CLLC resonant bidirectional DC-DC converter and control method thereof

Abstract

The invention provides a CLLC resonance type bidirectional DC-DC converter and a control method thereof, and relates to the technical field of power electronics, the converter comprises a primary side full-bridge inverter circuit having a first bridge arm midpoint and a second bridge arm midpoint, and a secondary side full-bridge rectifier circuit having a third bridge arm midpoint and a fourth bridge arm midpoint; the primary side resonant cavity comprises a resonant inductor and a resonant capacitor which are connected in series, the free end of the resonant inductor is electrically connected with the midpoint of the first bridge arm, and the free end of the resonant capacitor is electrically connected with the midpoint of the second bridge arm; the connection point of the resonant inductor and the resonant capacitor is electrically connected with the primary side of the high-frequency transformer; the secondary side resonant cavity comprises a resonant inductor and a resonant capacitor which are connected in series, the free end of the resonant inductor is electrically connected with the midpoint of the third bridge arm, and the free end of the resonant capacitor is electrically connected with the midpoint of the fourth bridge arm; the connection point of the resonant inductor and the resonant capacitor is electrically connected with the secondary side of the high-frequency transformer; the stability of the output voltage can be maintained, and the requirements of two-way energy transmission under different working conditions are met.

Description

Technical Field

[0001] The present application generally relates to the field of power electronics technology, and specifically to a CLLC resonant bidirectional DC-DC converter and a control method thereof. Background Art

[0002] As an advanced power electronic device, CLLC resonant converter is widely used in power electronic systems due to its unique advantages of high efficiency, high power density and wide input range.

[0003] In actual operation, when encountering different loads and input voltages, traditional control methods often rely solely on pulse frequency modulation (PFM) or pulse width modulation (PWM). However, this single control method is difficult to flexibly respond to rapid changes in system conditions. Under extreme operating conditions, such as sudden extreme load changes or drastic input voltage fluctuations, the converter's energy conversion efficiency decreases and system stability may be compromised, resulting in unstable output voltage, abnormal device operation, or even failure. Therefore, we propose a CLLC resonant bidirectional DC-DC converter and its control method to address these issues. Summary of the Invention

[0004] In view of the above-mentioned defects or deficiencies in the prior art, it is desired to provide a CLLC resonant bidirectional DC-DC converter and a control method thereof that meet the requirements of bidirectional energy transmission under different working conditions.

[0005] In a first aspect, the present application provides a CLLC resonant bidirectional DC-DC converter, comprising: a primary full-bridge inverter circuit, a secondary full-bridge rectifier circuit, a primary resonant cavity, a secondary resonant cavity, and a high-frequency transformer; The primary full-bridge inverter circuit has a first bridge arm midpoint and a second bridge arm midpoint, and the secondary full-bridge rectifier circuit has a third bridge arm midpoint and a fourth bridge arm midpoint; The primary resonant cavity includes a resonant inductor L1 and a resonant capacitor C1 connected in series, the free end of the resonant inductor L1 is electrically connected to the midpoint of the first bridge arm, and the free end of the resonant capacitor C1 is electrically connected to the midpoint of the second bridge arm; the connection point between the resonant inductor L1 and the resonant capacitor C1 is electrically connected to the primary side of the high-frequency transformer; The secondary side resonant cavity includes a resonant inductor L2 and a resonant capacitor C2 connected in series, the free end of the resonant inductor L2 is electrically connected to the midpoint of the third bridge arm, and the free end of the resonant capacitor C2 is electrically connected to the midpoint of the fourth bridge arm; the connection point between the resonant inductor L2 and the resonant capacitor C2 is electrically connected to the secondary side of the high-frequency transformer.

[0006] According to the technical solution provided by the present application, the primary full-bridge inverter circuit includes a first switch tube group and a second switch tube group connected in parallel, wherein the first switch tube group includes a power switch tube Q1 and a power switch tube Q2 connected in series, and the second switch tube group includes a power switch tube Q3 and a power switch tube Q4 connected in series; The connection point of the power switch tube Q1 and the power switch tube Q2 is the midpoint of the first bridge arm of the primary full-bridge inverter circuit, and the connection point of the power switch tube Q3 and the power switch tube Q4 is the midpoint of the second bridge arm of the primary full-bridge inverter circuit.

[0007] According to the technical solution provided by the present application, the secondary full-bridge rectifier circuit includes a third switch tube group and a fourth switch tube group connected in parallel, the third switch tube group includes a power switch tube Q5 and a power switch tube Q6 connected in series, and the fourth switch tube group includes a power switch tube Q7 and a power switch tube Q8 connected in series; The connection point of the power switch tube Q5 and the power switch tube Q6 is the midpoint of the third bridge arm of the secondary full-bridge rectifier circuit, and the connection point of the power switch tube Q7 and the power switch tube Q8 is the midpoint of the fourth bridge arm of the secondary full-bridge rectifier circuit.

[0008] The technical solution provided in this application also includes: DC input power supply V in , the DC input power supply V in connected in series with the first switch tube group; Input filter capacitor C i , the input filter capacitor C i connected in parallel with the first switch tube group; Output filter capacitor C o , the output filter capacitor C o connected in parallel with the third switch tube group; Load resistance R L , the load resistance R L Connected in parallel with the third switch tube group.

[0009] In a second aspect, the present application provides a control method for a CLLC resonant bidirectional DC-DC converter, comprising the following steps: Performing a soft start operation on the CLLC resonant bidirectional DC-DC converter and collecting a first input voltage in real time; Obtaining a reference voltage, and determining a modulation mode based on a relationship between the reference voltage and the first input voltage; the modulation mode being a boost mode or a buck mode; Obtaining a first load current of the CLLC resonant bidirectional DC-DC converter in the modulation mode; If the first load current is less than a preset lower limit, switching the current modulation mode to a light load mode; Obtaining a second load current and a second input voltage of the CLLC resonant bidirectional DC-DC converter in the light load mode; If the second load current is less than a preset upper limit and the second input voltage is less than or equal to the reference voltage, the switching frequency of each switch tube of the primary full-bridge inverter circuit is controlled to be adjusted to a preset switching frequency and the duty cycle is adjusted to a preset duty cycle; the preset upper limit is greater than the preset lower limit; Obtain a third input voltage and a third load current. If the third input voltage is greater than the reference voltage and the third load current is greater than the preset upper limit, exit the light load mode and enter the step-down mode. If the third input voltage is less than the reference voltage and the third load current is greater than the preset upper limit, exit the light load mode and enter the step-up mode.

[0010] According to the technical solution provided in this application, determining the modulation mode according to the relationship between the reference voltage and the first input voltage specifically includes the following steps: When the first input voltage is greater than the reference voltage, the modulation mode is a buck mode; When the first input voltage is lower than the reference voltage, the modulation mode is a boost mode.

