Application of robust nonlinear control for correct trajectory tracking in the face of machine faults

Servo applications, such as robot and machine tool drives, require high position accuracy. This demands that the system response is insensitive to parameter variations (due to inaccuracies or machine component failures) and modelling imprecision. Particularly, in a vector controlled induction machine, these uncertainties affect both the inertia and the friction model of the load. Therefore, it is necessary to synthesise a torque current component that leads to the command rotor position being reached, despite all parametric inaccuracies. Fixed gain controllers may be used to implement position servo systems based on vector controlled induction machines. A fixed gain controller is however designed around a unique operating point. This can cause the system to become unstable when operating substantially away from that point. Taking a vector controlled induction machine as starting point, the present paper develops different versions of a sliding mode control algorithm, so as to implement a position servo mechanism. Firstly, the sliding mode control fundamentals are applied to the specific case of a vector controlled drive system. The position servo system is then modelled and tested using the MATLAB/SIMULINK simulation package.