CN109469602B

CN109469602B - Compressed gas supply device and control method for compressed gas supply device

Info

Publication number: CN109469602B
Application number: CN201710804518.4A
Authority: CN
Inventors: 武田和树; 阪口贵行; 宇波厚
Original assignee: Anest Iwata Corp
Current assignee: Anest Iwata Corp
Priority date: 2017-09-07
Filing date: 2017-09-07
Publication date: 2021-07-02
Anticipated expiration: 2037-09-07
Also published as: CN109469602A; WO2019049987A1; JP6823186B2; JPWO2019049987A1

Abstract

The invention provides a compressed gas supply device and a control method of the compressed gas supply device, which have good following performance relative to load variation and can reduce energy consumption. The present invention relates to a compressed gas supply device capable of supplying compressed gas discharged from a plurality of compressors. The device has: a plurality of compressors configured in parallel; a load factor detection unit that detects a load factor of the compressed gas supply device; and a control unit for controlling the rotation rate of the compressor based on the load rate. The control unit is configured to control the plurality of compressors to have a common rotation rate in the common control region, to independently control at least one of the compressors to have a rotation rate smaller than that of the other compressors in the independent control region, and to stop at least one of the compressors and control the rotation rates of the other compressors in the independent control region.

Description

Compressed gas supply device and control method for compressed gas supply device

Technical Field

The present invention relates to a compressed gas supply device capable of supplying compressed gas discharged from a plurality of compressors and a method for controlling the compressed gas supply device.

Background

A compressed gas supply device including a plurality of compressors for generating compressed gas is known. In such a compressed gas supply device, for example, a plurality of compressors are arranged in parallel with respect to a demand side, and compressed air required by the demand side is supplied. In addition, such a compressed gas supply device has a backup function of continuously supplying compressed gas to a demand side by another compressor even when a specific compressor fails. In such a compressed gas supply device, energy saving is achieved by appropriately controlling the operating state of each compressor.

For example, patent document 1 describes the following: in a compressed gas supply device in which a plurality of compressors capable of controlling the rotation speed by an inverter are arranged in parallel, the number of compressors for variably controlling the rotation speed is limited to only one, thereby minimizing power consumption and saving energy. In this document, variable control of the rotation speed is performed in any one of the plurality of compressors, and if the rotation speed reaches a lower limit rotation speed as the load decreases, the compressor is stopped, and then the rotation speeds of the other compressors are sequentially and variably controlled.

Patent document 2 discloses the following: in a compressed gas supply device in which a plurality of compressors capable of controlling the number of revolutions by an inverter are arranged in parallel, the number of revolutions of all of the plurality of compressors in an operating state is variably controlled to be equal to a constant value, thereby reducing wasteful power consumption.

Prior art documents

Patent document 1: japanese laid-open patent publication No. 11-343986

Patent document 2: japanese laid-open patent publication No. 2002-

Disclosure of Invention

The efficiency of a compressor used in a compressed gas supply device decreases in a quadratic curve as the rotation speed decreases. This is because the lower the rotation speed, the more leakage of the gas compressed in the compression chamber, the more easily recompression is caused. In a normal compressor, the lower limit value of the practical rotation speed is about 30% of the rated rotation speed.

In patent document 1, only one of the plurality of compressors included in the compressed gas supply device is variably controlled in rotation speed, and the other compressors are uniformly operated at a rated speed. In such control, in a compressor in which the rotation speed is variably controlled, since the rotation speed varies over a wide range between the rated rotation speed and the lower limit rotation speed, the operation in the low rotation region becomes large, and it is difficult to obtain good efficiency.

In patent document 2, the rotation speeds of the plurality of compressors during operation are controlled to be always equal. If the rotational speed of these compressors reaches the lower limit rotational speed with the load fluctuation, the specific compressor is stopped. In this case, the rotation speed of the other compressor has to be increased by the stop of the specific compressor. For example, if one of the two compressors, which is operating at 50% of the rated rotational speed, is stopped, the rotational speed of the other compressor cannot be increased from 50% to 100% without a sudden change. However, in an actual compressed gas supply device, since such a drastic change cannot be followed, a phenomenon occurs in which the discharge amount of compressed gas is temporarily insufficient.

At least one embodiment of the present invention has been made in view of the above circumstances, and an object thereof is to provide a compressor gas supply device and a control method of the compressor gas supply device, which have good followability to load fluctuations and can reduce energy consumption.

(1) In order to solve the above problem, a compressed gas supply device according to at least one embodiment of the present invention is a compressed gas supply device capable of supplying compressed gas discharged from a plurality of compressors, including: a plurality of said compressors configured in parallel; a load factor detector for detecting a load factor of the compressed gas supply device; and a control unit that controls the rotation rates of the plurality of compressors based on the load rates detected by the load rate detection unit. The control unit (i) controls the plurality of compressors to have a common rotation rate in a common control region in which the load factor is equal to or greater than a first threshold, (ii) independently controls at least one of the plurality of compressors to have a rotation rate smaller than that of another compressor in an independent control region in which the load factor is from the first threshold to a second threshold smaller than the first threshold, and (iii) stops the at least one compressor and controls the rotation rate of the another compressor in an independent control region in which the load factor is smaller than the second threshold.

