DC / DC converter and applicable control method thereof

Abstract

The invention relates to a control method, which is applied to a direct current / direct current converter and is characterized in that the direct current / direct current converter comprises a low-voltage end, a low-voltage end full-bridge switching circuit, a transformer, a high-voltage end switching circuit and a high-voltage end, the low-voltage end full-bridge switching circuit comprises a first upper switching tube and a first lower switching tube which are connected in series, and a second upper switching tube and a second lower switching tube which are connected in series, and the control method comprises the following steps: when the DC / DC converter is in a starting mode, controlling the second lower switching tube to be switched off by delaying or leading the first upper switching tube for a first time, controlling the first lower switch tube to correspondingly delay or lead the second upper switch tube to be turned off at a second time; and when the DC / DC converter enters a boost mode, controlling the driving signal of the first upper switch tube to delay or lead the driving signal of the second lower switch tube by a first phase shift angle, and controlling the driving signal of the second upper switch tube to correspondingly delay or lead the driving signal of the first lower switch tube by a second phase shift angle.

Description

Technical Field

[0001] This case belongs to the field of a converter, especially a DC / DC converter and its applicable control method. Background Art

[0002] Based on the low voltage direct current (LVDC) converter designed with a bidirectional hard-switching secondary full-bridge topology, to prevent a large inrush current from being generated when the high-voltage battery is closed to the converter, before operation, it is necessary to pre-charge the capacitor at the high-voltage end of the converter through the low-voltage battery at the low-voltage end of the converter, so that the voltage of the capacitor at the high-voltage end is the same as the voltage of the high-voltage battery, thereby reducing the inrush current when closing.

[0003] The pre-charging strategy of the traditional low voltage DC converter needs to add an additional pre-charging circuit on the basis of the original circuit. For example, the pre-charging is realized by adding a flyback circuit. However, since the flyback circuit includes devices such as a flyback winding, a diode, and a capacitor, it leads to an increase in the volume and cost of the traditional low voltage DC converter. At the same time, due to the existence of leakage inductance in the traditional low voltage DC converter circuit, when the switching tube of the low voltage DC converter is turned off, a large voltage stress is also generated.

[0004] Therefore, it is really necessary to develop a DC / DC converter and its applicable control method to solve the problems faced by the prior art. Summary of the Invention

[0005] The purpose of this case is to provide a DC / DC converter and its applicable control method. Without the need to add a flyback circuit, the DC / DC converter and the control method directly realize reverse pre-charging by adjusting the duty ratio of the switching tube at the low-voltage end of the DC / DC converter. Therefore, the DC / DC converter saves the space and cost required for the flyback circuit. At the same time, the DC / DC converter and its applicable control method can further reduce the voltage stress of the switching tube.

[0006] To achieve the foregoing object, the present case provides a control method applicable to a DC / DC converter. The DC / DC converter includes a low-voltage terminal, a low-voltage full-bridge switching circuit, a transformer, a high-voltage switching circuit, and a high-voltage terminal. The low-voltage full-bridge switching circuit is electrically connected between the low-voltage terminal and the primary winding of the transformer, and includes a first bridge arm and a second bridge arm connected in parallel. The first bridge arm includes a first upper switching transistor and a first lower switching transistor connected in series, and the second bridge arm includes a second upper switching transistor and a second lower switching transistor connected in series. The high-voltage switching circuit is electrically connected between the secondary winding of the transformer and the high-voltage terminal. The control method includes: when the DC / DC converter is in the startup mode, controlling the duty ratios of the driving signals of the first upper switching transistor, the first lower switching transistor, the second upper switching transistor, and the second lower switching transistor to be less than or equal to 50%, and controlling the second lower switching transistor and the first upper switching transistor to be turned on simultaneously, controlling the first lower switching transistor and the second upper switching transistor to be turned on simultaneously, controlling the second lower switching transistor to turn off with a delay or lead of the first upper switching transistor by a first time, and controlling the first lower switching transistor to turn off with a corresponding delay or lead of the second upper switching transistor by a second time, so that the high-voltage terminal voltage of the high-voltage terminal increases in the startup mode; and when the high-voltage terminal voltage of the high-voltage terminal reaches the target voltage and the DC / DC converter enters the boost mode from the startup mode, controlling the duty ratios of the driving signals of the first upper switching transistor, the first lower switching transistor, the second upper switching transistor, and the second lower switching transistor to be equal and greater than 50%, and controlling the driving signal of the first upper switching transistor to have a delay or lead of the driving signal of the second lower switching transistor by a first phase shift angle, and controlling the driving signal of the second upper switching transistor to have a corresponding delay or lead of the driving signal of the first lower switching transistor by a second phase shift angle.

[0007] To achieve the foregoing object, the present case further provides a DC / DC converter, comprising: a low-voltage terminal; a low-voltage terminal full-bridge switching circuit electrically connected to the low-voltage terminal and comprising a first bridge arm and a second bridge arm connected in parallel, the first bridge arm comprising a first upper switching tube and a first lower switching tube, and the second bridge arm comprising a second upper switching tube and a second lower switching tube connected in series; a transformer comprising a primary winding and a secondary winding, the primary winding being electrically connected to the low-voltage terminal full-bridge switching circuit; a high-voltage terminal switching circuit electrically connected to the secondary winding; a high-voltage terminal electrically connected to the high-voltage terminal switching circuit; and a control unit electrically connected to the low-voltage terminal full-bridge switching circuit and the high-voltage terminal switching circuit for controlling the operation of the low-voltage terminal full-bridge switching circuit and the high-voltage terminal switching circuit; wherein when the DC / DC converter is in a startup mode, the duty ratios of the driving signals of the first upper switching tube, the first lower switching tube, the second upper switching tube and the second lower switching tube of the control unit are less than or equal to 50%, and the second lower switching tube and the first upper switching tube are controlled to turn on simultaneously, the first lower switching tube and the second upper switching tube are controlled to turn on simultaneously, the second lower switching tube is controlled to turn off with a delay or lead of a first time with respect to the first upper switching tube, and the first lower switching tube is controlled to turn off with a corresponding delay or lead of a second time with respect to the second upper switching tube, and the high-voltage terminal voltage of the high-voltage terminal increases in the startup mode; wherein when the high-voltage terminal voltage of the high-voltage terminal reaches the target voltage and the DC / DC converter enters the boost mode from the startup mode, the control unit controls the duty ratios of the driving signals of the first upper switching tube, the first lower switching tube, the second upper switching tube and the second lower switching tube to be equal and greater than 50%, and controls the driving signal of the first upper switching tube to have a delay or lead of a first phase shift angle with respect to the driving signal of the second lower switching tube, and the driving signal of the second upper switching tube to have a corresponding delay or lead of a second phase shift angle with respect to the driving signal of the first lower switching tube. Description of the Drawings

[0008] Figure 1 Flowchart of the steps of the control method for a preferred embodiment of the present case;

[0009] Figure 2 For Figure 1 Schematic circuit diagram of the DC / DC converter to which the control method is applied;

[0010] Figure 3 For Figure 2 When the DC / DC converter shown operates in the startup mode, the operation waveform diagram of the DC / DC converter under the first operation;

[0011] Figures 3A - 3F For Figure 2 When the DC / DC converter shown operates in the startup mode, the circuit operation diagram of the DC / DC converter under the first operation;

[0012] Figure 4 For Figure 2When the shown DC / DC converter operates in the startup mode, the operation waveform diagram of the DC / DC converter under the second operation;

[0013] Figure 5 For Figure 2 When the shown DC / DC converter operates in the boost mode, the operation waveform diagram of the DC / DC converter under the third operation;

[0014] Figures 5A - 5H For Figure 2 When the shown DC / DC converter operates in the boost mode, the circuit operation diagram of the DC / DC converter under the third operation;

[0015] Figure 6 For Figure 2 When the shown DC / DC converter operates in the boost mode, the operation waveform diagram of the DC / DC converter under the fourth operation;

[0016] Figure 7 For Figure 2 When the shown DC / DC converter operates in the startup mode and the boost mode, the schematic diagram of the voltage trend of the high-voltage terminal of the high-voltage terminal of the DC / DC converter 1;

[0017] Figure 8 For Figure 2 The schematic diagram of the detailed circuit architecture of the control unit of the shown DC / DC converter;

[0018] Figure 9 When Figure 1 When the shown DC / DC converter is in the startup mode or the boost mode, the schematic diagram of the step flow of the method for obtaining the duty cycle of the drive signals of the first upper switch tube, the first lower switch tube, the second upper switch tube, and the second lower switch tube.

