Detection-free zero-voltage switching-on method based on full-bridge inverter intermittent current mode

Abstract

The invention discloses a detection-free zero-voltage switching-on method based on a full-bridge inverter intermittent current mode, and relates to a power electronic converter. The micro inverter works in an inductive current intermittent conduction mode, zero-voltage switching-on of a switching tube can be realized on the basis of not adding any additional device and auxiliary circuit, and the efficiency of the inverter is effectively improved. The traditional scheme generally depends on a sampling circuit to detect a resonance current zero crossing point between an inductor and a switch tube shunt capacitor to determine the turn-on time, so that the hardware complexity is increased, and the zero-voltage turn-on effect depends on the reliability of a detection circuit. And when the switching frequency is relatively high, the inherent delay characteristic of the sampling circuit can limit the zero-voltage switching-on realization effect. The invention provides a zero-voltage turn-on moment determination strategy based on inverter behavior modeling in an intermittent conduction mode, a detection circuit is not needed, and the zero-voltage turn-on moment can be accurately determined only through discrete time control by a controller after modeling, so that full-period soft switching is realized, and the hardware complexity is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronic converters, and particularly relates to a detection-free zero-voltage turn-on method based on a discontinuous current mode of a full-bridge inverter. BACKGROUND

[0002] A photovoltaic grid-connected inverter is a key interface between a photovoltaic system and a power grid, and its performance directly affects the energy conversion efficiency and operation reliability of the system. To meet the design requirements of high power density and low cost, a micro inverter usually reduces the size of passive devices by increasing the switching frequency. However, high switching frequency can cause significant switching loss, thereby affecting the system efficiency.

[0003] Soft switching technology can effectively reduce switching loss and electromagnetic interference while maintaining a high operating frequency by reducing the voltage or current of a device at the switching instant, and thus becomes a key approach to solving the above-mentioned contradiction. However, existing soft switching schemes usually rely on additional auxiliary circuits or devices, resulting in increased system size and cost.

[0004] Discontinuous current mode (DCM) utilizes the natural resonance between the junction capacitance of a switching device and the inductance on the inverter side to naturally oscillate the device voltage to zero after switching off, thereby achieving zero-voltage turn-on (ZVS) without additional hardware. Therefore, accurately identifying the instant when the device voltage reaches zero is crucial for reliable implementation of ZVS.

[0005] However, a conventional full-bridge micro inverter operating in DCM usually relies on real-time current sampling to detect the zero-crossing point of inductor current to achieve accurate control of the switching tube. This not only increases the complexity of the current sampling circuit, but also introduces control deviation due to sampling delay, thereby reducing the implementation accuracy of ZVS. SUMMARY

[0006] The present application aims to solve the problems of current sampling dependence, circuit complexity, and low control accuracy in the implementation of ZVS in the DCM mode of a full-bridge inverter in the prior art, and provides a detection-free zero-voltage turn-on method based on the discontinuous current mode of a full-bridge inverter, which reduces the hardware complexity of the system and improves the switching efficiency. By model open-loop calculation or closed-loop control, the on-time T on of the switching tube in each switching period is obtained, and the time interval T off required for the next zero voltage to arrive is calculated based on the derived analytical model. When the time interval is reached, the controller drives the switching tube to turn on, thereby achieving accurate zero-voltage turn-on throughout the entire operating period without the need for real-time current sampling circuit, reducing the hardware complexity of the system and improving the control accuracy.

[0007] To achieve the above-mentioned application purposes, the present application provides the following technical solutions.

[0008] A detection-free zero-voltage turn-on method based on full-bridge inverter discontinuous current mode, the specific steps can be: using full-bridge inverter circuit with LCL filter, using the inductance, capacitance parameters of the inverter, input bus voltage and AC side voltage, establish the inductance current model, resonant capacitance voltage model and average current model under discontinuous current mode; based on the established model combined with the set target switching period, calculate the conduction time T on and the time interval T off from switching off to the next zero-voltage turn-on time of each switching cycle through average current model open-loop calculation or closed-loop control adjustment; the controller executes discrete time control according to the calculation result, switches the bridge arm switching tube of high-frequency control according to the polarity of the AC side voltage, and drives the switching tube to conduct after the time interval T off , ensures that the voltage across the switching tube drops to zero before the switching tube conducts, and realizes full-cycle zero-voltage turn-on of the full-bridge inverter.

