WO2023165346A1

WO2023165346A1 - Full-bridge inverter soft switching circuit and control method

Info

Publication number: WO2023165346A1
Application number: PCT/CN2023/076721
Authority: WO
Inventors: 许真剑
Original assignee: 许真剑
Priority date: 2022-03-01
Filing date: 2023-02-17
Publication date: 2023-09-07
Also published as: CN114553040A

Abstract

Disclosed is a full-bridge inverter soft switching circuit, comprising: a full-bridge inverter basic circuit and a soft switching circuit, the soft switching circuit being connected to a front end of the full-bridge inverter basic circuit; the soft switching circuit being divided into a PWM type soft switching circuit and a frequency modulation type soft switching circuit according to different control modes; and a driving circuit, the driving circuit being configured to drive the full-bridge inverter basic circuit and the soft switching circuit. Disclosed is a corresponding control method. The control method comprises PWM and frequency modulation type control methods. High-frequency and soft switching functions are achieved, shoot-through protection is obtained, and shoot-through loss caused by a freewheeling diode and the inter-electrode capacitance is eliminated, so that an inductor or a transformer of a load can select a smaller iron core and less inductance, and precious materials such as iron cores and copper wire windings are saved.

Description

A full-bridge inverter soft switching circuit and control method

technical field

The invention relates to the field of power electronics, in particular to a full-bridge inverter soft switch circuit and a control method.

Background technique

The full-bridge inverter circuit and its soft switching function are generally used in high-power high-frequency equipment, such as: switching power supply, induction heating equipment, electric welding machine, DC charging pile, etc.

The existing commonly used inverter methods include: single-ended flyback, single-ended forward, push-pull, half-bridge, full-bridge, etc., as well as related topologies of the above circuits. The main function of the soft switch is to replace the traditional hard switch, that is, the switching tube (SCR, mos tube, igbt, etc.), because the hard switch is easy to burn out when working at high frequency, and the power waste is serious.

Soft switching refers to zero-voltage turn-on and zero-current turn-off. That is to add some components to the circuit, and use the switch tube drive signal control at the same time to create a zero-voltage or zero-current state, so that the switch tube is turned on and off in this state, thereby greatly reducing the loss of the switch tube.

However, the existing full-bridge inverter circuit uses a large number of hard switches, resulting in large damage, inability to operate at high frequency, and the switch tube requires high current and high power. Furthermore, the switch tubes at both ends of the inductance bridge arm have the risk of direct connection, which will cause problems due to Mistakes lead to simultaneous opening and short circuit, and there is a through loss, which makes it difficult to use high frequency. Internal use of mos tubes or igbts due to the existence of inter-electrode capacitance and freewheeling diodes makes the fast recovery diodes turn from forward to reverse, and it takes tens to hundreds of nanoseconds to recover, and this time can pass Although the time of a large reverse current is very short, the impact on high frequency operation cannot be ignored.

Therefore, there is an urgent need for a full-bridge inverter soft switch that can solve the above one or more problems circuits and control methods.

Contents of the invention

In order to solve one or more problems existing in the prior art, the present invention provides a full-bridge inverter soft switching circuit and a control method. The technical solution adopted by the present invention to solve the above problems is: a full-bridge inverter soft switch circuit, including: a full-bridge inverter basic circuit, the full-bridge inverter basic circuit is provided with two bridge arms and four switch tubes V1, V2, V3, V4, the switch tubes V1, V2 are on the same bridge arm, the switch tubes V3, V4 are on the same bridge arm, the collectors of the switch tubes V1, V3 are connected to the same input terminal, the emitters of the switch tubes V2, V4 are connected to the same output end;

A soft switch circuit, the soft switch circuits are respectively a PWM type soft switch circuit and a frequency modulation type soft switch circuit, and the soft switch circuit is electrically connected to the front end of the full-bridge inverter basic circuit;

