Flow-Rate Observers in the Suppression of Compressor Surge Using Active Magnetic Bearings

Surge is a dynamic flow instability that can cause extensive damage to compressors and other components. One common challenge that many surge control methods in the literature face when implemented in industrial applications is the unavailability of the high performance actuators and accurate flow rate measurements that are required to suppress surge. In this paper we present the experimental results of employing active magnetic bearings in order to suppress the surge instability in a centrifugal compressor. In addition, we compare how the selection of the flow estimation method affects the effectiveness of the implemented surge suppression controller. The experimental data demonstrates that the best combination of controller and flow estimator tested in this work allows the compressor to operate deep into the former surge region when the controller is activated, moving the minimum flow rate at the surge initiation point by 21%. This allows the compression system to operate at the highest efficiency/pressure point in the characteristic curve, while still retaining a very conservative surge margin separating the allowed compressor operating region from the surge inception point even if unexpected system changes occur.