Soft switching bridge arm circuit and control method

Abstract

The invention discloses a soft switching bridge arm circuit and a control method, and belongs to the field of soft switching circuits, an inductor is led out from the midpoint of each of two bridge arms of the bridge arm circuit, and zero-current conduction of a switching device is realized in cooperation with conduction and turn-off sequential control of the switching device; on the basis that an inductor is introduced to the midpoint of each of two bridge arms, a capacitor is arranged between the two bridge arms, and zero-voltage turn-off of a switching device is realized based on the charge and discharge principle of the capacitor and through cooperation with turn-on and turn-off time sequence control of the switching device. The zero-current turn-on circuit and the zero-voltage turn-off circuit can adapt to all existing bridge arm type circuits, an LC resonance circuit does not need to be designed independently, and the application range is wide.

Description

Technical Field

[0001] The present invention relates to the field of soft switching circuits, and in particular to a soft switching bridge arm circuit and a control method. Background Art

[0002] Soft switching circuits are widely used in switching power supplies, motor drives, power regulation and other fields to reduce the loss and electromagnetic interference (EMI) generated by switching devices. Figure 1 As shown in the figure, in the traditional hard switching circuit, the voltage and current are not zero during the switching process, and there is overlap, resulting in switching loss; and the voltage and current change quickly, and the waveform has obvious overshoot, resulting in switching noise. Figure 2 As shown, the soft switching circuit adds a resonant element to the original circuit, introduces resonance before and after the switching process, eliminates the overlap of voltage and current, and thus reduces switching loss and switching noise.

[0003] Existing soft switching circuits usually use LC resonant circuits to generate resonance at both ends of the switch device, so that the switch device switches when the voltage or current is close to zero, reducing switching losses. Existing soft switching circuits are usually designed and controlled separately for a specific application circuit, that is, a resonant circuit needs to be designed separately for the original topology circuit, which cannot adapt to all scenarios and is not universal. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems of the prior art and provide a soft switching bridge arm circuit and a control method.

[0005] The objective of the present invention is achieved through the following technical solutions: a soft switching bridge arm circuit, the bridge arm circuit is a single bridge arm circuit, located between the power supply end and the load end; the single bridge arm circuit includes a first bridge arm and a second bridge arm, the upper bridge arm and the lower bridge arm of the first bridge arm are respectively provided with a first switching device and a second switching device, the upper bridge arm and the lower bridge arm of the second bridge arm are respectively provided with a third switching device and a fourth switching device, the four switching devices are connected to a control module, characterized in that the midpoint of the first bridge arm is connected to a first inductor, the midpoint of the second bridge arm is connected to a second inductor, and the first inductor is connected to the second inductor, the common connection point of the first inductor and the second inductor is connected to the power supply end, and the positive pole of the power supply end is provided with an energy transfer inductor, thereby forming a zero current conduction circuit.

[0006] In one example, a first capacitor is provided between the midpoint of the first bridge arm and the midpoint of the second bridge arm, thereby forming a zero voltage turn-off circuit.

[0007] In one example, a first capacitor and a fifth switching device connected in series are provided between the midpoint of the first bridge arm and the midpoint of the second bridge arm. The fifth switching device is connected to the control module. By controlling the shutdown and conduction of the fifth switching device, switching between the zero current conduction circuit and the zero voltage shutdown circuit is achieved, that is, a zero current conduction and zero voltage shutdown switching circuit is formed.

[0008] A soft switching bridge arm circuit of the present invention comprises at least two single bridge arm circuits formed by any one of the above examples or a combination of multiple examples. The single bridge arm circuits can be cascaded, parallel or mixedly connected, and each bridge arm circuit acts as an independent module to realize single bridge arm control in the switching power supply topology.

[0009] The present invention also includes a soft switch bridge arm circuit and a control method for controlling a zero current conduction circuit, with a control module as an execution subject, and the method includes the following steps:

[0010] The switching timing of the switch devices in each bridge arm is controlled to adjust the current changes of the first inductor and the second inductor, thereby delaying the rising speed of the current on the corresponding inductor, turning on the switch device at zero current, and realizing zero current conduction.

[0011] In one example, zero current conduction includes:

[0012] In the positive half cycle of the AC power supply, when the first and third switching devices are in the off state in the initial state:

[0013] When the second switch device is turned off and the fourth switch device is turned on, the current I1 on the first inductor is zero, and after the fourth switch device is turned off, the first switch device is turned on to achieve zero current conduction of the first switch device, and the current I3 flowing through the second inductor and the third switch device is zero;

[0014] When the fourth switch device is turned off and the second switch device is turned on, the current I3 flowing through the third switch device via the second inductor is zero, and the third switch device is turned on after the second switch device is turned off, so that the third switch device is turned on with zero current;

[0015] In the negative half cycle of the AC power supply, when the second switch device, the fourth switch device, and the fifth switch device are in the off state in the initial state:

[0016] When the first switch device is turned off and the third switch device is turned on, the current I2' on the second inductor is zero. After the third switch device is turned off, the second switch device is turned on to achieve zero current conduction of the second switch device. The current I4' flowing through the first inductor and the fourth switch device is zero.

[0017] When the fourth switch device is turned off and the second switch device is turned on, the current I4' flowing through the fourth switch device via the first inductor is zero. After the second switch device is turned off, the fourth switch device is turned on to achieve zero current conduction of the fourth switch device.

[0018] The present invention provides a soft switch bridge arm circuit and a control method for controlling a zero voltage shutdown circuit. The control module is used as an execution subject. The method comprises the following steps:

[0019] The switching timing of the switch devices in each bridge arm is controlled to charge and discharge the first capacitor. Through the charge and discharge process of the first capacitor, the switch device on the zero voltage side of the first capacitor is turned off to achieve zero voltage shutdown.

