Wide-range resonant soft-switching bidirectional dc-dc converter and control method thereof

Abstract

This invention relates to a wide-range resonant soft-switching bidirectional DC-DC converter and its control method. It includes a first DC power supply, an input energy storage filter capacitor, a primary bridge converter unit, a series resonant unit, an isolation transformer, a secondary converter unit, a resonant buffer unit, an output energy storage filter unit, and a second DC power supply. The series resonant unit includes a resonant capacitor and a resonant inductor connected in series. The resonant buffer unit includes a buffer switch and a buffer capacitor connected in series. This invention achieves wide-range soft-switching conversion of DC voltage in either the forward or reverse direction by applying appropriate frequency and timing drive signals to the switches in the primary bridge converter unit, secondary converter unit, and resonant buffer unit. Compared to traditional unidirectional or bidirectional converters, it achieves the current two-stage voltage regulation conversion effect, is suitable for connecting loads or power supply devices with a wide voltage range, such as batteries, and can achieve high power density and high efficiency.

Description

Technical Field

[0001] This application relates to the field of DC-DC converter technology, specifically to a wide-range resonant soft-switching bidirectional DC-DC converter and its control method. Background Technology

[0002] With the rapid development of energy storage products and battery equipment, the demand for power products capable of bidirectional conversion is increasing. Many devices now utilize batteries, requiring charging and discharging. Due to the inherently wide voltage range of batteries, and considering compatibility with different products, the corresponding voltage range is becoming increasingly wider. Therefore, it is conventional to use two separate circuits for charging and discharging. However, achieving bidirectional conversion is no longer cost-effective, and ordinary single-stage circuits are insufficient in terms of efficiency and ability to meet the demands of a wide voltage range for charging or discharging.

[0003] like Figure 1 As shown, current low-voltage battery pack conversion circuits typically employ two methods: one is a two-stage approach, usually involving a first-stage boost or buck converter followed by a second-stage DC / DC regulator. This two-stage approach is more expensive and reduces conversion efficiency. The other method uses a switching switch to change the transformer turns ratio. This is achieved by altering the transformer's turns ratio, or by adding or removing transformer coils using similar circuitry. The implementation method mentioned in patent CN107733236B is an example of this. Figure 2 As shown, its essence is to achieve different voltage ratios by adding or removing additional transformer conversion circuits. The control principle is simple and direct. However, the high turns ratio will cause higher stress on the switching transistors and will also change the inductance and leakage inductance parameters of the original main transformer, introducing new current loop interference. Sudden voltage changes may lead to a series of other control parameter changes. Step duty cycle adjustment is prone to oscillation and other problems. In addition, the soft switching coordination conditions of the two converters are relatively poor. Therefore, additional conversion circuits and transformers must be added, making the entire converter structure complex and difficult to promote and apply. Summary of the Invention

[0004] The purpose of this invention is to provide a wide-range resonant soft-switching bidirectional DC-DC converter and its control method, which can achieve efficient soft-switching conversion and relatively simple bidirectional conversion of a wide voltage range. It solves the technical problems of existing technologies that require two-stage converters for multiple conversions, have many conductive path devices, and suffer from high losses due to the use of soft switches that cannot achieve full conversion, making them unsuitable for applications with limited space or relatively high cost requirements.

[0005] The technical solution adopted in this invention is as follows: a wide-range resonant soft-switching bidirectional DC-DC converter, comprising a first DC power supply, an input energy storage filter capacitor, a primary bridge converter unit, a series resonant unit, an isolation transformer, a secondary converter unit, a resonant buffer unit, an output energy storage filter unit, and a second DC power supply; the input energy storage filter capacitor is connected in parallel with the primary bridge converter unit, and the primary bridge converter unit is also connected to the first DC power supply; the primary side of the isolation transformer is connected in series with the series resonant unit, and then connected to the primary bridge converter unit; the secondary side of the isolation transformer is connected to the secondary converter unit; the resonant buffer unit is connected in parallel with the secondary converter unit; the output energy storage filter unit is connected in parallel with the resonant buffer unit; and the second DC power supply is connected to the output energy storage filter unit.

[0006] The primary bridge converter unit is a full-bridge converter unit or a half-bridge converter unit; the secondary converter unit is a full-bridge converter unit or a full-wave rectifier converter; the series resonant unit includes a resonant capacitor and a resonant inductor connected in series; the resonant capacitor is connected to the primary bridge converter unit, and the resonant inductor is connected to the primary side of the isolation transformer; the resonant buffer unit includes a buffer switch and a buffer capacitor connected in series; the output energy storage filter unit includes an energy storage inductor and an output energy storage filter capacitor connected in series; the second DC power supply is connected to the output energy storage filter capacitor;

[0007] When the primary bridge converter unit is a full-bridge converter unit, the primary bridge converter unit includes a first switch, a second switch, a third switch, and a fourth switch; the first switch and the third switch are connected in series to form a first bridge arm, the second switch and the fourth switch are connected in series to form a second bridge arm, and the first bridge arm and the second bridge arm are connected in parallel; the drains of the first switch and the second switch are connected to the positive terminal of the first DC power supply and one end of the input energy storage filter capacitor, and the sources of the third switch and the fourth switch are connected to the negative terminal of the first DC power supply and the other end of the input energy storage filter capacitor; the resonant capacitor is connected to the drain of the third switch, and the primary side of the isolation transformer is connected to the drain of the fourth switch; When the primary bridge converter unit is a half-bridge converter unit, the primary bridge converter unit includes a first switch and a second switch connected in series. The drain of the first switch is connected to the positive terminal of the first DC power supply and one end of the input energy storage filter capacitor. The source of the second switch is connected to the negative terminal of the first DC power supply and the other end of the input energy storage filter capacitor. The resonant capacitor is connected to the drain of the second switch. The primary side of the isolation transformer is connected to the source of the second switch.

[0008] When the secondary conversion unit is a full-bridge conversion unit, the secondary conversion unit includes a fifth switch, a sixth switch, a seventh switch, and an eighth switch; the fifth and seventh switches are connected in series to form a third bridge arm, the sixth and eighth switches are connected in series to form a fourth bridge arm, and the third and fourth bridge arms are connected in parallel; the secondary side of the isolation transformer is connected to the drains of the seventh and eighth switches; when the secondary conversion unit is a full-wave rectifier converter, the secondary conversion unit includes a fifth switch and a sixth switch; the drains of the fifth and sixth switches are connected, and then connected to the source of the buffer switch and one end of the energy storage inductor; the sources of the fifth and sixth switches are connected to the secondary side of the isolation transformer, and the secondary side of the isolation transformer is also connected to one end of the buffer capacitor.

