WO2006129255A1

WO2006129255A1 - A cooling device and the control method

Info

Publication number: WO2006129255A1
Application number: PCT/IB2006/051683
Authority: WO
Inventors: Alper Soysal; Kerem Erenay
Original assignee: Arcelik Anonim Sirketi
Priority date: 2005-05-30
Filing date: 2006-05-26
Publication date: 2006-12-07
Also published as: EP1888983A1; ES2339049T3; EP1888983B1; BRPI0611215A2; DE602006011887D1; KR100946799B1; SI1888983T1; CN101184965A; CN100538220C; KR20080022547A; ATE456010T1

Abstract

The present invention relates to a cooling device (1) and a control method thereof, which prevent the motor of a variable speed compressor (2) performing the refrigerant cycle from unexpected stalls due to reasons of overheating or not being able to respond to the thermodynamic load resulting from heavy work load like high ambient temperature or the frequent opening closing of the door by means of a control method implemented via a control card (5).

Description

Description A COOLING DEVICE AND THE CONTROL METHOD

[0001] The present invention relates to a cooling device comprising a compressor that function efficiently under heavy operational load.

[0002] In cooling devices, the choice of the compressor in the cooling system takes into consideration the limit operational conditions according to the climatic zones, consequently the capacity of the compressor can be larger than is necessary since probable maximum operational loads are taken into account. The capacity of the compressor being larger than is necessary can result in increased number of stops-start ups and increased cyclic losses. In order to overcome this condition, the compressor choice is made according to real working conditions that spans the larger portion of the life expectancy of a compressor, and the compressor velocity i.e. the rotational speed (rpm) of the compressor motor is changed in cases when the cooling device should work in limit conditions. Various control algorithms have been devised in cooling devices utilizing variable speed compressor motors to determine when the compressor should function in normal velocity and when in higher velocity. The compressor velocity is accelerated with the help of an electronic card when the cooling device operates under heavy operational conditions such as high ambient temperatures or frequent opening closing of its door. In this case, the compressor is fed through the electronic card instead of the network power supply. Sometimes there can be overheating or stalls due to not being able to respond to the thermodynamic load under heavy operational conditions resulting in unexpected stalls in a compressor fed through the electronic card. When the compressor starts operating after the stall, the cut-out conditions are repeated in succession due to the algorithm requirement and the frequent cut-outs of the compressor lead to a reduction in efficiency.

[0003] In the United States Patent no. US 6231306, a gas turbine engine includes means for sensing a compressor stall, evaluating signals received from sensors and comparing the sensed signals to a predetermined threshold indicative of a healthy compressor, and for providing a processed signal indicative of an impending stall condition.

[0004] In the United States Patent no. US 6532433, in a method for monitoring and controlling a compressor, at least one compressor operational parameter is monitored to obtain a time-series data and this time-series data is filtered using a Kalman filter. A stall precursor of the compressor under heavy loading is detected before the compressor stalls as a result of this monitoring method.

[0005] In the Great Britain Patent no. GB 2292847, in a single-phase induction motor utilized in a compressor, a current detector detects stalling of the motor under high load and the relay cuts the power off the capacitor. [0006] In the Great Britain Patent no. GB 1109346, in a refrigerant compressor, the starting device acts to maintain energisation of the auxiliary winding after starting of the motor to overcome the extreme starting torque of the compressor for a long time to ensure that the running torque of the compressor will have fallen to a value lower than the normal stalling torque of the motor.

[0007] The aim of the present invention is the realization of a cooling device and a control method where the unexpected successive stalls of the compressor is prevented.

[0008] The cooling device and the control method realized in order to attain the aim of the present invention, the motor electronic card enables the compressor motor to operate under high loads and velocities in start up and stop periods with the instructions of the thermostat.

[0009] As the compressor continues operating in successive stop and start up periods, it is fed through the network for a period of time at every start up and the compressor motor functions at constant velocity. Thus, the electronic circuit controlling the motor speed is provided protection against the high current drawn at the start up.

[0010] While the compressor operates, the thermal protector that detects the motor temperature can cut off the feed current to stop the compressor due to overheating before the thermostat gives the stop instruction.

[0011] If the electronic card detects that the compressor has stopped as the thermal protector switches off the current, it concludes that this is a case of unexpected stall due to heavy load conditions.

