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.

Claims

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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The embodiments and other features, advantages and disclosures contained herein, and the manner of attaining them, will become apparent and the present disclosure will be better understood by reference to the following description of various exemplary embodiments of the present disclosure taken in conjunction with the accompanying drawings, wherein:

(2) FIG. 1 is a cross-sectional view of a positive displacement compressor incorporated into the exemplary embodiment;

(3) FIG. 2 illustrates a schematic view of an outdoor unit assembly incorporated into the exemplary embodiment.

(4) FIG. 3 is an exemplary embodiment of a method to remove a liquid from a compressor at start-up;

(5) FIG. 4A illustrates the speed profile of a positive displacement compressor motor in revolutions per second;

(6) FIG. 4B illustrates sinusoidal current profile applied to a positive displacement compressor motor; and

(7) FIG. 4C illustrates the motor angle position of a positive displacement compressor motor.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

(8) For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of this disclosure is thereby intended.

(9) FIG. 1 illustrates a positive displacement compressor, such as a scroll compressor to name one non-limiting example, incorporated into an exemplary embodiment of the present disclosure and indicated generally at 10. Particularly, the compressor 10 includes a sealed compressor shell 12. Disposed within the sealed compressor shell 12 is a compressor pump unit 14 including a fixed scroll 16, an orbiting scroll 18, and a crankcase 20. Further disposed within the sealed compressor shell 12 is a motor 22 including a motor rotor 24 spaced from a stator 26. A motor 22, such as a permanent magnet motor to name one non-limiting example, drives a shaft 28 which in turn drives the orbiting scroll 18. A variable speed drive 30 is schematically connected to drive the motor 22.

(10) A liquid 32, for example oil, fills an oil sump 34 and the bottom of the motor rotor 24, wherein shaft 28 rotates within the oil sump 34. As is known in the art, oil travels up a passage 36 to lubricate bearings, fixed scroll 16 and orbiting scroll 18. The fixed scroll 16 is supported by crankcase 20 and the shaft 28 is supported axially by lower bearing ring 38.

(11) During normal operation, a fluid, for example a refrigerant, enters the sealed compressor shell 12 through inlet 40 as a saturated vapor. The saturated vapor enters the compressor chamber (not shown) and as the motor rotor 24 rotates in a forward direction, orbiting scroll 18 rotates around the fixed scroll 16 to compress the saturated vapor into a high-pressure, high-temperature vapor. After motor rotor 24 stops, some uncompressed saturated vapor remains within the compressor chamber.

(12) FIG. 2 illustrates a schematic view of an outdoor unit assembly 42 which may be used for residential heating and cooling. In one embodiment, the outdoor unit assembly 42 includes a fan 44, compressor 10, and condenser 46 connected to compressor discharge line 48. A control 50 is in electrical communication with the fan 44 and the compressor 10 for control thereof.

(13) FIG. 3 illustrates an exemplary method for soft expulsion of a fluid from a compressor at start up. As shown in FIG. 3, an exemplary method 100 includes the step 102 of applying a first signal to windings of the motor 22 for a first duration of time to align the motor rotor 24 to an initial position. In one embodiment, the initial position of the motor rotor 24 is set by control 50 commanding the shaft 28 to rotate until sensing the placement of at least one magnet (not shown) disposed on the motor rotor 24. In other embodiments, the initial position of the motor rotor 24 is set by the placement of a stationary magnet (not shown) adjacent to the motor rotor 24. In one embodiment, as shown in FIG. 4C, a DC current is applied to the windings of motor 22 for a period of time to generate a DC flux, so that the motor rotor 24 position is forced to align with the at least one magnet. In other embodiments, a DC current is applied to the windings of motor 22 for a period of time to generate a DC flux, so that the motor rotor 24 position is forced to align with the stationary magnet fixed at the initial position. In one embodiment, the DC currents are applied to the windings of motor 22 for approximately 3.3 seconds. In other embodiments, the DC currents are applied for a duration sufficient to ensure alignment of the motor rotor 24 position with the stationary magnet flux. It will be appreciated that the amplitude of the DC current must be sufficient to overcome the resistive torque on the shaft 28. It will be appreciated that depending on the type of motor 22, such as a permanent magnet motor to name one non-limiting example, step 102 may not be necessary.

(14) Step 104 includes applying a second signal to the windings of the motor 22 to start rotation of the shaft 28. In one embodiment, as shown in FIG. 4B, a sinusoidal current of sufficient amplitude, for example two amperes in one non-limiting embodiment, is applied to the windings of motor 22 using an open speed loop vector control. The variable speed drive 30 outputs a pulse-width modulation (PWM) pattern to the motor 22. The PWM pattern is designed to generate a slow rotating flux pattern and induce the motor rotor 24 to rotate according to the rotating flux. The variable speed drive 30 may be used to vary the frequency of input voltage and current to the motor 22, thereby controlling the motor speed. The frequency, for example 0.5 Hertz, of the current/voltage is set to provide the correct speed of rotation for shaft 28. The maximum speed for a particular motor 22 may be determined by the viscosity of the liquid 32. In one embodiment, the shaft rotates at a speed of approximately one revolution per second. As the shaft 28 rotates slowly (in one embodiment, the shaft 28 rotates for at least one revolution), a fluid is discharged from the compression chamber (not shown) into the discharge chamber (not shown). It will be appreciated that depending on the power rating of the motor 22 and the volume of the compressor pump unit 14, the frequency may vary to slowly rotate the shaft 28.

(15) Step 106 includes applying a third signal to the windings of the motor 22 for a second duration of time to hold the shaft 28 in place. In one embodiment, once the shaft 28 has been rotated the desired number of revolutions to clear the compression chamber (not shown) of the excess fluid, a DC current is again applied to the windings of motor 22, for a second duration of time, at amplitudes necessary to hold the shaft 28 in place. In one embodiment, the DC currents are applied for a second duration of time sufficient to ensure alignment of the motor rotor 24 position to the initial position. It will be appreciated that depending on the type of motor 22, such as a permanent magnet motor to name one non-limiting example, step 106 may not be necessary.

(16) Step 108 includes applying a fourth signal to the windings of the motor 22 to accelerate the motor 22 to an operational speed. In one embodiment, as shown in FIGS. 4A and 4B, a sinusoidal current is applied to the windings of motor 22 using a speed ramp profile to bring the motor 22 up to an operational speed.

(17) It will be appreciated that, as the shaft 28 of compressor 10 is slowly rotated the desired number of revolutions, accumulated fluid in the compression chamber may be safely discharged into the discharge chamber prior to accelerating the compressor to an operational speed.

(18) While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only certain embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.