[0009] Furthermore, the first DC power supply and the second DC power supply can be a DC power supply, a rectified AC power supply, a step power supply with switch control, or a load that can provide power supply voltage.

[0010] Furthermore, when the primary bridge converter unit and the secondary converter unit perform unidirectional rectification and conversion, the first to eighth switching transistors can be diodes or high-frequency switching transistors equipped with anti-parallel diodes, wherein the anti-parallel diodes are integrated diodes, parasitic diodes, or external diodes.

[0011] Furthermore, the input energy storage filter capacitor and the output energy storage filter capacitor are non-polarized capacitors or polarized capacitors; when the first DC power supply or the second DC power supply is a power supply with a step change, the input energy storage filter capacitor and the output energy storage filter capacitor are equivalent capacitors of a controllable switch connected in series with a capacitor; the resonant inductor is an external inductor, the coupled leakage inductance inside the transformer, or the coupled inductance of an external inductor and the leakage inductance inside the transformer.

[0012] The control method for the aforementioned wide-range resonant soft-switching bidirectional DC-DC converter is as follows:

[0013] S100: Based on the power supply status setting circuit sampling or external communication detection of the voltage required to output by the DC circuit, determine whether the DC converter is in a forward or reverse operating state; the forward operating state means that the first DC power supply is the input and the second DC power supply is the output; the reverse operating state means that the second DC power supply is the input and the first DC power supply is the output.

[0014] S200: Determine whether the primary bridge converter unit and the secondary converter unit are in inverter or rectification mode, and determine whether the resonant buffer unit is in rectifier buffer resonant mode or inverter resonant mode; and perform corresponding timing logic configuration and PWM drive configuration; the duty cycle of the switching transistors in the primary bridge converter unit and the secondary converter unit shall not exceed 0.5, and sufficient dead time shall be reserved; the frequency of the drive signal applied to the buffer switch Q9 shall be twice the frequency of the drive signal of the switching transistors in the primary bridge converter unit or the secondary converter unit, and the operating frequency of the primary bridge converter unit and the secondary converter unit shall be the same;

[0015] S300: Based on the operating state determined in steps S100 and S200, PWM drive control signals are applied to the switching transistors of the primary bridge converter unit, secondary converter unit, and resonant buffer unit. When the operating state is determined to be forward, the primary bridge converter unit performs an inverter conversion, converting the voltage of the first DC power supply into a high-frequency pulse, which is coupled to the secondary side through the series resonant unit and the isolation transformer. After high-frequency rectification by the secondary converter unit, the pulse is transmitted to the resonant buffer unit, the output energy storage filter unit, and the second DC power supply. When the operating state is determined to be reverse, the secondary converter unit performs an inverter conversion, and the voltage of the second DC power supply is transmitted to the secondary converter unit through the output energy storage filter unit and the resonant buffer unit for high-frequency pulse conversion. The pulse is coupled from the secondary side to the primary side through the isolation transformer, then transmitted to the primary bridge converter unit through the series resonant unit for high-frequency rectification, and finally the DC voltage is transmitted to the input filter capacitor and the first DC power supply.

[0016] S400: When the DC-DC converter is operating in the forward operating state, if the voltage value of the first DC power supply is higher than the set voltage value of the second DC power supply after being coupled through the isolation transformer, the duty cycle of the PWM drive applied to the primary bridge converter unit is reduced; otherwise, the duty cycle is increased.

[0017] When the DC-DC converter is operating in reverse mode, if the voltage value of the second DC power supply is higher than the set voltage value of the first DC power supply after being coupled through the transformer, the duty cycle of the PWM drive applied to the secondary conversion unit is reduced; otherwise, the duty cycle is increased.

[0018] S500: After the switching transistors of the primary bridge converter and the secondary converter are turned on according to the settings, all drive signals of the primary bridge converter and the secondary converter are turned off, and the input energy storage filter capacitor and the output energy storage filter unit are allowed to freewheel.

[0019] Furthermore, in steps S300~S500, the PWM drive signals of the primary bridge converter unit and the secondary bridge converter switching transistors operate at the same frequency, and the frequency range is 95%~115% of the resonant inherent resonant frequency.

[0020] Further, in steps S300~S500, when the DC-DC converter is operating in the forward operating state, if increasing the duty cycle of the PWM drive applied to the primary bridge converter unit to the maximum limit value still cannot meet the requirement of the second DC power supply voltage value, then the duty cycle is fixed, the operating frequency is adjusted to the optimal operating frequency point, and the boost mode is entered. Before the next rectification conduction cycle is about to begin, PWM drive is added to one of the switching transistors of the rectifier conduction bridge arm in the secondary converter unit that is not in the current cycle. Conversely, the PWM drive duty cycle applied to the primary bridge converter unit is gradually reduced, and the boost mode is exited. When the DC-DC converter is operating in the reverse operating state, if increasing the duty cycle of the PWM drive applied to the secondary converter unit to the maximum limit value still cannot meet the requirement of the first DC power supply voltage value, then before the next rectification conduction cycle is about to begin, PWM drive is added to the switching transistors of the rectifier conduction bridge arm in the primary bridge converter unit that is not in the current cycle to boost the voltage. Conversely, the PWM drive duty cycle applied to the primary bridge converter unit is gradually reduced according to the control, and the boost mode is exited.

[0021] Furthermore, in steps S300~S500, when the DC-DC converter is operating in the forward operating state, if the secondary conversion unit is a full-bridge conversion unit, then before the next rectification conduction cycle begins, PWM drive is applied to only one of the switches in the rectifier conduction bridge arm that is not in the current cycle, or PWM drive is applied to both switches in the rectifier conduction bridge arm that is not in the current cycle; if the secondary conversion unit is a full-wave rectifier converter, then before the next rectification conduction cycle begins, PWM is applied to only the switches that are not in the current cycle. Drive; When the DC-DC converter is operating in reverse mode, if it is in boost mode and the primary bridge converter is a full-bridge converter, then before the next rectification cycle begins, only one switch of the rectifier conducting bridge arm that is not conducting in the current cycle is driven by PWM, or both switches of the rectifier conducting bridge arm that are not conducting in the current cycle are driven by PWM. If the primary bridge converter is a half-bridge converter, then before the next rectification cycle begins, only the switches that are not conducting in the current cycle are driven by PWM.

[0022] Further, in steps S300~S500, the output voltage within a certain range and the soft-switching state of the secondary converter unit are achieved by adjusting the duty cycle of the buffer switch in the corresponding conversion mode. When the DC converter operates in the forward mode, the PWM drive applied to the buffer switch is delayed compared to the PWM drive of the primary bridge converter unit, i.e., a certain turn-on dead time is left. At the same time, the PWM drive applied to the buffer switch at the turn-off time is consistent with the PWM drive of the primary bridge converter unit. When the DC converter operates in the reverse mode, the PWM drive applied to the buffer switch is delayed compared to the PWM drive of the secondary converter unit, i.e., a certain turn-on dead time is left. The minimum dead time after the PWM drive applied to the buffer switch turns off is consistent with the minimum dead time of the PWM drive of the secondary converter unit. If the DC converter operates in the boost mode of the reverse mode, the buffer switch must not turn off earlier than the switch connected to the opposite terminal of the primary bridge converter unit.

