Magnetic bearing system design for enhanced stability.

摘要

Magnetic bearings are essential components in the flywheel energy storage system because of their low friction loss and long life cycles. The magnetic bearings developed in past experiments were based on a linear model and failed to magnetically suspend the rotating flywheel at high speeds. Since the bearing operation is affected by different factors, including disturbances, flywheel, mechanical structure, control system, power electronics, and magnetic materials, there is a need for a system design to achieve stable bearing operations over a various range of speeds and design parameters.; The objective of this research is to principally analyze the magnetic bearing system for nonlinear effects in order to increase the region of stability, as determined by high speed and large air gap control. This is achieved by four tasks: (1) physical modeling, design, prototyping, and testing of a magnetically suspended flywheel energy storage system, (2) identification of problems that limits performance and their corresponding solutions, (3) development of a design methodology for magnetic bearings, and (4) design of an optimal controller for future high speed applications.; The physical modeling of the magnetic bearing system takes into consideration disturbances, gyroscopic motion, physical limitations, and other uncertainties of the system. The magnetic bearing design has important parameters such as stiffness, load capacity, linear operating range, magnetic materials, and power electronics. The design not only meets design constraints on these parameters but also maximizes the stable displacement range, which directly affects the stiffness, load capacity, and operating range of the bearings. An optimum controller design can accommodate disturbances and physical uncertainties with good tracking and disturbance rejection at low frequency and robustness at high frequency.; A prototype of the flywheel energy storage system was built with new magnetic bearings, adjustable stiffness and damping controllers, and improved power electronics. The system was tested at a maximum speed of 20,000 RPM with a total stored energy of 15.9 WH. The principal limitation was motor torque and magnetic core losses. The magnetic bearing achieved a DN number greater than 2.1 million (mm-RPM), which exceeds the capability of most mechanical bearings. Theoretical and experimental studies have identified the major power loss of the system to be caused by the eddy currents in non-laminated magnetic materials of the bearings. This power loss can be minimized by using a high resistivity laminated magnetic material.