Abstract
Recently, it is necessary for rotors of centrifugal compressors, industrial rolls and so on to operate at high speed rotation, and have long span and light weight to increase productivity. However, such rotors are more likely to have high order mode than other kind of rotors at the same rotational speed, and they may become unstable. In order to solve this problem, active magnetic bearings are used to support the flexible rotor. However, since a general active magnetic bearing uses bias current to control bearing force, it consumes large electricity. In this paper, a hybrid active magnetic bearing (HAMB) which consists of electromagnets and permanent magnets is used to reduce the power consumption. Two HAMBs are installed in both end of flexible rotor located horizontally to levitate it. The control method of levitation is central PID control with notch filter. The central PID controller regulates the displacement and the angle of center of rotor in horizontal direction and vertical direction. Only with PID controller, the levitation of flexible rotor becomes unstable because flexible mode stimulates vibration. In order to settle flexible mode vibration, notch filter is designed at frequency of flexible mode. Putting the notch filter against the displacement has few effects to vibration decrement, and against the angle, effect is huge. Therefore the notch filter is put only against the angle. Rotation test was implemented and experimental results show that the control system which uses HAMBs can pass through the second flexible mode rotation speed stably. Furthermore, to use merit of HAMB as reduce power consumption effectively, zero power control is adopted. It is able to reduce control current to use zero power control, then, the comparisons with another when levitating and rotating the flexible rotor are shown.
