Basic Study For Application Of AC-DC Three Degree-of-Freedom Hybrid Magnetic Bearing

Magnetic bearings have many advantages, such as no friction and abrasions, no lubrication and no sealing, high speed, high precision and long service life, and so on, which have innovated the traditional supporting forms fundamentally. In this dissertation, a novel AC-DC 3-degree freedom hybrid magnetic bearing (HMB) is proposed, which is driven by DC in axial direction and AC provided by a three-phase power converter in both radial directions respectively, and just one common permanent magnet ring provides the axial and radial biased magnetic flux. Therefore, this new magnetic bearing incorporates the merits of three-phase AC exciting, permanent magnet flux biased and axial-radial combined control, etc. The goal is to research and design a new compact magnetic bearing that can be applied in industry with lower manufacturing and operation costs.Firstly, based on the analysis to all kinds of magnetic bearings' structures and magnetic circuits, an innovated structure of three-degree freedom HMB is proposed. The novel magnetic bearing consists of an axial stator, two axial control coils in series, a radial stator with three poles, three radial control coils, a rotor and a permanent magnet ring magnetized radially, etc. Three radial coils are arranged around the rotor symmetrically, so a three-phase power converter can be used to feed the bearing to control two-degree freedom in radial directions since three-phase converters are compact in size and lower in cost, and it's controlled easily by a DSP processor.Secondly, the flux path is calculated by using equivalent magnetic circuit, the formulas and mathematics models of the axial and radial magnetic suspension forces are deduced respectively. Nonlinearities of suspension forces and cross coupling between different degree freedoms are studied further by calculating the suspension forces at different displacements and control currents to validate the feasibility of the mathematics models. Then based on the mathematics models, the control strategy is proposed. The methods on parameter design and calculation of the novel HMB are presented, a prototype and a mechanical test rig for this prototype are designed too. The prototype is simulated to analyze the magnetic circuits by using finite element analysis software ANSYS8.0. The simulation results have verified the feasibility of the theory study, and some parameters have been optimized by the simulation too.Lastly, both the software based on digital signal processor (DSP) and the hardware circuit PCB have been designed, the flow charts for main program and interrupt programs have been listed too. Power amplifier system is consisted by a linear amplifier in axis direction and a three-phase converter based on CRPWM principle in radial directions, the complete experimental test rig is constructed. Furthermore, detailed testing procedures have been proposed, which establishes a good foundation for the next parameters debugging and functions test.The theory analysis and testing results have shown that this new magnetic bearing reduces overall system size, has stronger magnetic suspension forces, higher efficiency and lower cost. This AC-DC three-degree freedom HMB has a wide application in super-speed and super-precision numerical control machine tools, bearingless motors, high-speed flywheel, artificial satellites, and so on.