An advanced harmonic elimination PWM technique for AC choppers

A novel harmonic elimination pulse width modulation (PWM) technique for AC choppers is proposed. The modulation function is derived from the input voltage signal. Compared with previous constant duty cycle control, it has advantage of eliminating all low order harmonic voltage contained in AC mains without need of processing harmonic frequency. Hence it reduces greatly the demand for bandwidth of controller and simplifies the control scheme. Operation principles and realization of the new PWM technique are discussed in detail. Theoretical analysis and simulation results indicate the superiority of the new method over existing constant duty cycle control. Cooperated with a simple low VA rate output passive filter, the proposed PWM scheme can efficiently suppress both low order and high order harmonics in AC mains. Experimental results of a 2 kVA single-phase prototype unit show that it has good performance in harmonic voltage suppression.