According to the configuration of the above (1), the rotation speed of each compressor constituting the compressed gas supply device is controlled by dividing three control regions (the common control region, the independent control region, and the individual control region) corresponding to the load factor. (i) In the common control region, when the load factor is equal to or greater than the first threshold value, the rotation speeds of the plurality of compressors in operation are controlled equally. Therefore, the rotation speed of each compressor is not included in the low rotation speed region where the efficiency is deteriorated, and good operation efficiency is obtained. (ii) In the independent control region, the rotation speed of at least one compressor stopped at the time of transition to the immediately subsequent independent control region is independently controlled so as to be lower than the rotation speeds of the other compressors. Thus, when the load factor is decreased and the operation mode is shifted from the independent control region to the independent control region, the amount of fluctuation when increasing the other compression rotation speed can be suppressed to a small value, and the amount corresponding to the stop of at least one compressor can be suppressed. As a result, when the number of compressors in operation is reduced, the following performance of the number of revolutions of the continuously operating compressors can be improved, and the phenomenon that the discharge amount of the compressed gas is temporarily insufficient can be alleviated.

(2) In some embodiments, in addition to the configuration of (1) above, the control unit controls the rotation rate of the at least one compressor in the independent control region to have a degree of change with respect to the load factor greater than a degree of change in the common control region.

According to the configuration of the above (2), in the independent control region, the degree of change with respect to the load factor is increased for at least one of the compressors that is stopped when the transition is made to the independent control region. Thus, when the independent control region is shifted to the independent control region, the rotation speed of the stopped compressor is reduced, and the amount of rotation speed fluctuation generated in another compressor when the compressor is stopped can be further suppressed. As a result, when the number of compressors in operation is reduced, the following performance of the number of revolutions of the continuously operating compressors can be further improved.

(3) In some embodiments, in addition to the configuration of (1) or (2), the control unit maintains the rotation rate of the at least one compressor to be constant in the independent control region when the load rate tends to decrease.

According to the configuration of the above (3), in the independent control region, the rotation speed of the compressor which is continuously operated when shifting to the independent control region is maintained constant. According to the verification of the inventors of the present application, it was found that by performing such control, good efficiency is obtained for the compressed gas supply apparatus as a whole.

(4) In some embodiments, in addition to any one of the configurations (1) to (3), when the load factor decreases and the control unit shifts from the independent control area to the individual control area, the control unit stops the at least one compressor on the condition that the load factor is maintained in the individual control area for a predetermined time.

According to the configuration of the above (4), when the load factor is decreased and the operation is shifted from the independent control area to the individual control area, the stop control of the at least one compressor is performed when the load factor is maintained in the individual control area for a predetermined time. This can avoid frequent repetition of the stop and start of the compressor due to the load factor frequently going to and from between the independent control area and the independent control area.

(5) In some embodiments, in addition to any one of the configurations (1) to (4), the control unit controls the rotation rate of the other compressor to the maximum rotation rate when the at least one compressor is stopped along with a decrease in the load factor.

According to the configuration of the above (5), when at least one compressor is stopped by shifting from the independent control area to the independent control area, the rotation rate of the other continuously operated compressor is controlled to the maximum rotation rate, so that the operation can be shifted to the most efficient state.

(6) In some embodiments, in addition to any one of the configurations (1) to (5), when the load factor is in an increasing trend, the control unit increases the rotation rate of the at least one compressor in accordance with the load factor and decreases the rotation rate of the other compressor in accordance with the load factor in the independent control region.

According to the configuration of the above (6), when the number of compressors is increased by shifting from the individual control region to the individual control region due to an increase in the load factor, the compressors in the stopped state are started at the lower limit rotation rate and controlled to increase with the increase in the load factor. At this time, the rotation rate of the other compressor is controlled to decrease in comparison with the increase in the rotation rate of the compressor that is started.

(7) In some embodiments, in addition to any one of the configurations (1) to (6), when the load factor increases and the individual control area shifts to the independent control area, the control unit starts the at least one compressor on the condition that the load factor is maintained in the independent control area for a predetermined time.

According to the configuration of the above (7), when the load factor is increased and the operation is shifted from the individual control area to the individual control area, the operation is performed such that at least one of the compressors is started when the load factor is maintained in the individual control area for a predetermined time. Therefore, the situation that the stop and the start of the compressor are frequently repeated because the load factor frequently comes between the independent control area and the independent control area can be avoided.

