Abstract
Active magnetic bearings (AMBs), being inherently nonlinear, are often modeled with linear approximations about the operating point. μ-synthesis control which offers robust stability in the presence of uncertain parameters also provides a method for overcoming the limitations that arise from this linear approximation. In the past, experimental measurements have been taken at the zero deflection point to determine the uncertainty range in the current stiffness and position stiffness parameters. This paper proposes an analytical method for deriving, from the non linear force equation, the nominal (minimum) range of uncertainty for the position stiffness and current stiffness in the μ-synthesis control of AMBs. This is of particular interest in applications where zero deflection is not expected at the bearing location. Stiffness range calculations for a high speed magnetic bearing machining spindle are also presented as a case study.
