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Analytical models are the key tools in the model-based control design of electric drives. The inductances together with the stator resistance are the fundamental parameters of these models. In this study three methods to determine the inductances of the decoupled d-q model of double-star permanent-magnet (PM) synchronous machines are studied. These methods have commonly been used to determine the inductances of conventional three-phase PM machines. Two of the evaluated methods are based on the phase-variable inductance waveforms and flux linkages and are thus analysed with finite-element analyses only. The third method, based on the analytical stator voltage equations, can be applied straightforwardly with the real drive system supplied with voltage-source inverters (VSIs). This method requires only the knowledge of the rotor position and the existing current measurements of the VSIs that are used for the current control. Experimental results are provided to verify the applicability of the voltage-equation-based method to determine the inductances. On the average, the presented methods provide similar values, but also some discrepancies between the obtained values can be observed. The measured inductance parameters are validated using model-based closed-loop controllers.

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This paper describes a finite element (FE) based phase-variable model for double-star permanent magnet synchronous machines. In a double-star configuration where two three-phase windings are spatially shifted by 30 electrical degrees, a high amount of the 5th and 7th current harmonics may be excited because of the winding layout. However, a conventional d-q axis model considers only fundamental components, and thus, the machine model may be oversimplified. Improvement in the accuracy can be obtained by introducing an FE-based phase-variable model that includes the higher-order harmonics occurring in the no-load flux linkages and in the self-and mutual inductances. Moreover, when compared with an FE analysis with controlled power electronics, significant reduction in the computation time can be achieved. The effects of the harmonics on the machine behavior are evaluated by simulations, and the accuracy of the proposed model is verified by measurements.