Phase-shifted full-bridge converter with low switching element losses

Abstract

The application relates to the field of power electronics, in particular to a low-switching-element-loss phase-shifted full-bridge converter, which comprises a full-bridge inverter circuit, a transformer, a resonant circuit connected between the full-bridge inverter circuit and a primary winding of the transformer, and a rectification filter circuit connected to a secondary winding of the transformer; when the secondary winding of the transformer is short-circuited, the resonant circuit is in a capacitive interval before the off time of a lagging arm element in the full-bridge inverter circuit, so that the resonant cavity current of the resonant circuit is reversed and zeroed, and the lagging arm element meets the soft-off condition. The application reduces the total switching loss of the full-bridge inverter circuit and the volume of the phase-shifted full-bridge converter, and improves the power density of the phase-shifted full-bridge converter without adding extra devices and sacrificing the performance of the power supply.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a phase-shifted full-bridge converter with low switching element losses. Background Technology

[0002] With the popularization and development of electronics, communications, welding and other fields, high-power switching power supplies using phase-shifted full-bridge topology have shown great advantages in terms of power conversion efficiency, control accuracy and power density.

[0003] A typical phase-shifting full-bridge converter topology is as follows: Figure 1 As shown, the phase-shifted full-bridge converter consists of a full-bridge inverter circuit, a resonant circuit, a transformer, and a rectifier and filter circuit. Due to the loss of duty cycle and the structure of the lagging arm circuit, it is difficult to achieve soft turn-off of the lagging arm components, which limits the further improvement of the power density of the phase-shifted full-bridge converter. Currently, the common method to achieve soft turn-off of the lagging arm components is to increase the primary-side inductance. However, this method adds additional magnetic components, increasing the primary-side loss, size, and circulating current loss in the freewheeling stage. At the same time, it reduces the output gain of the phase-shifted full-bridge converter, affecting the wide-range output performance of the phase-shifted full-bridge converter. Summary of the Invention

[0004] Therefore, it is necessary to provide a phase-shifted full-bridge converter with low switching element losses to address the aforementioned technical problems.

[0005] In a first aspect, embodiments of this application propose a phase-shifted full-bridge converter with low switching element losses, including a full-bridge inverter circuit, a transformer, a resonant circuit connected between the full-bridge inverter circuit and the primary side of the transformer, and a rectifier filter circuit connected to the secondary side of the transformer.

[0006] When the secondary winding of the transformer is short-circuited, before the turn-off time of the lagging arm element in the full-bridge inverter circuit, the resonant circuit is in the capacitive range, causing the resonant cavity current of the resonant circuit to cross zero in the reverse direction, so that the lagging arm element meets the soft turn-off condition.

[0007] In some embodiments, the resonant circuit includes a resonant capacitor and a resonant inductor connected in series;

[0008] By configuring the parameters of the resonant capacitor and resonant inductor, the hysteresis arm element is made to meet the soft turn-off condition.

[0009] In some embodiments, the parameters of the resonant capacitor and the resonant inductor satisfy the following conditions:

[0010]

[0011] in, C b This indicates the capacitance value of the resonant capacitor.L 1 represents the inductance value of the resonant inductor. Indicates the peak value of the resonant cavity current. This represents the voltage value corresponding to the peak value of the resonant cavity current. Output bus voltage value DC voltage value across the output load. Indicates the turns ratio of the transformer. This indicates the switching frequency of the full-bridge inverter circuit.

[0012] In some embodiments, the full-bridge inverter circuit includes switching elements Q1, Q2, Q3, and Q4, wherein switching elements Q1 and Q2 are leading arm elements, and switching elements Q3 and Q4 are lagging arm elements.

[0013] The expressions for the voltage values ​​of the resonant capacitor and the inductance values ​​of the resonant inductor in the first, second, third, and fourth states of the phase-shifted full-bridge converter are constructed respectively. The peak value of the resonant cavity current is obtained based on these expressions. and the corresponding voltage value ;

[0014] The first state is that both switching elements Q2 and Q4 are turned on, and the secondary winding of the transformer is in a non-short-circuit stage; the second state is that both switching elements Q2 and Q4 are turned on, and the secondary winding of the transformer is in a short-circuit stage; the third state is that both switching elements Q2 and Q3 are turned on, and the secondary winding of the transformer is in a short-circuit stage; the fourth state is that both switching elements Q2 and Q3 are turned on, and the secondary winding of the transformer is in a non-short-circuit stage.

