Symmetry Compensation using a H-Bridge Multilevel STATCOM with Zero Sequence Injection

This paper examines the use of a H-bridge cascade multilevel STATCOM for symmetry compensation. One of the particular problems H-bridge based STATCOMs have when used in these applications is maintaining correct voltages on the H-bridge capacitors for each of the individual phases of the STATCOM. This difficulty is the result of average real power flowing in or out of the individual phase legs. A solution has already been published for the delta connected STATCOM, but has not, until this paper, been solved for the wye connected topology. This paper uses a new approach to solve the phase leg power balance problem using zero sequence current and voltage injection. It allows the individual phase voltages for both the delta and wye connected cascaded H-bridge STATCOM to be controlled. Furthermore, when implemented for the delta connected STATCOM it leads to a more elegant and parameter independent control system architecture