Method for soft expulsion of a fluid from a compressor at start-up

Abstract

A method for expulsion of a fluid inside a compressor at start-up including the steps: applying a first signal to the motor windings for a first duration of time to align the motor rotor to the initial position; applying a second signal to the motor windings to start rotation of the compressor shaft; applying a third signal to the motor windings for a second duration of time to hold the compressor shaft in place; and applying a fourth signal to the motor windings to accelerate the motor to an operational speed.

What is claimed is: 
     
       1. A method of operating a positive displacement compressor, including a compressor shaft and a motor including a rotor coupled to the compressor shaft and further including motor windings, the method comprising the steps of:
 (a) applying a first signal to the motor windings for a first duration of time to align the rotor to an initial position; 
 (b) applying a second signal to the motor windings to start rotation of the compressor shaft; 
 (c) applying a third signal to the motor windings for a second duration of time to hold the compressor shaft in place; and 
 (d) applying a fourth signal to the motor windings to accelerate the motor to an operational speed. 
 
     
     
       2. The method of  claim 1 , wherein the initial position 1s aligned by a control commanding the shaft to rotate until sensing the placement of at least one magnet disposed on the rotor, and holding that position for a period of time. 
     
     
       3. The method of  claim 1 , wherein the first signal comprises a direct current signal. 
     
     
       4. The method of  claim 1 , wherein the second signal comprises a sinusoidal alternating current signal, wherein a frequency of the sinusoidal alternating current is approximately 0.5 Hz. 
     
     
       5. The method of  claim 1 , wherein the compressor shaft rotates at a speed of approximately one revolution per second. 
     
     
       6. The method of  claim 1 , wherein the third signal comprises a direct current signal. 
     
     
       7. The method of  claim 1 , wherein the second duration of time comprises a sufficient time to align the rotor to the initial position. 
     
     
       8. The method of  claim 1 , wherein the fourth signal comprises a sinusoidal alternating current signal, wherein the sinusoidal alternating current signal comprises a speed ramp profile. 
     
     
       9. A method of operating a positive displacement compressor, including a compressor shaft and a motor including a rotor coupled to the compressor shaft and further including motor windings, the method comprising the steps of:
 (a) applying a first signal to only one of the motor windings for a first duration of time to align the rotor to an initial position, wherein the first signal comprises a direct current signal; 
 (b) applying a second signal to the motor windings to start rotation of the compressor shaft; 
 (c) applying a third signal to the motor windings to accelerate the motor to an operational speed. 
 
     
     
       10. The method of  claim 9 , wherein the second signal comprises a sinusoidal alternating current signal, wherein a frequency of the sinusoidal alternating current is approximately 0.5 Hz. 
     
     
       11. The method of  claim 9 , wherein the compressor shaft rotates at a speed of approximately one revolution per second. 
     
     
       12. The method of  claim 9 , wherein the third signal comprises a sinusoidal alternating current signal, wherein the sinusoidal alternating current signal comprises a speed ramp profile.