[0019] Figure 10 For Figure 1 Another circuit structure diagram of the DC / DC converter to which the described control method is applied. Detailed implementation manners

[0020] Some typical embodiments reflecting the features and advantages of this case will be described in detail in the following description. It should be understood that this case can have various changes in different aspects, all of which do not depart from the scope of this case, and the descriptions and drawings therein are essentially for illustrative purposes and not for limiting this case.

[0021] Please refer to Figure 1 、 Figure 2 、 Figure 3 、 Figures 3A - 3F 、 Figure 4 、 Figure 5 、 Figures 5A - 5H 、 Figure 6, Figure 7 , Figure 8 and Figure 10 , where Figure 1 is the step flow chart of the control method of the preferred embodiment of this case, Figure 2 is Figure 1 the schematic circuit diagram of the DC / DC converter applied by the described control method, Figure 3 is Figure 2 the operation waveform diagram of the DC / DC converter under the first operation when the DC / DC converter shown operates in the startup mode, Figures 3A - 3F is Figure 2 the circuit operation diagram of the DC / DC converter under the first operation when the DC / DC converter shown operates in the startup mode, Figure 4 is Figure 2 the operation waveform diagram of the DC / DC converter under the second operation when the DC / DC converter shown operates in the startup mode, Figure 5 is Figure 2 the operation waveform diagram of the DC / DC converter under the third operation when the DC / DC converter shown operates in the boost mode, Figures 5A - 5H is Figure 2 the circuit operation diagram of the DC / DC converter under the third operation when the DC / DC converter shown operates in the boost mode, Figure 6 is Figure 2 the operation waveform diagram of the DC / DC converter under the fourth operation when the DC / DC converter shown operates in the boost mode, Figure 7 is Figure 2 the schematic diagram of the voltage trend at the high-voltage end of the high-voltage end of the DC / DC converter 1 when the DC / DC converter shown operates in the startup mode and the boost mode, Figure 8 is Figure 2 the schematic detailed circuit architecture diagram of the control unit 4 of the DC / DC converter shown, Figure 10 is Figure 1 another schematic circuit diagram of the DC / DC converter applied by the described control method. Figure 1 The control method shown can be applied to Figure 2In the DC / DC converter 1, the DC / DC converter 1 includes a low-voltage terminal, a low-voltage full-bridge switching circuit 2, a transformer T, a high-voltage terminal switching circuit 3, a high-voltage terminal, and a control unit 4. The low-voltage terminal includes a low-voltage positive terminal LV+ and a low-voltage negative terminal LV-, and the voltage on the low-voltage terminal is the low-voltage terminal voltage Vout. The high-voltage terminal includes a high-voltage positive terminal HV+ and a high-voltage negative terminal HV-, and the voltage on the high-voltage terminal is the high-voltage terminal voltage Vin. It can be understood that Vout and Vin are only simple markings for illustration. Since the DC / DC converter 1 in this case can be, for example, a bidirectional converter, Vout and Vin can also correspond to the high-voltage terminal voltage and the low-voltage terminal voltage, and this case does not impose any restrictions. The low-voltage full-bridge switching circuit 2 is electrically connected between the low-voltage terminal and the primary winding Np of the transformer T, and includes a first bridge arm and a second bridge arm connected in parallel. The first bridge arm, for example, includes a first upper switching transistor Tsra and a first lower switching transistor Tsrc connected in series in sequence, and the second bridge arm, for example, includes a second upper switching transistor Tsrb and a second lower switching transistor Tsrd connected in series in sequence. Among them, the connection point between the first upper switching transistor Tsra and the first lower switching transistor Tsrc and the connection point between the second upper switching transistor Tsrb and the second lower switching transistor Tsrd are correspondingly connected to the two end points of the primary winding Np. The high-voltage terminal switching circuit 3 is electrically connected between the secondary winding Ns of the transformer T and the high-voltage terminal. The primary winding Np and the secondary winding Ns of the transformer T are coupled to each other. The control unit 4 is electrically connected to the low-voltage full-bridge switching circuit 2 and the high-voltage terminal switching circuit 3 to control the operation of the DC / DC converter 1. For example, it outputs drive signals to control the operation of the first upper switching transistor Tsra, the first lower switching transistor Tsrc, the second upper switching transistor Tsrb, and the second lower switching transistor Tsrd of the low-voltage full-bridge switching circuit 2 and the operation of the high-voltage terminal switching circuit 3. The switching transistors in the low-voltage full-bridge switching circuit 2 and the high-voltage terminal switching circuit 3 can be devices of types such as Si MOSFET, SiC MOSFET, IGBT, GaN, etc.

[0022] In some embodiments, the DC / DC converter 1 further includes a power inductor Lo and a capacitive branch 5. The power inductor Lo is electrically connected between the low-voltage terminal and the low-voltage full-bridge switching circuit 2, and the actual current IL of the low-voltage terminal flows through the power inductor Lo. The capacitive branch 5 is connected in parallel with the first bridge arm of the low-voltage full-bridge switching circuit 2, and the capacitive branch 5 can form a freewheeling path for the power inductor Lo. In some embodiments, the capacitive branch 5 is composed of, for example, a single capacitive element or multiple capacitive elements. Among them, the multiple capacitive elements can be connected in series, in parallel, or in series-parallel connection. This case does not limit the number and connection method of the capacitive elements. Figure 10 The capacitive branch 5 of simply shows the series connection method of multiple capacitive elements. In some other embodiments, the capacitive branch 5 is, for example, any existing RCD circuit. As Figure 2In the illustrated embodiment, the capacitive branch 5 includes, for example, a first capacitor C, an active branch 50, and a diode D. The active branch 50 includes an active switch S and a resistor R connected in series, where the active switch S can be a P-type 00 metal oxide semiconductor field effect transistor. The first capacitor C is connected in series with the active branch 50, and the diode D is connected in parallel with the active branch 50. In some embodiments, the first capacitor C can be connected between the power inductor Lo and the active branch 50, or can also be connected between the low voltage negative terminal LV- and the active branch 50. Similarly, in some embodiments, the active switch S and the resistor R are sequentially connected in series between the low voltage positive terminal LV+ and the low voltage negative terminal LV-. At this time, the anode of the diode D is connected to one end point of the active switch S, and the cathode of the diode D is connected to one end point of the resistor R. In some other embodiments, the resistor R and the active switch S are sequentially connected in series between the low voltage positive terminal LV+ and the low voltage negative terminal LV-. At this time, the anode of the diode D is connected to one end point of the resistor R, and the cathode of the diode D is connected to one end point of the active switch S.

