Modelling and Control of Surge for a Centrifugal Compressor with Non-Constant Speed

Abstract

In this Chapter the compressor characteristic for a variable speed centrifugal compressor is investigated. This characteristic is incooperated in a model similar to that of Fink et al. (1992), and surge phenomena is studied in connection with varying compressor speed. Energy losses in the compressor components are used to derive the characteristic, making a departure from the usual cubic characteristic most commonly encountered in the surge control literature. Inspired by Ferguson (1963) and Watson and Janota (1982), fluid friction and incidence losses, as well as other losses, in the compressor components are modeled, and a variable speed compressor characteristic is developed based on this. Both annular and vaned diffusers are studied. Surge and speed controllers for variable speed centrifugal compressors are presented and analyzed. The speed is controlled with a PI-control law.