Seven-Level Inverter with Two-Level Boost Converter and Coupled Inductors

Abstract

For most multilevel inverters both the complexity of control method and the amount of components increase drastically when increasing output voltage levels Therefore this thesis proposes a seven-level inverter system which is composed of a two-level boost converter and a seven-level inverter with coupled inductors The overall system can be divided into two main parts First the boost converter utilizes the dc voltage as an input source and converts it into two voltages with multiple relationships Then the second part namely the seven-level inverter transforms these two voltages to a seven-level output voltage The two-level boost converter uses lower power switches and diodes to get one more voltage level than a conventional boost converter For regulating the two-level voltages this thesis proposes a simplified control strategy informed by the conduction states of switches Furthermore a seven-level inverter with coupled inductors can provide seven-level output voltage before a low pass filter of which the output is nearly a sine wave so that the system can achieve lower total harmonic distortion (THD) and minimize the size of the low pass filter Moreover by adopting the sinusoidal pulse width modulation (SPWM) modulation technique the dc component existing in the coupled inductors can be eliminated and core saturation can be avoided as well The coupled inductors with the adopted modulation technique can reduce both the conduction loss and switching loss of the seven-level inverter to thus improve the conversion efficiency In this thesis the operational principles steady-state analysis design and control strategies of the proposed seven-level inverter system are presented in detail Both simulation and an experiment were implemented to verify the effectiveness and feasibility of the proposed seven-level inverter system According to the experimental results with an input dc voltage of 190 V an output voltage of 220 Vrms and a rated power of 2 kW the THD of the output voltage was 1 06% and the maximal efficiency was as high as 97 97%

Date of Award	2016 Jul 27
Original language	English
Supervisor	Hong-Tzer Yang (Supervisor)