This disclosure relates to a centrifugal compressor for use in a refrigeration system and, in particular, to a variable-speed, multi-stage centrifugal compressor having at least one vaned diffuser.
Existing single-stage and two-stage centrifugal refrigeration compressors, with vaneless or vaned diffusers, typically have at least one set of variable inlet guide vanes at a compressor inlet to regulate compressor capacity during various operating conditions.
Variable-speed centrifugal compressors use speed variation as their primary capacity control mechanisms, but such compressors still need variable inlet guide vanes in order to operate surge-free at low capacity conditions.
Multi-stage centrifugal compressors have used stages with fixed, typically vaneless, diffusers with inlet guide vanes and variable speed as the capacity control mechanism. Single-stage refrigerant compressors have been introduced that employ a variable frequency drive (VFD) for capacity control in addition to a set of rotatable inlet guide vanes upstream of the impeller. In the case of a variable speed capability, a variable-geometry diffuser has been used downstream from the impeller to improve the compressor surge characteristics at part-load operating conditions.