A llcc resonant converter with reduced resonant current and resonant capacitor voltage stress

Abstract

The application relates to a LLCC resonant converter capable of reducing resonant current and resonant capacitor voltage stress, which comprises a direct-current input power supply, the direct-current input power supply is connected with a full-bridge inverter module, the output end of the full-bridge inverter module is connected with two ends A and B of a primary side coil of a high-frequency transformer T, the input end of a full-bridge rectifier module is connected with two ends C and D of a secondary side coil of the high-frequency transformer T, the input end of a filter module is connected with the output end of the full-bridge rectifier module, and a load R is connected with the output end of the filter module o The voltage between the two ends of the direct-current input power supply is a direct-current input voltage V in The voltage between the two ends of the load R o is a direct-current output voltage V o The application can realize ZVS opening of the primary side switch tube in a wide input voltage and wide load range under a phase shift control strategy; the application can reduce resonant current stress under heavy load and can reduce resonant capacitor voltage stress under the phase shift control strategy; and the application has simple topological structure, flexible design and regulation and strong practicability.

Description

Technical Field

[0001] This invention relates to the field of resonant converter technology, and in particular to an LLCC resonant converter that reduces resonant current and resonant capacitor voltage stress. Background Technology

[0002] DC-DC converters are widely used in new energy power generation, building energy storage, DC power distribution, and electric vehicles, making them a key research area in power electronics. Among them, resonant converters, which can achieve wide gain and wide soft-switching range, high-efficiency transmission, and high power density characteristics, are a particularly hot research topic. Series resonant converters (SRC) and parallel resonant converters (PRC) were the earliest proposed and applied resonant converters. SRCs have low circulating current losses and a wide switching frequency range, but cannot adjust voltage under no-load conditions; PRCs have larger circulating currents under light loads, a narrower switching frequency range, and can adjust voltage under no-load conditions. LCC resonant converters combine the advantages of both SRCs and PRCs, with low circulating current losses under light loads and adjustable voltage under no-load conditions, thus attracting widespread attention from researchers.

[0003] The LCC resonant converter adds an inductor-capacitor-capacitor system between the transformer and the bridge arm, putting the energy storage element in the circuit in a resonant state. This enables zero-voltage turn-on (ZVS) of the switching transistors, reducing switching losses. In frequency conversion control, the LCC resonant converter can achieve ZVS turn-on over a wide input voltage and load range, but it suffers from a large frequency variation range. In phase-shift control, the LCC resonant converter controls the converter by adjusting the conduction angle of the primary-side switching transistor, resulting in a fixed switching frequency and avoiding the large frequency variation problem. However, as the input voltage increases or the load decreases, the ZVS of the primary-side switching transistor in the phase-shift controlled LCC resonant converter is easily lost, and the peak resonant current of the converter increases with increasing load. Furthermore, the resonant capacitor voltage stress in the phase-shift controlled LCC resonant converter is also relatively large. Summary of the Invention

[0004] The purpose of this invention is to provide an LLCC resonant converter that can improve the ZVS performance of the converter, reduce the resonant current stress under heavy load, and reduce the resonant capacitor voltage stress under phase shift control.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: an LLCC resonant converter for reducing resonant current and resonant capacitor voltage stress, comprising a DC input power supply, a full-bridge inverter module, a resonant tank module, a full-bridge rectifier module, a filter module, and a load R. oThe resonant tank module includes a high-frequency transformer T; the DC input power supply is connected to a full-bridge inverter module, the output terminal of the full-bridge inverter module is connected to the two ends A and B of the primary winding of the high-frequency transformer T, the input terminal of the full-bridge rectifier module is connected to the two ends C and D of the secondary winding of the high-frequency transformer T, the input terminal of the filter module is connected to the output terminal of the full-bridge rectifier module, and the load R... o Connected to the output of the filter module, the voltage across the DC input power supply is the DC input voltage V. in Load R o The voltage across the terminals is the DC output voltage V. o .

