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 forward mode from the first voltage to the second voltage, sequentially working in the discharge stage of the clamping capacitor, the pre-charging stage of the clamping capacitor and the closed-loop starting stage with transformer magnetic saturation protection. 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: an on-board DC-DC converter, including: an on-board DC-DC converter, including: an on-board DC-DC converter, including: an on-board DC-DC converter, including: an on-board DC-DC converter, including: an on-board DC-DC converter, including: 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 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 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, 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 the first end of the clamping capacitor, the second end of the clamping capacitor being grounded;

[0009] The controller is used to output drive signals for driving the switching transistors in the first bridge unit, the synchronous rectification unit, and the clamping absorption circuit. During the startup phase of the on-board DC-DC converter in the forward mode (converting from the first voltage to the second voltage), it sequentially operates in the following stages: the discharge phase of the clamping capacitor, the pre-charge phase of the clamping capacitor, and the closed-loop startup phase with transformer magnetic saturation protection.

[0010] Furthermore, during the discharge phase of the clamping capacitor, the drive signal output by the controller causes the switching transistors in the first bridge unit to stop working, while the first clamping switching transistor and the second clamping switching transistor work to discharge the voltage on the clamping capacitor to the second 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.

[0012] 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 be turned on alternately.

[0013] Furthermore, during the discharge phase of the clamping capacitor, the drive signal output by the controller to control the first clamping switch and the second clamping switch is a cluster of narrow pulses with a phase shift angle of 180°.

[0014] Furthermore, the duration of the high level of one pulse cycle of the narrow pulse is 150ns to 200ns.

[0015] Furthermore, during the pre-charging phase of the clamping capacitor, the drive signal output by the controller causes the switching transistors in the first bridge unit to operate, and the first clamping switching transistor and the second clamping switching transistor operate to convert the first voltage into a voltage for charging the clamping capacitor.

[0016] Furthermore, during the pre-charging phase of the clamping capacitor, the controller outputs a drive signal with a fixed duty cycle to the switching transistor in the first bridge unit.

[0017] Furthermore, during the pre-charging phase of the clamping capacitor, the clamping switch transistor operating in the clamping absorption circuit is turned on after the corresponding switch transistor operating in the first bridge unit is turned on, and is turned off before the corresponding switch transistor operating in the first bridge unit is turned off.

[0018] Furthermore, the controller performs:

[0019] S1: The controller outputs a fixed duty cycle drive signal for one cycle to the switching transistors operating in the first bridge unit, and increments the count value by 1;

[0020] S2: Determine whether the count value is less than the maximum count value. If yes, proceed to step S3; otherwise, proceed to step S4.

[0021] S3: Determine whether the voltage on the clamping capacitor is greater than the voltage setting value. If yes, proceed to step S5; otherwise, proceed to step S1.

[0022] S4: Reporting pre-charging failure, ending the startup phase of the on-board DC-DC converter;

[0023] S5: Entering the closed-loop startup stage of the on-board DC-DC converter with transformer magnetic saturation protection.

[0024] Furthermore, the clamping capacitor is much smaller than the second capacitor.

[0025] Furthermore, during the closed-loop startup phase with transformer magnetic saturation protection, the on-board DC-DC converter operates in closed-loop mode.

[0026] Furthermore, during the closed-loop startup phase with transformer magnetic saturation protection, the controller executes:

[0027] S1: Calculate the duty cycle D of the drive signal that drives the switching transistor in the first bridge unit based on the input voltage of the vehicle-mounted DC-DC converter, the turns ratio of the transformer, and the output voltage.

[0028] S2: The controller outputs a drive signal with a duty cycle of D / 2 to drive the switching transistor in the first bridge unit to work, and after (2n-1) drive pulses, the controller outputs a drive signal with a duty cycle of D to drive the switching transistor in the first bridge unit to work, where n is a natural number greater than or equal to 1.

