Advanced PWM Switching Technique for Accurate Unity Power Factor of Bidirectional Three-Phase Grid-Tied DC–AC Converters

Matrix-based high-frequency linked (MBHFL) bidirectional dc-ac converters are getting much interest in grid-tied applications due to their high efficiency and the compacted footprint. This paper proposes a new PWM switching technique of the MBHFL dc-ac converters based on phase shift angle considering compensation of the LC filter current at the grid side in order to realize accurate unity power factor and to reduce the total harmonic distortion (THD) of the grid current waveform. The proposed technique estimates the phase shift angle error between the grid voltage and current waveforms due to the capacitor injected current that reduces the power factor at the grid side. It considers two operational modes based on the patterns of three-phase grid voltage and current waveforms. Therefore, it provides the matrix converter switches with different duties according to the pattern of the detected grid voltage and the reference grid current to compensate the phase shift angle error. Also, grid LC filter design and the system controllable limit of the matrix converter output voltage are presented. In addition, the PWM switching technique of the H-bridge circuit is modified to realize safe operation of the converter during step changes at the grid voltage. The effectiveness of the proposed PWM switching technique and its related mathematical model have been investigated experimentally using laboratory prototype based 200 V, 2 kW.