In-depth investigation of inter-turn short-circuit faults of surface-mounted permanent magnet machines with series-parallel coil connections

A general analytical model is developed in a concise block matrix form for surface-mounted permanent magnet (SPM) machines with series-parallel coil connections under inter-turn short circuit (ITSC) fault. In the model, branch currents are used as state variables and inductances of different series-parallel coil connections are calculated using an analytical method, namely winding function approach (WFA) together with slot permeance method. Based on the characteristics of the calculated inductances and the developed fault model, the multiphase Clarke transformation has been proposed to simplify the fault model. In the process of model simplification, the healthy machine model using branch currents as state variables have been proven to be equivalent to that using 3-phase currents as state variables. The proposed fault models of a 3kW 96-slot 32-pole SPM machine with different series-parallel coil connections have been built in Matlab/Simulink and validated by time-stepping 2D FE simulations. Simulation results show that different series-parallel coil connections have little influence on the amplitude of the ITSC current. Finally, a small scale 24-slot 8-pole SPM machine prototype has been built to further validate the accuracy of the proposed fault model.