[0023] In addition, as Figure 2 shown, the DC / DC converter 1 further includes a first capacitor unit 6, which is connected in parallel with the high voltage terminal switch circuit 3 at the high voltage terminal, where the high voltage Vin at the high voltage terminal is controlled to pre-charge the first capacitor unit 6. The first capacitor unit 6 can include two second capacitors Cin1 and Cin2 connected in series. At this time, the high voltage terminal switch circuit 3 is, for example, a half-bridge circuit architecture and includes a third upper switch tube Tpra and a third lower switch tube Tprb connected in series, where the connection point between the two second capacitors Cin1 and Cin2 and the connection point between the third upper switch tube Tpra and the third lower switch tube Tprb are correspondingly connected to both end points of the secondary winding Ns. In other embodiments, as Figure 10 shown, the high voltage terminal switch circuit 3 can also be a full-bridge circuit architecture and includes a third upper switch tube Tpra and a third lower switch tube Tprb connected in series, and a fourth upper switch tube Tprc and a fourth lower switch tube Tprd connected in series. In this embodiment, the DC / DC converter 1 can further include a first capacitor unit 6, which is connected in parallel with the high voltage terminal switch circuit 3 at the high voltage terminal, where the high voltage Vin at the high voltage terminal is controlled to pre-charge the first capacitor unit 6. The first capacitor unit 6 includes, for example, a third capacitor Cin.

[0024] In some embodiments, as Figure 2 shown, the DC / DC converter 1 further includes a second capacitor unit 7, which is connected in parallel with the low voltage terminal full-bridge switch circuit 2 at the low voltage terminal, where the second capacitor unit 7 can include a fourth capacitor Cout.

[0025] In this embodiment, the DC / DC converter 1 can operate in a startup mode or a boost mode. When the DC / DC converter 1 starts to operate, the control unit 4 controls the DC / DC converter 1 to operate in the startup mode. When the DC / DC converter 1 is in the startup mode, the control unit 4 controls the duty ratios of the drive signals of the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd to be less than or equal to 50%, and controls the second lower switch Tsrd and the first upper switch Tsra to turn on simultaneously, and controls the first lower switch Tsrc and the second upper switch Tsrb to turn on simultaneously. In addition, the control unit 4 further controls the second lower switch Tsrd to turn off after a first time delay with respect to the first upper switch Tsra, and controls the first lower switch Tsrc to turn off after a second time delay with respect to the second upper switch Tsrb correspondingly, that is, as shown in Figure 3 the DC / DC converter 1 in the first operation, or the control unit 4 further controls the second lower switch Tsrd to turn off before a first time with respect to the first upper switch Tsra, and controls the first lower switch Tsrc to turn off before a second time with respect to the second upper switch Tsrb correspondingly, that is, as shown in Figure 4 the DC / DC converter 1 in the second operation. When the DC / DC converter 1 is in the startup mode, the high-voltage terminal voltage Vin at the high-voltage terminal will gradually increase. When the DC / DC converter 1 is in the startup mode, since the control unit 4 controls the second lower switch Tsrd to turn off after or before a first time with respect to the first upper switch Tsra, and controls the first lower switch Tsrc to turn off after or before a second time with respect to the second upper switch Tsrb correspondingly, a freewheeling path can be provided for the leakage inductance of the transformer T, thereby reducing the stress when the first lower switch Tsrc and the second lower switch Tsrd turn off or reducing the stress when the first upper switch Tsra and the second upper switch Tsrb turn off.

[0026] When the high-voltage terminal voltage Vin at the high-voltage terminal of the DC / DC converter 1 increases and reaches the target voltage Vs, the control unit 4 controls the DC / DC converter 1 to enter the boost mode from the startup mode. When the DC / DC converter 1 is in the boost mode, the control unit 4 controls the duty ratios of the drive signals of the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd to be equal and greater than 50%. In addition, the control unit 4 further controls the drive signal of the first upper switch Tsra to lead the drive signal of the second lower switch Tsrd by a first phase shift angle, and controls the drive signal of the second upper switch Tsrb to lead the drive signal of the first lower switch Tsrc by a second phase shift angle correspondingly, that is, as shown in Figure 5The shown DC / DC converter 1, under the third operation, controls the driving signal of the first upper switching transistor Tsra to delay the driving signal of the second lower switching transistor Tsrd by a first phase shift angle, and controls the driving signal of the second upper switching transistor Tsrb to correspondingly delay the driving signal of the first lower switching transistor Tsrc by a second phase shift angle, that is, as Figure 6 The shown DC / DC converter 1, under the fourth operation. When the DC / DC converter 1 is in the boost mode, since the control unit 4 controls the driving signal of the first upper switching transistor Tsra to delay or lead the driving signal of the second lower switching transistor Tsrd by a first phase shift angle, and controls the driving signal of the second upper switching transistor Tsrb to correspondingly delay or lead the driving signal of the first lower switching transistor Tsrc by a second phase shift angle, the turn-off current of the switching transistors in the low-voltage full-bridge switching circuit 2 is relatively small when they are turned off. Therefore, the voltage stress on the switching transistors can be reduced.

[0027] In some embodiments, the first time is equal to the second time, and / or, the first phase shift angle is equal to the second phase shift angle. In addition, when the DC / DC converter 1 is in the startup mode, as Figure 3 and Figure 4 shown, the duty cycles of the driving signals of the first upper switching transistor Tsra and the second upper switching transistor Tsrb are equal, and the duty cycles of the driving signals of the first lower switching transistor Tsrc and the second lower switching transistor Tsrd are equal. The phase difference between the driving signals of the first upper switching transistor Tsra and the second upper switching transistor Tsrb is 180 degrees, and the phase difference between the driving signals of the first lower switching transistor Tsrc and the second lower switching transistor Tsrd is 180 degrees. When the DC / DC converter 1 is in the boost mode, as Figure 5 and Figure 6 shown, the phase difference between the driving signals of the first upper switching transistor Tsra and the second upper switching transistor Tsrb is 180 degrees, and the phase difference between the driving signals of the first lower switching transistor Tsrc and the second lower switching transistor Tsrd is 180 degrees.

[0028] In some embodiments, the lengths of the first time and the second time correspond to the magnitude of the leakage inductance of the transformer T and the step-down magnitude of the voltage stresses of the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd when the DC / DC converter 1 transfers electrical energy from the low-voltage end to the high-voltage end. The first time and the second time are, for example, in the order of hundreds of nanoseconds. And / or, the magnitudes of the first phase-shift angle and the second phase-shift angle correspond to the step-down magnitude of the voltage stresses of the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd when the DC / DC converter 1 transfers electrical energy from the low-voltage end to the high-voltage end. The first phase-shift and the second phase-shift are, for example, in the order of hundreds of nanoseconds. Additionally, in some embodiments, the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd are controlled to perform switching in a hard-switching manner.

[0029] Please refer to again Figure 7 , when the DC / DC converter 1 is in the startup mode, the high-voltage terminal voltage Vin will rise smoothly from 0 to the target voltage Vs, for example, rise to Vin / (Vout)*N, where N is the turns ratio of the primary winding Np to the secondary winding Ns of the transformer T. When the DC / DC converter 1 is in the boost mode, the high-voltage terminal voltage Vin continues to rise until it rises to the default voltage Vc and then remains stable.

