Determination of differential inductances of permanent magnet synchronous machines for sensorless control

This paper presents a novel approach for measuring the differential inductances in a permanent magnet synchronous machine (PMSM). The knowledge of their accurate values is a prerequisite for sensorless vector controlled systems with carrier signal injection. For the measurements a standard industrial power converter is used. Besides the determination of self-inductances in the rotor-fixed reference frame, the measurement of the cross-coupling differential inductances namely the cross saturation is a main part. A high frequency sine signal injection method is used for this purpose. The measurement is compared with the result of FEM calculations. In the second part the influence of the rotor position and the machine load in steady state on the high frequency current amplitude in the quadrature axis is analysed, while the signal is only injected in the direct axis. The results of these measurements are compared with saturation effects in the machine.