[0011] According to the technical solution provided by this application, the method further includes the following steps: When the modulation mode is the boost mode and the first load current is greater than or equal to a preset lower limit, controlling the duty cycle of each switch tube of the primary full-bridge inverter circuit to be adjusted to a preset duty cycle; obtaining a first switching frequency of the CLLC resonant bidirectional DC-DC converter in the boost mode, and controlling the CLLC resonant bidirectional DC-DC converter to enter a hysteresis delay link if the first switching frequency is greater than a preset resonant frequency; The second switching frequency after the delay by the hysteresis delay link is collected, and if the second switching frequency is greater than the preset resonant frequency, the CLLC resonant bidirectional DC-DC converter is controlled to switch from the boost mode to the buck mode.

[0012] According to the technical solution provided by this application, the method further includes the following steps: When the modulation mode is the buck mode and the first load current is greater than or equal to a preset lower limit, controlling the switching frequency of each switch tube of the primary full-bridge inverter circuit to be adjusted to a preset switching frequency; Obtaining a first duty cycle of the CLLC resonant bidirectional DC-DC converter in the buck mode, and if the first duty cycle is greater than a preset duty cycle upper limit, controlling the CLLC resonant bidirectional DC-DC converter to enter a hysteresis delay link; A second duty cycle after being delayed by the hysteresis delay link is collected, and if the second duty cycle is greater than the preset duty cycle upper limit, the CLLC resonant bidirectional DC-DC converter is controlled to switch from the buck mode to the boost mode.

[0013] According to the technical solution provided in this application, a soft start operation is performed on a CLLC resonant bidirectional DC-DC converter, specifically comprising the following steps: The switching frequency of the primary full-bridge inverter circuit is gradually reduced from a maximum value to a preset resonant frequency, and at the same time, the duty cycle of each switch tube of the primary full-bridge inverter circuit is gradually increased from zero to a preset duty cycle upper limit value.

[0014] According to the technical solution provided in this application, the light load mode is an intermittent working mode, which specifically includes the following steps: When the output voltage of the CLLC resonant bidirectional DC-DC converter is greater than the reference voltage upper limit, the driving signal is stopped from being sent to the primary full-bridge inverter circuit.

[0015] It can be seen from the above technical solution that this application has at least the following beneficial effects: The present application provides a CLLC resonant bidirectional DC-DC converter, comprising: a primary full-bridge inverter circuit, a secondary full-bridge rectifier circuit, a primary resonant cavity, a secondary resonant cavity, and a high-frequency transformer; the primary full-bridge inverter circuit has a first bridge arm midpoint and a second bridge arm midpoint, and the secondary full-bridge rectifier circuit has a third bridge arm midpoint and a fourth bridge arm midpoint; the primary resonant cavity comprises a resonant inductor and a resonant capacitor connected in series, the free end of the resonant inductor is electrically connected to the midpoint of the first bridge arm, and the free end of the resonant capacitor is electrically connected to the midpoint of the second bridge arm; the connection point of the resonant inductor and the resonant capacitor is electrically connected to the primary side of the high-frequency transformer; the secondary resonant cavity comprises a resonant inductor and a resonant capacitor connected in series, the free end of the resonant inductor is electrically connected to the midpoint of the third bridge arm, and the free end of the resonant capacitor is electrically connected to the midpoint of the fourth bridge arm; the connection point of the resonant inductor and the resonant capacitor is electrically connected to the secondary side of the high-frequency transformer.

[0016] This application realizes bidirectional energy flow through the coordination of the primary full-bridge inverter circuit and the secondary full-bridge rectifier circuit, combined with the design of the primary resonant cavity and the secondary resonant cavity, meeting the needs of bidirectional energy transmission under different working conditions and improving the applicable scenarios and flexibility of the converter; in addition, the primary resonant cavity is composed of a series resonant inductor and a resonant capacitor, and the secondary resonant cavity also adopts a series resonant inductor and resonant capacitor structure. This symmetrical resonant cavity design helps to optimize the resonant characteristics of the converter, making it easier to achieve soft switching during the operation of the converter, such as zero voltage turn-on of the primary switch tube and zero current turn-off of the secondary switch tube. Significantly reduce switching losses and improve energy conversion efficiency; this application also uses the connection method between the midpoint of the bridge arm of the primary full-bridge inverter circuit and the primary resonant cavity, and the connection method between the midpoint of the bridge arm of the secondary full-bridge rectifier circuit and the secondary resonant cavity to ensure the stable transfer of energy between the primary and secondary sides, which is beneficial to maintaining the stability of the output voltage and improving the working stability of the converter under different load and input voltage conditions; and the connection relationship of each component (primary full-bridge inverter circuit, secondary full-bridge rectifier circuit, primary resonant cavity, secondary resonant cavity, high-frequency transformer) is clear and the layout is reasonable, which is convenient for engineering implementation and production manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Other features, objects and advantages of the present application will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings.

[0018] Figure 1 This is the circuit diagram of a CLLC resonant bidirectional DC-DC converter.

[0019] Figure 2 Flowchart of a control method for a CLLC resonant bidirectional DC-DC converter.

[0020] Figure 3 The figure is the overall flow chart of the control method.

[0021] Figure 4 This is the soft start resonant current waveform.

[0022] Figure 5 This is the main waveform diagram of PFM modulation.

[0023] Figure 6 This is the main waveform diagram of CSPWM modulation.

[0024] Figure 7 The output voltage waveform diagram for switching between boost and buck modes.

[0025] Figure 8 This is the main waveform diagram of light load mode control.

[0026] Figure 9 This is the logic diagram for entering and exiting light load mode. DETAILED DESCRIPTION

[0027] The present application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the relevant invention and are not intended to limit the invention. It should also be noted that, for ease of description, only portions relevant to the invention are shown in the accompanying drawings.

[0028] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0029] like Figure 1 As shown, the present application provides a CLLC resonant bidirectional DC-DC converter, comprising: a primary full-bridge inverter circuit, a secondary full-bridge rectifier circuit, a primary resonant cavity, a secondary resonant cavity, and a high-frequency transformer; The primary full-bridge inverter circuit has a first bridge arm midpoint and a second bridge arm midpoint, and the secondary full-bridge rectifier circuit has a third bridge arm midpoint and a fourth bridge arm midpoint; The primary resonant cavity includes a resonant inductor L1 and a resonant capacitor C1 connected in series, the free end of the resonant inductor L1 is electrically connected to the midpoint of the first bridge arm, and the free end of the resonant capacitor C1 is electrically connected to the midpoint of the second bridge arm; the connection point between the resonant inductor L1 and the resonant capacitor C1 is electrically connected to the primary side of the high-frequency transformer; The secondary side resonant cavity includes a resonant inductor L2 and a resonant capacitor C2 connected in series, the free end of the resonant inductor L2 is electrically connected to the midpoint of the third bridge arm, and the free end of the resonant capacitor C2 is electrically connected to the midpoint of the fourth bridge arm; the connection point of the resonant inductor L2 and the resonant capacitor C2 is electrically connected to the secondary side of the high-frequency transformer.