(8) In order to solve the above problem, a method for controlling a compressed gas supply apparatus according to at least one embodiment of the present invention is a method for controlling a compressed gas supply apparatus capable of supplying compressed gas discharged from a plurality of compressors arranged in parallel, the method including: a load factor detection step of detecting a load factor of the compressed gas supply device; and a control step of controlling the rotation speeds of the plurality of compressors based on the detected load factors. In the control step, (i) the plurality of compressors are controlled so as to have a common rotation rate in a common control region in which the load factor is equal to or higher than a first threshold, (ii) the plurality of compressors are independently controlled so that the rotation rate of at least one of the plurality of compressors is lower than the rotation rate of the other compressor in an independent control region in which the load factor is equal to or higher than a second threshold lower than the first threshold, and (iii) the at least one compressor is stopped and the rotation rate of the other compressor is controlled in an independent control region in which the load factor is lower than the second threshold.

The method of the above (8) can be suitably performed by the above-described compressed gas supply device (including the above-described various embodiments).

Effects of the invention

According to at least one embodiment of the present invention, it is possible to provide a compressed gas supply apparatus and a control method of the compressed gas supply apparatus, which have good followability to load fluctuations and can reduce energy consumption.

Drawings

Fig. 1 is a schematic diagram showing an overall configuration of a compressed gas supply device according to at least one embodiment of the present invention.

Fig. 2 is a flowchart showing a method of controlling the compressed gas supply apparatus, which is performed by the control apparatus of fig. 1, in accordance with steps.

Fig. 3 is a graph showing an example of control of the rotation rate of the compressor with respect to the load rate of the compressed gas supply device when the load rate is decreased.

Fig. 4 is a graph showing the measurement results of the relationship between the rotation rate and the efficiency of the compressed gas supply device corresponding to fig. 3.

Fig. 5 is a detail of each compressor corresponding to the rotation rate in the compressed gas supply device of fig. 3.

Fig. 6 is a detail of each compressor of the rotation rate in the second comparative example.

Fig. 7 is a graph showing an example of control of the rotation rate of the compressor with respect to the load rate of the compressed gas supply device when the load rate increases.

Fig. 8 is a schematic diagram showing the overall configuration of a compressed gas supply device having three compressors.

Fig. 9 is a graph showing the measurement results of the efficiency with respect to the rotation rate of the compressed gas supply device corresponding to fig. 8.

Fig. 10 is a detail of each compressor corresponding to the rotation rate in the compressed gas supply device of fig. 8.

Fig. 11 is a detail of each compressor of the rotation rate in the sixth comparative example.

Description of reference numerals:

1 a compressed gas supply device;

2A, 2B compressors;

4A, 4B discharge pipe;

6, a main discharge pipe;

8, a storage box;

10 requirement side

12 a supply path;

14 adjusting the valve;

15 a pressure sensor;

16A, 16B electric motor

18A, 18B conversion means;

20A, 20B pressure sensors;

100 a control device;

102 a load factor detection unit;

104 a control unit.

Detailed Description

Hereinafter, several embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described as the embodiments and shown in the drawings are not intended to limit the scope of the present invention to these, and are merely illustrative examples.

For example, expressions such as "in a certain direction", "along a certain direction", "parallel", "perpendicular", "central", "concentric" or "coaxial" which indicate relative or absolute arrangements mean not only such arrangements strictly, but also states of relative displacement with a tolerance, or an angle and/or a distance to the extent that the same function is obtained.

For example, "the same", "equal", and "equal" indicate that the expression of the state where objects are equal not only indicates the state where the objects are exactly equal, but also indicates a state where there is a difference in tolerance or degree of obtaining the same function.

For example, the expression "a shape such as a square shape and/or a cylindrical shape" means not only a shape such as a geometrically strict square shape and/or a cylindrical shape but also a shape including a concave and convex portion and/or a chamfered portion as far as the same effect is obtained.

On the other hand, expressions such as "provided", "having", "provided", "including", or "having" one constituent element are not exclusive expressions that exclude the presence of other constituent elements.

Fig. 1 is a schematic diagram showing an overall configuration of a compressed gas supply apparatus 1 according to at least one embodiment of the present invention. The compressed gas supply apparatus 1 includes a plurality of compressors in a casing (not shown). In fig. 1, a compressed gas supply apparatus 1 having a plurality of

compressors

2A, 2B is illustrated. In the present embodiment, each of the plurality of

compressors

2A and 2B is a screw-type air compressor (hereinafter, collectively referred to as "compressor 2" as appropriate) that generates compressed gas from gas introduced from the outside. However, in the present invention, each compressor is not limited to a screw type air compressor, and may be, for example, a scroll type air compressor.

