Multi-stage compressor with single electric direct drive motor

1. A compressor system comprising:

a single electric motor having first and second ends;

a rotatable output shaft extending from the electric motor;

first, second and third compressor stages fluidly coupled to one another in series and mechanically connected to the output shaft, each of the first, second, and third compressor stages having a diffuser and outlet volute structured to receive a flow of compressed fluid; and

wherein the first compressor stage includes a first split impeller having a first fluid inlet and a second split impeller having a second fluid inlet, the first and the second fluid inlets being in fluid communication with a single source, the first and the second split impellers each discharging approximately one half of the fluid flow at a desired pressure to the second compressor stage; and

wherein the third compressor stage includes a third stage impeller, the second compressor stage includes a second stage impeller, wherein the third compressor stage is structured to receive the flow from the second compressor stage, and wherein the third stage impeller is smaller than the second stage impeller.

2. The compressor system of claim 1 , further comprising at least one additional compressor stage coupled to the output shaft.

3. The compressor system of claim 1 , wherein the output shaft extends from each of the first and second ends of the electric motor.

4. The compressor system of claim 3 , wherein at least one of the compressor stages is connected to the output shaft extending from the first end of the motor and at least two of the compressor stages are connected to the output shaft extending from the second end of the motor.

5. The compressor system of claim 1 , further comprising an aftercooler in downstream fluid communication with one of the compressor stages.

6. The compressor system of claim 1 , further comprising an aftercooler in downstream fluid communication with each compressor stage.

7. The compressor system of claim 1 , further comprising an active magnetic bearing operable to rotatably support the output shaft and measure rotor vibration and position.

8. The compressor system of claim 7 , wherein the active magnetic bearing further comprises:

first and second active magnetic bearings coupled to the output shaft between the motor and inner compressor impellers on either side of the of the motor; and

third and fourth active magnetic bearings coupled to the output shaft outward of outer compressor stages positioned outward of the inner compressor impellers on either side of the motor.

9. The compressor system of claim 1 , further comprising an electronic controller and a single frequency converter operably coupled to the electric motor.

10. The compressor system of claim 1 , wherein the second compressor stage includes a single impeller, wherein the second stage impeller is the single impeller of the second compressor stage, wherein the third compressor stage includes a single impeller, and wherein the third stage impeller is the single impeller of the third compressor stage.

11. A compressor system comprising:

an electric motor;

a rotatable output shaft extending from the electric motor;

an active magnetic bearing coupled to the output shaft;

a first compressor stage coupled to the output shaft;

a first aftercooler positioned downstream of the first compressor stage;

a second compressor stage coupled to the output shaft positioned downstream of the first aftercooler;

a second aftercooler positioned downstream of the second compressor stage;

a third compressor stage coupled to the output shaft positioned downstream of the second aftercooler;

a third aftercooler positioned downstream of the third compressor stage;

wherein the first compressor stage includes a first split impeller having a first fluid inlet and a second split impeller having a second fluid inlet, the first and the second fluid inlets being in fluid communication with a single source, the first and the second split impellers each compressing approximately one half of the fluid flow to a desired pressure in the first compressor stage;

wherein the first compressor stage includes a diffuser and outlet volute, the second compressor stage includes a diffuser and outlet volute, and the third compressor stage includes a diffuser and outlet volute; and

wherein the third compressor stage includes a third stage impeller, the second compressor stage includes a second stage impeller, wherein the third compressor stage is structured to receive the flow from the second compressor stage, and wherein the third stage impeller is smaller than the second stage impeller.

12. The compressor system of claim 11 , further comprising at least one additional compressor stage coupled to the output shaft.

13. The compressor system of claim 11 , wherein the output shaft extends from each of the first and second ends of the motor and at least one of the compressor stages is connected to the first end of the output shaft and at least two of the compressor stages are connected to the second end of the output shaft.

14. The compressor system of claim 11 , wherein the active magnetic bearing includes:

first and second magnetic bearings coupled to the output shaft between the motor and a compressor impeller on either side of the of the motor; and

third and fourth magnetic bearings coupled to the output shaft outward of outer compressor impellers on either side of the motor.

15. The compressor system of claim 11 , further comprising a controller operably coupled to the electric motor and the active magnetic bearings.

16. The compressor system of claim 11 , further comprising a single frequency convertor operably coupled to the motor.

17. The compressor system of claim 11 , wherein the active magnetic bearing measures vibration and position of the output shaft.

18. The compressor system of claim 11 , wherein the motor operates above a first bending critical speed of a rotor.

19. The compressor system of claim 11 , wherein the second compressor stage includes a single impeller, wherein the second stage impeller is the single impeller of the second compressor stage, wherein the third compressor stage includes a single impeller, and wherein the third stage impeller is the single impeller of the third compressor stage.

20. A method comprising:

compressing a fluid to a first predefined pressure with a first stage compressor;

discharging the fluid from the first stage compressor into a first stage diffuser and first stage volute;

compressing the fluid to a second predefined pressure with a second stage compressor;

discharging the fluid from the second stage compressor into a second stage diffuser and second stage volute;

compressing a fluid to a third predefined pressure with a third stage compressor, wherein the compressing the fluid to a third predefined pressure includes flowing the fluid through an impeller of the third stage compressor which is smaller than an impeller of the second stage compressor;

discharging the fluid from the third stage compressor into a third stage diffuser and third stage volute;

cooling the compressed fluid after one of the compressing steps;

rotating the first, second and third stage compressors at the same speed with a single electric motor; and

splitting the fluid entering the first stage compressor between a first split impeller having a first fluid inlet and a second split impeller having a second fluid inlet, each of the first and the second fluid inlets being in fluid communication with a single source.

21. The method of claim 20 further comprising rotatably supporting an output shaft of the electric motor with at least one active magnetic bearing.

22. The method of claim 21 further comprising measuring and controlling rotor vibration and rotor position with the active magnetic bearing.

23. The method of claim 21 further comprising controlling operation of the active magnetic bearing and the electric motor with an electronic controller.

24. The method of claim 20 , wherein the rotating speed of the electric motor is set such that the operating efficiency of the second stage compressor is maximized.