[0015] In some embodiments, the peak value of the resonant cavity current for:

[0016]

[0017] in, This represents the inductance value in the rectifier filter circuit. Indicates output power;

[0018] The voltage value corresponding to the peak value of the resonant cavity current for:

[0019]

[0020] in, ts This indicates the moment when the resonant cavity current crosses zero. t 0 indicates the start time of the first state.t 4 indicates the end time of the fourth state. This represents the resonant cavity current.

[0021] In some embodiments, the rectifier-filter circuit includes a rectifier circuit and a filter circuit; the rectifier circuit includes diodes D1 and D2 respectively connected to the positive and negative terminals of the secondary side of the transformer;

[0022] When diodes D1 and D2 are not simultaneously turned on, the secondary winding of the transformer is not short-circuited; when diodes D1 and D2 are simultaneously turned on, the secondary winding of the transformer is short-circuited.

[0023] In some embodiments, the resonant circuit includes a resonant capacitor;

[0024] By configuring the parameters of the resonant capacitor and the leakage inductance of the transformer, the hysteresis arm element is made to meet the soft turn-off condition.

[0025] In some embodiments, before the lead-arm element in the full-bridge inverter circuit is turned on, the resonant circuit is made to be in the inductive range, so that the lead-arm element meets the soft-turn-on condition.

[0026] In some embodiments, the full-bridge inverter circuit employs full-bridge phase-shift control.

[0027] In some embodiments, the full-bridge inverter circuit employs PWM control.

[0028] The aforementioned low-switching-element-loss phase-shifted full-bridge converter has the following technical advantages: When the secondary winding of the transformer is short-circuited, before the turn-off time of the lagging arm element in the full-bridge inverter circuit, the resonant circuit is in the capacitive range, causing the resonant cavity current of the resonant circuit to cross zero in the reverse direction, so that the lagging arm element meets the soft turn-off condition. This application reduces the total switching loss of the full-bridge inverter circuit, reduces the size of the phase-shifted full-bridge converter, and increases the power density of the phase-shifted full-bridge converter without adding additional components or sacrificing the performance of the phase-shifted full-bridge converter. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the topology of a phase-shifting full-bridge converter in the prior art;

[0030] Figure 2 This is a schematic diagram of the low-switching-element-loss phase-shifted full-bridge converter in the embodiments of this application;

[0031] Figure 3 This is an equivalent schematic diagram of the phase-shifted full-bridge converter with low switching element losses in the embodiments of this application at stage one;

[0032] Figure 4This is an equivalent schematic diagram of the phase-shifted full-bridge converter with low switching element losses in the embodiments of this application in stage two.

[0033] Figure 5 This is a schematic diagram of the drive signals, voltages across, and resonant cavity currents of switching elements Q2 and Q4 in the embodiments of this application. Figure 1 ;

[0034] Figure 6 This is a schematic diagram of the drive signals, voltages across, and resonant cavity currents of switching elements Q2 and Q4 in the embodiments of this application. Figure 2 ;

[0035] Figure 7 This is an equivalent circuit diagram of each state of the phase-shifted full-bridge converter in the embodiments of this application;

[0036] Figure 8 The resonant capacitance value C in the example embodiment of this application b A schematic diagram showing the selection of parameters for the resonant inductance value L1;

[0037] Figure 9 This is a comparison curve of switching transistor losses in an example embodiment of this application;

[0038] Figure 10 This is a schematic diagram of a phase-shifted full-bridge converter with low switching element losses in another embodiment of this application. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this application clearer, the application is described and illustrated below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application. Furthermore, it is understood that although the efforts made in such a development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, modifications to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0040] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application may be combined with other embodiments without conflict.

