Enhancement of Dynamic Stiffness and Precision of Active Magnetic Bearings by Using Integrated Flux Density Measurement and Fast Switching Converter Topologies
Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
Glass, Ceramics and Derived Composites
Polymer Materials
Final Report Abstract
The project was divided into three subprojects, procuring the goal of improving the stiffness and precision of active magnetic bearings. The project partners successfully produced flexible, ultra-thin Hall sensor systems with a total thickness of less than 150 µm. The actual sensors were manufactured on a polyimide basis. A reliable assembly and inter- connection technique was developed for the integration of these sensors, using an anisotropic conductive adhesive film. Additionally, the partners developed two-stage evaluation electronics, which can be partially integrated into the experimental setup, thus reducing the sensor length before the first signal amplification. The sensitivity and interference suppression of the overall system consisting of the sensor, the electronics, and the digital signal post-processing is sufficient to achieve an accuracy of the flux density measurement of approx. 20 mT in a measurement range of 0 to 1.5 T. In addition, the project partners developed analytical descriptions and simulation models for controller design and investigation of the flux density-based control algorithms‘ potential. Especially concerning the overshooting, typical for magnetic bearings during position jumps, flux density control offers significant advantages over conventional control. Since with flux density control, the position-dependent positive feedback leads to the fast, inner flux density control loop, this quickly compensates the control deviation after a setpoint change. This effect, which was shown by simulation, could be impressively validated by measurement: The overshoot drops from 131 % to 62 %, and the settling time drops from 218 ms to 17 ms. In the case of continuous disturbance (orbit during rotation), no improvement can be demonstrated. This is because the effect of eddy currents is small in laminated radial bearings. The technical disadvantage of the poorer signal quality of the flux density measurement compared to the current measurement, therefore, out- weighs the physical advantage in this case, which can be shown by simulation. In the course of the project, it was found that flux density measurement using sensors in the inhomogeneous air gap field of the thrust bearing is not practical. To improve the stiffness under these conditions, flux estimators should be used. Investigations on this subject can be found in a further project. In the last subproject, the project partners successfully built a power converter with GaN semiconductor switches. This converter enables switching frequencies of over 200 kHz and thus clearly exceeds the initial development goal. A reduction in the current ripple by increasing the switching frequency could not be demonstrated at all operating points. Therefore, the influence of several time constants was investigated - converter time constant, control time constant, measurement time constant. The control time constant has the greatest influence on the dynamics but is most difficult to reduce. - The switching frequency improves the system‘s behavior only at high setpoint voltages since at low voltages the influence of switch-on and switch-off effects has a negative effect. - A reduction of the measurement time constant and subsequent averaging has a positive influence on the bearing‘s behavior in all ranges. This underlines the importance of signal quality for controls with extreme dynamics and precision requirements. Overall, the project provides evidence that ultrathin Hall sensors and flux-density-based control can significantly improve the dynamic behavior of an active radial magnetic bearing. A design-related choice of measurement, control, and converter time constants provides an additional positive influence on the system’s dynamic stiffness.
Publications
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„Permanent Magnet Bias AMB Using Integrated Hall Sensor Based Air Gap Flux Density Feedback“, Proceedings of the 1st Brazilian Workshop on Magnetic Bearings, Brazil, 2013
Bahr, F. et al.
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„Optimisation of an Electrochemical Etching Approach for Flexible Hall Sensorics“,581. WE-Heraeus-Seminar: "Flexible, Stretchable and Printable High Performance Electronics", Bad Honnef, Germany, 12th - 14th of January 2015
Rost, K. et al.
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Analytical Asymmetric Air Gap Model for Active Magnetic Thrust Bearings of Mixed Materials Including Eddy Currents, 15th International Symposium on Magnetic Bearings ISMB15, Kitakyushu, Japan, 2016
R. Seifert, W. Hofmann
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Direct Field Control of AMBs using Flux Feedback based on Integrable Hall Sensors, 15th International Symposium on Magnetic Bearings ISMB15, Kitakyushu, Japan, 2016
F. Bahr, I. Mönch, D. Ernst, T. Zerna, O. G. Schmidt, W. Hofmann
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Flexible Magnetic Field Sensors with Ultra-Thin Silicon Interposers, 6th Electronics System-Integration Technology Conference ESTC 2016, Grenoble, France, 2016
D. Ernst, J. I. Mönch, F. Bahr, W. Hofmann, O. G. Schmidt, T. Zerna
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Performance of Flux Density Based Control Approaches for Active Magnetic Bearings – an Overview, 16th International Symposium on Magnetic Bearings, Beijing, China, 2018
R. Liebfried, W. Hofmann
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Untersuchung des Übertragungsverhaltens eines aktiven Magnetlagers mit Flussdichtemessung im Luftspalt, Tagungsband 12. Workshop Magnetlagertechnik Zittau-Chemnitz, pp. 11-18, Zittau, Germany, 2019
R. Liebfried, W. Hofmann
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Packaging of Ultrathin Flexible Magnetic Field Sensors with Polyimide Interposer and Integration in an Active Magnetic Bearing, IEEE Transactions on Components, Packaging and Manufacturing Technology, pp. 39-43, 2020
D. Ernst, M. Faghih, R. Liebfried, M. Melzer, D. Karnaushenko, W. Hofmann, O. G. Schmidt, T. Zerna
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Effect of the System’s Time Constants on the Dynamic Behavior of an Active Magnetic Bearing with a GaN-H-Bridge-Converter, 23rd European Conference on Power Electronics and Applications EPE, 2021
R. Liebfried, W. Hofmann