A driving circuit, the driving circuit is electrically connected to the soft switching circuit and the full-bridge inverter basic circuit, and the driving circuit is used to drive the soft switching circuit and the full-bridge inverter basic circuit;

The PWM type soft switching circuit includes: a first switching tube, a second switching tube, a first inductor, a first resistor, a fast recovery diode and a first capacitor, and the first switching tube and the first inductor are connected in series in the main On the circuit, the first resistor and the fast recovery diode are connected in series and recorded as a protection circuit, the protection circuit is connected in parallel with the first inductor, the protection circuit is connected in series with the first switching tube, and the first The capacitor is connected in series with the second switching tube and recorded as a working circuit, the working circuit is connected in parallel with the protection circuit, the working circuit is connected in series with the first switching tube, and the working circuit is connected in series with the first inductor ;

After subtracting the second switching tube, the PWM type soft switching circuit becomes the regulation Frequency soft switching circuit.

Further, the first switch tube and the second switch tube are equipped with freewheeling diodes or capacitors inside or outside.

And a control method of a full-bridge inverter soft switching circuit, the switching of the two bridge arms of the full-bridge inverter basic circuit is carried out when the first switching tube is disconnected, and the first switch in the PWM type soft switching circuit Turn off the second switch tube before turning it on, and turn on the second switch tube before turning off the first switch tube;

When the soft switching circuit is the PWM type soft switching circuit, the duty cycle of the full bridge is taken as T, and the control method includes:

First half cycle: the second switching tube is turned off, the switching tubes V1 and V4 are turned on/off, then the switching tubes V3 and V2 are turned off/on, then the first switching tube is turned on, and the first switching tube Turning on the second switching tube after X microseconds is turned on, then turning off the first switching tube, and then delaying for Y microseconds;

The second half cycle: the second switching tube is turned off, the switching tubes V3 and V2 are turned on/off, then the switching tubes V1 and V4 are turned off/on, then the first switching tube is turned on, and the first switching tube Turning on the second switching tube after X microseconds is turned on, then turning off the first switching tube, and then delaying for Y microseconds;

The steps of the first half cycle and the second half cycle are repeated as required, and X microseconds is the conduction time of the first switching tube, which is also the power-on time of the load in the first half cycle and the second half cycle.

Further, when the soft switching circuit is the frequency modulation soft switching circuit, the duty cycle of the full bridge is taken as T, and the control method includes:

First half cycle: switch tubes V1 and V4 are turned on/off, then switch tubes V3 and V2 are turned off/ conduction, then the first switching tube is turned on for X microseconds and then turned off, and then delayed for Y microseconds;

The second half cycle: the switching tubes V3 and V2 are turned on/off, then the switching tubes V1 and V4 are turned off/on, then the first switching tube is turned on for X microseconds and then turned off, and then delayed for Y microseconds;

Further, the value of X is less than 0.5T, and Y is equal to 0.5T-X.

Further, when shutting down, all switching tubes are disconnected.

Further, when the input voltage and output power change greatly, the PWM type soft switching circuit and its control method are adopted;

When the input voltage and output power change little, the frequency modulation type soft switch circuit and its control method are adopted.

The beneficial value obtained by the present invention is: the present invention connects the soft switching circuit to the existing full-bridge inverter basic circuit, cooperates with the corresponding switching tube drive circuit and control method, and divides the PWM type and the control method according to different requirements. The frequency modulation control circuit and method realize the purpose of high frequency and soft switching function, and obtain through protection, eliminate the through loss caused by freewheeling diode and inter-electrode capacitance, so that the load inductance or transformer can choose a smaller iron core and inductance, saving precious materials such as iron core and copper wire winding; it has strong versatility, no specific equipment and circuits are required to cooperate, and there is no specific requirement for the secondary side circuit of the transformer, thereby greatly improving the compatibility; the said The second switching tube belongs to the auxiliary circuit and can be used in a small size. The switching tube in the basic circuit of the full-bridge inverter performs soft switching after the first switching tube cuts off the main circuit. The loss is very low and can be used in a small size. use, so even if one of the first switching tubes is added, the cost of the overall switching tube is reduced; The energy savings gained are even more pronounced when on the road. The above greatly improves the practical value of the present invention.

