Study On Permanent Magnet Biased Magnetic Bearing And Its Control Method

The micro-turbine generating system is one of the important study regions in the distributed power system. The rotational speed of high speed generator driven by micro-turbine directly is usually from several ten thousand to some hundred thousand revolutions per minute. Conventional mechanical bearings are not suitable for such high speed of rotation. The magnetic suspension bearing is one of the ideal bearings for supporting high speed rotating equipment. Because the biasing current in the active magnetic bearing is substituted for a magnet in the permanent magnet biased magnetic bearing to produce magnetic bias, the power consumption of the permanent magnet biased magnetic bearing is decreased. In this dissertation, the permanent magnet biased magnetic bearing and its control method is studied in-depth. The main works have been done as follows:A new structure of the permanent magnet biased radial-axial magnetic bearing is proposed. The SIMULINK based electromagnetic force model of the magnetic bearing is established, in which the saturation effect of ferromagnetic material is taken into account. The relationship between bias magnetic flux and electromagnetic force with air gap is analyzed at off-center position of the rotor.Under variable area and distance measuring conditions, the influence of different target materials on static characteristic of the eddy current displacement sensor is analyzed and a mathematic model of static characteristic of the eddy current displacement sensor is proposed. The algorithm for radial and axial displacement of rotor is derived. According to the four-pole structure feature of the magnet biased radial magnetic bearing, the radial and axial displacements of rotor are measured with the eddy current sensors located between poles of radial magnetic bearing. The experimental result shows that the proposed measuring method for radial and axial displacements is feasible.A novel hybrid power amplifier which the supply voltage of a linear power amplifier is adjusted by the DC-DC converter is proposed. It has not only advantages of linear power amplifier, small current ripple and fast response, but also lower power loss. The simulation result shows that proposed hybrid power amplifier has faster dynamic response and lower power consumption compared with the Linear power amplifier. The feasibility is verified by the experiment.The coupling of magnetic force between two DOF in the permanent magnet biased radial magnetic bearing is analyzed and the mathematic model of magnetic force considered coupling effect is deduced. The feed-forward decoupling control strategy and the feed-forward decoupling algorithm is proposed. The simulation results show that feed-forward decoupling control proposed can reduce magnetic force coupling between two DOF and improve control precision of rotor position.