Analysis and Performance Investigation of a Cascaded Multilevel STATCOM for Power System Voltage Regulation

Abstract

 This paper presents an analysis of a cascaded multilevel STATCOM based on space vector theory. Simple relationships between reactive current, capacitor current and delayed angle are derived from the steady state analysis. The switching pattern design and the optimization technique to achieve the output voltage waveform which conforms to the IEC standard for harmonics are described and the design results are verified by the harmonics analysis. A typical 230 kV power system with a 100 MVA cascaded 5-link, 11-level STATCOM is simulated on PSCAD/EMTDC digital simulator. Due to unequal duty cycles, the voltage drops across DC capacitors of the converters are unequal and a simple voltage equalization technique without additional control loop is proposed. The dynamic performances of the casc  aded multilevel STATCOM, which was subjected to disturbances and change of commands, are illustrated. Simulation results indicate that the proposed system can provide fast reactive current response and fast equalization the DC capacitor voltages. The harmonics content of the output voltage waveform can be controlled within an acceptable level even it is only a 5-link, 11-level cascaded STATCOM.