English

Abstract

This study deals with simulation of Sine PWM VSI inverter fed induction motor drive. By varying the modulation index of SPWM then vary the voltage of VSI. This technique minimizes the lower order harmonics, heating and improves the response of VSI. The transient rotor current, electromagnetic torque and rotor speed of the Induction Motor will improve. The drive system is modeled using matlab simulink and the results are presented. Fixed AC is converted into DC and this DC is converted into variable voltage and variable frequency AC using Sine PWM inverter. The output of inverter is applied to the stator of induction motor. The FFT analysis shows that the current spectrum has reduced harmonics compared to the conventional system. The three phase induction motor, which is most widely used AC motor type in the domestic, industry, has been favored because of its self starting capability, low inertia, simple & rugged structure, suitable to all applications, low cost, low maintenance cost, less weight per watt, high reliability and high efficiency. Along with variable frequency AC inverters induction motors are used in many adjustable speed applications, which do not require fast dynamic response. There are many possible PWM techniques like sinusoidal PWM, selected harmonic elimination PWM, space vector PWM etc used for speed control of induction motor. The PWM inverters are very commonly used in adjustable AC motor drive loads, where one needs to feed the motor with variable voltage variable supply frequency. For wide variation in drive speed, the frequency of the applied AC voltage needs to be varied over a wide range. The applied voltage also needs to vary almost linearly with the frequency. The switches of the PWM inverters are turned on and off at significant higher frequencies than the fundamental frequency of the output voltage waveform. In sine PWM Inverter, the width of the pole voltage pulses over the output cycle, vary in a sinusoidal manner. The scheme, in its simplified form, involves comparison of a high frequency triangular carrier voltage with a sinusoidal modulating signal that represents the desired fundamental component of the pole voltage waveform. The peak magnitude of the modulating signal should remain limited to the peak magnitude of the carrier signal. The comparator output is then used to control the high side and low side switches of the particular pole. Some of the following constraints for slow varying sinusoidal voltage be considered as the modulating signal are 1) the peak magnitude of the sinusoidal signal is less than or equal to the peak magnitude of the carrier signal. This ensures that the instantaneous magnitude of the modulating signal never exceeds the peak magnitude of the carrier signal. 2) The frequency of the modulating signal is several orders lower than the frequency of the carrier signal. A typical figure will be 50 Hz for the modulating signal and 20 KHZ for the carrier signal. Under such high frequency ratio's the magnitude of the modulating signal will be virtually constant over any particular carrier signal time period. 3) A three phase sine-PWM inverter would require a balanced set of three sinusoidal modulating signals along with a triangular carrier signal of high frequency. For a variable voltage- variable frequency (VVVF) type inverter, a typical requirement for adjustable speed drives of AC motor, the magnitude as well as frequency of the fundamental component of the inverters output voltage