A novel single pulse and PWM VAr compensator for high power applications

Although pulse-width-modulated (PWM) high power GTO-based voltage source inverters have unique control features, obstacles to their use in high power applications include reduced efficiency, and lower inverter utilization. This paper presents a low switching frequency pulse-width-modulation (PWM) technique that can be used in conjunction with the principle of harmonic neutralization. This allows the combination of the advantages of both multi-pulse and PWM GTO-based voltage source converters. The proposed converter can be operated in either the single pulse or the PWM modes. In the PWM mode, a special low switching frequency (3 pu) space vector strategy is used to maximize voltage utilization while maintaining a transfer linear characteristic. In the six-step mode, the switching frequency, and thus the switching losses are minimized. In addition the paper proposes an alternative to complicated zig-zag connected phase-shifting transformers used in standard implementations. The power structure and control methods are described and analyzed. Experimental results validate and demonstrate the performance of the proposed techniques.