[0023] Further, in steps S300~S500, when the DC-DC converter operates in the boost mode of reverse operation, the drive signal applied to the switch of the primary bridge converter unit that performs boost operation is earlier than the drive signal of the secondary converter unit. The drive signal applied to the switch of the primary bridge converter unit that performs boost operation is a delayed signal of the synchronous rectification signal of the previous cycle, that is, the period of the delayed signal is the sum of the synchronous rectification duty cycle, the boost duty cycle and the dead time. If the DC-DC converter operates in non-boost mode, the switch of the primary bridge converter unit and the secondary converter unit are applied with synchronous rectification drive signals.

[0024] The beneficial effects of this invention are as follows:

[0025] (1) In terms of structure and performance, it overcomes the traditional requirement of two-stage voltage regulator circuits to achieve a wide range of bidirectional DC-DC conversion, and also simplifies the complexity of multi-stage circuit conversion;

[0026] (2) In terms of control, the traditional series resonant converter requires wide-range frequency modulation to achieve voltage control mode. This invention mainly achieves voltage regulation by adjusting the duty cycle of the switching transistors of each converter unit, which is similar to the voltage regulation control principle of the traditional bridge converter and is relatively simple.

[0027] (3) In terms of soft switching implementation, the series resonant converter and the resonant buffer unit are used to realize the soft switching of wide-range bidirectional conversion, and realize the comprehensive performance of series resonant soft switching and traditional bridge converter with wide range; avoid high voltage peak stress and hard switching loss.

[0028] (4) In terms of applicability, it changes the traditional limitation that it can only be a relatively stable DC source. After connecting the input energy storage filter capacitor in series with a controllable switch, the input DC power supply can be a step power supply with switch control.

[0029] (5) In addition, due to the normalization control in the structure, the switching of multiple converters or transformer coils is overcome, resulting in more stable performance and high overall cost performance. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a block diagram of an existing DC-DC converter;

[0032] Figure 2 A schematic diagram of the existing bidirectional DC-DC converter implementation scheme;

[0033] Figure 3 This is a block diagram illustrating an embodiment of the present invention;

[0034] Figure 4 This is a circuit schematic diagram of an embodiment of the present invention;

[0035] Figure 5 This is a schematic diagram illustrating a specific implementation of the primary bridge converter unit connection in an embodiment of the present invention;

[0036] Figure 6 This is a schematic diagram illustrating a specific implementation of the secondary transformation unit connection in an embodiment of the present invention;

[0037] Figure 7 This is a circuit diagram of an embodiment of the present invention in the forward rectification working state;

[0038] Figure 8 This is a circuit diagram of an embodiment of the present invention in reverse rectification mode;

[0039] Figure 9 This is a waveform diagram of an embodiment of the present invention in the forward rectification working state;

[0040] Figure 10 This is a waveform diagram of the reverse rectification operation state in an embodiment of the present invention.

[0041] Explanation of reference numerals in the attached diagram: D1 - First diode, D2 - Second diode, D3 - Third diode, D4 ​​- Fourth diode, Q1 - First switching transistor, Q2 - Second switching transistor, Q3 - Third switching transistor, Q4 - Fourth switching transistor, Q5 - Fifth switching transistor, Q6 - Sixth switching transistor, Q7 - Seventh switching transistor, Q8 - Eighth switching transistor, Q9 - Buffer switching transistor, QA - Switch A, QB - Switch B, QC - Switch C, QD - Switch D, L1 - Energy storage inductor, Lr - Resonant inductor, Lm - Main magnetizing inductor, Tra - Isolation transformer, Cr - Resonant capacitor, Cr1 - First resonant capacitor, Cr2 - Second resonant capacitor, Cs - Buffer capacitor, C1 - Input energy storage filter capacitor, C2 - Output energy storage filter capacitor, DC1 - First DC power supply, DC2 - Second DC power supply. Detailed Implementation

[0042] To better understand the above-described objects, features, and advantages of the present invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Many specific details are set forth in the following description to provide a thorough understanding of the invention; however, the invention may be practiced in other ways different from those described herein, and therefore, the invention is not limited to the specific embodiments disclosed below.

[0043] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by one of ordinary skill in the art described herein. The terms “first,” “second,” and similar terms used in this patent application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms “an” or “a” and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms “connected” or “linked” and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The terms “upper,” “lower,” “left,” “right,” etc., are used only to indicate relative positional relationships, which change accordingly when the absolute position of the described object changes.

[0044] like Figures 3-4As shown, a wide-range resonant soft-switching bidirectional DC-DC converter includes a first DC power supply DC1, an input energy storage filter capacitor C1, a primary bridge converter unit, a series resonant unit, an isolation transformer Tra, a secondary converter unit, a resonant buffer unit, an output energy storage filter unit, and a second DC power supply DC2. The input energy storage filter capacitor C1 is connected in parallel with the primary bridge converter unit, and the primary bridge converter unit is also connected to the first DC power supply DC1. The primary side of the isolation transformer Tra is connected in series with the series resonant unit and then connected to the primary bridge converter unit. The secondary side of the isolation transformer Tra is connected to the secondary converter unit. The resonant buffer unit is connected in parallel with the secondary converter unit, and the output energy storage filter unit is connected in parallel with the resonant buffer unit. The second DC power supply DC2 is connected to the output energy storage filter unit.

[0045] The primary bridge converter unit is a full-bridge converter unit or a half-bridge converter unit; the secondary converter unit is a full-bridge converter unit or a full-wave rectifier converter; the series resonant unit includes a resonant capacitor Cr and a resonant inductor Lr connected in series; the resonant capacitor Cr is connected to the primary bridge converter unit, and the resonant inductor Lr is connected to the primary side of the isolation transformer Tra; the resonant buffer unit includes a buffer switch Q9 and a buffer capacitor Cs connected in series; the output energy storage filter unit includes an energy storage inductor L1 and an output energy storage filter capacitor C2 connected in series; the second DC power supply DC2 is connected to the output energy storage filter capacitor C2.

