Stability Margin Evaluation of AMB Rotor Systems Using Singular Value Decomposition

Active magnetic bearings (AMBs) are a proven technology that has been used in numerous rotating machines and is primarily being applied to many new turbomachines. Therefore, proper evaluation of rotordynamic performances is very important for OEM and end-users of AMBs. API 617 requires unbalance response limit and separation margin while ISO 14839-3 checks stability margin using measured sensitivity. In addition, singular value decomposition is mathematical tool used extensively in control community and can be used to analyze problems of rotating machines such as unbalance response, model reduction and stability margin. This paper presents stability margin evaluation of AMB rotor systems using singular value decomposition (SVD). First, Two AMB rotor systems and their frequency measurement are introduced. Then, we review linear control theory related to stability and performance evaluation using SVD. Identifications of two AMB rotor systems are performed and exact stability margins of two AMB rotor systems are analyzed based on linear control theory and SVD. Finally, stability margin evaluation of linear control theory and ISO 14839-3 are compared.