Patent Application
20120177514
This application relates to the use of motor current in a compressor to estimate a discharge pressure.
Compressors are an integral part of any refrigerant system. Modern compressors are provided with a large number of increasingly complex controls which take in data from any number of locations within an associated refrigerant system, and then develop ways to control the compressor most efficiently. One piece of data that is required is the discharge pressure of the compressor. Thus, a discharge pressure sensor is typically incorporated into modern systems.
Another competing factor in modern compressors is to lower cost. Each added component requires additional cost, and thus the elimination of a component would be desirable.
A compressor has a controller which is provided with current information for a current passing into a motor associated with the compressor. The compressor includes a compressor pump unit driven by the motor, and a discharge line. The controller is programmed to utilize the current information to predict a discharge pressure at the discharge of the compressor.
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.
A suction line 152 leads into a sealed compressor chamber, and to the compressor pump unit 50. The suction pressure refrigerant is compressed and then delivered to a discharge line 52. As mentioned above, it is desirable to know the pressure at the discharge 52.
Suction pressure is also an important variable which is typically utilized in modern compressor controls. A suction pressure sensor 23 is shown schematically on the suction line 152. This sensor could be at any number of other locations, and the entire structure of the compressor 22 is shown schematically. Downstream of the compressor 22 is a condenser 24. Downstream of the condenser 24 is an expansion device 28, and then an evaporator 30. Refrigerant passes from the compressor 22, through the condenser 24, the expansion device 28, the evaporator 30, and then back to through the suction line 152 to the compressor 22.
The controller 32 takes measurements from an inverter of at least current passing to the motor 51. In addition, the controller 32 may receive information from the suction pressure sensor 23. Many compressor motors are fixed speed, and thus the controller 32 will know the speed. If the motor 51 can operate at several speeds, that information will also be sent to controller 32.
A temperature sensor 26 may be associated with the condenser 24. The temperature sensor could be on a condenser return bend, or if the condenser is a microchannel heat exchanger, in the return header.
The curves are shown as examples only, and the actual current versus discharge pressure curves would be developed for each compressor 22 which would utilize this invention. However, it is known that there is a relationship between discharge pressure and current.
Further, one may fine-tune this determination by adding suction pressure to provide more accurate estimates of the discharge pressure. Further, a temperature at the motor 51 can also be sent to the controller 32, and provide further fine-control over the estimate.
However, for purposes of the broadest aspects of this invention, all that would be necessary is to know current, and then to estimate discharge pressure. In this manner, the discharge pressure can be utilized by the controller 32 to control operation of the motor and compressor for any number of other applications.
At the same time, and as shown in
Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