[0030] It's important to note that the primary full-bridge inverter circuit, as the core circuit on the energy input side, converts the input DC power into AC power, providing the AC signal for the subsequent resonance and voltage transformation processes. The secondary full-bridge rectifier circuit, located on the energy output side, rectifies the AC power, after transmission and processing through the high-frequency transformer, into DC power to meet the load's DC output requirements. The primary and secondary resonant cavities are key structures for achieving resonant characteristics. Through the resonant action of inductors and capacitors, they optimize energy transmission efficiency and facilitate soft switching. The high-frequency transformer performs voltage conversion and electrical isolation, adjusting the output voltage based on the turns ratio between the primary and secondary sides. It also provides electrical isolation between the input and output sides, ensuring circuit safety.

[0031] The primary full-bridge inverter circuit has first and second arm midpoints, which connect the primary circuit to the primary resonant cavity and transmit the inverted alternating signal. The secondary full-bridge rectifier circuit has third and fourth arm midpoints, which connect the secondary resonant cavity to the secondary rectifier circuit and receive the resonant alternating signal for transmission to the rectifier circuit.

[0032] The primary resonant cavity includes a resonant inductor L1 and a resonant capacitor C1 connected in series. The free end (non-series connection end) of the resonant inductor L1 is electrically connected to the midpoint of the first leg of the primary full-bridge inverter circuit, while the free end (non-series connection end) of the resonant capacitor C1 is electrically connected to the midpoint of the second leg. The series connection point between the resonant inductor L1 and the resonant capacitor C1 is directly electrically connected to the primary side of the high-frequency transformer, allowing the AC power output by the primary inverter circuit to be processed by the resonant cavity and then transmitted to the primary side of the high-frequency transformer.

[0033] The secondary resonant cavity includes a series-connected resonant inductor L2 and a resonant capacitor C2. The free end of the resonant inductor L2 is electrically connected to the midpoint of the third leg of the secondary full-bridge rectifier circuit, while the free end of the resonant capacitor C2 is electrically connected to the midpoint of the fourth leg. The series connection point between the resonant inductor L2 and the resonant capacitor C2 is electrically connected to the secondary side of the high-frequency transformer, receiving the AC power output from the secondary side of the high-frequency transformer and feeding it into the secondary rectifier circuit after resonant processing.

[0034] This application lays the hardware foundation for the converter to achieve bidirectional energy transmission, soft switching characteristics and stable voltage conversion through a symmetrical resonant cavity layout, a clear bridge arm midpoint connection and the isolation and transformation function of a high-frequency transformer. It also provides structural support for subsequent performance optimization through flexible control methods (such as boost, buck and light-load mode switching).

[0035] Further, if Figure 1 As shown, the primary full-bridge inverter circuit includes a first switch tube group and a second switch tube group connected in parallel. The first switch tube group includes a power switch tube Q1 and a power switch tube Q2 connected in series, and the second switch tube group includes a power switch tube Q3 and a power switch tube Q4 connected in series. The connection point of the power switch tube Q1 and the power switch tube Q2 is the midpoint of the first bridge arm of the primary full-bridge inverter circuit, and the connection point of the power switch tube Q3 and the power switch tube Q4 is the midpoint of the second bridge arm of the primary full-bridge inverter circuit.

[0036] Power switches Q1 and Q2 are connected in series to form a bridge arm. Current flows from Q1 to Q2 (or vice versa, depending on the switch state). Their coordinated operation controls the on and off states of the bridge arm. Power switches Q3 and Q4 are connected in series, identical to the structure of the first switch group, and also form an independent bridge arm. The first and second switch groups are connected in parallel, with the two ends of the bridge arms connected together and connected to a common DC input power supply. This parallel structure enables the two bridge arms to operate alternately. The coordinated on and off switching of the switches generates an alternating voltage signal at the midpoint of the bridge arm, providing the alternating current foundation for subsequent resonance and energy transfer.

[0037] The midpoint of the first bridge arm is the connection point between power switches Q1 and Q2. When power switch Q1 is on and power switch Q2 is off, the potential at the midpoint of the first bridge arm approaches the positive input power supply. When power switch Q1 is off and power switch Q2 is on, the potential at the midpoint of the first bridge arm approaches the negative input power supply. The high-frequency alternating switching of power switches Q1 and Q2 generates a high-frequency alternating voltage at the midpoint of the first bridge arm. The midpoint of the second bridge arm is the connection point between power switches Q3 and Q4. Its operating principle is similar to that of the first bridge arm. The high-frequency alternating switching of power switches Q3 and Q4 generates a high-frequency alternating voltage. This alternating voltage is typically 180° out of phase with the alternating voltage at the midpoint of the first bridge arm, and dead time is used to prevent shoot-through in the bridge arm.

[0038] The midpoints of the first and second bridge arms are connected to the resonant inductor L1 and resonant capacitor C1 of the primary resonant cavity, respectively. The alternating voltage signals generated by these two bridge arms are fed into the primary resonant cavity, triggering the resonant effect of L1 and C1, paving the way for energy to be transferred to the secondary side via the high-frequency transformer. Furthermore, the voltage variation at the midpoints of these bridge arms directly influences the resonant frequency and energy transfer efficiency of the resonant cavity, providing a key structural guarantee for achieving soft switching (e.g., zero-voltage turn-on of the primary switching transistor).

[0039] Further, if Figure 1 As shown, the secondary side full-bridge rectifier circuit includes a third switch tube group and a fourth switch tube group connected in parallel. The third switch tube group includes a power switch tube Q5 and a power switch tube Q6 connected in series. The fourth switch tube group includes a power switch tube Q7 and a power switch tube Q8 connected in series. The connection point of the power switch tube Q5 and the power switch tube Q6 is the midpoint of the third bridge arm of the secondary full-bridge rectifier circuit, and the connection point of the power switch tube Q7 and the power switch tube Q8 is the midpoint of the fourth bridge arm of the secondary full-bridge rectifier circuit.

[0040] Power switches Q5 and Q6 are connected in series to form an independent bridge arm. Specifically, the drain (or collector) of power switch Q5 is connected to the source (or emitter) of power switch Q6, together forming a bridge arm unit of the secondary-side rectifier circuit. Power switches Q7 and Q8 are connected in series, with a structure identical to that of the third switch group, forming another independent bridge arm.

[0041] The third and fourth switching tube groups are connected in parallel, with the two bridge arms connected at both ends and fed into the AC voltage output from the secondary side of the high-frequency transformer. This parallel structure enables the two bridge arms to work together. By coordinating the on and off switching of the switches, they rectify the AC voltage into a stable DC voltage, providing energy to the load.

[0042] The midpoint of the third bridge arm is the connection point between power switches Q5 and Q6, where the source of power switch Q5 connects to the drain of power switch Q6. The midpoint of the third bridge arm is directly electrically connected to the free end of resonant inductor L2 in the secondary resonant cavity, receiving the alternating signal processed by the secondary resonant cavity.