Description of drawings

Fig. 1 is the implementation schematic diagram I of PWM type soft switching circuit of the present invention;

Fig. 2 is the implementation schematic II of the PWM type soft switching circuit of the present invention;

Fig. 3 is the implementation schematic diagram I of the FM type soft switching circuit of the present invention;

Fig. 4 is the implementation schematic diagram II of the frequency modulation type soft switching circuit of the present invention;

Fig. 5 is the implementation schematic diagram III of the frequency modulation type soft switching circuit of the present invention;

Fig. 6 is the implementation waveform diagram of the PWM type soft switching circuit of the present invention;

Fig. 7 is an implementation waveform diagram of the frequency modulation soft switching circuit of the present invention.

Detailed ways

In order to make the above objects, features and advantages of the present invention more comprehensible, specific implementations of the present invention will be described in detail below in conjunction with the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention can be implemented in many other ways different from this description, and those skilled in the art can make similar improvements without departing from the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

As shown in Figures 1-5, the present invention discloses a full-bridge inverter soft switch circuit, including: a full-bridge inverter basic circuit, the full-bridge inverter basic circuit is provided with two bridge arms and four switches The tubes V1, V2, V3, V4, the switch tubes V1, V2 have the same bridge arm, the switch tubes V3, V4 have the same bridge arm, the collectors of the switch tubes V1, V3 are connected to the same input terminal, the emitters of the switch tubes V2, V4 are connected to the same output terminal;

Soft switch circuit, the soft switch circuit is PWM type soft switch circuit and frequency modulation A type soft switching circuit, the soft switching circuit is electrically connected to the front end of the full-bridge inverter basic circuit;

The PWM type soft switching circuit includes: a first switching tube V0, a second switching tube Q0, a first inductor L0, a first resistor R01, a fast recovery diode D01 and a first capacitor C0, the first switching tube V0 and the The first inductance L0 is connected in series on the main circuit, the first resistor R01 and the fast recovery diode D01 are connected in series and recorded as a protection circuit, the protection circuit is connected in parallel with the first inductance L0, and the protection circuit is connected with the The first switch tube V0 is connected in series, the first capacitor C0 and the second switch tube Q0 are connected in series and are recorded as a working circuit, the working circuit is connected in parallel with the protection circuit, and the working circuit is connected to the first switch The tube V0 is connected in series, and the working circuit is connected in series with the first inductor L0;

After subtracting the second switching tube Q0 (that is, the working circuit does not include the second switching tube Q0, only the first capacitor C0), the PWM soft switching circuit becomes the frequency modulation type soft switching circuit. The number of switching tubes in the driving circuit in Fig. 1-Fig. 5 is set as required.

It should be noted that the full-bridge inverter basic circuit is an existing common technology, and there are many different variations. The first switching tube V0 generally needs to be used with a large switching tube. The higher the operating frequency of the first capacitor C0 and the first inductance L0, the smaller the value; in the PWM type soft switching circuit, the second The switch tube Q0 only bears the discharge current from the first capacitor C0, so the power consumption is not large, and the switch tube is small in size. As shown in Figure 4 and Figure 5 first, The second switch tube is provided with a freewheeling diode or capacitor inside or outside, and the capacitor and the freewheeling diode can be used instead of each other. The load L of the full-bridge inverter basic circuit includes an inductor and a transformer.

It should be pointed out that the operation of the protection circuit is: when the circuit fails, the first switching tube V0 needs to be turned off immediately. At this time, it may be turned off by a hard switch, and the fast recovery diode D01 is needed to provide the The first inductor L0 freewheels; the first resistor R01 is used to limit the reverse current formed when the first switch tube V0 is turned on, so the recovery time of the fast recovery diode D01 should be as small as possible to reduce the Describe the power consumption of the first resistor R01. In the case of normal operation, the power consumption of the first resistor R01 and the fast recovery diode D01 is very small, and small components can be selected.