[0041] Unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms “a,” “an,” “an,” “the,” and similar words used in this application do not indicate quantity limitation and may indicate singular or plural. The terms “comprising,” “including,” “having,” and any variations thereof used in this application are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or device that includes a series of steps or modules (units) is not limited to the listed steps or units, but may also include steps or units not listed, or may include other steps or units inherent to these processes, methods, products, or devices. The terms “connected,” “linked,” “coupled,” and similar words used in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. “Multiple” used in this application means two or more. “And / or” describes the relationship between related objects, indicating that three relationships may exist; for example, “A and / or B” can represent: A alone, A and B simultaneously, and B alone. The terms “first,” “second,” “third,” etc., used in this application are merely to distinguish similar objects and do not represent a specific ordering of the objects.

[0042] Figure 2 A schematic diagram of a phase-shifted full-bridge converter with low switching element losses is provided in one embodiment of this application. Figure 2 As shown, the phase-shifting full-bridge converter includes a full-bridge inverter circuit, a transformer TF, a resonant circuit connected between the full-bridge inverter circuit and the primary side of the transformer, and a rectifier and filter circuit connected to the secondary side of the transformer.

[0043] The full-bridge inverter circuit, connected to the input power supply Vin, consists of switching elements Q1, Q2, Q3, and Q4, and is used to convert the input power supply... V in The output DC power is inverted into AC power.

[0044] Switching elements Q1, Q2, Q3, and Q4 are MOSFET switching transistors. Among them, switching elements Q1 and Q2 are leading-arm elements, and switching elements Q3 and Q4 are lagging-arm elements.

[0045] The resonant circuit includes a resonant capacitor Cb and a resonant inductor L1 connected in series, which are used to achieve soft turn-on or soft turn-off of the switching elements in the full-bridge inverter circuit.

[0046] Transformer TF is used for voltage transformation.

[0047] The rectifier-filter circuit includes a rectifier circuit and a filter circuit. The rectifier circuit includes rectifier diodes D1 and D2 connected to the two output terminals on the secondary side of the transformer, and the filter circuit includes inductor L2 and capacitor C2. The rectifier-filter circuit is used to rectify and filter the AC power before outputting it to the load.

[0048] The operation of a full-bridge inverter circuit is divided into two stages. Stage one is defined as the two diodes D1 and D2 on the secondary side of the transformer not conducting simultaneously, and stage two is defined as the two diodes D1 and D2 conducting simultaneously. In stage two, the primary and secondary sides of the transformer are electrically disconnected, and the energy of the junction capacitance of the lagging arm element can only be drawn away through the energy of the resonant inductor L1. Therefore, if the lagging arm element is to achieve soft turn-off, the resonant inductor L1 needs to have a large inductance value.

[0049] In the existing technology, in order to achieve soft turn-off of the lagging arm of the phase-shifted full-bridge converter, the inductance value of the resonant inductor L1 on the primary side of the transformer is increased or other components are added. This increases the primary side loss, size, and circulating current loss in the freewheeling stage, while reducing the output gain of the power supply and affecting the wide-range output performance of the phase-shifted full-bridge converter.

[0050] To address this technical problem, this application proposes a time-sharing resonant high power density phase-shifted full-bridge converter. Without requiring the use of larger inductors or reduced switching frequencies that would negatively impact the power density and performance of the phase-shifted full-bridge converter, this application ensures that when the secondary winding of the transformer is short-circuited, the resonant circuit is in the capacitive range before the turn-off time of the lagging arm element in the full-bridge inverter circuit. This causes the resonant cavity current of the resonant circuit to cross zero in the reverse direction, making the lagging arm element meet the soft-turn-off condition. This reduces the total switching losses of the full-bridge inverter circuit, decreases the size of the phase-shifted full-bridge converter, and increases its power density.

[0051] The following is in conjunction with the appendix Figures 3-5 The two-stage control process of a phase-shifted full-bridge converter with low switching element losses is described in detail.

[0052] In this embodiment, the full-bridge inverter circuit adopts full-bridge phase-shift control, and the positive periodic analysis of the resonant cavity current is used as an example for illustration.

