Study and analysis of three phase multilevel inverter

Abstract

The present project deals with study and analysis of three phase multilevel inverters and their different topologies and configurations. The main purpose of our study is to study the modulation techniques and compare them with each other analyzing their advantages and disadvantages. Their applications have been analyzed according to their functioning such as the cascaded inverter for example could also serve as a rectifier/charger for the batteries of an electric vehicle while the vehicle was connected to an ac supply. In our thesis, the three main multi-level inverters studied are cascading H bridge, diode clamped and flying capacitor structure. The term multilevel converter is utilized to refer to a power electronic circuit that could operate in an inverter or rectifier mode. One first impression of a multilevel power converter is that the large number of switches may lead to complex pulse-width modulation (PWM) switching algorithms. However, early developments in this area demonstrated the relatively straightforward nature of multilevel PWM. Our project presents the fundamental methods as well as reviews some novel research. The methods are divided into the traditional voltagesource and current-regulated methods. Some discrete current-regulated methods are presented herein, but due to their nature, the harmonic performance is not as good as that of voltage-source methods. Voltage-source methods also more easily lend themselves to digital signal processor (DSP) or programmable logic device (PLD) implementation. Although we have discussed numerous topologies and modulation methods, several more can be found. An additional goal of this project is to introduce concepts related to reducing the number of isolated voltage sources and sensors. This can be important in the high power quality cascaded multilevel inverters which require several voltage sources and knowledge of the dc voltage levels.