EP3537061A1

EP3537061A1 - Oil equalization control device, refrigerant circuit system, and oil equalization control method

Info

Publication number: EP3537061A1
Application number: EP17885453.5A
Authority: EP
Inventors: Takahiro Kato; Tatsuhiro Yasuda; Masayuki Takigawa
Original assignee: Mitsubishi Heavy Industries Thermal Systems Ltd
Current assignee: Mitsubishi Heavy Industries Thermal Systems Ltd
Priority date: 2016-12-28
Filing date: 2017-12-26
Publication date: 2019-09-11
Also published as: CN110114622A; WO2018124083A1; EP3537061A4; JP2018109452A

Abstract

An oil equalization control device, provided with: a sensor information acquisition unit for acquiring, in a refrigerant circuit provided with a plurality of compressors, a state quantity relating to the amount of refrigerating machine oil in a compressor, for each of the plurality of compressors; a control sequence determination unit for determining the control sequence for the compressors in oil equalization control in accordance with the amounts of the refrigerating machine oil in the compressors based on the state quantities; and an oil equalization control unit for varying the rotation speed of at least one of the plurality of compressors and performing oil equalization control on the basis of the order determined by the control sequence determination unit.

Description

Technical Field

The present invention relates to an oil equalization control device, a refrigerant circuit system, and an oil equalization control method.
This application claims priority based on JP 2016-256135 filed in Japan on December 28, 2016, of which the contents are incorporated herein by reference.

Background Art

In an air conditioner including a plurality of compressors in one outdoor unit, or in an air conditioning system including a plurality of outdoor units, a configuration in which low-pressure portions of the compressors are connected with each other by using piping (oil equalization pipe) may be employed to prevent an imbalance in refrigeration oil between the compressors. Furthermore, oil equalization control may be performed to correct an imbalance in the amount of refrigeration oil between the compressors. In typical oil equalization control, for example, the rotational speed of one of a plurality of compressors that normally operate at the same rotational speed is increased to make a pressure differential between the one compressor and the other compressor and thus to move refrigeration oil from a compressor having higher pressure to a compressor having lower pressure through an oil equalization pipe.
As a related technology, Patent Document 1 discloses a technology in which a liquid level sensor or the like detects the position of the liquid surface of refrigeration oil in each of compressors, and the rotational speeds of the compressors are controlled so that the difference between the positions of the liquid surfaces is decreased, thus eliminating unevenness of the refrigeration oil.

Citation List

Patent Document

Patent Document 1: JP 2005-241070 A

Summary of Invention

Problem to be Solved by the Invention

In the above-described typical oil equalization control, a sequence for the compressors is often preliminarily determined, and control of increasing the rotational speeds is performed, following this sequence. In consideration of the original purpose of oil equalization control, it is desirable to restore refrigeration oil in the order from a compressor having a smaller amount of refrigeration oil. In this case, it is required to increase the rotational speed of the compressor having a smaller amount of refrigeration oil to decrease pressure of this compressor and thus to take in refrigeration oil from another compressor having relatively high pressure. Unfortunately, in the above-described typical oil equalization control, without considering the amounts of refrigeration oil in individual compressors, the rotational speeds are increased in the predetermined sequence. Thus, in a case where the first compressor in the sequence stores a large amount of refrigeration oil from the beginning, for example, the amount of refrigeration oil in that compressor is further increased, which may result in an even greater imbalance.
The present invention provides an oil equalization control device, a refrigerant circuit system, and an oil equalization control method that can solve the above-described problem.

Solution to Problem

According to a first aspect of the present invention, an oil equalization control device includes, in a refrigerant circuit including a plurality of compressors connected in parallel with each other: a sensor information acquisition unit configured to acquire a state quantity relating to an amount of refrigeration oil in each of the plurality of compressors; a control sequence determination unit configured to determine a control sequence for the compressors in oil equalization control in accordance with the amounts of the refrigeration oil in the compressors based on the state quantities; and an oil equalization control unit configured to vary a rotational speed of at least one of the plurality of compressors and performing the oil equalization control on a basis of the control sequence determined by the control sequence determination unit.
According to a second aspect of the present invention, the control sequence determination unit determines the control sequence by listing the compressors in ascending order of the amounts of the refrigeration oil; and the oil equalization control unit varies the rotational speed of the compressor in its turn in the control sequence so that the compressor in its turn has a relatively low pressure.
According to a third aspect of the present invention, the sensor information acquisition unit acquires a measurement value of a pressure on a low pressure side of each of the plurality of compressors; and the control sequence determination unit sets a sequence of relatively decreasing pressures of the compressors by listing the compressors in descending order of the measurement values of the pressures.
According to a fourth aspect of the present invention, the sensor information acquisition unit acquires a measurement value of a temperature below a dome of each of the plurality of compressors; and the control sequence determination unit sets a sequence of relatively decreasing pressures of the compressors by listing the compressors in ascending order of the measurement values of the temperatures.
According to a fifth aspect of the present invention, the oil equalization control unit increases the rotational speed of each of the plurality of compressors in a predetermined period in the control sequence.
According to a sixth aspect of the present invention, a refrigerant circuit system includes: a plurality of compressors connected in parallel with each other; an oil equalization pipe connecting the plurality of compressors with each other; and the oil equalization control device according to any one of the above-described aspects.
According to a seventh aspect of the present invention, an oil equalization control method includes the steps of: acquiring a state quantity relating to an amount of refrigeration oil in each of a plurality of compressors in a refrigerant circuit including the plurality of compressors connected in parallel with each other; determining a control sequence for the compressors in oil equalization control in accordance with the amounts of the refrigeration oil in the compressors based on the state quantities; and varying a rotational speed of at least one of the plurality of compressors and performing the oil equalization control on a basis of the control sequence; the steps being performed by an oil equalization control device.

