Trapezoidal wave current soft switching method of interleaved DC-DC converter

Abstract

The invention discloses a trapezoidal wave current soft switching method of an interleaving DC-DC converter, which is used for a two-phase interleaving bidirectional DC-DC converter based on a coupling inductor and a multi-phase interleaving converter thereof, and is characterized in that an inductive current adopts a trapezoidal wave mode, so that the converter works in an approximate critical conduction mode; a fixed switching frequency control or hybrid control method is adopted, so that the device can work in a Buck mode and can also work in a Boost mode. The method for realizing the soft switching is characterized in that the parasitic capacitance or the external resonant capacitor of the switching tube is discharged to be zero under the resonance action of the inductor and the capacitor in the dead zone time when the upper bridge arm switch and the lower bridge arm switch are alternately switched on, so that the zero-voltage switching-on of all the switching tubes is realized. And each phase current sharing control is adopted in the multi-phase interleaving parallel topological structure. According to the invention, the problems of large current peak value and high turn-off loss of a traditional triangular wave current mode are solved, the output ripple current is reduced, a soft switching method is provided, the switching loss is reduced, and the conversion efficiency of the converter is improved.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, and in particular relates to a trapezoidal current soft-switching method for interleaved parallel DC-DC converters. Background Technology

[0002] With the rapid development of big data, AI, and cloud computing technologies, the demand for DC power supply in AI data centers and computing centers is constantly increasing. High-power DC-DC converters have become a research hotspot in various fields. As the "dual carbon" goals are implemented, high-power DC-DC converters are needed in large quantities in fields such as photovoltaic power generation and energy storage batteries.

[0003] Compared with traditional bidirectional DC-DC converters, multiphase interleaved parallel bidirectional DC-DC converters based on coupled inductors have advantages such as high conversion efficiency, high power density, large output current, and low output current ripple, making them more suitable for applications such as energy storage batteries, CPU / GPU power supplies, and UPS.

[0004] For the traditional delta inductor current modulation method, the peak and effective values ​​of the inductor current are relatively large, resulting in large copper losses and switching losses in the converter. In the continuous conduction mode, it is a hard switching operation, which has large switching losses, low efficiency, and serious electromagnetic interference. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a trapezoidal wave current soft-switching method for interleaved parallel DC-DC converters. By employing a trapezoidal wave instead of the traditional triangular wave modulation, the peak and effective values ​​of the inductor current are reduced while maintaining the same average inductor current, effectively improving conversion efficiency. Furthermore, this method enables soft switching, further reducing switching losses and electromagnetic interference, thus enhancing efficiency.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a trapezoidal wave current soft-switching method for an interleaved parallel DC-DC converter, applied to a two-phase interleaved parallel bidirectional DC-DC converter based on coupled inductors, including two two-quadrant chopper modules composed of upper and lower bridge arm switches; Including the following steps: Step 1: Sample the input voltage, output voltage, coupling inductor current, inductor current, and output current of the converter; Step 2: Calculate the average inductor current; Step 3: Establish the relationship between duty cycle and input voltage, output voltage, and average inductor current; Step 4: Calculate the duty cycle D under fixed switching frequency control. 1a and D 2bThis generates a three-mode level 2-1-0, which controls the inductor current based on an approximate trapezoidal wave under the approximate critical conduction mode, and alternately changes the duty cycle of the switching transistor. Step 5: Based on the average current value I avg The magnitude of the positive and negative values ​​determines the operating mode. Iavg>0 and Iavg<0 correspond to Buck mode and Boost mode, respectively. If the duty cycle is within the set threshold range, the inductor current of the converter is controlled by a constant switching frequency control method to form a trapezoidal waveform based on the near-critical conduction mode. The inductor current has positive and negative values ​​in each switching cycle, enabling all switches to achieve zero-voltage conduction. If the duty cycle exceeds the set threshold, a hybrid control method of variable switching frequency and variable duty cycle is used to control the inductor current of the converter to form a trapezoidal waveform based on the near-critical conduction mode. The inductor current has positive and negative values ​​in each switching cycle, enabling all switches to achieve zero-voltage conduction.

