Advanced Control Performance in Compressor Surge

Single stage compressors supported in magnetic bearings are known to exhibit compromised capacity to handle loads associated with compressor surge and stall - generally in a frequency range from about 10 Hz to 100 Hz. The present work studies utilization of advanced control in order to achieve high machine load capacity at these frequencies. A case study of a machine similar to a chiller compressor was used to study the performance with a generalized, multiple-input multiple-output (MIMO) H-infinity control with different input weighting. In the study, the machine load capacity, i.e., radial load at impeller location at different frequencies is studied. It was found that H-infinity control can achieve high machine load capacity over surge and stall frequencies (0 to 100 Hz) and in addition, it can achieve nearly the theoretical capacity limit. This type of controller enables the design of the input weighting to achieve good performance over the desired frequency range. This observation provides motive to more strongly consider advanced MIMO control methods for active magnetic bearings especially in compressor type applications.