SELECTIVE HARMONIC ELIMINATION IN CURRENT SOURCE INVERTER FED INDUCTION MOTOR DRIVE

Abstract

With the advent of power electronic devices, the use of AC motors for variable speed drives is increasing. PWM Inverters are mainly used to feed the induction motor because of the ease of obtaining variable frequency and variable voltage. Among various PWM techniques, the Selective Harmonic Elimination (SHE) PWM technique has the advantage of operating at reduced inverter switching frequency, besides eliminating the desired harmonics. CSI fed induction motor drives are used in high power adjustable speed drives because of its inherent advantages such as four quadrant operation, short circuit protection, supply voltage variation immunity etc. In this thesis work SHE technique is applied to the CSI to eliminate the lower order harmonics, besides minimizing the THD. Switching angles are calculated for eliminating lower order harmonics by equating the corresponding harmonic current equation (obtained from Fourier series expansion of the output waveform) to zero. This requires numerical techniques to obtain the switching angles as the equations are transcendental in nature. NAG subroutine E04UCF is used for solving such a set of Non linear, transcendental equations. A SIMULINK model of SHE CSI is simulated using the switching angles calculated above and its harmonic spectrum is to be studied. A logic circuit is developed to generate the firing pulses sequences for the CSI to obtain the desired SHE output pattern. A model of SHE CSI fed Induction motor drive is simulated using the SIMULINK software of MATLAB. An effort is made to achieve the speed control of Induction motor fed from SHE CSI by using slip speed control.