[0029] This application also provides an electric vehicle, including: the above-described on-board DC-DC converter. Attached Figure Description

[0030] Figure 1 This is a circuit diagram of an on-board DC-DC converter.

[0031] Figure 2 This is a schematic diagram of an on-board DC-DC converter according to an embodiment of the present invention.

[0032] Figure 3 for Figure 2 A schematic diagram of the vehicle-mounted DC-DC converter operating in the first mode of the startup phase.

[0033] Figure 4 for Figure 2 A schematic diagram of the vehicle-mounted DC-DC converter operating in the second mode during the startup phase.

[0034] Figure 5 The diagram shows the drive signal waveform output by the controller in one embodiment when the on-board DC-DC converter is operating in the discharge phase of the clamping capacitor during the startup phase.

[0035] Figure 6 The waveform diagram of the drive signal output by the controller in another 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 7 for Figure 2 A schematic diagram of the vehicle-mounted DC-DC converter operating in the third mode during the startup phase.

[0037] Figure 8 for Figure 2 A schematic diagram of the vehicle-mounted DC-DC converter operating in the fourth mode during the startup phase.

[0038] Figure 9 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

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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 1 As 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.

[0043] Please refer to the following: Figure 1The 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 first secondary winding LS2 and the ground terminal GND. The second synchronous rectifier SR2 is connected between the first end of the second 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.

[0044] 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 terminal of the first secondary winding LS2 and the first terminal of the clamping capacitor Clamp. The second clamping switch AC2 is connected between the first terminal of the second secondary winding LS3 and the first terminal of the clamping capacitor Clamp. The second terminal of the clamping capacitor Clamp is grounded (i.e. connected to the ground terminal GND).

[0045] During forward startup, i.e., when starting up in a mode that converts a high-voltage first voltage V1 (e.g., 400V) to a low-voltage second voltage V2 (e.g., 12V), this application provides an on-board DC-DC converter device to ensure reliable forward startup 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 forward start-up phase.

[0046] Under normal circumstances, the on-board DC-DC converter needs to go through a forward start-up phase to transition from an inactive state to a state where it converts a high voltage (V1, e.g., 400V) to a low voltage (V2, e.g., 12V). After a safe and reliable forward start-up, it enters the normal operation phase. During 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 within the converter, thereby stepping down the first voltage (V1) to the desired second voltage (V2).

[0047] Please refer to the following for specific implementation details. Figure 1The 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.

[0048] 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.

[0049] In this application, during the forward start-up 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 that the vehicle-mounted DC-DC converter 100 operates sequentially in the following phases: the discharge phase of the clamping capacitor Clamp, the pre-charge phase of the clamping capacitor Clamp, and the closed-loop start-up phase with transformer magnetic saturation protection.

[0050] Research has revealed that after a DC-DC converter completes its 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, when the first voltage V1 changes abruptly or is suddenly short-circuited, the clamping capacitor (Clamp) may not be fully discharged during the second startup. At this time, the high-voltage side is essentially short-circuited. When the first clamping switch AC1 or the second clamping switch AC2 is turned on, it will rapidly discharge to the high-voltage side. This hard-turn-on and hard-turn-off of the first clamping switch AC1 or the second clamping switch AC2 at this time causes significant interference, which can damage the driver chip of the first clamping switch AC1 or the second clamping switch AC2, and further damage 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.

[0051] After the clamping capacitor Clamp has discharged, if the first bridge unit 110 operates directly, when the switching transistor inside it is turned on, the first capacitor C1 is directly connected to the clamping capacitor Clamp. In order to prevent the capacitor from discharging instantaneously and causing safety issues, the clamping capacitor Clamp must be pre-charged to the desired value.

[0052] After pre-charging the clamp capacitor Clamp, the initial pulse width of the DC-DC converter is emitted, causing the transformer to be energized from zero. This may cause the transformer to be biased, which may lead to the risk of core saturation and cause the DC-DC converter to malfunction.