Advantageous Effect of Invention

The above-described oil equalization control device, refrigerant circuit system, and oil equalization control method can correct an imbalance in the refrigeration oil between the plural compressors and improve reliability of the system.

Brief Description of Drawings

FIG. 1 is a first schematic diagram illustrating an example of a refrigerant circuit system according to an embodiment of the present invention.
FIG. 2 is a schematic block diagram illustrating a control device according to the embodiment of the present invention.
FIG. 3 is an explanatory diagram illustrating a control sequence for compressors according to the embodiment of the present invention.
FIGS. 4A to 4D are explanatory diagrams illustrating an example of rotational speed control of compressors according to the embodiment of the present invention.
FIG. 5 is a flowchart illustrating an example of oil equalization control according to the embodiment of the present invention.
FIG. 6 is a second schematic diagram illustrating an example of the refrigerant circuit system according to the embodiment of the present invention.

Description of Embodiments

Embodiment

A refrigerant circuit system according to an embodiment of the present invention will be described below with reference to FIG. 1 to FIG. 6.
FIG. 1 is a first schematic diagram illustrating an example of the refrigerant circuit system according to the embodiment of the present invention.
The refrigerant circuit system 100 is, for example, a refrigerant circuit system used in an air conditioner. As illustrated in FIG. 1, the refrigerant circuit system 100 includes compressors 1A and 1B, oil separators 2A and 2B, emission pipes 3A and 3B, oil return pipes 4A and 4B, solenoid valves 5A and 5B, intake pipes 6A and 6B, an oil equalization pipe 7, a four-way valve 8, an accumulator 9, an outdoor heat exchanger 10, a receiver 11, an expansion valve 12, an indoor heat exchanger 13, a liquid pipe 14, gas pipes 15, 16, and 17, and a control device 20. FIG. 1 schematically illustrates a basic configuration of the refrigerant circuit system 100, and another constituent element may further be included.
The compressors 1A and 1B compress a refrigerant and supply the compressed high-pressure refrigerant to a refrigerant circuit. The compressors 1A and 1B are connected in parallel with each other, and are controlled so as to operate with the same displacement in normal operation. When the compressors 1A and 1B are of the same model, for example, the compressors 1A and 1B operate at the same rotational speed.
The oil separators 2A and 2B are respectively disposed on the emission sides of the compressors 1A and 1B, and are devices separating refrigeration oil from the refrigerant that is fed through the emission pipes 3A and 3B and is mixed with the refrigeration oil. The oil separators 2A and 2B each have, for example, a cylindrical shape of which the top side and bottom side are closed, and store the separated refrigeration oil.
The oil return pipes 4A and 4B each have one end connected with a lower portion of the vessel of the corresponding one of the oil separators 2A and 2B. The oil return pipes 4A and 4B each have the other end connected with the corresponding one of the compressors 1A and 1B. The oil return pipe 4A is provided with the solenoid valve 5A. The degree of opening of the solenoid valve 5A is adjusted to enable adjustment of the amount of the refrigeration oil returning from the oil separator 2A to the compressor 1A. Similarly, the oil return pipe 4B is provided with the solenoid valve 5B. The degree of opening of the solenoid valve 5B is adjusted to enable adjustment of the amount of the refrigeration oil returning from the oil separator 2B to the compressor 1B.
The oil equalization pipe 7 allows communication between the compressors 1A and 1B and equalizes the refrigeration oil stored in the two compressors.
The four-way valve 8 switches the flow direction of the refrigerant between a direction in heating operation and a direction in cooling operation. For example, in heating operation, the high-pressure refrigerant emitted by the compressors 1A and 1B is guided to the gas pipe 15 by using the four-way valve 8, and the indoor heat exchanger 13 (condenser) radiates heat of the refrigerant to the interior of the room. The refrigerant liquefied by passing through the indoor heat exchanger 13 is decreased in pressure by the expansion valve 12, passes through the liquid pipe 14, and is supplied to the outdoor heat exchanger 10 (evaporator). The receiver 11 disposed on the liquid pipe 14 stores the liquid refrigerant that has been liquefied. The refrigerant gasified by the outdoor heat exchanger 10 passes through the gas pipe 17, reaches the four-way valve 8, and is supplied through the gas pipe 16 to the accumulator 9. The accumulator 9 is a pressure vessel disposed upstream from the compressors 1A and 1B. The accumulator 9 performs vapor-liquid separation on the refrigerant supplied to the compressors 1A and 1B. The refrigerant gas separated by the accumulator 9 passes through the intake pipes 6A and 6B and is taken into the compressors 1A and 1B.
In cooling operation, the refrigerant circulates in the direction opposite to the direction in heating operation. That is, the high-pressure refrigerant emitted by the compressors 1A and 1B is guided to the gas pipe 17 by using the four-way valve 8, and is supplied to the outdoor heat exchanger 10 (condenser), the liquid pipe 14, the expansion valve 12, and the indoor heat exchanger 13 (evaporator). The refrigerant of which the heat is exchanged for indoor air by the indoor heat exchanger 13 passes through the gas pipe 15, is guided to the gas pipe 16 by using the four-way valve 8, and is taken into the compressors 1A and 1B through the accumulator 9.
