JPH09287580A - Screw compressor and operation method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power of a compressor and generation of drain in an oil separator by reducing the discharge pressure of a screw compressor at no load operation, when the capacity of a screw compressor is controlled corresponding to its load by closing a suction throttle valve. SOLUTION: When the discharge pressure of a pressure sensor 18 reaches the set pressure in an operation range in which the discharge air quantity is under 30% of the specification discharge air quantity, rotating speed of a compressor is held at the set lower limit rotating speed. Further, a solenoid valve 21 is opened, and a suction throttle valve 2 is closed. In addition, discharge pressure of the compressor is reduced so as to change to the capacity control of no load operation. Hereby, the pressure at the discharge port 4 of the compressor is reduced, and the consumed power can be remarkably reduced. By reducing the discharge pressure, an oil feed quantity to the compressor rotor 3 part can be also reduced. Because pressure in an oil separator 5 is also reduced at no load operation, possibility of generation of drain is also reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw compressor operating method and a screw compressor in which the rotational speed of a drive motor is changed by using an inverter to adjust the capacity of the compressor.

[0002]

2. Description of the Related Art In a conventional screw compressor, as described in Japanese Patent Application Laid-Open No. 7-35079, the compressor has a suction throttle valve at its suction port, and this suction throttle valve rotates the inverter. It was opened and closed by a solenoid valve that opens and closes according to several signals.

[0003]

In the above-mentioned prior art, the suction throttle valve is closed to control the capacity at the time of low load, so that the following points have not been fully taken into consideration. Although the suction throttle valve is fully closed with the compressor rotating at a low load: Power reduction is insufficient. 2. The discharge pressure of the compressor stays at the specified pressure, but the suction pressure decreases, so the amount of oil supply increases compared to at full load. When the amount of oil supply increases at low speed rotation, operating power and required drive torque increase, and in an inverter drive machine in which the drive torque decreases in the low speed rotation range, there is a risk of inverter trips and the like. 3. Since the work of the compressor is reduced when the discharge pressure of the compressor is at or above the specified pressure, the capacity of the upper oil cooler is relatively increased and the oil supply temperature to the compressor is lowered. Along with this, the discharge temperature of the compressor is lowered, and the possibility of occurrence of drain inside the oil separator increases.

By the way, in order to improve power under a low load, (a) a state in which the suction throttle valve is fully closed to release the pressure in the oil separator, and (b) a state in which the suction throttle valve is fully opened. There is also proposed a method of repeating the two states (a) and (b). But in this way,
A pressure margin is required to shift to the states of (a) and (b), which may cause a pressure drop below the set pressure. Further, even when the control pressure is secured, the frequency of operation of the suction throttle valve and the solenoid valve increases, which may reduce the durability of these valves.

It is an object of the present invention to reduce the power of the compressor while maintaining and improving the reliability of the compressor, and to reduce the generation of drain in the oil separator.

[0006]

In order to achieve the above object, in a method of operating a screw compressor which is driven by an electric motor using an inverter and is capable of variable speed operation, the rotational speed of the compressor is changed to reduce the load. A rotation speed control method corresponding to the change and the rotation speed of the compressor is set to the lower limit rotation speed used in this rotation speed control method, and the suction throttle valve provided on the suction side of the screw compressor is closed to close the screw compressor. And a capacity control method for controlling the capacity in accordance with the load, and the discharge pressure of the screw compressor is reduced in the capacity control method during no-load operation.

[0007] Preferably, at least one of the no-load operation is continued for a predetermined time or more, and the time ratio between the no-load operation and the load operation in the capacity control method exceeds a predetermined rate. At some point, the screw compressor was stopped. Further, preferably, when the load is reduced to keep the rotation speed constant and the suction throttle valve is closed, and further, the discharge pressure of the compressor is reduced to enter the capacity control area of the no-load operation from the rotation speed control area. , The upper limit pressure P ₁ of the control to the set pressure P ₀ in the rotation speed control region,
Control was performed so that P ₁ > P ₀ . More preferably, when the pressure of the compressor is reduced and the compressor is restarted, the operation of the compressor is continued for a predetermined time (t ₁ ) even if the load is reduced,
The compressor was stopped after a lapse of a predetermined time (t ₁ ).