[0046] When the primary bridge converter unit is a full-bridge converter unit, the primary bridge converter unit includes a first switch Q1, a second switch Q2, a third switch Q3, and a fourth switch Q4; the first switch Q1 and the third switch Q3 are connected in series to form a first bridge arm, the second switch Q2 and the fourth switch Q4 are connected in series to form a second bridge arm, and the first bridge arm and the second bridge arm are connected in parallel; the drains of the first switch Q1 and the second switch Q2 are connected to the positive terminal of the first DC power supply DC1 and one end of the input energy storage filter capacitor C1, and the sources of the third switch Q3 and the fourth switch Q4 are connected to the negative terminal of the first DC power supply DC1 and the other end of the input energy storage filter capacitor C1; the resonant capacitor C... r is connected to the drain of the third switch Q3, and the primary side of the isolation transformer Tra is connected to the drain of the fourth switch Q4; when the primary bridge converter unit is a half-bridge converter unit, the primary bridge converter unit includes a first switch Q1 and a second switch Q2 connected in series. The drain of the first switch Q1 is connected to the positive terminal of the first DC power supply DC1 and one end of the input energy storage filter capacitor C1, and the source of the second switch Q2 is connected to the negative terminal of the first DC power supply DC1 and the other end of the input energy storage filter capacitor C1; the resonant capacitor Cr is connected to the drain of the second switch Q2, and the primary side of the isolation transformer Tra is connected to the source of the second switch Q2;

[0047] When the secondary conversion unit is a full-bridge conversion unit, the secondary conversion unit includes a fifth switch Q5, a sixth switch Q6, a seventh switch Q7, and an eighth switch Q8; the fifth switch Q5 and the seventh switch Q7 are connected in series to form the third bridge arm, the sixth switch Q6 and the eighth switch Q8 are connected in series to form the fourth bridge arm, and the third bridge arm and the fourth bridge arm are connected in parallel; the secondary side of the isolation transformer Tra is connected to the drain of the seventh switch Q7 and the eighth switch Q8; when the secondary conversion unit is a full-wave rectifier converter, the secondary conversion unit includes a fifth switch Q5 and a sixth switch Q6; the drain of the fifth switch Q5 is connected to the drain of the sixth switch Q6, and then connected to the source of the buffer switch Q9 and one end of the energy storage inductor L1; the sources of the fifth switch Q5 and the sixth switch Q6 are connected to the secondary side of the isolation transformer Tra, and the secondary side of the isolation transformer Tra is also connected to one end of the buffer capacitor Cs.

[0048] In this embodiment of the invention, the first DC power supply DC1 and the second DC power supply DC2 are DC power supplies, rectified AC power supplies, step-change power supplies with switch control, or loads that can provide power supply voltage. When the rectified three-phase AC is used as a DC source input, the voltage of each phase is different. When the series switch controls the switching, the rectified three-phase AC will be a step-change input power supply. This embodiment of the invention is also applicable to step-change power supplies with switch control. The input energy storage filter capacitor C1 and the output energy storage filter capacitor C2 are non-polarized capacitors or polarized capacitors. When the first DC power supply DC1 or the second DC power supply DC2 is a step-change power supply, the input energy storage filter capacitor C1 and the output energy storage filter capacitor C2 are equivalent capacitors of a controllable switch connected in series with a capacitor. The resonant inductor Lr is an external inductor, the coupled leakage inductance inside the transformer, or the coupled inductance of an external inductor and the leakage inductance inside the transformer.

[0049] When the primary bridge converter unit and the secondary converter unit perform only unidirectional rectification and conversion, the first to eighth switching transistors Q8 can be diodes or high-frequency switching transistors equipped with anti-parallel diodes. The anti-parallel diodes can be integrated diodes, parasitic diodes, or external diodes.

[0050] like Figure 5 As shown, the primary bridge converter unit can be either a full-bridge converter unit or a half-bridge converter unit. Figure 5 (a) is the circuit diagram of the full-bridge converter unit. The full-bridge converter is composed of switching transistors A QA, B QB, C QC and D QD. The resonant capacitor Cr and the resonant inductor Lr together form a series resonant unit. Figure 5 (b) is a connection method of half-bridge converter unit, in which switching transistors A and C form bridge arms, and resonant capacitor Cr and resonant inductor Lr together form a series resonant unit. Figure 5 (c) is another connection method for the half-bridge converter unit. Switches AQA and CQC form the first bridge arm, and the first resonant capacitor Cr1 and the second resonant capacitor Cr2 are connected in series to form the other bridge arm, where cr1 = cr2 = 1 / 2 * cr, where cr1 is the capacitance of the first resonant capacitor Cr1, cr2 is the capacitance of the second resonant capacitor Cr2, and cr is... Figure 5 In (a), the capacitance value of the resonant capacitor Cr, the first resonant capacitor Cr1, the second resonant capacitor Cr2, and the resonant inductor Lr together constitute a series resonant unit. The series connection relationship between the series resonant unit and the transformer coil, and the connection order of the resonant capacitor Cr and the resonant inductor Lr in the series loop can all be adjusted.

[0051] like Figure 6As shown, the secondary conversion unit can be either a full-bridge conversion unit or a full-wave rectifier converter. Figure 6 (a) is the circuit diagram of the full-bridge converter unit, which uses switching transistors AQA, BQB, CQC and DQD to form a full-bridge converter; Figure 6 (b) and Figure 6 (c) shows two different connection methods for a full-wave rectifier converter, also known as a push-pull converter; Figure 6 (b) Switch C QC and switch D QD are connected in a common drain configuration. When used for rectification, it is called a full-wave rectifier. Figure 6 (c) Switch A (QA) and switch B (QB) are connected in a common-source configuration, and the circuit function is the same as... Figure 6 The circuit shown in (b) is the same.

[0052] like Figure 5 and Figure 6 The rectifier or inverter circuits shown are well-known circuits, and their specific working principles should be understood by those skilled in the art; therefore, they will not be analyzed in detail here. This invention is not limited to the above-described implementation examples; other combinations that can achieve the functions of this invention also fall within this scope.

[0053] The control method adopted in this embodiment of the invention includes the following steps:

[0054] S100: Based on the power supply status setting circuit sampling or external communication detection of the voltage required to output by the DC circuit, determine whether the DC converter is in a forward or reverse operating state; the forward operating state means that the first DC power supply DC1 is the input and the second DC power supply DC2 is the output; the reverse operating state means that the second DC power supply DC2 is the input and the first DC power supply DC1 is the output.