[0009] The inverter topology used is a full-bridge inverter circuit with LCL filter; wherein the full-bridge inverter circuit includes input bus voltage V DC , two bridge arms with four switching tubes Q1, Q2, Q3, Q4, four resonant capacitors C1, C2, C3, C4, common-mode resonant inductor L , filter inductor, filter capacitor and grid voltage V AC ; the controller is connected to the control end of the four switching tubes, the four resonant capacitors are connected in parallel across the corresponding switching tubes, and the two input ends of the common-mode resonant inductor are connected to the midpoints of the two bridge arms, and the output ends are connected in parallel to one end of the filter capacitor.

[0010] The set target switching period can divide each switching cycle into 6 state stages, and the key time parameter calculation can determine the duration of each state stage and the time interval T off from switching off to zero-voltage turn-on through formula solution based on the established model, and satisfy the following relationship:

[0011]

[0012] In the formula, T1 represents the duration of stage 1, T2 represents the duration of stage 2, T3 represents the duration of stage 3, T4 represents the duration of stage 4, T r represents the duration of stage 5; V DC is the input bus voltage; V AC is the grid voltage; L represents the common-mode resonant inductor; C represents the value of a single resonant capacitor; i L (t1) represents the corresponding common-mode resonant inductor current value at the end of stage 1; T onis the on-time of the switch tube in each switching cycle; T off is the time interval from the switch-off of the switch to the next zero-voltage on-time; π is the circular constant.

[0013] In a preferred embodiment, to establish the average current model, each switching cycle is divided into the following 6 stages:

[0014] Stage 1: the switch tube is in the on state, and the duration is T on ;

[0015] Stage 2: after the switch tube is turned off, energy transfer is performed between the inductor and the capacitor until the capacitor voltage is discharged to 0;

[0016] Stage 3: the switch tube body diode is turned on, and the inductor current continues to discharge to 0;

[0017] Stage 4: after the body diode is turned off, the inductor and the capacitor continue to transfer energy;

[0018] Stage 5: the other body diode is turned on until the inductor current is discharged to 0;

[0019] Stage 6: pure LC resonant waveform oscillation;

[0020] When stage 6 ends, the system reenters stage 1, and the cycle continues.

[0021] Through the average current model, the average equivalent current in each switching cycle changes in a sinusoidal manner, thereby outputting a sinusoidal wave current; the on-time T on of stage 1 can be obtained through open-loop calculation of the average current model or can be adjusted in real time through a closed-loop control strategy.

[0022] The inductance and capacitance parameters used in the modeling process can be nominal values of the devices or equivalent values obtained through online parameter identification and self-calibration, so as to improve the robustness in the case of device parameter drift.

[0023] The number of pure LC resonance cycles T r can be adaptively adjusted according to the switching frequency requirement to meet the control requirements under different operating conditions.

[0024] The timing control and calculation steps of the method are realized by any one of a digital signal processor (DSP), a microcontroller (MCU), a field programmable gate array (FPGA), or a combination thereof.

[0025] The polarity switching can specifically include the following steps:

[0026] In the positive half cycle of the alternating current side voltage, the first bridge arm upper tube and the second bridge arm lower tube are controlled to perform high-frequency switching, and the other two switches remain turned off.

[0027] During the negative half-cycle of the AC side voltage, the lower transistor of the first bridge arm and the upper transistor of the second bridge arm are controlled by high-frequency switching, while the other two switches remain off.

[0028] The filtering structure of the full-bridge inverter of this invention can be other forms that include inductors.

[0029] Compared with the prior art, the outstanding advantages and technical effects of the present invention are as follows:

[0030] This invention innovatively employs a detection-free ZVS implementation scheme, abandoning the traditional reliance on current sampling. It calculates the conduction time and zero-voltage turn-on time interval using inductor current, resonant capacitor voltage, and average current models, reducing the need for sensors and signal conditioning modules, thus lowering costs and reducing size. Simultaneously, it avoids accuracy loss caused by sampling noise and delay. This invention divides the switching cycle into several state stages, finely analyzing the energy transfer process in each stage and accurately calculating T. off Achieving full-cycle ZVS turn-on; pure LC resonant period T r The number of inverters can be flexibly adjusted according to the switching frequency, maintaining stable performance even under scenarios such as device aging and load changes, and is compatible with different operating conditions. It is compatible with mainstream digital control platforms, requiring no complex synchronization processing, and is easy to implement in engineering applications. This invention achieves zero-voltage turn-on without relying on current sensing devices, effectively reducing system hardware costs and complexity, while improving the inverter's switching performance and overall efficiency in discontinuous current mode. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a single-phase full-bridge microinverter in the prior art.

