Implementation of the DSP-based Fractional Order PID Controller for a Centrifugal Compressor by AMBs

Active magnetic bearings (AMBs) have many advantages compared with the traditional bearings, especially in the non-contact characteristic that improves applicability of AMBs supported rotor to high rotation speed applications such as the centrifugal compressor that has played a key role in high-end air-conditioning systems. However, precise positioning and high stability are indispensable in controller design for AMBs. Unavoidably, there are many harmful elements which affect the AMBs supported rotor in actual operations. The conventional PID controller has gained popularity in AMBs systems because of easily implementation and tuning intuitive. However, the PID controller may not be sufficient to stabilize complex dynamics of AMBs supported rotor. In order to enhance the stability of the AMBs supported rotor, this study proposed to apply the fractional order PID (FOPID) controller to the centrifugal compressor, in which the centrifugal compressor equipped with five-degree of freedom AMBs and the FOPID has been implemented by digital signal processor (DSP). The discretization implementations are described in detail, including the difficulties encountered and the corresponding solutions. Experimental results show the performance of FOPID compared with the traditional integer order PID (IOPID), and the FOPID can exhibit satisfactory performance, that included levitation and rotation.