Periodic speed ripples minimization in PM synchronous motors using repetitive learning variable structure control

In this paper, we propose a simple repetitive learning variable structure control (RLVSC) scheme to reduce periodic speed ripples in a permanent magnet synchronous motor (PMSM). These speed ripples are induced by parasitic torque pulsations that vary periodically with rotor position. The conventional PI speed controller is able to reduce speed ripples to a certain extent but not sufficient enough for many high performance applications. During steady state, the RLVSC generates a reference compensation current that together with the outer loop PI speed controller is used to minimize the speed ripples. Being a plug-in module, the proposed RLVSC controller can be easily integrated to any of the existing PMSM drive systems. Experimental evaluation of the proposed scheme is carried out on a DSP-controlled PMSM drive platform. Test results obtained demonstrate the effectiveness of the proposed control scheme in reducing speed ripples by a factor of approximately 3 under various operating conditions.