[0030] Please refer to Figure 8 , in some embodiments, to obtain the minimum duty cycle of the drive signals of the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd when the DC / DC converter 1 is in this startup mode (denoted as the first duty cycle, for example Figure 3 shown in the DC / DC converter 1 under the first operation, the duty cycle of the first upper switch Tsra, or Figure 4When the DC / DC converter 1 shown is in the second operation, the duty ratio of the second lower switching transistor Tsrd), and when obtaining the duty ratio of the driving signal of any one of the first upper switching transistor Tsra, the first lower switching transistor Tsrc, the second upper switching transistor Tsrb, and the second lower switching transistor Tsrd when the DC / DC converter 1 is in the boost mode (simultaneously denoted as the first duty ratio, that is, the control method for obtaining the above two duty ratios includes the same following devices and steps), the control unit 4 includes a first subtractor 40, a first regulator 41, a second subtractor 42, a second regulator 43, and a controller 44. The first subtractor 40 receives the high-voltage terminal voltage Vin of the high-voltage terminal and subtracts the reference voltage Vref of the high-voltage terminal from the high-voltage terminal voltage Vin to obtain a voltage difference Voff. The first regulator 41 regulates the voltage difference Voff to obtain the reference current Iref of the low-voltage terminal. Specifically, the first regulator 41, for example, performs proportional-integral regulation on the voltage difference Voff to obtain the reference current Iref of the low-voltage terminal. The second subtractor 42 obtains the minimum value between the reference current Iref of the low-voltage terminal and the current upper limit value of the low-voltage terminal, and subtracts the actual current IL flowing through the low-voltage terminal from the minimum value between the two to obtain a current difference Ioff. The second regulator 43 regulates the current difference Ioff to obtain the duty ratio reference value Df of the first duty ratio. Specifically, the second regulator 43, for example, performs proportional-integral regulation on the current difference Ioff to obtain the duty ratio reference value Df of the first duty ratio. The controller 44 compares the duty ratio reference value Df with the duty ratio upper limit value and the duty ratio lower limit value, and outputs a corresponding driving signal according to the comparison result to control the operation of the first upper switching transistor Tsra, the first lower switching transistor Tsrc, the second upper switching transistor Tsrb, and the second lower switching transistor Tsrd. Among them, when the duty ratio reference value Df is greater than the duty ratio upper limit value, the first duty ratio is the duty ratio upper limit value; when the duty ratio reference value Df is less than the duty ratio lower limit value, the first duty ratio is the duty ratio lower limit value; when the duty ratio reference value is less than the duty ratio upper limit value and greater than the duty ratio lower limit value, the first duty ratio is the duty ratio reference value Df. In some embodiments, the duty ratio upper limit value is, for example, 97%, and the duty ratio lower limit value is, for example, 3%. It can be understood that in these embodiments, the duty ratio upper limit value and the duty ratio lower limit value can be adjusted within a reasonable error range.

[0031] Specifically, when the DC / DC converter 1 is in this startup mode, the control unit 4 further includes a third regulator 39. The third regulator 39 controls the reference voltage Vref at the high-voltage end to increase at a specific slope. When it increases to the target voltage Vs, the voltage difference Voff is obtained by subtracting the high-voltage-end voltage Vin at the high-voltage end. Additionally, in an embodiment, the control unit 4 further includes a first driver 45. The first driver 45 obtains the drive signals of the first upper switch Tsra, the second upper switch Tsrb, the first lower switch Tsrc, and the second lower switch Tsrd according to the first duty cycle (i.e., the minimum of the duty cycles of the drive signals of the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd when the DC / DC converter 1 is in this startup mode), the first time, the second time, the phase difference between the first upper switch Tsra and the second upper switch Tsrb, and the phase difference between the first lower switch Tsrc and the second lower switch Tsrd.

[0032] Specifically, when the DC / DC converter 1 is in this boost mode, the control unit 4 further includes a second driver 46. The second driver 46 obtains the drive signals of the first upper switch Tsra, the second upper switch Tsrb, the first lower switch Tsrc, and the second lower switch Tsrd according to the first duty cycle (i.e., the duty cycle of any one of the drive signals of the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd when the DC / DC converter 1 is in the boost mode), the first phase-shift angle, the second phase-shift angle, the phase difference between the first upper switch Tsra and the second upper switch Tsrb, and the phase difference between the first lower switch Tsrc and the second lower switch Tsrd.

[0033] The operation modes of the DC / DC converter 1 in the startup mode and the boost mode will be described in detail below. First, the operation mode of the DC / DC converter 1 in an embodiment where the control unit 4 controls the second lower switch Tsrd to turn off with a delay of the first time after the first upper switch Tsra turns off, and controls the first lower switch Tsrc to turn off with a delay of the second time after the second upper switch Tsrb turns off will be described. As Figure 3 and Figure 3AAs shown, during the startup mode of operation of the DC / DC converter 1, taking one switching cycle as an example, in the time period t0 - t1, the first upper switch Tsra and the second lower switch Tsrd are turned on, the first lower switch Tsrc and the second upper switch Tsrb are turned off, and at the same time, the active switch S of the active branch 50 of the capacitive branch 5 is also turned on. At this time, the actual current IL at the low voltage end flows into the primary winding Np of the transformer T from top to bottom, and the induced secondary current charges the second capacitor Cin1 through the third upper switch Tpra, while the second capacitor Cin2 discharges, and at the same time, the first capacitor C of the capacitive branch 5 discharges. In the time period t1 - t2, Figure 3B As shown, the first upper switch Tsra is turned off, and the second lower switch Tsrd continues to be turned on. The leakage inductance Lk2 on the transformer T continues to flow through the parasitic diodes of the second lower switch Tsrd and the first lower switch Tsrc, thereby reducing the voltage stress when the second lower switch Tsrd is turned off. The power inductor Lo and the leakage inductance Lk1 on the line of the DC / DC converter 1 continue to flow through the capacitive branch 5. At this time, the first capacitor C is charged. At the same time, the induced secondary current charges the second capacitor Cin1 through the third upper switch Tpra, while the second capacitor Cin2 discharges. In the time period t2 - t3, Figure 3C As shown, the second lower switch Tsrd is turned off. At this time, the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd are all turned off, and no current flows through the transformer T. The high voltage end supplies power to the load through the second capacitors Cin1 and Cin2. At the same time, the power inductor Lo and the leakage inductance Lk1 continue to flow through the capacitive branch 5. At this time, the first capacitor C is charged. In the time period t3 - t4, as Figure 3D As shown, the first lower switch Tsrc and the second upper switch Tsrb are turned on, the first upper switch Tsra and the second lower switch Tsrd are turned off, and at the same time, the active switch S of the active branch 50 of the capacitive branch 5 is also turned on. At this time, the actual current IL at the low voltage end flows into the primary winding Np of the transformer T from bottom to top, and the induced secondary current charges the second capacitor Cin2 through the third lower switch Tprb, the second capacitor Cin1 discharges, and at the same time, the first capacitor C of the capacitive branch 5 discharges. In the time period t4 - t5, as Figure 3EAs shown, the second upper switch tube Tsrb is turned off, and the first lower switch tube Tsrc continues to conduct. The leakage inductance Lk2 on the transformer T freewheels through the parasitic diode of the first lower switch tube Tsrc and the second lower switch tube Tsrd, thereby reducing the voltage stress when the first lower switch tube Tsrc is turned off. The power inductor Lo and the leakage inductance Lk1 on the line of the DC / DC converter 1 freewheel through the capacitive branch 5, and at this time, the first capacitor C is charged. At the same time, the induced secondary current charges the second capacitor Cin2 through the third lower switch tube Tprb, while the second capacitor Cin1 discharges. During the time period t5 - t6, as Figure 3F shown, the first lower switch tube Tsrc is turned off. At this time, the first upper switch tube Tsra, the first lower switch tube Tsrc, the second upper switch tube Tsrb, and the second lower switch tube Tsrd are all turned off, and no current flows through the transformer T. The high-voltage terminal supplies power to the load through the second capacitors Cin1 and Cin2. At the same time, the power inductor Lo and the leakage inductance Lk1 freewheel through the capacitive branch 5, and the first capacitor C is charged.

