Speed and Position Observer for Non-sinusoidal PMSM Based on a PSD+PLL Structure

This paper presents a sensorless control strategy for non-sinusoidal permanent magnet synchronous machines (PMSM) based on a positive sequence detector + phase-locked loop (PSD+PLL) approach. The non-sinusoidal characteristic of the back-EMF results in oscillations when the speed and position are estimated through conventional methods. The proposed approach estimates the back-EMF using a Luenberger observer on stationary reference frame. Furthermore, a PSD is built using a dual second-order generalized integrator (DSOGI), which is tuned in the synchronous frequency estimated by the PLL and is employed to calculate the observed back-EMF fundamental component. Thus, it is possible to re-reduce the back-EMF harmonic content through the proposed scheme. The PLL is adjusted by a PI mechanism and the gain design is performed using pole-placement. The design analysis is also presented and the constrains regarding the PLL natural frequency and damping ratio are investigated. Simulation and experimental results demonstrate that the proposed sensorless control scheme allows the position and speed to be properly estimated even in a machine with non-sinusoidal back-EMF.