The

compressors

2A and 2B have

discharge pipes

4A and 4B for discharging the generated compressed gas, respectively. The

discharge pipes

4A, 4B merge at the downstream side with the main discharge pipe 6, and are connected to a storage tank 8 for storing compressed gas. In this way, the plurality of

compressors

2A, 2B are connected in parallel to the storage tank 8, and the compressed gas discharged from the

compressors

2A, 2B is stored in the storage tank 8 via the main discharge pipe 6. In the present invention, the storage box 8 may be included in the housing or may be disposed outside the housing.

The storage tank 8 is provided with a supply path 12 for supplying compressed gas to the demand side 10. The supply path 12 is provided with an adjustment valve 14 capable of controlling the opening degree. The compressed gas supply device 1 can supply a predetermined compressed gas to the demand side 10 by adjusting the opening degree of the adjustment valve 14. In addition, a pressure sensor 15 for detecting the pressure in the storage tank 8 is provided in the storage tank 8. In the present invention, the control valve 14 may be included in the housing or may be disposed outside the housing. In the present invention, the tank 8 may be contained in the housing or may be disposed outside the housing, and therefore, the pressure sensor 15 provided in the tank 8 may be contained in the housing or may be disposed outside the housing as well.

The

compressors

2A and 2B have

electric motors

16A and 16B as power sources, and

conversion devices

18A and 18B capable of controlling the rotation speeds of the

electric motors

16A and 16B, respectively. The

inverters

18A, 18B can steplessly control the rotation speeds of the

electric motors

16A, 16B, and adjust the outputs of the

compressors

2A, 2B via the rotation speed control of the

electric motors

16A, 16B. This makes it possible to adjust the rotation speeds of the

compressors

2A and 2B independently of each other.

In the present embodiment, the case where the

compressors

2A and 2B have the same specification is exemplified, but the present invention is also applicable to the case where the

compressors

2A and 2B have different specifications from each other. In the following description, in order to perform a normal description that does not depend on the specifications of the

compressors

2A and 2B, a rotation rate defined as a ratio of the rotation rate to the rated rotation speed (i.e., the rated rotation speed is equivalent to the rotation rate of 100%) is appropriately used instead of the rotation rate of the

compressors

2A and 2B.

In the present embodiment, the upper limit rotation rate is defined as 100% and the lower limit rotation rate is defined as 30% for the

compressors

2A and 2B having the same specification. The lower limit rotation rate may be defined as a lower limit value at which the

compressors

2A and 2B mechanically move, or may be defined as a lower limit value at which the efficiency of the

compressors

2A and 2B is lower than a reference value.

The

compressors

2A and 2B are provided with

pressure sensors

20A and 20B for detecting respective discharge pressures. The pressures detected by the

pressure sensors

20A and 20B are transmitted to, for example, a control device 100 described later, and compared with a target set pressure stored in advance in the control device 100. When the detected pressure is lower than the set pressure, the

inverter devices

18A and 18B control the

electric motors

16A and 16B so as to increase the duty ratios of the

electric motors

16A and 16B. When the detected pressure is equal to or higher than the set pressure, the

inverter devices

18A and 18B control the

electric motors

16A and 16B so as to reduce the load factor of the

electric motors

16A and 16B.

The compressed gas supply apparatus 1 further includes a control device 100. The control device 100 is a controller of the compressed gas supply device 1, and is configured to be able to exhibit a predetermined function by installing a predetermined program in advance on an electronic computer such as a computer, for example. For example, the control device 100 controls the

inverters

18A and 18B to adjust the rotation speeds of the

compressors

2A and 2B. Further, the control device 100 adjusts the opening degree of the regulator valve 14 to constantly control the pressure in the tank 8 to the pressure required by the demand side 10.

Fig. 1 representatively shows functional blocks related to control contents described later in the internal configuration of the control device 100. The control device 100 includes: a load factor detection unit 102 that detects a load factor L of the compressed gas supply device 1; and a control unit 104 for controlling the rotation speeds of the plurality of

compressors

2A and 2B based on the load factor L detected by the load factor detection unit 102.

Next, a method of controlling the compressed gas supply apparatus 1 by the control apparatus 100 will be specifically described. Fig. 2 is a flowchart showing a method of controlling the compressed gas supply apparatus 1, which is performed by the control apparatus 100 of fig. 1, in accordance with steps.

First, the load factor detector 102 acquires detection values of the

pressure sensors

20A and 20B provided in the two

compressors

2A and 2B of the compressed gas supply device 1 (step S1). Next, the load factor detector 102 calculates the load factor L of the compressed gas supply device 1 based on the pressures obtained from the

pressure sensors

20A and 20B (step S2).

Here, the load factor is defined as a ratio of a load to a rated load (a load when the electric motor is operated at a rated rotation speed and a specification pressure is obtained). In step S2, for example, the load based on the actual measurement values of the pressures of the

compressors

2A and 2B detected by the

pressure sensors

20A and 20B is divided by the predetermined rated loads of the

compressors

2A and 2B, thereby calculating the load factors of the

compressors

2A and 2B, respectively. Next, the load factor detector 102 calculates the load factor L of the compressed gas supply device 1 by adding the load factors of the

compressors

2A and 2B calculated in this way (for example, when the load factors of the

compressors

2A and 2B are 100%, respectively, the load factor of the compressed gas supply device 1 is 200%).

