Digital second order sliding mode control of PM DC motor

This paper deals with the variable structure system (VSS) approach to the permanent magnet (PM) DC motor speed control. The aim of this treatment is that of proposing a novel scheme based on second order sliding mode control (SOSMC) technique. The main features of the proposed scheme are the robustness against heavy motor parameters variations and the avoidance of the current loop implementation, which is generally requested by traditional approaches. The precise knowledge of the motor parameters is not requested, and the insensitivity to smooth unknown load torque disturbance is obtained. Moreover, some issues associated with the practical implementation of the control scheme, mainly linked to the current ripple amplitude, are discussed, and experimental investigations are reported to show the effectiveness of the proposed approach.