GB2096363A

GB2096363A - Refrigerator

Info

Publication number: GB2096363A
Application number: GB8207874A
Authority: GB
Original assignee: Necchi SpA
Current assignee: Necchi SpA
Priority date: 1981-03-18
Filing date: 1982-03-18
Publication date: 1982-10-13
Also published as: JPH064554U; DE3209509A1; ES8302328A1; IT1147229B; JPS57202475A; IN156165B; ES510497A0; BR8201475A; KR830009451A; IT8142908A0

Abstract

A refrigerator comprises a motor- compressor unit (16) having a definite rated power and piston displacement but arranged to operate with different performance characteristics which, in a conventional system, would require different rated power and piston displacement values. This is achieved by varying both the frequency and voltage fed by a variable electrical power supply (26) to the electric motor of the unit (16), the value of the supplied power at any given time being determined by an electronic control system (24) processing temperature data determined by sensors (18, 20, 22) in the refrigerator. As shown the sensors are respectively in the refrigerator cabinet (10), on the evaporator (12), and on the condenser (14). The control system (24) includes a microprocessor and keeps the ratio V/f of the motor supply constant. The system may be used to maximise efficiency by giving the lowest possible condenser temperature and the highest possible evaporator temperature, or to keep the sensed temperatures constant. <IMAGE>

Description

SPECIFICATION Refrigerator The present invention relates to a refrigerator and has particular reference to a refrigerator having a motor-compressor unit with a variable electrical supply, and to the means for providing different electrical supply conditions for the motor-compressor unit in accordance with the required performance.

In known refrigeration systems, the motorcompressor unit is operated intermittently (on-off system) in order to maintain the temperature of the volume to be cooled around a value chosen by the user. The thermostats, of the bimetallic strip type, used as temperature controllers switch the motor on and off at two temperatures which lie somewhat above and below a value chosen by the user. These thermostats are thus not able to ensure high thermo-dynamic efficiency of the system because of the temperature variations (At) in the volume to be cooled, in the condenser and in the evaporator, due to the intermittent operation of said controllers.

According to the present invention there is provided a refrigerator comprising an electrically powered motor-compressor unit, a controllable power source to supply operating power to the motor-compressor unit, and control means for processing temperature data determined in the refrigerator and applying control signals to the power source to control the supply frequency and voltage of the operating power in dependence on the processed data.

In a preferred embodiment, the refrigerator comprises control means arranged to process temperature data determined in the refrigerator and to provide control signals to the input of a power supply unit for the motor-compressor unit such as to determine different supply frequency and voltage conditions in accordance with the control signals. As a result, it may be possible to use a motor-compressor unit with a single rated power and piston displacement for systems requiring different refrigeration capacities, instead of having to provide a range of motor-compressor units characterised by rated powers which are fairly close to each other (e.g. 1/12 HP, 1/10 HP, 1/8 HP, 1/6 HP etc.). In motor-compressor units for refrigerator systems, the refrigeration power is known to be proportional to the rotational speed of the motor and thus to its supply frequency.

The advantages of such an arrangement are fairiy apparent, especially in the case of mass production-simplification of equipment, stocking, spare parts-and, even more significantly, when automatic control means are provided for the electrical supply to the motor and are arranged to allow the system to operate at its maximum efficiency.

An embodiment of the present invention will now be more particulariy described by way of example with reference to the accompanying drawing, the single figure of which is a block diagram of a refrigerator according to the said embodiment.

Referring now to the accompanying drawing, there is shown a refrigerator comprising a refrigerator cabinet 10 fitted in the usual manner with an evaporator 12 and a condenser 14 connected into a circuit which includes a motorcompressor unit 1 6 of the piston type driven by a single-phase induction motor.

Temperature sensors 18, 20 and 22 are disposed in the cabinet 10 and on the surfaces of the evaporator 12 and condenser 14, respectively, and are arranged to continuously and accurately provide signals indicative of the temperature values at the monitored points. The temperature sensors are connected to an electronic control unit 24 provided with a microprocessor for processing the temperature data originating from the sensors 18, 20 and 22, and for transmitting suitable signals to a power supply unit 26, which feeds operating power at a voltage V and frequency f to the motor-compressor unit 1 6 in accordance with the signals received from the control unit 24. The power supply unit may comprise an inverter and a voltage regulator. With regard to the V and f values of power supplied to the motor, the criterion has been chosen of keeping the ratio V/f constant.Under such a supply condition, the rated power of the motor varies in proportion to the frequency f, and its operating characteristics remain practically unchanged.

The refrigeration power required of the motorcompressor unit and thus the power supply conditions to the motor are automatically adapted to the performance of the refrigeration system by processing the temperature values determined by the sensor 1 8 in the control unit 24, in the sense of determining the temperature variations in the volume to be cooled with respect to time and then determining the required operating conditions of the system in accordance with these values.

In order to obtain high thermodynamic efficiency of the system, the temperature values originating from all three sensors 1 8, 20 and 22 are processed in the control unit 24 and the control signals for the power supply unit 26 are such that the temperature variations (At) at the monitored points will be of minimum value.

