Full-speed Range Sensorless Control of BLDC Motor Based on HFI-SMO Composite Observation

Brushless Direct Current (BLDC) motors are widely utilized in industrial automation, intelligent robotics, military, new energy vehicles, consumer electronics, and aerospace due to their high efficiency and reliability. To meet the demand for sensorless control across the full-speed range, this paper investigates and implements a composite rotor position observation method based on High-Frequency Injection (HFI) and Sliding Mode Observer (SMO) under the Field-Oriented Control (FOC) framework: the HFI method is employed to extract rotor position information during zero and low-speed stages, while the system switches to the robust SMO for observation during medium and high-speed stages. Secondly, to address the chattering issue commonly occurring at the switching instant between the two algorithms, a smooth weight switching algorithm based on a cubic S-curve is designed. Matlab/Simulink simulation results demonstrate that the proposed scheme not only ensures stable motor operation across the full-speed range but also reduces the peak angular error of chattering by approximately 50% compared to non-switching algorithms, verifying the effectiveness and superiority of the proposed composite rotor position observation method in full-speed range sensorless control.