A second aspect of the present invention for achieving the above object has a pair of male and female rotors rotatably supported by bearings, an electric motor for driving the rotors, and an inverter for controlling the electric motors. In a screw compressor provided with a suction throttle valve for adjusting the flow rate on the suction side, a rotation speed control means for controlling the capacity of the screw compressor by changing the rotation speed of the electric motor by an inverter, and this rotation speed control means. And a capacity control means for controlling the suction throttle valve to be closed while driving the compressor at the minimum rotation speed set to.

Preferably, the capacity control means sets P ₁ to the upper limit value of the discharge pressure of the compressor, P ₂ the lower limit value of the discharge pressure of the compressor, and P ₁ when the set pressure is P _0. >
At P ₀ , P ₂ = <P ₀ is controlled. Also preferably, the rotational speed control means, when the compressor is automatically stopped by a reduction in the load, it becomes to the set pressure P ₀ with P _3> P ₀ P ₃
It is controlled so that the pressure rises up to and then stops. More preferably, the rotation speed control means controls so that P ₄ > = P ₀ when the pressure for restarting the compressor is P ₄ . Further, preferably, a discharge pressure detection means for detecting the discharge pressure of the compressor is provided on the discharge side of the compressor, and the set pressure (P ₀ ) of the capacity control means and the upper limit value (P ₁ ) of the rotational speed control means are set. ) And the lower limit (P ₂ ),
According to the storage means for storing the upper limit value (P ₃ ) of the pressure before the automatic stop and the restart pressure (P ₄ ) after the automatic stop, the detected pressure detected by the discharge pressure detection means and the drive frequency of the inverter. Switching means for switching the operations of the rotation speed control means and the capacity control means, and P ₀ stored in the storage means,
An input means for changing the values of P ₁ , P ₂ , P ₃ , and P ₄ is provided.

More preferably, pressure setting means for automatically calculating and setting four setting pressures P _{1 to} P ₄ based on the setting pressure (P ₀ ) of the capacity control means is provided.

In the present invention thus constructed, for example, the electric motor is controlled by using an inverter in the range of 100% to 30% of the rated discharge air amount of the compressor, and the rotational speed of the compressor is changed to change the capacity. Control. Air consumption is 30%
When it decreases below, the rotation speed of the compressor is fixed to the rotation speed at 30% load (lower limit rotation speed), the suction throttle valve is closed, and at the same time, the discharge pressure of the compressor is reduced. Since the pressure on the discharge side of the compressor is reduced at the same time when the inflow of air into the compressor is cut off, the power consumption is significantly reduced. 3
In the load region of 0% or less, this no-load operation and the load operation at the lower limit rotation speed are repeatedly performed to adjust the capacity.

Further, for example, when no load operation continues for 10 minutes, the compressor is automatically stopped. Alternatively, for example, the compressor is set to automatically stop in a load region of 10% or less.
In addition, when the load decreases, for example, when the air usage decreases to 30% or less, the rotation speed of the compressor is maintained at the set value (lower limit rotation speed), and when the air usage decreases, the lower limit is also maintained. Continue operation at the frequency. Then, the suction throttle valve is closed to reduce the discharge pressure of the compressor. When the discharge pressure of the compressor reaches the pressure P ₁ where P ₁ > P ₀ when the set pressure in the rotation speed control region is set to P ₀ and enters the capacity control region of this no-load operation, the suction throttle valve Is closed, and the discharge pressure of the compressor is reduced to start no-load operation. The above method is also performed when the compressor has an automatic stop function.

Further, the pressure P ₂ (lower limit pressure) for returning from the no-load operation to the load operation is set to a pressure equal to or higher than the set pressure P ₀ . When the amount of air used is 100% to 30% of the rated discharge air amount of the compressor, the number of revolutions is controlled and the compressor is operated so as to have a constant pressure near the set pressure P ₀ . On the other hand, when the amount of air used is 30% or less, P ₁ > P ₂ > =
Between the pressures of P ₁ and P _{2, which} are P ₀ , the no-load operation and the load operation at the lower limit rotation speed are repeated according to the amount of air used.

When the amount of air used further decreases and the condition for automatically stopping the compressor is satisfied, a period of load operation at the lower limit rotation speed is provided and P _{3 is} set with respect to the set pressure P ₀ described above.
After the pressure rises to P ₃ where> P ₀ , the compressor is stopped. When the consumption of air begins and the pressure becomes P ₄ > = P ₀ , P
_When it drops to _4, restart the compressor.

