Enhancement of Dynamic Stiffness and Precision of Active Magnetic Bearings by Using Integrated Flux Density Measurement and Fast Switching Converter Topologies

• Applicants: Professor Dr.-Ing. Wilfried Hofmann; Professor Dr. Oliver G. Schmidt; Professor Dr.-Ing. Thomas Zerna
• Subject Area: Electrical Energy Systems, Power Management, Power Electronics, Electrical Machines and Drives ; Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering ; Glass, Ceramics and Derived Composites ; Polymer Materials
• Term: from 2013 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 221322256

Within the last years magnetic bearing technology has been pushed by a significant upturn in oil & gas industry as well as in machining applications. Nowadays, specific high speed spindles are equipped with industrially standardized active magnetic bearing systems (AMB) allowing for highly precise rotor positioning due to their contact-free and low-maintenance operation. However, compared to conventional ball bearings well-established AMB systems are limited by their relatively low stiffness. In order to improve dynamic performance flux based control algorithms have been suggested for the last decades already. The main challenge is how to integrate commercially available magnetic field sensors into the tiny air gap of typically 500 micro meter. Therefore, ultra-thin and preferably even flexible sensor elements meeting the strong requirements in lifetime and reliability are essentially needed. Within this project ultra-thin Bismuth Hall sensors with a total thickness of less than 150 micro meter are under development. After fabrication the sensor functionality and suitability for detection of time-varying magnetic fields in AMB systems are to be investigated intensely. Finally the sensor signal is intended to be used as directly integrated feedback for flux based AMB control strategies. Besides Hall sensorics precise rotor positioning strongly demands fast switching converters operated with high pulse frequencies (50 kHz) in order to achieve both accurate flux density/current control as well as a high bandwidth of the carrier frequency based position measurement system. Therefore, fast switching Gallium-Nitride-FETs (GaN) will be used for an H-bridge-converter powering the AMB coils. By using GaN-FETs a fast switching converter featuring substantially reduced dead times and low conduction losses can be realized.

• DFG Programme: Research Grants
• International Connection: Austria
• Cooperation Partners: Professor Dr. Manfred Albrecht; Professor Dr.-Ing. Martin Kaltenbrunner; Dr.-Ing. Michael Löser; Dr. Denys Makarov