Frequency Converter with Multilevel Voltage Source Inverter

Abstract

Some systems need a three phase AC source with variable voltage and frequency so the frequency converter is used. However, use of frequency converter is becoming popular in the recent years for speed control of AC motors. In this project we will construct a six pulse controlled rectifier (B6C) which provides a variable dc voltage to the DC-link to get a number of voltage levels that will provide a seven level diode- clamped inverter which will provide a variable output voltage and frequency. The personal computer is used for the needed control (to generate suitable digital signals). The technique is diode-clamped using the topology of selective harmonic eliminated pulse width modulation (PWM), but in this project we can't apply the PWM technique as well as to get no harmonic because of the limitations of the hardware devices (power transistors). Also, in this project we will put the ability of changing the voltage and frequency in controlling purposes (drive speed control), with obtaining a constant ratio between the changing of voltage and frequency. This project has the ability to work as an open loop system, but the hardware of this project can't work as a closed loop system because we used an external circuit to control of the voltage, whereas, we use the PC to control of the frequency, so we can't control of the voltage and frequency together.