A brushless DC motor velocity regulator using a variable structure controller with varying switching surfaces

A system using a variable structure controller (VSC) in the sliding mode is robust to disturbances. However, this advantage cannot be obtained in the reaching phase. The remedial approach adopted here is that a small switching surface slope is used at the beginning and then it is increased continuously when the system output approaches the reference setting. This method reduces the duration of the reaching phase and hence the sensitivity to disturbances during the early control period. Simulation of a brushless DC motor velocity regulator system to illustrate the effectiveness of the approach is included in this paper