A Speed and Flux Observer using Square Root Cubature Kalman Filter for Induction Motor Drive

An introduction of a new observer for estimating speed and flux of induction motor drive is done in this paper. The main tool of designing the observer is cubature Kalman filter (CKF). In order to compute multivariate integrals for moment estimation the CKF uses spherical-radial transformation followed by a third degree spherical-radial rule. The utmost advantage of CKF lies on capturing the system nonlinearity using the spherical-radial transformation giving it and edge over Extended Kalman Filter (EKF), as the errors is in it are minimized by linearizing the state model of the system. In this paper square root form of CKF (SRCKF) is used to eliminate the most hazardous situation of the loss of positive definiteness of error covariance matrix in each update which can stop the CKF from running continuously. The sensor less direct torque control is used for an Induction motor of 0.75Kw, 1475 rpm, for conducting performance test of the proposed observer. For simpler design of SRCKF, state space model of IM in stationary reference frame has been used. Effectiveness of the proposed observer is validated using simulation result for a VSI fed IM drive and compared with that of an EKF observer.