[0007] Furthermore, in the fixed switching frequency control and the mixed control of variable switching frequency and variable duty cycle, closed-loop control of the voltage and current of the converter and waveform control of the trapezoidal wave of the inductor current in the near critical conduction mode are adopted.

[0008] Furthermore, the duty cycle in the constant switching frequency control is calculated from the switching frequency, the average inductor current, the input voltage, and the output voltage. By using the relationship between the duty cycle and the average inductor current, the variable duty cycle control is finally achieved.

[0009] Furthermore, the switching frequency of the variable switching frequency and variable duty cycle hybrid control is calculated from the duty cycle, the average inductor current, the input voltage, and the output voltage. By using the relationship between the switching frequency and the average inductor current, the variable switching frequency and variable duty cycle hybrid control is finally achieved.

[0010] Furthermore, the two-phase interleaved parallel converter module based on coupled inductors is treated as one phase; applied to an N-phase interleaved parallel converter, where N≥2; including the following steps: Step 1: Sample the input voltage, output voltage, inductor current of each phase, and output current of the converter; Step 2: Calculate the average inductor current and the current imbalance in each phase; Step 3: Establish the relationship between duty cycle and input voltage, output voltage, and average inductor current; Step 4: Under fixed switching frequency control, calculate the duty cycle of each phase. The duty cycle of the k-th phase is D. ka and D kd This generates a three-mode 2-1-0 level, which controls the inductor current of each phase based on an approximate trapezoidal wave under the approximate critical conduction mode, and alternately changes the duty cycle of the switching transistor. Step 5: Based on the average current value Iavg The magnitude of the positive or negative value determines the selection of different working modes, I avg >0、I avg <0 corresponds to Buck mode and Boost mode, respectively. If the duty cycle is within the set threshold range, the inductor current of the converter is controlled by a constant switching frequency control method to form a trapezoidal waveform based on the near-critical conduction mode. The inductor current has positive and negative values ​​in each switching cycle, so that all switches achieve zero-voltage conduction. If the duty cycle exceeds the set threshold, a hybrid control of variable switching frequency and variable duty cycle is used to control the inductor current of the converter to form a trapezoidal waveform based on the near-critical conduction mode. The inductor current has positive and negative values ​​in each switching cycle, so that all switches achieve zero-voltage conduction. At the same time, current balancing control is performed on each phase.

[0011] Furthermore, in the two-phase interleaved parallel bidirectional DC-DC converter and the N-phase interleaved parallel converter based on coupled inductors, the upper bridge arm switch and the lower bridge arm switch are complementary in conduction, and a dead time is set between the upper bridge arm switch being turned off and the lower bridge arm switch being turned on, and between the upper bridge arm switch being turned on and the lower bridge arm switch being turned off. By utilizing the dead time during which the upper and lower bridge arm switches alternately conduct, the inductor-capacitor resonance effect discharges the parasitic capacitance of the switching transistor or the external resonant capacitor to zero, thereby achieving zero-voltage turn-on of all switching transistors.

[0012] Furthermore, within a 360° switching cycle, the upper bridge arm switches of the N interleaved parallel bidirectional DC-DC converters based on coupled inductors are turned on alternately, and the conduction phase difference between two adjacent modules is 360° / N.

[0013] The beneficial effects of adopting this technical solution are: This invention relates to a two-phase interleaved parallel bidirectional DC-DC converter based on coupled inductors and its multi-phase interleaved parallel converter. The inductor current employs a trapezoidal wave mode, enabling the converter to operate in near-critical conduction mode. A constant switching frequency control or hybrid control method is used, allowing operation in both Buck and Boost modes. Soft switching is achieved by utilizing the inductor-capacitor resonance during the dead time of the alternating conduction of the upper and lower bridge arm switches, causing the parasitic capacitance of the switching transistors or the external resonant capacitor to discharge to zero, thus achieving zero-voltage turn-on for all switches. Current sharing control is employed in the multi-phase interleaved parallel topology. This invention solves the problems of large current peaks and high turn-off losses in the traditional triangular wave current mode, reducing output ripple current. Simultaneously, the proposed soft-switching method reduces switching losses and improves the converter's conversion efficiency.