A pressure sensor is used to detect the P ₁ ,
The pressures of P ₂ , P ₃ , P _4, etc. may be detected and each set pressure may be stored in the storage device. Each set pressure P ₁ ~ P ₄
May be automatically calculated and set by a calculation device when the pressure P ₀ is set. Moreover, you may provide the input means which changes a setting value manually. As a result, each set pressure can be properly set and the set value can be easily changed.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, some embodiments of the present invention will be described with reference to the drawings. FIG.
FIG. 1 shows a schematic diagram of a screw compressor device according to an embodiment of the present invention. The air sucked from the suction filter 1 passes through the suction throttle valve 2 and is then compressed between the rotors 3 of the screw compressor and discharged from the discharge port 4. Lubricating oil is injected into the rotor 3 part of the screw compressor 12 in order to cool the compression heat generated by the compression and for lubrication and sealing. The compressed air discharged from the discharge port 4 together with the lubricating oil flows into the oil separator tank 5, is separated from the lubricating oil by the oil separator element 6, and is sequentially passed from the discharge pipe 7 through the check valve 8 and the pressure regulating valve 9. , Aftercooler 10
And is cooled in the aftercooler 10 and then discharged to an external device (not shown).

On the other hand, the lubricating oil is the oil separator tank 5
It is separated from the compressed air inside and is guided to the oil cooler 11 from the bottom of the oil separator tank 5. Lubricating oil cooled by the oil cooler 11 and uncooled lubricating oil not passing through the oil cooler are mixed in the temperature control valve 13 to lubricate the screw compressor 12. The oil cooler 11 and the aftercooler 10 are cooled by the cooling air from the cooling fan 14.

Three shafts of a screw compressor rotor and an electric motor 1
The rotation is connected to the six axes by a belt 15. Electric motor 1
The inverter 6 can be operated at a variable speed by the inverter 17. A pressure sensor 18 is provided on the downstream side of the check valve 8 to detect the pressure discharged from the screw compressor 12. The output signal of the pressure sensor 18 is input to the input / output unit 19. The control unit 20a includes a storage unit and a P
It has an ID function. Then, the stored set pressure is compared with the pressure detected by the pressure sensor 18, and the inverter 17 is provided with a frequency at which the detected pressure becomes the target pressure P _0, and the rotation speed of the electric motor 16 is changed. The various pressure set values stored in the storage means and the control unit 20a are automatically set to proper values only by setting the target pressure P ₀ . Further, the setting value can be changed by using the setting input unit and the display unit 20b connected to the control device unit 20a. Further, the setting input means and the display section 20b are provided with a display means (LED, liquid crystal element, etc.) so as to display the set value of pressure and the operating frequency.

In the valve plate 2a of the suction throttle valve 2 provided on the upstream side of the screw compressor 12, the piston 2b has a solenoid valve 2
When it receives pressure from the 1 side, it operates in the closing direction. That is, when the solenoid valve 21 is opened, the high pressure in the oil separator 5 is guided to the suction throttle valve 2, and the pressure is applied to the piston 2b. Further, a part of the air in the oil separator 5 is discharged to the suction side of the suction throttle valve 2 via the discharge pipe 22 at the same time when the electromagnetic valve 21 is opened. At this time, the flow rate is adjusted by the orifice 23. Instead of the pipe 22, a structure may be used in which air is directly discharged to the atmosphere. In addition,
The solenoid valve 21 compares the set pressure, which is automatically or manually set in the storage means and control device section 20a, with the pressure signal from the input / output section 19 input to the storage means and control device section 20a. It is opened and closed based on.

The operation of the screw compressor device thus constructed will be described below. If the oil-cooled screw compressor is driven by an electric motor that uses an inverter, the rotation speed of the compressor 12 can be reduced as the amount of air used decreases, and the power consumption is greater than that of other capacity control systems. A reduction effect can be obtained. This is well known in the art, but if the rotation speed is controlled in the entire region of the discharge air amount, the following disadvantages will be brought about.

