Modified scalar discontinuous pulse‐width modulation method for two‐level three‐wire voltage source inverters under unbalanced and distorted conditions

Abstract

The discontinuous pulse-width modulation (DPWM) method is well known and has a wide range of applications. This method uses phase values as reference signals. DPWM modulator improves the inverter efficiency and linearity range, while a poor inverter output is experienced at lower modulation indices. Under unbalanced and distorted conditions, online conversion of line-to-line values into phase values is not possible. However, the line-to-line voltages are measurable in any application. The proposed technique is the first scalar method that directly uses line-to-line voltages as reference signals. A modified DPWM method that shows better performance characteristics is introduced for three-phase three-wire two-level voltage source inverters. The proposed method achieves the maximum possible output voltage with an appreciable performance in terms of harmonic distortion and switching losses without injecting a zero-sequence signal. Therefore, the method is referred as implicit zero-sequence DPWM (IZDPWM). IZDPWM was verified under balanced, unbalanced and distorted conditions in both simulation and experimental testes. Simulation and experimental results demonstrate the validity and the performance of the proposed method.