[0020] In one example, zero voltage shutdown includes:

[0021] When the first switch device, the second switch device, and the third switch device are in the off state and the fourth switch device is in the on state, the first switch device is turned on again. At this time, the voltages at both ends of the fourth switch device are zero, and the voltage difference at both ends is zero. The fourth switch device is turned off, and the voltage at one end of the first capacitor close to the midpoint of the second bridge arm rises slowly, and the fourth switch device is turned off with zero voltage;

[0022] When the second switch device, the third switch device, and the fourth switch device are in the off state, and the first switch device is in the on state, the fourth switch device is turned on, at which time the voltages at both ends of the first switch device are both rectified DC voltages, and the voltage difference between the two ends is zero, and the first switch device is turned off, and the voltage at one end of the first capacitor close to the midpoint of the first bridge arm slowly decreases, and at this time the first switch device is turned off with zero voltage;

[0023] When the first switch device, the second switch device, and the fourth switch device are in the off state and the third switch device is in the on state, the second switch device is turned on, the voltages at both ends of the third switch device are both rectified DC voltages, and the voltage difference between the two ends is zero. When the third switch device is turned off, the voltage at one end of the first capacitor close to the midpoint of the second bridge arm slowly decreases, and at this time, the third switch device is turned off with zero voltage;

[0024] When the first switch device, the third switch device, and the fourth switch device are in the off state and the second switch device is in the on state, the third switch device is turned on. At this time, the voltages at both ends of the second switch device are zero, and the voltage difference between the two ends is zero. The second switch device is turned off, and the voltage at one end of the first capacitor close to the midpoint of the first bridge arm slowly decreases, and the second switch device is turned off with zero voltage.

[0025] The present invention provides a soft switch bridge arm circuit and control method, which is characterized in that it is used to control the zero current conduction and zero voltage shutdown switching circuit, and the method comprises the following steps:

[0026] Controlling the fifth switch device to turn off, controlling the switching timing of the switch devices in each bridge arm, so as to adjust the current change of the first inductor and the second inductor, thereby delaying the rising speed of the current on the corresponding inductor, turning on the switch device at zero current, and realizing zero current conduction;

[0027] The fifth switch device is controlled to be turned on, and the switching timing of the switch devices in each bridge arm is controlled to charge and discharge the first capacitor. Through the charging and discharging process of the first capacitor, the switch device on the zero voltage side of the first capacitor is turned off to achieve zero voltage shutdown.

[0028] In one example, when the fifth switch device is controlled to be turned off, the method includes the following steps:

[0029] In the negative half cycle of the AC power supply, when the first switch device, the third switch device, and the fifth switch device are in the off state in the initial state:

[0030] When the second switch device is turned off and the fourth switch device is turned on, the current I1 on the first inductor is zero, and after the fourth switch device is turned off, the first switch device is turned on to achieve zero current conduction of the first switch device, and the current I3 flowing through the second inductor and the third switch device is zero;

[0031] When the fourth switch device is turned off and the second switch device is turned on, the current I3 flowing through the third switch device via the second inductor is zero, and the third switch device is turned on after the second switch device is turned off, so that the third switch device is turned on with zero current;

[0032] In the negative half cycle of the AC power supply, when the second switch device, the fourth switch device, and the fifth switch device are in the off state in the initial state:

[0033] When the first switch device is turned off and the third switch device is turned on, the current I2' on the second inductor is zero. After the third switch device is turned off, the second switch device is turned on to achieve zero current conduction of the second switch device. The current I4' flowing through the first inductor and the fourth switch device is zero.

[0034] When the fourth switch device is turned off and the second switch device is turned on, the current I4' flowing through the fourth switch device via the first inductor is zero, and the fourth switch device is turned on after the second switch device is turned off, so that the fourth switch device is turned on with zero current;

[0035] When the fifth switch device is controlled to be turned on, the method comprises the following steps:

[0036] When the first switch device, the second switch device, and the third switch device are in the off state and the fourth switch device is in the on state, the first switch device is turned on again, at which time the voltages at both ends of the fourth switch device are both zero, and the voltage difference at both ends is zero, the fifth switch device is turned on, and the fourth switch device is turned off, the voltage at one end of the first capacitor close to the midpoint of the second bridge arm rises slowly, and the fourth switch device is turned off with zero voltage;

[0037] When the second switch device, the third switch device, and the fourth switch device are in the off state, and the first switch device is in the on state, the fourth switch device is turned on, at which time the voltages at both ends of the first switch device are both rectified DC voltages, and the voltage difference between the two ends is zero, and the first switch device is turned off, and the voltage at one end of the first capacitor close to the midpoint of the first bridge arm slowly decreases, and at this time the first switch device is turned off with zero voltage;

[0038] When the first switch device, the second switch device, and the fourth switch device are in the off state and the third switch device is in the on state, the second switch device is turned on, the voltages at both ends of the third switch device are both rectified DC voltages, and the voltage difference between the two ends is zero. When the third switch device is turned off, the voltage at one end of the first capacitor close to the midpoint of the second bridge arm slowly decreases, and at this time, the third switch device is turned off with zero voltage;

[0039] When the first switch device, the third switch device, and the fourth switch device are in the off state and the second switch device is in the on state, the third switch device is turned on, at which time the voltages at both ends of the second switch device are zero and the voltage difference between the two ends is zero, the fifth switch device is turned on, and the second switch device is turned off, the voltage at one end of the first capacitor close to the midpoint of the first bridge arm slowly decreases, and the second switch device is turned off with zero voltage.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] 1. In one example, an inductor is introduced at the midpoint of each of the two bridge arms to slow down the rate of current rise. The zero-current conduction of the switching device is achieved by coordinating the on- and off-timing control of the switching device. This can be applied to all existing bridge arm circuit application scenarios. Soft switching processing can be achieved without the need to design an LC resonant circuit separately, thereby reducing switching losses and having a wide range of applications.

[0042] 2. In one example, an inductor is introduced at the midpoint of each of the two bridge arms, and a capacitor is set between the two bridge arms. Based on the capacitor charging and discharging principle and the on-and-off timing control of the switching device, zero-voltage shutdown of the switching device is achieved. This can be applied to all existing bridge arm circuit application scenarios, and soft switching processing can be achieved without the need to design an LC resonant circuit separately, thereby reducing switching losses and having a wide range of applications.