[0043] The midpoint of the fourth bridge arm is the connection point of the power switch tube Q7 and the power switch tube Q8, that is, the connection point between the source of the power switch tube Q7 and the drain of the power switch tube Q8. The midpoint of the fourth bridge arm is electrically connected to the free end of the resonant capacitor C2 in the secondary side resonant cavity, and is also used to receive the alternating signal output by the secondary side resonant cavity.

[0044] The midpoints of these two bridge arms serve as the interface between the secondary resonant cavity and the secondary rectifier circuit, introducing the resonant alternating voltage into the rectifier bridge arms. By controlling the on / off state of power switches Q5-Q8 (based on the phase of the alternating signal), the alternating voltage is converted into a unidirectional DC voltage, achieving rectification. Furthermore, the signal characteristics at the bridge arm midpoints match the resonant state of the secondary resonant cavity, helping to achieve zero-current shutdown (ZCS) of the secondary switches, reducing switching losses and improving converter efficiency.

[0045] Here, the structural design of the secondary full-bridge rectifier circuit forms a symmetrical correspondence with the primary full-bridge inverter circuit. Through the precise connection between the bridge arm midpoint and the secondary resonant cavity, efficient energy transfer is achieved from the secondary side of the high-frequency transformer, the secondary resonant cavity, the secondary rectifier circuit, and the load. Specifically, when the converter operates in forward mode (primary input, secondary output), secondary switches Q5-Q8, controlled by rectification logic, rectify the AC voltage output from the secondary resonant cavity into a DC voltage for supply to the load. When operating in reverse mode (secondary input, primary output), the circuit switches to an inverter function, leveraging the controllability of the switches to achieve bidirectional rectification / inversion, cooperating with the primary circuit to complete reverse energy transfer, thus embodying the core characteristics of a bidirectional DC-DC converter.

[0046] Further, if Figure 1 As shown, the converter also includes: DC input power supply V in , DC input power supply V in connected in series with the first switch tube group; Input filter capacitor C i , input filter capacitor C i connected in parallel with the first switch tube group; Output filter capacitor C o , output filter capacitor C o connected in parallel with the third switch tube group; Load resistance R L , load resistance R L Connected in parallel with the third switch tube group.

[0047] Here, the DC input power supply V in As the energy source of the entire converter, it provides initial DC power. DC input power supply V in It is connected in series with the first switch group in the primary full-bridge inverter circuit. This series connection allows the power from the DC input power supply to be directly input into the first switch group, and through the switching action of the power switch tubes Q1 and Q2, it participates in the inverter process and provides basic energy for the primary circuit.

[0048] Input filter capacitor C i It is a key filter component on the primary side, usually an electrolytic capacitor or a ceramic capacitor, whose main function is to filter out the DC input power supply V in The input filter capacitor C i Connected in parallel with the first switch tube group. Since the voltage of the parallel circuit is equal, the input filter capacitor C i It can directly absorb the voltage fluctuations generated during the primary side inversion process, avoid high-frequency ripples affecting the stability of the power supply, and provide instantaneous energy replenishment for the rapid switching action of the primary side switch tube, reducing the loss of the switch tube caused by voltage mutation.

[0049] Output filter capacitor C o It is the core filter component on the secondary side, used to filter out the residual AC ripple in the DC voltage output by the secondary full-bridge rectifier circuit, making the output voltage smoother and more stable. o The voltage after secondary side rectification is output through the third switch tube group and the output filter capacitor C o Through the parallel relationship, it acts directly on the output end and uses the characteristics of capacitors to block DC and pass AC to absorb ripple, ensuring that the voltage supplied to the load is stable near the target value.

[0050] Load resistance R L It represents the energy output object of the converter and is the final consumer of electric energy. In practical applications, it can be used for various devices that require DC power supply. L This parallel connection allows the stable DC voltage after secondary side rectification and filtering to be directly applied to the load resistor R L At the same time, the size of the load resistance will affect the load current of the converter, and thus affect the working mode (such as switching to light load mode).

[0051] DC input power supply V in Provide energy, input filter capacitor C i This ensures the stability of the input voltage. When the primary switch tubes (Q1-Q4) switch at high frequency, the input current will fluctuate, and the input filter capacitor C i This ensures the stability of the input voltage. When the primary switch tube (Q1-Q4) switches at high frequency, the input current will i By charging and discharging, this fluctuation is offset, large ripples in the input voltage are avoided, and a stable operating voltage is provided for the primary full-bridge inverter circuit, which indirectly ensures the stability of the resonant characteristics of the primary resonant cavity.

[0052] Although the output voltage of the secondary full-bridge rectifier circuit has been converted to DC, there is still a small amount of AC ripple. The output filter capacitor C o By charging and discharging, these ripples are filtered out to smooth the output voltage. The load resistor RL is the energy consumption end, and its resistance change will change the output current, while the output filter capacitor C o When the load current fluctuates (such as R L The output voltage is temporarily stable and the sudden voltage drop is avoided to affect the load operation.

[0053] The power comes from the DC input power supply V in Starting from the input filter capacitor C i After stabilization, it enters the primary full-bridge inverter circuit, and after being transmitted through the inverter, resonance, and high-frequency transformer, it is rectified by the secondary full-bridge rectifier circuit and then passes through the output filter capacitor C o Filtering, and finally supplying the load resistor R L , realizing complete energy conversion and transmission from input to output.

[0054] like Figure 2 As shown, the present application provides a control method for a CLLC resonant bidirectional DC-DC converter, comprising the following steps: S100: Perform a soft start operation on the CLLC resonant bidirectional DC-DC converter and collect a first input voltage in real time.

[0055] The soft start operation of the CLLC resonant bidirectional DC-DC converter specifically includes the following steps: The switching frequency of the primary full-bridge inverter circuit is gradually reduced from the maximum value to the preset resonant frequency, and at the same time, the duty cycle of each switch tube of the primary full-bridge inverter circuit is gradually increased from zero to the preset duty cycle upper limit value.

[0056] Soft-start operation is a key control step during the converter's startup phase, aiming to prevent damage to components caused by the sudden surge in current. Soft-start is achieved by gradually reducing the switching frequency and increasing the duty cycle of the primary switch, allowing the startup current to rise smoothly and the output voltage to gradually approach the reference voltage. For example, from the maximum switching frequency of 500kHz to the resonant frequency of 390kHz, the duty cycle of the primary switch decreases from 0 to 0.48.

[0057] The first input voltage is the input voltage monitored in real time during the soft start process, such as the DC input power supply V in The voltage provides raw data for subsequent judgment of the modulation mode.

[0058] like Figure 4 The waveform shown in Figure 1 shows time (t / ms) on the horizontal axis and resonant current (iL / A) on the vertical axis. This waveform reflects the dynamic changes in the resonant current in the primary or secondary resonant cavity from converter startup to soft-start completion. The resonant current rises gently during startup, with a peak value not exceeding 15A and no noticeable instantaneous high current surges (as can occur with traditional hard-start, where surge currents far exceed the rated value).

