Development of a switched inductor quasi-Z-source inverter

In power electronics applications, large-size transformers were preferred to increase the output voltage in the past while performing DC-AC conversion, in later times the step-up DC-DC converters with smaller volume were used. Due to the additional cost and losses of the transformer and DC-DC converter structure, Z-source inverter (ZSI) circuit has been proposed as a new and unique converter topology in recent years. Unlike conventional inverters, ZSI impedance network can perform buck-boost operation in single stage, increase the efficiency by reducing the cost with the eliminating of the transformers and converters, and minimize the distortions in the output waveform since it does not use dead time. Therefore ZSI is preferred as an alternative converter circuit structure. In this thesis study, a quasi-Z-source inverter (QZSI) circuit, which is an improved version of ZSI and offers a unique power conversion concept by eliminating the conceptual and theoretical limitations of the conventional current and voltage source inverters, was designed and realized. Simple boost PWM control technique has been employed to the switches using NUCLEO-F411RE development board since this technique doesn't involve low-frequency ripples on the passive components of the impedance network and has lower distortions at the output. In order to improve the circuit parameters of the designed QZSI circuit, the impedance network has been modified. An inductor and three fast recovery diodes are added to the input inductor of the impedance network in order to increase the voltage gain and the boost factor of the circuit. The input inductor has been transformed into a circuit form called switched inductor (SL) and this is integrated into the impedance network. Using the operating principle of the SL circuit form, an increase between 12% and 68% in the boost factor and a decrease over 10% in the voltage stress and the inrush current were observed depending on the applied modulation index. Low distortion sinusoidal AC output voltage is obtained at the output of the developed QZSI circuit with SL circuit form. Simulation and experimental results carried out in the laboratory environment clearly show that the proposed circuit provides high boost DC-AC inversion ability.