Sensorless Field Orientation Control of Induction Motor Using Reduced Order Observer

The composite method of the flux observer and reduced order speed observer and its design procedure for a nonlinear dynamic system is presented. The traditional approach with flux and speed observer and derive six order nonlinear model that describes motor model in field oriented coordinates. The model takes into the error in flux estimation. For flux regulation traditional PI controllers are used. For speed regulation, model is simplified by assuming that the flux regulation is relatively fast and high gain PI controller to regulate qaxis current to its command. This outcome is in a third order nonlinear model in which the speed and two flux estimation errors are state variables, the q-axis current is a control input and speed estimate provided by observer is a measured output. This nonlinear model is a main contribution to paper. The design of controller is takes place via linearization. The analysis concede an important role by the steady state product of flux frequency and q-axis current in determining control property of system.