Start-stop control systems and methods for gas foil bearing machine

A controller for controlling a centrifugal compressor with a gas foil bearing supporting a shaft of an impeller driven by a motor, the controller comprising:

• a VFD including a motor interface for connection to the motor;
• an unloading interface for connection to an unloading device;
• a processor;
• and
• a memory containing instructions that, when executed by the processor, cause the controller to:
• start the centrifugal compressor from a stopped condition by:
• operating the unloading device to remove a load from the centrifugal compressor,
• accelerating the motor to a first speed above a liftoff speed of the gas foil bearing and below an operating speed of the centrifugal compressor,
• running the motor at the first speed for a period of time,
• operating the unloading device to apply the load to the centrifugal compressor, and
• accelerating the motor to the operating speed.

A method of controlling a centrifugal compressor with a gas foil bearing supporting a shaft of an impeller driven by a motor, the method comprising:

• starting the centrifugal compressor from a stopped condition by:
• operating an unloading device to remove a load from the centrifugal compressor,
• accelerating the motor to a first speed above a liftoff speed of the gas foil bearing and below an operating speed of the centrifugal compressor,
• running the motor at the first speed for a period of time,
• operating the unloading device to apply the load to the centrifugal compressor, and
• accelerating the motor to the operating speed.