Variable speed motor control method and apparatus

1. An HVAC system, comprising:

an HVAC motor;

a motor controller coupled to the HVAC motor and configured to:

receive a first command signal of the HVAC motor and a second command signal of the HVAC motor;

decode a first operating level of the HVAC motor from the received first command signal of the HVAC motor; and

decode a second operating level of the HVAC motor from the received second command signal of the HVAC motor;

a system controller coupled to the motor controller and configured to:

receive a first energy unit cost at a first time;

determine a digitally encoded operating level of the HVAC motor based at least upon the first energy unit cost;

modulate the first command signal with the digitally encoded operating level of the HVAC motor in response to a service demand;

transmit the modulated first command signal to the motor controller;

receive a second energy unit cost at a second time;

update the digitally encoded operating level of the HVAC motor based at least upon the second energy unit cost;

modulate the second command signal with the updated digitally encoded operating level; and

transmit the modulated second command signal to the motor controller;

a feedback loop coupled to the system controller and the motor controller, the feedback loop including a summing node that is configured to receive the first command signal from the system controller, the second command signal from the system controller, and a feedback signal representative of an actual level of operation of the HVAC motor; and

the system controller is further configured to:

receive the feedback signal from the summing node;

determine a total energy consumption of the HVAC system based on the feedback signal;

based on the determined total energy consumption of the HVAC system, determine a new digitally encoded operating level of the HVAC motor to reduce an energy consumption of the HVAC system; and

modulate a third command signal with the new digitally encoded operating level.

2. The HVAC unit as recited in claim 1 , wherein the first operating level is encoded on the first command signal of the HVAC motor with pulse-width modulation.

3. The HVAC unit as recited in claim 1 , wherein the first operating level is encoded on the first command signal with pulse-frequency modulation.

4. The HVAC unit as recited in claim 1 , wherein the HVAC motor is configured to send a feedback signal to the system controller indicating an actual speed of the HVAC motor.

5. The HVAC unit as recited in claim 4 , wherein the first operating level is a torque, and the system controller is configured to control the HVAC motor to operate at a constant speed in response to the feedback signal.

6. The HVAC unit as recited in claim 1 , wherein the HVAC motor drives a blower, and the system controller controls the HVAC motor in response to a signal reported by a sensor configured to determine a temperature of a refrigerant coil associated with the blower.

7. The HVAC unit as recited in claim 1 , wherein a first ambient condition at the first time is substantially similar to a second ambient condition at the second time.

8. A method of manufacturing an HVAC system, comprising:

receiving, at a system controller, a first energy unit cost at a first time;

determining, at the system controller, a digitally encoded operating level of an HVAC motor based at least upon the first energy unit cost;

modulating, at the system controller, a first command signal with the digitally encoded operating level of the HVAC motor in response to a service demand;

transmitting, from the system controller to a motor controller, the first decoding, at the motor controller, a first operating level of the HVAC motor from the received first command signal;

controlling, at the motor controller, an operation of the HVAC motor in response to the decoded first operating level of the HVAC motor;

receiving, at the system controller, a second energy unit cost at a second time;

updating, at the system controller, the digitally encoded operating level of the HVAC motor based at least upon the second energy unit cost;

modulating, at the system controller, a second command signal with the updated digitally encoded operating level;

transmitting, from the system controller to the motor controller, the second command signal;

decoding, at the motor controller, a second operating level of the HVAC motor from the received second command signal;

controlling, at the motor controller, the operation of the HVAC motor in response to the decoded second operating level;

receiving, at a summing node in a feedback loop, the first command signal from the system controller, the second command signal from the system controller, and a feedback representative of an actual level of the HVAC motor;

receiving, at the system controller, the feedback from the summing node;

determining, at the system controller, a total energy consumption of the HVAC system based on the feedback;

based on the determined total energy consumption of the HVAC system, determining a new digitally encoded operating level of the HVAC motor to reduce an energy consumption of the HVAC system; and

modulating, at the system controller, a third command signal with the new digitally encoded operating level.

9. The method as recited in claim 8 , wherein the first operating level is encoded on the first digital command signal with pulse-width modulation.

10. The method as recited in claim 8 , wherein the first operating level is encoded on the first digital command signal with pulse-frequency modulation.

11. The method as recited in claim 8 , further comprising configuring the motor controller to send a feedback signal to the system controller indicating an actual speed of the HVAC motor.

12. The method as recited in claim 11 , further comprising configuring the system controller to control the HVAC motor to operate at a constant speed in response to the feedback signal.

13. The method as recited in claim 8 , wherein the HVAC motor drives a blower, and further comprising configuring the system controller to control the HVAC motor to maintain a temperature of a refrigerant coil associated with the HVAC motor.

14. The method as recited in claim 8 , wherein a first ambient condition at the first time is substantially similar to a second ambient condition at the second time.