Development of a single phase multilevel voltage source inverter FED from multiple capacitive isolated DC sources

Abstract

The aim of this thesis is to develop a single phase multilevel voltage source inverter fed by multiple capacitive isolated DC source. The multiple sources have been generated from a single DC source using capacitor isolated DC-DC converters. This removes the requirement of multiple sources but uses complicated switching scheme. A new switching scheme has also been proposed to eliminate the use of complicated switching techniques of conventional multilevel inverter. The new scheme uses only one switching signal phase shifted as required by the number of stages of multilevel inverter. Conventional DC-DC converters have been modified by using only one capacitor to isolate the output from the input. Multiple outputs have been generated from a single DC source using the modified converters. These outputs have been fed to the input of conventional multilevel voltage source inverter. Later, a new switching scheme for multilevel voltage source inverter has been proposed and the outputs from the multiple output DC-DC converters have been fed to the multilevel inverter. The working principles of all the circuits have been explained. The output and circuit behavior for each DC-DC converter have been shown and the results have been compared with conventional converters. The results obtained from conventional multilevel inverter using separate DC sources and outputs from multiple outputs DC-DC converter have been compared. Result obtained from applying the new switching scheme has also been shown. This thesis has introduced two new concepts: i) use of capacitors to generate multiple isolated DC sources from single DC source that can be fed to conventional multilevel inverters and ii) new concept of switching of multilevel inverter using the concept of synchronous generator waveform synthesis. The first concept will help to develop a module for generating isolated DC outputs from a single DC source with limited additional costs. The second concept will help to eliminate the use of complicated switching techniques of conventional multilevel inverter. It uses only one switching signal phase shifted as required by the number of stages of multilevel inverter.