Temperature dependency of the efficiency of Line Start Permanent Magnet Machines

Induction machines have nearly reached their maximum efficiency. In order to further increase the efficiency of electrical machines the use of permanent magnets in combination with the robust design of the induction machine is being extensively researched. Many experimental designs have been suggested in literature, but recently these Line Start Permanent Magnet Machines have also become commercially available in a power range to 10kW. It is commonly known that the induction from the magnets is function of the temperature of the permanent magnet. As a consequence, this temperature dependency of induction will affect almost every electrical quantity of the machine, including current, torque and efficiency. In this paper, the efficiency of an off-the-shelf 4kW three phase Line Start Permanent Magnet Machine is evaluated in function of the ambient temperature by practical measurement. A detailed loss evaluation is given to explain the results.