That is, in the low rotation speed or small air amount range,
It is necessary to also use capacity control using a suction throttle valve, etc., and further, (1) when the rotational speed becomes low, the electric motor 1
6, the rotation speed of the cooling fan 16a integrally provided with 6 also decreases, the electric motor cannot be cooled, and the electric motor coil temperature exceeds a predetermined temperature range. (2) Oil supply to the compressor 12 and the oil separator 5 and the screw Since the differential pressure inside the compressor 12 is used, the oil supply amount does not decrease even if the rotation speed becomes low and the discharge air amount of the screw compressor significantly decreases. There is a problem that liquid compression occurs and an overload state occurs.

In order to avoid these problems, various methods such as providing a fan driven by a dedicated motor for cooling the electric motor and providing a valve for adjusting the amount of oil supply in the low rotational speed range are available. It is conceivable, but the structure is complicated and unrealistic.

Therefore, in the one disclosed in Japanese Patent Laid-Open No. 7-35079, the capacity control by the rotation speed control is not performed in the small air amount range, and the suction throttle valve 2 is closed at the same time as the set lower limit rotation speed is reached. I was in a no-load operation state. However, although this method can be expected to save energy compared to the conventional method, it is still insufficient. Therefore, in the present invention, the device is configured as shown in FIG. 1 to control the capacity of the screw compressor. The detailed flow is shown in FIG.

About 30% to 10% of the specified discharge air amount
In the operating range of 0% air amount, the drive frequency of the electric motor 16 is changed by the inverter to control the rotation speed. On the other hand, when the discharge air amount reaches the operating range of 30% or less of the specified discharge air amount, the discharge pressure of the compressor detected by the pressure sensor 18 reaches the set pressure P ₁ stored in the storage means and the control output unit. If so, the rotation speed of the screw compressor is held at the lower limit rotation speed set in the rotation speed control. Then, the solenoid valve 21 is opened to close the suction throttle valve 2. Further, the discharge pressure of the compressor 3 is reduced to switch to capacity control for no-load operation. As a result, the pressure at the discharge port 4 of the compressor 12 is lowered, and the power consumption can be significantly reduced as compared with the conventional technique.

FIG. 2 shows the ratio of power consumption to discharge air amount ratio in this case. In FIG. 2, line A is the power consumption characteristic of the conventional method, and line B is the power consumption characteristic of the embodiment of the present invention. When the discharge air amount ratio is near 0%, the power consumption is reduced to about half of the conventional power consumption.

Since the discharge pressure is reduced, the compressor rotor 3
The amount of oil supplied to the parts can also be reduced, and there is no risk of an abnormal increase in the torque generated when the lubricating oil is liquid-compressed. In addition, when the screw compressor is operated under a low load, the oil supply temperature is lowered and drainage is likely to occur in the oil separator 5, but the pressure in the oil separator 5 is also reduced during no-load operation, so drainage can occur. Less likely.

Furthermore, as a result of maintaining the rotation speed of the compressor at this lower limit rotation speed and operating the suction throttle valve 2 in the closed state, the discharge pressure of the compressor 3 decreases and the setting time is set to no load. The rotation speed of the compressor is held at the lower limit rotation speed, and the time of load operation in which the suction throttle valve 2 is opened and the operation is determined by the storage means and the timer means incorporated in the control output unit. If the load of the former is, for example, 10% or less, or if the operating time of the former exceeds 3 minutes in a row,
Stop the compressor. Further, the pressure sensor 18 continues to monitor the pressure even during the stop, and the compressor is restarted when the pressure is reduced to the set pressure P ₄ stored in the storage means and the control unit. If the operation of the compressor is controlled in this way, the power consumption characteristic becomes as shown by the line C in FIG.
Further, it is possible to reduce power in an operating region where the air consumption is small.

In the above embodiment, when the amount of air consumed is reduced and the number of revolutions of the compressor reaches the set lower limit number of revolutions, the target set pressure P ₀ in the number of revolutions control region and no-load operation (hereinafter referred to as rotation (The operation state in which the number of discharges of the compressor 3 is reduced at the same time as closing the suction throttle valve 2 with a constant number is referred to as no-load operation.) The upper limit pressure P ₁ is the same, and the air consumption is controlled. When the switching point of the method is matched, an unstable ON-OFF command may be generated in the solenoid valve 21, and hunting of the suction throttle valve 2 may occur.