Next, the control unit 104 controls the rotation speeds of the plurality of

compressors

2A and 2B based on the load factor L of the compressed gas supply device 1 detected by the load factor detection unit 102, respectively (step S3). The control of the

compressors

2A and 2B by the control unit 104 is performed by controlling the corresponding

inverter devices

18A and 18B, respectively.

Here, the details of the control in step S3 in fig. 2 will be described. First, the load factor L of the compressed gas supply device 1 is set from the rated load L_max(200%) is changed in a gradually decreasing manner as an example. Fig. 3 is a graph showing an example of control of the rotation rate of the

compressors

2A and 2B with respect to the load rate L of the compressed gas supply device 1 when the load rate L decreases.

The load factor L is defined as the rated load L_maxIn the common control region R1 from (200%) to the first threshold value L1, the plurality of

compressors

2A and 2B are controlled to have a common rotation rate. That is, as the load factor L decreases, the variable control is performed so that the rotation rates of the

compressors

2A and 2B decrease while being maintained equal to each other. That is, in the common control region R1, control substantially equivalent to the case where the rotation rates of the two

compressors

2A and 2B are controlled by the common inverter is performed.

In the independent control region R2 in which the load factor is defined as the first threshold value L1 to the second threshold value L2 (100%), the control is independently performed such that the rotation rate of at least one of the plurality of

compressors

2A, 2B is smaller than the rotation rate of the other compressor. In the present embodiment, the rotation rate of the compressor 2B is controlled to be smaller than the rotation rate of the compressor 2A. Such control is achieved by independently controlling the

compressors

2A, 2B by the

inverter devices

18A, 18B.

In the independent control region R2, the compressor 2B is controlled such that the degree of change in the rotation rate with respect to the load rate is greater than the degree of change in the common control region R1. As shown in fig. 3, the inclination of the rotation rate transition of the compressor 2B with respect to the load factor L in the independent control region R2 is steeper than the inclination of the rotation rate transition of the compressor 2B with respect to the load factor L in the common control region R1.

On the other hand, in the independent control region R2, the compressor 2A is controlled so as to maintain the rotation rate constant. In fig. 3, the rotation rate at the first threshold L1 is maintained at a constant value a1 across the independent control region R2.

In the individual control region R3 in which the load factor L is smaller than the second threshold value L2, the compressor 2B is stopped and only one compressor 2A is operated individually. Here, the second threshold L2 defining the boundary between the independent control region R2 and the individual control region R3 is a load factor at which the compressor 2B reaches a preset lower limit rotation rate (for example, 30%) while the compressor 2A is maintained at the constant rotation rate a 1. In other words, the second threshold value L2 is defined as a load factor for stopping the compressor 2B when the load factor is smaller than this value. Therefore, while the independent control region R2 is operated using two

compressors

2A and 2B, the number of compressors to be operated is reduced by stopping the compressor 2B in the independent control region R3.

Here, it is assumed that if a comparative example without the independent control region R2 is considered (that is, the load factor L is the rated load factor L_maxTo the second threshold value L2, in the case where the

compressors

2A, 2B are controlled to have a common rotation rate, as in the common control region R1), when one compressor 2B is stopped and only the other compressor 2A is switched to operation at the second threshold value L2, the target rotation rate of the compressor 2A that is continuously operating is abruptly increased to the rated rotation rate of 100%. However, the actual rotation rate of the compressor 2A does not follow the target rotation rate thus abruptly increased, resulting in occurrence of hysteresis and temporary shortage of the discharge amount of the compressed gas.

In contrast, in the compressed gas supply apparatus 1 of the present embodiment, as shown in fig. 3, in the independent control region R2, the rotation speed of the compressor 2B stopped in the independent control region R3 is smaller than that of the compressor 2A in the continuous operation. Therefore, when the load factor reaches the second threshold value L2 and the compressor 2B is stopped, the rotation rate of the compressor 2A is increased, but the fluctuation amount thereof is small. As a result, the following performance of the rotation rate when the number of operating compressors 2 is changed is improved, and the shortage of the discharge amount can be reduced.

When the load factor L reaches the second threshold value L2 and the compressor 2B is stopped, the rotation rate of the compressor 2A in the continuous operation is increased, but the rotation rate of the compressor 2A in this case is set to the maximum rotation rate (100%). As a result, the compressor 2A after shifting to the individual control region R3 can be operated in a region with good energy efficiency.

