Design, modeling, and robust control of the flexible rotor to pass the first bending critical speed with active magnetic bearing

Recently, magnetic bearings have been applied to many rotating machines such as turbo-molecular pumps, cooling gas compressor, flywheel energy storage systems. And high-power density is the future development trend of these machines, which demands that the rotor characterizes slender and high rotating speed and operates above the critical speeds. However, it is a big challenge for a flexible rotor to pass the bending critical speeds and operate above the critical speeds steadily and reliably. Based on above reasons, this article presented the design, modeling, and analysis framework of a flexible rotor test rig with active magnetic bearing (AMB). Special attention was paid to the flexible rotor dynamic model development, dynamic analysis, and model-based robust control design. First, the main structure features were illustrated in detail, including the key dimensions and parameters of the AMB components and rotor. Then models of components including power amplifier and displacement sensor were developed. The finite element method based on Timoshenko beam theory was applied to the rotor dynamics model. The dynamic analysis of the rotor is the foundation of the controller design. Hence, modal analysis had been done, obtaining rotor dynamic properties via synthesis of natural frequency, mode shapes, and Campbell plots. Reduced order model was obtained for controller design convenience. A robust H controller was designed based on the system model and controller performance was validated with numerical simulation. The results indicate that the controller has good vibration suppression performance and makes the flexible rotor pass the first bending critical speed.