Thermal analysis of the cooling system with the circulation between rotor holes of enclosed PMSMs based on modified models

Abstract

• Novel cooling structure of circulation between rotor holes is designed. • The deflector pressure is calculated based on the element-momentum theory. • The air friction pressure drop is modified by introducing a spiral correction coefficient. • The convective heat transfer coefficient of each heat transfer surface is refined. • Adopting the designed cooling structure, the temperature rise is greatly reduced. Accurate temperature predictions and cooling structure design for permanent magnet machines are essential to ensure safe and stable operation. In this paper, a cooling system with circulation between rotor holes for enclosed permanent magnet synchronous machines is proposed. The modified lumped parameter models of airflow network and thermal network are established, respectively, so as to predict the air velocity and temperature distribution quickly and accurately. In the airflow network model, the calculation method of deflector pressure is proposed based on blade element theory. The equation for the pressure drops in the rotor holes is modified, and the influence of rotor rotation on air velocity is better considered. To improve the accuracy of the thermal network model, each part of the motor is equivalent to three typical heat transfer surfaces, and the corresponding calculation methods of the convective heat transfer coefficient are listed. The parameters of the cooling structure are analyzed and designed based on the lumped parameter models. Compared with the original motor without the deflector, the maximum temperature-rise of the rotor is decreased by 16%. The accuracy of the calculation models is verified by experiment and simulation.