Control and Performance of a Medium-Voltage Transformerless Cascade PWM STATCOM with Star-Configuration

This paper presents a three-phase transformerless cascade PWM STATCOM intended for installation on industrial and utility power distribution systems. It proposes a control method that devotes itself mainly to meeting a demand of reactive power, as well as to voltage-balancing of the multiple isolated and split dc capacitors. The control method is characterized by fast and stable voltage-balancing performance and easy expansion into a higher number of levels. Experimental waveforms confirm that a 200-V, 10-kVA cascade PWM STATCOM with star-configuration has the capability of inductive to capacitive (or capacitive to inductive) operation at the rated reactive power of 10 kVA within 20 ms, keeping the nine DC mean voltages controlled and balanced, even during the transient state