Sensorless control of IM using MRAS strategy and its closed loop stability analysis

In this paper, we have proposed FOC (Field Oriented Control) of Induction motor, Controller design technique and design of flux and speed observer for sensorless control of induction motor. We have used a non-linear sixth order model of induction motor as a plant. Further, analysis of Induction Motor model has been done using Bode plot in order to find out the in stability of the system with and without the controller. The simulation results obtained can be used to show that the stability of the system remain unaffected in closed loop even after giving perturbations in the load. Then we have elaborated FOC strategy used for the control of IM. Flux and speed are regulated to their reference values using PI controllers. PI controller uses error of current along d and q axis as control input to compute Flux and Speed. A reduced model for sensorless control of IM is also derived. Sensored control of Induction motor may lead to improper outputs if sensor somehow gets damaged. So, we have also proposed sensorless control of Induction Motor using Model Reference Adaptive Scheme (MRAS) based observer. MRAS technique uses an error between reference and an adaptive model to track the speed of motor which is then given to the speed controller to regulate the speed to its reference value. A flux estimator is also used which estimates the flux using current daxis current. Loop shaping design technique has been used in this paper to tune PI controllers. The simulink results obtained using reduced model are then used to conclude the paper.