City Research Online

Abstract

Phase control is used as a voltage control when it is applied to the stator winding of induction motors; torque and speed can then be controlled.

Previous models have been used for many years to predict the steady state performance of induction motors under phase control. Assumptions were made in these models and there was no satisfactory agreement between theoretical and experimental results.

A single-phase induction motor is used as case study in this research. A new method of analysis is presented; which enables the steady state performance of the motor to be accurately and quickly predicted. The analysis is based upon the analytical solution of the differential equations during conduction and cut-off periods using Laplace transforms. The analysis is continued over several cycles of the supply voltage by an iteration process until a steady state solution is obtained. Exact equations have been obtained for the current and voltage over the whole cycle of the supply voltage. The saturation effect on the mutual inductance was taken into consideration and the solution is repeated by an iteration process with a corrected value of the mutual inductance depending upon the voltage level which is calculated at each solution.

As soon as the exact waveforms of voltage and current are accurately determined, the steady state performance can be determined either numerically or analytically. Harmonic formulae are given for current and voltage, and the performance can be predicted either by current analysis or by voltage analysis.

Some effects of phase control are studied, such as: modification of the motor efficiency, production of phase displacement of the fundamental voltage component and the possibility of starting-torque production without a capacitor.

Formulae are given to determine the harmonic loss in terms of the fundamental component only and to predict the phase shift of the fundamental component.

Harmonic torques have been accurately predicted by a direct analysis applied to the developed torque waveform. A formula is given to predict the harmonic torque in terms of stator current harmonics.

Experimental work was carried out with a good agreement between predicted and measured performance. The comparison has included the input power, current, voltage, torque, conduction angle, current and voltage wave shapes and harmonics of voltage and current. The measured vibration spectra were compared to those of predicted harmonic torques with a good agreement.

Noise measurements were carried out and the effect on noise production was shown, with some correlation with the developed harmonic torques.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology T Technology > TA Engineering (General). Civil engineering (General) T Technology > TK Electrical engineering. Electronics Nuclear engineering
Departments:	School of Science & Technology > Department of Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

Export

Downloads