An Analytical Discontinuous Space-Vector PWM for Three-Level Inverters With Unbalanced DC-Link Voltages

When faced with unbalanced dc-link voltages of three-level inverters, extra harmonics will be generated with reduced linear modulation region if the conventional pulsewidth modulation (PWM) for balanced dc-link voltages is adopted. In this article, in order to suppress output harmonics and maximize the linear modulation region, as well as to reduce switching losses, the discontinuous space-vector PWM (DSVPWM) is investigated and improved for three-level inverters with unbalanced dc-link voltages. First, subsectors in the vector diagram with unbalanced dc-link voltages are optimally redivided for low switching losses, and concisely determined by a cutting-line method. Then, the modulation waves are analytically derived based on the calculated dwell times of the vector states. And an analytical DSVPWM for dealing with unbalanced dc-link voltages is proposed and implemented by a carrier-based algorithm, which can significantly reduce the computation burden. Finally, the proposed analytical DSVPWM is verified through comparative experiments, presenting its merits of high linear modulation region, high efficiency, and relatively low output harmonics.