[0014] This invention utilizes an approximate critical conduction mode to achieve zero-voltage soft switching by forming a resonant circuit with parasitic capacitance or external capacitance and inductors in the circuit without the need for additional passive components. It is applied to a two-phase interleaved parallel bidirectional DC-DC converter topology based on coupled inductors. Its advantages are that it requires fewer components, has a simple circuit structure, and is small in size. It utilizes its reverse current to achieve zero-voltage switching of the power switching transistor.

[0015] This invention also proposes a trapezoidal inductor current control method, which is applied to a two-phase interleaved parallel bidirectional DC-DC converter topology based on coupled inductors. It can operate in Buck mode and Boost mode. Compared with the delta inductor current, the trapezoidal or approximately trapezoidal inductor current has a lower peak current and RMS value under the same average value, which can better reduce losses and reduce the ripple of the output current.

[0016] This invention combines constant switching frequency control with a hybrid control of variable switching frequency and variable duty cycle to maintain the reverse current and keep the circuit in a near-critical conduction mode, thereby achieving soft switching of all power switching transistors. This can significantly reduce switching losses, improve converter efficiency, and adapt to various load currents and output voltages.

[0017] This invention addresses the multiphase interleaved parallel topology of a two-phase interleaved parallel bidirectional DC-DC converter based on coupled inductors. On the basis of the trapezoidal current mode, it adds phase current equalization control, which facilitates current distribution, reduces losses, improves system power density and stability, and reduces output current ripple. Attached Figure Description

[0018] Figure 1 This is a schematic flowchart of a trapezoidal current soft-switching method for an interleaved parallel DC-DC converter according to the present invention; Figure 2 This is a schematic diagram of the trapezoidal current mode of an interleaved parallel DC-DC converter in an embodiment of the present invention; Figure 3 This is a schematic diagram of a trapezoidal current mode of an interleaved parallel DC-DC converter utilizing parasitic capacitance or an external resonant capacitor in an embodiment of the present invention; Figure 4 The modulation waveform and voltage / current waveform of the trapezoidal current mode operating in Buck mode in this embodiment of the invention; Figure 5 The modulation waveform and voltage / current waveform of the trapezoidal current mode operating in Boost mode are shown in the embodiments of the present invention. Figure 6 This is a waveform diagram showing the zero-voltage turn-on of switching transistors S1b and S2a in an embodiment of the present invention. Figure 7This is a waveform diagram showing the zero-voltage turn-on of switching transistors S1a and S2b in an embodiment of the present invention. Figure 8 This is a schematic diagram of a trapezoidal current mode applied to a multiphase interleaved parallel topology DC-DC converter in an embodiment of the present invention; Figure 9 This is a schematic diagram of the three-phase interleaved parallel trapezoidal current and superimposed current operating in Buck mode in an embodiment of the present invention; Figure 10 This is a schematic diagram of the three-phase interleaved parallel trapezoidal current and superimposed current operating in Boost mode in an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below with reference to the accompanying drawings.

