A position detection strategy for sensorless surface mounted permanent magnet motors at low speed using transient finite-element analysis

A novel solution for sensorless starting of conventional surface mounted PM motors is proposed. The strategy of the proposed scheme is to creatively formulate a combination of electromagnetic field with transient finite element method (FEM). The proposed solution is an improvement over and above conventional methods in that it is based on rotor position detection at zero speed with high frequency signal injection and back EMF detection. Previous researches tend to consider the induced signal from different winding terminals independently. The proposed methodology however exploits the induced voltage signals from two of the motor winding terminals, using the third terminal as the signal injection point. The strategy also eliminates the process of polarity tests. The relationship between the dependency of induced signals and the rotor position angle is summarized, and a simple motor starting scheme is proposed. Effects arising from the transient characteristics of the injected/induced signals are fully addressed using FEM.