[0012] When the compressor is about to start operating again, a predetermined waiting period of time elapses before the start up so that the stalls do not repeat, and since the pressure unbalance is reduced between the suction and compression parts of the compressor during this time period the compressor is enabled to make an easier start up after this stop period.

[0013] When the compressor starts operating after waiting for a certain time period, it is fed through the network power supply resulting in an operational time period at constant velocity that is longer than the time period when it starts operating with the signal of the thermostat.

[0014] When the compressor is operated after the unexpected stall period, whether the thermal protector is open or not should be immediately detected, therefore utilization of a separate heat sensor detecting the temperature of the thermal protector is beneficial for sending the thermal protector data to the electronic card.

[0015] The cooling device and the control method realized in order to attain above mentioned aim of the present invention is shown in the attached figures, where:

[0016] Figure 1 - is the schematic view of a cooling device.

[0017] Figure 2 - is the flow chart of a control method. [0018] Figure 3 - are the velocity - time and temperature - time graphs of a cooling device compressor operation.

[0019] Elements shown in the figures are numbered as follows:

1. Cooling device

2. Compressor

3. Thermal protector

4. Thermostat

5. Electronic card

6. Thermal protector heat sensor

[0020] The cooling device (1) comprises a variable speed compressor (2) providing to perform the refrigerant cycle, a thermal protector (3) that detects the temperature of the compressor (2), opening at values higher than the preset temperatures and switching off the current (J) to stop the operation of the compressor (2) and closing at values lower than the preset temperatures to provide the restart of the compressor (2), a thermostat (4) that gives cut-in and cut-out instructions to the compressor (2) and an electronic card (5) which provides the implementation of an algorithm that controls the operational speed and the start up - stop durations of the compressor (2).

[0021] While the compressor carries out its normal operation in the consecutive start-stop periods (T-on, T-off) triggered by the cut-in and cut-out instructions of the thermostat (4), in every passage from the T-off period to the T-on period, since high current (I) will be drawn at every start up of the compressor (2), the required current (I) for the motor is drawn directly from the network power supply for a predetermined period of time (Tl) to protect the electronic card (5) and during this time period (Tl) the compressor (2) operates at constant velocity (Vo). When the time period (Tl) ends, the compressor (2) starts operating by being fed through the electronic card (5) at a variable velocity, that is a velocity different from the constant velocity (Vo), e.g. a higher velocity (Vl) to provide the required cooling (Figure 3).

[0022] As the compressor (2) operates, the current (I) passes through the thermal protector (3) reaching the compressor (2) motor. The thermal protector (3) is positioned in the electrical connection box on the compressor (2) shell, and opens or closes depending on the changes in the ambient temperature. The thermal protector (3) opens at temperatures higher than the preset value, switching off the current (I) from the network power supply to the compressor (2) motor, and closes allowing the current (I) from the network power supply to reach the compressor (2) motor when the temperature falls below the preset value. When the compressor (2) motor is overheated, the thermal protector (3) switches off the current (I) providing to stop the compressor (2) and pro tecting the electronic card (5).

[0023] In cases when the thermal protector (3) switches off the current (I) stopping the compressor (2) without receiving an instruction from the thermostat (4) for a cut-out, current (I) is not supplied to the compressor (2) for a preset pause time period (T2) so that the pressures in the refrigerant system can be balanced and a cut-in instruction that might be given by the thermostat (4) during this time period is not heeded. When the (T2) period ends, the compressor (2) starts up with the current (I) supplied independently from the thermostat (4). After the start, the compressor (2) operates at constant velocity (Vo) for a time period (T3) longer than the time period (Tl) it operates at constant velocity (Vo), being fed by the current (I) from the network power supply that is applied for each first start up, later on, the current (I) is supplied through the electronic card (5) and it operates at a velocity of (Vl). If a cut-out instruction is received from the thermostat (4) while the compressor (2) operates at velocities of Vo or Vl, this instruction is obeyed, starting the T-off period.