[0053] Phase 1: such as Figure 3 and Figure 5 As shown, diode D1 is conducting, and diode D2 is cut off. ta is the turn-on time of switching element Q2. Before this time, the full-bridge inverter circuit is in stage one. The prerequisite for soft turn-on of switching element Q2 is that the primary resonant inductance L1 and the secondary inductance L2 of the transformer have sufficient energy to remove the charge from the junction capacitance of switching element Q2, ensuring that when switching element Q2 is turned on at time ta, the voltage drop across it is 0V, thus achieving soft turn-on of switching element Q2.

[0054] In some embodiments, to ensure the stability of the output DC voltage, the secondary inductance L2 of the phase-shifted full-bridge converter transformer is generally large, and the lead-arm components are more likely to achieve soft turn-on.

[0055] Phase Two: such as Figure 4 and Figure 5 As shown, tb represents the turn-off moment of switch element Q4. Before this moment, the circuit is in stage two. Due to the simultaneous conduction of diodes D1 and D2 on the secondary side of the transformer, the secondary winding of the transformer is short-circuited. In this stage, the primary and secondary sides of the transformer are electrically disconnected. Only the resonant capacitor Cb and the resonant inductor L1 in the primary circuit of the transformer participate in resonance. By configuring the parameters of the resonant capacitor Cb and the resonant inductor L1, the circuit is in the capacitive range when switch element Q4 is turned off. The resonant cavity current flows in reverse through the body diode of switch element Q4 before the bridge arm operates. Therefore, during the turn-off transient of switch element Q4, the voltage across its terminals is clamped to 0V. The turn-off of switch element Q4 is a zero-voltage turn-off, that is, no turning-off loss occurs, thus achieving soft turn-off of switch element Q4.

[0056] The principle for configuring the parameters of resonant capacitor Cb and resonant inductor L1 is as follows:

[0057] One duty cycle of a phase-shifted full-bridge converter is actually composed of four states combined. Figure 6 Detailed analysis of each state:

[0058] First state: such as Figure 6 As shown, the t0~t1 stage is the first state stage, during which switching elements Q2 and Q4 are turned on. The circuit in this stage can be equivalent to... Figure 7 As shown in (a), let time t0 be the initial time of this stage, at which time the resonant capacitor voltage is... The resonant inductor current is Then the resonant inductor current of the resonant circuit in this stage and resonant capacitor voltage The expression is:

[0059]

[0060] in The transformer turns ratio This represents the DC voltage value across the output load.

[0061] Second state: such as Figure 6 As shown, the t1~t2 stage is the second state stage. During this stage, switching elements Q2 and Q4 are turned on, and the transformer is in a state where the primary and secondary sides are disconnected. The circuit in this stage can be equivalent to... Figure 7 As shown in (b), let time t1 be the initial time of this stage, at which time the resonant capacitor voltage is... The resonant inductor current is Then the expressions for each state quantity of the resonant circuit in this stage are:

[0062]

[0063] Third state: such as Figure 6 As shown, the t2~t3 stage is the third state stage. During this stage, switching elements Q2 and Q3 are turned on. Since both diodes on the secondary side are fully conducting, this stage is a duty cycle loss stage. The circuit in this stage can be equivalent to... Figure 7 As shown in (c), let time t2 be the initial time of this stage, at which time the resonant capacitor voltage is... The resonant inductor current is Then the expressions for each state quantity of the resonant circuit in this stage are:

[0064]

[0065] in This is the output bus voltage value.

[0066] Fourth state: such as Figure 6 As shown, the t3~t4 stage is the fourth state stage. During this stage, switching elements Q2 and Q3 are turned on, and energy is transferred between the primary and secondary sides through the transformer. The circuit in this stage can be equivalent to... Figure 7 As shown in (d), let time t3 be the initial time of this stage, at which time the resonant capacitor voltage is... The resonant inductor current is Then the expressions for each state quantity of the resonant circuit in this stage are:

[0067]

[0068] From the phase-shifted full-bridge converter, the peak value of the resonant cavity current is the current value at time t0. as follows:

[0069]

[0070] in, For switching frequency, This refers to the output power.