The refrigerant emitted by the compressors 1A and 1B contains the refrigeration oil. A major portion of the refrigeration oil emitted by the compressors 1A and 1B is captured by the oil separators 2A and 2B and returns to the compressors 1A and 1B via the oil return pipes 4A and 4B. The remaining portion of the refrigeration oil circulates through the refrigeration cycle formed as described above and is introduced into the accumulator 9. One portion of the refrigeration oil introduced into the accumulator 9 returns to the compressors 1A and 1B together with the gasified refrigerant, and the other portion is stored in the accumulator 9.
A deficiency of the amount of the refrigeration oil collected into the compressors 1A and 1B causes a fault such as seizure of the compressors 1A and 1B. Thus, the control device 20 performs, for example, oil return control to enable an appropriate amount of the refrigeration oil to be collected at intervals of certain operating time. There are various ways of oil return control, and in the refrigerant circuit system 100, control of collecting the refrigeration oil into the accumulator 9 is performed, for example. Thereafter, the control device 20 performs control of returning the refrigeration oil collected into the accumulator 9 to the compressors 1A and 1B little by little over time. At this time, the control device 20 performs oil equalization control to prevent an imbalance in the refrigeration oil stored in the compressors 1A and 1B caused by the control of returning the refrigeration oil from the accumulator 9 to the compressors 1A and 1B.
A pressure sensor PA is disposed on the intake side of the compressor 1A, and a pressure sensor PB is disposed on the intake side of the compressor 1B. A temperature sensor TA is disposed below the dome of the compressor 1A, and a temperature sensor TB is disposed below the dome of the compressor 1B. Furthermore, a liquid level detecting sensor LA detecting the level of the oil surface of the refrigeration oil is disposed inside the compressor 1A, and similarly, a liquid level detecting sensor LB is disposed inside the compressor 1B. Not all of these sensors are necessarily provided. For example, only the pressure sensors PA and PB may be provided, or only the temperature sensors TA and TB may be provided.
On the basis of the pressures on the intake sides (low pressure sides) of the compressors 1A and 1B measured by the pressure sensors PA and PB, the temperatures below the domes of the compressors 1A and 1B measured by the temperature sensors TA and TB, or the levels of the oil surfaces measured by the liquid level detecting sensors LA and LB, the control device 20 of the refrigerant circuit system 100 performs the oil equalization control so that the refrigeration oil returns by priority to a compressor that is deficient in the refrigeration oil in the order from that compressor. The control device 20 will be described in detail with reference to FIG. 2.
FIG. 2 is a schematic block diagram illustrating the oil equalization control device according to the embodiment of the present invention.
The control device 20 is, for example, a computer device such as a microcomputer. The control device 20 is connected with the pressure sensors PA and PB, the temperature sensors TA and TB, the liquid level detecting sensors LA and LB, and the compressors 1A and 1B. As illustrated in FIG. 2, the control device 20 includes a sensor information acquisition unit 21, a control sequence determination unit 22, an oil equalization control unit 23, and a storage unit 24. The control device 20 performs various types of control of the refrigerant circuit system 100 in addition to the oil equalization control; however, description of functions relating to the other control is omitted in this specification.
The sensor information acquisition unit 21 acquires a state quantity relating to the amount of the refrigeration oil in each of the compressors 1A and 1B. For example, the sensor information acquisition unit 21 acquires the pressures of the refrigerant on the intake sides of the compressors 1A and 1B measured by the pressure sensors PA and PB. The sensor information acquisition unit 21 acquires the temperatures below the domes of the compressors 1A and 1B measured by the temperature sensors TA and TB. The sensor information acquisition unit 21 acquires the levels of the liquid surfaces in the compressors 1A and 1B measured by the liquid level detecting sensors LA and LB.
The control sequence determination unit 22 determines a control sequence for the compressors in the oil equalization control in accordance with the amounts of the refrigeration oil in the compressors 1A and 1B based on the state quantities acquired by the sensor information acquisition unit 21. In specific, the control sequence determination unit 22 determines to increase the rotational speeds in the order from a compressor having a smaller amount of the refrigeration oil. Hereinafter, the order of increasing the rotational speeds of the compressors is referred to as a control sequence. For example, the control sequence determination unit 22 determines the control sequence by listing the compressor 1A and the like in descending order of the pressures on the intake sides. For example, the control sequence determination unit 22 determines the control sequence by listing the compressor 1A and the like in ascending order of the temperatures below the domes. For example, the control sequence determination unit 22 determines the control sequence by listing the compressor 1A and the like in ascending order of the levels of the oil surfaces of the refrigeration oil.
The oil equalization control unit 23 performs the oil equalization control by varying the rotational speed of at least one of the plural compressors 1A and the like on the basis of the control sequence determined by the control sequence determination unit 22. In specific, the oil equalization control unit 23 increases the rotational speed of one in its turn of the compressors in a predetermined period in the control sequence so that the pressure of the one compressor is low relative to that of the other compressor.