[0006] The full-bridge inverter module includes a leading arm module and a lagging arm module. The leading arm module includes a first switching module and a second switching module, and the lagging arm module includes a third switching module and a fourth switching module. The first switching module includes a switching transistor S1 and a body diode D. S1 and parasitic capacitance C S1 Body diode D S1 The cathode is connected to the drain of the switching transistor S1, and the body diode D... S1 The anode of the transistor is connected to the source of the switching transistor S1, and the parasitic capacitance C S1 Parallel in-body diode D S1 At both ends; the second switching module includes a switching transistor S2 and a body diode D S2 and parasitic capacitance C S2 Body diode D S2 The cathode of the diode is connected to the drain of the switching transistor S2, and the body diode D... S2 The anode of the transistor is connected to the source of the switching transistor S2, and the parasitic capacitance C S2 Parallel in-body diode D S2 At both ends; the third switching module includes a switching transistor S3 and a body diode D. S3 and parasitic capacitance C S3 Body diode D S3 The cathode of the diode is connected to the drain of the switching transistor S3, and the body diode D... S3 The anode of the transistor is connected to the source of the switching transistor S3, and the parasitic capacitance C S3 Parallel in-body diode D S3 At both ends; the fourth switching module includes a switching transistor S4 and a body diode D. S4 and parasitic capacitance C S4 Body diode D S4 The cathode is connected to the drain of the switching transistor S4, and the body diode D... S4 The anode of the transistor is connected to the source of the switching transistor S4, and the parasitic capacitance C S4 Parallel in-body diode D S4The primary winding of the high-frequency transformer T is connected at both ends; the A end of the primary winding of the high-frequency transformer T is connected between the first switch module and the second switch module; the B end of the primary winding of the high-frequency transformer T is connected between the third switch module and the fourth switch module.

[0007] The resonant slot module includes an auxiliary inductor L. a and an LCC resonant network, wherein the LCC resonant network consists of a resonant inductor L r Series resonant capacitor C s and parallel resonant capacitor C p Composition, resonant inductor L r Series resonant capacitor C s and parallel resonant capacitor C p It forms an inductor-inductor-capacitor-capacitor topology; the resonant inductor L r The auxiliary inductor L is connected in series with the primary winding of the high-frequency transformer T. a The series resonant capacitor C is connected in parallel with the primary winding of the high-frequency transformer T. s The parallel resonant capacitor C is connected in series with the secondary coil of the high-frequency transformer T. p It is connected in parallel with the secondary coil of the high-frequency transformer T.

[0008] The full-bridge rectifier module includes rectifier diodes D1, D2, D3, and D4; the C-terminal of the secondary winding of the high-frequency transformer T is connected between rectifier diodes D1 and D2; and the D-terminal of the secondary winding of the high-frequency transformer T is connected between rectifier diodes D3 and D4.

[0009] The filtering module includes a filter inductor L. f and filter capacitor C f The filter inductor L f and filter capacitor C f They are connected in series and then in parallel across the two ends of the full-bridge rectifier module.

[0010] As can be seen from the above technical solution, the beneficial effects of the present invention are as follows: First, under the phase-shift control strategy, the present invention can achieve ZVS turn-on of the primary-side switching transistor within a wide input voltage and wide load range; Second, under the phase-shift control strategy, the present invention can reduce the resonant current stress under heavy load and simultaneously reduce the resonant capacitor voltage stress; Third, the present invention has a simple topology, flexible design and adjustment, and strong practicality. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the topology of the present invention;

[0012] Figure 2 This is a schematic diagram of the control circuit of the present invention;

[0013] Figure 3 This is a schematic diagram of the steady-state waveform of the present invention;

[0014] Figure 4 This is a schematic diagram of the first stage of the present invention;

[0015] Figure 5 This is a schematic diagram of the second stage of the present invention;

[0016] Figure 6 This is a schematic diagram of the third stage of the present invention;

[0017] Figure 7 This is a schematic diagram of the fourth stage of the present invention;

[0018] Figure 8 This is a schematic diagram of the fifth stage of the present invention. Detailed Implementation

[0019] like Figure 1 As shown, an LLCC resonant converter for reducing resonant current and resonant capacitor voltage stress includes a DC input power supply 1, a full-bridge inverter module 2, a resonant tank module 3, a full-bridge rectifier module 4, a filter module 5, and a load R. o The resonant slot module 3 includes a high-frequency transformer T; the DC input power supply 1 is connected to the full-bridge inverter module 2, the output terminal of the full-bridge inverter module 2 is connected to the two ends A and B of the primary winding of the high-frequency transformer T, the input terminal of the full-bridge rectifier module 4 is connected to the two ends C and D of the secondary winding of the high-frequency transformer T, the input terminal of the filter module 5 is connected to the output terminal of the full-bridge rectifier module 4, and the load R... o Connected to the output of filter module 5, the voltage across DC input power supply 1 is the DC input voltage V. in Load R o The voltage across the terminals is the DC output voltage V. o .

