Soft-Switching Techniques For PWM Boost Full-Bridge Converters

According its circuit structure, the full-bridge (FB) converter can be classed into two kinds: Buck type and Boost type. The soft-switching techniques of the Buck FB converter have been studied extensively and used widely in the past two decades, however, less attention has been paid to the soft-switching techniques of the Boost FB converter.In high output voltage applications, the output inductance of the Buck FB converter will be sustain high voltage, resulting in complicated manufacture method. In multi-output applications, the Buck FB converter has poor cross regulation. In addition, the Buck FB converter has the risk of flux imbalance of transformer and voltage oscillation and voltage spike across the output rectifier diodes resulted by the reverse recovery. The Boost FB converter can overcome the above shortcomings, and it can be used as single stage PFC, bi-directional converters, the chargers for electric vehicle and front-end converter in distributed power systems. This dissertation will focus on the soft-switching techniques of the Boost FB converter.Soft-switching PWM converters integrates the advantages of PWM converters and resonant converters, they not only achieve soft-switching for the power switches, but realize constant frequency control, leading to high efficiency, high power density and high reliability. Based on the analysis of the basic Boost FB converter, this dissertation proposes a family of PWM modulation strategies, and discusses the possibility to achieve soft-switching. In order to realize soft-switching, the diagonal pairs of switches of the bridge legs should stagger their turn-on instance, the early turned-on switches are called the leading switches, and the later turned-on switches are called the lagging switches as well. The leading switches can only realize zero-current-switching (ZCS), and the lagging switches can realize either ZCS or zero-voltage-switching (ZVS). So the soft-switching PWM Boost FB converter can be divided into two kinds: ZCS PWM Boost FB converter and ZCZVS PWM Boost FB converter.