[0034] Continue to describe the operation mode of the DC / DC converter 1 of another embodiment in which, in the startup mode, the control unit 4 controls the second lower switch tube Tsrd to turn off a first time ahead of the first upper switch tube Tsra, and controls the first lower switch tube Tsrc to turn off a second time ahead of the second upper switch tube Tsrb accordingly. As Figure 4 shown and in cooperation with Figures 3A - 3FIt is described that during the startup mode of the operation of the DC / DC converter 1, taking one switching cycle as an example, in the time period from t0 to t1, the first upper switching tube Tsra and the second lower switching tube Tsrd are turned on, the first lower switching tube Tsrc and the second upper switching tube Tsrb are turned off, and at the same time, the active switch S of the active branch 50 of the capacitive branch 5 is also turned on. At this time, the actual current IL at the low-voltage end flows into the primary winding Np of the transformer T from top to bottom, the induced secondary current charges the second capacitor Cin1 through the third upper switching tube Tpra, while the second capacitor Cin2 discharges, and at the same time, the first capacitor C of the capacitive branch 5 discharges. In the time period from t1 to t2, the first upper switching tube Tsra continues to be turned on, the second lower switching tube Tsrd is turned off, and the leakage inductance Lk2 on the transformer T continues to flow through the parasitic diodes of the first upper switching tube Tsra and the second upper switching tube Tsrb, thereby reducing the voltage stress when the first upper switching tube Tsra is turned off. The power inductor Lo and the leakage inductance Lk1 on the line of the DC / DC converter 1 continue to flow through the capacitive branch 5, and at this time, the first capacitor C is charged. At the same time, the induced secondary current charges the second capacitor Cin1 through the third upper switching tube Tpra, while the second capacitor Cin2 discharges. In the time period from t2 to t3, the first upper switching tube Tsra is turned off. At this time, the first upper switching tube Tsra, the first lower switching tube Tsrc, the second upper switching tube Tsrb, and the second lower switching tube Tsrd are all turned off, and no current flows through the transformer T. The high-voltage end supplies power to the load through the second capacitors Cin1 and Cin2, and at the same time, the power inductor Lo and the leakage inductance Lk1 continue to flow through the capacitive branch 5, and at this time, the first capacitor C is charged. In the time period from t3 to t4, the first lower switching tube Tsrc and the second upper switching tube Tsrb are turned on, the first upper switching tube Tsra and the second lower switching tube Tsrd are turned off, and at the same time, the active switch S of the active branch 50 of the capacitive branch 5 is also turned on. At this time, the actual current IL at the low-voltage end flows into the primary winding Np of the transformer T from bottom to top, the induced secondary current charges the second capacitor Cin2 through the third lower switching tube Tprb, while the second capacitor Cin1 discharges, and at the same time, the first capacitor C of the capacitive branch 5 discharges. In the time period from t4 to t5, the second upper switching tube Tsrb continues to be turned on, the first lower switching tube Tsrc is turned off, and the leakage inductance Lk2 on the transformer T continues to flow through the parasitic diodes of the second upper switching tube Tsrb and the first upper switching tube Tsra, thereby reducing the voltage stress when the second upper switching tube Tsrb is turned off. The power inductor Lo and the leakage inductance Lk1 on the line of the DC / DC converter 1 continue to flow through the capacitive branch 5, and at this time, the first capacitor C is charged. At the same time, the induced secondary current charges the second capacitor Cin2 through the third lower switching tube Tprb, while the second capacitor Cin1 discharges.During the time period from t5 to t6, the second upper switch Tsrb is turned on. At this time, the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd are all turned off, and no current flows through the transformer T. The high-voltage terminal supplies power to the load through the second capacitors Cin1 and Cin2. At the same time, the power inductor Lo and the leakage inductance Lk1 discharge through the capacitive branch 5, and the first capacitor C is charged.

[0035] Continuing to describe the operation mode of the DC / DC converter 1 according to an embodiment in the boost mode, the control unit 4 controls the driving signal of the first upper switch Tsra to lead the driving signal of the second lower switch Tsrd by a first phase shift angle, and controls the driving signal of the second upper switch Tsrb to lead the first lower switch Tsrc by a second phase shift angle correspondingly. As Figure 5 shown, as Figure 5A shown, when the DC / DC converter 1 operates in the boost mode, taking one switching cycle as an example, during the time period from t0 to t1, the first upper switch Tsra and the second lower switch Tsrd are turned on, the first lower switch Tsrc and the second upper switch Tsrb are turned off, and the active switch S of the active branch 50 of the capacitive branch 5 is also turned on, and the first capacitor C of the capacitive branch 5 is charged. At this time, the actual current IL flowing through the power inductor Lo decreases and flows from top to bottom into the primary winding Np of the transformer T. At the same time, the third upper switch Tpra of the high-voltage terminal switching circuit 3 is turned on, and the induced secondary current charges the second capacitor Cin1 through the third upper switch Tpra, while the second capacitor Cin2 discharges. During the time period from t1 to t2, as Figure 5B shown, the second upper switch Tsrb is also turned on. At this time, the actual current IL increases, and at the same time, the first capacitor C discharges. The leakage inductance currents of the primary and secondary sides of the transformer T flow through the first upper switch Tsra and the second upper switch Tsrb for freewheeling until the voltage of the first capacitor C drops to 0. At this time, the actual current IL flowing through the power inductor Lo rises and flows from top to bottom into the second bridge arm. The third upper switch Tpra of the high-voltage terminal switching circuit 3 is turned on, and the induced secondary current charges the second capacitor Cin1 through the third upper switch Tpra, while the second capacitor Cin2 discharges. During the time period from t2 to t3, as Figure 5C shown, the first lower switch Tsrc is also turned on. At this time, the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd of the low-voltage terminal full-bridge switching circuit 2 are all turned on, and the actual current IL continues to increase, which is equivalent to increasing the duty cycle of the driving signals of the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd. At this time, the first capacitor C discharges, and the current on the secondary winding Ns of the transformer T is 0. During the time period from t3 to t4, as Figure 5DAs shown, the first upper switch Tsra is turned off. At this time, the actual current IL flows through the second bridge arm, and the actual current IL increases. At the same time, the first capacitor C discharges, and the current in the secondary winding Ns of the transformer T is 0. In the stage from time t4 to t5, as Figure 5E shown, the second lower switch Tsrd is turned off. At this time, the actual current IL flows into the transformer T through the first lower switch Tsrc and the second upper switch Tsrb. The actual current IL decreases. At the same time, the first capacitor C is charged, and the third lower switch Tprb is turned on. In the stage from time t5 to t6, as Figure 5F shown, the first upper switch Tsra is also turned on. At this time, the actual current IL increases, and at the same time, the first capacitor C discharges. The leakage inductance currents of the primary and secondary sides of the transformer T continue to flow through the second lower switch Tsrd and the first lower switch Tsrc until the voltage of the first capacitor C drops to 0. At this time, the actual current IL flowing through the power inductor Lo increases and flows into the first bridge arm from top to bottom. At the same time, the third lower switch Tprb of the high-voltage terminal switching circuit 3 is turned on, and the induced secondary current charges the second capacitor Cin2 through the third lower switch Tprb, while the second capacitor Cin1 discharges. In the stage from time t6 to t7, as Figure 5G shown, the second lower switch Tsrd is also turned on. At this time, all the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd of the low-voltage terminal full-bridge switching circuit 2 are turned on, and the actual current IL continues to increase, which is equivalent to increasing the duty cycle of the drive signals of the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd. At this time, the first capacitor C discharges, and the current in the secondary winding Ns of the transformer T is 0. In the stage from time t7 to t8, as Figure 5H shown, the second upper switch Tsrb is turned off. At this time, the actual current IL flows through the first bridge arm, and the actual current IL increases. At the same time, the first capacitor C discharges, and the current in the secondary winding Ns of the transformer T is 0.

