DSP-Based Modified SPWM Switching Technique with Two-Degrees-of-Freedom Voltage Control for Three-Phase AC–DC Buck Converter

This paper presents a modified sinusoidal pulse-width modulation (SPWM) switching technique in three-phase ac–dc buck converter with new modulation strategy. The modulation strategy used two reference signals (0°–60° and 120°–180° sine wave) and one type of carrier signal, instead of two types of carrier signal to generate pulse-width modulation signals. A conventional 6-switch three-phase ac–dc buck converter is extended by comprising four diodes in each switch to achieve bidirectional power flow capability. A digital feedback voltage control using two-degrees-of-freedom-control approach is implemented to achieve the output voltage to equal the reference voltage with high dynamic performance and to obtain sinusoidal ac current with unity power factor. The modified SPWM switching strategy of ac–dc power flow and vice versa is discussed and verified via mathematical model. The validity of the proposed three-phase ac-dc buck converter with bidirectional capability its PWM and the feedback control strategy is verified through simulation and is implemented in a prototype using TMS320F28335 Digital Signal Processor.