The development of a fully suspended AMB system for a high-speed flywheel application

Abstract

The School of Electrical, Electronic and Computer Engineering at the North-West University is currently in the process of developing an active magnetic bearing (AMB) laboratory. The idea is to establish a knowledge base on AMBs within the school to support industries that make use of the technology. AMBs are seen as an enabling technology in a number of applications e.g. high-speed blowers and the Pebble Bed Modular Reactor (PBMR) where the oil in the bearings on the blowers poses a contamination risk. This project will be an application of the knowledge gained from past research on AMBs and control algorithms. Currently the most advanced AMB model within the McTronX research group is limited to four axes of freedom. The main purpose of the project is the development of a fully suspended (five degrees of freedom) active magnetic bearing (AMB system for a flywheel energy storage system (FESS) application. The FESS will be able to deliver 2 kW of electrical energy to a load for a period of 3 minutes. A high-speed permanent magnet synchronous machine (PMSM) is developed within the McTronX research group for the specific FESS application. The developed PMSM propels the rotor/flywheel at 30,000 rpm in order to mechanically store 527 kJ of energy. The rotor/flywheel is suspended by two radial AMBs and one axial AMB. The areas of focus that are addressed include the AMB system, the electrical control enclosure that will house the electrical system and the user interface. The system will be developed to and industrial standard. An iterative design process was devised together with a simulation model for the AMB system in order to develop the 5-axis AMB system. The output parameters of the AMB design process were implemented in the simulation model in order to accurately simulate the responses of the AMBs. After the AMB designs were verified by means of simulation, the AMBs were implemented and the electrical components were sourced according to the specifications derived from the design process. The electrical control enclosure was also designed by means of simulation and the required components were sourced after verification by means of simulation. The interface board, the RTD drivers and the over-speed protection system were developed in-house along with the ControlDesk graphical user interface (GUI) which enables the user to control the entire Fly-UPS system from a standalone personal computer. The system was extensively tested to verify the stiffness and damping characteristics of the AMBs and the electrical system is determined to be fully functional. The sensitivity of the AMBs are characterized as being a zone A (which is the zone in which newly commissioned machines fall) in accordance to the ISO CD 14839-3 standard on magnetic bearings. The project will enable future research on the development and optimization of flywheel energy storage systems as well as the optimisations of control algorithms and the implementation of redundancy within AMB systems