A Single-Phase High-Frequency Isolated Quasi-Z-Source AC-AC Converter Without Commutation Problem and Step-Change Frequency Operation

In this paper, a single-phase high-frequency isolated (HFI) AC-AC converter based on quasi-Z-source (QZS) cell with step-change frequency is proposed. In the proposed converter, creating electrical isolation and regulating the output voltage in a wide range is achieved with only one quasi-Z-source cell. Also, only one high-frequency switch is modulated with PWM signal in each positive and negative half-cycles. Due to the proposed converter’s inherent commutation feature, needing a snubber circuit or implementing a safe commutation strategy is eliminated. Consequently, the output voltage amplitude and frequency are adjusted with a simple control method. Since the voltage gain of the proposed AC-AC converter is controlled by the transformer turn ratio and duty cycle hence a wide range of output voltage can be achieved by choosing the proper values for the high frequency transformer (HFT) turn ratio and duty cycle. The operating principle of the proposed converter is described in different operational modes, and its key relationships are calculated. Finally, to verify the accuracy of the claims, the simulation results of the proposed converter in PSCAD/EMTDC software at frequencies of 25 Hz, 50 Hz, and 100 Hz is provided.