GB2133586A

GB2133586A - Temperature control of a refrigerator

Info

Publication number: GB2133586A
Application number: GB08317726A
Authority: GB
Inventors: Jung Su Kim
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 1982-12-27
Filing date: 1983-06-30
Publication date: 1984-07-25
Also published as: KR840002972A; KR850000323B1; GB8317726D0

Abstract

A refrigerator circuit having a microprocessor based control unit (C) which receives input signals from measuring sensors (4,5, T2, 6, R, 7) in the refrigerator in order to develop a digital frequency-fixing signal in accordance with a chosen program, based at least partly on the difference between the interior temperature and a reference temperature. A frequency- converting unit (A') receiving the temperature- fixing signal thus supplies to the compressor motor a three phase AC of frequency fixed according to said difference, whereby the speed of operation of the compressor is controlled in accordance with the difference between the interior temperature and the predetermined reference. <IMAGE>

Description

SPECIFICATION Refrigerator Circuit The present invention relates to a refrigerator circuit with automatically controlled freezing and refrigerating capabilities corresponding to loads.

The usual freezing or refrigerating circuit comprises a thermostat in which Freon gas is injected and an electronic F-thermostat using the temperature sensor.

In case of such refrigerators, the compressor is operated at a fixed rotational frequency with a fixed freezing and refrigerating capability corresponding to the interior temperature condition; i.e., the compressor stops operating when the interior temperature decreases to a certain level (OFF-temperature) and starts to operate again when the interior temperature rises to a cetain level (ON-temperature).

Thus, the interior temperature is kept within a certain range by repeated ON-OFF operations of the compressor corresponding to the freezing or refrigerating loads, which results in some material disadvantages.

Firstly, frequent ON-OFF operations ofthe compressor require unnecessary electric consumption due to the high current surge at each starting of the compressor, the life span ofthe starting relay is comparatively short and noise is produced at the starting operation of the compressor.

Secondly, when the temperature rises to a high level, as in summer, and also a large volume of foods requires to be refrigerated, the conventional refrigerator often cannot meet such requirement due to lack of freezing and refrigerating capability.

It is an object of the invention to keep the interiortemperature ofthe refrigerator in a predetermined range, in which the differences between the lower and upper temperature limits ofthe interiortemperature are divided into several zones, the rotational frequency ofthe compressor-motorchanges automatically corresponding to such difference for each zone.

In orderto achieve this object, this invention uses a frequency-conversion unit of the digital-controlling type for the purpose of changing the rotational frequency of the compressor-motor.

Thus, the difference ranges between the inner temperature and the lower and upper temperature limit are divided into several zones, digital signals corresponding to each zone are transmitted to a frequency conversion unit in which the frequency of the source power to the compressor-motor are converted according to the digital signal, and the rotational frequency of the compressor-motor is thus changed in accordance with the freezing and refrigerating ability.

An embodiment of the invention will now be described with reference to the accompanying drawings, wherein: Figure 1 is a circuit diagram of a refrigerator in accordance with the invention; Figure2 is a graph showing several zones corresponding to difference ranges of interiortemperature; and Figure 3 and Figure 4 are graphs showing conversion of frequency of the power source for the compressor-motor when the loads are, respectively, comparatively heavy and light.

In the refrigerator circuit of Figure 1, an AC power source supplies a bridge-rectifying unit (B), a fan motor (2) and a defrosting unit (D) comprising defrost-switch (SW2) and defrost-heater (1), through power-input switch (SW1) and transformer (T1).

The bridge-rectifying circuit (B) is connected to a control unit (C), including a microprocessor having input signals such as signals from a temperature-fixing unit (3), signals from a temperature sensor (4), temperature data from a refrigerant temperature sensor (5), signals from an excess current detector (T2), signals from thermostat (6) in the compressor, and inputs from a resistance (R) for detecting voltage and a bimetal strip (7) in the defrosting unit (D).

The microprocessor converts the above signals to frequency-fixing signal by means of the prearranged programming.

The frequency-converting unit (A') comprising power-switching transistors (Q1 to Q6) and a frequencyconverting circuit (A) is connected to the outputterminals ofthe control unit(C), and the emitters oftransistors (Q., Q2, Q3) and collectors of transistors (04, Qs, Q6) are further connected to the three-phase motor (M) of the compressor.

In Figure 1, the references T3,L and 5W3 denote a voltage-dropping transformer, an inner light and a door-switch respectively; F. and F2 are power fuses and F3 is a temperature fuse.

The operation of the embodiment of the invention shown in Figure 1 is as follows: The control unit(C) suppliesthefrequency-fixing signal, of digital value, which is produced by analysing the difference between the fixed temperature oftemperature-fixing unit (3) and the interiortemperature detected by the temperature sensor, to the frequency-converting circuit (A).

On receiving the signal of fixed frequency from the frequency-converting circuit (A), the power transistors (Q. to Q,) are switched into operation and three-phase AC of fixed frequency is supplied to the compressormotor (M).

