Design Methodology for Cascaded Multilevel Converter (CMC)-Based Transmission-Type STATCOM (T-STATCOM)

Abstract

This paper deals with the design methods of Cascaded Multilevel Converter (CMC) based Transmission STATCOM (T-STATCOM) and development of star-connected, 11-level CMC. Number of H-Bridges in the CMC, AC voltage ratings, the number of paralleled CMC modules in the T-STATCOM system, optimum value of series filter reactors are discussed. In the CMC module, the AC voltages are approximated to sinusoidal waves by stair case modulation and by the use of an optimized series input filter reactor. The stair case modulation and equalization of DC link capacitor voltages is achieved according to Modified Selective Swapping (MSS) algorithm. MSS is applied for every 400μs period if needed to obtain a perfect equalization of DC link capacitor voltages at the expense of higher switching frequency and hence switching losses. In extension we proposed 25 level cascaded multilevel converter based transmission type STATCOM. The simulation is carried over by the MATLAB-SIMULINK software