And a control method of a full-bridge inverter soft-switching circuit, which includes: the switching of the two bridge arms of the full-bridge inverter basic circuit is carried out under the condition that the first switching tube V0 is disconnected, and the PWM-type soft-switching circuit Turn off the second switch tube Q0 before the first switch tube V0 is turned on, and turn on the second switch tube Q0 before the first switch tube V0 is turned off;

First half cycle: the second switching tube Q0 is turned off, the switching tubes V1 and V4 are turned on/off, then the switching tubes V3 and V2 are turned off/on, and then the first switching tube V0 is turned on, and in the first After the switching tube V0 is turned on for X microseconds, the second switching tube Q0 is turned on, and then the first switching tube V0 is turned off, followed by a delay of Y microseconds;

The second half cycle: the second switching tube Q0 is turned off, the switching tubes V3 and V2 are turned on/off, then the switching tubes V1 and V4 are turned off/on, and then the first switching tube V0 is turned on. After the switching tube V0 is turned on for X microseconds, the second switching tube Q0 is turned on, and then the second switching tube Q0 is turned off. Describe the first switching tube V0, and then delay Y microseconds;

As mentioned above, the switching order of the two bridge arms can be reversed.

The steps of the first half cycle and the second half cycle are repeated as required, and X microseconds is the conduction time of the first switching tube V0, which is also the power-on time of the load in the first half cycle and the second half cycle. As shown in Figure 1, the load current is repeatedly switched from A to B of the coil L, and then from B to A, so that the load coil L receives high-frequency alternating current.

When the soft switching circuit is the frequency modulation soft switching circuit, the duty cycle of the full bridge is taken as T, and the control method includes:

The first half cycle: the switching tubes V1 and V4 are turned on/off, then the switching tubes V3 and V2 are turned off/on, then the first switching tube V0 is turned on for X microseconds and then turned off, and then delayed for Y microseconds;

The second half cycle: the switching tubes V3 and V2 are turned on/off, then the switching tubes V1 and V4 are turned off/on, then the first switching tube V0 is turned on for X microseconds and then turned off, and then delayed for Y microseconds;

As mentioned above, the switching order of the two bridge arms can be reversed.

The steps of the first half cycle and the second half cycle are repeated as required, and X microseconds is the conduction time of the first switching tube V0, which is also the power-on time of the load in the first half cycle and the second half cycle. As shown in Figure 3, the load current is switched from A to B of the coil L, and then from B to A repeatedly, so that the load coil L receives high-frequency alternating current.

It should be pointed out that the value of X is less than 0.5T, and Y is equal to 0.5T-X. At shutdown, all switching tubes are disconnected. In order to better adapt to the use scenario, when the input voltage and output power change greatly, the PWM type soft switching circuit and its control method are adopted; when the input voltage and output power do not change much, the frequency modulation soft switching circuit is adopted circuit and its control method.

It should be noted that, in the PWM type soft switching circuit and its control method, the lead The on-time X is used to regulate the output power, the larger the value of X, the larger the output power, otherwise the smaller the output power. In the frequency modulation soft switching circuit and its control method, the output power is regulated by the duty cycle T, the smaller the T, the greater the frequency, the greater the output power, otherwise the smaller the output power, when high frequency is required , select the smaller first inductance L0 and the first capacitance C0, then the conduction time X can be made very small; especially, the smaller the frequency here, does not mean that the conduction time of the half cycle of the load coil L The longer the on-time, the larger the iron core and inductance are required. The on-time is always X microseconds. The design and selection of the load coil L, the selection of the iron core and inductance, only need to be considered according to this point .

