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Method of controlling compressor speed in Variable Speed Refrigerator

IP.com Disclosure Number: IPCOM000031222D
Publication Date: 2004-Sep-17
Document File: 3 page(s) / 12K

Publishing Venue

The IP.com Prior Art Database

Abstract

A variable speed refrigerator has the ability to run at multiple speeds. Some compressors run at multiple discrete (for example 30, 45, 60, 75 Hz) speeds. Others vary "infinitely" within a range of speeds (for example 30-75 Hz, in +/- 1 Hz increments). Either discrete speed variable speed compressors or infinitely variable speed compressors may be applied into a refrigerator (or other device using a compressor Le. central or room A/C or heat pump, dehumidifier, etc) as a discrete speed compressor. This disclosure tells how to control the speed of the compressor/system so that the temperature set point can be achieved.

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TECHNICAL DISCLOSURE

Subject: Method of controlling compressor speed in Variable Speed Refrigerator

Sketch and Description:

Summary:

A variable speed refrigerator has the ability to run at multiple speeds. Some compressors run at multiple discrete (for example 30, 45, 60, 75 Hz) speeds. Others vary "infinitely" within a range of speeds (for example 30-75 Hz, in +/- 1 Hz increments). Either discrete speed variable speed compressors or infinitely variable speed compressors may be applied into a refrigerator (or other device using a compressor Le. central or room A/C or heat pump, dehumidifier, etc) as a discrete speed compressor. This disclosure tells how to control the speed of the compressor/system so that the temperature set point can be achieved.

Problem to be Solved

The problem is temperature management for variable speed refrigerators that allows the compressor speed to be changed from a low to a higher speed or from high to a lower speed.

Assume that for a 3 discrete speed variable speed design that the following operating speeds are established:

System Off @ <=0 F Offset.

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Low Speed Operation @ 0-3 F Offset

Medium Speed Operation @ 3-6 F Offset
High Speed Operation @ >6 F Offset

Offset = actual Temperature of either FF or FZ compartment - target Temperature for same compartment.

Typical Targets FF = 37 F, FZ = O.

The compressor speed is increased when an offset, in either the FF or FZ compartment, exceeds a predetermined limit. The increased compressor speed translates into increased cooling being supplied to the compartment that is increasing in temperature. The fan speed for that compartment will typically match the speed range (low, medium, or high) that the compressor runs. The increase in temperature can be due to a number of factors 1) normal heat migration through walls of refrigerator, 2) door openings, 3) change in ambient temperature, 4) introduction of warm food into compartment. It is a benefit to food preservation to maintain the target FF, FZ set points. Increasing temperature in either compartment will negatively effect food preservation. To counter the temperature rise, the compressor speed is immediately increased when crossing predetermined offsets. The result is cooling increases to counter the negative effects of increasing temperature, improving temperature stability and therefore food preservation.

Reducing system operating speeds from high speed operation is trickier. The goal is to reach the target temperature for the FF or FZ compartment. It is important to hit the target temperature and not overshoot the target temperature. Over cooling the FF compartment will cause freezing of items. Over cooling either compartment results in unnecessary energy consumption.

Using the offset and speed ranges defined above, let's consider a refrigerator system reducing the operating speed. A refrigerator may have sufficient cooli...