Enhancing sliding mode control with proportional feedback and feedforward: an experimental investigation on speed sensorless control of PM DC motor drives

This paper investigates the enhancement of sliding mode control (SMC) with the combined use of feedforward torque compensation and proportional error feedback control. The proposed enhancement is adapted to the control of permanent magnet (PM) DC motor drives by synthesis of the equivalent control equation augmented as proportional feedback and feedforward terms. A novel sliding function, introduced by utilizing the estimated load torque and the estimated rotor current, is examined and compared with another known sliding function obtained by nonideal differentiation of the estimated rotor speed. The significance of the proposed enhancements to SMC consists of the elimination of disturbance, the reduction of the discontinuous control gain magnitude, and the reduction of chattering. The contribution of this study is demonstrated by a performance comparison between several control versions, where the aim is the achievement of good performances in both the speed estimation and state tracking accuracy in the speed sensorless control of PM DC motor drives under varying load inertia. These latter statements are verified by several comparative simulations and experiments.