Multi-capacity compressor with variable speed drive and method of use

1. A heating ventilation and air conditioning (HVAC) system, comprising:

a multi-capacity compressor configured to operate selectively at a high-capacity setting, a medium-capacity setting, and a low-capacity setting to provide a compressor output;

a variable-voltage variable-frequency drive coupled to said multi-capacity compressor and configured to power said multi-capacity compressor to operate at a variable speed; and

a processor coupled to said multi-capacity compressor and said variable-voltage variable-frequency drive, said processor configured to:

determine a load for said multi-capacity compressor;

select the high-capacity setting, the medium-capacity setting, or the low-capacity setting at which said multi-capacity compressor should operate based on the determined load, and

based on the selection, during operation of said multi-capacity compressor:

employ said variable-voltage variable-frequency drive to power said multi-capacity compressor to operate at the variable speed to match the compressor output to the load when operating said multi-capacity compressor at the medium-capacity setting or the low-capacity setting; and

bypass said variable-voltage variable-frequency drive when operating said multi-capacity compressor at the high-capacity setting for a compressor heating output based on the load including all heating loads.

2. The HVAC system of claim 1 , wherein said processor is further configured to, when the high-capacity setting is selected, couple said multi-capacity compressor to an alternating current (AC) line voltage source.

3. The HVAC system of claim 1 , wherein said processor is further configured to:

determine the variable speed based on the load including a cooling load; and

transmit a speed control signal to said variable-voltage variable-frequency drive to power said multi-capacity compressor to operate at the variable speed.

4. The HVAC system of claim 1 , wherein said processor is further configured to bypass said variable-voltage variable-frequency drive when operating said multi-capacity compressor at each of the medium-capacity setting or the low-capacity setting based on the load including a cooling load.

5. A control system for a multi-capacity compressor, said control system comprising:

an alternating current (AC) line voltage source configured to power the multi-capacity compressor;

a variable-voltage variable-frequency drive coupled to said AC line voltage source and configured to power the multi-capacity compressor to operate at a variable speed; and

a processor coupled to said AC line voltage source and said variable-voltage variable-frequency drive, said processor configured to:

during operation of the multi-capacity compressor, selectively couple said AC line voltage source and said variable-voltage variable-frequency drive to the multi-capacity compressor to power the multi-capacity compressor, based on a load determined for the multi-capacity compressor, and

transmit a capacity control signal to the multi-capacity compressor, the control signal instructive to operate the multi-capacity compressor in one of a high-capacity setting, a medium-capacity setting, or a low-capacity setting, while the multi-capacity compressor is being powered by the selectively coupled one of said AC line voltage source or said variable-voltage variable-frequency drive.

6. The control system of claim 5 , wherein said processor is further configured to:

determine one of a cooling load or a heating load for the multi-capacity compressor;

select, based on the one of the cooling load or the heating load, a capacity setting at which the multi-capacity compressor is to operate, the capacity setting selected from among the high-capacity setting, the medium-capacity setting, and the low-capacity setting.

7. The control system of claim 6 , wherein said processor is further configured to select the high-capacity setting when any heating load for the multi-capacity compressor is determined.

8. The control system of claim 6 , wherein said processor is further configured to:

select the high-capacity setting when the cooling load is above a first threshold;

select the medium-capacity setting when the cooling load is below the first threshold and above a second threshold; and

select the low-capacity setting when the cooling load is below the second threshold.

9. The control system of claim 5 , wherein said processor is further configured to transmit a speed control signal to said variable-voltage variable-frequency drive to set the variable speed at which the multi-capacity compressor operates.

10. The control system of claim 9 , wherein said processor is further configured to select the variable speed at which the multi-capacity compressor operates according to a measured cooling load that is based on a function of a temperature set point for an interior space and a measured ambient temperature of an exterior space.

11. The control system of claim 5 , wherein said processor is further configured to:

estimate one of a cooling load or a heating load for the multi-capacity compressor; and

selectively couple said AC line voltage source and said variable-voltage variable-frequency drive to the multi-capacity compressor based on the one of the estimated cooling load or the estimated heating load.

12. The control system of claim 5 further comprising a bypass circuit coupled to said variable-voltage variable-frequency drive, said bypass circuit configured to supply power to the multi-capacity compressor using said AC line voltage source coupled in series with a run capacitor, and bypass said variable-voltage variable-frequency drive.

13. The control system of claim 12 , wherein said processor is further configured to operate the multi-capacity compressor exclusively at the high-capacity setting when coupling said AC line voltage source to the multi-capacity compressor to power the multi-capacity compressor with said AC line voltage source and bypassing said variable-voltage variable-frequency drive.

14. The control system of claim 5 , wherein said processor is further configured to operate the multi-capacity compressor exclusively at the high-capacity setting when operating according to a measured heating load that is based on a function of a temperature set point for an interior space and a measured ambient temperature of an exterior space.

15. A control system for a multi-capacity compressor configured to operate in at least two capacity settings, said control system comprising:

an alternating current (AC) line voltage source configured to operate the multi-capacity compressor;

a variable-voltage variable-frequency drive coupled to said AC line voltage source and configured to power the multi-capacity compressor to operate at a variable speed; and

a processor coupled to said AC line voltage source and said variable-voltage variable-frequency drive, said processor configured to:

during operation of the multi-capacity compressor, selectively couple said AC line voltage source and said variable-voltage variable-frequency drive to the multi-capacity compressor to operate the multi-capacity compressor, based on a load determined for the multi-capacity compressor, and

transmit a capacity control signal to the multi-capacity compressor, the control signal configured to select one of the at least two capacity settings at which the multi-capacity compressor is to operate while the multi-capacity compressor is being powered by the selectively coupled one of said AC line voltage source or said variable-voltage variable-frequency drive.

16. The control system of claim 15 , wherein said processor is further configured to transmit a speed control signal to said variable-voltage variable-frequency drive to set the variable speed at which the multi-capacity compressor operates.

17. The control system of claim 16 , wherein said processor is further configured to select the variable speed at which the multi-capacity compressor operates according to a measured cooling load that is based on a function of a temperature set point for an interior space and a measured ambient temperature of an exterior space.

18. The control system of claim 15 , wherein said processor is further configured to alternatively couple said AC line voltage source and said variable-voltage variable-frequency drive based on one of an estimated cooling load or an estimated heating load.

19. The control system of claim 15 , wherein said AC line voltage source comprises a switch network through which an AC line voltage is switched, the AC line voltage comprising a 60 Hertz 240 volt signal.

20. The control system of claim 15 , wherein said AC line voltage source comprises a switch network through which an AC line voltage is switched, the AC line voltage comprising a 115 volt signal.

21. The control system of claim 15 further comprising a bypass circuit coupled to said variable-voltage variable-frequency drive, said bypass circuit configured to supply power to the multi-capacity compressor using said AC line voltage source coupled in series with a capacitor, and bypass said variable-voltage variable-frequency drive.

22. The control system of claim 15 , wherein said processor is further configured to operate the multi-capacity compressor exclusively at the high-capacity setting when powering the multi-capacity compressor with said AC line voltage source.