Loss reduction of outer-rotor type high-speed interior permanent magnet motors

Many communication servers are being installed in order to develop information technology (IT). The servers require not only high-performance processer but also its cooling system. Among the cooling systems, a cooling fan is the most suitable due to good balance between performance and cost. In order to further improve the fan's performance, both torque and speed of cooling fan motors are increased. However, iron loss and eddy current loss are also increased along with larger torque and higher speed, which worsens the efficiency. This paper investigates the optimum rotor structure for the fan motor in order to obtain sinusoidal flux distribution in air gap, which can reduce the iron and eddy current losses.