In a general constant speed electric motor driven screw compressor, when the capacity control for closing only the suction throttle valve is not performed, the specified pressure P ₀ * of the compressor and the set upper limit for no load operation are set. The pressure P ₁ * is set to the same pressure. This is because the electric motor is designed to have an allowable maximum output when operating under full load at the specified pressure. That is, if the set upper limit pressure P ₁ * at the start of no-load operation is made higher than the specified pressure P ₀ *, the electric motor becomes overloaded, while the set upper limit pressure P 1 * at the start of the no-load operation becomes the specified pressure P _0. * Because if it is lower than the specified pressure, there will be a problem that the operation will start without load before the specified pressure is reached.

On the other hand, in the present invention, since the no-load operation is started at the lower limit rotation speed of the rotation speed control region by the inverter, there is no limitation of the compressor driven by the constant speed electric motor, and the target in the rotation speed control region is set. Even if the starting pressure P ₁ for no-load operation is set higher than the set pressure P ₀ (that is, the specification pressure in the case of a compressor driven by a constant speed electric motor), no problem such as overload of the electric motor occurs. Therefore, in the present invention, P
Set P ₁ so that ₁ > P ₀ . For example, P ₀ is 0.6
In the case of 9 Mpa, P ₁ is set to 0.79 Mpa. By setting in this way, a time delay can be provided between the rotation speed control region and the constant speed control at the lower limit rotation speed,
There is no risk of hunting as described above.

Depending on the set pressure, the control condition suitable for the compressor may be deviated, which may cause inconvenience. Therefore, when the target set pressure P ₀ is input, an appropriate value is automatically calculated to determine P _{1 to} P ₄ . This P ₁ ~ P ₄
An example of the determination method of is shown below. Now, the pressure P ₀ is P ₀ =
It is assumed to be 0.69 MPa. If the load becomes low in this state, increase the maximum pressure by 0.098 MPa to P ₁
= P ₀ + 0.098 = 0.79 MPa is calculated. Here, the blowout pressure of the safety valve is 0.93 MPa.
Therefore, the control upper limit pressure satisfies the condition that it is less than or equal to this blowing pressure. Next, the condition for the stoppable pressure P ₂ is P ₂ > = P ₁ . That is, until P1 = P2 is b - de driving, unload Once become P ₁ = P ₂ - from switch to de operation, the unload - a from when switching to de operation until the pressure drops to P ₀ time If this time is calculated and the time is longer than a predetermined time, it is stopped, and if it is within the predetermined time, the controller is operated so that the road operation is performed. The pressure P ₃ for returning to the load operation is P ₃ = <P ₀ . Further, the pressure P ₄ for restarting after the operation stop is P ₄ =
And P ₀ -0.098MPa = 0.59MPa.

When the respective pressures P _{0 to} P ₄ are set in this way, when P ₀ = 0.83 MPa or more, P ₁ = (P ₀ +
0.098)> 0.93 MPa, which exceeds the blowout pressure of the safety valve. Therefore, P ₁ = P ₀ + (0.07
/ P ₀ ) MPa The empirical formulas suitable for the respective specifications are stored in the storage means of the compressor control device. That is, each set pressure can be automatically determined only by inputting P ₀ by storing an arithmetic expression according to the specification according to the pressure setting of each compressor. In this embodiment, the relationship between the set pressures is given by an arithmetic expression, but discrete values may be interpolated and used. Further, although this relational expression is stored in the storage means, it may be stored in an external storage means such as a floppy disk.

By the way, conventionally, when a constant-speed electric motor is used, it is unavoidable that a pressure difference is generated due to the opening / closing operation of the suction throttle valve and the electromagnetic valve. For example, even if the minimum required pressure was 0.59 MPa, the load operation and the no-load operation were repeated between 0.69 MPa and 0.59 MPa. On the other hand, in the rotation speed control method using the inverter, it becomes possible to change the rotation speed while keeping the pressure constant by the PID control, and the minimum required pressure is 0.59 Mp.
By setting a as the target set pressure P ₀ in the rotation speed control region, it is not necessary to unnecessarily increase the pressure to a high pressure, and the power saving effect can be obtained. However, during no-load operation in the low load region where the rotation speed is not controlled, for example, 0.59 Mpa and 0.49 Mpa
This effect is halved when the pressure is controlled during the period and the pressure drops to 0.59 MPa or less. That is, the pressure is 0.59
In the case where there is a hindrance when it is reduced to Mpa or less, P ₀ cannot be reduced after all.