[0059] By slowly adjusting the frequency and duty cycle, the sudden change of the resonant cavity current caused by the sudden turn-on of the switch tube at the startup moment is avoided, thereby protecting components such as the power switch tube, resonant inductor, and resonant capacitor from excessive current shock, ensuring the safety and reliability of the converter startup process.

[0060] As the switching frequency gradually decreases from 500kHz to 390kHz, the resonant characteristics of the resonant cavity gradually stabilize, reducing current fluctuations. Simultaneously, the duty cycle gradually increases from 0 to 0.48, allowing input energy to be slowly injected into the resonant cavity, preventing instantaneous energy accumulation. This effectively limits the current peak to a safe range (≤15A). This gradual current change ultimately achieves the goal of gradually approaching the reference voltage, laying the foundation for the converter to enter stable boost / buck mode.

[0061] S200 , obtaining a reference voltage, and determining a modulation mode according to a relationship between the reference voltage and the first input voltage; the modulation mode is a boost mode or a buck mode.

[0062] Here, the reference voltage refers to the target voltage that the converter expects to output, such as the stable voltage required by the load.

[0063] The modulation mode is determined according to the relationship between the reference voltage and the first input voltage, specifically comprising the following steps: When the first input voltage is greater than the reference voltage, the modulation mode is the buck mode; center-symmetrical pulse width modulation (CSPWM) control is adopted to achieve voltage reduction by adjusting the duty cycle.

[0064] When the first input voltage is less than the reference voltage, the modulation mode is the boost mode; pulse frequency modulation (PFM) control is adopted to achieve voltage boost by adjusting the switching frequency.

[0065] Furthermore, the boost mode adopts PFM modulation, and the driving signals of the primary side Q1 switch tube and Q4 switch tube are the same, both are square wave signals with a duty cycle of 0.48; the driving signals of the Q2 switch tube and Q3 switch tube are the same, both are square wave signals with a duty cycle of 0.48, and are complementary to the driving signals of the Q1 and Q4 switch tubes, with a phase difference of 180°. The reserved dead time prevents the bridge arm from directly breaking down the components; the secondary side uses a diode for uncontrolled rectification; when using PFM modulation, the voltage is boosted by changing the driving signal frequency of the primary side switch tube.

[0066] from Figure 5 It can be seen from the displayed waveforms that when PFM modulation is used, the primary side switch tube achieves zero voltage turn-on (ZVS) and the secondary side switch tube achieves zero current shutdown (ZCS), which effectively reduces the loss of the converter and improves the working efficiency of the converter.

[0067] The buck mode uses CSPWM modulation, and the switching frequency of the four primary switches is fixed at the resonant frequency of 390kHz. The drive signals for switches Q1 and Q4 are center-symmetrical square wave signals with a duty cycle satisfying D1+D4=0.96, and the initial duty cycle is 0.48. The drive signals for switches Q2 and Q3 are also center-symmetrical square wave signals with a duty cycle satisfying D2+D3=0.96, and the initial duty cycle is 0.48. The drive signals for switches Q2 and Q3 are complementary to the drive signals for switches Q1 and Q4, respectively, with a phase difference of 180°. The reserved dead time prevents direct breakdown of the bridge arms and components. Diodes are used for uncontrolled rectification on the secondary side. When using CSPWM modulation, the voltage is stepped down by reducing the duty cycle of the drive signal for switch Q1.

[0068] from Figure 6 As can be seen from the displayed waveforms, the drive signals of Q1 and Q4 are center-symmetrical, and the drive signals of Q2 and Q3 are center-symmetrical. When using CSPWM modulation, the primary-side switch tube achieves zero voltage turn-on (ZVS) and the secondary-side switch tube achieves zero current shutdown (ZCS), effectively reducing the loss of the converter and improving the converter's operating efficiency.

[0069] S300: Obtain a first load current of a CLLC resonant bidirectional DC-DC converter in a modulation mode.

[0070] Here, the first load current is the real-time load current of the converter in the current boost / buck mode, reflecting the severity of the load. For example, a high current corresponds to a heavy load, and a low current corresponds to a light load. The purpose of collecting the first load current is to determine whether to switch to light load mode to optimize efficiency under light load conditions.

[0071] S400: If the first load current is less than a preset lower limit, switch the current modulation mode to a light load mode.

[0072] Here, the preset lower limit value is a threshold value (such as a smaller current value) for distinguishing “light load” from “heavy load / rated load”.

[0073] If the first load current is less than the preset lower limit, it means that the load is light. Continuing to use the boost / buck mode will result in a decrease in efficiency due to excessive switching losses. Therefore, the system switches to the light load mode and adopts the intermittent working mode to reduce switching action and reduce losses.

[0074] like Figure 7 As shown in the waveform diagram, it can be seen that when switching from PFM to CSPWM modulation or from CSPWM to PFM modulation, the output voltage can recover to the given value within a short fluctuation.

[0075] S500: Obtain a second load current and a second input voltage of a CLLC resonant bidirectional DC-DC converter in a light-load mode.

[0076] Here, in the light load mode, the second load current (the current after the load changes) and the second input voltage (the real-time value of the input side voltage) are monitored in real time to determine whether the control strategy in the light load mode needs to be adjusted.

[0077] S600. If the second load current is less than the preset upper limit value and the second input voltage is less than or equal to the reference voltage, the switching frequency of each switch tube of the primary full-bridge inverter circuit is controlled to be adjusted to the preset switching frequency, and the duty cycle is adjusted to the preset duty cycle; the preset upper limit value is greater than the preset lower limit value.

[0078] When the second load current is less than a preset upper limit (another threshold greater than a preset lower limit, forming a current hysteresis loop to avoid frequent switching), and the second input voltage is less than or equal to the reference voltage, it indicates that the load is still in the light load range and the output voltage needs to be maintained or increased. At this time, the switching frequency of the primary full-bridge inverter circuit is fixed to the preset switching frequency, and the duty cycle is fixed to the preset duty cycle. Intermittent energy output is achieved through stable switching parameters, balancing efficiency and voltage stability under light load conditions.

[0079] Here, the preset switching frequency is, for example, 230 kHz, and the preset duty cycle is, for example, 0.48.

[0080] S700. Obtain a third input voltage and a third load current. If the third input voltage is greater than a reference voltage and the third load current is greater than a preset upper limit, exit the light load mode and enter the step-down mode. If the third input voltage is less than the reference voltage and the third load current is greater than the preset upper limit, exit the light load mode and enter the step-up mode.

[0081] Among them, when the load becomes heavier (the third load current is greater than the preset upper limit value), the light load mode is no longer applicable, and it is necessary to exit and re-enter the boost / buck mode. The judgment logic is: if the third input voltage is greater than the reference voltage: the voltage needs to be reduced, and the buck mode is entered; if the third input voltage is less than the reference voltage: the voltage needs to be increased, and the boost mode is entered; through the dual judgment of voltage and current, it is ensured that after exiting the light load mode, it can immediately switch to the adapted heavy load control strategy to avoid output voltage fluctuations.

