Real time implementation of a first order thermal model for induction motor drives

Induction motors are often subjected to stress caused by repeated fast and short torque transients. These working conditions could lead to overheating some parts of the motor, among which the most sensitive are the stator windings. This thesis deals with the implementation of a temperature estimator of the stator windings obtained through a first order thermal model. The first step of the project concerns the development of a model which is capable to simulate and evaluate the dynamic and magnetic parameters of the induction motor in different working condition. In particular joule losses, iron losses and magnetic saturation are taken in account and the reference frames used to model the motor are: three-phase time-domain (a,b,c), stationary (α,β) and rotating frame (d,q). Furthermore analysis and validation of the model were performed in MATLAB/Simulink environment. Then we moved on to design the torque and speed control of the motor using a "field oriented control" (FOC) scheme. Induction motor speed control is a process of manipulating currents in order to regulate speed. Field-oriented control regulates Id and Iq such that the flux is proportional to Id and the torque is proportional to Iq. The performance of the control strategy is tested and compared on the model already developed on MATLAB/Simulink and then on a real induction motor, in the laboratories of the Politecnico di Torino, comparing the obtained responses with those provided by dSPACE. The thermal model, based on the first order system, was implemented inside the drive control and compared with the temperature values of the windings measured in the laboratories.