Pre- and post-filtering approach to sensorless VSS speed control of a permanent magnet DC motor subject to Hammerstein and Wiener nonlinearities

•Identification and linearization of a PMDC system subject to static nonlinearities.•Novel VSS system configuration with a pre-filter and a post-filter.•Dynamic filter that converts the armature current to the sliding variable.•Robust sensorless speed control against partial parameter variations.

In this paper, we propose a pre- and post-filtering approach to output feedback variable structure control of a permanent magnet DC servo motor under constant inertial load. The proposed control method is to regulate the motor speed by using the armature current measurement alone. Both the Hammerstein nonlinearity for the system input end and the Wiener nonlinearity for the output end are considered. With these static nonlinear functions carefully identified and their inverses fitted, the linearized model renders a simple dynamic mapping from the armature current to the sliding variable, which is designed as a dynamic function of the motor angular velocity. The pre-filter is the inverse of the Hammerstein function. The post-filter consists of two blocks in series: the inverse of the Wiener function and the concatenating dynamic filter, which is a linear relationship between the armature current and the sliding variable. The proposed method is robust against parameter variations in the electric subsystem such as the armature inductance and resistance.