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.
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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.
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.
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This application claims the benefit of and incorporates by reference herein the disclosure of U.S. Ser. No. 61/822,076, filed May 10, 2013. The present application is also a U.S. nationalization of PCT Application No. PCT/US2014/036938, filed May 6, 2014, the text and drawings of which are hereby incorporated by reference in their entireties.
The presently disclosed embodiments generally relate to positive displacement compressors, and more particularly, to a method for soft expulsion of a fluid from a compressor at start-up.
Positive displacement compressors are widely used in refrigerant compressor applications. One known type, a scroll compressor, includes compression elements and an electric motor disposed within a sealed compressor shell. A quantity of lubricant is also received in the compressor shell. In such compressors, the refrigerant passes over the motor on its way to the inlet of the compression elements, cooling the motor.
At start-up, the oil located in the compressor's sump may contain a quantity of fluid, such as a liquid refrigerant. At start-up, the sump and the motor are cool, and pre-heating does not occur. Therefore, idle compressors often accumulate liquid refrigerant and/or oil in the compression pocket and in the suction plenum. Because the fluids are incompressible, detrimental forces can result if the compressor is rapidly started.
Electric heaters are occasionally used to pre-heat the compressor and thus reduce the amount of accumulated fluid present at start-up. However, this approach has numerous issues. Use of electric heaters adds cost and complexity to the system, and it is ineffective on expelling oil, to name only two examples. Another approach used to prevent accumulation of fluid involves the addition of valves to isolate the compressor during off periods. This approach also adds cost, and adds detrimental stress cycles to the motor and valves. There is therefore a need for a method to remove accumulated fluids from a compressor's compression chamber before operational start-up.
In one aspect, a method for soft expulsion of a fluid from a compressor at start-up is provided. The method includes the step of applying a first signal to windings of the motor for a first duration of time to align the motor rotor to an initial position. In one embodiment, the initial position of the motor rotor is set by a control determining the placement of a magnet within the motor rotor and holding that position for a period of time. In one embodiment, a DC current is applied to the windings of motor for a period of time to generate a DC flux, so that the motor rotor 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 for approximately 3.3 seconds. In other embodiments, the DC current is applied for a duration sufficient to ensure alignment of the motor rotor position with the stationary magnet flux.
The method also includes the step of applying a second signal to the windings of the motor to start rotation of the shaft. In one embodiment, a sinusoidal current of sufficient amplitude, is slowly applied to the windings of the motor using an open speed loop vector control. The frequency of the current waveforms are set to provide the correct speed of rotation for shaft. In one embodiment, the shaft rotates at a speed of approximately one revolution per second. As the shaft rotates slowly, fluid is discharged from the compression chamber into the discharge chamber.
The method also includes the step of applying a third signal to the windings of the motor for a second duration of time to hold the shaft in place. In one embodiment, once the shaft has been rotated the desired number of revolutions to clear the compression chamber of the excess fluid, the DC currents are again applied to the windings of the motor at amplitudes necessary to hold the shaft in place. In one embodiment, DC currents are applied for a second duration of time of approximately four seconds. In other embodiments, the DC currents are applied for a duration of time sufficient to align the motor rotor position with the stationary magnet flux.
The method also includes the step of applying a fourth signal to the windings of the motor to accelerate the motor to an operational speed. In one embodiment, a sinusoidal current is applied to the windings of motor using a speed ramp profile to bring the motor up to an operational speed.
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:
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.
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.
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.
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
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.
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
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.
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.
Perdikakis, William, Zhang, Da, Pandzik, Richard T., Rollins, Mark E.
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May 28 2013 | ZHANG, DA | Carrier Corporation | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 036813 | /0585 | |
May 28 2013 | PANDZIK, RICHARD T | Carrier Corporation | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 036813 | /0585 | |
May 28 2013 | PERDIKAKIS, WILLIAM | Carrier Corporation | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 036813 | /0585 | |
May 28 2013 | ROLLINS, MARK E | Carrier Corporation | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 036813 | /0585 | |
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