Discrete-Time Position Sensorless Current Control for Permanent Magnet Synchronous Motors With an Accuracy-Improved Phase-Locked Loop

In this article, a discrete-time sensorless current control for permanent magnet synchronous motors with an accuracy-improved phase-locked loop is proposed. The proposed current control method is designed directly in the discrete-time domain, which guarantees the control performance in digital implementations. In the proposed scheme, a discrete-time double-vector model is constructed for permanent magnet synchronous motor (PMSM). Then, the complex principle-based discrete-time current regulator is extended to PMSM with better performance and higher robustness. In order to reduce the error between the estimated and actual back electromotive force (back-EMF), a discrete-time sliding-mode back-EMF observer is designed based on an exact discretized state-space model. Then according to the rotational mode of the back-EMF in the discrete synchronous reference frame, a fully discretized back-EMF model is established with the angular error between the estimated angle and the actual angle. Based on the back-EMF model, the proposed phase-locked loop (PLL) can estimate the electrical angle more accurately. The angular error which increases with the rising speed in the conventional angle estimation method is suppressed by the proposed PLL. Finally, the comparative experiments verify the effectiveness of the proposed method.