Control and Performance of a Transformerless Cascade PWM STATCOM With Star Configuration

Abstract— A three-phase transformer-less cascade pulsewidth-modulation (PWM) STATic synchronous COMpensator (STATCOM) intended for installation on industrial and utility power distribution systems. It proposes a control al-gorithm that devotes itself not only to meeting the demand of reactive power but also to voltage balancing of multiple galvan-ically isolated and floating dc capacitors. The control algorithm based on a phase-shifted carrier modulation strategy is prominent in having no restriction on the cascade number. Experimental waveforms verify 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 while keeping the nine dc mean voltages controlled and balanced even during the transient state. The control algorithm considered in this paper devotes itself not only to meeting a demand of reactive power but also to controlling and balancing all the dc capacitor voltages. It is characterized by easy expansion into a high number of voltage levels. Experimental waveforms verify that the 200-V 10-kVA STATCOM can adjust the rated reactive power of 10 kVA from inductive to capacitive (or capacitive to inductive) within 20 ms while keeping the nine dc capacitor voltages controlled and balanced even during the transient state. < final year projects >