Control of STATCOM using cascade multilevel inverter for high power application

This paper proposes the novel control scheme of a static synchronous compensator (STATCOM) with cascade multilevel inverter which employs an H-bridge inverter (HBI). The STATCOM system is modeled using the D-Q transform which calculates the instantaneous reactive power. This model is used to design a control strategy based on the control of the phase angle of the fundamental switching pattern. This switching method produces the staircase type waveform in a cascade multilevel inverter. The selective harmonic elimination (SHE) allows keeping the total harmonic distortion (THD) low in the output voltage of the inverter. The switching pattern is used as a programmed switching pattern stored in an EPROM. A rotated switching scheme of fundamental frequency is switched to be on and off equally for each device and applied to control the DC voltage balancing. As a result, it makes the DC voltage of STATCOM balance and the control response fast to the step change of reactive power.