The storage unit 24 stores various pieces of information such as various measurement values acquired by the sensor information acquisition unit 21 and control parameters including the increased rotational speeds of the compressors and the like. The storage unit 24 stores a program achieving the function of the control device 20.
A Central Processing Unit (CPU) included in the control device 20 achieves functions of the control sequence determination unit 22 and the oil equalization control unit 23 by reading out the program from the storage unit 24 and executing the program.
Next, the oil equalization control according to the present embodiment will be described with reference to FIG. 3.
FIG. 3 is an explanatory diagram illustrating the control sequence for the compressors according to the embodiment of the present invention.
FIG. 3 illustrates relationships among the intake side pressures of the compressors, the temperatures below the domes, the positions of the oil surfaces of the refrigeration oil, the amounts of the refrigeration oil, and a control sequence for the rotational speeds of the compressors. The refrigerant circuit system 100 exemplified in FIG. 1 has two compressors; however, to more clearly describe the features of the oil equalization control of the present embodiment, the table in FIG. 3 exemplifies the above-described relationships in a case of a system including three compressors 1 to 3 connected in parallel with each other.
In the case of the example illustrated in FIG. 3, the compressor 1 has a medium intake side pressure, a medium temperature below the dome, and a medium level of the oil surface of the refrigeration oil among the three compressors. Similarly, the compressor 2 has the highest pressure, the lowest temperature, and the lowest level of the oil surface among the three, and the compressor 3 has the lowest pressure, the highest temperature, and the highest level of the oil surface among the three.
A higher intake side pressure indicates that the compressor stores a smaller amount of the refrigeration oil. Thus, for example, the pressure "HIGH" of the compressor 2 indicates that the compressor 2 has the smallest amount of the refrigeration oil among the three.
The refrigeration oil in the compressor has a property of absorbing heat released from a motor of the compressor, so that, as the amount of the refrigeration oil is larger, the temperature below the dome is higher, and as the amount of the refrigeration oil is smaller, the temperature below the dome is lower. Thus, for example, the temperature "LOW" of the compressor 2 indicates that the compressor 2 has the smallest amount of the refrigeration oil among the three.
A higher value of "OIL SURFACE" indicates that the compressor stores a larger amount of the refrigeration oil, and a lower value indicates a smaller amount. For example, the oil surface "LOW" of the compressor indicates that the compressor 2 stores the smallest amount of the refrigeration oil among the three.
The above description indicates that, in the case of the compressors 1 to 3 exemplified in FIG. 3, the compressor 2 stores the smallest amount of the refrigeration oil, the compressor 1 stores the second smallest amount of the refrigeration oil, and the compressor 3 stores the largest amount of the refrigeration oil. The control sequence determination unit 22 determines the amounts of the refrigeration oil in the compressors 1 to 3 as described above and determines to increase the rotational speeds in the order from a compressor having a smaller amount of the refrigeration oil, on the basis of the state quantities (pressures, temperatures, oil surface levels) relating to the amounts of the refrigeration oil in the compressors 1 to 3 acquired by the sensor information acquisition unit 21. That is, in the case of the above-described example, the control sequence determination unit 22 determines to increase the rotational speed of the compressor 2 having the smallest amount of the refrigeration oil first, then increase the rotational speed of the compressor 1 having the second smallest amount of the refrigeration oil, and lastly increase the rotational speed of the compressor 3 having the largest amount of the refrigeration oil. Then, the oil equalization control unit 23 increases the rotational speed of the compressor 2 in the predetermined period first on the basis of the sequence determined by the control sequence determination unit 22. This operation decreases the pressure of the compressor 2 and moves the refrigeration oil from the other compressors 1 and 3 having higher pressures to the compressor 2 via the oil equalization pipe 7. After the elapse of the predetermined period, the oil equalization control unit 23 returns the rotational speed of the compressor 2 to the original speed and then increases the rotational speed of the compressor 1 in the predetermined period. After another elapse of the predetermined period, the oil equalization control unit 23 returns the rotational speed of the compressor 1 to the original speed and lastly increases the rotational speed of the compressor 3 in the predetermined period. In this way, in the present embodiment, such oil equalization control is performed that the rotational speeds are increased in the predetermined period in the order from a compressor having a smaller amount of the refrigeration oil. This can correct an imbalance in the refrigeration oil among the plural compressors 1 to 3, prevent the compressors 1 to 3 from stopping because of a deficiency of the refrigeration oil or the like, and improve reliability of the system.
Next, the oil equalization control of the refrigerant circuit system 100 exemplified in FIG. 1 will be described with reference to FIGS. 4A to 4D.
FIGS. 4A to 4D are explanatory diagrams illustrating rotational speed control of the compressors according to the embodiment of the present invention.