[0032] Figure 2 The waveforms are the drive waveform, midpoint voltage VAB waveform, inductor current, and voltage waveforms of capacitors C1 and C2 within one switching cycle under discontinuous current mode; where (a) is the positive half-power frequency cycle and (b) is the negative half-power frequency cycle.

[0033] Figure 3 This is a schematic diagram of six operating modes of a single-phase full-bridge inverter during the positive half-cycle of the power frequency, provided for an embodiment of the present invention; wherein, (a) is the [0–t0] stage, (b) is the [t0–t1] stage, (c) is the [t1–t2] stage, (d) is the [t2–t3] stage, (e) is the [t3–t4] stage, and (f) is the [t4–t5] stage;

[0034] Figure 4This is a schematic diagram of six operating modes of a single-phase full-bridge inverter during the negative half-cycle of the power frequency, provided for an embodiment of the present invention; wherein, (a) is the [0–t0] stage, (b) is the [t0–t1] stage, (c) is the [t1–t2] stage, (d) is the [t2–t3] stage, (e) is the [t3–t4] stage, and (f) is the [t4–t5] stage;

[0035] Figure 5 A flowchart of a control method for a single-phase full-bridge inverter provided in an embodiment of the present invention;

[0036] Figure 6 These are the waveforms of the inductor current and AC current during simulation in discontinuous current mode.

[0037] Figure 7 These are waveforms showing the implementation of zero-voltage switching at various random moments. Among them, (a) represents a moment during the positive half-cycle of the current; and (b) represents a moment during the negative half-cycle of the current. Detailed Implementation

[0038] The following embodiments will describe in detail the specific implementation of the method of the present invention with reference to the accompanying drawings.

[0039] Figure 1 This diagram illustrates the single-phase full-bridge grid-connected inverter topology used in this invention. The inverter topology employed is a full-bridge inverter circuit coupled with an LCL filter. The inductor current is denoted as i. L The drain-source voltages of switching transistors Q1 and Q2 are denoted as V. c1 and V c2 All are defined according to the directions shown in the diagram. V DC For the input DC bus voltage, V AC This is the AC voltage of the power grid at this time. During the positive half-cycle, switches Q1 and Q3 alternately turn on and off at high frequency, while Q2 and Q4 remain off. During the negative half-cycle, switches Q2 and Q4 operate at high frequency, while Q1 and Q3 remain off. This operating mode avoids complex switching within the same half-cycle, greatly simplifying the control process.

[0040] Figure 2 Provide the switch drive signal and the inductor current i. L The drain-source voltage waveforms of Q1 and Q2 are also shown to further illustrate the operation of the switching devices. Figure 2 In the example, (a) represents the result of the positive half-cycle, while... Figure 2 (b) represents the result of the negative half-cycle. In actual operation, when the inductor current i L After dropping to zero, the parallel capacitor of the switching transistor and the inverter-side inductor form an LC resonant circuit, causing current oscillation. This resonant process can be divided into two main stages: the first stage T1, during which the inductor current briefly enters a negative value; the second stage T...reson Then it exhibits pure LC resonant oscillation.

[0041] In discontinuous current mode, the second-stage resonant period T can be adjusted. r The number of resonant cycles controls the switching frequency. When the frequency is too high, the frequency can be reduced by appropriately increasing the number of resonant cycles.

[0042] Figure 3 The equivalent circuit of the inverter during the positive half-cycle is shown, a process that can be divided into six stages. Taking the positive half-cycle as an example, its operation is as follows:

[0043] Phase I [0–t0]: such as Figure 3 As shown in (a), when Q1 and Q4 are turned on, the inductor current i L A linear increase can be expressed by the following formula:

[0044]

[0045] And T on Then the inductor current i during the entire switching cycle can be calculated. L The average value is determined by the alternating current.

