A Novel Single Phase Modified Quasi-Z-Source Inverter Circuit Design and Analysis

This study presents a novel single phase modified quasi-Z-source inverter (qZSI) with high boost voltage conversion ability by using an additional switching device across the impedance network. Compared with traditional qZSI, the boost ability of the presented circuit is increased. Furthermore, the total harmonic distortion (THD) for the voltage and current at the output is reduced because of a modified unipolar pulse width modulation (PWM) technique adapted for the qZSI. Therefore, the overall efficiency of the circuit is improved. The operation principle of the single phase modified qZSI is analysed using theoretical calculations. Simulations are performed to prove the effectiveness of the high boost voltage conversion ability for different modulation indexes using Matlab/Simulink. The applied modulation technique is compared with the traditional PWM control techniques to show reduced THD value which is very close to the IEEE distortion limit. A laboratory prototype is developed to validate the proposed theory.

I. Introduction

Today, inverters that changes DC power from batteries, renewable energy sources or fuel cells to AC power are utilized in numerous areas ranging from AC motor control to photovoltaic (PV) systems, from uninterruptible power supplies to variable speed drives. [1]. Considering the type of power supply and operation principle, conventional inverters can be classified as voltage source inverter (VSI) and current source inverter (CSI) [2]. VSI operates only in buck mode by switching a voltage source. The switching devices of the same leg cannot be in shoot-through state. As opposed to VSI, CSI operates only in boost mode by switching a current source. Similarly, in a CSI the switching devices of the same leg cannot be off at the same time. Furthermore, VSI and CSI have some other drawbacks such as two-stage power conversion indispensability, vulnerability to the effect of electromagnetic interference (EMI) and dead time requirement between top and bottom switch of the same leg which causes output waveform distortion [2]. In order to prevent the mentioned drawbacks, in [3] a relatively new Z-Source inverter (ZSI) topology was introduced as shown in Fig. 1. Fig. 1.

The ZSI circuit topology.