[0020] In this embodiment, see Figure 1 As shown, this invention proposes a trapezoidal current soft-switching method for interleaved parallel DC-DC converters, which is applied to a two-phase interleaved parallel bidirectional DC-DC converter based on coupled inductors, including two two-quadrant chopper modules composed of upper and lower bridge arm switches; Including the following steps: Step 1: Sample the input voltage, output voltage, coupling inductor current, inductor current, and output current of the converter; Step 2: Calculate the average inductor current; Step 3: Establish the relationship between duty cycle and input voltage, output voltage, and average inductor current; Step 4: Calculate the duty cycle D under fixed switching frequency control. 1a and D 2b This generates a three-mode level 2-1-0, which controls the inductor current based on an approximate trapezoidal wave under the approximate critical conduction mode, and alternately changes the duty cycle of the switching transistor. Step 5: Based on the average current value I avg The magnitude of the positive and negative values ​​determines the operating mode. Iavg>0 and Iavg<0 correspond to Buck mode and Boost mode, respectively. If the duty cycle is within the set threshold range, the inductor current of the converter is controlled by a constant switching frequency control method to form a trapezoidal waveform based on the near-critical conduction mode. The inductor current has positive and negative values ​​in each switching cycle, enabling all switches to achieve zero-voltage conduction. If the duty cycle exceeds the set threshold, a hybrid control method of variable switching frequency and variable duty cycle is used to control the inductor current of the converter to form a trapezoidal waveform based on the near-critical conduction mode. The inductor current has positive and negative values ​​in each switching cycle, enabling all switches to achieve zero-voltage conduction.

[0021] As an optimization of the above embodiments, in the fixed switching frequency control and the mixed control of variable switching frequency and variable duty cycle, closed-loop control of the voltage and current of the converter and waveform control of the trapezoidal wave of the inductor current in the near critical conduction mode are adopted.

[0022] The duty cycle in the constant switching frequency control is calculated from the switching frequency, average inductor current, input voltage, and output voltage. By understanding the relationship between the duty cycle and the average inductor current, variable duty cycle control is ultimately achieved.

[0023] The switching frequency of the variable switching frequency and variable duty cycle hybrid control is calculated from the duty cycle, the average inductor current, the input voltage, and the output voltage. By using the relationship between the switching frequency and the average inductor current, the variable switching frequency and variable duty cycle hybrid control is finally achieved.

[0024] As an optimization of the above embodiment, the two-phase interleaved parallel converter module based on coupled inductors is considered as one phase; applied to an N-phase interleaved parallel converter, where N≥2; including the following steps: Step 1: Sample the input voltage, output voltage, inductor current of each phase, and output current of the converter; Step 2: Calculate the average inductor current and the current imbalance in each phase; Step 3: Establish the relationship between duty cycle and input voltage, output voltage, and average inductor current; Step 4: Under fixed switching frequency control, calculate the duty cycle of each phase. The duty cycle of the k-th phase is D. ka and D kd This generates a three-mode 2-1-0 level, which controls the inductor current of each phase based on an approximate trapezoidal wave under the approximate critical conduction mode, and alternately changes the duty cycle of the switching transistor. Step 5: Based on the average current value I avg The magnitude of the positive or negative value determines the selection of different working modes, I avg >0、I avg <0 corresponds to Buck mode and Boost mode, respectively. If the duty cycle is within the set threshold range, the inductor current of the converter is controlled by a constant switching frequency control method to form a trapezoidal waveform based on the near-critical conduction mode. The inductor current has positive and negative values ​​in each switching cycle, so that all switches achieve zero-voltage conduction. If the duty cycle exceeds the set threshold, a hybrid control of variable switching frequency and variable duty cycle is used to control the inductor current of the converter to form a trapezoidal waveform based on the near-critical conduction mode. The inductor current has positive and negative values ​​in each switching cycle, so that all switches achieve zero-voltage conduction. At the same time, current balancing control is performed on each phase.

[0025] Preferably, in the two-phase interleaved parallel bidirectional DC-DC converter and the N-phase interleaved parallel converter based on coupled inductors, the upper bridge arm switch and the lower bridge arm switch are complementaryly turned on, and a dead time is set between the upper bridge arm switch being turned off and the lower bridge arm switch being turned on, and between the upper bridge arm switch being turned on and the lower bridge arm switch being turned off. By utilizing the dead time during which the upper and lower bridge arm switches alternately conduct, the inductor-capacitor resonance effect discharges the parasitic capacitance of the switching transistor or the external resonant capacitor to zero, thereby achieving zero-voltage turn-on of all switching transistors.

