Optimum PWM pattern for a three-phase boost DCM PFC rectifier

A lot of effort has been devoted to improving the input current THD of a three-phase single-switch boost discontinuous conduction mode (DCM) power factor correcting (PFC) rectifier. However, there is no explicit answer to the question of what the optimum solution is. In this paper, a new optimization rule is proposed by using space vector analysis. Instead of being based on a cumbersome mathematical derivation, the proposed method relies on a good insight to the optimization problem. It is interesting to observe that at each time instant, by varying the duty cycle, only current vector length can be changed, while the current vector angle is solely dictated by the voltage transfer ratio. The current vector angle error sets the upper limits to the optimization. The resultant optimum PWM pattern shows improved input current THD over both constant-duty-cycle control and the 6th-harmonic-injected PWM, although the latter is very close to the optimum solution.