FIGS. 4A to 4D illustrate an example of the oil equalization control according to the present embodiment that is performed at two different points in time in operation of the refrigerant circuit system 100.
FIG. 4A and FIG. 4B are correspondence tables showing state quantities and order of increasing the speeds of the compressors 1A and 1B at two points in time (start timings 1, 2). FIG. 4C illustrates transition of the rotational speed of the compressor 1A. FIG. 4D illustrates transition of the rotational speed of the compressor 1B.
With reference to FIG. 4A illustrating state quantities of the compressors 1A and 1B at the start timing 1 in the oil equalization control, the compressor 1A has a pressure "HIGH", the compressor 1B has a pressure "LOW", and the like. That is, at the start timing 1, the compressor 1A has a smaller amount of the refrigeration oil than that in the compressor 1B. In this case, the control sequence determination unit 22 determines to increase the rotational speeds in the predetermined period in the order of the compressor 1A and then the compressor 1B. First, on the basis of this determination, the compressor 1A is operated with its rotational speed increased by the oil equalization control unit 23 to a predetermined rotational speed in a predetermined period H1. On the other hand, the compressor 1B may be operated with its rotational speed remaining unchanged or being decreased to a predetermined rotational speed in the predetermined period HI as illustrated in FIG. 4D. Decreasing the rotational speed of the compressor 1B can increase a pressure differential between the compressors 1A and 1B. This can, for example, reduce the degree of an increase in the rotational speed of the compressor 1A and prevent a stop of operation of the compressor 1A or the like due to actuation of protective control. Next, after the elapse of the predetermined period H1, the compressors 1A and 1B are switched, which means that the compressor 1B is operated with its rotational speed increased by the oil equalization control unit 23 to a predetermined value in the predetermined period H1 and that the compressor 1A is operated with its rotational speed decreased by the oil equalization control unit 23 to a predetermined value in the predetermined period HI. After all the compressors 1A and 1B are operated once with their rotational speeds increased, the oil equalization control unit 23 returns the rotational speeds of the compressors 1A and 1B to the original speed and ends the oil equalization control. Thereafter, the control device 20 normally operates the compressors 1A and 1B at a rotational speed in accordance with a load for a while.
After the normal operation continues in a predetermined period, the control device 20 performs the oil return control. Then, after the elapse of a predetermined period, the control device 20 performs the control of returning the refrigeration oil from the accumulator 9 to the compressors 1A and 1B. At the same time, the control device 20 starts the oil equalization control (start timing 2).
FIG. 4B illustrates state quantities, acquired by the sensor information acquisition unit 21, of the compressors 1A and 1B at the start timing 2. Unlike the state at the start timing 1, the compressor 1A has a larger amount of the refrigeration oil than that in the compressor 1B at the start timing 2. The control sequence determination unit 22 determines to perform control of increasing the rotational speeds in the order of the compressor 1B and then the compressor 1A as a control sequence for the compressor 1A and the compressor 1B in the oil equalization control. Then, first, the compressor 2 is operated with its rotational speed increased by the oil equalization control unit 23 to a predetermined value in the predetermined period HI, and on the other hand, the compressor 1A is operated with its rotational speed decreased to a predetermined value in the predetermined period HI. After these operations continue in the predetermined period HI, the compressors 1A and 1B are then switched, which means that the compressor 1A is operated with its rotational speed increased by the oil equalization control unit 23 to a predetermined value in the predetermined period HI and that the compressor 1B is operated with its rotational speed decreased to a predetermined value in the predetermined period HI. After these operations continue in the predetermined period H1, the oil equalization control unit 23 returns the rotational speeds of the compressors 1A and 1B to the original speed and ends the second oil equalization control.
Known oil equalization control often increases the rotational speeds, following a predetermined sequence, without considering the amounts of refrigeration oil in the compressors. In this case, for example, such control may be performed first that refrigeration oil is given to a compressor having a relatively large amount of refrigeration oil, which conversely causes a greater imbalance. In a case where, for example, a protective function is actuated in this state to prematurely end the oil equalization control, the execution of the oil equalization control may cause an even greater imbalance in the refrigeration oil. In contrast, in the present embodiment, in accordance with the amounts of the refrigeration oil in the compressors at the start of the oil equalization control. Such control is performed that the rotational speeds are increased in the order from a compressor having the smallest amount of the refrigeration oil in order to return the refrigeration oil to the compressor. The control is intended to balance the refrigeration oil, so that the imbalance does not increase in the oil equalization control and that, even in a case where actuation of a protective function or the like prevents the oil equalization control from being completed, the imbalance in the refrigeration oil does not become greater than a state before the start of the oil equalization control.
