Soft-switching AC-DC Vienna converter and control method

Abstract

The present invention relates to a soft-switching AC-DC Vienna converter topology structure and a control method, wherein the structure comprises a first rectifier diode D1, a second rectifier diode D2, a first main switch S1, a second main switch S2, a first output DC link capacitor C 01 and the first output DC link capacitor C 01 The converter also includes an active buffer circuit, which includes a buffer inductor L S , the first auxiliary active switch S S1 , the first buffer capacitor C S1 , the second auxiliary active switch S S2 and the second buffer capacitor C S2 , the snubber inductor L S Through the first auxiliary active switch S S1 and the first buffer capacitor C S1 connected to the cathode of the first rectifier diode D1 and sequentially through the second auxiliary active switch S S2 and the second buffer capacitor C S2 It is connected to the cathode of the second rectifier diode D2 and is grounded via the first main switch S1 and the second main switch S2 in sequence. Compared with the prior art, the present invention has the advantages of reducing the reverse recovery loss of the rectifier diode and avoiding the ringing problem.

Description

Technical Field

[0001] The invention relates to circuit topology technology, in particular to a soft-switching AC-DC Vienna converter and a control method. Background Art

[0002] In the existing literature, there are many circuit topologies that use active and passive snubber circuits to produce soft switching conditions for semiconductor devices and rectifier diodes. These snubber circuits are used to limit the rate of change of diode current and create soft switching conditions for the semiconductor components of the circuit.

[0003] The existing converter circuit using active snubber circuit has the function of reducing current and voltage stress in addition to soft switching of switch conduction and rectifier shutdown. However, the auxiliary switch of the active snubber circuit has a higher current stress and works under hard switching conditions. In the boost topology described in the prior art, both the main switch and the auxiliary switch work under soft switching conditions. However, the voltage stress of the main switch is higher than that of the converter circuit using active snubber circuit (controlled by appropriately selecting the snubber inductance value and the switching frequency). In addition, the requirements for the gate drive circuit are complex and expensive. Summary of the invention

[0004] The purpose of the present invention is to provide a soft-switching AC-DC Vienna converter and a control method in order to overcome the defects of the prior art.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A soft-switching AC-DC Vienna converter comprises a first rectifier diode D1, a second rectifier diode D2, a first main switch S1, a second main switch S2, a first output DC link capacitor C 01 and the first output DC link capacitor C 01 The structure also includes an active buffer circuit, which includes a buffer inductor L S , the first auxiliary active switch S S1 , the first buffer capacitor C S1 , the second auxiliary active switch S S2 and the second buffer capacitor C S2 , the buffer inductor L S Through the first auxiliary active switch S S1 and the first buffer capacitor C S1 connected to the cathode of the first rectifier diode D1 and sequentially through the second auxiliary active switch S S2 and the second buffer capacitor C S2 It is connected to the cathode of the second rectifier diode D2 and is grounded via the first main switch S1 and the second main switch S2 in sequence.

[0007] The first auxiliary active switch S S1 Using N-channel MOSFET tube, the first auxiliary active switch S S1 and the first buffer capacitor C S1 It is used to provide a discharge path for the residual energy stored in the snubber inductor.

[0008] The second active auxiliary switch S S2 Using N-channel MOSFET tube, the second auxiliary active switch S S2 and the second buffer capacitor C S2 It is used to provide a discharge path for the residual energy stored in the snubber inductor.

[0009] The snubber inductor L S With the first active auxiliary switch S S1 The source of the first buffer capacitor C S1 Set in the first active auxiliary switch S S1 between the drain of and the cathode of the first rectifier diode D1.

[0010] The snubber inductor L S With the second auxiliary active switch S S2 The source of the second buffer capacitor C S2 Set in the second active auxiliary switch S S2 between the drain of and the cathode of the second rectifier diode D2.

[0011] The first main switch S1 and the second main switch S2 are both N-channel MOSFET tubes. The source of the first main switch S1 is connected to the source of the second main switch S2, and the drain of the second main switch S2 is grounded.

[0012] A control method for a soft-switching AC-DC Vienna converter, during the positive half cycle of the input voltage, when the first rectifier diode D1 and the first auxiliary active switch Ss1 are turned off, the current Is1 of the first main switch S1 is equal to the input current Ii, when the first main switch S1 is disconnected, its voltage increases linearly from zero to V0+Vsc1, and the voltage of the first auxiliary active switch Ss1 decreases from V0+Vsc1 to zero, when the switch voltage across the rectifier diode D1 exceeds the conduction voltage V0 of the first rectifier diode D1, the first rectifier diode D1 starts to conduct, and the current of the buffer inductor Ls starts to decrease, when the voltage on the first main switch S1 reaches V0+Vs1 and the anti-parallel diode on the first active auxiliary switch Ss1 is turned on, the first active auxiliary switch Ss1 is turned on, and current starts to flow through the buffer inductor Ls.