[0046] Phase II [t0–t1]: such as Figure 3 As shown in (b), after Q1 and Q4 are turned off, i L The parallel capacitor C1 of Q1 is charged while the parallel capacitor C2 of Q2 is discharged, and energy transfer begins. During this process, the inductor current i... L The voltage between C1 and C1 satisfies the following equation:

[0047]

[0048] Calculate how much capacitor C1 is charged to V. DC The required time can be used to determine the duration of Phase II:

[0049]

[0050] Phase III [t1–t2]: as Figure 3 As shown in (c), after charging and discharging is complete, the inductor current i L With the freewheeling current flowing through the body diodes of Q2 and Q3, the current begins to decrease linearly. The duration of this phase satisfies the following equation:

[0051]

[0052] Where i L (t1) represents the inductor current at time t1.

[0053] Phase IV [t2–t3]: asFigure 3 As shown in (d), under the action of reverse voltage, capacitor C1 begins to discharge, i L The inductor current i begins to increase in the reverse direction during this process. L The voltage across capacitor C1 connected in parallel with Q1 satisfies the following equation:

[0054]

[0055] The duration of phase IV is:

[0056]

[0057] Stage V [t3–t4]: such as Figure 3 As shown in (e), when capacitor C1 discharges to zero, the corresponding body diodes of Q1 and Q4 conduct, and the inductor current begins to decrease again. The duration of this process is:

[0058]

[0059] Phase VI [t4–t5]: such as Figure 3 As shown in (f), when the inductor current drops to zero, it begins to enter the resonant period T of pure LC oscillation. r The duration of this process is:

[0060]

[0061] In summary, the duration of each stage between the switch being turned off and the next zero-voltage turn-on can be precisely refined, thereby obtaining a total time interval T. off The corresponding formula is shown below:

[0062]

[0063] It can be seen that for each conduction time T on Each has a corresponding conduction interval T off From T on The timer starts when the end is reached, and it continues until the calculated time reaches T. off The on-time for the next cycle is determined at this point. This method can calculate the time when the voltage is zero without the need for sampling circuitry. Through the above calculations, this invention locates the ZVS instant without requiring any voltage or current sensing circuitry, simplifying the hardware.

[0064] Figure 4 The equivalent circuit of the inverter during the negative half-cycle is shown, a process that can be divided into six stages. Taking the negative half-cycle as an example, its operation is as follows:

[0065] Phase I [0–t0]: such as Figure 4As shown in (a), when Q2 and Q3 are turned on, the inductor current i L Linear descent can be expressed by the following formula:

[0066]

[0067] And T on Then the inductor current i during the entire switching cycle can be calculated. L The average value is determined by the alternating current.

[0068] Phase II [t0–t1]: such as Figure 4 As shown in (b), after Q2 and Q3 are turned off, i L The parallel capacitor C1 of Q1 discharges while the parallel capacitor C2 of Q2 charges, and energy transfer begins. During this process, the inductor current i... L The voltage between C2 and C2 satisfies the following equation:

[0069]

[0070] Calculate how much capacitor C2 is charged to V. DC The required time can be used to determine the duration of Phase II:

[0071]

[0072] Phase III [t1–t2]: as Figure 4 As shown in (c), after charging and discharging is complete, the inductor current i L The current begins to rise linearly through the body diodes of Q1 and Q4, and the duration of this phase satisfies the following equation:

[0073]

[0074] Where i L (t1) represents the inductor current at time t1.

[0075] Phase IV [t2–t3]: as Figure 4 As shown in (d), under the action of reverse voltage, capacitor C2 begins to discharge, i L The inductor current i begins to increase in the reverse direction during this process. L The voltage across capacitor C2 connected in parallel with Q2 satisfies the following equation:

[0076]

[0077] The duration of phase IV is:

[0078]

[0079] Stage V [t3–t4]: such asFigure 4 As shown in (e), when capacitor C2 discharges to zero, the corresponding body diode of Q2 conducts, and the inductor current begins to decrease again. The duration of this process is:

[0080]

[0081] Phase VI [t4–t5]: such as Figure 4 As shown in (f), when the inductor current drops to zero, it begins to enter the resonant period T of pure LC oscillation. r The duration of this process is:

[0082]

[0083] In summary, the duration of each stage between the switch being turned off and the next zero-voltage turn-on can be precisely refined, thereby obtaining a total time interval T. off The corresponding formula is shown below:

[0084]

[0085] Figure 5 This invention presents the control flow for zero-voltage turn-on (ZVS) of a single-phase full-bridge inverter, and calculates the on-time T of the switching transistors using a closed-loop control algorithm and analytical model. on and the waiting time T from shutdown to the next zero-voltage turn-on. off The system then drives the switching transistor to turn on and off based on the calculation results, achieving zero-voltage turn-on. The specific steps are as follows:

[0086] Step 1: Sample the power frequency AC current to obtain the current information on the grid side, and calculate the on-time T of the switching transistor in the current switching cycle based on the closed-loop control algorithm and the sampled current and other parameters. on After the calculation is completed, the drive switch is turned on to start the operation of the current switching cycle.