[0053] 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 closed-loop start-up phase with transformer magnetic saturation protection. The discharge phase discharges the clamping capacitor (Clamp) to below a safe voltage, and the pre-charge phase pre-charges it to the desired value. Then, the closed-loop start-up phase with transformer magnetic saturation protection prevents core saturation caused by transformer bias during start-up. These three start-up phases ensure reliable forward start-up of the on-board DC-DC converter 100.

[0054] Furthermore, in specific implementation, during the discharge phase of the clamping capacitor Clamp, the drive signal output by the controller 200 controls the switching transistors in the first bridge unit 110 to be inactive, while the first clamping switch AC1 and the second clamping switch AC2 are active to discharge the voltage on the clamping capacitor Clamp to the second capacitor C2. Since in this application, the switching transistors in the first bridge unit 110 are inactive, and only the first clamping switch AC1 and the second clamping switch AC2 are active to discharge the voltage on the clamping capacitor Clamp to the second capacitor C2, rapid discharge to the high-voltage side can be avoided. This also prevents interference from the first clamping switch AC1 or the second clamping switch AC2, thus avoiding damage to the driver chip of the first clamping switch AC1 or the second clamping switch AC2, and further damage to the first clamping switch AC1 or the second clamping switch AC2.

[0055] Furthermore, in practical 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. The operation of the first clamp switch AC1 and the second clamp switch AC2 in the amplification region prevents backflow of low-voltage side current, which could trigger the overcurrent protection on the high-voltage side and cause startup failure.

[0056] Furthermore, in practical implementation, during the discharge phase of the clamping capacitor Clamp, the drive signal output by the controller 200 controls the first clamping switch AC1 and the second clamping switch AC2 to conduct alternately. For details, please refer to [link to relevant documentation]. Figure 3 shown Figure 2 A schematic diagram of the vehicle-mounted DC-DC converter operating in the first mode of the startup phase. (See diagram below.) Figure 3As shown, when the first clamping switch AC1 is turned on and all other switches in the vehicle-mounted DC-DC converter 100 are turned off, a discharge circuit is formed 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, thus discharging the voltage on the clamping capacitor Clamp to the second capacitor C2. 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 clamping switch AC2 is turned on, all other switches in the vehicle-mounted DC-DC converter 100 are turned off, forming a discharge circuit 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, thus discharging the voltage on the clamping capacitor Clamp to the second capacitor C2. The drive signal output by the controller 200 controls the first clamping switch AC1 and the second clamping switch AC2 to alternately turn on, thus enabling the vehicle-mounted DC-DC converter 100 to... Figure 3 and Figure 4 Switching between the two modes allows the voltage on the clamping capacitor Clamp to be discharged to the second capacitor C2.

[0057] In practical implementation, the controller 200 can also output a drive signal to drive the first synchronous rectifier SR1 and the second synchronous rectifier SR2 to work alternately, while other switches in the vehicle DC-DC converter 100 do not work. When the first synchronous rectifier SR1 and the second synchronous rectifier SR2 work alternately, the voltage on the second capacitor C2 can discharge to the bootstrap drive capacitors of the first clamping switch AC1 and the second clamping switch AC2, so as to ensure that the voltage on the bootstrap drive capacitors of the first clamping switch AC1 and the second clamping switch AC2 remains high enough, so that the first clamping switch AC1 and the second clamping switch AC2 can be reliably turned on. Furthermore, during the period when the first synchronous rectifier SR1 and the second synchronous rectifier SR2 work alternately, the inductor L is reverse-magnetized; during the period when the first clamping switch AC1 and the second clamping switch AC2 work alternately, the inductor L is forward-magnetized, which can prevent inductor saturation due to bias magnetization and improve the start-up reliability of the vehicle DC-DC converter 100.

[0058] Furthermore, the controller 200 also controls the first synchronous rectifier tube SR1 and the second synchronous rectifier tube SR2 to operate in the amplification region to prevent backflow of low-voltage side current, triggering the overcurrent protection on the high-voltage side, and causing startup failure.

