Centrifugal compressor startup control

1. A method for controlling a centrifugal compressor having an inlet, an outlet, an impeller mounted for rotation about an impeller axis, a motor coupled to the impeller to drive the impeller about the impeller axis, and a variable inlet guide vane array controllable for movement between a relatively closed first condition and a relatively open second condition, the method comprising:

determining a saturation temperature difference between a heat rejection heat exchanger and a heat absorption heat exchanger;

determining an allowable guide vane condition based upon said saturation temperature difference;

closing the variable inlet guide vane array to said determined allowable guide vane condition; and

accelerating the impeller from a dead stop to an operational speed.

2. The method of claim 1 performed as a restart after an uncommanded shutdown.

3. The method of claim 1 wherein the determining of the allowable guide vane condition comprises an iterative calculation.

4. The method of claim 3 wherein the iterative calculation uses the equations:

DT _ sat at GV _ Pos=A+B*e{circumflex over ( )}C

A=DTs _Low− B

B =( DTs _High− DTs _Low)/( e{circumflex over ( )}D− 1)

C =(Shapefac*( GV _ Pos−GV _Low))

D =(Shapefac*( GV _High− GV _Low)),

wherein:

GV_Low=guide vane angular position when the guide vane is closed;

DTs_Low=maximum allowable lift at 100% speed at GV_Low without causing surge;

GV_High=guide vane angular position when the guide vane is fully open;

DTs_High=maximum allowable lift at 100% speed at GV_high without causing surge;

and

Shapefac=a constant, dependent upon the compressor aerodynamics.

5. The method of claim 1 wherein said closing of the variable inlet guide vane array to said determined allowable condition is part of an iterative process comprising:

measuring a guide vane condition;

comparing the measured guide vane condition to the determined allowable guide vane condition; and

if said measured guide vane condition is more open than said determined allowable condition, closing the variable inlet guide vane array.

6. The method of claim 5 wherein:

the closing comprises:

an incremental closing.

7. A controller configured to implement the method of claim 1 .

8. The controller of claim 7 configured to determine the allowable guide vane condition via an iterative calculation wherein:

DT _ sat at GV _ Pos=A+B*e{circumflex over ( )}C

A=DTs _Low− B

B =( DTs _High− DTs _Low)/( e{circumflex over ( )}D− 1)

C =(Shapefac*( GV _ Pos−GV _Low))

D =(Shapefac*( GV _High− GV _Low)),

wherein:

GV_Low=guide vane angular position when the guide vane is closed;

DTs_Low=maximum allowable lift at 100% speed at GV_Low without causing surge;

GV_High=guide vane angular position when the guide vane is fully open;

DTs_High=maximum allowable lift at 100% speed at GV_High without causing surge; and

Shapefac=a constant, dependent upon the compressor aerodynamics.

9. The controller of claim 8 wherein:

GV _Low=0%;

DTs _Low=5° C . to 15° C.;

GV _High=100%;

DTs _High=20° C . to 30° C .; and

Shapefac=−1 to 0.

10. A chiller system comprising:

the controller of claim 7 ;

said centrifugal compressor;

said heat rejection heat exchanger downstream of the centrifugal compressor along a refrigerant flowpath; and

said heat absorption heat exchanger downstream of the heat rejection heat exchanger along the refrigerant flowpath.

11. A method for reprogramming a controller to become the controller of claim 7 , the method comprising:

adding instructions for said determining said allowable guide vane condition and said closing the variable inlet guide vane array to said determined allowable guide vane condition.

12. The method of claim 1 wherein:

the closing is while the compressor is at the dead stop.

13. The method of claim 1 wherein:

the allowable guide vane condition is a condition for avoiding surge.

14. The method of claim 1 wherein:

GV_Low=guide vane angular position when the guide vane is closed;

GV_High=guide vane angular position when the guide vane is fully open; and

the allowable guide vane condition is greater than GV_Low and less than GV_high.

15. The method of claim 14 wherein:

the closing is while the compressor is at the dead stop.

16. A method for controlling a centrifugal compressor having an inlet, an outlet, an impeller mounted for rotation about an impeller axis, a motor coupled to the impeller to drive the impeller about the impeller axis, and a variable inlet guide vane array controllable for movement between a relatively closed first condition and a relatively open second condition, the method comprising:

after an uncommanded shutdown, determining a lift value;

determining an allowable guide vane condition based upon said lift value;

closing the variable inlet guide vane array to said determined allowable guide vane condition; and

accelerating the impeller to an operational speed.

17. The method of claim 16 wherein said closing of the variable inlet guide vane array to said determined allowable condition is part of an iterative process comprising:

measuring a guide vane condition;

comparing the measured guide vane condition to the determined allowable guide vane condition; and

if said measured guide vane condition is more open than said determined allowable condition, closing the variable inlet guide vane array.

18. A method for controlling a centrifugal compressor having an inlet, an outlet, an impeller mounted for rotation about an impeller axis, a motor coupled to the impeller to drive the impeller about the impeller axis, and a variable inlet guide vane array controllable for movement between a relatively closed first condition and a relatively open second condition, the method comprising:

determining a lift value;

determining an allowable guide vane condition based upon said lift value, and comprising an iterative calculation;

closing the variable inlet guide vane array to said determined allowable guide vane condition; and

accelerating the impeller to an operational speed,

wherein the iterative calculation uses the equations:

DT _ sat at GV _ Pos=A+B*e{circumflex over ( )}C

A=DTs _Low− B

B =( DTs _High− DTs _Low)/( e{circumflex over ( )}D− 1)

C =(Shapefac*( GV _ Pos−GV _Low))

D =(Shapefac*( GV _High− GV _Low)),

wherein:

GV_Low=guide vane angular position when the guide vane is closed;

DTs_Low=maximum allowable lift at 100% speed at GV_Low without causing surge;

GV_High=guide vane angular position when the guide vane is fully open;

DTs_High=maximum allowable lift at 100% speed at GV_High without causing surge; and

Shapefac=a constant, dependent upon the compressor aerodynamics.

19. The method of claim 18 wherein said closing of the variable inlet guide vane array to said determined allowable condition is part of an iterative process comprising:

measuring the guide vane condition;

comparing the measured guide vane condition to the determined allowable guide vane condition; and

if said measured guide vane condition is more open than said determined allowable condition, closing the variable inlet guide vane array.

20. The method of claim 18 wherein:

the allowable guide vane condition is greater than GV_Low and less than GV_high.