Adaptive sliding-mode observer for field oriented sensorless control of SPMSM

This paper proposes a new scheme to guarantee speed sensorless control and optimal field orientation of surface permanent magnet synchronous motors (SPMSMs) even if parameter deviations occur and initial rotor position is unknown. A novel adaptive sliding-mode observer is used for field oriented speed sensorless control. First the induced e.m.f. components are observed using the sliding-mode technique with an adaptive switching gain. Then a low-pass filter with an adaptive amplitude compensator, that works as derivative observer, is used to get rid of the chattering noise of estimated e.m.f. components and to calculate rotor speed and position. The current components in rotor reference frame are estimated from the active and reactive electromagnetic torques calculated in both the stationary reference frame and the estimated rotor one. The latter is also used as control reference frame. Inverter, filters and observer cause unavoidable and unpredictable time-delay in rotor position estimation, so that the control reference frame is delayed as to the actual rotor one. As a consequence, field orientation and maximum torque/current ratio do not occur when the desired field oriented current references are imposed in the control reference frame. An original field orientation PI controller is used to provide the appropriate current references in the control reference frame. Test results are presented to prove the approach effectiveness.