FIG. 5 is a flowchart illustrating an example of the oil equalization control according to the embodiment of the present invention.
A flow of oil equalization processing will be described with reference to FIG. 5, exemplifying the refrigerant circuit system 100 in FIG. 1. Assume that, for example, oil return operation has been performed, a predetermined period has elapsed, and a start timing of the oil equalization control has arrived.
First, the sensor information acquisition unit 21 acquires sensor information on all the compressors (1A, 1B) (step S11). In specific, the sensor information acquisition unit 21 acquires measurement values of the pressures on the intake sides of the compressors 1A and 1B from the pressure sensors PA and PB. The sensor information acquisition unit 21 acquires measurement values of the temperatures below the domes of the compressors 1A and 1B from the temperature sensors TA and TB. The sensor information acquisition unit 21 acquires measurement values of the levels of the oil surfaces in the compressors 1A and 1B from the liquid level detecting sensors LA and LB. The sensor information acquisition unit 21 outputs these measurement values acquired to the control sequence determination unit 22.
Next, the control sequence determination unit 22 determines a control sequence that is ascending order of the amounts of the refrigeration oil in the compressors, for all the compressors 1A and 1B on the basis of the measurement values acquired by the sensor information acquisition unit 21 (step S12). For example, in a case where the control sequence determination unit 22 determines the control sequence on the basis of the measurement values from the pressure sensors PA and PB, and when the measurement value from the pressure sensor PA is smaller than the measurement value from the pressure sensor PB, the control sequence determination unit 22 sets a sequence of the compressor 1B and then the compressor 1A, which is ascending order of the amounts of the refrigeration oil. The control sequence determination unit 22 determines to increase the rotational speeds in the order of the compressor 1B and then the compressor 1A. In a case where the measurement value from the pressure sensor PA is larger than the measurement value from the pressure sensor PB, the control sequence determination unit 22 sets a control sequence of the compressor 1A and then the compressor 1B, which is ascending order of the amounts of the refrigeration oil, and determines to increase the rotational speeds in the order of the compressor 1A and then the compressor 1B.
For example, in a case where the control sequence determination unit 22 determines the control sequence on the basis of the measurement values from the temperature sensors TA and TB, and when the measurement value from the temperature sensor TA is smaller than the measurement value from the temperature sensor TB, the control sequence determination unit 22 sets a control sequence of the compressor 1A and then the compressor 1B, which is ascending order of the amounts of the refrigeration oil, and determines to increase the rotational speeds in the order of the compressor 1A and then the compressor 1B. For example, when the control sequence determination unit 22 determines the control sequence on the basis of the measurement values from the liquid level detecting sensors LA and LB, and when the measurement value from the liquid level detecting sensor LA is smaller than the measurement value of the liquid level detecting sensor LB, the control sequence determination unit 22 sets a control sequence of the compressor 1A and then the compressor 1B, which is ascending order of the amounts of the refrigeration oil, and determines to increase the rotational speeds of the compressors in the order of the compressor 1A and then the compressor 1B.
The refrigerant circuit system 100 exemplified in FIG. 1 includes three types of sensors including the pressure sensor PA and the like, the temperature sensor TA and the like, and the liquid level detecting sensor LA and the like; however, at least one of these types of sensors may be included to perform the oil equalization control according to the present embodiment. The control sequence determination unit 22 determines the control sequence for all the compressors 1A and 1B on the basis of the measurement values measured by at least one type of sensors among the measurement values measured by various sensors. The control sequence determination unit 22 outputs the determined control sequence to the oil equalization control unit 23.
Next, the oil equalization control unit 23 increases the rotational speeds of the compressors in the control sequence determined by the control sequence determination unit 22 (step S13). For example, in the case of a control sequence of the compressor 1A and then the compressor 1B, the oil equalization control unit 23 increases the rotational speed of the compressor 1A in a predetermined period and then returns the rotational speed to the original rotational speed. At this time, the oil equalization control unit 23 may perform control to increase the rotational speed of the compressor 1A and at the same time decrease the rotational speed of the compressor 1B in the predetermined period, and then to return the rotational speeds to the original speed. The storage unit 24 stores information on the increased rotational speed and the decreased rotational speed, and the oil equalization control unit 23 performs the control of the rotational speeds of the compressors 1A and 1B on the basis of this information.
