Damping resonant modes in DC motors using sliding mode control

This paper presents an output-feedback sliding mode positioning controller that can damp resonant modes in DC motors. Ironless (also known as coreless) DC motors have several attractive advantages over conventional DC motors. However, undesirable resonant effects may arise at certain frequencies impairing the closed-loop control performance. To deal with uncertainties, disturbances and to damp resonant modes, a variable structure controller with sliding modes combined with a high-gain observer is adopted. The objective is to specify the desired damped modes by means of a reference model. Simulation results illustrate the proposed design technique and the effects of the resonant modes in closed-loop control. The dynamic model of the DC motor considered in the design and simulations was obtained experimentally from the frequency response of an actual ironless DC motor. Uncertainties in the plant parameters and input disturbances were simulated in order to verify the robustness of the control system. Some classic techniques to deal with vibrations in electric motor control are discussed to show the advantages of the proposed controller.