[0059] Furthermore, in specific implementation, during the discharge phase of the clamp capacitor, the drive signal output by the controller 200 to control the first clamp switch AC1 and the second clamp switch AC2 is a cluster of narrow pulses with a phase shift angle of 180°. For details, please refer to... Figure 5 The diagram shows the drive signal waveform output by the controller in one embodiment when the on-board DC-DC converter is operating in the discharge phase of the clamping capacitor during the startup phase. It can be seen that the phase shift angle of the drive signals for the first clamping switch AC1 and the second clamping switch AC2 is 180°, and they consist of a cluster of narrow pulses.

[0060] 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.

[0061] Furthermore, in specific implementations, as described above, the controller 200 can also output drive signals to drive the first synchronous rectifier SR1 and the second synchronous rectifier SR2 to work alternately, and these signals are also a set of complementary narrow pulses. For details, please refer to... Figure 6 The diagram shows the drive signal waveform output by the controller in another 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 clamping switch AC1 and the second clamping switch AC2 is 180°, and they are a cluster of narrow pulses; 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 also a cluster of narrow pulses. Furthermore, 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 a specific implementation, during the pre-charging phase of the clamping capacitor Clamp, the drive signal output by the controller 200 controls the switching transistors within the first bridge unit 110 to operate, and the first clamping switch AC1 and the second clamping switch AC2 operate to convert the first voltage V1 into a voltage for charging the clamping capacitor Clamp. That is, the clamping capacitor Clamp is charged through the first bridge unit 110, the transformer 120, and the clamping absorption circuit 140.

[0063] For details, please refer to Figure 7 shown Figure 2A schematic diagram of the vehicle-mounted DC-DC converter operating in the third mode during the startup phase, as shown below. Figure 7 As shown, the first switch S1 and the fourth switch S4 in the first bridge unit 110 are turned on, and simultaneously the first clamping switch AC1 is turned on. The first voltage V1, through the turned-on first switch S1 and fourth switch S4 and the transformer, is transformed into the voltage on the first secondary winding LS2 and the second secondary winding LS3. This forms a circuit that charges the clamping capacitor Clamp from the first terminal of the first secondary winding LS2, the first clamping switch AC1, the first terminal of the clamping capacitor Clamp, the body diode of the second synchronous rectifier SR2, and the second terminal of the second secondary winding LS3. For details, please refer to [reference needed]. Figure 8 shown Figure 2 A schematic diagram of the vehicle-mounted DC-DC converter operating in the fourth mode during the startup phase, as shown below. Figure 8 As shown, the second switch S2 and the third switch S3 in the first bridge unit 110 are turned on, and the second clamping switch AC2 is also turned on simultaneously. The first voltage V1 is then transformed into voltages on the first secondary winding LS2 and the second secondary winding LS3 through the turned-on second switch S2 and third switch S3 and the transformer. This forms a circuit that charges the clamping capacitor Clamp from the first terminal of the second secondary winding LS3, the second clamping switch AC2, the first terminal of the clamping capacitor Clamp, the body diode of the first synchronous rectifier SR1, and the second terminal of the first secondary winding LS2. The drive signal output by the controller 200 controls the first switch S1 and the fourth switch S4 to alternately turn on with the second switch S2 and the third switch S3, and the first clamping switch AC1 and the second clamping switch AC2 to alternately turn on. Thus, the on-board DC-DC converter 100... Figure 7 and Figure 8 Switching between the two modes enables pre-charging of the clamp capacitor (Clamp).

[0064] 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; instead, the controller 200 outputs a drive signal with a certain duty cycle or a gradually changing duty cycle. Of course, it can also operate in closed-loop mode.

[0065] In practical implementation, during the pre-charging phase of the clamp capacitor Clamp, the controller 200 outputs a drive signal with a fixed duty cycle to the switching transistor in the first bridge unit 110, making control simpler.