[0043] 3. In one example, an inductor is introduced at the midpoint of each of the two bridge arms, a capacitor is set between the bridge arms, and a fifth switching device connected in series with the capacitor is introduced. By controlling the on and off of the fifth switching device, switching between a zero voltage shutdown circuit and a zero current conduction circuit is achieved, which can well meet the soft switching on and off requirements of the circuit and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The specific implementation methods of the present invention are further described in detail below in conjunction with the accompanying drawings. The accompanying drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The same reference numerals are used in these drawings to represent the same or similar parts. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0045] Figure 1 It is a curve diagram of voltage and current during the switching process of the existing hard switching circuit;

[0046] Figure 2 The voltage and current curves during the switching process of the soft switching circuit with the added resonant element;

[0047] Figure 3 A schematic diagram of a zero current conduction circuit provided for an example of the present invention;

[0048] Figure 4 A schematic diagram of a zero voltage shutdown circuit provided for an example of the present invention;

[0049] Figure 5 A schematic diagram of a zero current conduction and zero voltage shutdown circuit provided for an example of the present invention;

[0050] Figure 6 It is the schematic diagram of the existing Boost converter circuit;

[0051] Figure 7 A circuit schematic diagram of applying a zero voltage turn-off circuit to a Boost converter is provided as an example of the present invention. DETAILED DESCRIPTION

[0052] The technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] In the description of the present invention, it should be noted that the directions or positional relationships indicated by "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. are directions or positional relationships based on the drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the use of ordinal numbers (e.g., "first and second", "first to fourth", etc.) is to distinguish objects, and is not limited to this order, and cannot be understood as indicating or implying relative importance.

[0054] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0055] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0056] The present invention provides a soft switch bridge arm circuit, which is a single bridge arm circuit or a double bridge arm circuit, or even a plurality of cascaded bridge arm circuits, and the bridge arm circuit is located between a power supply end and a load end.

[0057] In one example, a single bridge arm circuit is taken as an example. At this time, the single bridge arm circuit includes a first bridge arm and a second bridge arm, and the first bridge arm and the second bridge arm form an H-bridge circuit (single bridge arm), and the second bridge arm is connected to the load end. Optionally, the second bridge arm is connected to the load end via a voltage transformation processing circuit, such as the second bridge arm is connected to the load end via a boost circuit. The upper bridge arm and the lower bridge arm of the first bridge arm are respectively provided with a first switching device Q1 and a second switching device Q2, and the upper bridge arm and the lower bridge arm of the second bridge arm are respectively provided with a third switching device Q3 and a fourth switching device Q4, and Q1, Q2, Q3, and Q4 are connected to the controller in the control module. The switching device is a transistor, such as any one or more of MOSFET, IGBT, BJT, triode, etc. A diode is provided between the source and drain of the transistor or between the emitter and collector of the transistor. Of course, if the transistor emitter and collector are integrated with diodes themselves, no new diodes can be integrated, such as IGBT without integrating diodes. This example uses an IGBT, in which the emitter of Q1 is connected to the collector of Q2, the collector of Q1 is connected to the collector of Q3, the emitter of Q3 is connected to the collector of Q4, the emitter of Q4 is connected to the emitter of Q2, and the gates of Q1, Q2, Q3, and Q4 are connected to a controller (not shown in the figure).

[0058] like Figure 3 As shown, the single bridge arm circuit of the present invention is based on the existing circuit, in which the first inductor L1 is connected to the midpoint of the first bridge arm, the second inductor L2 is connected to the midpoint of the second bridge arm, and the first inductor L1 is connected to the second inductor L2, and the common connection point of the first inductor L1 and the second inductor L2 is connected to the power supply end, and the positive pole of the power supply end is provided with an energy transfer inductor, that is: the common connection point of the first inductor L1 and the second inductor L2 is connected to the energy transfer inductor L, and the energy transfer inductor L is connected to the positive pole of the AC power supply. This example introduces inductors L1 and L2 to slow down the rate of current rise and form a zero current conduction circuit. The zero current conduction working principle of the bridge arm circuit of the present invention is as follows:

[0059] In the positive half cycle of the AC power supply, when Q1 and Q3 are initially in the off state:

[0060] When Q2 is turned off and Q4 is turned on, the current on L1 is 0, so I1=0. At this time, Q4 is turned off, and the current on L2 flows through the diode on Q3. At this time, Q1 is turned on, I1 rises slowly, Q1 is turned on at zero current, and the current I3 on ​​L2 will gradually be pulled to 0 current; similarly, when Q4 is turned off and Q2 is turned on, the current on L2 is 0, so I3=0. At this time, Q2 is turned off, and the current on L1 flows through the diode on Q1. At this time, Q3 is turned on, I3 rises slowly, Q3 is turned on at zero current, and the current I1 on L1 will gradually be pulled to 0 current.

[0061] In the negative half cycle of the AC power supply, when Q2 and Q4 are initially off:

[0062] When Q1 is turned off and Q3 is turned on, the current I1 on L1 will gradually decrease to 0, and the current I2' on L2 is 0. After Q3 is turned off, Q2 is turned on, and the current on L2 begins to flow through the diode on Q3, turning on Q2, achieving zero current conduction of Q2, and the current I4' flowing through Q4 through the first inductor is zero;

[0063] When Q4 is turned off and Q2 is turned on, the current I3 on ​​the second inductor L2 will gradually decrease to 0, and the current I4' flowing through Q4 through the first inductor is zero. After turning off Q2, the current on L1 begins to flow through the diode on Q1, turning on Q4, and achieving zero current conduction of Q4; as Q4 is turned on, the current I3 on ​​L2 will gradually be pulled to 0 current.

[0064] Preferably, the zero current conduction circuit of the present invention is used to replace the existing bridge arm circuit. At this time, at the circuit control level, the soft switch control of the present invention is embedded in the control of the original circuit, which essentially adds a layer of judgment to the original circuit control method. While realizing the level conversion process, zero current conduction can be achieved, thereby reducing the conduction loss of the switching device. Of course, the bridge arm circuit of the present invention can also be integrated with the existing circuit.

[0065] Based on the previous example, Figure 4 As shown, a first capacitor C is provided between the midpoint of the first bridge arm and the midpoint of the second bridge arm to form a zero voltage shutdown circuit. At this time, the connection point between the first capacitor C and the midpoint of the first bridge arm is defined as B1, the connection point between the first capacitor C and the midpoint of the second bridge arm is defined as B2, the end of the first capacitor close to B1 is defined as end 1, and the end of the first capacitor close to B2 is defined as end 2. At this time, the zero voltage shutdown working principle of the bridge arm circuit of the present invention is as follows:

[0066] 1. When Q2 and Q3 are in the off state and Q1 and Q4 are in the on state, there are two situations in which this state is entered:

[0067] (1) This state may be caused by Q1, Q2, and Q3 being in the off state and Q4 being in the on state, and Q1 being turned on to enter this state.

