Date of Award

8-1-2002

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical Engineering

Abstract

The inverters transfer energy from a DC source to a controlled process in the form of pulse trains, using semiconductor switches which are turned on and off at fast repetition rates. This thesis explains in depth how these pulse trains synthesize sine waves. AC waveform generation techniques such as the square wave and Pulse Width Modulation (PWM) are compared in terms of their harmonic elimination capability and fundamental gain control. Various PWM techniques such as bipolar switching, unipolar switching, selective harmonic elimination switching and Space Vector PWM (SVPWM) switching are analyzed and compared in terms of their ability to control harmonic distortion (THD), minimize switching losses, control fundamental gain and maximize DC bus utilization capacity. The selective harmonic elimination technique is covered in depth including a technique that utilizes a neural network controller to remove a selected set of harmonics. This thesis focuses on Space Vector PWM (SVPWM) technique since it has many advantages over other conventional methods such as sine wave PWM. Thus, the SVPWM theory and experimental analysis is presented in depth. The SVPWM technique was realized using the state-of-the- art power electronics hardware and Digital Signal Processing (DSP) software. The experimental procedure and harmonics analysis of the DSP based SVPWM output waveforms and inverter output voltages and currents are presented. The experiments were carried out using power electronics development modules such as the Texas Instrument’s TMS320LF2407 DSK (eZdsp), Digital Motor Controller (DMC1500), and the VisSim™/TI C2000 Rapid Prototyper software package and a three-phase AC induction motor. The VisSim™/TI C2000 Rapid Prototyper was extensively used to model an AC induction motor control sub system that generates real time SVPWM waveforms to control a three-phase induction motor. The AC induction motor control sub-system was implemented using the principle of constant Volts/Hertz (V/Hz) profile. S' averal measurements and observations of the phase-voltages, line-voltages and phase currents were made to observe the quality of the power produced using the SVPWM technique. The SVPWM waveforms were simulated using MATi_AB™ software and the VisSim™/TI C2000 Rapid Protctyper software. These simulated SVPWM waveforms were compared with the DSP generated SVPWM waveforms and the inverter output. The completed project will give the user the ability to use the VisSim™/TI C2000 Rapid Prototyper software to generate SVPWM waveform and power the DSP controller (eZdsp), interface the DMC1500 (inverter) with the eZdsp and control a three-phase induction motor. An extension of the conventional three-phase SVPWM to higher order phase systems is reviewed. An overview of the principle of sensorless variable speed three-phase AC motor drives with closed-loop speed control is included.

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