A Double-Input Three-Level Quasi-Z Source Converter Using GaN Switches with Reduced Voltage Stress for Multiple Energy Interface

A step-up double-input three-level quasi-Z source DC-DC converter (DITLQZC) using Gallium Nitride (GaN) is proposed in this paper to deal with the problem of the mismatched voltage levels between the dynamic lower voltage of the photovoltaic and the constant voltage of the de-link bus for renewable energy system, which is derived from the conventional three-level flying-capacitor boost converter. It can increase the voltage gain highly without utilizing any transformer, and reduce the voltage stress of switches as well. The steady-state operation and the control strategy for a wide range voltage-gain performance are investigated based on the actual switching sequence of the converter. To do so, the correlation between the modulation index, the output voltage, and the quasi-Z source net capacitor voltages is studied. Then, to understand the dynamic and the static behavior of proposed converter, the fundamental concept of self-balance operation of the flying-capacitor voltage is expressed. To increase both the efficiency and power density, GaN switches with small drain-source resistance RDS(ON) are employed, which inherit the outstanding advantage in terms of small size. Finally, a 1kW prototype has been simulated using the actual model of switches provided by the company in LTSpice to verify the operating principles and theoretical analysis.