Successful operation of Permanent Magnet (PM) Machine and Switched Reluctance Machine (SRM) needs adequate synchronization between stator excitation and magnetic field status variation caused by the movement of rotor/mover. Researchers at U.T. Dallas have developed specific techniques for sensorless operation of electrical machine based on generalized principle of detecting position dependent, variant magnetic field status via machine terminal measurement. The combination of these techniques potentially have wide speed range and can be applied to the families of switched reluctance machine and permanent magnet machines. Thus, eliminate the need of physical position encoder/ resolver.
In order to properly control SRM and PM machines, the stator excitation needs to be synchronized with rotor position. Position sensors like optical encoders, resolvers and Hall-effect sensors generally increase the system cost and require extra space for installation. The relatively low cost incremental encoder and Hall-effect sensor has limitation on initial position measurement which prohibits full load non-reversal start up. Further more they are considered to be unreliable under harsh operational environments and have very limited resolution under super high speed operation. Thus sensorless methods which cover entire speed ranges will greatly benefit the operation of SRM and PM machines.
The developed technologies for SRM take advantage of both inductance and power variation rather than the flux variation and issue commute commands according to the signal characteristics. This eliminates the storage of complex multi-dimensional look up tables. More importantly, it covers initial start up to full speed. The initial and low speed position detection utilizes variation of magnetic core permeability caused by PM material. It guarantees reliable start up and low speed operation under full load.