Specifically, as shown in FIG. 6, when T=t1, a cycle is entered, at this time, the second switching tube Q0 is turned off, the switching tubes V1 and V4 are turned on, the switching tubes V2 and V3 are turned off, and then the first switching tube Q0 is turned on. Switch tube V0. When the first switch tube V0 is turned on, the first inductor L0 generates an electromotive force as large as Vd to prevent sudden changes in current, so that the first switch tube V0 can be turned on with zero voltage. After the first switching tube V0 is turned on, the current of the load coil L increases continuously from A to B, and at the same time, the freewheeling diode QD0 of the second switching tube Q0 charges the first capacitor C0, so After the voltage of the first capacitor C0 continues to increase until it is twice the input voltage Vd, because the second switching transistor Q0 is turned off and the freewheeling diode QD0 is blocked, the first capacitor C0 cannot be discharged, and the first capacitor C0 cannot be discharged. The voltage Vc0 of a capacitor remains unchanged at twice the Vd, and the load coil L continues to receive current;

When T=t2, when the turn-off time of the first switching tube V0 is reached, the second switching tube Q0 is first turned on, so that the first capacitor C0 is discharged, the current of the first inductor L0 drops rapidly, and at the same time The voltage Vc0 of the first capacitor also discharges to the load coil L and drops, and when the current of the first inductor L0 drops to 0, the voltage Vc0 of the first capacitor remains is higher than the input voltage Vd, then the first inductor L0 is flyback, the current direction is to the left, the freewheeling diode D0 of the first switching tube is turned on, and the first capacitor C0 discharges to the input power supply Vd, at this time the drive The first switching tube V0 is turned off to realize zero-current shutdown;

After the first switching tube V0 is disconnected, the parasitic capacitances of the first capacitor C0 and the switching tubes V3 and V2 discharge to the load coil L. Since the load coil L tries to maintain the original current at this time, the current is relatively large, and the The first capacitor C0 is small, and the parasitic capacitances of the switch tubes V3 and V2 are even smaller, and they are discharged in a short time. According to the formula IT=CU, current*time=capacitance*voltage, hundreds of nanoseconds can be achieved through circuit design within.

After the first capacitor C0 is fully discharged, the load coil L passes through the freewheeling diode D3 of the switching tube V3 and the switching tube V1 to carry on the current from point A——point B——D3——V1——point A. At the same time, the freewheeling diode D2 of the switch tube V4 and the switch tube V2 freewheels, from point A——point B——V4——D2——point A. At this time, the voltages across the parasitic capacitances of the switching tubes V3 and V2 have been discharged to zero. This state has only been maintained.

When T=t3, when it is time to switch the other half cycle, the second switching tube Q0 is turned off, and since the load coil L maintains continuous current, when the switching tubes V3 and V2 are turned on, zero-voltage conduction is realized. Then the switch tubes V1 and V4 are disconnected. During the disconnection process, since the voltage of the first capacitor C0 is 0 at this time, the freewheeling current of the load coil L turns to the first capacitor C0 for charging, so that the switch tubes V1 and V4 achieve zero current shutdown. The loop of L freewheeling is: Point A——Point B——D3——C0——D2——Point A. When the second switch tube Q0 is turned on, it only bears the discharge current of the first capacitor C0, and when it is turned off, Vc0 is close to 0, and the consumption is not large. The first switching tube V0 is turned on, and the second half cycle continues, and the first switching tube V0 is turned off after X microseconds, and the process is the same as that of the first half cycle.

It should be pointed out that, for example, in a full bridge, it is possible to disconnect the bridge arm that is being turned on first, and then turn on the other pair of bridge arms that are still turned off. For example, when T=t3 above, the switching tubes V1 and V4 can be disconnected first, and then the switching tubes V3 and V2 are turned on, then the soft switching process is: the second switching tube Q0 is disconnected, and then the switching tubes V1 and V4 are disconnected During the disconnection process, since the voltage of the first capacitor C0 is 0 at this time, the freewheeling current of the load coil L is diverted to the first capacitor C0, so that the switch tubes V1 and V4 are turned off with zero current. The freewheeling loop of the load coil L is: Point A——Point B——D3——C0——D2——Point A. Next, before the process of freewheeling the load coil L to charge the first capacitor C0 is completed, the switch tubes V3 and V2 are turned on to realize zero-voltage turn-on.

