Abstract
In parallel with the progress of power electronics technology and the more strict requirement of power quality, single-phase power factor correctors have been widely used in various products. Hence, one can expect that application of three-phase systems will become more and more popular as well. However, due to the higher power rating, the resulting switching noise, loss and electrical stress of the power devices resulting from turning on and off of the active devices will also become much larger. Therefore, it is the main purpose of this thesis to propose a novel soft switching pulse-width-modulation(PWM) strategy for a popularly used three-phase boost power factor corrector(PFC).Basically, major contributions of this thesis may be summarized as follows. First, a discontinuous PWM(DPWM) strategy is proposed for the adopted three phase boost PFC such that for any time only two active switches are switched ON/OFF to control the three-phase line currents to track the ideal sinusoidal currents and achieve unity power factor. As a result, the switching number and the switching loss of the PFC can be greatly reduced. Second, an existing single-phase soft switching subcircuit is applied to the three-phase boost PFC of this thesis to extend its application. Detailed soft switching mechanism in the three-phase case is analyzed in the context. Third, from previous analyses, a very simple duty ratio control formula is proposed for matching the proposed soft switching DPWM strategy. It turns out that with this analytical duty ratio law, current sensors of the AC side line currents can be omitted and the hardware system can be simplified. Finally, a hardware prototype system is constructed by using a DSP, namely TMS320F240, to verify the effectiveness of the novel soft switching strategy.