A robust force controller for an SRM based electromechanical brake system

In this paper, we propose a robust nonlinear force controller for a switched reluctance motor (SRM) electromechanical brake system which is a promising replacement for hydraulic brakes in the automotive industry. A detailed model of the motor including current dependent inductance coefficients is used. The load exerted on the motor by the caliper may be modeled as a spring; however, the actual load model is taken to be an unknown nonlinear function of position to allow for uncertainties in the model. Hence, the developed controller works for a wide variety of loads including brake systems. The controller is designed using backstepping and incorporates a novel voltage commutation scheme. The controller does not require knowledge of the mechanical parameters of the motor and the functional forms of the relationships among the motor position, the brake force, and the motor load torque. Moreover, the controller provides significant robustness to uncertainty in the inductances. Furthermore, practical current and voltage constraints are addressed. The performance and robustness of the controller are demonstrated through simulation studies.