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

在过去的几年里，磁轴承技术在石油和天然气工业以及机械加工应用中得到了显著的发展。如今，特定的高速主轴配备了工业标准化的主动磁轴承系统（AMB），允许高度精确的转子定位，因为它们的无接触和低维护操作。然而，与传统的滚珠轴承相比，完善的AMB系统受到其相对较低的刚度的限制。为了提高系统的动态性能，基于磁链的控制算法已经被提出了几十年。主要的挑战是如何将商业上可用的磁场传感器集成到通常为500微米的微小气隙中。因此，需要超薄的、最好是柔性的传感器元件，以满足对寿命和可靠性的严格要求。在这个项目中，总厚度小于150微米的超薄铋霍尔传感器正在开发中。在制造完成后，传感器的功能和在AMB系统中检测时变磁场的适用性将被深入研究。最后，将传感器信号作为直接集成反馈用于基于磁链的电磁轴承控制策略。除了霍尔传感器之外，精确的转子定位强烈要求使用高脉冲频率（50 kHz）的快速开关转换器，以实现精确的磁通密度/电流控制以及基于载波频率的高带宽位置测量系统。因此，快速开关氮化镓场效应管（GaN）将用于为AMB线圈供电的h桥转换器。通过使用gan - fet，可以实现大大减少死区时间和低导通损耗的快速开关变换器。

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.