[0068] (2) This state may also be entered when Q2, Q3, and Q4 are in the off state and Q1 is in the on state, and Q4 is turned on.

[0069] If this state is entered from (1), since the voltages at both ends of Q4 are both 0, the voltage difference between the two ends is 0, Q4 is turned off, and the voltage at both ends of the capacitor slowly rises. At this time, Q4 is turned off with zero voltage. After Q4 is completely turned off, Q5 is turned off.

[0070] If this state is entered from (2), since the voltages at both ends of Q1 are Vdc, the voltage difference between the two ends is 0. When Q1 is turned off, the voltage at end 1 of the capacitor slowly decreases. At this time, Q1 is turned off with zero voltage.

[0071] 2. When Q1 and Q4 are in the off state and Q2 and Q3 are in the on state, there are two situations in which this state can be entered:

[0072] (3) This state may be entered when Q1, Q2, and Q4 are in the off state and Q3 is in the on state, and Q2 is turned on.

[0073] (4) This state may also be entered when Q1, Q3, and Q4 are in the off state and Q2 is in the on state, and Q3 is turned on.

[0074] If this state is entered from (3), since the voltage across Q3 is Vdc, the voltage difference across the two ends is 0, Q3 is turned off, and the voltage across the capacitor slowly decreases. At this time, Q3 is turned off with zero voltage.

[0075] If this state is entered from (4), since the voltages at both ends of Q2 are 0, the voltage difference between the two ends is 0, Q2 is turned off, and then the voltage at end 1 of the capacitor slowly decreases. At this time, Q2 is turned off with zero voltage. After Q2 is completely turned off, Q5 is turned off.

[0076] Based on the previous example, Figure 5 As shown, a fifth switch device Q5 connected in series with the first capacitor C is provided between the midpoint of the first bridge arm and the midpoint of the second bridge arm, and Q5 is connected to the control module. At this time, when Q5 is turned off, the circuit is equivalent to a zero current conduction circuit; when Q5 is turned on, the circuit is equivalent to a zero voltage turn-off circuit, and Q5 needs to be turned on a moment before Q4 or Q2 is turned off, and turned off after Q4 or Q2 is completely turned off. Specifically, the working principle of the bridge arm circuit at this time is as follows:

[0077] For zero current conduction control, in the positive half cycle of the AC power supply, the initial state Q1, Q3, and Q5 are in the off state. When Q2 is turned off and Q4 is turned on, at this time, the current on L1 is 0, then I1 = 0, at this time turn off Q4, the current on L2 flows through the diode on Q3, at this time turn on Q1, I1 rises slowly, Q1 is zero current conduction, and the current I3 on ​​L2 will gradually be pulled to 0 current. When Q4 is turned off and Q2 is turned on, at this time, it can be seen from the first item above that the current on L2 is 0, then I3 = 0, at this time turn off Q2, the current on L1 flows through the diode on Q1, at this time turn on Q3, I3 rises slowly, Q3 is zero current conduction, and the current I1 on L1 will gradually be pulled to 0 current.

[0078] For zero current conduction control, in the negative half cycle of the AC power supply, the initial states of Q2, Q4, and Q5 are off.

[0079] When Q1 is turned off and Q3 is turned on, the current I1 on L1 will gradually decrease to 0, and the current I2' on L2 is 0. After Q3 is turned off, Q2 is turned on, and the current on L2 begins to flow through the diode on Q3, turning on Q2, achieving zero-current conduction of Q2, and the current I4' flowing through Q4 through the first inductor is zero; when Q4 is turned off and Q2 is turned on, the current I3 on ​​the second inductor L2 will gradually decrease to 0, and the current I4' flowing through Q4 through the first inductor is zero. After Q2 is turned off, the current on L1 begins to flow through the diode on Q1, turning on Q4, achieving zero-current conduction of Q4; as Q4 is turned on, the current I3 on ​​L2 will gradually be pulled to 0 current.

[0080] For zero voltage turn-off control, the fifth switch device is controlled to be turned on. At this time:

[0081] When Q1, Q2, and Q3 are in the off state and Q4 is in the on state, Q1 is turned on again. At this time, the voltages at both ends of Q4 are both 0, and the voltage difference between the two ends is 0. Q5 is turned on, Q4 is turned off, and the voltage at the capacitor 2 end rises slowly. Q4 is turned off at zero voltage. After Q4 is completely turned off, Q5 is turned off. Q4 is turned off at zero voltage. After Q4 is completely turned off, Q5 is turned off; when Q2, Q3, and Q4 are in the off state and Q1 is in the on state, Q4 is turned on. At this time, the voltages at both ends of Q1 are both Vdc, and the voltage difference between the two ends is 0. Q1 is turned off, and the voltage at the capacitor 1 end slowly decreases. At this time, Q1 is turned off at zero voltage;

[0082] When Q1, Q2, and Q4 are in the off state and Q3 is in the on state, Q2 is turned on, the voltage across Q3 is Vdc, and the voltage difference across the two ends is 0. Q3 is turned off, and the voltage across capacitor 2 slowly decreases. At this time, Q3 is turned off with zero voltage; when Q1, Q3, and Q4 are in the off state and Q2 is in the on state, Q3 is turned on, and the voltage across Q2 is 0, and the voltage difference across the two ends is 0. Q5 is turned on, Q2 is turned off, the voltage across capacitor 1 slowly decreases, and Q2 is turned off with zero voltage. After Q2 is completely turned off, Q5 is turned on.