[0066] In specific implementation, during the pre-charging phase of the clamping capacitor Clamp, the clamping switch transistor operating in the clamping absorption circuit 140 turns on after the corresponding switch transistor operating in the first bridge unit 110 turns on, and turns off before the corresponding switch transistor operating in the first bridge unit 110 turns off. For example... Figure 7 As shown, the first clamping switch AC1 is a switch corresponding to the first switch S1 and the fourth switch S4. The first switch S1 and the fourth switch S4 work synchronously. 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 are turned off, thus achieving soft turn-on of the first clamping switch AC1. Figure 8 As shown, the second clamping switch AC2 is the switch corresponding to the second switch S2 and the third switch S3. The second switch S2 and the third switch S3 operate synchronously. 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 are turned off, thus achieving soft turn-on of the second clamping switch AC2. This improves the startup efficiency of the on-board DC-DC converter 100.

[0067] In actual operation, after the first switch S1 and the fourth switch S4 are turned on and before the first clamping switch AC1 is turned on, the body diode of the first clamping switch AC1 can be turned on to form a circuit for pre-charging the clamping capacitor Clamp. Similarly, after the second switch S2 and the third switch S3 are turned on and before the second clamping switch AC2 is turned on, the body diode of the second clamping switch AC2 can be turned on to form a circuit for pre-charging the clamping capacitor Clamp.

[0068] 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.

[0069] In actual operation, during the third mode of the startup phase, the second synchronous rectifier SR2 is also synchronously turned on along with the first switch S1 and the fourth switch S4, allowing the voltage on the second secondary winding LS3 to discharge to the second capacitor C2. During the fourth mode of the startup phase, the first synchronous rectifier SR1 is also synchronously turned on along with the second switch S2 and the third switch S3, allowing the voltage on the first secondary winding LS2 to discharge to the second capacitor C2. This avoids transformer magnetization and improves the startup reliability of the on-board DC-DC converter 100.

[0070] In one specific embodiment, during the pre-charging phase of the clamp capacitor (Clamp), see [reference needed]. Figure 9 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:

[0071] S1: The controller 200 outputs a fixed duty cycle drive signal for one cycle to the switching transistor working in the first bridge unit 110, and increments the count value Cnt by 1;

[0072] 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.

[0073] 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.

[0074] S4: Reporting pre-charging failure, ending the startup phase of the on-board DC-DC converter;

[0075] S5: Entering the closed-loop startup stage of the on-board DC-DC converter with transformer magnetic saturation protection.

[0076] 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.

[0077] Furthermore, the clamping capacitor Clamp is much smaller than the second capacitor C2.

[0078] Furthermore, in practical implementation, after completing the discharge and pre-charge phases of the clamping capacitor, the system enters a closed-loop startup phase with transformer magnetic saturation protection. Specifically, during this closed-loop startup phase with transformer magnetic saturation protection, the on-board DC-DC converter 100 operates in closed-loop mode. That is, the controller 200 needs to output a drive signal based on the sampled signal.

[0079] Specifically, during the closed-loop startup phase with transformer magnetic saturation protection, controller 200 executes:

[0080] S1: Calculate the duty cycle D of the drive signal for driving the switching transistor in the first bridge unit 110 based on the input voltage (i.e., the first voltage V1), the turns ratio of the transformer, and the output voltage (i.e., the second voltage V2) of the vehicle-mounted DC-DC converter 100.

[0081] S2: The controller 200 outputs a drive signal with a duty cycle of D / 2 to drive the switching transistor in the first bridge unit 110 to work, and after (2n-1) drive pulses, the controller 200 outputs a drive signal with a duty cycle of D to drive the switching transistor in the first bridge unit 110 to work, where n is a natural number greater than or equal to 1.

[0082] The input voltage (i.e., the first voltage V1) and the output voltage (i.e., the second voltage V2) can be obtained from sampling.

