Common-mode and phase-to-ground voltage reduction in back-to-back power converters with discontinuous PWM

Abstract

Discontinuous space vector pulsewidth modulation (DSVPWM) techniques are an interesting option for three-phase, two-level power converters when efficiency is a key factor. Such is the case of back-to-back (B2B) power converters used mainly in wind energy conversion systems and electrical drives. The application of DSVPWMs to B2B converters increases the common-mode (CM) and phase-to-ground (PG) voltages by 50%, compared to conventional space vector pulsewidth modulation (SVPWM7). Higher CM and PG voltages cause bearing currents and insulation stress, which reduce system reliability. In this article, this problem is addressed and two DSVPWM strategies are presented to reduce the CM and PG voltages in B2B power converters. In the first proposal, the CM and PG are both limited to the same values as the conventional SVPWM7 without introducing additional commutations. In the second proposal, a further modification is added to reduce the CM by 50%, compared to the SVPWM7, although this modulation strategy eventually requires two additional commutations in certain periods. Experimental and simulation results validate the performance of the proposed strategies.