New Mathematical Modeling of Bidirectional Grid-Tie DC-AC-AC Converter for Low THD and Unity Power Factor

摘要

This paper presents a new mathematical modeling and PWM switching technique for controlling a bidirectional three-phase grid-tie DC-AC-AC converter. The matrix converter high-frequency link (HFL) type is used to interface the DC battery power with the grid. The primary side has an H-bridge converter to convert the battery voltage to high-frequency single-phase square-waveform. The secondary side has a single-to three-phase matrix converter that interfaces the primary side with the grid. Therefore, a single-phase high-frequency transformer (HFT) is used as a galvanic isolation to link the primary and secondary sides. The PWM technique controls the battery DC current to match the reference value in addition to injecting a sinusoidal three-phase current waveforms to the grid at unity power factor. The mathematical model of the DC-AC-AC converter calculates the accurate duty cycles by compensating the trapezoidal approximated current waveform of the HFT, which reduces the total harmonic distortion (THD) at the grid side. Also, the model compensates the capacitor current of the LC filter at the grid side to accurately achieve unity power factor. Moreover, the performance of the system is investigated under low voltage grid condition. Experimental prototype has been carried out to verify the effectiveness of the proposed technique.