After returning the rotational speed of the compressor 1A to the original rotational speed, the oil equalization control unit 23 then performs control to increase the rotational speed of the compressor 1B in the predetermined period and then return the rotational speed to the original speed. At this time, the oil equalization control unit 23 may perform control to increase the rotational speed of the compressor 1B and at the same time decrease the rotational speed of the compressor 1A in the predetermined period, and then to return the rotational speeds to the original speed. This ends one cycle of the oil equalization control. In one cycle of the oil equalization control, the control of increasing the rotational speeds of all the compressors once in the control sequence determined by the control sequence determination unit 22 may be repeated a plurality of times instead of being performed once.
At a subsequent start timing of the oil equalization control, the control device 20 also performs the control of the rotational speeds of the compressors 1A and 1B in the same procedure. Controlling in accordance with the actual amounts of the refrigeration oil stored in the compressors 1A and 1B at the start of the oil equalization control in this way can reduce the possibility of the oil equalization control that may cause an even greater imbalance in the amount of the refrigeration oil. Such control to increase the rotational speeds of all the compressors 1A and 1B once in the control sequence determined by the control sequence determination unit 22 enables the refrigeration oil to be more equally provided to all the compressors 1A and 1B.
Next, another configuration example of the refrigerant circuit including a plurality of compressors will be described.
FIG. 6 is a second schematic diagram illustrating an example of the refrigerant circuit system according to the embodiment of the present invention.
A refrigerant circuit system 100' includes two outdoor units 30A and 30B. The outdoor unit 30A includes a compressor 1A, an oil separator 2A, an emission pipe 3A, an oil return pipe 4A, an intake pipe 6A, a four-way valve 8A, an accumulator 9A, an outdoor heat exchanger 10A, and the like. The outdoor unit 30B includes a compressor 1B, an oil separator 2B, an emission pipe 3B, an oil return pipe 4B, an intake pipe 6B, a four-way valve 8B, an accumulator 9B, an outdoor heat exchanger 10B, and the like. The compressors 1A and 1B respectively included in the outdoor unit 30A and the outdoor unit 30B are connected with each other by using an oil equalization pipe 7. The outdoor units 30A and 30B, an expansion valve 12, and an indoor heat exchanger 13 are connected with each other by using a liquid pipe 14 and a gas pipe 15. A pressure sensor PA is disposed on the intake side of the compressor 1A, a temperature sensor TA is disposed below the dome, and a liquid level detecting sensor LA is disposed inside the compressor 1A. Similarly, the compressor 1B is also provided with sensors. Not all of these sensors are necessarily provided. Only any one type of sensors may be disposed in the outdoor unit 30A and the outdoor unit 30B. FIG. 6 schematically illustrates a basic configuration of the refrigerant circuit system 100', and another constituent element may further be included. For example, two or more indoor units 40 including the expansion valve 12 and the indoor heat exchanger 13 may be provided.
Also in the refrigerant circuit system 100', the compressors 1A and 1B are connected in parallel with each other and operate at the same rotational speed in normal operation. The control device 20 executes oil return operation at intervals of predetermined periods, and then, after the elapse of the predetermined period, executes the oil equalization control. In this way, the oil equalization control of the present embodiment can also be applied to the refrigerant circuit system 100' including the plural outdoor units 30A and 30B.
The oil equalization control will be described, exemplifying the refrigerant circuit system 100'. For example, the sensor information acquisition unit 21 acquires measurement values from the pressure sensor PA of the outdoor unit 30A and the pressure sensor PB of the outdoor unit 30B (step S11). The control sequence determination unit 22 acquires these measurement values and determines a control sequence (step S12). For example, in a case where the measurement value from the pressure sensor PA is larger than the measurement value of the pressure sensor PB, the control sequence determination unit 22 determines to increase the rotational speeds of the compressors in the order of the compressor 1A of the outdoor unit 30A first and then the compressor 1B of the outdoor unit 30B. Next, the oil equalization control unit 23 increases the rotational speed of the compressor 1A first in a predetermined period in the control sequence determined by the control sequence determination unit 22 and then returns the rotational speed to the original rotational speed. Next, the oil equalization control unit 23 performs control to increase the rotational speed of the compressor 1B in the predetermined period and then to return the rotational speed to the original rotational speed (step S13). This corrects an imbalance in the amount of the refrigeration oil between the compressor 1A of the outdoor unit 30A and the compressor 1B of the outdoor unit 30B.
In addition, the constituent elements in the embodiments as described above can be replaced as appropriate with commonly known constituent elements, to the extent that it does not depart from the intention of the present invention. Also, the technical scope of the present invention is not limited to the above-mentioned embodiments, and various modifications may further be made without departing from the spirit of the present invention. For example, the number of the compressors connected in parallel with each other in the configuration in FIG. 1 may be three or more. For example, the number of the outdoor unit 30A and the like in the configuration in FIG. 6 may be three or more. In the control of the rotational speeds of the compressors in the oil equalization control, control of decreasing the rotational speeds of the compressors in descending order of the amounts of the refrigeration oil in the compressors may be performed.