[0026] Preferably, within one switching cycle of 360°, the upper bridge arm switches of the N interleaved parallel bidirectional DC-DC converters based on coupled inductors are turned on alternately, and the conduction phase difference between two adjacent modules is 360° / N.

[0027] like Figure 2 The diagram shown is a trapezoidal current mode schematic of an interleaved parallel DC-DC converter according to the present invention. By controlling S... 1a and S 2b Duty cycle D 1a and D 2b By alternating the duty cycle, it operates in near-critical conduction mode, achieving trapezoidal waveform control of the inductor current. Under the same current average value as the delta current, the peak and effective current values ​​are reduced, switching losses are reduced, and conversion efficiency is improved.

[0028] like Figure 3 The diagram shown illustrates a trapezoidal current mode design of an interleaved parallel DC-DC converter according to the present invention, utilizing parasitic capacitance or an external resonant capacitor. Operating in trapezoidal current mode, the parasitic capacitance of the switching transistor or an external resonant capacitor is used, through the resonance effect of the inductor and capacitor, to achieve zero-voltage turn-on of the switching transistor without the need for additional passive components. This reduces switching losses, improves efficiency, and reduces electromagnetic interference.

[0029] like Figure 4 The figure shows the modulation waveform and voltage-current waveform of the trapezoidal current mode operating in Buck mode in this embodiment. By controlling S... 1a and S 2b Duty cycle D 1a and D 2b Alternating duty cycles control the chopper output to achieve three mode levels: 2-1-0, and voltage V. ox The output is V dc When the inductor current rises, the voltage v ox The output is 0.5V. dc At this time, the inductor current remains constant or approximately constant, and the voltage v oxWhen the output is 0, the inductor current decreases and the average inductor current is positive, operating in near-critical conduction mode. This ensures that there is positive and negative current in each cycle to maintain the zero-voltage conduction of the switching transistor. This constitutes complete trapezoidal current or near-trapezoidal current control in Buck mode, which can achieve high-efficiency forward energy transfer of the converter while ensuring low current ripple.

[0030] like Figure 5 The figure shows the modulation waveform and voltage-current waveform of the trapezoidal current mode operating in Boost mode in this embodiment. By controlling S... 1a and S 2b Duty cycle D 1a and D 2b Alternating duty cycles control the chopper output to achieve three mode levels: 0, 1, and 2, with voltage V. ox When the output is 0, the inductor current decreases, and the voltage v ox The output is 0.5V. dc At this time, the inductor current remains constant or approximately constant, and the voltage v ox The output is V dc When the inductor current rises, the average inductor current is negative, and it operates in near-critical conduction mode, ensuring that there are positive and negative currents in each cycle to maintain zero voltage conduction of the switching transistor. This constitutes a complete trapezoidal current or near-trapezoidal current control in Boost mode, which can achieve high-efficiency reverse energy transfer of the converter while ensuring low current ripple.

[0031] like Figure 6 As shown, the switch S in Buck mode of this embodiment... 1b and S 2a Achieve zero-voltage turn-on waveform diagram. In S... 1a and S 1b The dead zone of alternating conduction, i.e., S 1a Conduction becomes S 1b When S is turned on, 1a When the circuit is turned off, a positive inductor current flows through C. 1a C 1b L1, L3, C L Forming a resonant circuit, C 1a Charging, C 1b Discharge, when C 1a Charge to V dc C 1b When discharged to 0, S 1b It can be turned on at zero voltage; in S 2b and S 2a The dead zone of alternating conduction, i.e., S 2b Conduction becomes S 2a When S is turned on, 2b When the circuit is turned off, a positive inductor current flows through C.2a C 2b L1, L3, C L Forming a resonant circuit, C 2b Charging, C 2a Discharge, when C 2b Charge to V dc C 2a When discharged to 0, S 2a It can be turned on at zero voltage, and the same applies in Boost mode.

