Design and control of Radial Homopolar Hybrid Magnetic Bearing

Abstract

Now a day the magnetic bearing system use in vacuum technology, machine tools, turbomachinery, artificial heart system etc. The use of magnetic bearing is rising day by day because of some advantages compare to mechanical bearing such as control capability, contact less, long life and has no lubrication [1,2]. In spite of the fact that the magnetic bearing has many superiority, it can make some weaknesses such as hysteresis loss, needing bias current and back up bearing to protect the rotor [3]. Magnetic bearings are categorized in three main structures such as Passive Magnetic Bearing(PMB), Active Magnetic Bearing(AMB) and the last but not the least is Hybrid Magnetic bearing(HMB). [4]. PMBs levitate rotor by using permanent magnets which mostly use as backup bearing or axial bearing. Radial Magnetic bearings are classified by Heteropolar and Homopolar configurations. The Heteropolar Magnetic bearings has more applications because of easy produced and low cost, but if we need more efficiency Homopolar configuration must be used. The hysteresis loss, eddy current loss, rotational loss and field variation can be reduced by using homopolar configuration bearings. HMBs use a permanent magnet to generate bias flux and electromagnet to control the flux to reduce copper loss and price of power amplifier [3,5]. In control point of view magnetic bearing is difficult to control because the system is nonlinear, time variant, multi input-multi output, and strongly unstable that’s why we must use the robust controller. [6,7].