[0036] Continue to describe the operation mode of the DC / DC converter 1 of an embodiment in the boost mode, where the control unit 4 controls the drive signal of the first upper switch Tsra to delay the drive signal of the second lower switch Tsrd by a first phase shift angle, and controls the drive signal of the second upper switch Tsrb to lag behind the first lower switch Tsrc by a second phase shift angle correspondingly. As Figure 6 shown and in cooperation with Figures 5A - 5H, when the DC / DC converter 1 operates in the boost mode, taking a switching cycle as an example, during the period from time t0 to t1, the first upper switching tube Tsra and the second lower switching tube Tsrd are turned on, the first lower switching tube Tsrc and the second upper switching tube Tsrb are turned off, and the active switch S of the active branch 50 of the capacitive branch 5 is also turned on, and the first capacitor C of the capacitive branch 5 is charged. At this time, the actual current IL flowing through the power inductor Lo decreases and flows into the primary winding Np of the transformer T from top to bottom. At the same time, the third upper switching tube Tpra of the high-voltage terminal switching circuit 3 is turned on, and the induced secondary current charges the second capacitor Cin1 through the third upper switching tube Tpra, while the second capacitor Cin2 discharges. During the period from time t1 to t2, the first lower switching tube Tsrc is also turned on. At this time, the actual current IL increases, and at the same time, the first capacitor C discharges. The leakage inductance currents of the primary and secondary sides of the transformer T flow through the first lower switching tube Tsrc and the second lower switching tube Tsrd for freewheeling until the voltage of the first capacitor C drops to 0. At this time, the actual current IL flowing through the power inductor Lo increases and flows into the first bridge arm from top to bottom. At the same time, the third upper switching tube Tpra of the high-voltage terminal switching circuit 3 is turned on, and the induced secondary current charges the second capacitor Cin1 through the third upper switching tube Tpra, while the second capacitor Cin2 discharges. During the period from time t2 to t3, the second upper switching tube Tsrb is also turned on. At this time, all the first upper switching tube Tsra, the first lower switching tube Tsrc, the second upper switching tube Tsrb, and the second lower switching tube Tsrd of the low-voltage terminal full-bridge switching circuit 2 are turned on, and the actual current IL continues to increase, which is equivalent to increasing the duty ratio of the drive signals of the first upper switching tube Tsra, the first lower switching tube Tsrc, the second upper switching tube Tsrb, and the second lower switching tube Tsrd. At this time, the first capacitor C discharges, and the current on the secondary winding Ns of the transformer T is 0. During the period from time t3 to t4, the second lower switching tube Tsrd is turned off. At this time, the actual current IL flows through the first bridge arm, and the actual current IL increases. At the same time, the first capacitor C discharges, and the current on the secondary winding Ns of the transformer T is 0. During the period from time t4 to t5, the first upper switching tube Tsra is turned off. At this time, the actual current IL flows into the transformer T through the first lower switching tube Tsrc and the second upper switching tube Tsrb, the actual current IL decreases, and at the same time, the first capacitor C is charged, and the third lower switching tube Tprb is turned on. During the period from time t5 to t6, the second lower switching tube Tsrb is also turned on. At this time, the actual current IL increases, and at the same time, the first capacitor C discharges. The leakage inductance currents of the primary and secondary sides of the transformer T flow through the second lower switching tube Tsrd and the first lower switching tube Tsrc for freewheeling until the voltage of the first capacitor C drops to 0. At this time, the actual current IL flowing through the power inductor Lo increases and flows into the second bridge arm from top to bottom. At the same time, the third lower switching tube Tprb of the high-voltage terminal switching circuit 3 is turned on, and the induced secondary current charges the second capacitor Cin2 through the third lower switching tube Tprb, while the second capacitor Cin1 discharges.In the time period from t6 to t7, the first upper switch Tsra is also turned on. At this time, the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd of the full-bridge switching circuit 2 at the low-voltage end are all turned on. The actual current IL continues to increase, which is equivalent to increasing the duty cycle of the driving signals of the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd. At this time, the first capacitor C discharges, and the current in the secondary winding Ns of the transformer T is 0. In the time period from t7 to t8, the second upper switch Tsrb is turned off. At this time, the actual current IL flows through the second bridge arm, and the actual current IL increases. At the same time, the first capacitor C discharges, and the current in the secondary winding Ns of the transformer T is 0.

[0037] As Figure 1 shown, the control method of this embodiment can be executed by the control unit 4 and includes the following steps.

[0038] S1: When the DC / DC converter 1 is in the startup mode, control the duty cycle of the driving signals of the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd to be less than or equal to 50%, and control the second lower switch Tsrd to be turned on simultaneously with the first upper switch Tsra, control the first lower switch Tsrc to be turned on simultaneously with the second upper switch Tsrb, and control the second lower switch Tsrd to turn off with a first time delay or lead with respect to the first upper switch Tsra, and control the first lower switch Tsrc to turn off with a second time delay or lead with respect to the second upper switch Tsrb correspondingly, and the high-voltage terminal voltage Vin at the high-voltage end increases.

[0039] S2: When the high-voltage terminal voltage Vin at the high-voltage end reaches the target voltage Vs and the DC / DC converter 1 enters the boost mode from the startup mode, control the duty cycles of the driving signals of the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd to be equal and greater than 50%, and control the driving signal of the first upper switch Tsra to have a first phase shift angle with a time delay or lead with respect to the driving signal of the second lower switch Tsrd, and control the driving signal of the second upper switch Tsrb to have a second phase shift angle with a time delay or lead with respect to the first lower switch Tsrc correspondingly.

[0040] Please refer to Figure 9 , which is when Figure 1When the shown DC / DC converter is in the startup mode, a schematic diagram of the step flow of the method for obtaining the minimum of the duty ratios of the driving signals of the first upper switch, the first lower switch, the second upper switch, and the second lower switch, and when the DC / DC converter is in the boost mode, obtaining any one of the duty ratios of the driving signals of the first upper switch, the first lower switch, the second upper switch, and the second lower switch. In some embodiments, the method of obtaining the smaller of the duty ratios of the driving signals of the first upper switch Tsra and the second lower switch Tsrd as the first duty ratio in the foregoing step S1, and / or, in step S2, obtaining the duty ratio of any one of the driving signals of the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd, and simultaneously recording it as the first duty ratio includes the following steps.

[0041] S10, subtract the reference voltage Vref of the high-voltage end from the high-voltage end voltage Vin of the high-voltage end to obtain the voltage difference Voff.

[0042] S11, adjust the voltage difference Voff to obtain the reference current Iref of the low-voltage end.

