Minimization of Smoothing Capacitor and Operation Characteristics under Unbalanced Power Source of Direct-Power-Controlled PWM Rectifier

Abstract

This paper describes direct power control of a PWM rectifier. The key of this strategy is a direct selection of switching modes on the basis of instantaneous errors of active and reactive power. In addition, this paper presents a theoretical analysis on relation between the instantaneous power and the switching modes, which is essential to compose a switching-mode table. The feature of this method is high-speed response owing to direct-instantaneous-power control with relay elements; hence a DC-bus smoothing capacitor can be minimized. Controllability of the proposed technique was examined through various experimental tests, and it was confirmed that the maximum total input power factor and efficiency were 99.6% and 96.6% over a load power range from 400 to 1600W, respectively. Moreover this paper discusses operation characteristics of the direct-power-controlled PWM rectifier, compared with a conventional subharmonic PWM rectifier, under unbalanced power source condition. Experimental data prove that the proposed technique achieves more than 95-% power factor and less than 6-% DC bus ripples.