Refrigeration – Automatic control – Refrigeration producer
Patent
1999-04-09
2000-10-24
Tanner, Harry B.
Refrigeration
Automatic control
Refrigeration producer
62157, 62229, F25B 4902
Patent
active
061349011
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a method for speed control of a compressor, particularly a refrigeration compressor, and a control arrangement using this method. The speed control is effected in that a control arrangement varies the speed of an electric motor in dependence of simple ON/OFF signals from a thermostat placed in the surroundings to be cooled.
The task on which the application is based, is the development of a control method and a control arrangement for a variable speed compressor, which is simple compared with the state of the art, and which can be fitted into existing constructions, e.g. refrigerators, which normally operated at fixed speed, but which can be changed to operation with variable speed by a quick intervention of a service technician. It is known to control the speed of compressors in dependence of the pressure conditions in the refrigeration system or in dependence of electronic temperature signals, but a common feature of these solutions is that they require relatively expensive pressure and temperature meters, and can only in rare cases directly replace existing solutions.
U.S. Pat. No. 5,410,230 describes a compressor control with an ON/OFF thermostat controlling the motor speed on the basis of the cyclic parameter, i.e. the duty cycle. The ON and OFF times of the thermostat are measured, and the duty cycle is calculated. If the duty cycle is lower than a predetermined value, the starting speed in the next cycle is reduced, and if it is higher, the starting speed is increased. When the thermostat is closed and the compressor operates, the motor speed is ramped upwards during the ON period, and correspondingly the motor speed is ramped downwards during the OFF period of the thermostat.
The control described in U.S. Pat. No. 5,410,230 is developed with a view to sawing a control component, e.g. a temperature controlling microprocessor, and in stead of having a price increasing component like a microprocessor measure and treat a temperature signal from an electronic thermostat, U.S. Pat. No. 5,410,230 uses a cheaper solution with an ON/OFF thermostat. However, the control method described is relatively complicated, as both ON and OFF times are measured, and at least three speed calculations are made during an ON/OFF cycle, viz. a first calculation of the starting speed, then a second continuous calculation of the speed in the ON period and a third calculation of the speed in the OFF period. Besides, the described method involving speed control during both the ON and the OFF period causes a relatively large energy consumption.
One of the purposes is thus to develop a control method and a control arrangement for a compressor having a lower energy consumption than the controls known from the state of the art.
Another purpose of the invention is to make a control method and a control arrangement for a compressor, which can be directly integrated in existing constructions, by which existing elements, such as an ON/OFF thermostat, are used for compressor speed control.
According to the invention, this is done by letting the conventional ON/OFF thermostat, which are already available in large numbers in the refrigerators, control the compressor speed so that the starting speed in a following ON period is reduced in relation to the final speed in a previous ON period by making the control arrangement subtract a predetermined speed from the final speed in the previous ON period and letting the result of this calculation be the starting speed in the following ON period, through which the speed is either increased or kept constant.
Using this control method enables an adaptive control, which automatically lets the motor operate at the speed required, which results in the refrigeration compressor working with averagely low speeds during long operation periods, which gives a low energy consumption. The operation or ON time is a function of the size of the subtracted rpm and the time it takes to increase the motor speed.
The invention describes in a first embodiment, how the speed in an actual ON peri
REFERENCES:
patent: 4831313 (1989-05-01), Beilfuss
patent: 5074120 (1991-12-01), Kitamoto
patent: 5410230 (1995-04-01), Bessler et al.
patent: 5673568 (1997-10-01), Isshiki
Aarestrup Jan
Harvest Nils-Ole
Danfoss Compressors GmbH
Tanner Harry B.
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