Application of a sliding mode observer for switched reluctance motor drives

A sliding mode observer is applied towards the operation of a switched reluctance motor drive. The sliding mode observer estimates rotor position and velocity to control the conduction angles of the machine. The particular case of an automotive hydraulic brake system motor is considered in detail where the conduction angles are modified with velocity feedback to provide optimum time response to brake system commands. Nonlinear modeling of a switched reluctance motor is described and a computer simulation is developed based on data from an experimental switched reluctance motor system. The sliding mode observer is implemented with a fixed-point digital signal processor and the discrete-time implementation is first examined under locked rotor conditions. After confirming the accuracy of the computer simulation with experimental data, the design considerations in selecting observer coefficients with regard to sampling time, convergence rate and transient stability are discussed. In conclusion, the effects of flux estimation errors on the system time response during a start-up transient are examined.