[0082] like Figure 8 As shown in the waveform diagram, it can be seen that the resonant current waveform is generated and stopped periodically, and the output voltage also changes regularly within the set voltage hysteresis loop, which is in line with the characteristics of intermittent mode operation; and under light load mode operation, the primary side switch tube achieves zero voltage turn-on (ZVS) and the secondary side switch tube achieves zero current shutdown (ZCS), which effectively reduces the loss of the converter and improves the working efficiency of the converter.

[0083] In light load mode, if the load current is detected to be greater than the hysteresis current upper limit, the light load mode is exited and the boost mode or buck mode is selected according to the working conditions. A current hysteresis is set between the load current for entering and exiting the light load mode to prevent frequent switching of the working mode due to disturbances.

[0084] like Figure 9 As shown, the mode switching current is set with a current hysteresis loop, which can effectively prevent the problem that the converter frequently switches the working mode due to disturbances, resulting in reduced working efficiency.

[0085] This method first ensures startup safety through soft start, and then selects the modulation mode according to the voltage difference to achieve safe startup and precise voltage regulation; then it judges the load severity by the load current, and switches to intermittent mode when the load is light, solving the problem of low light load efficiency in the traditional mode; moreover, in light load mode, the efficiency is maintained by fixed parameters, and when the load increases, it quickly switches back to boost / buck mode to ensure adaptability over the full load range.

[0086] Furthermore, the method further comprises the following steps: When the modulation mode is the boost mode and the first load current is greater than or equal to the preset lower limit value, the duty cycle of each switch tube of the primary full-bridge inverter circuit is controlled to be adjusted to a preset duty cycle; Obtaining a first switching frequency of the CLLC resonant bidirectional DC-DC converter in a boost mode, and if the first switching frequency is greater than a preset resonant frequency, controlling the CLLC resonant bidirectional DC-DC converter to enter a hysteresis delay link; The second switching frequency after the delay of the hysteresis loop is collected. If the second switching frequency is greater than the preset resonant frequency, the CLLC resonant bidirectional DC-DC converter is controlled to switch from the boost mode to the buck mode.

[0087] It should be noted that When the converter is in boost mode and the first load current is greater than or equal to the preset lower limit (i.e., the load is in a heavy or rated load state), the duty cycle of each switch in the primary full-bridge inverter circuit is first fixed to the preset duty cycle. In boost mode, pulse frequency modulation (PFM) control is used, and the duty cycle of the primary switches is fixed at 0.48. For example, the duty cycle of the drive signals for Q1 and Q4, and Q2 and Q3, are all 0.48, and the two sets of signals are complementary. This fixed duty cycle design is designed to support the core logic of PFM modulation, which achieves voltage regulation by adjusting the switching frequency rather than the duty cycle. It also creates conditions for the primary switches to achieve zero voltage conduction (ZVS), thereby reducing switching losses.

[0088] In boost mode, output voltage regulation is primarily achieved by varying the switching frequency of the primary-side switching transistor (the core mechanism of PFM). When the output voltage needs to be increased, the switching frequency is reduced; when the voltage needs to be limited, the switching frequency is increased. However, there is an upper limit to the switching frequency increase, which is referred to in the document as the preset resonant frequency. Here, the preset resonant frequency is, for example, 390kHz.

[0089] The first switching frequency is the current switching frequency in the boost mode acquired in real time. If the first switching frequency exceeds the preset resonant frequency, it means that it is difficult to stabilize the output voltage through PFM alone, or further increasing the frequency will lead to reduced efficiency and soft switching failure, and a mode switching judgment needs to be triggered.

[0090] The hysteresis delay stage is designed to prevent false switching due to transient disturbances, such as input voltage fluctuations or sudden load changes. In these cases, the converter enters the hysteresis delay stage, with a delay of 5ms, for example. This delay stage waits and verifies that the switching frequency exceeds the resonant frequency continuously, rather than briefly, improving the reliability of mode switching.

[0091] After the hysteresis delay, the second switching frequency is collected again and a second determination is made. If the second switching frequency is still greater than the preset resonant frequency, the boost mode can no longer meet the current operating conditions. For example, if the input voltage rises or the load changes, causing the required voltage to decrease, the converter is controlled to switch from boost mode to buck mode. If the second switching frequency returns to below the resonant frequency, it is determined to be a transient disturbance and the converter returns to boost mode to continue operation without switching.

[0092] Buck mode uses center-symmetric pulse width modulation (CSPWM), with the switching frequency fixed at the preset resonant frequency. Voltage regulation is achieved by adjusting the duty cycle. Therefore, switching from boost mode (PFM, variable frequency) to buck mode (CSPWM, fixed frequency) essentially switches the modulation method to maintain voltage stability when PFM frequency regulation reaches its limit, preventing converter efficiency degradation or hardware damage caused by excessively high frequency.

[0093] Furthermore, the method further comprises the following steps: When the modulation mode is the buck mode and the first load current is greater than or equal to the preset lower limit value, the switching frequency of each switch tube of the primary full-bridge inverter circuit is controlled to be adjusted to the preset switching frequency; Obtaining a first duty cycle of the CLLC resonant bidirectional DC-DC converter in a buck mode, and if the first duty cycle is greater than a preset duty cycle upper limit, controlling the CLLC resonant bidirectional DC-DC converter to enter a hysteresis loop delay link; The second duty cycle after the delay of the hysteresis loop is collected. If the second duty cycle is greater than a preset duty cycle upper limit, the CLLC resonant bidirectional DC-DC converter is controlled to switch from the buck mode to the boost mode.

[0094] It should be noted that when the converter is in step-down mode and the first load current is greater than or equal to the preset lower limit value (that is, the load is in a heavy load or rated load state), the switching frequency of each switching tube in the primary full-bridge inverter circuit is first fixed to the preset switching frequency.

[0095] Buck mode utilizes center-symmetric pulse-width modulation (CSPWM) control, with the switching frequency fixed at a preset resonant frequency of 390kHz. This fixed frequency optimizes the converter's soft-switching characteristics (zero voltage turn-on of the primary switch and zero current turn-off of the secondary switch) at the resonant frequency, minimizing switching losses. Furthermore, the fixed frequency facilitates the design and optimization of magnetic components (such as the resonant inductor and high-frequency transformer), improving overall efficiency.

[0096] In buck mode, output voltage regulation is primarily achieved by varying the duty cycle of the primary-side switching transistors (the core mechanism of CSPWM). To reduce the output voltage, the duty cycle is reduced; to increase the output voltage, the duty cycle is increased. However, there is an upper limit to the duty cycle increase, which is preset to 0.48. For example, the sum of the duty cycles of Q1 and Q4, and Q2 and Q3, is fixed at 0.96, and the initial duty cycle of each switch is 0.48.

[0097] The first duty cycle is the current duty cycle in the buck mode acquired in real time. If the first duty cycle exceeds the preset upper limit of 0.48, it means that it is difficult to stabilize the output voltage through CSPWM alone. Or further increasing the duty cycle will lead to insufficient dead time of the bridge arm and failure of soft switching, and a mode switching judgment needs to be triggered.