The three-phase AC is transformed from integrated waveform to sine waveform, the change being controlled substantially in proportion to the frequency fixed in the frequency4ixing circuit (A), varying continuously within the range of about 30Hz to 75Hz.

Accordingly, the rotational frequencies of the compressor-motor (M) change within the range of about 1,700 r.p.m. to 4.400 r.p.m.

For a defrosting operation, the control unit (C) sends a signal, produced by a time function component ofthe microprocessor after a certain period of the compressor's operation, causing the defrost-switch (SW2) to be switched to the defrost-heater (1).

When the defrosting operation is completed, the bimetal strip (7) of the defrosting unit sends a signal to the control unit in order that the defrost-switch is switched to the fan motor (2) and the compressor-motor (M) is restarted.

The zones corresponding to the differences between the interior temperature and the fixed temperature, and the process of converting the rotational frequencies of the compressor-motor in accordance with the loads, are now described in detail.

The load corresponds to the heat capacity being lost to maintain the temperature of the freezing and refrigerating space at the required level.

For example, in the casethatthe differences between the interiortemperature and the fixed temperature are divided into six zones (A, B, C, D, E and F) and the power frequencies for operating the compressor are determined as in Table 1, the operating frequencies of the compressor define the graph of Figure 2.

In the Table 1 and Figure 2, X represents the range of the interior temperature in falling slope and Y shows the range of the interior temperature in rising slope.

Table 1

Contents Difference between interior temp. and Fixed fixed temp. Frequency Zones X Y A more than 1"C more than 1.5 C 75Hz B 0.5"C-1.O"C 1.O"C--1.5"C 60Hz C O"C-0.50C 0.5"C--1.O"C 50Hz D -0.5,C0T 0 C~0.5 C 40Hz E -1 .O"C- -0.5"C -0.5"C--O"C 35Hz F less than -1.O"C less than -0.5"C compressor stop When the interior temperature of the refrigerator lies in the A zone, the interior temperature drops more rapidly in comparison with the conventional refrigerator due to the fixed frequency of75Hz and in case of B zone, the interior temperature drops gradually due to the fixed frequency of 60Hz.

When the interior temperature comes into the D zone, although the interior temperature rises up to a temperature 0.5"C higherthan the fixed temperature because ofthe increased freezing and refrigerating loads, the compressor operates continuously at the fixed frequency of 40Hz.

In other words, in so far as the interior temperature is maintained between D zone of X slope and D zone of Y slope, which is near to the fixed temperature, the compressor operates smoothly without having frequent changes of the fixed frequencies.

As can be seen in Figure 4, when the interior temperature drops and comes into the E zone due to a light load during the operation in the D zone ofthe X slope, a fixed frequency of 35Hz is applied to the compressor-motor.

If the interior temperature is maintained after three minutes of the operation of the compressor at the the fixed frequency of 35Hz, that is, at the point Ts, the compressor operates at the fixed frequency of 30Hz and thus the interior temperature begins to rise, while if the interior temperature comes into the D zone ofthe slope, that is, at the point Ts, the compressor begins to operate at the fixed frequency of 35Hz.

Accordingly, by this invention, excessive refrigerating is prevented and the compressor is protected from being frequently stopped and restarted.

As illustrated above, by the present invention, as the interior temperature of the refrigerator can be maintained within a certain range corresponding to the preset value by means of the frequency-converting unit of the digital controlling type and the control unit including the microprocessor, unnecessary consumption ofthe electric power required for starting the motor can be lessened, togetherwith electric power rates of usage, whilst the precise controlling of the interior temperature gives a substantial improvement in the refrigerating condition for the stored goods.

Further, the reliability of the refrigerator is raised by excluding the starting relay and noise produced by the starting operation of the motor can be reduced, because the number of the motor starting times is strictly controlled.

Claims

1. A refrigerator circuit having automatically controlled freezing and refrigerating capabilities corresponding to loads, in which an AC power source is connected to a fan motor, a bridge-rectifying circuit and a defrosting unit including a defrost-switch and defrost-heater, through a power-input switch and a power transformer, and including a frequency-converting unit of the digital-controlled type which controls the frequency of the electric power supplied to the compressor, resulting in control of the rotational frequency of the compressor, and a control unit which sends signals determined by the differences between the interior temperature and a preset temperature standard to the above frequency-converting unit, whereby the rotational frequency of the compressor is controlled in accordance with the difference between the interior temperature and the preset temperature standard.

2. A refrigerator circuit according to claim 1, wherein the control unit produces and transmits signals for the fixed frequencies corresponding to several zones divided according to the differences between the possible interior temperatures, and also signals for a fixed frequency lower than the frequency at which the compressor-motor operates, when the compressor keeps operating in a particular zone longer than a preset time, to the frequency-converting unit.

3. A refrigerator circuit substantially as hereinbefore described with reference to the accompanying drawings.