VARIABLE PID ENABLE FOR COMPRESSOR CONTROL ALGORITHM

1 . A method for operating a control scheme comprising the steps of:

a controller establishing a desired output condition of a controlled system, and an initial operating condition of said controlled system;

said controller detecting an actual operating condition of said controlled system and determining a difference between said initial operating condition and said actual operating condition;

said controller initiating a control cycle when a magnitude of said difference between said initial operating condition and said actual operating condition exceeds a predetermined value; and

said controller establishing a new initial operating condition based on said actual operating condition.

2 . The method of claim 1 , wherein said control system comprises a proportional integral derivative (PID) control scheme.

3 . The method of claim 2 , wherein said step of said controller initiating a control cycle when a magnitude of said difference between said initial operating condition and said actual operating condition exceeds a predetermined value comprises operating said PID control scheme when a preset time has elapsed and said difference between said initial operating condition and said actual operating condition is less than or equal to said predetermined value.

4 . The method of claim 2 , wherein said initial operating condition comprises an evaporator temperature.

5 . The method of claim 4 , wherein said step of said controller detecting an actual operating condition of said controlled system and determining a difference between said initial operating condition and said actual operating condition comprises sensing an evaporator temperature, comparing said sensed evaporator temperature to an initial evaporator temperature, and determining a difference between said sensed evaporator temperature and said initial evaporator temperature.

6 . The method of claim 1 , wherein said step of a controller establishing a desired output condition of a controlled system, and an initial operating condition of said controlled system further comprises storing said initial operating condition in a memory component of said controller.

7 . The method of claim 6 , wherein said step of said controller establishing a new initial operating condition based on said actual operating condition comprises sensing an actual condition of a component and overwriting a currently stored initial condition with said sensed actual condition.

8 . The method of claim 1 , wherein said step of said controller detecting an actual operating condition of said controlled system and determining a difference between said initial operating condition and said actual operating condition comprises sensing a component at an established frequency, thereby determining a current value of said actual operating condition.

9 . The method of claim 8 , wherein said step of said controller detecting an actual operating condition of said controlled system and determining a difference between said initial operating condition and said actual operating condition further comprises comparing said current value of said actual operating condition to said initial operating condition value, thereby determining a change in said operating condition.

10 . The method of claim 9 , further comprising the step of comparing said change in said operating condition to said predetermined value.

11 . A method for controlling compressor speed comprising the steps of;

establishing a target evaporator temperature and a minimum change in an actual temperature;

establishing an initial evaporator temperature value;

determining an actual evaporator temperature;

determining a change in evaporator temperature based on said actual evaporator temperature and said initial evaporator temperature;

comparing an actual evaporator temperature with said target evaporator temperature and determining a difference between said actual evaporator temperature and said target evaporator temperature;

inputting said difference between said actual evaporator temperature and said target evaporator temperature into a control algorithm when said change in evaporator temperature exceeds said minimum change in temperature, thereby operating a control cycle; and

adjusting a compressor speed based on an output of said control cycle.

12 . The method of claim 11 , further comprising the step of establishing a maximum time between control cycles.

13 . The method for controlling a compressor speed of claim 11 , wherein said step of inputting said difference between said actual evaporator temperature and said target evaporator temperature into a control algorithm when said change in evaporator temperature exceeds said minimum change in temperature further comprises inputting said difference between said actual evaporator temperature and said target evaporator temperature into a control algorithm when said change in evaporator temperature has not exceeded said minimum change in temperature and a maximum time has elapsed.

14 . The method of claim 11 , wherein said control algorithm comprises a Proportional Integral Derivative (PID) control system

15 . The method of claim 11 , further comprising the step of determining a target or desired compressor speed.

16 . The method of claim 15 , wherein said step of inputting said difference between said actual evaporator temperature and said target evaporator temperature into a control algorithm when said change in evaporator temperature exceeds said minimum change in temperature further comprises inputting an actual compressor speed into said control algorithm.

17 . The method of claim 1 , wherein said step of inputting said difference between said actual evaporator temperature and said target evaporator temperature into a control algorithm when said change in evaporator temperature exceeds said minimum change in temperature further comprises resetting said initial evaporator temperature to said actual evaporator temperature.