[0032] like Figure 7 As shown, in this embodiment, the switching transistor S in Buck mode... 1a and S 2b Achieve zero-voltage turn-on waveform diagram. In S... 1b and S 1a The dead zone of alternating conduction, i.e., S 1b Conduction becomes S 1a When S is turned on, 1b When the circuit is turned off, a positive inductor current flows through C. 1a C 1b L1, L3, C L Forming a resonant circuit, C 1b Charging, C 1a Discharge, when C 1b Charge to V dc C 1a When discharged to 0, S 1a It can be turned on at zero voltage; in S 2a and S 2b The dead zone of alternating conduction, i.e., S 2a Conduction becomes S 2b When S is turned on, 2a When the circuit is turned off, a positive inductor current flows through C. 2a C 2b L1, L3, C L Forming a resonant circuit, C 2a Charging, C 2b Discharge, when C 2a Charge to V dc C 2b When discharged to 0, S 2b It can be turned on at zero voltage, and the same applies in Boost mode.

[0033] like Figure 8The diagram shown illustrates the trapezoidal current mode of a DC-DC converter with a multiphase interleaved parallel topology, as described in this embodiment. Each module, following the trapezoidal current waveform control and soft-switching method, operates with staggered switching of the upper bridge arm switches in the N inductor-based two-phase interleaved parallel bidirectional DC-DC converter modules within a 360° switching cycle. The phase difference between adjacent modules is 360° / N. Combined with phase current balancing control and phase offsetting, this results in ripple current subtraction, significantly reducing output ripple current and increasing current output capability.

[0034] like Figure 9 The diagram shows the three-phase interleaved parallel trapezoidal current and superimposed current in Buck mode of this embodiment. Taking the three-phase interleaved parallel topology as an example, the three-phase currents are 120° out of phase. In Buck mode, the average inductor current is positive. Under current sharing control, the three-phase currents are balanced, resulting in a small ripple in the final output superimposed current.

[0035] like Figure 10 The diagram shown illustrates the three-phase interleaved parallel trapezoidal current and superimposed current in Boost mode of this embodiment. Taking the three-phase interleaved parallel topology as an example, the three-phase currents are 120° out of phase. In Boost mode, the average inductor current is negative. Under current sharing control, the three-phase currents are balanced, resulting in a small ripple in the final output superimposed current.

[0036] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A trapezoidal current soft-switching method for an interleaved parallel DC-DC converter, characterized in that, It is applied in a two-phase interleaved parallel bidirectional DC-DC converter based on coupled inductors, including two two-quadrant chopper modules composed of upper and lower bridge arm switches; Including the following steps: Step 1: Sample the input voltage, output voltage, coupling inductor current, inductor current, and output current of the converter; Step 2: Calculate the average inductor current; Step 3: Establish the relationship between duty cycle and input voltage, output voltage, and average inductor current; Step 4: Calculate the duty cycle D under fixed switching frequency control. 1a and D 2b This generates a three-mode level 2-1-0, which controls the inductor current based on an approximate trapezoidal wave under the approximate critical conduction mode, and alternately changes the duty cycle of the switching transistor. Step 5: Based on the average current value I avg The magnitude of the positive and negative values ​​determines the operating mode. Iavg>0 and Iavg<0 correspond to Buck mode and Boost mode, respectively. If the duty cycle is within the set threshold range, the inductor current of the converter is controlled by a constant switching frequency control method to form a trapezoidal waveform based on the near-critical conduction mode. The inductor current has positive and negative values ​​in each switching cycle, enabling all switches to achieve zero-voltage conduction. If the duty cycle exceeds the set threshold, a hybrid control method of variable switching frequency and variable duty cycle is used to control the inductor current of the converter to form a trapezoidal waveform based on the near-critical conduction mode. The inductor current has positive and negative values ​​in each switching cycle, enabling all switches to achieve zero-voltage conduction.