[0024] The cooling device (1) control method that prevents the repeated unexpected stalls of the compressor (2) is composed of the following steps :

- The compressor (2) starts operating with the cut-in instruction of the thermostat (4) (100)

- The compressor (2) is operated at constant velocity (Vo) at start up and during the time period (Tl) (101)

- After the (Tl) time period is completed, current (I) is supplied through the electronic card (5) and the compressor (2) is operated at velocity (V!) (102) The thermal protector (3) is controlled whether or not it has switched off the current (I) (103)

If the thermal protector (3) has not switched off the current (I), then go to the step where the thermostat (4) is controlled (106) for whether or not it has given the cut-out instruction

- If the thermal protector (3) has switched off the current (I), pause for (T2) time period without supplying current (I) to the compressor (2) (104)

- The compressor (2) is operated at a constant velocity (Vo) for a time period (T3) longer than the time period (Tl) with current (I) supplied by the network power supply (105)

The thermostat (4) is controlled for whether or not it has given the cut-out instruction (106)

If the thermostat (4) has not given the cut-out instruction, then go back to the step (102) where the compressor (2) is operated at velocity (Vl) If the thermostat (4) has given the cut-out instruction, the compressor (2) starts the pause period (Toff) (107) [0025] In one embodiment of the present invention, the cooling device (1) comprises a thermal protector heat sensor (6) which detects the temperature of the thermal protector (3). The thermal protector heat sensor (6) detects the temperature of the thermal protector (3) reaching below the preset value at which the thermal protector (3) closes and hence the thermal protector (3) allows the current (I) to flow. When the thermal protector (3) stops the compressor (2) by switching off the current (I), if the temperature falls back to normal values at the end of the pause period (T2), the thermal protector (3) closes, allowing the current (I) to flow and the electronic card (5) operates the compressor (2) at the moment or a little while after the thermal protector (3) closes with the data received from the thermal protector heat sensor (6).

[0026] With the cooling device (1) control method implemented by means of the electronic card (5), the repetition of the stalls is prevented in the start up trials after the unexpected stalls of the compressor (2) and the start up trials after the unexpected stalls are successful.

[0027] In the embodiment of the present invention, unexpected stalls of the compressor (2) are prevented without the need for measuring and evaluating the various parameters of the compressor (2) by implementing a simple control method, and an efficient performance is accomplished, attaining the desired cooling values within the cooling device (1) under heavy duty work loads like high ambient temperature or frequent opening closing of the cooling device (1) door.

Claims

[0001] A cooling device (1) comprising a variable speed compressor (2) providing the performance of the refrigerant cycle, a thermal protector (3) that detects the temperature of the compressor (2), a thermostat (4) that gives cut-in and cut-out instructions to the compressor (2) in T-on and T-off periods and characterized by an electronic card (5), that does not supply current (I) to the compressor (2) for a preset time period (T2 ) without heeding a cut-in instruction that might be given by the thermostat (4), when the thermal protector (3) switches off the current (J) stopping the compressor (2) without receiving the instruction from the thermostat (4) for a cut-out while the compressor (2) operates, and at the end of this (T2) period, starts the compressor (2) with the current (I) supplied independently from the thermostat (4) and after the start up, operates the compressor (2) at a constant velocity (Vo) for a time period (T3) that is longer than the time period (Tl) preset for each start up.

[0002] A cooling device (1) as in Claim 1, characterized by a thermal protector heat sensor (6) which detects the temperature of the thermal protector (3), enabling the electronic card (5) to start the compressor (2) at the moment or a little while after the thermal protector (3) closes.

[0003] For a cooling device (1) as in Claim 1 or 2, a control method comprising the following steps :the compressor (2) starts operating with the cut-in instruction of the thermostat (4) (100); the compressor (2) is operated at constant velocity (Vo) at start up and during the time period (T I) (IOl); after the (Tl) time period is completed, current (I) is supplied through the electronic card (5) and the compressor (2) is operated at velocity (V!) (102); the thermal protector (3) is controlled whether or not it has switched off the current (I) (103); if the thermal protector (3) has not switched off the current (I), then go to the step where the thermostat (4) is controlled (106) for whether or not it has given the cut-out instruction ; if the thermal protector (3) has switched off the current (I), pause for (T2) time period without supplying current (I) to the compressor (2) (104); the compressor (2) is operated at a constant velocity (Vo) for a time period (T3) longer than the time period (Tl) with current (I) supplied by the network power supply (105); the thermostat (4) is controlled for whether or not it has given the cut-out instruction (106); if the thermostat (4) has not given the cut-out instruction, then go back to the step (102) where the compressor (2) is operated at velocity (Vl); if the thermostat (4) has given the cut-out instruction, the compressor (2) starts the pause period (Toff) (107).

[0004] A control method as in Claim 3, where the stop period (T2) after the thermal protector (3) switches off the current (I) at step no (104) is as long as the time period that is required for balancing the pressures in the cooling system.