[0020] The full-bridge inverter module 2 includes a leading arm module and a lagging arm module. The leading arm module includes a first switching module and a second switching module, and the lagging arm module includes a third switching module and a fourth switching module. The first switching module includes a switching transistor S1 and a body diode D. S1 and parasitic capacitance C S1 Body diode D S1 The cathode is connected to the drain of the switching transistor S1, and the body diode D... S1 The anode of the transistor is connected to the source of the switching transistor S1, and the parasitic capacitance C S1 Parallel in-body diode D S1 At both ends; the second switching module includes a switching transistor S2 and a body diode D S2 and parasitic capacitance CS2 Body diode D S2 The cathode of the diode is connected to the drain of the switching transistor S2, and the body diode D... S2 The anode of the transistor is connected to the source of the switching transistor S2, and the parasitic capacitance C S2 Parallel in-body diode D S2 At both ends; the third switching module includes a switching transistor S3 and a body diode D. S3 and parasitic capacitance C S3 Body diode D S3 The cathode of the diode is connected to the drain of the switching transistor S3, and the body diode D... S3 The anode of the transistor is connected to the source of the switching transistor S3, and the parasitic capacitance C S3 Parallel in-body diode D S3 At both ends; the fourth switching module includes a switching transistor S4 and a body diode D. S4 and parasitic capacitance C S4 Body diode D S4 The cathode is connected to the drain of the switching transistor S4, and the body diode D... S4 The anode of the transistor is connected to the source of the switching transistor S4, and the parasitic capacitance C S4 Parallel in-body diode D S4 The primary winding of the high-frequency transformer T is connected at both ends; the A end of the primary winding of the high-frequency transformer T is connected between the first switch module and the second switch module; the B end of the primary winding of the high-frequency transformer T is connected between the third switch module and the fourth switch module.

[0021] The resonant slot module 3 includes an auxiliary inductor L. a and an LCC resonant network, wherein the LCC resonant network consists of a resonant inductor L r Series resonant capacitor C s and parallel resonant capacitor C p Composition, resonant inductor L r Series resonant capacitor C s and parallel resonant capacitor C p It forms an inductor-inductor-capacitor-capacitor topology; the resonant inductor L r The auxiliary inductor L is connected in series with the primary winding of the high-frequency transformer T. a The series resonant capacitor C is connected in parallel with the primary winding of the high-frequency transformer T. s The parallel resonant capacitor C is connected in series with the secondary coil of the high-frequency transformer T. p It is connected in parallel with the secondary coil of the high-frequency transformer T.

[0022] The full-bridge rectifier module 4 includes rectifier diodes D1, D2, D3, and D4; the C-terminal of the secondary winding of the high-frequency transformer T is connected between rectifier diodes D1 and D2; and the D-terminal of the secondary winding of the high-frequency transformer T is connected between rectifier diodes D3 and D4.

[0023] The filtering module 5 includes a filtering inductor L. f and filter capacitor C f The filter inductor L f and filter capacitor C f They are connected in series and then in parallel across the two ends of the full-bridge rectifier module 4.

[0024] The following combination Figures 1 to 7 The present invention will be further described below.

[0025] The primary winding of the high-frequency transformer T is the high-turns side, denoted as the high-voltage side; the secondary winding of the high-frequency transformer T is the low-turns side, denoted as the low-voltage side. An LLCC resonant converter that reduces resonant current and resonant capacitor voltage stress is denoted as an LLCC resonant converter. When the LLCC resonant converter is working, each switch on the high-voltage side is phase-shift controlled. The control of the LLCC resonant converter is achieved by adjusting the conduction angle of each switch. During operation, energy is transferred from the high-voltage side to the low-voltage side. At this time, the auxiliary inductor L... a Clamped by the DC input power supply 1, it does not participate in resonance; the resonant network consists of the resonant inductor L. r The series resonant capacitor C s and the parallel resonant capacitor C p constitute.