[0055] S200: Determine whether the primary bridge converter unit and the secondary converter unit are in inverter or rectification mode, and determine whether the resonant buffer unit is in rectifier buffer resonant mode or inverter resonant mode; and perform corresponding timing logic configuration and PWM drive configuration; the duty cycle of the switching transistors in the primary bridge converter unit and the secondary converter unit shall not exceed 0.5, and sufficient dead time shall be reserved; the frequency of the drive signal applied to the buffer switch Q9 shall be twice the frequency of the drive signal of the switching transistors in the primary bridge converter unit or the secondary converter unit, and the operating frequency of the primary bridge converter unit and the secondary converter unit shall be the same;

[0056] S300: Based on the operating state determined in steps S100 and S200, PWM drive control signals are applied to the switching transistors of the primary bridge converter unit, secondary converter unit, and resonant buffer unit. When the operating state is determined to be forward, the primary bridge converter unit performs an inverter conversion, converting the voltage of the first DC power supply DC1 into a high-frequency pulse, which is coupled to the secondary side through the series resonant unit and the isolation transformer Tra. After high-frequency rectification by the secondary converter unit, the pulse is transmitted to the resonant buffer unit, the output energy storage filter unit, and the second DC power supply DC2. When the operating state is determined to be reverse, the secondary converter unit performs an inverter conversion, and the voltage of the second DC power supply DC2 is transmitted to the secondary converter unit through the output energy storage filter unit and the resonant buffer unit for high-frequency pulse conversion. The voltage is coupled from the secondary side to the primary side through the isolation transformer Tra, and then transmitted to the primary bridge converter unit through the series resonant unit for high-frequency rectification. Finally, the DC voltage is transmitted to the input filter capacitor and the first DC power supply DC1.

[0057] S400: When the DC-DC converter is operating in the forward operating state, if the voltage value of the first DC power supply DC1 is higher than the set voltage value of the second DC power supply DC2 after being coupled through the isolation transformer Tra, the PWM drive applied to the primary bridge converter unit will be adjusted to reduce the duty cycle; otherwise, the duty cycle will be adjusted to increase.

[0058] When the DC-DC converter is operating in reverse mode, if the voltage value of the second DC power supply DC2 is higher than the set voltage value of the first DC power supply DC1 after being coupled through the transformer, the duty cycle of the PWM drive applied to the secondary conversion unit is reduced; otherwise, the duty cycle is increased.

[0059] S500: After the switching transistors of the primary bridge converter and the secondary converter are turned on according to the settings, all drive signals of the primary bridge converter and the secondary converter are turned off, and the input energy storage filter capacitor and the output energy storage filter unit are allowed to freewheel.

[0060] In steps S300-S500, the PWM drive signals of the primary bridge converter unit and the secondary bridge converter switching transistors operate at the same frequency, and the frequency range is 95% to 115% of the resonant natural resonant frequency. In this embodiment of the invention, the operating frequency of the PWM drive signals of the primary bridge converter unit and the secondary converter unit switching transistors is 105% of the resonant natural resonant frequency.

[0061] When the DC-DC converter is operating in the forward mode, if increasing the duty cycle of the PWM drive applied to the primary bridge converter unit to the maximum limit still cannot meet the voltage requirement of the second DC power supply DC2, then the duty cycle is fixed, the operating frequency is adjusted to the optimal operating frequency point, and the converter enters boost mode. Before the next rectification cycle begins, PWM drive is added to one of the switches in the rectifier conduction bridge arm of the secondary converter unit that is not in the current cycle. Conversely, the duty cycle of the PWM drive applied to the primary bridge converter unit is gradually reduced, and the converter exits boost mode. When the DC-DC converter is operating in the reverse mode, if increasing the duty cycle of the PWM drive applied to the secondary converter unit to the maximum limit still cannot meet the voltage requirement of the first DC power supply DC1, then before the next rectification cycle begins, PWM drive is added to the switches in the rectifier conduction bridge arm of the primary bridge converter unit that is not in the current cycle to boost the voltage. Conversely, the duty cycle of the PWM drive applied to the primary bridge converter unit is gradually reduced, and the converter exits boost mode.

[0062] When the DC-DC converter operates in forward mode, if the secondary converter unit is a full-bridge converter, PWM drive is applied to only one switch of the rectifier arm that is not in the current cycle before the start of the next rectification cycle, or PWM drive is applied to both switches of the rectifier arm that is not in the current cycle. If the secondary converter unit is a full-wave rectifier converter, PWM drive is applied to only the switches that are not in the current cycle before the start of the next rectification cycle. When the DC-DC converter operates in reverse mode, if it is in boost mode and the primary bridge converter unit is a full-bridge converter, PWM drive is applied to only one switch of the rectifier arm that is not in the current cycle before the start of the next rectification cycle, or PWM drive is applied to both switches of the rectifier arm that is not in the current cycle. If the primary bridge converter unit is a half-bridge converter, PWM drive is applied to only the switches that are not in the current cycle before the start of the next rectification cycle.

[0063] The output voltage can be adjusted within a certain range and the soft-switching state of the secondary converter unit can be achieved by adjusting the duty cycle of the buffer switch Q9 in the corresponding conversion mode. When the DC-DC converter is operating in the forward mode, the PWM drive applied to the buffer switch Q9 is delayed compared to the PWM drive of the primary bridge converter unit, i.e., a certain turn-on dead time is left. At the same time, the PWM drive applied to the buffer switch Q9 at the turn-off time is consistent with the PWM drive of the primary bridge converter unit. When the DC-DC converter is operating in the reverse mode, the PWM drive applied to the buffer switch Q9 is delayed compared to the PWM drive of the secondary converter unit, i.e., a certain turn-on dead time is left. The minimum dead time after the PWM drive applied to the buffer switch Q9 turns off is consistent with the minimum dead time of the PWM drive of the secondary converter unit. If the DC-DC converter is operating in the boost mode of the reverse mode, the buffer switch Q9 must not turn off earlier than the switch connected to the opposite terminal of the primary bridge converter unit.

[0064] When the DC-DC converter operates in boost mode with reverse operation, the drive signal applied to the primary bridge converter unit's boost switching transistor is earlier than the drive signal applied to the secondary converter unit. The drive signal applied to the primary bridge converter unit's boost switching transistor is a delayed signal of the previous cycle's synchronous rectification signal, meaning the period of the delayed signal is the sum of the synchronous rectification duty cycle, the boost duty cycle, and the dead time. If the DC-DC converter operates in non-boost mode, the primary bridge converter unit and the secondary converter unit's switching transistors are driven by synchronous rectification signals.

[0065] If the external signal indicates a positive operating mode, meaning the voltage of the first DC power supply (DC1) is converted to the voltage of the second DC power supply (DC2), then according to the aforementioned control method, the operating frequency of the primary-side bridge converter is set to the resonant frequency of the series resonant unit. ,in, Let Lr be the inductance value of the resonant inductor. Here is the capacitance value of the resonant capacitor Cr. The switching frequency of the buffer switch Q9 in the resonant buffer unit is 2f0. At this time, the function of the secondary converter unit is a full-bridge rectifier. To obtain high efficiency, a synchronous rectification signal can be applied to the secondary converter unit. For ease of discussion, no drive signal can be applied, and the fifth switch Q5 and the sixth switch Q6 can be regarded as diode rectification. Figure 4 It can be simplified to, for example Figure 7 The circuit diagram shown.

