An implementation of a programmable cascaded low-pass filter for a rotor flux synthesizer for an induction motor drive

Digital implementation of integrators for the estimation of the rotor flux of an induction motor from the stator voltages and stator currents, poses problems associated with the offset in the sensor amplifiers. Traditional low-pass filters can replace an integrator, however the poor dynamic response of the estimator calls for a programmable cascaded low-pass filter (PCLPF) implemented in software. The use of a cascaded low pass filter for stator flux synthesis has previously been applied to stator flux oriented vector controlled drives. In this paper, the performance of such an estimator is investigated with simulation studies and experimental results, implemented for the rotor resistance identification of a rotor flux oriented induction motor drive. The three stage programmable cascaded low-pass filters discussed in this paper have resulted in excellent steady-state and transient responses, such that they are successfully used for the on-fine rotor resistance identification with PI/fuzzy estimators and using artificial neural networks.