In the PWM type soft switching circuit, the values of the first capacitor C0 and the first inductance L0 cannot be selected too large, and it is better to make their resonant frequency higher, so as to reduce the power consumption of the load coil L. empty ratio loss. The driving circuit can be realized by a single-chip microcomputer or a PWM driving chip+op amp+timer. When a single-chip microcomputer is used, the stability is ensured by independently supplying power to the drive circuit, differential-mode common-mode filtering, isolation, and metal shell shielding.

Specifically, as shown in Fig. 6 and Fig. 7, Fig. 7 is a working waveform diagram of one period of the frequency modulation soft switching circuit, Fig. 6 and Fig. 7 realize the same working principle of soft switching, but remove the first After the second switching tube, its high frequency capability is stronger. In particular, referring to FIG. 3 , FIG. 4 , and FIG. 7 , after the first switch tube V0 is turned on, after the voltage of the first capacitor C0 rises to 2Vd, since there is no freewheeling current of the second switch tube Q0 The diode D01 is blocked, the first capacitor C0 can be released to reduce the voltage, the voltage of the first capacitor is not maintained at 2Vd, and then the first inductor L0 flyback, the direction is left, the first The freewheeling diode D0 of the switching tube V0 is turned on, and the first capacitor C0 discharges to the input power supply Vd, And the first switching tube V0 is turned off at this time to obtain soft switching.

In the frequency modulation type soft switching circuit, when the first capacitor C0 discharges to the input power supply Vd, the current of the first inductor L0 is reversed, and the energy is fed back to the power supply, so that the inductive magnetic communication is quickly reset. This process takes a certain period of time. The duty cycle of the load is lost, but because the frequency can be made very high, under the same power condition, the inductance and magnetic core of the load coil L or transformer can still be made smaller, saving material costs.

In summary, the present invention connects the soft switching circuit to the existing full-bridge inverter basic circuit, cooperates with the corresponding switch tube drive circuit and control method, and divides PWM control and frequency modulation control according to different needs The circuit and method achieve the purpose of high frequency and soft switching functions, and obtain through protection, eliminate the through loss caused by the freewheeling diode and inter-electrode capacitance, so that the load inductance or transformer can use smaller iron core and inductance , save precious materials such as iron core and copper wire winding; it has strong versatility, does not need specific equipment and circuits to cooperate, and has no specific requirements for the secondary side circuit of the transformer, thereby greatly improving the compatibility; the second switch The tube belongs to the auxiliary circuit and can be used in a small size. The switching tube in the basic circuit of the full-bridge inverter performs soft switching after the first switching tube cuts off the main circuit. The loss is very low and can be used in a small size. Therefore Even if one of the first switching tubes is added, the cost of the overall switching tube is reduced; when applied to a high-power circuit, the obtained energy saving effect is more remarkable. The above greatly improves the practical value of the present invention.

The above-mentioned embodiments only represent one or more implementations of the present invention, and the description thereof is more specific and detailed, but should not be construed as a limitation to the patent of the present invention. It should be noted that, for those of ordinary skill in the art, without departing from the concept of the present invention, some modifications and improvements can also be made, and these all belong to the protection scope of the present invention. around. Therefore, the protection scope of the present invention should be determined by the appended claims.