[0066] According to calculations, if the output voltage is the highest voltage point of the second DC power supply DC2, after being referred to the input side via the turns ratio of the isolation transformer Tra, the referred output voltage is slightly lower than the input voltage. Therefore, according to the aforementioned control method, the bridge converter drive duty cycle applied to the first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4 is approximately 50%, preferably 45%. Due to the presence of the series resonant unit in the primary side circuit of the isolation transformer Tra, the operating frequency of the primary side bridge converter needs to be adjusted to make the operating frequency of the primary side bridge converter higher than the resonant frequency, such as 105%*f0. At this point, the full-bridge converter is equivalent to an LLC full-bridge converter. The first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4 all implement soft switching. Simultaneously, to achieve soft turn-on of the buffer switch Q9, the PWM drive applied to Q9 is slightly delayed. Initially, the current charges the buffer capacitor Cs through the anti-parallel diode of the buffer switch Q9. Then, the buffer switch Q9 is driven to turn on, thus achieving zero-voltage turn-on. As time progresses, the secondary rectified current gradually increases and exhibits a sinusoidal shape, while the output current changes linearly due to the presence of the energy storage inductor L1. Therefore, the current charging the buffer capacitor Cs at this point is the secondary rectified current I-rec-sec minus the energy storage inductor L1 current I-L1. As time progresses, the secondary rectified current gradually decreases, and the output current gradually increases. Therefore, the buffer capacitor Cs begins to store energy, and the energy storage inductor L1 discharges.

[0067] When the primary bridge converter's switching transistor is turned off, it can be approximated that the voltage before the energy storage inductor L1 is about to disappear. If the snubber switch Q9 turns off immediately or with a slight delay, it means that the energy storage inductor L1 needs to immediately freewheel through the secondary converter. Before freewheeling, the energy storage inductor L1 draws current equivalent to the parasitic capacitance of the secondary converter and gradually reduces to zero voltage. Therefore, the snubber switch Q9 can be considered as zero-voltage turn-off. Before the primary bridge converter turns on again and the current in the energy storage inductor L1 is interrupted and reversed, the current in the energy storage inductor L1 can only freewheel through the secondary rectifier bridge. Therefore, the isolation transformer Tra is always clamped to zero, preparing for the next zero-voltage turn-on. Meanwhile, during the conversion process, the buffer switch Q9 and buffer capacitor Cs assist in the soft turn-on or soft turn-off of the secondary conversion unit, and absorb and buffer the excess current of the primary bridge conversion unit, allowing the energy storage inductor L1 to operate in a state where a pulse voltage is applied, similar to a buck converter state. This effectively solves the shortcomings of the original series resonant converter, which could only rely on frequency conversion for voltage regulation with a limited adjustment range and nonlinear duty cycle voltage regulation. Through the cooperation of the resonant buffer unit, this embodiment of the invention achieves both the advantages of soft-switching conversion and the control simplicity of a buck converter. Relevant waveform diagrams are shown below. Figure 9 As shown.

[0068] Therefore, when the embodiment of the present invention is in the forward operating state, if voltage regulation is required, the buffer switch Q9 needs to work with the series resonant unit on the primary side to adjust the duty cycle, thereby achieving stable voltage regulation and soft switching. If increasing the duty cycle of the PWM drive applied to the primary bridge converter unit to the maximum limit still cannot meet the voltage requirement of the second DC power supply DC2, the PWM drive applied to the primary bridge converter unit is fixed to the maximum duty cycle, and the operating frequency of the primary bridge converter unit is adjusted to the optimal operating frequency point to enter the boost mode. Before the next rectification conduction cycle begins, PWM drive is added to one of the switches of the rectifier conduction bridge arm of the secondary converter unit outside the current cycle. The output voltage is regulated by adjusting the duty cycle of the PWM drive. If the voltage requirement of the second DC power supply DC2 can be met without boosting, the boost mode is exited.

[0069] If it is determined that the embodiment of the present invention needs to operate in reverse mode, that is, to convert the voltage of the second DC power supply DC2 to the voltage of the first DC power supply DC1, then the primary bridge converter unit mainly operates in rectification mode. If, according to calculations, the voltage of the second DC power supply DC2, after being reverse-reduced through the turns ratio of the isolation transformer Tra, does not need to enter the boost mode, then... Figure 4 It can be simplified as follows Figure 8 As shown, the relevant principles are common knowledge to those skilled in the art. For ease of discussion, it is assumed that the embodiments of the present invention need to enter boost mode, so even if it is only reverse rectification, it must be a converter with bridge switches. Therefore, the drive duty cycles of the fifth switch Q5, the sixth switch Q6, the seventh switch Q7, and the eighth switch Q8 in the secondary conversion unit are applied to the maximum, and PWM drive is added to one of the switches in the rectifier conduction bridge arm of the primary bridge conversion unit that is not in the current cycle, that is, only for Figure 4In this cycle, either the third switch Q3 or the fourth switch Q4, which is not rectified and conducting within the current cycle, is driven by PWM. The applied drive signal should be slightly earlier than the drive signal of the secondary converter unit, typically at least 2% to 5% of the cycle. In this embodiment, the drive signal applied by the primary bridge converter unit is 200ns earlier than the drive signal of the secondary converter unit. Because two of the switches in the primary bridge converter unit are not rectified and conducting within the current cycle (i.e., rectified and conducting in the previous cycle or forming a forward path for the electromotive force of the transformer rectifier circuit), the method for turning on the switches in advance is zero-voltage turn-on. When the next working cycle begins, due to the reverse electromotive force, it is similar to a short circuit. The voltage that should be applied to the input port of the primary bridge converter unit forms a return path in the third switch Q3 and the fourth switch Q4. Since the voltage of the resonant capacitor Cr of the series resonant unit cannot change abruptly, and the port voltage of the isolation transformer Tra is directly coupled, it is equivalent to applying energy storage to the resonant inductor Lr. At the same time, the energy storage inductor L1 on the secondary side is also in an energy storage state due to the current flow. When the drive signal is applied to the buffer switch Q9, it is turned on. The buffer switch Q9 acts as a voltage source to supply power to the isolation transformer Tra, making up for the part of the current that the energy storage inductor L1 cannot supply.

