Dr. Syed Abdul Rahman Kashif

Induction motor is the most widely used electrical machine in industrial applications. Dynamic response of an induction motor has to be improved to optimize its energy consumption and to obtain the desired torque-speed response. Constant Volts/Hertz algorithm enables us to run motor at its rated torque and variable speed simultaneously. In short we can obtain the desired dynamic response of induction motor using V/f control. The basic theme behind V/f control is to keep the magnetic flux of the machine constant at all operating points to obtain the electromagnetic torque independent of the frequency as well as to avoid core saturation of the motor due to low frequency operation at high voltage. V/f control necessitates the variation of voltage amplitude and power frequency simultaneously. Space vector modulation (SVM) is the most advance PWM technique to dynamically vary the voltage and frequency using a 3-phase inverter. In space vector modulation, a reference voltage vector rotating at the desired electrical frequency and having desired magnitude is sampled at high frequency to approximate its circular trajectory. Closer the sampled trajectory of voltage vector to the circular one, closer will be the phase currents to the sinusoidal resulting in less losses. Closed-loop control enables us to precisely control the speed of the motor independent of the slip. The present speed of the motor is compared with the input speed and error is fed to the PI controller to generate the actuating signal having the rate of change corresponding to the parameters of the PI controller. This helps to �smooth� the dynamic response of the machine no matter how much jerky is the input speed signal.