Investigation of the rotor temperature of a turbo-molecular pump with different motor drive methods

When a turbo-molecular pump (TMP) runs at high speed, the eddy current loss induced by harmonic components of stator currents increases the rotor temperature. With no effective cooling method, the rotor temperature is much higher than the stator temperature under high vacuum environment. Furthermore, rotor overheat may result in a loss of magnetism and expansion deformation of the rotor sheath, which degrade both performance and stability of the TMP system. In this paper, the factors of the rotor temperature are analyzed firstly. Eddy current loss is the main heat source of the rotor of a TMP system. In order to control the rotor temperature, two different kinds of motor drive methods including square currents and sinusoidal currents are investigated to minimize eddy current loss. Although the square current drive method is popular for its simplicity and low-cost, the sinusoidal current method is much more suitable for a TMP drive since it has less harmonic current components, which reduces the eddy current loss in the rotor. At last, it is tested at a magnetically suspended TMP system with 4100 L/s pumping speed and the experimental results verify the analysis.