Soft-switching technique for a three-phase bidirectional grid-tie DC-AC-AC converter

Abstract

This paper presents a new mathematical model and a soft-switching technique for the bidirectional three-phase grid-tie DC-AC-AC converter of the matrix converter high-frequency link type. The converter topology consists of a conventional H-bridge circuit linked to a single-phase-to-three-phase matrix converter through a single-phase high-frequency transformer (HFT). The proposed control technique regulates battery current and injects three-phase sinusoidal current to grid at unity power factor. The proposed mathematical model uses a trapezoidal approximation of the high-frequency (HF) current to obtain the accurate duty cycles for all matrix converter switches, which results in low total harmonic distortion (THD) at the grid side. Also, the proposed soft-switching technique enhances the system overall efficiency. Moreover, using HFT as a galvanic isolation between the battery and grid sides enhances the system efficiency and reduces the overall size and weight. The mathematical model of the DC-AC-AC converter and the circuit operational modes for soft-switching are presented along with the voltage controllable limits. The system validity has been verified experimentally using laboratory prototype.