On-Site Unmodeled Process Forces Integration in AMB Turboexpander Control

High-performance controllers are essential for safe operation of turbomachinery equipped with active magnetic bearings (AMBs). Although rotor models can be highly accurate-particularly when updated using factory frequency response data-discrepancies still occur between these models and real-world, on-site measurements. These discrepancies are primarily attributed to the influence of fluids, which significantly affect rotor dynamics. In this work, on-site measurements obtained via AMBs are exploited to estimate the unmodeled aerodynamic forces acting on the turbomachinery impellers by analysing the frequency response of the on-site process. By utilizing an updated rotor model, the process frequency responses related to aerodynamic forces can be identified and subsequently estimated. Once these aerodynamic forces are estimated, they are integrated into the control design. This integration allows for the optimization of the current supplied to the magnetic bearings, ensuring the system avoids actuator saturation and operates within safe limits. This approach significantly enhances overall plant performance by improving stability and safety, even when complex aerodynamic forces are difficult to model explicitly.