[0026] To address the shortcomings of phase-shift controlled LCC resonant converters, this invention adds an auxiliary inductor L in parallel on the high-voltage side, based on the LCC resonant converter topology. a And the series resonant capacitor C s and parallel resonant capacitor C p By placing it on the low-voltage side of the converter, a novel LLCC resonant converter is formed. Under phase-shift control, the LLCC resonant converter can effectively improve the converter's ZVS performance, reduce the resonant current stress under heavy load, and also reduce the resonant capacitor voltage stress.

[0027] like Figure 2As shown, the control module includes an output voltage sampling module, an MCU controller, and a switch drive circuit. The output voltage sampling module samples the output voltage of the LLCC resonant converter and feeds the voltage signal back to the MCU controller. The MCU controller dynamically adjusts the conduction angle of the primary-side switch of the LLCC resonant converter according to the output voltage signal and generates a switch control drive signal, which is then fed back to the switch drive circuit. Finally, the switch drive circuit controls the on / off state of the primary-side switch of the LLCC resonant converter according to the switch control drive signal.

[0028] like Figure 3 As shown, whether the LLCC resonant converter and the LCC resonant converter can achieve ZVS during normal operation depends on whether the current flows through the body diode of the switching transistor first at the moment of conduction. The switching transistor ZVS condition of the LCC resonant converter is θ > (π - δ) / 2, where θ is the output voltage v of the full-bridge inverter module 2. AB The fundamental component and the resonant current i r The phase difference is called the impedance angle; δ is the phase-shift control conduction angle between the leading and lagging bridge arm module switches. When the input voltage of the LCC resonant converter increases or the load decreases, both the conduction angle δ and the impedance angle θ will decrease, which will cause the LCC resonant converter to easily lose the ZVS condition. If a larger θ is selected in the LCC resonant converter parameter design, the resonant current i can be achieved at the moment the switch is turned on. r First, the current flows through the body diode, which can effectively solve the problem of ZVS loss in the LCC resonant converter switch. However, a larger θ will increase the resonant current i during energy transfer. r Size. The LLCC resonant converter is no longer limited by the condition θ>(π-δ) / 2, and it can be controlled by the auxiliary inductor current i La and resonant current i r The combined effect achieves the ZVS condition of the LLCC resonant converter, such that the current (i) at the moment the switch is turned on... La +i r The current first flows through the body diode. Simultaneously, a smaller θ can reduce the resonant current i during energy transfer in the LLCC resonant converter. r Size. From Figure 3 As can be seen from the diagram, the LLCC resonant converter has 10 operating stages within one switching cycle, divided into 5 stages in the first half of the cycle and 5 stages in the second half. Since the operating stages of the LLCC resonant converter in the first half of the cycle are symmetrical, it is only necessary to analyze the operating stages of half a cycle. Taking the 5 operating stages of the first half of the cycle as an example, the specific working process is as follows:

[0029] Phase 1 [t0-t1]: (e.g.) Figure 4As shown, the LLCC resonant converter is in phase [t0-t1]. Ignoring the dead time, at time t0, the switch S3 is turned off, and at this time the resonant current i r The current i flowing through the auxiliary inductor is negative. La The current is negative, and the current flowing through the fourth switching module is the sum of the resonant current and the auxiliary inductor current, flowing from the source of switching transistor S4 to the drain of switching transistor S4. At this time, the current (i...) La +i r The current does not immediately flow from the switching transistor S4, but first flows from the body diode D of the switching transistor S4. S4 Before switch S4 is turned on, the voltage across switch S4 has already dropped to 0, achieving ZVS turn-on for switch S4. Throughout the first stage, primary-side switches S1 and S4 are on, and the output voltage of the full-bridge inverter module 2 is v. AB +V in Auxiliary inductor L a v AB Clamped, not participating in resonance. Secondary-side parallel resonant capacitor voltage v Cp Since the polarity is negative, rectifier diodes D2 and D3 are turned on. This phase continues until the resonant current i... r Until the reversal time t1.

