Discontinuous Space-Vector Modulation for Three-Level PWM Rectifiers

This paper presents the implementation and experimental verification of two discontinuous pulsewidth modulation (DPWM) methods for three-phase, three-level rectifiers. DPWM's features, such as improved waveform quality, lower switching losses, reduced ac-side passive component size, are investigated and compared to the conventional continuous pulsewidth modulation (CPWM). These features allow higher power density and/or efficiency to be achieved and are important targets for the next generation of power rectifiers. The implementation of the two DPWM strategies is explained by means of space-vectors representation and modulation functions. A detailed analysis of both ac-side and dc-side current waveforms is presented, and there is excellent agreement between the analytical, simulated and experimental results for the mains current ripple amplitude and output center-point current over the practical modulation range. Finally, the control of the center-point voltage is discussed.