28-07-2011, 11:59 AM
ABSTRACT
This paper describes the design and implementation of a Three Phase Power Converter (AC/DC/AC) as a fourth year group project for the Power Electronics and Drives B subject at Victoria University. The system implemented converts a three phase input voltage of 400 Vrms at a power rating of 500 W to DC by using a three phase diode bridge rectifier, and a Capacitive filter which assists in stabilising the output DC voltage produced. After that, the system provides the gate drive signal to a three phase pulse width modulated (PWM) inverter driving an induction motor. The pulse width modulation signal is generated by MATLAB using the Data Acquisition. The three phase MOSFET inverter uses the DC voltage supplied from the 3 phase bridge and the gate drive signals to produce a balanced three phase sinusoidal output which drives the induction motor. This project/paper can be useful for future power system students as more properties and specifications can be added to the designed product in order to investigate further issues and applications of Three Phase Power Converters.
1. INRTODUCTION
Over the past decade the field of power electronics has passed through rapid development due to the advancement of many modern technologies such as; DSP Cards, Data Acquisition Cards and Microprocessors. The aforementioned technologies made power electronics projects and applications easier to implement and more accessible. In this project we were to implement a Three Phase Power Converter (AC/DC/AC) to control the speed of an induction motor using Data Acquisition Cards.
The complete system will consist of two sections; a Power Circuit and a Control Circuit. The power circuit consists of the three phase bridge rectifier, C Filter and Three Phase PWM Inverter. On the other hand, the control circuit consists of the Computer (Data Acquisition Card/PWM Program), Opto-Couplers and Gate Drivers.
An AC voltage input that is fed to a three phase diode bridge rectifier to produce DC output voltages which across a C filter will feed the three phase PWM inverter. The PWM inverter is controlled by a three phase sinusoidal PWM signal generated by a control circuit. The PWM inverter will then convert the DC voltage at the input to AC output voltage. The AC output voltage can be controlled in both magnitude and frequency (V/F Open Loop Control). This control of voltage and frequency is required as it permits the user control the speed of an induction motor at different rates.
The project utilised many electronic components such as; Diodes, MOSFETs, Capacitors, Opto-isolators and Gate Drivers, to construct the full circuit. So, in order to achieve this, a full understanding of the characteristics and theory of each section had to be achieved, which assisted in completing the design and implementation of the product according to the required specifications.
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