Carrier-Based Discontinuous PWM for a Five-Level Unidirectional Rectifier

In applications, where bidirectional power flow is not required, unidirectional pulsewidth modulated (PWM) rectifiers are advantageous in terms of power density, hardware simplicity, and reliability compared to the conventional PWM rectifiers. For high-power medium-voltage applications, a discontinuous pulsewidth modulation (DPWM) strategy is useful in reducing the switching loss. This article proposes a DPWM strategy for a recently proposed five-level unidirectional rectifier. The rectifier is analyzed in the space vector (SV) domain to determine the switching sequences for DPWM. Two such DPWM sequences (i.e., DPWMA and DPWMB) are identified. Implementation of these DPWM sequences in the SV domain is known to be very computation intensive. Therefore, carrier-based implementation of both the DPWM strategies is proposed, which are derived following the SV approach. The proposed strategies are found to be very simple with very few computations. A new voltage-balancing method for the dc-link capacitors is also proposed in this article. Performances of these DPWM strategies over the entire operating range are predicted analytically and verified experimentally. This article is accompanied by MATLAB files demonstrating various performance indexes of the proposed DPWM sequences.