System and method for extending the operating range of a dynamic compressor

A controller for a dynamic compressor having a motor, a first compressor stage driven by the motor, and a second compressor stage driven by the motor, the controller comprising:

• a processor;
• and
• a memory, the memory storing instructions that program the processor to:
• operate the dynamic compressor at a current speed, a first position of a first variable inlet guide vane (VIGV) of the first compressor stage, and a second position of a second VIGV of the second compressor stage to compress a working fluid, the first VIGV being controllable to selectively introduce pre-whirl into working fluid entering the first compressor stage and the second VIGV being controllable to selectively introduce pre-whirl into working fluid entering the second compressor stage;
• determine, while operating the dynamic compressor, if a condition is satisfied;
• continue to operate the compressor at the current speed, the first position of the first VIGV, and the second position of the second VIGV when the condition is not satisfied;
• and
• change the second position of the second VIGV to a third position different than the second position and maintain the first position of the first VIGV when the condition is satisfied.

A method of extending an operating range of a dynamic compressor that is compressing a working fluid, the dynamic compressor having a motor, a first compressor stage driven by the motor, and a second compressor stage driven by the motor, a valve being in fluid communication with the dynamic compressor between the first compressor stage and the second compressor stage, the method comprising:

• operating the dynamic compressor at a current speed, a first position of a first variable inlet guide vane (VIGV) of the first compressor stage, and a second position of a second VIGV of the second compressor stage to compress the working fluid, the first VIGV being controllable to selectively introduce pre-whirl into working fluid entering the first compressor stage and the second VIGV being controllable to selectively introduce pre-whirl into working fluid entering the second compressor stage;
• determining, while operating the dynamic compressor, if a condition is satisfied;
• continuing to operate the compressor at the current speed, the first position of the first VIGV, and the second position of the second VIGV when the condition is not satisfied;
• and
• changing the second position of the second VIGV to a third position different than the second position and maintaining the first position of the first VIGV when the condition is satisfied.