[0087] Step 2: When the conduction duration of the switching transistor reaches the set value T on When the current conduction phase ends, the controller issues a command to turn off the switching transistor.

[0088] Step 3: Based on the current conduction time T on The time interval T from the switch being turned off to the next zero voltage arrival is calculated using an analytical model. off The analytical model, based on inverter topology and inductor / capacitor parameters, is used to describe the energy transfer and voltage oscillation between the inductor and resonant capacitor after the switching transistor is turned off.

[0089] Step 4: When the main controller detects that the running time after the switching transistor is turned off reaches the calculated T...off When the voltage drops to zero, the drive switch is turned on again, achieving zero-voltage turn-on. This turn-on method effectively reduces switching losses and improves the efficiency and reliability of the inverter.

[0090] Figure 6 Given the inductor current i in discontinuous current mode. L1 (Blue waveform, scale 5A / div) and the average current i corresponding to each switching cycle avg (Red waveform, scale 1A / div) Simulated waveforms that vary with time (time base 2ms / div) and are interconnected.

[0091] The circuit is converted and used in conjunction with an LCL filter. The inductor current is denoted as i. L The drain-source voltages of switching transistors Q1 and Q2 are denoted as V. c1 and V c2 All are defined according to the directions shown in the diagram. V DC For the input DC bus voltage, V AC This is the AC voltage of the power grid at this time. During the positive half-cycle, switches Q1 and Q3 alternately turn on and off at high frequency, while Q2 and Q4 remain off. During the negative half-cycle, switches Q2 and Q4 operate at high frequency, while Q1 and Q3 remain off. This operating mode avoids complex switching within the same half-cycle, greatly simplifying the control process.

[0092] Figure 7 shows the waveforms of zero-voltage turn-on (ZVS) in a power electronic circuit at different random times. Figure 7 In the diagram, (a) and (b) represent the driving pulses (PWM1, PWM2) and inductor current (i) of the relevant power devices, respectively. L1 ), and the drain-source voltage Q1-V across power devices Q1 and Q2. DS Q2-V DS Waveform. As can be seen from the marked ZVS region, the power device can complete the turn-on operation in a near-zero voltage state, effectively reducing the losses during the switching process. Experiments show that the circuit of this invention has the soft-switching characteristics of stably achieving zero-voltage turn-on at random times.

[0093] This invention eliminates the need for detection circuits. After modeling, the zero-voltage turn-on time can be accurately determined by discrete-time control through a controller, thereby achieving full-cycle soft switching and reducing hardware complexity.

[0094] The above embodiments are merely preferred embodiments of the present invention and should not be considered as limiting the scope of the present invention. All equivalent variations and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A detection-free zero-voltage turn-on method based on the discontinuous current mode of a full-bridge inverter, characterized in that... The specific steps are as follows: Using a full-bridge inverter circuit with an LCL filter, and utilizing the inverter's inductor and capacitor parameters, input bus voltage, and AC side voltage, establish the inductor current model, resonant capacitor voltage model, and average current model under discontinuous current mode; based on the established models and the set target switching cycle, calculate the conduction time T of each switch in each switching cycle. on and the time interval T from when the switch is turned off to when the next zero-voltage turn-on occurs. off The controller adjusts the current through open-loop calculation or closed-loop control using an average current model. Based on the calculation results, it performs discrete-time control, switching the high-frequency controlled bridge arm switching transistors according to the AC side voltage polarity, and controlling the time interval T through timing control. off The subsequent drive switch is turned on to ensure that the voltage across the switch drops to zero before the switch is turned on, thus achieving zero-voltage turn-on of the full-bridge inverter throughout its entire cycle.

