Asymmetrical DC link voltage balance of a cascaded two level inverter based STATCOM

Voltage unbalance is one of the main limitation of cascaded based multilevel STATCOM. This paper presents a simple control strategy for the voltage balance of a cascaded two level inverter based STATCOM. The topology consists of two conventional three phase two level inverters connected in cascade. The two inverters operate at two different dc link voltages to obtain four level operation at STATCOM output. Simulation studies are carried out to predict the performance of the proposed control strategy. A laboratory prototype is developed to validate the results. Small signal stability analysis of cascaded inverter is also carried out to predict the system behavior.