A novel DC-link voltage control of PWM-switched cascade cell multi-level inverter applied to STATCOM

The cascade cell multi-level inverter (CCMLI) is a multi-level inverter topology, which offers the advantage of avoiding clamping devices. Usually, this inverter is switched in block mode, i.e. single pulse operation. However, this operation needs a high number of levels or large filters to achieve an adequate THD of the current. To improve performance, it should be switched with PWM when it is connected to transmission lines. If a CCML is used as a STATCOM with PWM switching, a DC-link control method has not yet been proposed till present. The authors developed a novel method to control each DC-link voltage individually and verified it with a lab model and various simulations.