Performance analysis of Inverter fed Induction Motor with minimum settling time control

Variable speed Induction Motors are the work horses of Industry. For many Industrial processes variable speed operation to control output and quality of production is essential. Because of the availability of high frequency and high power switching devices voltage source converters with PWM control for variable voltage and variable frequency operation have become common for the control of Induction Motors. The control of input frequency to get the set speed for the motor has to be done in such a manner that the motor reaches the set speed in a minimum time following the change in load torque. This method of control is termed as the “Minimum settling Time Control”. The change in the output voltage magnitude of the Inverter following the change in the frequency is done through the PWM control. This maintains the ratio between the magnitude and the frequency of the voltage applied to the Motor by the Inverter so that air gap flux in the motor remains constant. This paper develops the dynamic model for the Induction Motor to study its dynamic performance under load disturbances. The nonlinear model is linearized around the operating point to enable the application of minimum settling time control algorithm for obtaining the optimal Gain and Time constant for the controller used to adjust the Inverter frequency. The results obtained from the linearized model are compared with those from the Non-linear model using the same controller. Performance of the motor without controller for the same load variation is also given and the benefits of feedback control with minimum settling time are brought out.