A Novel Approach to Robust Motion Control of Electrical Drives with Model order Uncertainty

A novel approach to the control of plants with model order uncertainty as well as parametric errors and externaldisturbances is presented, which yields a specified settling time of the step response with zero overshoot. The method is applied to amotion control system employing a permanent magnet synchronous motor. A single controller is designed to cater for mechanicalloads that may exhibit significant vibration modes. The order of the complete controlled system (i.e., the plant) will therefore dependon the number of significant vibration modes. The controller is of the cascade structure, comprising an inner drive speed control loopand an outer position control loop. The main contribution of the paper is a completely new robust control strategy for plants withmodel order uncertainty, which is used in the outer position control loop. Its foundations lie in sliding mode control, but the set ofoutput derivatives fed back extend to a maximum order depending on the maximum likely rank of the plant, rather than its knownrank. In cases where the maximum order of output derivative exceeds the plant rank, in theory, virtual states are created that raise theorder of the closed-loop system while retaining the extreme robustness properties of sliding mode control.