Identification of differential inductances of permanent magnet synchronous machines using test current signal injection

In this paper a new kind of identification method for differential self and mutual inductances of permanent magnet synchronous machines (PMSMs) is proposed. The precise knowledge of the parameters of PMSMs has become an important issue for many applications in electrical drive engineering. Thereby not only the differential self but also the differential mutual inductances are of interest. To identify these parameters the well-known methods that use high frequency (hf) test voltage injection provide unsatisfying results. The method proposed in this paper uses, in contrast, hf test current injection to identify the differential inductances. A machine model that includes cross saturation is the basis for the identification method. Considering the standstill of the machine, the voltage equations can be simplified. For differential inductance identification the hf test current signal is injected either in the dor q-axis of the rotor-oriented (dq) reference frame. Therefore a proportional-resonant (PR) current controller which is in parallel to the fundamental current controller is utilized. Using the output of the Goertzel algorithm, both the differential self and mutual inductances can be determined. Finally, test bench measurement results of a permanent magnet synchronous linear machine prove the proposed method.