It is also considered that, even if the load factor L monotonically decreases to reach the second threshold value L2, a transition between the independent control region R2 and the independent control region R3 frequently occurs due to a fluctuation in the load factor L thereafter. In such a case, if the number of compressors 2 is changed every time of transfer, it results in wasteful consumption of energy, and deterioration or the like may progress. Therefore, when the load factor L reaches the second threshold value L2, the compressor 2B may be stopped on the condition that the load factor L is maintained in the individual control region R3 for a predetermined time.

Fig. 4 is a graph showing the measurement results of the relationship between the rotation rate and the efficiency of the compressed gas supply device 1 corresponding to fig. 3.

Fig. 4 shows the measurement results of three comparative examples in combination with the measurement results of the present embodiment. The first comparative example is from the rated load L at the load factor L_max(200%) an example in which the compressor 2A is variably controlled according to the load factor L while maintaining the compressor 2A in the rated operation (100% rotation rate) up to the first threshold value L1, and the compressor 2B reaching the lower limit rotation rate is stopped when the load factor L is less than the first threshold value L1, and the compressor 2A is variably controlled according to the load factor L (that is, a control example in which only one of the plurality of compressors 2 is variably controlled). The second comparative example is from the rated load L at the load factor L_max(200%) to a second threshold value L2 (100%) and variably controls the

compressors

2A and 2B so that they have a common rotation rate, and when the rotation rate is less than the second threshold value L2 (100%), stops one compressor 2B and variably controls only the other compressor 2A (that is, as in the common control region R1 of the present embodiment, controls the rotation rates of all the compressors 2 in operation to be the same until the load rate L reaches the second threshold value L2). The third comparative example is a case where only a single compressor is used, and the magnitude of the load factor and the rotation rate is doubly represented for comparison with the present embodiment and/or other comparative examples.

As shown in fig. 4, when the rotation rate of the compressed gas supply device 1 is 170% or more, there is no significant difference between the present embodiment and the first to third comparative examples, but if the rotation rate of the compressed gas supply device 1 is less than 170%, both the present embodiment and the second comparative example obtain good efficiency compared to the first comparative example. This indicates that, in the common control region R1, by controlling the rotation rates of the two

compressors

2A and 2B in common, good efficiency can be obtained as compared with the case where only one compressor is variably controlled as in the first comparative example.

In addition, if the rotation rate of the compressed gas supply device 1 is less than 100%, the present embodiment obtains better efficiency than the second comparative example. Here, fig. 5 is a detail of the

compressors

2A and 2B corresponding to the rotation rate in the compressed gas supply device 1 of fig. 3, and fig. 6 is a detail of the

compressors

2A and 2B corresponding to the rotation rate in the second comparative example. As is clear from a comparison between fig. 5 and 6, in the present embodiment, the operation ratio in the unfavorable low rotation region is effectively reduced as compared with the second comparative example, and as a result, good efficiency is obtained.

As described above, in the independent control region R2, the rotation speed of the compressor 2B stopped in the independent control region R3 is lower than that of the compressor 2A in the continuous operation, so that the variation amount of the target rotation rate of the compressor 2A accompanying the stop of the compressor 2B is smaller than that of the other comparative examples when the load factor reaches the second threshold value L2. As a result, the following ability of the rotation rate when the number of compressors 2 is reduced is improved, and the shortage of the discharge amount that occurs temporarily can be reduced.

As shown in fig. 4, since the operation is possible until the rotation rate reaches 30% in the present embodiment, the rotation rate can be wider than that in the third comparative example (the rotation rate of 60% is the operation limit in the third comparative example, whereas the rotation rate of 30% is the operation limit in the present embodiment).

Then, the load factor of the compressed gas supply device 1 is set from the lower limit load factor L_min(30%) the control content of the rotation rate when the rotation rate is changed gradually and largely will be specifically described. Fig. 7 is a graph showing an example of control of the rotation rate of the

compressors

2A and 2B with respect to the load rate L of the compressed gas supply device 1 when the load rate L increases.

First, in the individual control region R3, the rotation rate of the one compressor 2A is controlled to monotonically increase according to the load rate L. At this time, since the other compressor 2B is in a stopped state, useless energy is not consumed, and the compressed gas supply apparatus 1 as a whole obtains good efficiency.

If the load factor L increases to reach the second threshold value L2, the compressor 2B is started. The rotation rate of the compressor 2B at the time of start-up is set to a lower limit rotation rate (30%) predetermined as a standard. Next, in the independent control region R2, the rotation rate of the compressor 2B is increased according to the load rate L, and the rotation rate of the compressor 2A is decreased according to the load rate L. In the example of fig. 3, the rotation rates of the

compressors

2A and 2B in the independent control region R2 are controlled to vary in a quadratic function with respect to the load rate.

The rotation rates of the

compressors

2A and 2B independently controlled in the independent control region R2 are controlled so as to be equal to the first threshold value L1 which is the boundary between the independent control region R2 and the common control region R1. The rotation rate at the first threshold value L1 is set to be equal to a value a1 that maintains the rotation rate of the compressor 2A constant in the independent control region R2 when the load rate L is reduced (refer to fig. 3).