Claims

A full-bridge inverter soft switching circuit, comprising: a full-bridge inverter basic circuit, the full-bridge inverter basic circuit is provided with two bridge arms and four switch tubes V1, V2, V3, V4, switch tubes V1, V2 is the same bridge arm, the switch tubes V3 and V4 are the same bridge arm, the collectors of the switch tubes V1 and V3 are connected to the same input terminal, and the emitters of the switch tubes V2 and V4 are connected to the same output terminal. It is characterized in that the soft switching circuit, said The soft switching circuits are respectively a PWM type soft switching circuit and a frequency modulation type soft switching circuit, and the soft switching circuit is electrically connected to the front end of the full bridge inverter basic circuit;

A driving circuit, the driving circuit is electrically connected to the soft switching circuit and the full-bridge inverter basic circuit, and the driving circuit is used to drive the soft switching circuit and the full-bridge inverter basic circuit;

The PWM type soft switching circuit includes: a first switching tube, a second switching tube, a first inductor, a first resistor, a fast recovery diode and a first capacitor, and the first switching tube and the first inductor are connected in series in the main On the circuit, the first resistor and the fast recovery diode are connected in series and recorded as a protection circuit, the protection circuit is connected in parallel with the first inductor, the protection circuit is connected in series with the first switching tube, and the first The capacitor is connected in series with the second switching tube and recorded as a working circuit, the working circuit is connected in parallel with the protection circuit, the working circuit is connected in series with the first switching tube, and the working circuit is connected in series with the first inductor ;

After subtracting the second switching tube, the PWM soft switching circuit becomes the frequency modulation soft switching circuit.
The full-bridge inverter soft-switching circuit according to claim 1, wherein the first switch tube and the second switch tube are equipped with freewheeling diodes or capacitors inside or outside.
A control method for a full-bridge inverter soft switching circuit, characterized in that the full-bridge inverter The switching of the two bridge arms of the basic circuit is carried out when the first switching tube is turned off. In the PWM type soft switching circuit, the second switching tube is turned off before the first switching tube is turned on, and the first switching tube is turned off. Turning on the second switch tube before turning on;

When the soft switching circuit is the PWM type soft switching circuit, the duty cycle of the full bridge is taken as T, and the control method includes:

First half cycle: the second switching tube is turned off, the switching tubes V1 and V4 are turned on/off, then the switching tubes V3 and V2 are turned off/on, then the first switching tube is turned on, and the first switching tube Turning on the second switching tube after X microseconds is turned on, then turning off the first switching tube, and then delaying for Y microseconds;

The second half cycle: the second switching tube is turned off, the switching tubes V3 and V2 are turned on/off, then the switching tubes V1 and V4 are turned off/on, then the first switching tube is turned on, and the first switching tube Turning on the second switching tube after X microseconds is turned on, then turning off the first switching tube, and then delaying for Y microseconds;

The steps of the first half cycle and the second half cycle are repeated as required, and X microseconds is the conduction time of the first switching tube, which is also the power-on time of the load in the first half cycle and the second half cycle.
The control method of a full-bridge inverter soft switching circuit according to claim 3, wherein when the soft switching circuit is a frequency modulation soft switching circuit, the duty cycle of the full bridge is taken as T, and the control method comprises:

First half cycle: the switching tubes V1 and V4 are turned on/off, then the switching tubes V3 and V2 are turned off/on, then the first switching tube is turned on for X microseconds and then turned off, and then delayed for Y microseconds;

The second half cycle: the switching tubes V3 and V2 are turned on/off, then the switching tubes V1 and V4 are turned off/on, then the first switching tube is turned on for X microseconds and then turned off, and then delayed for Y microseconds;

The steps of the first half cycle and the second half cycle are repeated as required, and X microseconds is the conduction time of the first switching tube, which is also the power-on time of the load in the first half cycle and the second half cycle.
The control method of a full-bridge inverter soft switching circuit according to claim 3 or 4, wherein the value of X is less than 0.5T, and Y is equal to 0.5T-X.
The control method of a full-bridge inverter soft-switching circuit according to claim 3, characterized in that, when the system is shut down, all the switching tubes are disconnected.
The control method of a full-bridge inverter soft switching circuit according to claim 4, characterized in that, when the input voltage and output power vary greatly, the PWM type soft switching circuit and its control method are adopted;

When the input voltage and output power change little, the frequency modulation type soft switch circuit and its control method are adopted.