The Study On The Soft Switching Of Asymmetrical Half Bridge

Soft switching technology has been one of the hot points of power electronic technologies for smaller and lighter and modularization converter. "Soft switching" is zero voltage switching or zero current switching, which the voltage (or current) of the switch varies by law of sine or quasi sine, the switch is on when its voltage reaches zero (or switch is off when its current reaches zero) by resonance. It makes switch loss is zero, so it can increase the operating frequency and raise power density, minimize the size of transformer and inductor. However, it makes the circuit complex, which means it cost more, which affects the competitiveness of commercial product. A topology of asymmetrical half bridge soft switching is researched in this thesis, which has inherent zero voltage switching (ZVS) capability and thus potentially higher efficiency by its resonating of the leakage of power transformer with the parasitic capacitances of the power MOSFT switches, whereas it doesn't raise the expense of the converterThese studies in the thesis have been done as follows:(1) The topology of asymmetrical half bridge is introduced, and its principle and the relation of duty cycle and input voltage and output voltage discussed, the method of eliminating the deflection magnetism is also brought forward .(2) Each state of the total switching period has been studied in detail, in which the voltage of block capacitor and current of leakage inductance of main transformer and keeping time of each state have been discussed, then the condition of zero voltage switching is attained, which gives theory guidance for setting reasonable dead time, finally, the possibility of zero voltage switching is proved by simulation of Saber software.(3) Modeling of the asymmetrical half bridge converterIn the thesis, a small average circuit model of asymmetrical half bridge converter power stage is established by method of state space averaging. In term of it, a system model of total converter is founded. The characteristic of stabilization and dynamic is analysed and the compensator is designed basing of it.The stability of the converter is validated by simulation of Matlab and dynamic approved by simulation of Saber.(4) The experiment of asymmetrical half bridge converter design and the result of it Base of the above analysis, the DC/DC converter is designed, it is proved thatasymmetrical half bridge can realize zero voltage switching when it satisfies the condition of load current and deadtime by the experiment.