Improved PLL-Based Sensorless Control of PMSM Drive System at Low Carrier Ratios

Conventional PLL typically uses fixed PI parameters to estimate the rotor position of PMSM, but due to the fact that PMSM parameters vary with actual operating conditions, the robustness of rotor position estimation is poor. In addition, conventional structure PLL cannot achieve zero static tracking of rotor position under acceleration and deceleration ramp input conditions, and as the carrier ratio decreases, the leading angle error caused by angle feedback delay gradually increases. And with carrier ratio further decreases, PLL based on Euler discretization has poles outside the unit circle, and the system is no longer stable. To ensure high observation accuracy of position under low carrier ratio, the principle of finite set model predictive control is referenced. The model prediction method is combined with PLL to implement a position identification scheme based on finite position set PLL (FPS-PLL). Targeted design is made to improve the computational efficiency of FPS-PLL, and an improved FPS-PLL based on Newton iteration method is proposed. Simulation results show that Newton FPS-PLL has better observation accuracy and stability under low carrier ratio.