2. The detection-free zero-voltage turn-on method based on the discontinuous current mode of a full-bridge inverter as described in claim 1, characterized in that... The inverter topology used is a full-bridge inverter circuit with an LCL filter; the full-bridge inverter circuit includes the input bus voltage V. DC The bridge has four switching transistors (Q1, Q2, Q3, Q4) in two arms, four resonant capacitors (C1, C2, C3, C4), a common-mode resonant inductor (L), a filter inductor, a filter capacitor, and the mains voltage (V). AC The controller is connected to the control terminals of the four switching transistors respectively. The four resonant capacitors are connected in parallel across the two ends of the corresponding switching transistors. The two input terminals of the common-mode resonant inductor are connected to the midpoints of the two bridge arms respectively, and one end of the filter capacitor is connected in parallel between its output terminals.

3. The detection-free zero-voltage turn-on method based on the discontinuous current mode of a full-bridge inverter as described in claim 1, characterized in that... The set target switching cycle is divided into 6 state stages. Key time parameters are calculated, and based on the established model, the duration of each state stage and the time interval T from switch off to zero voltage turn-on are determined by solving formulas. off And satisfy the following relationship: In the formula, T1 represents the duration of phase 1, T2 represents the duration of phase 2, T3 represents the duration of phase 3, T4 represents the duration of phase 4, and T... r Indicates the duration of phase 5; V DC V is the input bus voltage; AC The mains voltage is represented by L; L represents the common-mode resonant inductance; C represents the value of a single resonant capacitor; i L (t1) represents the common-mode resonant inductor current value at the end of stage 1; T on The on-time of the switching transistor during each switching cycle; T off The time interval between the switch being turned off and the next zero-voltage turn-on; π is the mathematical constant pi.

4. The detection-free zero-voltage turn-on method based on the discontinuous current mode of a full-bridge inverter as described in claim 3, characterized in that... To establish the average current model, each switching cycle is divided into the following 6 stages: Phase 1: The switching transistor is in the on state, with a duration of T. on ; Phase 2: After the switching transistor is turned off, energy is transferred between the inductor and the capacitor until the capacitor voltage discharges to 0. Stage 3: The switching diode is turned on, and the inductor current continues to discharge to 0; Stage 4: After the body diode is turned off, the inductor and capacitor continue to transfer energy; Stage 5: The other diode turns on until the inductor current discharges to 0; Stage 6: Pure LC resonant waveform oscillation; After phase 6 ends, the system re-enters phase 1, and so on.

5. The detection-free zero-voltage turn-on method based on the discontinuous current mode of a full-bridge inverter as described in claim 4, characterized in that... By using an average current model, the average equivalent current in each switching cycle varies sinusoidally, thus outputting a sinusoidal current; the conduction time T in stage 1... on It can be obtained through open-loop calculation using an average current model, or it can be adjusted in real time using a closed-loop control strategy.

6. The detection-free zero-voltage turn-on method based on the discontinuous current mode of a full-bridge inverter as described in claim 1, characterized in that... The inductance and capacitance parameters used in the modeling process can be either the nominal values ​​of the device or equivalent values ​​obtained through online parameter identification and self-calibration, in order to improve robustness under device parameter drift.

7. The detection-free zero-voltage turn-on method based on the discontinuous current mode of a full-bridge inverter as described in claim 1, characterized in that... Pure LC resonant period T r The number of switches can be adaptively adjusted according to the switching frequency requirements to meet the control requirements under different operating conditions.

8. The detection-free zero-voltage turn-on method based on the discontinuous current mode of a full-bridge inverter as described in claim 1, characterized in that... The timing control and calculation steps of the method are implemented by any one or a combination of digital signal processors, microcontrollers, and field-programmable gate arrays.

9. The detection-free zero-voltage turn-on method based on the discontinuous current mode of a full-bridge inverter as described in claim 1, characterized in that... The specific steps for the polarity switching are as follows: During the positive half-cycle of the AC side voltage, the high-frequency switching control is performed by the upper transistor Q1 of the first bridge arm and the lower transistor Q4 of the second bridge arm, while the other two switches remain off. During the negative half-cycle of the AC side voltage, the lower transistor Q2 of the first bridge arm and the upper transistor Q3 of the second bridge arm are controlled by high-frequency switching, while the other two switches remain off.

10. The detection-free zero-voltage turn-on method based on the discontinuous current mode of a full-bridge inverter as described in claim 1, characterized in that... The filtering structure of a full-bridge inverter can be any form that includes an inductor.

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