Therefore, the pressure sensor 1 indicates that the compressed air is consumed and the discharge pressure decreases after the no load operation is started.
Detect at 8. Further, the pressure (lower limit pressure) P ₂ when returning to the load operation is set equal to or higher than the target set pressure P ₀ in the rotation speed control region. Due to this, even when the air usage amount further decreases from the rotation speed control area,
The operation can always be performed at a pressure higher than the target set pressure in the rotation speed control area. Further, even if the control pressure is increased, the increase of the driving power is very small because it is in the low load region.

Next, a modification of the present invention will be shown. This modification is about control when the load is reduced. When the load decreases, the timer function described above causes automatic stop and automatic restart. At this time, if the automatic stop condition of the compressor is satisfied, the load operation is forcibly performed once, and the discharge pressure of the compressor is temporarily set to the target set pressure P in the rotational speed control region.
₀ to raise the pressure to P ₃ which is a P _3> P _0, and then stops the compressor. Further, the pressure P ₄ for restarting the compressor is P ₄ > with respect to the target set pressure P ₀ in the rotation speed control region.
= P ₀ . As a result, the compressor can be stably controlled even in the low load region in which the rotation speed is kept constant. That is, according to this modification, since the target set pressure in the rotation speed control region can be maintained in all load regions, the power saving effect of the rotation speed control by the above-described inverter that the compressor can be operated at the minimum necessary pressure can be achieved. You can maximize it.

In the above embodiment, the set value of the control pressure is stored in the storage means 20a and can be displayed when necessary using the display and input means 20b. Although these set values are automatically calculated and determined when the control pressure P ₀ is input, they can be easily performed by using the display and input means 20b. For example, in the example in which the maximum pressure is limited by the pressure, the above-mentioned five control pressures P ₀ , P ₁ , P ₂ , P ₃ , P ₄ are set as P ₁ = P ₃ = P ₀ + (0.07 / P ₀ ) Mpa P ₂ = P ₄ = P ₀ It is set using the equation and stored in advance in the storage means.
Change only ₀ . In this case, the operating pressure can be easily changed.

Needless to say, each set pressure can be manually determined. For example, P ₁ = P ₂ = P ₃ =
With P ₀ + X, P ₄ = P ₀ -Y, the values of X and Y are input using an input switch or the like provided on the surface of the control panel while watching the momentary values displayed on the display device. Where 0.0
01> X or Y> 0.098.

Further, a timer for starting counting after the automatic restart is provided in the storage means and the control device section 20a, and the compressor is not stopped for a predetermined time t ₁ even if the load is reduced,
After this time t ₁ , the compressor is automatically stopped when the load condition of the compressor still satisfies the automatic stop condition.
As a result, it is possible to prevent the compressor from stopping before the oil temperature rises sufficiently to cause drainage in the oil separator 5 due to the compressor being repeatedly operated and stopped.

FIG. 3 shows an example of changes in the air usage and pressure when the above-described screw compressor control method is used, and FIG. 4 shows an example of the operation control flow of the screw compressor. In the present invention, rotation speed control using an inverter,
In the screw compressor combined with capacity control and its operation method, there is no operation area of the conventional method in which capacity control is performed by closing only the suction throttle valve during capacity control operation.Therefore, it is possible to reduce power consumption and generation of drainage. .

As described above, according to the present embodiment, by inputting the control set pressure, it becomes easy to set the pressure in the capacity control under low load, and there is no inconvenience of the machine due to the pressure condition. Further, since the input value can be changed and confirmed, the operating state of the compressor can be always grasped, and the reliability in the operation of the compressor can be improved.

[0041]

According to the present invention, when the load of the screw compressor is low and the screw compressor is operated at a reduced rotation speed, (1) the power reduction effect is great.

(2) The required drive torque does not increase and the inverter drive compressor does not trip the inverter.

(3) Since the discharge pressure of the compressor also drops,
There is no risk of drainage inside the oil separator.

(4) Even if the load is further reduced and the compressor is stopped, the pressure required for the rotation speed control can be secured.
The set pressure for rotation speed control can be lowered, and power can be reduced to near ideal.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a screw compressor device according to an embodiment of the present invention.

FIG. 2 is a graph showing characteristics of power consumption.

FIG. 3 is a graph showing an example of changes in air usage and pressure.

FIG. 4 is a flowchart of an example of operation control.

