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.
