Optimized Carrier-Based Discontinuous PWM Without Regulating NP Voltage for Three-Level Vienna Rectifier

Discontinuous pulsewidth modulation (DPWM) is widely used in three-level ac/dc converters due to its higher efficiency. For dual-output load applications, the vector synthesis error caused by the unbalanced neutral point (NP) voltage results in severe input current distortion with conventional DPWM. Moreover, the computational burden is further aggravated by the complicated subsector identification and dwelling time calculation resulting from partial vector redistribution after considering unbalanced NP voltage. In this article, modified subsector division and clamping modes are analyzed to eliminate vector synthesis errors. Then, an optimized carrier-based DPWM (OCB-DPWM) scheme with simple zero-sequence components (ZSCs) injection is proposed. Thus, the input current distortion under unbalanced NP voltages can be effectively suppressed. Compared with the modulation method of adjusting the NP voltage, which results in additional switching operations, the switching loss can be effectively reduced. In addition, the calculation of the ZSCs is extremely simple, and the program execution time is reduced by more than 60% compared with the existing modulation method. Finally, the simulation and experimental results of the Vienna rectifier are presented to validate the performance in terms of improved current total harmonic distortion (THD) and switching loss with different load conditions.