High Frequency Transformer Isolated Quasi Z-Source Cascade Multilevel Inverter

In this paper, a new structure of HFTI-qZS-CMI has been proposed. The proposed structure is capable of generating high-voltage for medium to high power applications. By adding a switch, a capacitor and a high-frequency transformer and also eliminating an inductor from each qZS-CMI cell, the HFTI-qZS-CMI structure will be created. Using the high-frequency transformer in the proposed structure, leads to electrical isolation between the input and the output, increase or decrease the output voltage, increase the system reliability and reduce the electromagnetic interference. The number of elements in the proposed structure is less than three stage cascade multilevel inverter. Moreover, in comparison to the qZS-CMI with the same input and output voltages, it has lower voltage stress on the diode and the switches as well as higher boost factor and larger modulation index.To control the on and off state of the switches, the Improved phase-shifted sinusoidal pulse width modulation with third harmonic injection is used which increases the modulation index more than one and improve the quality of inverter output power. The proposed structure simulation has been carried out in MATLAB / SIMULINK software. The results of analysis and simulation show better performance for the proposed inverter comparing to other structures.