[0083] In one example, a soft switching bridge arm circuit includes a plurality of single bridge arm circuits described in any one or more of the above examples, and each single bridge arm circuit can be cascaded, paralleled or mixedly connected, and each bridge arm circuit is used as an independent module to realize single bridge arm control in the switching power supply topology. Taking the cascade between single bridge arm circuits as an example, a dual bridge arm circuit or a multi-level conversion circuit is formed. The two inductors derived from the midpoints of the two bridge arms in the first-stage single bridge arm circuit (the single bridge arm circuit close to the power supply end) are connected to the energy transfer inductor, and the energy transfer inductor is connected to the positive pole of the power supply, and the two inductors derived from the midpoints of the two bridge arms in the subsequent single bridge arm circuit are both connected to the negative pole of the power supply. Taking the dual bridge arm circuit as an example, at this time, the two single bridge arm circuits are cascaded. Specifically, the dual bridge arm includes a first single bridge arm circuit and a second single bridge arm circuit, the first bridge arm circuit includes a first bridge arm and a second bridge arm, the upper bridge arm and the lower bridge arm of the first bridge arm are respectively provided with switching devices Q1 and Q2, the upper bridge arm and the lower bridge arm of the second bridge arm are respectively provided with switching devices Q3 and Q4, the midpoint of the first bridge arm is connected to the inductor L1, the midpoint of the second bridge arm is connected to the inductor L2, and the inductors L1 and L2 are connected, and the common connection point of the inductors L1 and L2 is connected to the energy transfer inductor; the second bridge arm circuit includes a third bridge arm and a fourth bridge arm, the fourth bridge arm is connected to the load end, and optionally, the fourth bridge arm is connected to the load end via a voltage transformation processing circuit. The upper bridge arm and the lower bridge arm of the third bridge arm are provided with switch devices Q1' and Q2', respectively, the upper bridge arm and the lower bridge arm of the fourth bridge arm are provided with switch devices Q3' and Q4', respectively, the midpoint of the third bridge arm is connected to the inductor L1', the midpoint of the fourth bridge arm is connected to the inductor L1', and the inductors L1' and L2' are connected, the common connection point of the inductors L1' and L2' is connected to the negative pole of the AC power supply, and the positive pole of the AC power supply is connected to the energy transfer inductor. Preferably, a first capacitor C is provided between the midpoint of the first bridge arm and the midpoint of the second bridge arm, and a second capacitor C' is provided between the midpoint of the third bridge arm and the midpoint of the fourth bridge arm. More preferably, a switch device Q5 connected in series with the first capacitor C is provided between the midpoint of the first bridge arm and the midpoint of the second bridge arm, and a switch device Q5' connected in series with the second capacitor C' is provided between the midpoint of the third bridge arm and the midpoint of the fourth bridge arm.

[0084] The application of the bridge arm circuit of the present invention is now further described. This example takes the application of the zero voltage shutdown circuit to a conventional boost converter as an example. Figure 6 As shown, the zero voltage shutdown circuit of the present invention can be integrated into a conventional boost converter. It should be noted that we only illustrate the soft switching principle, and the voltage conversion process is simplified in the present invention, that is, the boost processing circuit cascaded after the bridge arm circuit is not illustrated. At this time, combined with the bridge arm circuit of the conventional boost converter, as shown in FIG. Figure 7As shown, the boost converter with soft switching function includes two bridge arm circuits (a first bridge arm circuit and a second bridge arm circuit), and the two bridge arm circuits are cascaded. Specifically, the first bridge arm circuit includes a first bridge arm and a second bridge arm, the upper bridge arm and the lower bridge arm of the first bridge arm are respectively provided with switch devices Q1 and Q2, the upper bridge arm and the lower bridge arm of the second bridge arm are respectively provided with switch devices Q3 and Q4, the midpoint of the first bridge arm is connected to the inductor L1, the midpoint of the second bridge arm is connected to the inductor L2, and the inductors L1 and L2 are connected, and the common connection point of the inductors L1 and L2 is connected to the energy transfer inductor; the second bridge arm circuit includes a third bridge arm and a fourth bridge arm, and the fourth bridge arm is connected to the load end (the capacitor C2 and the resistor R connected in parallel with the fourth bridge arm). The upper bridge arm and the lower bridge arm of the third bridge arm are respectively provided with switch devices Q1' and Q2', the upper bridge arm and the lower bridge arm of the fourth bridge arm are respectively provided with switch devices Q3' and Q4', the midpoint of the third bridge arm is connected to the inductor L1', the midpoint of the fourth bridge arm is connected to the inductor L1', and the inductors L1' and L2' are connected, the common connection point of the inductors L1' and L2' is connected to the negative pole of the AC power supply, and the positive pole of the AC power supply is connected to the energy transfer inductor. Further, a first capacitor C1 is provided between the midpoint of the first bridge arm and the midpoint of the second bridge arm, and a second capacitor C1' is provided between the midpoint of the third bridge arm and the midpoint of the fourth bridge arm.

[0085] To apply the scheme of the present invention to a conventional boost converter, it is only necessary to insert the corresponding soft switch control sequence into the control sequence and duty cycle of the conventional scheme. Q1 / Q3, Q2 / Q4, Q1' / Q3', Q2' / Q4' of the soft switch scheme correspond to Q1, Q2, Q3, Q4 of the conventional scheme respectively (hereinafter Q1o, Q2o, Q3o, Q4o are used instead). At this time, the control mode is: during the positive half cycle of AC, Q4o is turned on, and Q1o and Q2o are turned on alternately; during the negative half cycle of AC, Q3o is turned on, and Q1o and Q2o are turned on alternately.

[0086] Assuming that this is the AC positive half cycle, during the switching process of Q1o and Q2o being alternately turned on, the switching time (corresponding to the duty cycle) is consistent with that of the conventional boost converter, and the switching method can be directly inserted into the control method of the previous zero voltage shutdown scheme. At this time, the working principle of zero voltage shutdown is: when Q2 and Q3 are turned off and Q1 and Q4 are turned on, the voltage at B1 is Vdc (the DC voltage processed by the bridge arm circuit), and the voltage at B2 is 0. At this time, when Q4 is turned off, the 2 ends of capacitor C1 will slowly rise to Vdc, and Q4 is zero voltage shutdown. Similarly, when Q4 and Q1 are turned off and Q3 and Q2 are turned on, the voltage at B2 is Vdc, and the voltage at B1 is 0. At this time, when Q2 is turned off, the 1 end of capacitor C1 will slowly rise to Vdc, and Q2 is zero voltage shutdown.

