Study on a soft switching method for high efficiency bridgeless power factor correction rectifier

Abstract

Power systems are one of the most important parts in power systems because they transfer the operating power to the electric devices. In those power systems, there have been continual demands for high efficiency. Moreover, since a standard of efficiency is continuously increased, the needs to study for high efficiency are also grown. On the other hand, power systems normally consists of three stages: 1) a bridge diode to converter AC input voltage to DC voltage, 2) a power factor correction stage to satisfy the power factor requirements from IEC 61000-3-2 and ENERGY STAR, and 3) DC/Dc stage to regulate the required output voltage and to ensure the galvanic isolation. Due to the large conduction loss of bridge diode and the large switching losses by the hard-switching operation in PFC stage, the efficiency improvement of power systems is restricted. In this dissertation, among the attractive candidates of the bridgeless converter, which is employed for a reduction of the conduction loss on bridge diode, the soft-switching methods for two promising bridgeless converters, the dual boost rectifier and totem-pole bridgeless converter, are investigated to obtain high efficiency of power systems. This research is divided into two parts according to the conventional bridgeless topologies as follows:

*Part 1. Dual Boost Rectifier Having Soft Switching Capability

In this part, a bridgeless dual boost rectifier having soft-switching capability is proposed to reduce switching losses. In the proposed converter, based on the conventional bridgeless dual boost rectifier, an auxiliary circuit is employed to perform zero-voltage-switching (ZVS) of the main switches and zero-current-switching (ZCS) of the auxiliary switches. As a result, switching losses can be significantly reduced. In addition, the design guideline for the optimized turn-on time of the auxiliary switches is presented to minimize the additional conduction loss in the auxiliary circuit. The validity of the proposed converter is confirmed by the experimental results of a prototype converter with 100-240 $V_{AC}$ universal-line input and 800 W (400 V/2 A) output.

*Part 2. Soft Switching Totem-pole Bridgeless Rectifier by Merging Inrush Current Limit Circuit

In this part, a totem-pole bridgeless rectifier having soft-switching capability is proposed. To complete ZVS of main switches, the proposed converter is re-arranging the inrush current limit circuit, which is basically applied to satisfy the inrush current limit requirement. It results that switching losses in the proposed converter can be significantly reduced, and the additional components for soft-switching operation are also minimized. Moreover, to reduce the circulating current in the auxiliary circuit, the design guideline for turning-on time of the auxiliary switches is also presented. The verification of the proposed converter is proceeded by the experimental results of a prototype converter with 100-240 $V_{AC}$ universal-line input and 800 W (400 V/2 A) output.

Consequently, this dissertation studied for the soft-switching methods of two promising bridgeless converter to achieve high efficiency of power systems. Moreover, the additional components and cost are minimized, and the additional conduction loss is also analyzed with the design guideline. Therefore, the proposed converter is expected to be very attractive solutions for a high efficiency of various power system.