Next, in the common control region R1, the

compressors

2A and 2B are controlled to have a common rotation rate and the rotation rate monotonically increases as the load rate increases.

It is also considered that, even if the load factor L increases and reaches the second threshold value L2, a subsequent change frequently occurs between the individual control region R3 and the individual control region R2 due to a fluctuation in the load factor L. In such a case, if the number of compressors 2 is changed every time of the transfer, energy is uselessly consumed, and deterioration may progress. Therefore, when the load factor L reaches the second threshold value L2, the compressor 2B can be started on the condition that the load factor L is maintained in the independent control region R2 for a predetermined time.

As described above, the rotation speed of each compressor 2 constituting the compressed gas supply device 1 is controlled by dividing the three control regions (the common control region R1, the independent control region R2, and the independent control region R3) corresponding to the load factor L. (i) In the common control region R1, when the load factor L is equal to or greater than the first threshold value L1, the rotation speeds of the plurality of compressors in operation are controlled equally. Therefore, the ratio of the operation of the compressed gas supply device in the low rotation speed region where the efficiency is deteriorated is reduced, and good efficiency is obtained. (ii) In the individual control region R2, the rotation speed of at least one compressor 2B stopped at the time of the transition to the immediately subsequent individual control region R3 is independently controlled to be smaller than the rotation speed of the other compressors 2A. Thus, when the load factor L is decreased and the operation is shifted from the individual control range R2 to the individual control range R3, the amount of fluctuation when the rotation speed of the other compressor 2A is increased can be suppressed to a small level, and the amount corresponding to the stop of at least one compressor 2B can be suppressed. As a result, when the number of compressors 2 in operation is reduced, the following performance of the number of revolutions of the compressor 2 in continuous operation can be improved, and the phenomenon of temporary shortage of the compressed gas discharge amount can be alleviated.

The above-described compressed gas supply apparatus 1 has been described as having two

compressors

2A and 2B, but may have a larger number of compressors 2. Fig. 8 is a schematic diagram showing the overall configuration of the compressed gas supply apparatus 1 having three compressors 2. In this example, in the case of fig. 1, a third compressor 2C is provided in addition to the

compressors

2A and 2B, and the three compressors 2 have the same structure.

The compressor 2C has an electric motor 16C whose rotation speed can be controlled by an inverter 18C, and discharges the generated compressed air from the discharge pipe 4C. The discharge pipe 4C merges with the

discharge pipes

4A and 4B into the main discharge pipe 6. Further, the load of the compressor 2C can be detected by the pressure sensor 20C.

The load factor detector 102 acquires the detection values of the

pressure sensors

20A, 20B, and 20C to acquire the load factors of the

compressors

2A, 2B, and 2C, and calculates the load factor L of the entire compressed gas supply device 1 by summing them. In the present embodiment, since the compressed gas supply apparatus 1 includes three compressors 2, the maximum load factor L is obtained_maxIs 300%.

The control unit 104 controls the rotation rates of the

compressors

2A, 2B, and 2C based on the load factor L of the compressed gas supply device 1 calculated by the load factor detection unit 102. The rotation rate control of the

compressors

2A, 2B, and 2C can be applied by expanding the rotation rate control in the case where the two

compressors

2A and 2B are provided. That is, if the load factor L is reduced from the rated load factor (300%), the

compressors

2A, 2B, and 2C are driven until the load factor L reaches 200%, but if the load factor L reaches 200%, the compressor 2C is stopped, and if the load factor L is less than 200%, only the

compressors

2A and 2B are driven. When the compressor 2C is stopped at the load factor of 200% in this way, the three

compressors

2A, 2B, 2C are controlled to have a common rotation rate until the load factor reaches a predetermined value (with respect to the first threshold value L1) which is greater than 200%, and when the load factor is from the predetermined value to 200% (corresponding to the second load factor L2), the rotation rate of the compressor 2C is independently controlled to be smaller than the rotation rates of the

compressors

2A, 2B. In this case, even if the load factor is less than 200%, the rotation rate of the continuously operated

compressors

2A and 2B can be maintained constant. Thus, when the compressor 2C is stopped at a load factor of 200%, the rotation rates of the

compressors

2A and 2B easily follow the target rotation rate, and the shortage of the discharge amount can be suppressed.

When the load factor is less than 200%, two compressors 2 are used in operation, and therefore, the operation is the same as in the above embodiment.