[0087] When the AC positive and negative half cycles are switched, Q4o will switch to Q2o to turn on. The switching time point is also consistent with the conventional boost converter, and the switching method can also be directly inserted into the control method of the previous zero voltage shutdown scheme. Assuming that during the AC positive half cycle, Q4' in Q4o is turned on, Q2' in Q4o and Q1' and Q3' in Q3o are all turned off. When switching, Q1' is turned on. At this time, the state and control method of the right bridge arm (the third bridge arm and the fourth bridge arm) refer to the zero voltage shutdown control method: when Q2' and Q3' are turned off and Q1' and Q4' are turned on, the voltage at B1' is Vdc, and the voltage at B2' is 0. At this time, Q4' is turned off, and the two ends of capacitor C1' will slowly rise to Vdc, and Q4' is zero voltage shutdown.

[0088] After that, during the switching process of Q1o and Q2o being alternately turned on, the switching time (corresponding to the duty cycle) is consistent with that of a conventional boost converter, and the switching method can also be directly inserted into the control method of the previous zero voltage shutdown scheme. At this time, the control principle of the zero voltage shutdown scheme is: when Q2 and Q3 are turned off and Q1 and Q4 are turned on, the voltage at B1 is Vdc, and the voltage at B2 is 0. At this time, when Q4 is turned off, the voltage at the 2 ends of capacitor C1 will slowly rise to Vdc, and Q4 is turned off at zero voltage. Similarly, when Q4 and Q1 are turned off and Q3 and Q2 are turned on, the voltage at B2 is Vdc, and the voltage at B1 is 0. At this time, when Q2 is turned off, the voltage at the 1 end of capacitor C1 will slowly rise to Vdc, and Q2 is turned off at zero voltage.

[0089] The present invention controls each single bridge arm circuit as an independent part, and can realize soft switching processing on the basis of completing the voltage conversion processing of the boost converter. Of course, this is only one application of the present invention. For all bridge arm type circuits, the zero current conduction and zero voltage shutdown scheme of the present invention are applicable. Of course, the bridge arm circuit of the present invention can also be directly used to replace the existing bridge arm circuit, and soft switching processing can also be realized on the basis of realizing the voltage conversion processing of the existing bridge arm circuit, which has a wider range of applications.

[0090] The present invention also includes a control method for a soft switching bridge arm circuit, which is used to control a zero current conduction circuit, with a control module as the execution body. The core concept of the method is: controlling the switching timing of the switching devices in each bridge arm, adjusting the current changes of the first inductor L1 and the second inductor L2, and then delaying the rising speed of the current on the corresponding inductor, turning on the switching device at zero current, thereby achieving zero current conduction.

[0091] Specifically, zero current conduction includes:

[0092] In the positive half cycle of the AC power supply, when Q1 and Q3 are initially in the off state:

[0093] When Q2 is turned off and Q4 is turned on, the current I1 on the first inductor L1 is zero. When Q4 is turned off, the current on L2 flows through the diode on Q3. At this time, Q1 is turned on, and the current I1 slowly rises from zero, that is, when Q1 is turned on, it is zero current conduction, and the current I3 flowing through Q3 through the second inductor L2 is zero;

[0094] When Q4 is turned off and Q2 is turned on, the current I3 flowing through Q3 through the second inductor L2 is zero. Q2 is turned off, and the current on L1 flows through the diode on Q1. At this time, Q3 is turned on, and I3 slowly rises from zero, that is, when Q3 is turned on, it is zero current conduction, and the current I1 on L1 will gradually be pulled to zero current.

[0095] In the negative half cycle of the AC power supply, when Q2 and Q4 are initially off:

[0096] When Q1 is turned off and Q3 is turned on, the current I1 on L1 will gradually decrease to 0, and the current I2' on L2 is 0. After Q3 is turned off, Q2 is turned on, and the current on L2 begins to flow through the diode on Q3, turning on Q2, achieving zero current conduction of Q2, and the current I4' flowing through Q4 through the first inductor is zero;

[0097] When Q4 is turned off and Q2 is turned on, the current I3 on ​​the second inductor L2 will gradually decrease to 0, and the current I4' flowing through Q4 through the first inductor is zero. After turning off Q2, the current on L1 begins to flow through the diode on Q1, turning on Q4, and achieving zero current conduction of Q4; as Q4 is turned on, the current I3 on ​​L2 will gradually be pulled to 0 current.

[0098] The present invention also includes a control method for a soft switching bridge arm circuit, which is used to control a zero voltage shutdown circuit, with a control module as the execution body. The core concept of the method is: controlling the switching timing of the switching devices in each bridge arm to charge and discharge the capacitor C, and through the charging and discharging process of the capacitor C, turning off the switching device on the zero voltage side of the capacitor C to achieve zero voltage shutdown.

[0099] Specifically, zero voltage shutdown includes:

[0100] When Q1, Q2, and Q3 are in the off state and Q4 is in the on state, Q1 is turned on. At this time, the voltage across Q4 is 0, and the voltage difference across the two ends is 0. Q5 is turned on, Q4 is turned off, and the voltage across capacitor 2 rises slowly. Q4 is turned off with zero voltage. After Q4 is completely turned off, Q5 is turned off; when Q2, Q3, and Q4 are in the off state and Q1 is in the on state, Q4 is turned on. At this time, the voltage across Q1 is Vdc, and the voltage difference across the two ends is 0. Q1 is turned off, and the voltage across capacitor 1 slowly decreases. At this time, Q1 is turned off with zero voltage;

[0101] When Q1, Q2, and Q4 are in the off state and Q3 is in the on state, Q2 is turned on, the voltage across Q3 is Vdc, and the voltage difference across the two ends is 0. Q3 is turned off, and the voltage across capacitor 2 slowly decreases. At this time, Q3 is turned off with zero voltage; when Q1, Q3, and Q4 are in the off state and Q2 is in the on state, Q3 is turned on, and the voltage across Q2 is 0, and the voltage difference across the two ends is 0. Q5 is turned on, Q2 is turned off, the voltage across capacitor 1 slowly decreases, and Q2 is turned off with zero voltage. After Q2 is completely turned off, Q5 is turned on.