[0071] When the phase-shifted full-bridge operates in steady state, the resonant capacitor voltage period is symmetrical. Based on the expressions for the first to fourth states, the value at time t0 can be obtained. as follows:

[0072]

[0073] Where ts is the moment when the resonant cavity current crosses zero.

[0074] To achieve soft turn-off of the lagging arm elements Q3 and Q4 in the phase-shifted full-bridge, it is necessary to ensure that the resonant cavity current crosses zero in the reverse direction before the turn-off time of the lagging arm element Q4. That is, the zero-crossing time of the resonant cavity current must be before time t2. In actual design, to quickly enter the electrical disconnection state of the transformer's primary and secondary sides (t1~t2 stage) and allow the resonant capacitor Cb and resonant inductor L1 to begin resonance, the design parameters will make the t1~t2 time length much longer than the t0~t1 time length. Therefore, the t0~t1 time can be ignored in the design. Under this premise... , Let the time from t1 to ts be t1, t1~t2 time is t2, that is, satisfying t1< A soft shutdown can be achieved at t2. t1 and The expression for t2 is as follows:

[0075]

[0076]

[0077] The resonant capacitance value C that satisfies the soft turn-off condition b The range of the resonant inductance value L1 is as follows:

[0078]

[0079] Theoretically, under steady-state conditions, by connecting the beginning and end conditions of all states within a cycle and solving the simultaneous state equations, the analytical expressions for each state variable of the phase-shifted full-bridge converter over the entire cycle can be obtained. However, as the above analysis clearly shows, directly solving for the analytical expressions of the state variables is extremely difficult, and may even result in no analytical solution after solving the simultaneous equations. Therefore, simulation calculations using numerical simulation software are typically a more efficient analytical method.

[0080] Figure 8 The resonant capacitance C for achieving soft turn-off of the hysteresis arm element across the entire load range in this example phase-shifted full-bridge topology is given. b A schematic diagram showing the selection of parameters for the resonant inductance value L1 is shown below. Figure 8 As shown, the resonant capacitance value C b The parameters of the resonant inductance value L1 can be selected on the left side of the curve to satisfy the soft turn-off condition of the hysteresis arm element across the entire load range.

[0081] Figure 9 Two different resonant capacitance values ​​C are given. bThe curves comparing the switching losses of different output powers under the resonant inductance value L1 are shown. Since the turn-off loss of the leading arm is consistent with existing solutions, a separate loss curve is not plotted here. The total loss is the sum of the leading arm conduction loss, the lagging arm switching loss, and the lagging arm conduction loss. As can be seen from the curves, using the parameters selected in the proposed technical solution (… Compared to the parameters used in existing solutions () The switching losses and conduction losses of the switching elements are reduced, and the total loss is reduced more as the load increases.

[0082] In summary, under the premise of time-sharing operation of the circuit, the proposed solution can simultaneously achieve soft turn-on of the leading arm and soft turn-off of the lagging arm at different stages through different technical methods, thereby reducing switching losses and circulating current losses, eliminating the need for additional components, and improving the power density of the power supply.

[0083] It is understandable that the switching elements Q1 and Q3 are structurally the same as those Q2 and Q4, and their soft-switching method is also the same as that of the switching elements Q2 and Q4, so it will not be elaborated here.

[0084] In other embodiments, the full-bridge inverter circuit can also be controlled by PWM to make the resonant circuit intermittently in the inductive or capacitive range, thereby achieving soft turn-on of the leading arm element and soft disconnection of the lagging arm element.

[0085] Figure 10 A schematic diagram of a phase-shifted full-bridge converter with low switching element losses is provided in another embodiment of this application. (See attached diagram.) Figure 10 As shown, the resonant circuit includes only the resonant capacitor Cb. In this embodiment, by configuring the parameters of the resonant capacitor Cb and the leakage inductance Lb of the transformer, the hysteresis arm element meets the soft-turn-off condition.