[0098] The hysteresis delay link is to avoid false switching due to transient disturbances, such as a sudden drop in input voltage or a sudden increase in load. At this time, the converter enters the hysteresis delay link; the role of this link is to verify continuity and ensure that the duty cycle exceeds the upper limit in a stable state rather than a short-term fluctuation, thereby improving the reliability of mode switching.

[0099] After the hysteresis delay, the second duty cycle is collected again and a second determination is made. If the second duty cycle is still greater than the preset duty cycle upper limit of 0.48, it indicates that buck mode can no longer meet the current operating conditions (such as a drop in input voltage or an increase in load demand voltage). At this time, the converter is controlled to switch from buck mode to boost mode. If the second duty cycle returns to 0.48 or below, it is determined to be a transient disturbance and the converter returns to buck mode to continue operation without switching.

[0100] The boost mode uses pulse frequency modulation (PFM) with a fixed duty cycle of 0.48, achieving voltage boost by adjusting the switching frequency (below the preset resonant frequency of 390kHz). Therefore, switching from buck mode (CSPWM, fixed frequency) to boost mode (PFM, variable frequency) essentially switches the modulation method to maintain voltage stability when the CSPWM duty cycle reaches its limit, thus avoiding hardware risks (such as bridge arm shoot-through) or efficiency loss caused by excessively high duty cycles.

[0101] Furthermore, the light load mode is an intermittent working mode, which specifically includes the following steps: When the output voltage of the CLLC resonant bidirectional DC-DC converter is greater than the upper limit of the reference voltage, the driving signal is stopped from being sent to the primary full-bridge inverter circuit.

[0102] It should be noted that the upper limit of the reference voltage is the sum of the reference voltage and the maximum value of the allowable voltage fluctuation range, and is the threshold for determining whether the output voltage exceeds the standard.

[0103] When the load current falls below a preset lower limit, the converter switches from boost / buck mode to light-load mode. This reduces switching losses at light loads by minimizing switching activity. The core control method for light-load mode is intermittent operation, which periodically turns the primary-side switch drive signal on and off to achieve intermittent energy transfer, balancing output voltage stability with improved efficiency.

[0104] In the intermittent working mode, the output voltage is stabilized by monitoring the deviation between the output voltage and the reference voltage. Among them, stopping the driving signal to the primary full-bridge inverter circuit is a regulatory action for excessively high output voltage.

[0105] When the output voltage V o When the voltage exceeds the upper limit of the reference voltage, it indicates that the current output energy exceeds the load's requirements. Continuing to transfer energy will cause the voltage to rise further, affecting load safety or circuit stability. At this point, by stopping the drive signal, the switches (Q1-Q4) in the primary-side full-bridge inverter circuit cease operation. The primary side no longer transfers energy to the secondary side, thereby utilizing the load's own consumption to reduce the output voltage.

[0106] Through closed-loop control that stops the drive when the output voltage exceeds the upper limit, the output voltage is constrained within the reference voltage upper limit, achieving output voltage stability under light load. Stopping the drive signal when the output voltage is too high is equivalent to putting the converter into a "sleep" state. During this time, the primary side switch tube does not switch, avoiding ineffective switching losses (switching losses account for a higher proportion under light load) and significantly improving energy conversion efficiency under light load mode. Furthermore, soft switching characteristics (zero voltage turn-on on the primary side, zero current turn-off on the secondary side) must still be maintained under light load mode. Stopping the drive signal is an orderly control when the output voltage exceeds the limit, which will not disrupt the soft switching conditions of the switch tube, ensuring safety and reliability during intermittent operation.

[0107] like Figure 3 As shown in the figure, during the soft-start phase, this is achieved by gradually reducing the switching frequency (from a maximum of 500kHz to a resonant frequency of 390kHz) and gradually increasing the duty cycle of the primary switch (from 0 to 0.48). This step aims to avoid the sudden surge in current at startup, allowing the output voltage to rise smoothly to near the reference voltage. Simultaneously, the first input voltage (such as the voltage of the DC input power supply Vin) is collected in real time to provide basic data for subsequent mode determination.

[0108] After the soft start is completed, the relationship between the reference voltage and the first input voltage determines whether to enter the boost mode or the buck mode. If the reference voltage is greater than the first input voltage, the output voltage needs to be increased and the boost mode is entered. Pulse frequency modulation (PFM) control is used to adjust the switching frequency of the primary switch tube to achieve voltage regulation. If the reference voltage is less than the first input voltage, the output voltage needs to be reduced and the buck mode is entered. Center-symmetric pulse width modulation (CSPWM) control is used to adjust the duty cycle of the primary switch tube to achieve voltage regulation.

[0109] In the boost / buck mode (collectively referred to as the "buck-boost mode"), the first load current is collected in real time. If the first load current is ≥ the preset lower limit (heavy load or rated load), the current buck-boost mode is maintained and the voltage continues to be regulated through PFM or CSPWM. If the first load current is < the preset lower limit (light load): switch to the light load mode, and use the intermittent working mode to reduce switching action and reduce light load losses.

[0110] In light-load mode, intermittent control is achieved by monitoring the deviation between the output voltage and a reference voltage. When the output voltage is less than the lower limit of the reference voltage, the primary switch operates at a fixed frequency (230kHz) and a duty cycle (0.48) to replenish energy and boost the output voltage. When the output voltage is greater than the upper limit of the reference voltage, the primary switch drive signal is stopped, energy transfer ceases, and the output voltage is reduced by load consumption. Simultaneously, the secondary load current is monitored in real time. If it is greater than or equal to the preset upper limit (light load to heavy load), light-load mode is exited and the voltage is returned to boost or buck mode based on the voltage relationship.

[0111] To avoid the regulation limit of a single modulation method, a switching mechanism between modes is also designed. In boost mode, if the switching frequency adjusted by PFM is greater than the resonant frequency (390kHz) and is still exceeded after a 5ms hysteresis delay, the mode switches to buck mode (CSPWM). In buck mode, if the duty cycle adjusted by CSPWM is greater than the upper limit (0.48) and is still exceeded after a 5ms hysteresis delay, the mode switches to boost mode (PFM).

[0112] This application achieves efficient operation and soft switching characteristics within the full load range through the logic of soft start to prevent shock, mode adaptation to improve efficiency, light load intermittent loss reduction, and mode switching to ensure stability. At the same time, the hysteresis delay design avoids frequent mode switching and improves system reliability.

[0113] The above description is merely a preferred embodiment of the present application and an illustration of the technical principles employed. Those skilled in the art should understand that the scope of the invention herein is not limited to the technical solutions formed by the specific combination of the above-mentioned technical features, but also encompasses other technical solutions formed by any combination of the above-mentioned technical features or their equivalents without departing from the inventive concept. For example, a technical solution formed by replacing the above-mentioned features with (but not limited to) technical features having similar functions disclosed in this application.