[0013] According to the input current I i = Buffer inductor current iLs +The first rectifier diode D1 current i D1 , the buffer inductor current i Ls As the current in the first rectifier diode D1 continues to decrease, D1 Continue to increase at an equal rate. When the buffer inductor current iLs reaches zero level, the anti-parallel diode of the first active auxiliary switch Ss1 stops conducting. Ls Before reaching zero, the first active auxiliary switch Ss1 is turned on. After the first active auxiliary switch Ss1 is turned on, the buffer inductor current i Ls Continue to flow in the reverse direction through the first active auxiliary switch Ss1. At this time, the current i D1 Continue increasing at the same rate.

[0014] During the positive half cycle of the input voltage, when the first active auxiliary switch Ss1 is turned off, the buffer inductor current i Ls flows through the output capacitor of the first main switch S1, causing its voltage to drop from V0+Vsc1 to zero. At this time, the buffer inductor current i Ls From negative value to zero, the current i D1 When the input current level Ii is reduced, the energy stored in the snubber inductor Ls is greater than the energy required by the output capacitor of the first main switch S1.

[0015] When the energy stored in the buffer inductor Ls is sufficient to discharge the output capacitor of the first main switch S1, the anti-parallel diode of the first main switch S1 begins to conduct, and the buffer inductor current i Ls linearly increases to zero, the first main switch S1 is turned on at ZVS when the anti-parallel diode is turned on, and when the first main switch S1 is turned on, the buffer inductor current i Ls The current i of the first rectifier diode D1 increases linearly. D1 The current i of the first rectifier diode D1 decreases linearly at an equal rate. D1 The decreasing rate of is determined by the value of the snubber inductance Ls, then:

[0016]

[0017] Among them, V0 is the on-state voltage.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] In the circuit technology proposed by the present invention, the snubber inductor of the auxiliary switch reduces the reverse recovery loss of the rectifier diode by controlling the rate of change of the current of the rectifier diode. In addition, the energy stored in the snubber inductor is used to discharge the output capacitor to zero before the main switch is turned on, thereby generating zero capacitance conduction switching loss. When the main switch is turned off, the auxiliary switch and the snubber capacitor of the active snubber circuit provide a discharge path for the residual energy stored in the snubber inductor. The circuit topology effectively solves the ringing problem caused by the interaction between the rectifier diode junction capacitance and the snubber inductor. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural circuit diagram of the present invention.

[0021] Figure 2 These are the working stages of the AC-DC converter during the positive half cycle of the input voltage, wherein Figure (2a) is the first stage, Figure (2b) is the second stage, Figure (2c) is the third stage, Figure (2d) is the fourth stage, Figure (2e) is the fifth stage, Figure (2f) is the sixth stage, Figure (2g) is the seventh stage, and Figure (2h) is the eighth stage.

[0022] Figure 3 This is the control waveform corresponding to the positive half cycle of the input voltage. DETAILED DESCRIPTION

[0023] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Example

[0025] The present invention provides a circuit for reducing reverse recovery loss and switching loss associated with a rectifier diode and a semiconductor element by adopting an active buffer circuit in a Vienna rectifier circuit topology. The circuit does not impose any additional voltage stress on the rectifier diode, and the circuit topology can be applied to a high-voltage and high-power AC / DC conversion system.

[0026] like Figure 1 As shown, Figure 1The invention discloses a circuit structure of a soft-switching AC-DC Vienna converter using an active snubber circuit. The active snubber reduces the reverse recovery loss of the rectifier diode and realizes the zero voltage switching of the semiconductor main switch. The active snubber circuit is composed of an auxiliary active switch, a snubber capacitor and a snubber inductor. By controlling the di / dt rate of the rectifier diode, a soft switching condition is created for the semiconductor main switch and the auxiliary active switch. The snubber inductor reduces the reverse recovery loss by controlling the change rate di / dt of the rectifier diode current. The snubber inductor is connected to the series path of the rectifier diode and the semiconductor main switch. The energy stored in the snubber inductor is used to discharge the output capacitance of the semiconductor main switch before the switch rotates, thereby preventing its capacitance conduction loss. The auxiliary active switch and the snubber capacitor connected in series in the snubber circuit discharge the energy stored in the snubber inductor to the output DC link capacitor when the switch is turned off.