[0102] The present invention also includes a control method for a soft switch bridge arm circuit, which is used to control a zero current conduction and zero voltage shutdown switching circuit, with a control module as an execution subject. The core concept of the method is:

[0103] Control Q5 to turn off, control the switching timing of the switch devices in each bridge arm, adjust the current changes of the first inductor L1 and the second inductor L2, thereby delaying the rising speed of the current on the corresponding inductor, turning on the switch device at zero current, and realizing zero current conduction;

[0104] Control Q5 to turn on, control the switching timing of the switching devices in each bridge arm, charge and discharge the capacitor C, and through the charging and discharging process of the capacitor C, turn off the switching device on the zero voltage side of the capacitor C to achieve zero voltage shutdown.

[0105] Specifically, when Q5 is controlled to be turned off, zero current conduction control is achieved, and the method includes the following steps:

[0106] In the positive half cycle of the AC power supply, the initial state of Q1, Q3, and Q5 is the off state. When Q2 is turned off and Q4 is turned on, at this time, the current on L1 is 0, so I1 = 0, at this time, Q4 is turned off, and the current on L2 flows through the diode on Q3. At this time, Q1 is turned on, I1 rises slowly, Q1 is turned on at zero current, and the current I3 on ​​L2 will gradually be pulled to 0 current. When Q4 is turned off and Q2 is turned on, at this time, it can be seen from the first item above that the current on L2 is 0, so I3 = 0, at this time, Q2 is turned off, and the current on L1 flows through the diode on Q1. At this time, Q3 is turned on, I3 rises slowly, Q3 is turned on at zero current, and the current I1 on L1 will gradually be pulled to 0 current.

[0107] In the negative half cycle of the AC power supply, the initial states of Q2, Q4, and Q5 are off.

[0108] When Q1 is turned off and Q3 is turned on, the current I1 on L1 will gradually decrease to 0, and the current I2' on L2 is 0. After Q3 is turned off, Q2 is turned on, and the current on L2 begins to flow through the diode on Q3, turning on Q2, achieving zero-current conduction of Q2, and the current I4' flowing through Q4 through the first inductor is zero; when Q4 is turned off and Q2 is turned on, the current I3 on ​​the second inductor L2 will gradually decrease to 0, and the current I4' flowing through Q4 through the first inductor is zero. After Q2 is turned off, the current on L1 begins to flow through the diode on Q1, turning on Q4, achieving zero-current conduction of Q4; as Q4 is turned on, the current I3 on ​​L2 will gradually be pulled to 0 current.

[0109] Further, when Q5 is controlled to be turned on, zero voltage shutdown control is achieved, and the method includes the following steps:

[0110] When Q1, Q2, and Q3 are in the off state and Q4 is in the on state, Q1 is turned on. At this time, the voltage across Q4 is 0, and the voltage difference across the two ends is 0. Q5 is turned on, Q4 is turned off, and the voltage across capacitor 2 rises slowly. Q4 is turned off with zero voltage. After Q4 is completely turned off, Q5 is turned off; when Q2, Q3, and Q4 are in the off state and Q1 is in the on state, Q4 is turned on. At this time, the voltage across Q1 is Vdc, and the voltage difference across the two ends is 0. Q1 is turned off, and the voltage across capacitor 1 slowly decreases. At this time, Q1 is turned off with zero voltage;

[0111] When Q1, Q2, and Q4 are in the off state and Q3 is in the on state, Q2 is turned on, the voltage across Q3 is Vdc, and the voltage difference across the two ends is 0. Q3 is turned off, and the voltage across capacitor 2 slowly decreases. At this time, Q3 is turned off with zero voltage; when Q1, Q3, and Q4 are in the off state and Q2 is in the on state, Q3 is turned on, and the voltage across Q2 is 0, and the voltage difference across the two ends is 0. Q5 is turned on, Q2 is turned off, the voltage across capacitor 1 slowly decreases, and Q2 is turned off with zero voltage. After Q2 is completely turned off, Q5 is turned on.

[0112] The above specific implementation methods are detailed descriptions of the present invention. It cannot be determined that the specific implementation methods of the present invention are limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions and substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A soft switch bridge arm circuit, the bridge arm circuit is a single bridge arm circuit, located between the power supply end and the load end; the single bridge arm circuit comprises a first bridge arm and a second bridge arm, the upper bridge arm and the lower bridge arm of the first bridge arm are respectively provided with a first switch device and a second switch device, the upper bridge arm and the lower bridge arm of the second bridge arm are respectively provided with a third switch device and a fourth switch device, the four switch devices are connected to a control module, characterized in that, The midpoint of the first bridge arm is connected to the first inductor, the midpoint of the second bridge arm is connected to the second inductor, the first inductor is connected to the second inductor, and the common connection point of the first inductor and the second inductor is connected to the power supply end, which is provided with an energy transfer inductor.

2. The soft switching bridge arm circuit according to claim 1, characterized in that: A first capacitor is provided between the midpoint of the first bridge arm and the midpoint of the second bridge arm.

3. The soft switching bridge arm circuit according to claim 1, characterized in that: A first capacitor and a fifth switch device connected in series are provided between the midpoint of the first bridge arm and the midpoint of the second bridge arm, and the fifth switch device is connected to the control module.

4. A soft switching bridge arm circuit, characterized in that: It comprises at least two single bridge arm circuits as described in any one of claims 1 to 3.

5. A control method for a soft switching bridge arm circuit, characterized in that: The method for controlling the circuit according to claim 1, with the control module as the execution subject, comprises: The switching timing of the switch devices in each bridge arm is controlled to adjust the current changes of the first inductor and the second inductor, thereby delaying the rising speed of the current on the corresponding inductor, turning on the switch device at zero current, and realizing zero current conduction.

6. The control method of the soft switching bridge arm circuit according to claim 5, characterized in that: Zero current conduction includes: In the positive half cycle of the AC power supply, when the first and third switching devices are in the off state in the initial state: When the second switch device is turned off and the fourth switch device is turned on, the current I1 on the first inductor is zero, and after the fourth switch device is turned off, the first switch device is turned on to achieve zero current conduction of the first switch device, and the current I3 flowing through the second inductor and the third switch device is zero; When the fourth switch device is turned off and the second switch device is turned on, the current I3 flowing through the third switch device via the second inductor is zero, and the third switch device is turned on after the second switch device is turned off, so that the third switch device is turned on with zero current; In the negative half cycle of the AC power supply, when the second switch device, the fourth switch device, and the fifth switch device are in the off state in the initial state: When the first switch device is turned off and the third switch device is turned on, the current I2' on the second inductor is zero. After the third switch device is turned off, the second switch device is turned on to achieve zero current conduction of the second switch device. The current I4' flowing through the first inductor and the fourth switch device is zero. When the fourth switch device is turned off and the second switch device is turned on, the current I4' flowing through the fourth switch device via the first inductor is zero. After the second switch device is turned off, the fourth switch device is turned on to achieve zero current conduction of the fourth switch device.

