Fast Determination of Transient Short-Circuit Current of PM Synchronous Machines via Magnetostatic Flux Maps

The three-phase symmetric short-circuit is a reference fault condition for the qualification of a newly designed permanent magnet (PM) synchronous machine against the risk of irreversible demagnetization. To date, the accurate determination of the peak transient short-circuit current condition requires coupled circuital and transient Finite Element Analysis (FEA) to properly account for magnetic saturation, and several simulations to determine the worst-case pre-fault conditions. This work presents a method for the fast evaluation of the transient short-circuit current of a PM synchronous machine by manipulation of extended flux linkage maps, obtained with magnetostatic FEA or experimental measures. Besides providing a fast and accessible computational tool, the flux-map based method gives insights into the effect of pre-fault conditions, showing that the higher the pre-fault torque and thus flux amplitude, the higher the transient peak current after a fault. Moreover, the paper shows that braking is a more severe pre-fault condition. Finally, the hyper-worst-case short circuit current is also defined as the magnetic property of the machine under test and computed by means of quick FEA iterations without the need for pre-determined flux-linkage maps. The proposed methods are validated against transient FEA using a commercial software and verified experimentally on a commercial motor for traction applications.