On the use of high frequency inductance vs. high frequency resistance for sensorless control of AC machines

Up to the date, high frequency signal injection sensorless control techniques normally assume a purely inductive behavior of the machine at high frequency, the rotor position-dependent differential inductance being the term tracked and from which the rotor position is estimated. However, certain machine designs show a rotor position-dependent high frequency resistance, which can also be used for sensorless control purposes. The differential rotor resistance occurs due to the differences in the electrical conductivity between rotor materials, and been found to be, depending on the machine design, less sensitive to operating condition than the differential inductance. This paper compares the use of the high frequency inductance and the high frequency rotor resistance for sensorless control of AC machines, particularly surface permanent magnet synchronous machines (SPMSM), using high frequency signal injection. It will be shown that the behavior of these two quantities strongly depends on the machine design, but can also be influenced by its operating condition -mainly the load level-, which needs to be considered for the design of the rotor position estimation strategy.