duty cycle of the drive signal of the switching transistor in the low-voltage side synchronous rectifier unit 130 increases to greater than 50%, the switching transistor in the synchronous rectifier unit 130 and the corresponding switching transistor in the first bridge unit 110 work in a complementary manner, which can accelerate the reverse pre-charge speed, quickly complete the reverse pre-charge, and improve the working efficiency. At this point, the startup phase of the on-board DC-DC converter 100 is completed, and it then enters the normal closed-loop working mode, with high reliability during the startup phase.

[0084] In one embodiment, this application also provides an electric vehicle that includes the on-board DC-DC converter described above. Its structure, working principle, and advantages are the same as described above, and will not be repeated here.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A vehicle-mounted DC-DC converter, characterized in that, include: An on-board DC-DC converter includes: a first bridge unit for receiving or outputting a first voltage; a center-tapped transformer for the secondary winding, the first bridge unit being connected to the primary winding; a synchronous rectification unit, wherein a first synchronous rectifier diode and a second synchronous rectifier diode are respectively connected between the two ends of the secondary winding and a ground terminal, wherein an inductor is connected between the center tap and a first terminal of a second capacitor, the second terminal of the second capacitor being grounded, and the second capacitor being used to output or receive a second voltage; and a clamping snubber circuit, wherein a first clamping switch diode and a second clamping switch diode are respectively connected between the two ends of the secondary winding and a first terminal of a clamping capacitor, the second terminal of the clamping capacitor being grounded. The controller is used to control the on-board DC-DC converter to operate sequentially during the startup phase when it is in reverse mode (converting from a second voltage to a first voltage): a discharge phase of the clamping capacitor, a pre-charge phase of the clamping capacitor, and a startup phase with a gradually increasing duty cycle. During the discharge phase of the clamping capacitor, the drive signal output by the controller first controls the switching transistors in the first bridge unit to be inactive, and the first and second synchronous rectifiers to operate in the amplification region to store energy in the inductor in the forward direction; then it controls the first and second clamping switching transistors to operate in the amplification region, and the switching transistors in the first bridge unit to operate, so as to discharge the voltage on the clamping capacitor to the first capacitor. During the pre-charging phase of the clamping capacitor, the clamping switch in the clamping absorption circuit turns on after the corresponding switch in the first bridge unit turns on, and turns off before the corresponding switch in the first bridge unit turns off; the synchronous rectifier in the synchronous rectifier unit turns on and off synchronously with the corresponding switch in the first bridge unit. During the startup phase where the duty cycle gradually increases, when the duty cycle of the drive signal of the switching transistor in the low-voltage side synchronous rectification unit is less than 50%, the switching transistor in the synchronous rectification unit works synchronously with the corresponding switching transistor in the first bridge unit, and the duty cycle gradually increases synchronously. When the duty cycle of the drive signal of the switching transistor in the low-voltage side synchronous rectification unit increases to greater than 50%, the switching transistor in the synchronous rectification unit works complementaryly with the corresponding switching transistor in the first bridge unit.

2. The vehicle-mounted DC-DC converter according to claim 1, characterized in that, During the discharge phase of the clamping capacitor, the drive signal output by the controller causes the first synchronous rectifier and the second synchronous rectifier to conduct alternately.

3. The vehicle-mounted DC-DC converter according to claim 2, characterized in that, During the discharge phase of the clamping capacitor, the drive signal output by the controller causes the first clamping switch and the second clamping switch to conduct alternately, and the switch corresponding to the first bridge unit to operate.

4. The vehicle-mounted DC-DC converter according to claim 3, characterized in that, During the discharge phase of the clamping capacitor, the drive signal output by the controller to control the first synchronous rectifier and the second synchronous rectifier is a cluster of narrow pulses with a phase shift angle of 180°, and the drive signal to control the first clamping switch and the second clamping switch is a cluster of narrow pulses with a phase shift angle of 180°. Furthermore, a cluster of narrow pulses alternately emitted by the first synchronous rectifier and the first clamping switch, and a cluster of narrow pulses alternately emitted by the second synchronous rectifier and the second clamping switch.

5. The vehicle-mounted DC-DC converter according to claim 4, characterized in that, The duration of the high level in one pulse cycle of the narrow pulse is 150ns to 200ns.

6. The vehicle-mounted DC-DC converter according to claim 1 or 5, characterized in that, During the pre-charging phase of the clamping capacitor, the controller performs: S1: The controller outputs a drive signal with a fixed duty cycle for one cycle to the switching transistor working in the vehicle DC-DC converter, and increments the count value Cnt by 1; S2: Determine whether the count value Cnt is less than the maximum count value Cntr. If yes, proceed to step S3; otherwise, proceed to step S4. S3: Determine whether the voltage Vclamp on the clamping capacitor is greater than the voltage setting value Vr. If yes, proceed to step S5; otherwise, proceed to step S1. S4: Reporting pre-charging failure, ending the startup phase of the on-board DC-DC converter; S5: Entering the startup phase where the duty cycle of the on-board DC-DC converter gradually increases.

7. The vehicle-mounted DC-DC converter according to claim 6, characterized in that, During the pre-charging phase of the clamping capacitor, the on-board DC-DC converter operates in open-loop mode.

8. The vehicle-mounted DC-DC converter according to claim 7, characterized in that, During the pre-charging phase of the clamping capacitor, the controller outputs a drive signal with a fixed duty cycle.

9. An electric vehicle, characterized in that, include: The vehicle-mounted DC-DC converter as described in claim 1.

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