[0030] Phase 2 [t1-t2]: (e.g.) Figure 5 As shown, the LLCC resonant converter is in phase [t1-t2], during which the resonant current i r The current i flowing through the auxiliary inductor is positive. La The voltage is negative. Primary-side switches S1 and S4 are turned on, and the output voltage of the full-bridge inverter module 2 is negative. AB +V in Auxiliary inductor L a v AB Clamped, not participating in resonance. Secondary-side parallel resonant capacitor voltage v Cp The voltage gradually rises from negative to 0, therefore rectifier diodes D2 and D3 continue to conduct. This stage continues until the voltage of the parallel resonant capacitor v... Cp Until the reversal time t2.

[0031] Phase 3 [t2-t3]: (e.g.) Figure 6 As shown, the LLCC resonant converter is in stage [t2-t3], during which the resonant current i r The current i flowing through the auxiliary inductor is positive. La The voltage gradually rises from negative to 0. Primary-side switches S1 and S4 are turned on, and the output voltage v of the full-bridge inverter module 2 increases. AB +V in Auxiliary inductor L a v ABClamped, not participating in resonance. Secondary-side parallel resonant capacitor voltage v Cp Since the polarity is positive, rectifier diodes D1 and D4 are turned on. This phase continues until the auxiliary inductor current i... La Until the reversal time t3.

[0032] Phase 4 [t3-t4]: (e.g.) Figure 7 As shown, the LLCC resonant converter is in stage [t3-t4], during which the resonant current i r and the current i flowing through the auxiliary inductor La All are positive, with the auxiliary inductor current i flowing through it. La The voltage rises from 0 to its maximum value. Primary-side switches S1 and S4 are turned on, and the output voltage of the full-bridge inverter module 2 increases from 0 to its maximum value. AB +V in Auxiliary inductor L a v AB Clamped, not participating in resonance. Secondary-side parallel resonant capacitor voltage v Cp Since the polarity is positive, rectifier diodes D1 and D4 continue to conduct. This stage continues until switch S1 is turned off.

[0033] Phase 5 [t4-t5]: (e.g.) Figure 8 As shown, the LLCC resonant converter is in phase [t4-t5]. Ignoring the dead time, at time t4, the switch S1 is turned off, and at this time the resonant current i r The current i flowing through the auxiliary inductor is positive. La When the current is positive, the current flowing through the second switching module is the sum of the resonant current and the auxiliary inductor current, and it flows from the source of switching transistor S2 to the drain of switching transistor S2. At this time, the current (-i) La -i r The current does not immediately flow from the switching transistor S2, but first flows from the body diode D of the switching transistor S2. S2 Before switch S2 is turned on, the voltage across switch S2 has already dropped to 0, achieving ZVS turn-on for switch S2. Throughout stage 5, primary-side switches S2 and S4 are turned on, and the output voltage of the full-bridge inverter module 2 is v. AB The voltage v of the parallel resonant capacitor on the secondary side is 0. Cp Since the polarity is positive, rectifier diodes D1 and D4 continue to conduct. This stage continues until switch S4 is turned off.

[0034] Due to the symmetry of the first and second half of the operating phases within one cycle of the LLCC resonant converter, the phase [t6-t] 10 The working process is similar to that of stage [t0-t5], and will not be explained further here.

[0035] In summary, this invention, under a phase-shift control strategy, can achieve ZVS turn-on of the primary-side switch over a wide input voltage and load range; under the phase-shift control strategy, this invention can reduce the resonant current stress under heavy load and also reduce the resonant capacitor voltage stress; this invention has a simple topology, flexible design and adjustment, and strong practicality.

