Pumps – Condition responsive control of pump drive motor – In response to pump speed
Reexamination Certificate
1998-12-15
2001-05-29
Walberg, Teresa (Department: 3742)
Pumps
Condition responsive control of pump drive motor
In response to pump speed
C417S019000
Reexamination Certificate
active
06238188
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for controlling compressor operation under extreme power supply conditions of line frequency and voltage.
Compressors are utilized in different refrigerant vapor compression applications, including refrigeration, air conditioning, heat pumps, etc. Typically, these compressors include an electric motor driving a compressor pump unit. The compressor pump unit compresses the refrigerant and delivers it into the refrigerant system.
For the compressor to operate property the compressor operating speed must fall within a certain range. The compressor speed is a function of the line frequency, voltage, and the load on the compressor. This can be explained as follows. The speed of the electrical motor used in typical refrigerant compressing applications is proportional to line frequency minus motor slip. The motor slip increases as supplied voltage is decreased or a compressor load is increased. Therefore, the compressor motor speed will decrease if the frequency decreases, if the load increases, or if the voltage decreases. Compressors are not designed to operate properly below a certain speed.
For example, scroll compressors may have a feature called radial compliance in which centrifugal force keeps an orbiting scroll pressed against fixed scroll in a radial direction. If the scroll compressor operates below a certain speed, the radial compliance can be lost, because centrifugal force keeping the scrolls together drops below the minimum acceptable value. Further, if an oil pump is employed, oil will not be delivered to lubricate scroll compressor components below a certain operating speed. These are undesirable effects of operating scroll compressor at reduced speed.
The overall force acting on a main scroll compressor bearing consists of two components. The first component of the force is proportional to compressor load; and the second component, caused by rotating shaft counterweights, is proportional to speed squared. Thus, as speed increases to an undesirably high level at a given compressor load, the overall force acting on the bearing can become excessively high, which is undesirable. Then, to decrease the force acting on the bearing the compressor speed must be decreased or compressor load decreased.
The operation under extreme conditions of line frequency and voltage and resultant operating speed excursions are especially common where the electric power is supplied by a generator set, since in this application frequency and voltage often fluctuate extensively, especially on start up.
SUMMARY OF THE INVENTION
In the disclosed embodiment of this invention, line frequency and voltage, as well as compressor suction and discharge pressure are monitored. If the line frequency or voltage is such that the compressor speed is not within a target range for a measured pressure rise across the compressor, then the compressor load is decreased to adjust the operating speed or force acting on the bearings. Of course, variables other than line frequency or voltage could be monitored. As an example, the motor speed could be monitored directly. However, this approach is often difficult, as it requires installation of a dedicated speed sensing transducer.
If the compressor speed is below the target value, which may occur if the line frequency or voltage are undesirably low, then the compressor load is decreased. This would, in turn, boost the compressor speed. The compressor speed will then move within, or at least towards, an acceptable range. The load can be reduced, for example, by engaging an unloader valve, shutting off an economizer line or throttling a suction modulation valve, either independently or in combination with each other.
As the load is reduced, the motor slip is reduced and the speed will increase, even though the line frequency or voltage have not changed and are still below the desired value.
On the other hand, if the line frequency is too high then the compressor speed may exceed the specified value. The load is again reduced by engaging the compressor unloader mechanism. By performing this compressor load reduction, the force on the bearings is reduced and bearing overload due to over speeding is avoided.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
REFERENCES:
patent: 4145161 (1979-03-01), Skinner
patent: 4330237 (1982-05-01), Battah
patent: 4335582 (1982-06-01), Shaw et al.
patent: 4486148 (1984-12-01), Battah
patent: 4912932 (1990-04-01), Malaker et al.
patent: 4946350 (1990-08-01), Suzuki et al.
patent: 5211026 (1993-05-01), Linnert
patent: 5362210 (1994-11-01), Richardson, Jr.
patent: 5419146 (1995-05-01), Sibik et al.
patent: 5603227 (1997-02-01), Holden et al.
patent: 5768901 (1998-06-01), Dormer et al.
patent: 5885062 (1999-03-01), Inoue et al.
patent: 6042344 (2000-03-01), Lifson
Carlson & Gaskey & Olds
Carrier Corporation
Robinson Daniel
Walberg Teresa
LandOfFree
Compressor control at voltage and frequency extremes of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Compressor control at voltage and frequency extremes of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Compressor control at voltage and frequency extremes of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2483322