Application of a five-level PWM inverter to SVC

Abstract

Multi-level PWM inverters, (including five-level inverters), have significant operational advantages, such as the ability to drive a motor with nearly sinusoidal current waveforms and at higher output. Consequently, the consideration of their applications is of increasing interest. When one looks in detail at their possibilities, the requirement for larger capacity inverters is also anticipated for use in large AC motor drives, SVCs (static VAr compensators) and the like. In this paper, the possibility of applying the technology to SVCs is discussed. By controlling the phase and the amplitude of the modulating sinusoidal signal, the capacitor voltage and the output current can be controlled successfully, which can play an important role in SVC applications. In addition, a third order harmonic can be injected, and the capacitor voltage can be controlled by shifting its phase with reference to the modulating sinusoidal waveform. By using these characteristics, coupled with an adequate feedback control circuit, each capacitor voltage can be controlled, even with respect to fluctuations in the load or unbalanced states of the individual capacitor voltages.