Claims

1. A CLLC resonant bidirectional DC-DC converter, characterized in that: include: Primary side full-bridge inverter circuit, secondary side full-bridge rectifier circuit, primary side resonant cavity, secondary side resonant cavity and high frequency transformer; The primary full-bridge inverter circuit has a first bridge arm midpoint and a second bridge arm midpoint, and the secondary full-bridge rectifier circuit has a third bridge arm midpoint and a fourth bridge arm midpoint; The primary resonant cavity includes a resonant inductor L1 and a resonant capacitor C1 connected in series, the free end of the resonant inductor L1 is electrically connected to the midpoint of the first bridge arm, and the free end of the resonant capacitor C1 is electrically connected to the midpoint of the second bridge arm; the connection point between the resonant inductor L1 and the resonant capacitor C1 is electrically connected to the primary side of the high-frequency transformer; The secondary side resonant cavity includes a resonant inductor L2 and a resonant capacitor C2 connected in series, the free end of the resonant inductor L2 is electrically connected to the midpoint of the third bridge arm, and the free end of the resonant capacitor C2 is electrically connected to the midpoint of the fourth bridge arm; the connection point between the resonant inductor L2 and the resonant capacitor C2 is electrically connected to the secondary side of the high-frequency transformer.

2. A CLLC resonant bidirectional DC-DC converter according to claim 1, characterized in that: The primary full-bridge inverter circuit includes a first switch tube group and a second switch tube group connected in parallel, wherein the first switch tube group includes a power switch tube Q1 and a power switch tube Q2 connected in series, and the second switch tube group includes a power switch tube Q3 and a power switch tube Q4 connected in series; The connection point of the power switch tube Q1 and the power switch tube Q2 is the midpoint of the first bridge arm of the primary full-bridge inverter circuit, and the connection point of the power switch tube Q3 and the power switch tube Q4 is the midpoint of the second bridge arm of the primary full-bridge inverter circuit.

3. A CLLC resonant bidirectional DC-DC converter according to claim 2, characterized in that: The secondary full-bridge rectifier circuit includes a third switch tube group and a fourth switch tube group connected in parallel, the third switch tube group includes a power switch tube Q5 and a power switch tube Q6 connected in series, and the fourth switch tube group includes a power switch tube Q7 and a power switch tube Q8 connected in series; The connection point of the power switch tube Q5 and the power switch tube Q6 is the midpoint of the third bridge arm of the secondary full-bridge rectifier circuit, and the connection point of the power switch tube Q7 and the power switch tube Q8 is the midpoint of the fourth bridge arm of the secondary full-bridge rectifier circuit.

4. A CLLC resonant bidirectional DC-DC converter according to claim 3, characterized in that: Also includes: DC input power supply V in , the DC input power supply V in connected in series with the first switch tube group; Input filter capacitor C i , the input filter capacitor C i connected in parallel with the first switch tube group; Output filter capacitor C o , the output filter capacitor C o connected in parallel with the third switch tube group; Load resistance R L , the load resistance R L Connected in parallel with the third switch tube group.

5. A control method for a CLLC resonant bidirectional DC-DC converter, characterized in that: The following steps are involved: Performing a soft start operation on the CLLC resonant bidirectional DC-DC converter and collecting a first input voltage in real time; Obtaining a reference voltage, and determining a modulation mode based on a relationship between the reference voltage and the first input voltage; the modulation mode being a boost mode or a buck mode; Obtaining a first load current of the CLLC resonant bidirectional DC-DC converter in the modulation mode; If the first load current is less than a preset lower limit, switching the current modulation mode to a light load mode; Obtaining a second load current and a second input voltage of the CLLC resonant bidirectional DC-DC converter in the light load mode; If the second load current is less than a preset upper limit and the second input voltage is less than or equal to the reference voltage, the switching frequency of each switch tube of the primary full-bridge inverter circuit is controlled to be adjusted to a preset switching frequency and the duty cycle is adjusted to a preset duty cycle; the preset upper limit is greater than the preset lower limit; Obtain a third input voltage and a third load current. If the third input voltage is greater than the reference voltage and the third load current is greater than the preset upper limit, exit the light load mode and enter the step-down mode. If the third input voltage is less than the reference voltage and the third load current is greater than the preset upper limit, exit the light load mode and enter the step-up mode.

6. The control method of a CLLC resonant bidirectional DC-DC converter according to claim 5, characterized in that: Determining a modulation mode according to a relationship between the reference voltage and the first input voltage specifically includes the following steps: When the first input voltage is greater than the reference voltage, the modulation mode is a buck mode; When the first input voltage is lower than the reference voltage, the modulation mode is a boost mode.

7. The control method of a CLLC resonant bidirectional DC-DC converter according to claim 6, characterized in that: The method further comprises the following steps: When the modulation mode is the boost mode and the first load current is greater than or equal to a preset lower limit, controlling the duty cycle of each switch tube of the primary full-bridge inverter circuit to be adjusted to a preset duty cycle; obtaining a first switching frequency of the CLLC resonant bidirectional DC-DC converter in the boost mode, and controlling the CLLC resonant bidirectional DC-DC converter to enter a hysteresis delay link if the first switching frequency is greater than a preset resonant frequency; The second switching frequency after the delay by the hysteresis delay link is collected, and if the second switching frequency is greater than the preset resonant frequency, the CLLC resonant bidirectional DC-DC converter is controlled to switch from the boost mode to the buck mode.

8. The control method of a CLLC resonant bidirectional DC-DC converter according to claim 6, characterized in that: The method further comprises the following steps: When the modulation mode is the buck mode and the first load current is greater than or equal to a preset lower limit, controlling the switching frequency of each switch tube of the primary full-bridge inverter circuit to be adjusted to a preset switching frequency; Obtaining a first duty cycle of the CLLC resonant bidirectional DC-DC converter in the buck mode, and if the first duty cycle is greater than a preset duty cycle upper limit, controlling the CLLC resonant bidirectional DC-DC converter to enter a hysteresis delay link; A second duty cycle after being delayed by the hysteresis delay link is collected, and if the second duty cycle is greater than the preset duty cycle upper limit, the CLLC resonant bidirectional DC-DC converter is controlled to switch from the buck mode to the boost mode.

9. The control method of a CLLC resonant bidirectional DC-DC converter according to claim 5, characterized in that: The soft start operation of the CLLC resonant bidirectional DC-DC converter includes the following steps: The switching frequency of the primary full-bridge inverter circuit is gradually reduced from a maximum value to a preset resonant frequency, and at the same time, the duty cycle of each switch tube of the primary full-bridge inverter circuit is gradually increased from zero to a preset duty cycle upper limit value.

10. The control method of a CLLC resonant bidirectional DC-DC converter according to claim 5, characterized in that: The light load mode is an intermittent working mode, which specifically includes the following steps: When the output voltage of the CLLC resonant bidirectional DC-DC converter is greater than the reference voltage upper limit, the driving signal is stopped from being sent to the primary full-bridge inverter circuit.

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