[0043] S12, obtain the minimum of the reference current Iref of the low-voltage end and the current upper limit value of the low-voltage end, and subtract the actual current IL flowing through the low-voltage end from the minimum of the two to obtain the current difference Ioff.

[0044] S13, adjust the current difference Ioff to obtain the duty ratio reference value Df of the first duty ratio.

[0045] S14, compare the duty ratio reference value Df with the duty ratio upper limit value and the duty ratio lower limit value, and output the corresponding driving signal according to the comparison result to control the operation of the first upper switch Tsra, the first lower switch Tsrc, the second upper switch Tsrb, and the second lower switch Tsrd. When the duty ratio reference value Df is compared with the duty ratio upper limit value and the duty ratio lower limit value, when the duty ratio reference value Df is greater than the duty ratio upper limit value, the first duty ratio is the duty ratio upper limit value; when the duty ratio reference value Df is less than the duty ratio lower limit value, the first duty ratio is the duty ratio lower limit value; when the duty ratio reference value is less than the duty ratio upper limit value and greater than the duty ratio lower limit value, the first duty ratio is the duty ratio reference value Df.

[0046] In some embodiments, when the DC / DC converter 1 is in the startup mode, step S10 further includes controlling the reference voltage of the high-voltage end to increase at a specific slope, and when it increases to the target voltage Vs, subtracting the high-voltage end voltage Vin of the high-voltage end to obtain the voltage difference Voff.

[0047] In summary, the present case provides a DC / DC converter and a control method applicable thereto. When the DC / DC converter is in the startup mode, since the second lower switching transistor turns off with a delay or ahead of the first upper switching transistor by a first time, the first lower switching transistor correspondingly turns off with a delay or ahead of the second upper switching transistor by a second time, thus providing a freewheeling path for the leakage inductance of the transformer, thereby reducing the stress when the first lower switching transistor and the second lower switching transistor turn off or reducing the stress when the first upper switching transistor and the second upper switching transistor turn off. And when the DC / DC converter is in the boost mode, since the driving signal of the first upper switching transistor is delayed or ahead of the driving signal of the second lower switching transistor by a first phase shift angle, and the driving signal of the second upper switching transistor is correspondingly delayed or ahead of the driving signal of the first lower switching transistor by a second phase shift angle, the turn-off current of the switching transistors in the low-voltage full-bridge switching circuit is small when turning off, thus reducing the voltage stress of the switching transistors.

[0048] The present invention may be variously modified by those skilled in the art, but all such modifications shall fall within the scope of protection as defined by the appended claims.

Claims

1. A control method, applied to a DC / DC converter, characterized in that: The DC / DC converter comprises a low voltage end, a low voltage end full bridge switch circuit, a transformer, a high voltage end switch circuit and a high voltage end, the low voltage end full bridge switch circuit is electrically connected between the low voltage end and a primary winding of the transformer, and comprises a first bridge arm and a second bridge arm connected in parallel, wherein the first bridge arm comprises a first upper switch tube and a first lower switch tube connected in series, the second bridge arm comprises a second upper switch tube and a second lower switch tube connected in series, the high voltage end switch circuit is electrically connected between a secondary winding of the transformer and the high voltage end, and the control method comprises: When the DC / DC converter is in a startup mode, the duty ratio of the driving signals of the first upper switch tube, the first lower switch tube, the second upper switch tube and the second lower switch tube is controlled to be less than or equal to 50%, and the second lower switch tube is controlled to be turned on at the same time as the first upper switch tube, the first lower switch tube is controlled to be turned on at the same time as the second upper switch tube, the second lower switch tube is controlled to be turned off by a first time delay or ahead of the first upper switch tube, and the first lower switch tube is controlled to be turned off by a second time delay or ahead of the second upper switch tube accordingly, and a high voltage end voltage of the high voltage end is increased in the startup mode; and When the high-voltage end voltage of the high-voltage end reaches a target voltage and the DC / DC converter enters a boost mode from the startup mode, the duty cycles of the drive signals of the first upper switch tube, the first lower switch tube, the second upper switch tube and the second lower switch tube are controlled to be equal and greater than 50%, and the drive signal of the first upper switch tube is controlled to delay or lead the drive signal of the second lower switch tube by a first phase shift angle, and the drive signal of the second upper switch tube is controlled to correspondingly delay or lead the drive signal of the first lower switch tube by a second phase shift angle.

2. The control method as claimed in claim 1, wherein the first time is equal to the second time, and / or the first phase shift angle is equal to the second phase shift angle.

3. The control method as claimed in claim 1, wherein in the startup mode and the boost mode, the phase difference between the driving signals of the first upper switch tube and the second upper switch tube is 180 degrees, and the phase difference between the driving signals of the first lower switch tube and the second lower switch tube is 180 degrees.

4. The control method as claimed in claim 1, wherein in the start-up mode, the duty ratios of the driving signals of the first upper switch tube and the second upper switch tube are equal, and the duty ratios of the driving signals of the first lower switch tube and the second lower switch tube are equal.

5. The control method according to claim 4, wherein when the DC / DC converter is in the startup mode, the method of obtaining the smallest duty cycle of the driving signals of the first upper switch tube, the first lower switch tube, the second upper switch tube and the second lower switch tube (referred to as the first duty cycle), and / or when the DC / DC converter is in the boost mode, the method of obtaining the duty cycle of the driving signals of the first upper switch tube, the first lower switch tube, the second upper switch tube and the second lower switch tube (referred to as the first duty cycle) comprises: Subtracting a reference voltage of the high-voltage end from the high-voltage end voltage of the high-voltage end to obtain a voltage difference; The voltage difference is adjusted to obtain a reference current of the low voltage end; Obtaining a minimum value between the reference current of the low voltage end and a current upper limit value of the low voltage end, and subtracting the minimum value from an actual current of the low voltage end to obtain a current difference; Adjusting the current difference to obtain a duty cycle reference value of the first duty cycle; as well as The duty cycle reference value is compared with a duty cycle upper limit value and a duty cycle lower limit value, and when the duty cycle reference value is greater than the duty cycle upper limit value, the first duty cycle is the duty cycle upper limit value; When the duty cycle reference value is less than the duty cycle lower limit value, the first duty cycle is the duty cycle lower limit value; When the duty cycle reference value is less than the duty cycle upper limit value and greater than the duty cycle lower limit value, the first duty cycle is the duty cycle reference value.

6. The control method as claimed in claim 5, wherein when the DC / DC converter is in the startup mode, the step of "subtracting a reference voltage of the high-voltage end from a high-voltage end voltage of the high-voltage end to obtain a voltage difference" comprises: controlling the reference voltage of the high-voltage end to increase at a specific slope and when it increases to the target voltage, subtracting it from the high-voltage end voltage of the high-voltage end to obtain the voltage difference.

7. The control method as described in claim 1, wherein the DC / DC converter further comprises a power inductor and a capacitive branch, wherein the power inductor is electrically connected between the low-voltage end and the low-voltage end full-bridge switch circuit, the capacitive branch is connected in parallel with the first bridge arm of the low-voltage end full-bridge switch circuit, and the capacitive branch is a freewheeling path of the power inductor.

8. The control method as claimed in claim 7, wherein the capacitive branch comprises a capacitor, an active branch and a diode, the active branch comprises an active switch and a resistor connected in series, wherein the capacitor is connected in series with the active branch, and the diode is connected in parallel with the active branch. 9 . The control method as claimed in claim 8 , wherein the capacitive branch is composed of a capacitor, or the capacitive branch is an RCD circuit. 10 . The control method as claimed in claim 1 , wherein when the DC / DC converter is in the boost mode, the high voltage terminal voltage of the high voltage terminal is increased to a default voltage and then remains stable.

