Abstract
This study examines a method for obtaining a fixed pulse pattern for a neutral-point-clamped PWM rectifier; the method involves the consideration of harmonic regulations. In the PWM rectifier system, a neutral-point-clamped PWM rectifier is connected to the secondary winding of a transformer connected to the grid, and the current is controlled by varying only the phase difference between the fixed pulse pattern and the power source. Therefore, it is possible to use a pulse pattern with reduced harmonics. Two typical types of harmonic regulations were selected. The harmonic regulations described in Harmonic Guidelines and IEEE-519 for high-capacity PWM rectifiers were considered in the above-mentioned method for obtaining the fixed pulse pattern. The fixed pulse pattern was obtained so as to minimize the ratio of the harmonic current content to the regulation values for each harmonic order. For evaluating the effectiveness of the proposed method, the pattern obtained was compared with the patterns obtained by using two other methods—cancellation of low-order harmonics and THD minimization.