7. A control method for a soft switching bridge arm circuit, characterized in that: The method for controlling the circuit according to claim 2, with the control module as the execution subject, comprises the following steps: The switching timing of the switch devices in each bridge arm is controlled to charge and discharge the first capacitor. Through the charge and discharge process of the first capacitor, the switch device on the zero voltage side of the first capacitor is turned off to achieve zero voltage shutdown.

8. The control method of the soft switching bridge arm circuit according to claim 7, characterized in that: Zero voltage shutdown includes: When the first switch device, the second switch device, and the third switch device are in the off state and the fourth switch device is in the on state, the first switch device is turned on again. At this time, the voltages at both ends of the fourth switch device are zero, and the voltage difference at both ends is zero. The fourth switch device is turned off, and the voltage at one end of the first capacitor close to the midpoint of the second bridge arm rises slowly, and the fourth switch device is turned off with zero voltage; When the second switch device, the third switch device, and the fourth switch device are in the off state, and the first switch device is in the on state, the fourth switch device is turned on, at which time the voltages at both ends of the first switch device are both rectified DC voltages, and the voltage difference between the two ends is zero, and the first switch device is turned off, and the voltage at one end of the first capacitor close to the midpoint of the first bridge arm slowly decreases, and at this time the first switch device is turned off with zero voltage; When the first switch device, the second switch device, and the fourth switch device are in the off state and the third switch device is in the on state, the second switch device is turned on, the voltages at both ends of the third switch device are both rectified DC voltages, and the voltage difference between the two ends is zero. When the third switch device is turned off, the voltage at one end of the first capacitor close to the midpoint of the second bridge arm slowly decreases, and at this time, the third switch device is turned off with zero voltage; When the first switch device, the third switch device, and the fourth switch device are in the off state and the second switch device is in the on state, the third switch device is turned on. At this time, the voltages at both ends of the second switch device are zero, and the voltage difference between the two ends is zero. The second switch device is turned off, and the voltage at one end of the first capacitor close to the midpoint of the first bridge arm slowly decreases, and the second switch device is turned off with zero voltage.

9. A control method for a soft switching bridge arm circuit, characterized in that: For controlling the circuit according to claim 3, the method comprises the following steps: Controlling the fifth switch device to turn off, controlling the switching timing of the switch devices in each bridge arm, so as to adjust the current change of the first inductor and the second inductor, thereby delaying the rising speed of the current on the corresponding inductor, turning on the switch device at zero current, and realizing zero current conduction; The fifth switch device is controlled to be turned on, and the switching timing of the switch devices in each bridge arm is controlled to charge and discharge the first capacitor. Through the charging and discharging process of the first capacitor, the switch device on the zero voltage side of the first capacitor is turned off to achieve zero voltage shutdown.

10. The control method of the soft switching bridge arm circuit according to claim 9, characterized in that: When the fifth switch device is controlled to be turned off, the method comprises the following steps: In the negative half cycle of the AC power supply, when the first switch device, the third switch device, and the fifth switch device are in the off state in the initial state: When the second switch device is turned off and the fourth switch device is turned on, the current I1 on the first inductor is zero, and after the fourth switch device is turned off, the first switch device is turned on to achieve zero current conduction of the first switch device, and the current I3 flowing through the second inductor and the third switch device is zero; When the fourth switch device is turned off and the second switch device is turned on, the current I3 flowing through the third switch device via the second inductor is zero, and the third switch device is turned on after the second switch device is turned off, so that the third switch device is turned on with zero current; In the negative half cycle of the AC power supply, when the second switch device, the fourth switch device, and the fifth switch device are in the off state in the initial state: When the first switch device is turned off and the third switch device is turned on, the current I2' on the second inductor is zero. After the third switch device is turned off, the second switch device is turned on to achieve zero current conduction of the second switch device. The current I4' flowing through the first inductor and the fourth switch device is zero. When the fourth switch device is turned off and the second switch device is turned on, the current I4' flowing through the fourth switch device via the first inductor is zero, and the fourth switch device is turned on after the second switch device is turned off, so that the fourth switch device is turned on with zero current; When the fifth switch device is controlled to be turned on, the method comprises the following steps: When the first switch device, the second switch device, and the third switch device are in the off state and the fourth switch device is in the on state, the first switch device is turned on again, at which time the voltages at both ends of the fourth switch device are both zero, and the voltage difference at both ends is zero, the fifth switch device is turned on, and the fourth switch device is turned off, the voltage at one end of the first capacitor close to the midpoint of the second bridge arm rises slowly, and the fourth switch device is turned off with zero voltage; When the second switch device, the third switch device, and the fourth switch device are in the off state, and the first switch device is in the on state, the fourth switch device is turned on, at which time the voltages at both ends of the first switch device are both rectified DC voltages, and the voltage difference between the two ends is zero, and the first switch device is turned off, and the voltage at one end of the first capacitor close to the midpoint of the first bridge arm slowly decreases, and at this time the first switch device is turned off with zero voltage; When the first switch device, the second switch device, and the fourth switch device are in the off state and the third switch device is in the on state, the second switch device is turned on, the voltages at both ends of the third switch device are both rectified DC voltages, and the voltage difference between the two ends is zero. When the third switch device is turned off, the voltage at one end of the first capacitor close to the midpoint of the second bridge arm slowly decreases, and at this time, the third switch device is turned off with zero voltage; When the first switch device, the third switch device, and the fourth switch device are in the off state and the second switch device is in the on state, the third switch device is turned on, at which time the voltages at both ends of the second switch device are zero and the voltage difference between the two ends is zero, the fifth switch device is turned on, and the second switch device is turned off, the voltage at one end of the first capacitor close to the midpoint of the first bridge arm slowly decreases, and the second switch device is turned off with zero voltage.

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