SERIES CONNECTED VOLTAGE-SOURCE CONVERTER MODULES FOR FORCE-COMMUTATED SVC AND DC-TRANSMISSION

In force-commutated SVC and DC Transmission stations, series-connected, multi-converter modules are necessary to build up the dc link voltage rating. Based on digital simulations of 8 modules, it is shown that the Total Harmonic Distortion (THD) of 5% can be achieved from harmonic cancellations by using phase shifting of the triangular carriers in the Sinusoidal Pulse Width Modulation technique. The requirement of the dc link capacitor size to ensure ripple-free dc voltage is studied. The 8-module case-study points to the ability to achieve 1% THD for higher voltage rating by increasing the number of modules connected in series.