A further control over the power supply can be determined by the control unit 24 by processing the temperature data originating from the sensors 20 and 22 in such a manner as to take into account the fact that in order to attain the best theoretical efficiency of the system it is advantageous to condense at the lowest possible temperature and evaporate at the highest possible temperature.

Claims

1. A refrigerator comprising an electrically powered motor-compressor unit, a controllable power source to supply operating power to the motor-compressor unit, and control means for

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Refrigerator The present invention relates to a refrigerator and has particular reference to a refrigerator having a motor-compressor unit with a variable electrical supply, and to the means for providing different electrical supply conditions for the motor-compressor unit in accordance with the required performance. In known refrigeration systems, the motorcompressor unit is operated intermittently (on-off system) in order to maintain the temperature of the volume to be cooled around a value chosen by the user. The thermostats, of the bimetallic strip type, used as temperature controllers switch the motor on and off at two temperatures which lie somewhat above and below a value chosen by the user. These thermostats are thus not able to ensure high thermo-dynamic efficiency of the system because of the temperature variations (At) in the volume to be cooled, in the condenser and in the evaporator, due to the intermittent operation of said controllers. According to the present invention there is provided a refrigerator comprising an electrically powered motor-compressor unit, a controllable power source to supply operating power to the motor-compressor unit, and control means for processing temperature data determined in the refrigerator and applying control signals to the power source to control the supply frequency and voltage of the operating power in dependence on the processed data. In a preferred embodiment, the refrigerator comprises control means arranged to process temperature data determined in the refrigerator and to provide control signals to the input of a power supply unit for the motor-compressor unit such as to determine different supply frequency and voltage conditions in accordance with the control signals. As a result, it may be possible to use a motor-compressor unit with a single rated power and piston displacement for systems requiring different refrigeration capacities, instead of having to provide a range of motor-compressor units characterised by rated powers which are fairly close to each other (e.g. 1/12 HP, 1/10 HP, 1/8 HP, 1/6 HP etc.). In motor-compressor units for refrigerator systems, the refrigeration power is known to be proportional to the rotational speed of the motor and thus to its supply frequency. The advantages of such an arrangement are fairiy apparent, especially in the case of mass production-simplification of equipment, stocking, spare parts-and, even more significantly, when automatic control means are provided for the electrical supply to the motor and are arranged to allow the system to operate at its maximum efficiency. An embodiment of the present invention will now be more particulariy described by way of example with reference to the accompanying drawing, the single figure of which is a block diagram of a refrigerator according to the said embodiment. Referring now to the accompanying drawing, there is shown a refrigerator comprising a refrigerator cabinet 10 fitted in the usual manner with an evaporator 12 and a condenser 14 connected into a circuit which includes a motorcompressor unit 1 6 of the piston type driven by a single-phase induction motor. Temperature sensors 18, 20 and 22 are disposed in the cabinet 10 and on the surfaces of the evaporator 12 and condenser 14, respectively, and are arranged to continuously and accurately provide signals indicative of the temperature values at the monitored points. The temperature sensors are connected to an electronic control unit 24 provided with a microprocessor for processing the temperature data originating from the sensors 18, 20 and 22, and for transmitting suitable signals to a power supply unit 26, which feeds operating power at a voltage V and frequency f to the motor-compressor unit 1 6 in accordance with the signals received from the control unit 24. The power supply unit may comprise an inverter and a voltage regulator. With regard to the V and f values of power supplied to the motor, the criterion has been chosen of keeping the ratio V/f constant.Under such a supply condition, the rated power of the motor varies in proportion to the frequency f, and its operating characteristics remain practically unchanged. The refrigeration power required of the motorcompressor unit and thus the power supply conditions to the motor are automatically adapted to the performance of the refrigeration system by processing the temperature values determined by the sensor 1 8 in the control unit 24, in the sense of determining the temperature variations in the volume to be cooled with respect to time and then determining the required operating conditions of the system in accordance with these values. In order to obtain high thermodynamic efficiency of the system, the temperature values originating from all three sensors 1 8, 20 and 22 are processed in the control unit 24 and the control signals for the power supply unit 26 are such that the temperature variations (At) at the monitored points will be of minimum value. A further control over the power supply can be determined by the control unit 24 by processing the temperature data originating from the sensors 20 and 22 in such a manner as to take into account the fact that in order to attain the best theoretical efficiency of the system it is advantageous to condense at the lowest possible temperature and evaporate at the highest possible temperature. Claims

1. A refrigerator comprising an electrically powered motor-compressor unit, a controllable power source to supply operating power to the motor-compressor unit, and control means for processing temperature data determined in the refrigerator and applying control signals to the power source to control the supply frequency and voltage of the operating power in dependence on the processed data.

2. A refrigerator as claimed in claim 1, wherein the motor-compressor unit comprises a piston compressor driven by an electric motor and has a single rated power and piston displacement, the unit being operable to provide different levels of performance corresponding to different power ratings above and below said single rated power.

3. A refrigerator as claimed in either claim 1 or claim 2, the control means comprising a microprocessor.

4. A refrigerator as claimed in any one of the preceding claims, wherein the power source comprises an inverter and a voltage regulator.

5. A refrigerator substantially as hereinbefore described with reference to the accompanying drawing.