[0070] When the driving voltage applied to the third switch Q3 or the fourth switch Q4 ends, the short circuit disappears, and the current in the resonant inductor Lr cannot immediately reverse. The induced electromotive force of the resonant inductor Lr can only freewheel in the reverse direction. Therefore, the coupling voltage on the secondary side of the isolation transformer Tra, superimposed on the voltage of the series resonant unit, turns on the primary bridge converter unit, thus completing the conversion process from the second DC source to the first DC source. Simultaneously, the switching on and off of the buffer switch Q9 directly affects the discharge and energy replenishment of the buffer capacitor Cs. Therefore, the driving voltage of the buffer switch Q9 cannot be turned off before the rectification process of the primary bridge converter unit ends. After the buffer capacitor Cs begins to reverse charge, the buffer switch Q9 must be turned off before the turned-on bridge arms of the fifth switch Q5, sixth switch Q6, seventh switch Q7, and eighth switch Q8 are turned off to achieve zero-voltage turn-off. As the previously turned-on bridge arms of the fifth switch Q5, sixth switch Q6, seventh switch Q7, and eighth switch Q8 begin to turn off, the current in the isolation transformer Tra cannot immediately reverse. It can only freewheel through the anti-parallel diodes of the previously unturned bridge arms in these switches. That is, the current in the primary winding of the isolation transformer Tra is released in reverse towards the second DC power supply DC2. Since the current direction of the energy storage inductor L1 cannot be reversed or abruptly changed, the voltage at the junction of the two currents continuously increases and is eventually clamped and absorbed by the buffer capacitor Cs through the anti-parallel diode of the buffer switch Q9. Therefore, if the fifth switch Q5 and the eighth switch Q8 were previously turned on, the freewheeling current would be generated by the anti-parallel diodes of the sixth switch Q6 and the seventh switch Q7. Thus, in the next turn-on stage, the sixth switch Q6 and the seventh switch Q7 achieve zero-voltage turn-on.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A control method for a wide-range resonant soft-switching bidirectional DC-DC converter, characterized in that, The wide-range resonant soft-switching bidirectional DC-DC converter includes a first DC power supply, an input energy storage filter capacitor, a primary bridge converter unit, a series resonant unit, an isolation transformer, a secondary converter unit, a resonant buffer unit, an output energy storage filter unit, and a second DC power supply. The input energy storage filter capacitor is connected in parallel with the primary bridge converter unit, and the primary bridge converter unit is also connected to the first DC power supply. The primary side of the isolation transformer is connected in series with the series resonant unit and then connected to the primary bridge converter unit. The secondary side of the isolation transformer is connected to the secondary converter unit. The resonant buffer unit is connected in parallel with the secondary converter unit, and the output energy storage filter unit is connected in parallel with the resonant buffer unit. The second DC power supply is connected to the output energy storage filter unit. The primary bridge converter unit is a full-bridge converter unit or a half-bridge converter unit; the secondary converter unit is a full-bridge converter unit or a full-wave rectifier converter; the series resonant unit includes a resonant capacitor and a resonant inductor connected in series; the resonant capacitor is connected to the primary bridge converter unit, and the resonant inductor is connected to the primary side of the isolation transformer; the resonant buffer unit includes a buffer switch and a buffer capacitor connected in series; the output energy storage filter unit includes an energy storage inductor and an output energy storage filter capacitor connected in series; the second DC power supply is connected to the output energy storage filter capacitor; When the primary bridge converter unit is a full-bridge converter unit, the primary bridge converter unit includes a first switch, a second switch, a third switch, and a fourth switch; the first and third switches are connected in series to form a first bridge arm, the second and fourth switches are connected in series to form a second bridge arm, and the first and second bridge arms are connected in parallel; the drains of the first and second switches are connected to the positive terminal of the first DC power supply and one end of the input energy storage filter capacitor, and the sources of the third and fourth switches are connected to the negative terminal of the first DC power supply and the other end of the input energy storage filter capacitor; the resonant capacitor... The primary side of the isolation transformer is connected to the drain of the third switching transistor, and the primary side of the isolation transformer is connected to the drain of the fourth switching transistor. When the primary bridge converter unit is a half-bridge converter unit, the primary bridge converter unit includes a first switching transistor and a second switching transistor connected in series. The drain of the first switching transistor is connected to the positive terminal of the first DC power supply and one end of the input energy storage filter capacitor. The source of the second switching transistor is connected to the negative terminal of the first DC power supply and the other end of the input energy storage filter capacitor. The resonant capacitor is connected to the drain of the second switching transistor, and the primary side of the isolation transformer is connected to the source of the second switching transistor. When the secondary conversion unit is a full-bridge conversion unit, the secondary conversion unit includes a fifth switch, a sixth switch, a seventh switch, and an eighth switch; the fifth and seventh switches are connected in series to form a third bridge arm, the sixth and eighth switches are connected in series to form a fourth bridge arm, and the third and fourth bridge arms are connected in parallel; the secondary side of the isolation transformer is connected to the drains of the seventh and eighth switches; when the secondary conversion unit is a full-wave rectifier converter, the secondary conversion unit includes a fifth switch and a sixth switch; the drain of the fifth switch is connected to the drain of the sixth switch, and then connected to the source of the buffer switch and one end of the energy storage inductor; the sources of the fifth and sixth switches are connected to the secondary side of the isolation transformer, and the secondary side of the isolation transformer is also connected to one end of the buffer capacitor; The control method includes the following steps: S100: Based on the power supply status setting circuit sampling or external communication detection of the voltage required to output by the DC circuit, determine whether the DC converter is in a forward or reverse operating state; the forward operating state means that the first DC power supply is the input and the second DC power supply is the output; the reverse operating state means that the second DC power supply is the input and the first DC power supply is the output. S200: Determine whether the primary bridge converter unit and the secondary converter unit are in inverter mode or rectifier mode, and determine whether the resonant buffer unit is in rectifier buffer resonant mode or inverter resonant mode; and perform corresponding timing logic configuration and PWM drive configuration; the duty cycle of the switching transistors in the primary bridge converter unit and the secondary converter unit shall not exceed 0.5, and sufficient dead time shall be reserved. The frequency of the drive signal applied to the buffer switch (Q9) is twice the frequency of the drive signal of the switch in the primary-side bridge converter unit or the secondary converter unit. The primary-side bridge converter unit and the secondary converter unit have the same operating frequency. S300: Based on the operating state determined in steps S100 and S200, PWM drive control signals are applied to the switching transistors of the primary bridge converter unit, secondary converter unit, and resonant buffer unit. When the operating state is determined to be forward, the primary bridge converter unit performs an inverter conversion, converting the voltage of the first DC power supply into a high-frequency pulse, which is coupled to the secondary side through the series resonant unit and the isolation transformer. After high-frequency rectification by the secondary converter unit, the pulse is transmitted to the resonant buffer unit, the output energy storage filter unit, and the second DC power supply. When the operating state is determined to be reverse, the secondary converter unit performs an inverter conversion, and the voltage of the second DC power supply is transmitted to the secondary converter unit through the output energy storage filter unit and the resonant buffer unit for high-frequency pulse conversion. The pulse is coupled from the secondary side to the primary side through the isolation transformer, then transmitted to the primary bridge converter unit through the series resonant unit for high-frequency rectification, and finally the DC voltage is transmitted to the input filter capacitor and the first DC power supply. S400: When the DC-DC converter is operating in the forward operating state, if the voltage value of the first DC power supply is higher than the set voltage value of the second DC power supply after being coupled through the isolation transformer, the duty cycle of the PWM drive applied to the primary bridge converter unit is reduced; otherwise, the duty cycle is increased. When the DC-DC converter is operating in reverse mode, if the voltage value of the second DC power supply is higher than the set voltage value of the first DC power supply after being coupled through the transformer, the duty cycle of the PWM drive applied to the secondary conversion unit is reduced; otherwise, the duty cycle is increased. S500: After the switching transistors of the primary bridge converter and the secondary converter are turned on according to the settings, all drive signals of the primary bridge converter and the secondary converter are turned off, and the input energy storage filter capacitor and the output energy storage filter unit are allowed to freewheel.

