Unified Graphical Model of High-Frequency Signal Injection Methods for PMSM Sensorless Control

High-frequency (HF) signal injection methods have proved to be good candidates for permanent magnet synchronous motor sensorless control at zero or low speed. However, conventional methods have some shortcomings, and several improved methods have been put forward by scholars. In order to analyze the essential relationships among these methods, a unified graphical model is proposed in this paper based on the analysis of mechanism of conventional HF signal injection methods. According to the unified graphical model, the signal modulation modes can be categorized into phase-modulated-based HF injection (PMHI) and amplitude-modulated-based HF injection (AMHI), meanwhile the demodulation modes can be classified into open-loop calculation and close-loop convergence. Besides, novel methods are easily deduced from the unified graphical model. Furthermore, the effects of adverse factors, including resistance, digital control delay, inverter nonlinearity, and cross saturation on PMHI and AMHI are analyzed, respectively. Finally, experimental results prove the validity of the theoretical analysis.