Torque estimation of permanent magnet synchronous machine using improved voltage model flux estimator

Abstract

A torque estimator for permanent magnet synchronous machines is presented based on flux estimation. The voltage model of the machine (Faraday's law) is employed to estimate the flux where pure integrators are applied to the electromotive force (EMF) of the machine. To solve the problem of DC drift due to pure integrators, a current-model flux estimator modified by a Kalman-like observer is temporarily switched on to reinitialise the pure integrators. The current-model estimator with its associated observer is activated only if the difference between the reference and estimated torque exceeds a predefined threshold. For the remainder of the operating time, only pure integrators are used to estimate flux. Furthermore, an online EMF offset detector is designed to compensate EMF offsets before integral action to avoid divergence of the estimated flux. The proposed approach allows smooth estimation at standstill compared with existing approaches that use filters. Moreover, the method allows space to be freed up at the central processing unit because it is not always highly occupied during motor operating times. The simulation and experimental results show the capabilities of the proposed torque/flux estimator.