Industrial Applicability

Reference Signs List

100, 100' Refrigerant circuit system
1A, 1B Compressor
2A, 2B Oil separator
3A, 3B Emission pipe
4A, 4B Oil return pipe
5A, 5B Solenoid valve
6A, 6B Intake pipe
7 Oil equalization pipe
8, 8A, 8B Four-way valve
9, 9A, 9B Accumulator
10, 10A, 10B Outdoor heat exchanger
11, 11A, 11B Receiver
12, 12A, 12B Expansion valve
13 Indoor heat exchanger
14 Liquid pipe
15, 16, 16A, 16B, 17, 17A, 17B Gas pipe
20 Control device
21 Sensor information acquisition unit
22 Control sequence determination unit
23 Oil equalization control unit
24 Storage unit
PA, PB Pressure sensor
TA, TB Temperature sensor
LA, LB Liquid level detecting sensor

Claims

An oil equalization control device comprising, in a refrigerant circuit including a plurality of compressors connected in parallel with each other:
a sensor information acquisition unit configured to acquire a state quantity relating to an amount of refrigeration oil in each of the plurality of compressors;

a control sequence determination unit configured to determine a control sequence for the compressors in oil equalization control in accordance with the amounts of the refrigeration oil in the compressors based on the state quantities; and

an oil equalization control unit configured to vary a rotational speed of at least one of the plurality of compressors and perform the oil equalization control on a basis of the control sequence determined by the control sequence determination unit.
The oil equalization control device according to claim 1, wherein
the control sequence determination unit determines the control sequence by listing the compressors in ascending order of the amounts of the refrigeration oil, and
the oil equalization control unit varies the rotational speed of the compressor in its turn in the control sequence so that the compressor in its turn has a relatively low pressure.
The oil equalization control device according to claim 2, wherein
the sensor information acquisition unit acquires a measurement value of a pressure on a low pressure side of each of the plurality of compressors, and
the control sequence determination unit sets a sequence of relatively decreasing pressures of the compressors by listing the compressors in descending order of the measurement values of the pressures.
The oil equalization control device according to claim 2, wherein
the sensor information acquisition unit acquires a measurement value of a temperature below a dome of each of the plurality of compressors, and
the control sequence determination unit sets a sequence of relatively decreasing pressures of the compressors by listing the compressors in ascending order of the measurement values of the temperatures.
The oil equalization control device according to any one of claims 1 to 4, wherein the oil equalization control unit increases the rotational speed of each of the plurality of compressors in a predetermined period in the control sequence.
A refrigerant circuit system comprising:
a plurality of compressors connected in parallel with each other;

an oil equalization pipe connecting the plurality of compressors with each other; and

the oil equalization control device according to any one of claims 1 to 5.
An oil equalization control method comprising the steps of:
acquiring a state quantity relating to an amount of refrigeration oil in each of a plurality of compressors in a refrigerant circuit including the plurality of compressors connected in parallel with each other;

determining a control sequence for the compressors in oil equalization control in accordance with the amounts of the refrigeration oil in the compressors based on the state quantities; and

varying a rotational speed of at least one of the plurality of compressors and performing the oil equalization control on a basis of the control sequence;

the steps being performed by an oil equalization control device.