Design and implementation of nonlinear state and parameter estimation schemes for three phase induction motor

Abstract

The thesis reports a critical evaluation of model based nonlinear estimation schemes for the state and parameter estimation of a three phase squirrel cage induction motor. This work in particular deals with design and implementation of nonlinear Kalman filters for the estimation of states and a parameter of a squirrel cage type three phase induction motor. In recent years model based estimation of speed and flux using measured supply voltage and motor current has become a trend in control strategies such as field oriented (FOC) and direct torque (DTC) control schemes. Though both deterministic and stochastic techniques are available, stochastic filters namely Kalman filter, Extended Kalman filter (EKF), Unscented Kalman filter (UKF) and Particle filter (PF) are extensively utilized in various fields. First part of the thesis deals with design, implementation and analysis of EKF, UKF and Neural state filter (NSF) for the estimation of states of a three-phase induction motor, specifically to estimate the rotor speed under various operating conditions. Extensive Monte Carlo simulation study and an offline experimental data based study have been carried out to assess their relative performances. The experimental studies conducted on the AC drive system corroborate completely the inferences we have obtained through simulation studies. Second part of the thesis deals with design and implementation of Joint Extended Kalman filter (JEKF), Joint Unscented Kalman filter (JUKF), Dual Extended Kalman filter (DUKF) and Dual Unscented Kalman filter (DUKF) for simultaneous state and parameter estimation of three phase induction motor, specifically to determine and track the value of rotor resistance. It can be inferred that JEKF is able to generate fairly accurate estimate of rotor resistance under most of the operating conditions. While DEKF and DUKF show better sensitivity towards rotor resistance changes but their performances are not found to be satisfactory especially in the presence of load changes. newline