Study of a permanent magnet motor for an electric car during three phase short circuit

Report, 2016

Permanent magnet synchronous motors are often used in drive trains for electric and hybrid vehicles. They are exposed to high loading, temperature and sometimes to short circuit of the stator. The short circuit currents are analysed with the use of Maxwell and Simulink. The nonlinear inductances are calculated in Maxwell and used in a Simulink model by means of interpolation. In this report, the calculations show that the currents in d and q-direction oscillates and the amplitudes are high which means that the model need an input of inductances that are analysed up to four times the normal peak current. The worst case is when the short circuit starts from an operating point that generates maximal negative torque. I.e. when the machine is generating maximum power and operates on maximum torque per ampere. At higher speed the starting torque will be lower due to field weakening. For the investigated machine, the flux density in one of the magnet corners will be as low as -0.3 T in the worst case, but 2 mm's from the corner the conditions are better and the flux density is -0.15 T.