Efficiency contours and loss minimization over a driving cycle of a variable-flux flux-intensifying interior permanent magnet machine

In this paper, experimental evaluations for the efficiency of a novel interior permanent magnet (IPM) machine with variable-flux characteristics using low coercive force magnets is presented. The variable-flux characteristics allow improving the efficiency of machine and also reducing the usage of rare-earth material in the high-coercive magnets, which are currently used for the IPM machines in electrified vehicles. A flux-intensifying interior permanent magnet (FI-IPM) type having positive saliency is employed for a positive d-axis current to mitigate a demagnetizing field in the magnet due to a q-axis current. A proof-of-principle machine is designed, fabricated and evaluated. A series of experiments are conducted to capture the efficiency contours with different magnetization states of the low coercive force magnets. The designed machine shows benefits in improving efficiency when the magnetization state is optimally operated. With these results, the loss over a driving cycle is then simulated and the benefits of changing the magnetization state are quantified.