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Development of a low voltage three phase power supply for educational use

Chapman, Michael (2013) Development of a low voltage three phase power supply for educational use. Other thesis, Murdoch University.

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Electricity is supplied and consumed within our power system via alternating current (AC) using a three phase distribution systems which normally consists of the generation and transmission of three sinusoidal voltages of equal amplitudes with phases 120° spaced apart [1, p. 267].

Courses such as Murdoch University’s Electrical Power Engineering undergraduate degree exist to prepare future engineers for a career within the power industry; to be successful such courses need to incorporate exposure to both theoretical and practical concepts including the investigation of three phase power.

Currently Murdoch University does not possess equipment suitable to expose students to practical three phase concepts at low “safe” voltages. Students in their later years of study have achieved suitable knowledge to safely practice concepts at mains voltage levels but students in their first and second years of studies are restricted to considering concepts at a theoretical level only.

This project was concerned with developing a low voltage three phase function generator that could be used in teaching environments to allow students to proceed with experiments safely and relatively unsupervised. The design goals were to produce a device capable of producing a three phase supply at safe levels (around 12 volts RMS) with a controllable frequency switchable between at least 50 and 60 Hz. Features were to include real time voltage measurements of each phase and an ability to simulate an unbalanced supply fault.

The project was completed by incorporating an Arduino Uno microcontroller using direct digital synthesis to produce three distinct outputs in the form of pulse width modulated (PWM) signals representing sinusoidal waveforms. These PWM signals were used in turn to feed a three phase full bridge integrated circuit to produce amplified signals which, after being fed through a low pass filter, produce three sinusoidal waveforms spaced with 120° phase differences.

The output waveforms produced are considered to be of sufficient quality for the application as described; waveforms appear within 2.7° of the target 120° phase difference and total harmonic distortion values measured during testing phases range from 0.847% to 2.39%.

It has been recommended that future revisions of this device incorporate features including over voltage and over current protection to protect against misuse. Additionally, refinements to the output filter and peak follower circuit would provide improvements to the overall performance of the device.

This project is considered to have been successfully completed. The function generator prototype developed over the course of this project satisfied most design objectives and could be used immediately within a classroom environment.

Publication Type: Thesis (Other)
Murdoch Affiliation: School of Engineering and Information Technology
Supervisor: Lee, Gareth
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