New PWM technique for grid-tie isolated bidirectional DC-AC inverter based high frequency transformer

Abstract

This paper presents a new PWM switching technique for controlling a bidirectional isolated DC-AC-AC inverter along with its soft-switching technique. The proposed PWM technique has the ability to control the input DC current and to inject a sinusoidal three-phase current to the grid at unity power factor. In the first stage, an H-bridge converter is used to convert the DC voltage to a high-frequency square-wave single-phase voltage. In the second stage, a matrix converter is used to convert the high-frequency voltage waveform to conventional three-phase voltage synchronized with the grid. Therefore, a high-frequency transformer is used to link the H-bridge output voltage to the matrix converter input voltage. The proposed soft-switching technique is achieved by connecting shunt capacitors across the DC-AC-AC converter switches. The mathematical model and the circuit operation for soft-switching are presented along with the voltage controllable limits. The effectiveness of the proposed technique has been verified experimentally using a laboratory prototype.