Claims

1. An LLC resonant converter that reduces resonant current and resonant capacitor voltage stress, characterized in that: It includes a DC input power supply (1), a full-bridge inverter module (2), a resonant tank module (3), a full-bridge rectifier module (4), a filter module (5), and a load R. o The resonant slot module (3) includes a high-frequency transformer T; the DC input power supply (1) is connected to the full-bridge inverter module (2), the output terminal of the full-bridge inverter module (2) is connected to the two ends A and B of the primary winding of the high-frequency transformer T, the input terminal of the full-bridge rectifier module (4) is connected to the two ends C and D of the secondary winding of the high-frequency transformer T, the input terminal of the filter module (5) is connected to the output terminal of the full-bridge rectifier module (4), and the load R o Connected to the output terminal of the filter module (5), the voltage across the DC input power supply (1) is the DC input voltage V. in Load R o The voltage across the terminals is the DC output voltage V. o ; The full-bridge inverter module (2) includes a leading arm module and a lagging arm module. The leading arm module includes a first switching module and a second switching module, and the lagging arm module includes a third switching module and a fourth switching module. The first switching module includes a switching transistor S1 and a body diode D. S1 and parasitic capacitance C S1 Body diode D S1 The cathode is connected to the drain of the switching transistor S1, and the body diode D... S1 The anode of the transistor is connected to the source of the switching transistor S1, and the parasitic capacitance C S1 Parallel in-body diode D S1 At both ends; the second switching module includes a switching transistor S2 and a body diode D S2 and parasitic capacitance C S2 Body diode D S2 The cathode of the diode is connected to the drain of the switching transistor S2, and the body diode D... S2 The anode of the transistor is connected to the source of the switching transistor S2, and the parasitic capacitance C S2 Parallel in-body diode D S2 At both ends; the third switching module includes a switching transistor S3 and a body diode D. S3 and parasitic capacitance C S3 Body diode D S3 The cathode of the diode is connected to the drain of the switching transistor S3, and the body diode D... S3 The anode of the transistor is connected to the source of the switching transistor S3, and the parasitic capacitance C S3 Parallel in-body diode D S3 At both ends; the fourth switching module includes a switching transistor S4 and a body diode D. S4 and parasitic capacitance C S4 Body diode D S4 The cathode is connected to the drain of the switching transistor S4, and the body diode D... S4 The anode of the transistor is connected to the source of the switching transistor S4, and the parasitic capacitance C S4 Parallel in-body diode D S4 At both ends; The A end of the primary coil of the high-frequency transformer T is connected between the first switch module and the second switch module; the B end of the primary coil of the high-frequency transformer T is connected between the third switch module and the fourth switch module. The resonant slot module (3) includes an auxiliary inductor L. a and an LCC resonant network, wherein the LCC resonant network consists of a resonant inductor L r Series resonant capacitor C s and parallel resonant capacitor C p Composition, resonant inductor L r Series resonant capacitor C s and parallel resonant capacitor C p It forms an inductor-inductor-capacitor-capacitor topology; the resonant inductor L r The auxiliary inductor L is connected in series with the primary winding of the high-frequency transformer T. a The series resonant capacitor C is connected in parallel with the primary winding of the high-frequency transformer T. s The parallel resonant capacitor C is connected in series with the secondary coil of the high-frequency transformer T. p It is connected in parallel with the secondary coil of the high-frequency transformer T; The full-bridge rectifier module (4) includes rectifier diodes D1, D2, D3 and D4; the C end of the secondary coil of the high-frequency transformer T is connected between rectifier diodes D1 and D2; the D end of the secondary coil of the high-frequency transformer T is connected between rectifier diodes D3 and D4. The filtering module (5) includes a filtering inductor L f and filter capacitor C f The filter inductor L f and filter capacitor C f They are connected in series and then in parallel across the two ends of the full-bridge rectifier module (4); The primary winding of the high-frequency transformer T is the high-turns side, denoted as the high-voltage side; the secondary winding of the high-frequency transformer T is the low-turns side, denoted as the low-voltage side. When the LLCC resonant converter is working, each switch on the high-voltage side is controlled by phase shifting, and the LLCC resonant converter is controlled by adjusting the conduction angle of each switch. During operation, energy is transferred from the high-voltage side to the low-voltage side, at which time the auxiliary inductor L... a Clamped by