Fig. 9 is a graph showing the measurement results of the efficiency with respect to the rotation rate of the compressed gas supply device 1 corresponding to fig. 8. Fig. 9 shows a fifth comparative example (in which the

compressors

2A and 2B maintain a rotation rate of 100% and variably control only the compressor 2C, in which the compressor 2A maintains a rotation rate of 100% and variably controls the compressor 2B and stops the compressor 2C, in which the load rate L is 200% to 100%, and in which the compressor 2A maintains a rotation rate of 100% and variably controls only the compressor 2A and stops the

compressors

2B and 2C when the load rate L is less than 100%), a sixth comparative example (in which the three

compressors

2A, 2B and 2C are controlled to have a common rotation rate in a range of 300% to 200%, and in which the two

compressors

2A and 2B are controlled to have a common rotation rate and stop the compressor 2C in a range of 200% to 100%, when the load factor L is less than 100%, only the compressor 2A is operated and the

compressors

2B and 2C are stopped), and a seventh comparative example (only one compressor 2 is variably controlled, and the indicated magnitudes of the rotation factor and the load factor are tripled in order to evaluate the same as those of the other embodiments and/or the comparative examples).

As shown in fig. 9, the present embodiment has good efficiency over a wide range compared to the fifth to seventh comparative examples. This shows that, referring to fig. 4, the same effect is obtained even in the case where the number of compressors 2 is increased, corresponding to the above-described effect.

Fig. 10 is a detail of the

compressors

2A, 2B, and 2C corresponding to the rotation rate in the compressed gas supply device 1 of fig. 8, and fig. 11 is a detail of the

compressors

2A, 2B, and 2C corresponding to the rotation rate in the sixth comparative example. Fig. 10 shows that the operation region of the present embodiment with a low rotation rate is narrower than that of fig. 11. This shows that the present embodiment achieves good energy efficiency by reducing the low rotation region where energy efficiency is low.

As described above, according to the above embodiment, it is possible to provide a compressed gas supply apparatus and a control method of the compressed gas supply apparatus, which have good follow-up performance with respect to load fluctuation and can reduce energy consumption.

Claims

1. A compressed gas supply device capable of supplying compressed gas discharged from a plurality of compressors,

wherein,

the compressed gas supply device is provided with:

a plurality of said compressors arranged in parallel;

a load factor detection unit that detects a load factor of the compressed gas supply device; and

a control unit that controls rotation rates of the plurality of compressors based on the load rates detected by the load rate detection unit,

the control unit is configured to control the plurality of compressors to have a common rotation rate in a common control region in which the load factor is equal to or greater than a first threshold value, to independently control the plurality of compressors to have a rotation rate less than a rated rotation rate and to have a rotation rate of at least one of the plurality of compressors less than that of the other compressors in an independent control region in which the load factor is equal to or greater than a second threshold value, and to stop the at least one compressor and control the rotation rate of the other compressors in an independent control region in which the load factor is less than the second threshold value.

2. The compressed gas supply apparatus according to claim 1,

the control unit controls the rotation rate of the at least one compressor in the independent control region to have a degree of change with respect to the load factor greater than a degree of change in the common control region.

3. The compressed gas supply apparatus according to claim 1,

the control unit maintains the rotation rate of the at least one compressor to be constant in the independent control region when the load factor is in a decreasing trend.

4. The compressed gas supply apparatus according to claim 1,

the control unit stops the at least one compressor on the condition that the load factor is maintained in the individual control area for a predetermined time when the load factor is decreased and the individual control area is shifted from the individual control area to the independent control area.

5. The compressed gas supply apparatus according to claim 1,

the control unit controls the rotation rate of the other compressor to the maximum rotation rate when the at least one compressor is stopped in accordance with a decrease in the load factor.

6. The compressed gas supply apparatus according to claim 1,

the control unit increases the rotation rate of the at least one compressor in accordance with the load factor and decreases the rotation rate of the other compressor in accordance with the load factor in the independent control region when the load factor is in an increasing trend.

7. The compressed gas supply apparatus according to claim 1,

the control unit starts the at least one compressor on the condition that the load factor is maintained in the independent control area for a predetermined time when the load factor is increased and the individual control area is shifted to the independent control area.

8. A control method of a compressed gas supply apparatus capable of supplying compressed gas discharged from a plurality of compressors arranged in parallel,

wherein,

the control method of the compressed gas supply device comprises the following steps:

a load factor detection step of detecting a load factor of the compressed gas supply device; and

a control step of controlling the rotational speeds of the plurality of compressors based on the detected load factors,

in the control step, the plurality of compressors are controlled so as to have a common rotation rate in a common control region in which the load factor is equal to or greater than a first threshold value, the plurality of compressors are independently controlled so that the rotation rates of all of the plurality of compressors are smaller than a rated rotation rate and the rotation rate of at least one of the plurality of compressors is smaller than the rotation rate of the other compressor in an independent control region in which the load factor is equal to or greater than a second threshold value that is smaller than the first threshold value, and the at least one compressor is stopped and the rotation rate of the other compressor is controlled in an independent control region in which the load factor is smaller than the second threshold value.