Method for controlling a variable speed drive for multiple cooling units

摘要

The invention uses a variable speed drive (VSD) (10) only on a range of capacities corresponding from zero to standard point conditions, and if conditions correspond to higher than rated point current, the VSD (10) is disconnected and the compressor is connected directly on line. This approach allows using a smaller size VSD (10). At the same time, if there are several compressors (12,14,16) operating in the same machine, only one VSD (10) is needed. The VSD (10) drives a first compressor from zero to the speed corresponding to the line frequency. Controls then switch the first compressor to direct on line (DOL) and disconnects the VSD (10) from the first compressor. The VSD (10) is then available to drive a second compressor. This process can be repeated through multiple compressors. IMAGE