the DC input power supply (1), it does not participate in resonance. The resonant network is composed of the resonant inductor L. r The series resonant capacitor C s and the parallel resonant capacitor C p constitute; The LLCC resonant converter has 10 operating stages within one switching cycle, divided into 5 stages in the first half of the cycle and 5 stages in the second half of the cycle. The specific working process of the 5 operating stages in the first half of the cycle is as follows: Phase 1 [t0-t1]: The LLCC resonant converter is in phase [t0-t1]. Ignoring the dead time, at time t0, switch S3 is turned off, and the resonant current... i r The current flowing through the auxiliary inductor is negative. i La The current flowing through the fourth switching module is negative, and is the sum of the resonant current and the auxiliary inductor current, flowing from the source of switching transistor S4 to the drain of switching transistor S4; at this time, the current ( i La + i r The current does not immediately flow from the switching transistor S4, but first flows from the body diode D of the switching transistor S4. S4 Before the switching transistor S4 is turned on, the voltage across the switching transistor S4 has dropped to 0, and the switching transistor S4 achieves ZVS turn-on; throughout the first stage, the primary-side switching transistors S1 and S4 are turned on, and the output voltage of the full-bridge inverter module (2) is... v AB +V in Auxiliary inductor L a quilt v AB Clamped, not participating in resonance; voltage of the parallel resonant capacitor on the secondary side. v Cp With the polarity negative, rectifier diodes D2 and D3 conduct, and the first stage continues until the resonant current. i r Until the reversal time t1; Phase 2 [t1-t2]: The LLCC resonant converter is in phase [t1-t2], during which the resonant current... i r The current flowing through the auxiliary inductor is positive. i La The voltage is negative; primary-side switches S1 and S4 are turned on, and the output voltage of the full-bridge inverter module (2) is negative. v AB +V in Auxiliary inductor L a quilt v AB Clamped, not participating in resonance; voltage of the parallel resonant capacitor on the secondary side. v Cp The voltage gradually rises from negative to 0, so rectifier diodes D2 and D3 continue to conduct, and the second stage continues until the voltage of the parallel resonant capacitor reaches zero. v Cp Until the reversal time t2; Phase 3 [t2-t3]: The LLCC resonant converter is in phase [t2-t3], during which the resonant current... i r The current flowing through the auxiliary inductor is positive. i La The voltage gradually rises from negative to 0; primary-side switches S1 and S4 are turned on, and the output voltage of the full-bridge inverter module (2) increases. v AB +V in Auxiliary inductor L a quilt v AB Clamped, not participating in resonance; voltage of the parallel resonant capacitor on the secondary side. v Cp The polarity is positive, therefore rectifier diodes D1 and D4 are turned on; the third stage continues until the auxiliary inductor current is reached. i La Until the reversal time t3; Phase 4 [t3-t4]: The LLCC resonant converter is in phase [t3-t4], during which the resonant current... i r and the current flowing through the auxiliary inductor i La All are positive, with the current flowing through the auxiliary inductor being [missing information]. i La The voltage rises from 0 to its maximum value; primary-side switches S1 and S4 are turned on, and the output voltage of the full-bridge inverter module (2) increases. v AB +V in Auxiliary inductor L a quilt v AB Clamped, not participating in resonance; voltage of the parallel resonant capacitor on the secondary side. v Cp Since the polarity is positive, rectifier diodes D1 and D4 continue to conduct; the fourth stage continues until the switch S1 is turned off. Phase 5 [t4-t5]: The LLCC resonant converter is in phase [t4-t5]. Ignoring the dead time, at time t4, switch S1 is turned off, and the resonant current... i r The current flowing through the auxiliary inductor is positive. i La When the current is positive, the current flowing through the second switching module is the sum of the resonant current and the auxiliary inductor current, and it flows from the source of switching transistor S2 to the drain of switching transistor S2; at this time, the current (- i La - i r The current does not immediately flow from the switching transistor S2, but first flows from the body diode D of the switching transistor S2. S2 Before the switching transistor S2 is turned on, the voltage across the switching transistor S2 has dropped to 0, and the switching transistor S2 achieves ZVS turn-on; throughout the 5th stage, the primary-side switching transistors S2 and S4 are turned on, and the output voltage of the full-bridge inverter module (2) is... v AB The voltage of the parallel resonant capacitor on the secondary side is 0. v Cp Since the polarity is positive, rectifier diodes D1 and D4 continue to conduct; stage 5 continues until switch S4 is turned off. The first half-cycle and the second half-cycle of the LLCC resonant converter are symmetrical.

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