A new type of STATCOM based on cascading voltage-source inverters with phase-shifted unipolar SPWM

In this paper, a new type of static compensator (STATCOM) is proposed. This new STATCOM is constructed by cascading several identical full-bridge (H bridge) voltage-source inverters (VSIs). A so-called phase-shifted sinusoidal pulsewidth modulation (SPWM) unipolar voltage switching scheme is applied to control the switching devices of each VSI. The harmonics in STATCOM current caused by the DC voltage ripple is rejected by a new method developed in this paper. As a result, the size of inductor and DC capacitors can be further reduced. A very effective startup procedure is proposed to start up the STATCOM. The proposed STATCOM has the advantage of a fewer number of VSIs, the VSIs being identical and extremely fast in response to reactive power change.