[0027] To simplify the analysis, the line inductor L is replaced by a constant current source Ii, and the output DC link capacitor is replaced by a DC voltage source. In addition, it is assumed that the on-state resistance of the semiconductor switch is zero, but the output capacitance and reverse recovery charge of the rectifier diode are not zero. Figure 2 shows the working phase of the proposed AC-DC converter during the positive half cycle of the input voltage, and its corresponding key operating waveforms are shown in Figure 3 shown.

[0028] When the rectifier diode D1 and the first auxiliary active switch Ss1 are turned off, the current of the first main switch S1 is equal to the input current Ii, and the voltage V0 (the conduction voltage of the rectifier diode) and V0+Vsc1 (junction capacitor voltage) are blocked before the first main switch S1 is turned off. When the first main switch S1 is turned off, its voltage increases linearly from zero to V0+Vsc1. The voltage of the auxiliary active switch Ss1 drops from V0+Vsc1 to zero. When the switch voltage across the rectifier diode D1 exceeds the V0 level, the rectifier diode D1 starts to conduct, and the current of the snubber inductor Ls starts to decrease. When the voltage on the first main switch S1 reaches V0+Vs1 and the anti-parallel diode on the active auxiliary switch Ss1 is turned on, Ss1 can be turned on, and current starts to flow through the snubber inductor Ls.

[0029] Since the input current I i =i Ls +i D1 , buffer inductor current i Ls Continues to decrease, and the current i of the rectifier diode D1 D1 Continue to increase at an equal rate. When iLs reaches zero level, the anti-parallel diode of the active auxiliary switch Ss1 stops conducting. Ls Before reaching zero, the active auxiliary switch Ss1 is turned on. After turning on the active auxiliary switch Ss1, i LsContinues to flow in the reverse direction through the active auxiliary switch, so the current i in the rectifier diode D1 D1 Continue to increase at the same rate, its magnitude exceeds the input current I i , unless the active auxiliary switch Ss1 is turned off, the energy stored in the auxiliary capacitor Cs1 returns to the auxiliary inductor Ls through the active auxiliary switch Ss1.

[0030] When the active auxiliary switch Ss1 is turned off, the buffer inductor current i Ls flows through the output capacitor of the first main switch S1, causing its voltage to drop from V0+Vsc1 to zero. Therefore, the buffer inductor current i Ls From negative value to zero, i D1 The energy stored in the snubber inductor Ls should be greater than the energy required to discharge the output capacitor of the first main switch S1, otherwise the main switch voltage Vs1 will not return to zero completely and oscillate unless the first main switch S1 is turned on after the main switch voltage Vs1 reaches the minimum value.

[0031] When the buffer inductor energy is sufficient to discharge the output capacitor of S1, the anti-parallel diode of the first main switch S1 begins to conduct, and the buffer inductor current i Ls The first main switch S1 can be turned on at the zero voltage switch ZVS when the anti-parallel diode is turned on. When the first main switch S1 is turned on, the buffer inductor current i Ls The current i of the rectifier diode D1 increases linearly. D1 The current i of the rectifier diode D1 decreases linearly at an equal rate. D1 The decreasing rate of is determined by the value of the snubber inductance Ls, so:

[0032]

[0033] The higher the value of the snubber inductor Ls, the more di D1 The smaller the / dt rate, the smaller the reverse recovery loss will be.

[0034] Linearly increasing snubber inductor current i Ls When the Iin level is reached, the linearly decreasing current i of the rectifier diode D1 D1 reaches a zero current value and continues to decrease in the reverse direction due to the remaining stored charge, thereby generating an overshoot in the switching current that exceeds the input current Ii level. If a proper snubber inductor Ls is not applied, this overshoot will be larger and may damage the device.

[0035] In addition to the residual charge that must be recovered before the rectifier diode blocks the voltage, it also has a junction capacitance SC1 that can resonate in series with the snubber inductor Ls, which causes parasitic ringing and increases the voltage stress on the rectifier diode. This problem is solved by a heavy RCD snubber. The voltage stress on the first main switch S1 and the active auxiliary switch Ss1 is similar and equal to V0+Vsc1. In order to keep the voltage stress within a reasonable range, it is important to choose the voltage across Cs1. The voltage on Cs1 depends on the load, the line voltage V in , switching frequency f s and snubber inductance L s , as shown below

[0036]

[0037] For a given input current I 0 , Line voltage V in and V 0 , by reducing L s f s The voltage on Cs1 can be reduced.

