Research On The Active Soft Switching Topologies For Boost Converters

Soft switching technology presents one of the directions for power electronics. It is used to reduce switching losses and EMI, which plays more and more important role with the increase of power conversion and frequency.The dissertation focuses on the active soft switching Boost circuit and proposes several simplified soft switching topologies for Boost circuits.An active soft switching circuit based on interleaving two Boost converters and adding two simple auxiliary commutation circuits is proposed in this dissertation. Compared to the conventional interleaved Boost converters, the main switches are ZCS at turn-on transition and ZVS at turn-off transition. The added auxiliary switches do not cause extra voltages on the main switches and are ZVT during the whole switching transition. Compared to the previous published soft switching interleaved Boost converters, no extra inductor is needed in the auxiliary unit, so the auxiliary unit is simple. A 1.2kW prototype of the circuit is built to confirm the effectiveness of the converter.To reduce the number of the auxiliary switches in the soft switching topology for the interleaved Boost converter, a ZCS PWM switching circuit is proposed in this dissertation. Only one auxiliary switch is used in the active soft switching circuit. By using this ZCS converter topology, zero current turn-on and zero current turn-off of the main switches can be achieved and the reverse-recovery loss of Boost diode can be reduced. In addition, the auxiliary switches are ZCS during the turn-on and turn-off switching transition. But in this soft switching circuit, an extra resonant inductor should be used and there is a voltage spike across the main switch and the main diode.Likewise, to reduce the number of the auxiliary switches in the soft switching topology for the three level Boost converter, a soft switching cell of three-level Boost converter for power factor preregulator is proposed in this dissertation. This circuit has been added with two auxiliary diodes so that one of the auxiliary active switch can be reduced. Using this proposed soft switching cell, a fully soft-switched extended-period quasi-resonant three-level Boost converter for PFC circuit can be obtained. The simulation results show that all of the semiconductors achieve soft switching. Applying the proposed soft switching cell again, a simplified ZVT-PWM three-level Boost converter for PFC circuit can be obtained. Although only one auxiliary switch is used, the main switches and diodes are all ZVT. But the auxiliary switch is still hard switching when it is turned off. To solve this problem, an improved ZVT-PWM three level Boost converter is proposed in the dissertation. The experimental results show that with the proposed active snubber cell, all the main switches and diodes are zero voltage turn-on and zero voltage turn-off. What's more, the auxiliary switch is ZCS turn-on and nearly ZVS turn-off. And the voltage stress of the switches is also half of the output voltage.In the last chapter of the dissertation, an active ZVT soft switching topology for the bridgeless Boost PFC converter is proposed. In this converter, AH of the switches and diodes achieve soft switching, so the switching losses of the converter are reduced. What's more, only one auxiliary switch is used.