[0083] As described above, at the initial stage of the closed-loop startup phase with transformer magnetic saturation protection, the switching transistor in the first bridge unit 110 is driven with half the duty cycle D of the actual required switching transistor drive signal (i.e., a duty cycle of D / 2). This is because at the initial stage of startup, the transformer is energized from zero. If a drive signal with a duty cycle of D is given, the magnetic flux density will oscillate between 0 and 2Bm. This not only causes transformer bias, but the maximum value of 2Bm also poses a risk of core saturation, resulting in the DC-DC converter failing to operate normally. In this application, a drive signal with a duty cycle of D / 2 (where n is a natural number greater than or equal to 1) is given in the initial (2n-1) drive pulses. The magnetic flux density will oscillate between 0 and Bm, preventing transformer bias and eliminating the risk of core saturation at the maximum value of Bm, thus enabling reliable startup of the DC-DC converter. Furthermore, after (2n-1) drive pulses, a drive signal with the duty cycle D calculated in the closed loop is given, causing the on-board DC-DC converter 100 to enter a stable closed-loop conversion mode that converts the first voltage V1 into the second voltage V2, which is the normal operation phase. At this point, the startup phase of the on-board DC-DC converter 100 is completed, and the reliability of the startup phase is high.

[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 in the forward mode, where it is converting a first voltage to a second voltage, by performing the following operations: a discharge phase of the clamping capacitor, a pre-charge phase of the clamping capacitor, and a closed-loop startup phase with transformer magnetic saturation protection. During the discharge phase of the clamping capacitor, the drive signal output by the controller controls the switching transistor in the first bridge unit to not work, and the first clamping switching transistor and the second clamping switching transistor work in the amplification region to discharge the voltage on the clamping capacitor to the second capacitor. During the pre-charging phase of the clamping capacitor, the drive signal output by the controller controls the switching transistors in the first bridge unit to operate, and the first clamping switching transistor and the second clamping switching transistor operate to convert the first voltage into a voltage for charging the clamping capacitor. During the closed-loop startup phase with transformer magnetic saturation protection, the controller executes: S1: Calculates the duty cycle D of the drive signal for driving the switching transistor in the first bridge unit based on the input voltage of the on-board DC-DC converter, the turns ratio of the transformer, and the output voltage; S2: The controller outputs a drive signal with a duty cycle of D / 2 to drive the switching transistor in the first bridge unit, and after (2n-1) drive pulses, the controller outputs a drive signal with a duty cycle of D to drive the switching transistor in the first bridge unit, where n is a natural number greater than or equal to 1.

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 clamping switch and the second clamping switch to be turned on 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 to control the first clamping switch and the second clamping switch is a cluster of narrow pulses with a phase shift angle of 180°.

4. The vehicle-mounted DC-DC converter according to claim 1, characterized in that, During the pre-charging phase of the clamping capacitor, the controller outputs a drive signal with a fixed duty cycle to the switching transistor in the first bridge unit.

5. The vehicle-mounted DC-DC converter according to claim 4, characterized in that, During the pre-charging phase of the clamping capacitor, the clamping switch transistor operating in the clamping absorption circuit is turned on after the corresponding switch transistor operating in the first bridge unit is turned on, and is turned off before the corresponding switch transistor operating in the first bridge unit is turned off.

6. The vehicle-mounted DC-DC converter according to claim 5, characterized in that, The controller performs: S1: The controller outputs a fixed duty cycle drive signal for one cycle to the switching transistors operating in the first bridge unit, and increments the count value by 1; S2: Determine whether the count value is less than the maximum count value. If yes, proceed to step S3; otherwise, proceed to step S4. S3: Determine whether the voltage on the clamping capacitor is greater than the voltage setting value. 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 closed-loop startup stage of the on-board DC-DC converter with transformer magnetic saturation protection.

7. The vehicle-mounted DC-DC converter according to claim 1 or 6, characterized in that, During the closed-loop startup phase with transformer magnetic saturation protection, the on-board DC-DC converter operates in closed-loop mode.

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

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