2. The control method for a wide-range resonant soft-switching bidirectional DC-DC converter according to claim 1, characterized in that, The first DC power supply and the second DC power supply are DC power supplies, rectified AC power supplies, step power supplies with switch control, or loads capable of providing power supply voltage.

3. The control method for a wide-range resonant soft-switching bidirectional DC-DC converter according to claim 1, characterized in that, When the primary bridge converter unit and the secondary converter unit perform unidirectional rectification and conversion, the first to eighth switching transistors are diodes or high-frequency switching transistors equipped with anti-parallel diodes, wherein the anti-parallel diodes are integrated diodes, parasitic diodes, or external diodes.

4. The control method for a wide-range resonant soft-switching bidirectional DC-DC converter according to claim 1, characterized in that, The input energy storage filter capacitor and the output energy storage filter capacitor are non-polarized capacitors or polarized capacitors; when the first DC power supply or the second DC power supply is a power supply with a step change, the input energy storage filter capacitor and the output energy storage filter capacitor are equivalent capacitors of a controllable switch connected in series with a capacitor; the resonant inductor is an external inductor, the coupled leakage inductance inside the transformer, or the coupled inductance of an external inductor and the leakage inductance inside the transformer.

5. The control method for a wide-range resonant soft-switching bidirectional DC-DC converter according to claim 1, characterized in that, In steps S300 to S500, the PWM drive signals of the primary bridge converter unit and the secondary bridge converter switching transistors operate at the same frequency, and the frequency range is 95% to 115% of the resonant inherent resonant frequency.

6. The control method for a wide-range resonant soft-switching bidirectional DC-DC converter according to claim 1, characterized in that, In steps S300-S500, when the DC-DC converter is operating in the forward mode, if increasing the duty cycle of the PWM drive applied to the primary bridge converter unit to the maximum limit still fails to meet the requirement of the second DC power supply voltage, the duty cycle is fixed, the operating frequency is adjusted to the optimal operating frequency point, and the converter enters boost mode. Before the next rectification cycle begins, PWM drive is added to one of the switches in the rectifier conduction bridge arm of the secondary converter unit that is not in the current cycle. Conversely, the duty cycle of the PWM drive applied to the primary bridge converter unit is gradually reduced, and the converter exits boost mode. When the DC-DC converter is operating in the reverse mode, if increasing the duty cycle of the PWM drive applied to the secondary converter unit to the maximum limit still fails to meet the requirement of the first DC power supply voltage, PWM drive is added to the switches in the rectifier conduction bridge arm of the primary bridge converter unit that is not in the current cycle to boost voltage before the next rectification cycle begins. Conversely, the duty cycle of the PWM drive applied to the primary bridge converter unit is gradually reduced according to control, and the converter exits boost mode.

7. The control method for a wide-range resonant soft-switching bidirectional DC-DC converter according to claim 1, characterized in that, In steps S300 to S500, when the DC-DC converter is operating in the forward operating state, if the secondary conversion unit is a full-bridge conversion unit, then before the next rectification conduction cycle is about to begin, only one of the switching transistors of the rectifier conduction bridge arm that is not in the current cycle is driven by PWM, or both switching transistors of the rectifier conduction bridge arm that is not in the current cycle are driven by PWM; if the secondary conversion unit is a full-wave rectifier converter, then before the next rectification conduction cycle is about to begin, only the switching transistors that are not in the current cycle are driven by PWM. When the DC-DC converter operates in reverse mode, if it is in boost mode and the primary bridge converter is a full-bridge converter, then before the next rectification cycle begins, PWM drive is applied to only one of the switches in the rectifier conducting arm that is not conducting in the current cycle, or PWM drive is applied to both switches in the rectifier conducting arm that is not conducting in the current cycle. If the primary bridge converter is a half-bridge converter, then before the next rectification cycle begins, PWM drive is applied to only the switches that are not conducting in the current cycle.

8. The control method for a wide-range resonant soft-switching bidirectional DC-DC converter according to claim 1, characterized in that, In steps S300~S500, the output voltage is adjusted within a certain range and the soft-switching state of the secondary converter unit is achieved by adjusting the duty cycle of the buffer switch in the corresponding conversion mode. When the DC converter is operating in the forward mode, the PWM drive applied to the buffer switch is delayed compared to the PWM drive of the primary bridge converter unit, i.e., a certain turn-on dead time is left. At the same time, the PWM drive applied to the buffer switch at the turn-off time is consistent with the PWM drive of the primary bridge converter unit. When the DC converter is operating in the reverse mode, the PWM drive applied to the buffer switch is delayed compared to the PWM drive of the secondary converter unit, i.e., a certain turn-on dead time is left. The minimum dead time after the PWM drive applied to the buffer switch turns off is consistent with the minimum dead time of the PWM drive of the secondary converter unit. If the DC converter is operating in the boost mode of the reverse mode, the buffer switch must not turn off earlier than the switch connected to the opposite terminal of the primary bridge converter unit.

9. The control method for a wide-range resonant soft-switching bidirectional DC-DC converter according to claim 1, characterized in that, In steps S300 to S500, when the DC-DC converter operates in boost mode with reverse operation, the drive signal applied to the boost switching transistor in the primary bridge converter unit is earlier than the drive signal in the secondary converter unit. The drive signal applied to the boost switching transistor in the primary bridge converter unit is a delayed signal of the previous cycle synchronous rectification signal, that is, the period of the delayed signal is the sum of the synchronous rectification duty cycle, the boost duty cycle, and the dead time. If the DC-DC converter operates in non-boost mode, the switching transistors in the primary bridge converter unit and the secondary converter unit are given synchronous rectification drive signals.

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