Research On Control System Of Active Magnetic Bearing

Active magnetic bearing(AMB)can provide electromagnetic force to levitate the rotor in rotating machinery,which has the advantages of no contact,no mechanical wear,no lubrication,etc.It has been used in the field of high-speed rotating machinery and some special applications.However,displacement sensors,controllers and power amplifiers are necessary in AMB systems to achieve active control.Compared with traditional mechanical bearings,AMB has more complex structure and higher cost,so it is also subject to some restrictions in some applications.In order to reduce the size and cost of the magnetic bearing controller,making it more suitable for industrial applications,this paper has done the optimization work on the power amplifier and the position sensor,which are two main components of AMB system.First,modeling and analysis of the components in AMB system have been done.Electromagnetic force of the single-degree-of-freedom magnetic bearing and its linearization model were derived.Then,control method of position loop was introduced.Control method and stability of the current loop were analyzed,and position sensor was introduced and analyzed.Moreover,effects of current loop and position sensor on stability of position loop was further studied.Research indicates that fast and accurate current control through power electronic converters is the basis for reliable operation of magnetic bearing,and fast and low-noise position feedback signals are also an important part of magnetic bearing system.Based on the existing research of magnetic bearing power amplifier,three novel power electronic converter topologies applied to multi-degree-of-freedom AMB system were introduced,which are common-bridge converter,reversed-common-bridge converter,and four-phase four-leg converter.With the global optimization of device,the requirement of the number of power electronics devices are greatly reduced in novel converters,thereby the cost and size of the controller can be reduced.The principle and the control methods of novel converters were introduced,and the advantages and disadvantages of each topology were discussed.Then,based on the analysis of the research status of position sensors,the optimization of the displacement sensor in this paper is mainly aimed at the problem of higher cost of the displacement sensor on the market.Accordingly,a low-cost eddy current displacement sensor was designed.The principle design and parameter selection of the hardware circuit were detailed in this paper.Finally,prototypes of the above optimization schemes were established,and experimental verification was carried out on the magnetic bearing experimental platform.Suspension experiments and rotation experiments were performed,which proved the feasibility of novel power electronic converters and low-cost displacement sensors.