[0086] In this embodiment, the leakage inductance Lb of the transformer is used to replace the resonant inductance L1, and the parameters of the resonant capacitor Cb and the leakage inductance Lb satisfy the following conditions:

[0087]

[0088] By having the leakage inductance Lb of the transformer resonate with the resonant capacitor Cb, the hysteresis arm element meets the soft turn-off condition, thereby further improving the power density.

[0089] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0090] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A phase-shifted full-bridge converter with low switching element losses, characterized by The full-bridge inverter circuit, the transformer, the resonant circuit connected between the full-bridge inverter circuit and the primary winding of the transformer, and the rectification filter circuit connected to the secondary winding of the transformer; the resonant circuit comprises a resonant capacitor and a resonant inductor connected in series; When the secondary winding of the transformer is short-circuited, the resonant circuit is in a capacitive interval before the off time of the lagging arm element in the full-bridge inverter circuit, so that the resonant cavity current of the resonant circuit reverses zero, and the parameters of the resonant capacitor and the resonant inductor are configured to make the lagging arm element meet the soft off condition. The parameters of the resonant capacitor and the resonant inductor satisfy the following conditions: wherein, C b represents a capacitance value of a resonance capacitor, L 1 represents an inductance value of a resonance inductor, represents a resonance cavity current peak value, represents a voltage value corresponding to the resonance cavity current peak value, represents an output bus voltage value, represents a DC voltage value across an output load, represents a turns ratio of a transformer, represents a switching frequency of a full-bridge inverter circuit.

2. The low switching element loss phase-shifted full-bridge converter of claim 1, wherein, The full-bridge inverter circuit comprises switching elements Q1, Q2, Q3 and Q4, the switching elements Q1 and Q2 are leading arm elements, and the switching elements Q3 and Q4 are lagging arm elements; The expressions of the voltage value of the resonance capacitor and the inductance value of the resonance inductor when the phase-shift full-bridge converter is in a first state, a second state, a third state and a fourth state are constructed, and the resonance cavity current peak value is obtained according to the expressions and the corresponding voltage value ; The first state is that the switching elements Q2 and Q4 are both turned on, and the secondary winding of the transformer is in an unshort-circuited stage; the second state is that the switching elements Q2 and Q4 are both turned on, and the secondary winding of the transformer is in a short-circuited stage; the third state is that the switching elements Q2 and Q3 are both turned on, and the secondary winding of the transformer is in a short-circuited stage; and the fourth state is that the switching elements Q2 and Q3 are both turned on, and the secondary winding of the transformer is in an unshort-circuited stage.

3. The phase-shifted full-bridge converter with low switching element loss according to claim 2, wherein, The resonant cavity current peak value Is: wherein, represents an inductance value in the rectifying filter circuit, represents an output power; The voltage value corresponding to the resonance cavity current peak value Is: wherein, ts represents the moment of the resonant cavity current zero crossing, t 0 represents the first state start moment, t 4 represents the fourth state end moment, represents the resonant cavity current.

4. The low switching element loss phase-shifted full-bridge converter of claim 1, wherein, The rectification filter circuit comprises a rectification circuit and a filter circuit; the rectification circuit comprises diodes D1 and D2 connected to the positive and negative terminals of the secondary winding of the transformer, respectively; When the diodes D1 and D2 are not turned on at the same time, the secondary winding of the transformer is not short-circuited; when the diodes D1 and D2 are turned on at the same time, the secondary winding of the transformer is short-circuited.

5. The low switching element loss phase-shifted full-bridge converter of claim 1, wherein, The resonant circuit comprises a resonant capacitor; The parameters of the resonant capacitor and the leakage inductance of the transformer are configured to make the lagging arm element meet the soft off condition.

6. The low switching element loss phase-shifted full-bridge converter of claim 1, wherein, Before the leading arm element in the full-bridge inverter circuit is turned on, the resonant circuit is in an inductive interval, so that the leading arm element meets the soft on condition.

7. The low switching element loss phase-shifted full-bridge converter of claim 1, wherein, The full-bridge inverter circuit adopts full-bridge phase-shifted control.

8. The low switching element loss phase-shifted full-bridge converter of claim 1, wherein, The full-bridge inverter circuit adopts PWM control.

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