An embedded controller for an active magnetic bearing and drive electronic system

Abstract

The North-West University is currently conducting research in the area of active magnetic bearings (AMBs). The aim of this research is to establish a foundation for the development of AMB systems to be used in industrial applications. These systems should be reliable, effective and economical. The main research objective for this project is to further develop key technologies in order to realize an economical, reliable high-speed AMB drive system to be used in high-speed machinery. The proposed system is the AMB and drive electronic system (ADES), which is a digital control system for controlling AMBs in an industrial environment. The development of the ADES was a group effort. The focus of this dissertation was on selecting and implementing a suitable controller to be used in the ADES. The specification for the ADES was obtained from an industrial high-speed helium blower system. Selecting the controller was done by concurrently evaluating the conceptual main controller architectures and proposed system architectures. The system architecture is based on an industrial form factor, called compact peripheral component interconnect (PCI), or cPCI, which is an industrial version of PCI. The architectures were evaluated by performing trade-off studies and by weighing each architecture against a decision matrix, which weighs the architectures according to robustness, efficiency, cost, risk, reliability, flexibility and expandability. The selected system architecture includes a single board computer (SBC) with two PCI mezzanine cards (PMCs); a Virtex®-5 field programmable gate array (FPGA) based PMC module, for scheduling real-time tasks, and a Profibus PMC module, which will be used in future iterations of this project to interface the ADES with a programmable logic controller (PLC). The specified functions were designed, verified and implemented on the selected controller. The digital control was implemented on the FPGA-embedded PowerPC whereas the communication and filters were implemented on the FPGA. The sensitivity analysis placed the system into zone C, which implies a system normally considered unsatisfactory for long-term continuous operation. The system may operate in this condition for a limited period, until a suitable opportunity arises for remedial action. It was also determined that the system is stable for a step-input added to the reference position. Due to the stability of the control, it was possible to suspend the rotor at its designed rating of 19,000 r/min, but due to the high sensitivity rating, prolonged operation at this speed is not recommended. The selected architecture is versatile and powerful. The FPGA as a co-processor can be used to alleviate the load on the PowerPC, if additional features are required and not enough clock cycles are left on the PowerPC to implement them. The solution is compact, powerful and robust. These features, together with the industrial-based architecture of the system, make the ADES a suitable controller for controlling AMBs in an industrial system.