Claims

1. A soft-switching AC-DC Vienna converter, comprising a first rectifier diode D1, a second rectifier diode D2, a first main switch S1, a second main switch S2, a first output DC link capacitor C 01 and the first output DC link capacitor C 01 , characterized in that, The converter also includes an active buffer circuit, which includes a buffer inductor L S , the first auxiliary active switch S S1 , the first buffer capacitor C S1 , the second auxiliary active switch S S2 and the second buffer capacitor C S2 , the buffer inductor L S Through the first auxiliary active switch S S1 and the first buffer capacitor C S1 connected to the cathode of the first rectifier diode D1 and sequentially through the second auxiliary active switch S S2 and the second buffer capacitor C S2 connected to the cathode of the second rectifier diode D2 and connected to ground via the first main switch S1 and the second main switch S2 in sequence; The first auxiliary active switch S S1 Using N-channel MOSFET tube, the first auxiliary active switch S S1 and the first buffer capacitor C S1 To provide a discharge path for the residual energy stored in the buffer inductor; The second active auxiliary switch S S2 Using N-channel MOSFET tube, the second auxiliary active switch S S2 and the second buffer capacitor C S2 To provide a discharge path for the residual energy stored in the buffer inductor; The snubber inductor L S With the first active auxiliary switch S S1 The source of the first buffer capacitor C S1 Set in the first active auxiliary switch S S1 Between the drain of and the cathode of the first rectifier diode D1; The snubber inductor L S With the second auxiliary active switch S S2 The source of the second buffer capacitor C S2 Set in the second active auxiliary switch S S2 Between the drain of and the cathode of the second rectifier diode D2; The first main switch S1 and the second main switch S2 are both N-channel MOSFET tubes. The source of the first main switch S1 is connected to the source of the second main switch S2, and the drain of the second main switch S2 is grounded.

2. A control method for a soft-switching AC-DC Vienna converter according to claim 1, characterized in that: During the positive half cycle of the input voltage, when the first rectifier diode D1 and the first auxiliary active switch Ss1 are turned off, the current Is1 of the first main switch S1 is equal to the input current Ii. When the first main switch S1 is turned off, its voltage increases linearly from zero to V0+Vsc1, and the voltage of the first auxiliary active switch Ss1 decreases from V0+Vsc1 to zero. When the switch voltage across the rectifier diode D1 exceeds the conduction voltage V0 of the first rectifier diode D1, the first rectifier diode D1 starts to conduct, and the current of the snubber inductor Ls starts to decrease. When the voltage on the first main switch S1 reaches V0+Vs1 and the anti-parallel diode on the first active auxiliary switch Ss1 is turned on, the first active auxiliary switch Ss1 is turned on, and current starts to flow through the snubber inductor Ls.

3. The control method of a soft-switching AC-DC Vienna converter according to claim 2, characterized in that: According to the input current I i = Buffer inductor current i Ls +The first rectifier diode D1 current i D1 , the buffer inductor current i Ls As the current in the first rectifier diode D1 continues to decrease, D1 Continue to increase at an equal rate. When the buffer inductor current iLs reaches zero level, the anti-parallel diode of the first active auxiliary switch Ss1 stops conducting. Ls Before reaching zero, the first active auxiliary switch Ss1 is turned on. After the first active auxiliary switch Ss1 is turned on, the buffer inductor current i Ls Continue to flow in the reverse direction through the first active auxiliary switch Ss1. At this time, the current i D1 Continue increasing at the same rate.

4. The control method of a soft-switching AC-DC Vienna converter according to claim 3, characterized in that: During the positive half cycle of the input voltage, when the first active auxiliary switch Ss1 is turned off, the buffer inductor current i Ls flows through the output capacitor of the first main switch S1, causing its voltage to drop from V0+Vsc1 to zero. At this time, the buffer inductor current i Ls From negative value to zero, the current i D1 When the input current level Ii is reduced, the energy stored in the snubber inductor Ls is greater than the energy required by the output capacitor of the first main switch S1.

5. The control method of a soft-switching AC-DC Vienna converter according to claim 4, characterized in that: When the energy stored in the buffer inductor Ls is sufficient to discharge the output capacitor of the first main switch S1, the anti-parallel diode of the first main switch S1 begins to conduct, and the buffer inductor current i Ls linearly increases to zero, the first main switch S1 is turned on at ZVS when the anti-parallel diode is turned on, and when the first main switch S1 is turned on, the buffer inductor current i Ls The current i of the first rectifier diode D1 increases linearly. D1 The current i of the first rectifier diode D1 decreases linearly at an equal rate. D1 The decreasing rate of is determined by the value of the snubber inductance Ls, and then: Among them, V0 is the on-state voltage.

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