2. The trapezoidal current soft-switching method for an interleaved parallel DC-DC converter according to claim 1, characterized in that, In the fixed switching frequency control and the mixed control of variable switching frequency and variable duty cycle, closed-loop control of the voltage and current of the converter and waveform control of the trapezoidal wave of the inductor current in the near critical conduction mode are adopted.

3. The trapezoidal current soft-switching method for an interleaved parallel DC-DC converter according to claim 2, characterized in that, The duty cycle in the constant switching frequency control is calculated from the switching frequency, average inductor current, input voltage, and output voltage. By understanding the relationship between the duty cycle and the average inductor current, variable duty cycle control is ultimately achieved.

4. The trapezoidal current soft-switching method for an interleaved parallel DC-DC converter according to claim 2, characterized in that, The switching frequency of the variable switching frequency and variable duty cycle hybrid control is calculated from the duty cycle, the average inductor current, the input voltage, and the output voltage. By using the relationship between the switching frequency and the average inductor current, the variable switching frequency and variable duty cycle hybrid control is finally achieved.

5. A trapezoidal current soft-switching method for an interleaved parallel DC-DC converter according to any one of claims 1-4, characterized in that, A two-phase interleaved parallel converter module based on coupled inductors is considered as one phase; this is applied to an N-phase interleaved parallel converter, where N≥2; including... step: Step 1: Sample the input voltage, output voltage, inductor current of each phase, and output current of the converter; Step 2: Calculate the average inductor current and the current imbalance in each phase; Step 3: Establish the relationship between duty cycle and input voltage, output voltage, and average inductor current; Step 4: Under fixed switching frequency control, calculate the duty cycle of each phase. The duty cycle of the k-th phase is D. ka and D kd This generates a three-mode 2-1-0 level, which controls the inductor current of each phase based on an approximate trapezoidal wave under the approximate critical conduction mode, and alternately changes the duty cycle of the switching transistor. Step 5: Based on the average current value I avg The magnitude of the positive or negative value determines the selection of different working modes, I avg >0、I avg <0 corresponds to Buck mode and Boost mode, respectively. If the duty cycle is within the set threshold range, the inductor current of the converter is controlled by a constant switching frequency control method to form a trapezoidal waveform based on the near-critical conduction mode. The inductor current has positive and negative values ​​in each switching cycle, so that all switches achieve zero-voltage conduction. If the duty cycle exceeds the set threshold, a hybrid control of variable switching frequency and variable duty cycle is used to control the inductor current of the converter to form a trapezoidal waveform based on the near-critical conduction mode. The inductor current has positive and negative values ​​in each switching cycle, so that all switches achieve zero-voltage conduction. At the same time, current balancing control is performed on each phase.

6. The trapezoidal current soft-switching method for an interleaved parallel DC-DC converter according to claim 5, characterized in that, In the two-phase interleaved parallel bidirectional DC-DC converter and the N-phase interleaved parallel converter based on coupled inductors, the upper bridge arm switch and the lower bridge arm switch are complementary in conduction, and a dead time is set between the upper bridge arm switch being turned off and the lower bridge arm switch being turned on, and between the upper bridge arm switch being turned on and the lower bridge arm switch being turned off. By utilizing the dead time during which the upper and lower bridge arm switches alternately conduct, the inductor-capacitor resonance effect discharges the parasitic capacitance of the switching transistor or the external resonant capacitor to zero, thereby achieving zero-voltage turn-on of all switching transistors.

7. The trapezoidal current soft-switching method for an interleaved parallel DC-DC converter according to claim 6, characterized in that, Within a 360° switching cycle, the upper bridge arm switches of the N interleaved parallel bidirectional DC-DC converters based on coupled inductors are turned on alternately, and the conduction phase difference between two adjacent modules is 360° / N.

Images