11. The control method as described in claim 1, wherein the length of the first time and the second time corresponds to the leakage inductance of the transformer and the voltage reduction of the first upper switch tube, the first lower switch tube, the second upper switch tube and the second lower switch tube when the DC / DC converter transmits electrical energy from the low voltage end to the high voltage end; and / or, the magnitude of the first phase shift angle and the second phase shift angle corresponds to the voltage reduction of the first upper switch tube, the first lower switch tube, the second upper switch tube and the second lower switch tube when the DC / DC converter transmits electrical energy from the low voltage end to the high voltage end.

12. The control method as claimed in claim 1, wherein the DC / DC converter further comprises a capacitor unit, the capacitor unit is connected in parallel to the high-voltage end, wherein the high-voltage end voltage of the high-voltage end is controlled to pre-charge the capacitor unit.

13. The control method as described in claim 1, wherein the high-voltage end switch circuit is a half-bridge circuit architecture or a full-bridge circuit architecture; and / or wherein the first upper switch tube, the first lower switch tube, the second upper switch tube and the second lower switch tube are controlled to perform switch switching in a hard switching manner.

14. A DC / DC converter, characterized in that: Include: A low-pressure end; A low-voltage end full-bridge switch circuit is electrically connected to the low-voltage end and comprises a first bridge arm and a second bridge arm connected in parallel, the first bridge arm comprises a first upper switch tube and a first lower switch tube, and the second bridge arm comprises a second upper switch tube and a second lower switch tube connected in series; A transformer, comprising a primary winding and a secondary winding, wherein the primary winding is electrically connected to the low-voltage end full-bridge switch circuit; a high-voltage switch circuit electrically connected to the secondary winding; a high voltage end, electrically connected to the high voltage end switch circuit; as well as a control unit, electrically connected to the low-voltage full-bridge switch circuit and the high-voltage switch circuit, for controlling the operation of the low-voltage full-bridge switch circuit and the high-voltage switch circuit; Wherein, when the DC / DC converter is in a startup mode, the control unit controls the duty ratio of the driving signals of the first upper switch tube, the first lower switch tube, the second upper switch tube and the second lower switch tube to be less than or equal to 50%, and controls the second lower switch tube to be turned on simultaneously with the first upper switch tube, controls the first lower switch tube to be turned on simultaneously with the second upper switch tube, controls the second lower switch tube to be turned off by a first delay or ahead of the first upper switch tube, and controls the first lower switch tube to be turned off by a second delay or ahead of the second upper switch tube correspondingly, and a high voltage end voltage of the high voltage end is increased in the startup mode; When the high-voltage end voltage of the high-voltage end reaches a target voltage and the DC / DC converter enters a boost mode from the startup mode, the control unit controls the duty cycles of the driving signals of the first upper switch tube, the first lower switch tube, the second upper switch tube and the second lower switch tube to be equal and greater than 50%, and controls the driving signal of the first upper switch tube to delay or lead the driving signal of the second lower switch tube by a first phase shift angle, and controls the driving signal of the second upper switch tube to correspondingly delay or lead the first lower switch tube by a second phase shift angle. 15 . The DC / DC converter as claimed in claim 14 , wherein the first time is equal to the second time, and / or the first phase shift angle is equal to the second phase shift angle.

16. The DC / DC converter as claimed in claim 14, wherein in the startup mode and the boost mode, the phase difference between the driving signals of the first upper switch tube and the second upper switch tube is 180 degrees, and the phase difference between the driving signals of the first lower switch tube and the second lower switch tube is 180 degrees. 17 . The DC / DC converter as claimed in claim 14 , wherein in the startup mode, the duty ratios of the driving signals of the first upper switch tube and the second upper switch tube are equal, and the duty ratios of the driving signals of the first lower switch tube and the second lower switch tube are equal.

18. The DC / DC converter as claimed in claim 17, wherein the control unit comprises: a first subtractor, receiving the high-voltage terminal voltage and performing a subtraction between a reference voltage of the high-voltage terminal and the high-voltage terminal voltage to obtain a voltage difference; A first regulator adjusts the voltage difference to obtain a reference current of the low voltage end a second subtractor, obtaining a minimum value between the reference current and a current upper limit value of the low voltage end, and subtracting the minimum value between the reference current and an actual current flowing through the low voltage end to obtain a current difference; a second regulator, regulating the current difference to obtain a duty ratio reference value of a first duty ratio; as well as a controller, comparing the duty cycle reference value with a duty cycle upper limit value and a duty cycle lower limit value, and outputting the corresponding first duty cycle according to the comparison result, wherein when the duty cycle reference value is greater than the duty cycle upper limit value, the first duty cycle is the duty cycle upper limit value; When the duty cycle reference value is less than the duty cycle lower limit value, the first duty cycle is the duty cycle lower limit value; When the duty cycle reference value is less than the duty cycle upper limit value and greater than the duty cycle lower limit value, the first duty cycle is the duty cycle reference value; Wherein, when the DC / DC converter is in the startup mode, the smallest duty cycle of the driving signals of the first upper switch tube, the first lower switch tube, the second upper switch tube and the second lower switch tube is the first duty cycle, and / or, when the DC / DC converter is in the boost mode, the duty cycle of the driving signals of the first upper switch tube, the first lower switch tube, the second upper switch tube and the second lower switch tube is the first duty cycle.

19. The DC / DC converter of claim 18, wherein the control unit further comprises a third regulator, and when the DC / DC converter is in the startup mode, the third regulator controls the reference voltage to increase at a specific slope, and after increasing to the target voltage, the voltage difference is obtained by subtracting the voltage from the high-voltage terminal voltage through the first subtractor.

20. The DC / DC converter as claimed in claim 14, wherein the DC / DC converter further comprises a power inductor and a capacitive branch, wherein the power inductor is electrically connected between the low-voltage end and the low-voltage end full-bridge switch circuit, the capacitive branch is connected in parallel with the first bridge arm of the low-voltage end full-bridge switch circuit, and the capacitive branch is a freewheeling path of the power inductor.

21. The DC / DC converter of claim 20, wherein the capacitive branch comprises a capacitor, an active branch and a diode, the active branch comprises an active switch and a resistor connected in series, wherein the capacitor is connected in series with the active branch, and the diode is connected in parallel with the active branch. 22 . The DC / DC converter as claimed in claim 14 , wherein when the DC / DC converter is in the boost mode, the high voltage terminal voltage of the high voltage terminal is increased to a default voltage and then remains stable.

23. The DC / DC converter as described in claim 14, wherein the lengths of the first time and the second time correspond to the leakage inductance of the transformer and the voltage reduction of the first upper switch tube, the first lower switch tube, the second upper switch tube and the second lower switch tube when the DC / DC converter transmits electrical energy from the low-voltage end to the high-voltage end; and / or, the sizes of the first phase shift angle and the second phase shift angle correspond to the voltage reduction of the first upper switch tube, the first lower switch tube, the second upper switch tube and the second lower switch tube when the DC / DC converter transmits electrical energy from the low-voltage end to the high-voltage end.

24. The DC / DC converter of claim 14, wherein the DC / DC converter further comprises a capacitor unit, the capacitor unit is connected in parallel to the high-voltage end, wherein the high-voltage end voltage of the high-voltage end is controlled to pre-charge the capacitor unit.

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