Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
1998-12-23
2001-05-22
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C361S093100, C361S093700, C361S093800, C318S806000, C318S811000
Reexamination Certificate
active
06236184
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a variable speed cooling fan control particularly for use in cooling variable speed to constant frequency converters.
BACKGROUND OF THE INVENTION
Converters, such as variable speed to constant frequency converters which convert a variable speed mechanical input to a constant frequency electrical output, are typically required to handle large electrical power requirements. When such converters are required to operate in high load conditions, the converters can generate a substantial amount of heat which must be removed in order to protect the components of converters from damage. Accordingly, converters are cooled to prevent such damage.
For example, it is known to operate a fan at a constant speed in order to cool a converter. When a fan is operated at a constant speed to cool a converter, the fan must be run fast enough to cool the converter during the highest expected load condition. However, a fan running at high speed frequently entrains lint and other debris which tend to clog the cooling channels of the converter over time. As lint and debris build up in these cooling channels of a converter, both the cooling efficiency of the fan system and the life expectancy of the converter decrease.
One solution to this problem is to operate the fan at a speed that is dependant upon the load on the converter. Thus, at higher loads, the fan is run at a greater speed, and at lower loads, the fan is run at a slower speed. U.S. Pat. No. 3,059,164 discloses a variable speed fan control system for cooling a rectifier in response to load. However, the fan loads down the rectifier so that the fan unnecessarily contributes to the cooling needs of the rectifier.
U.S. Pat. No. 5,291,383 discloses a fan control system in which a cooling fan is run at a variable speed depending upon load as sensed at an input to an AC/DC/AC converter. Accordingly, the speed of the fan is not controlled directly by the load as sensed at the output of the converter but is controlled indirectly by sensing the input of the converter. This fan control introduces delay between changes in load and control of the fan.
The present invention is directed to a variable speed cooling fan control which solves one or more of the above noted problems.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a cooling system for a converter comprises a load sensor, a fan, and a fan control. The load sensor is arranged to sense load at an output of the converter. The fan is arranged to direct a cooling fluid to the converter, and the fan is arranged to receive electrical power upstream of the output of the converter. The fan control is coupled to the load sensor and to the fan, and the fan control is arranged to control the fan at a variable speed depending upon the sensed load.
According to another aspect of the present invention, a cooling system for a variable speed to constant frequency converter comprises a fan and a fan control. The fan is arranged to direct a cooling fluid to the variable speed to constant frequency converter. The fan control is coupled to the fan and is arranged to control the fan at a variable speed depending upon required cooling for the variable speed to constant frequency converter so as to vary cooling fluid delivered to the variable speed to constant frequency converter by the fan.
According to still another aspect of the present invention, a system comprises an AC to DC to AC converter, a load sensor, a fan, and a fan control. The AC to DC to AC converter has an input to receive input AC, a rectifier to rectify the input AC to DC, and an inverter to invert the DC to output AC. The load sensor is arranged to sense load on the AC to DC to AC converter. The fan is arranged to direct a cooling fluid to the AC to DC to AC converter. The fan control has first and second inputs, an inverter, and an output. The first input is coupled to the AC to DC to AC converter so as to receive DC therefrom, the second input is coupled to the load sensor, and the output is coupled to the fan.
The inverter is arranged to invert the DC on the first input to AC at the output as a function of the sensed load so as to control the fan at a variable speed in order to vary the cooling fluid delivered to the AC to DC to AC converter.
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patent: 2-307320 (1990-12-01), None
Hamilton Sundstrand Corporation
Marshall O'Toole Gerstein Murray & Borun
Martin Edgardo San
Nappi Robert E.
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