[Explanation of symbols]

2 ... Suction throttle valve, 5 ... Oil separator, 6 ... Oil separator element, 8 ... Check valve, 9 ... Pressure regulating valve, 16 ... Electric motor, 17 ... Inverter, 18 ... Pressure sensor, 19 ...... Input / output unit, 20a ...... Storage means and control device section, 20b ...... Display and setting input section, 2
1 ... Solenoid valve.

Claims (10)

[Claims] 1. A method of operating a screw compressor driven by an electric motor using an inverter, which is capable of variable speed operation, and a method of controlling the number of revolutions corresponding to a change in load by changing the number of revolutions of the compressor, While setting the rotation speed of the compressor to the lower limit rotation speed used in the rotation speed control method, the suction throttle valve provided on the suction side of the screw compressor is closed to control the capacity corresponding to the load of the screw compressor. The method for controlling a screw compressor, wherein the discharge pressure of the screw compressor is reduced in the capacity control method during no-load operation. 2. At least one of the operation when the no-load operation continues for a predetermined time or more and when the time ratio between the no-load operation and the load operation in the capacity control method exceeds a predetermined ratio. The method of operating a screw compressor according to claim 1, wherein the screw compressor is stopped at times. 3. When the load is reduced to keep the rotation speed constant and the suction throttle valve is closed, and further, the discharge pressure of the compressor is reduced to enter the capacity control area of the no-load operation from the rotation speed control area. The operating method of the screw compressor according to claim ₁ , wherein the control upper limit pressure P ₁ is controlled to P ₁ > P ₀ with respect to the set pressure P ₀ in the rotation speed control region. 4. A suction throttle valve having a pair of male and female rotors rotatably supported by bearings, comprising an electric motor for driving the rotor and an inverter for controlling the electric motor, and adjusting the flow rate on the suction side. In the screw compressor provided with, a rotation speed control means for controlling the capacity of the screw compressor by changing the rotation speed of the electric motor by an inverter,
A screw compressor comprising: a capacity control unit that drives the screw compressor at a minimum rotation speed set in the rotation speed control unit and controls to close the suction throttle valve. 5. When the upper limit of the discharge pressure of the compressor is P ₁ , the lower limit of the discharge pressure of the compressor is P ₂ , and the set pressure is P ₀ , P ₁ > At P ₀ , P ₂ =
The screw compressor according to claim 4, wherein the screw compressor is controlled to <P ₀ . 6. The rotation speed control means sets P _{3 with} respect to the set pressure P ₀ when the compressor automatically stops due to a decrease in load.
The screw compressor according to claim 5, wherein the screw compressor is controlled so that the pressure is increased to P ₃ where> P ₀ and then stopped. 7. The screw according to claim 6, wherein the rotation speed control means controls so that P ₄ > = P ₀ when the pressure for restarting the compressor is P _4. Compressor. 8. A discharge pressure detection means for detecting the discharge pressure of the compressor is provided on the discharge side of the compressor, and the set pressure (P ₀ ) of the capacity control means and the upper limit of the pressure of the rotational speed control means. A storage means for storing the value (P ₁ ) and the lower limit value (P ₂ ), the upper limit value (P ₃ ) of the pressure before the automatic stop, and the restart pressure (P ₄ ) after the automatic stop, and the discharge pressure detection. Switching means for switching the operations of the rotation speed control means and the capacity control means in accordance with the detected pressure detected by the means and the drive frequency of the inverter, and P ₀ stored in the storage means,
The screw compressor according to claim 4, further comprising: an input unit that can change the values of P ₁ , P ₂ , P ₃ , and P ₄ . 9. A set pressure (P ₀ ) of the capacity control means,
The upper limit value (P ₁ ) and the lower limit value (P ₂ ) of the pressure of the rotation speed control means, the upper limit value (P ₃ ) of the pressure before the automatic stop, and the restart pressure (P ₄ ) after the automatic stop are stored. Storage means and pressure setting means for calculating and setting the set pressures (P ₁ , P ₂ , P ₃ , P ₄ ) based on the set pressure (P ₀ ) of the capacity control means. The screw compressor according to claim 4. When 10. A compressor pressure of the compressor is reduced is restarted, the load continues to operate for a predetermined time (t ₁₎ compressor be reduced, the predetermined time (t ₁₎ has elapsed The method of operating the screw compressor according to claim 2, further comprising stopping the compressor.