Study On Novel Soft-Switching PWM Buck Converters

Soft-switching technology is one of the hot spots in the research area of the power electronics. With the use of it, the switching loss can be reduced, and the electromagnetic interference (EMI) also can be restrained, therefore it contributes to increase the switching frequency, which helps the power supplies to minimize their size and weight, to increase their efficiency, and to enhance their power density. The developmental course of the soft-switching is reviewed in this thesis, and the characteristics of several representative resonant converters are introduced. On the base of the analyses of the basic Buck converter, the operation principle and the circuit features of the traditional ZCS PWM Buck converter and novel ZCS PWM Buck converter are analyzed theoretically, and the converter is simulated with computer. To solve their problems, an improved ZCS PWM Buck converter is presented. Moreover, based on the study above, a novel ZCZVS PWM Buck converter is proposed.The novel ZCS PWM Buck converter overcomes some problems of the traditional ZCS PWM Buck converter, but it exits the problems of complex and high current stress of auxiliary switch. Therefore, improved ZCS PWM Buck converter reduces a resonant inductor and increases a clamping diode to overcome the problems that exits in the novel ZCS PWM Buck converter. The topology, operation principle and main characteristics of the improved ZCS PWM Buck converter are analyzed. Based on the circuit topology, calculation method of the resonant parameters and control and drive method are presented. The results of simulation and experiment show that the improved circuit is feasible and valid, and the performance of the ZVT PWM Buck converter is enhanced.Improved ZCS PWM Buck converter has a simple structure and a low cost, and is ease to control. So the converter is deemed suitable for the applications where the minority-carrier semiconductor devices, such as IGBT and MCT, are predominantly used as the power switches.There exit the problems of high current or voltage stress of main or auxiliary switch when resonant unit is in series with main switch. So this paper presents novel ZCZVS PWM Buck converter. In this structure, main switch works in ZCS, auxiliary switch works in ZCZVS. The auxiliary resonant cell of the novel ZCZVS PWM Buck converter offers the zero-current-switching condition for the main switch without additional current stress and conduction loss. Meanwhile, its auxiliary switch also achieves the soft turn-on and turn-off.The topology, operation principle and circuit features are described in detail. Then the calculation method of the resonant parameters and the design of main circuit are presented. The simulation results verify that all of the semiconductor devices in the converter are turned on and turned off under exact or near soft-switching, and there is almost no additional current stress in it.