Variable speed motor drive with integrated motor heating systems and methods

1. A variable speed drive (VSD) configured to drive a motor during an on-cycle and to heat motor windings of the motor during an off-cycle, wherein the variable speed drive comprises:

a rectifier configured to convert alternative-current (AC) power input to a direct-current (DC) power output;

a DC bus coupled to the rectifier and comprising a DC bus transistor, wherein the DC bus transistor is configured to:

pre-charge a DC capacitor of the DC bus to drive the motor during the on-cycles;

receive a first gate pulse having a first duty cycle in response to temperature differential between a temperature of the motor and an ambient temperature being less than a first threshold during the off-cycle;

receive a second gate pulse having a second duty cycle in response to the temperature differential being greater than the first threshold during the off-cycle, wherein the second duty cycle is less than the first duty cycle; and

an inverter comprising a plurality of inverter switches, wherein the inverter is configured to:

receive the first gate pulse having the first duty cycle or the second gate pulse having the second duty cycle applied to the DC bus transistor; and

transmit the first gate pulse having the first duty cycle or the second gate pulse having the second duty cycle to one of the motor windings to heat the one of the motor windings and prevent accumulation of moisture on the one of the motor windings.

2. The variable speed drive of claim 1 , wherein the temperature differential comprises a temperature difference between a temperature of a stator of the motor and the ambient temperature.

3. The variable speed drive of claim 1 , wherein the variable speed drive is configured to operate as a buck converter in response to the DC bus transistor receiving the first gate pulse, and the variable speed drive is configured to operate as the buck converter in response to the DC bus transistor receiving the second gate pulse.

4. The variable speed drive of claim 1 , wherein the variable speed drive comprises an inductor located between the DC bus transistor and the plurality of inverter switches and a first relay located between a positive side of the DC bus and a negative side of the DC bus, wherein the first relay is closed and the variable speed drive maintains a low voltage across the DC capacitor of the variable speed drive to operate the variable speed drive as a buck converter.

5. The variable speed drive of claim 1 , wherein each of the motor windings is configured to receive power over a respective phase path from the DC bus.

6. The variable speed drive of claim 5 , wherein the variable speed drive comprises at least three inverter switches of the plurality of inverter switches to be gated on to provide the respective phase path.

7. The variable speed drive of claim 1 , wherein the DC bus further comprises a first relay and a bleed-off resistor, wherein the first relay and the bleed-off resistor are electrically coupled to the DC capacitor in parallel to provide shock protection.

8. The variable speed drive of claim 7 , wherein the first relay is closed during the off-cycles to dissipate voltage stored on the DC capacitor.

9. The variable speed drive of claim 7 , wherein the DC bus transistor is coupled to a second relay, wherein the second relay is closed in response to the DC bus reaching a predetermined threshold.

10. The variable speed drive of claim 9 , wherein the closed second relay results in shorting the DC bus transistor to remove heat loss due to a voltage drop across the variable speed drive.

11. The variable speed drive of claim 9 , wherein the DC bus is configured to stop pre-charging of the DC capacitor of the DC bus in response to the DC bus reaching the predetermined threshold.

12. An environmental conditioning system, comprising:

a motor comprising stator windings;

a variable speed drive (VSD) configured to drive the motor during an on-cycle and to heat the stator windings during an off-cycle, wherein the variable speed drive comprises:

a rectifier configured to convert alternative-current (AC) power input to a direct-current (DC) power output;

a DC bus coupled to the rectifier and comprising a DC bus transistor, wherein the DC bus transistor is configured to:

pre-charge a DC capacitor of the DC bus to drive the motor during the on-cycle; and

receive a gate pulse with a duty cycle during the off-cycle, wherein the gate pulse is configured to heat the stator windings; and

an inverter comprising a plurality of inverter switches, wherein the inverter is configured to:

receive the gate pulse applied to the DC bus transistor; and

transmit the gate pulse to one of the stator windings to prevent accumulation of moisture on the one of the stator windings; and

a controller communicatively coupled to the variable speed drive, wherein the controller is configured to:

determine a temperature differential between a temperature of the motor and an ambient temperature during the off-cycle;

compare the temperature differential to a threshold temperature differential;

determine a value of the duty cycle of the gate pulse based on the comparison of the temperature differential to the threshold temperature differential; and

provide the gate pulse having the duty cycle with the value to the DC bus transistor during the off-cycle.

13. The environmental conditioning system of claim 12 , wherein the temperature differential is determined based on one or more measurements la one or more sensors comprising resistance temperature detectors (RTDs) located on the motor, within the motor, or a combination thereof.

14. The environmental conditioning system of claim 12 , wherein the controller is configured to instruct the variable speed drive to pre-charge the DC capacitor until the DC bus reaches a voltage threshold of 85% of a voltage peak value.

15. The environmental conditioning system of claim 12 , wherein the DC bus comprises an inductor located between the DC bus transistor and the plurality of inverter switches, and a diode in a reverse biased configuration between a positive side of the DC bus and a negative side of the DC bus to allow the variable speed drive to operate as a buck converter in the off-cycle.

16. The environmental conditioning system of claim 12 , wherein the controller is configured to provide a command to close a DC bus relay coupled in parallel with the DC bus transistor in response to the DC bus reaching a predetermined voltage threshold, wherein closing the DC bus relay shorts the DC bus transistor to stop the pre-charging and remove heat loss due to voltage drop across the variable speed drive.

17. The environmental conditioning system of claim 12 , wherein the AC power input is a single-phase power supply or a three-phase power supply.

18. A method for driving a motor at various speeds and providing heat to motor windings of the motor, using a variable speed drive, comprising:

pre-charging a DC capacitor of a DC bus of the variable speed drive during an off-cycle using a DC bus transistor, wherein pre-charging the DC capacitor enables driving the motor during an on-cycle, wherein the variable speed drive drives the motor at the various speeds during the on- cycle and provides heat to the motor windings during the off-cycle;

determining a temperature differential between a temperature of the motor and an ambient temperature during the off-cycle;

determining a value of a duty cycle of a gate pulse based on a comparison of the temperature differential with a threshold temperature differential;

providing the gate pulse having the duty cycle with the value to the DC bus transistor during the off-cycle; and

transmitting the gate pulse having the duty cycle with the value to the motor windings to heat the motor windings and prevent accumulation of moisture on the motor windings.

19. The environmental conditioning system of claim 12 , wherein the threshold temperature differential is a first threshold temperature differential, and the controller is configured to:

compare the temperature differential to a second threshold temperature differential;

select a first value as the value of the duty cycle of the gate pulse based on a determination that the temperature differential is less than the first threshold temperature differential and a determination that the temperature differential is less than the second threshold temperature differential; and

select a second value as the value of the duty cycle of the gate pulse based on the determination that the temperature differential is less than the first threshold temperature differential and a determination that the temperature differential is greater than the second threshold temperature differential.

20. The environmental conditioning system of claim 19 , wherein the first value is a first percentage, the second value is a second percentage, and the first percentage is greater than the second percentage.