JP3162013B2 - Operation method of inverter driven screw compressor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for operating a screw compressor driven by an inverter, and more particularly to a method for supplying compressed air at a constant pressure and a required pressure with respect to a change in the amount of air used. The present invention relates to an operation method of an inverter-driven screw compressor suitable for the invention.

[0002]

2. Description of the Related Art A conventional screw compressor driven by an inverter is disclosed in, for example, Japanese Patent Application Laid-Open No. 55-16479.
As described in Japanese Unexamined Patent Publication No. 2 (1994), the output of the inverter is controlled based on the speed data of the electric motor or the load data of the screw compressor. Has been proposed.

[0003]

The screw compressor has a characteristic that the starting torque in the low-speed rotation range at the time of starting is increased due to leakage of compressed air to the suction side as shown by a solid line in FIG. Therefore, when the inverter is driven by an inverter having a low generated torque in a low-speed rotation region indicated by a chain line, the starting torque of the screw compressor exceeds the generated torque of the inverter. On the other hand, the above-mentioned prior art does not consider this point, and may cause a problem that the compressor stops.

In addition, the amount of air used varies depending on the user's use of the pneumatic equipment, and the pressure fluctuates accordingly. On the other hand, in the above-mentioned prior art, no consideration was given to this point, and low-quality compressed air having a large pressure fluctuation was supplied.

The present invention has been made in view of the above-mentioned problems of the related art, and has as its object to provide an operation method of an inverter-driven screw compressor in which a screw compressor is smoothly started by an inverter.

[0006]

In order to achieve the above object, an operation method of an inverter-driven screw compressor according to the present invention is an operation method of an inverter-driven screw compressor, wherein a suction throttle valve is operated by an inverter command. After the motor is closed, the motor is operated, and when the rotation speed reaches a low torque after passing through the startup peak torque in the normal startup operation obtained in advance, the startup operation mode in which the suction throttle valve is opened by the command of the inverter, and after the startup operation mode Then, based on the pressure of the compressed air discharged from the screw compressor after smoothly starting the screw compressor, using the inverter to the rotation speed of the compressor to the rotation speed based on the output rotation speed signal from the PID control device. possess a load operation mode for controlling Te, the screw compressor starting torque of the inverter
This is to prevent the generated torque from exceeding.

[0007] Then, preferably, the pressure of the compressed air to be used for controlling the rotational speed of the compressor, Ru der those of the oil separator provided on the discharge side of the compressor with a pressure detected by the downstream.

According to the present invention, the screw compressor is started in a state where the suction side is closed by the suction side opening / closing means controlled by a signal from the inverter. Therefore, the screw compressor can be started smoothly because it is lower than the starting torque at the time of starting and the starting torque at the time of low load of the inverter.

When the rotation speed of the screw compressor gradually rises, passes a peak value at the time of normal load startup, and reaches a low startup torque rotation speed, control is performed by a rotation speed signal from the inverter. Since the suction side is opened by the suction side opening / closing means and the screw compressor performs the load operation, the screw compressor can smoothly compress air to a predetermined pressure.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to FIGS. In FIG. 1, reference numeral 1 denotes a screw compressor, which is provided with a driving rotor 2 that is driven to rotate by a motor 5 via a coupling 4 and a driven rotor 3 that meshes with the driving rotor 2 and rotates; The discharge side is connected to the oil separator 6 via the discharge pipe 13.
Connected to

The oil separator 6 separates the compressed air from the oil contained in the compressed air, sends the compressed air to the aftercooler 7 through the discharge pipe 14, and sends the oil to the oil cooler 8 through the oil pipe 17. .

The aftercooler 7 cools the compressed air,
Supply to the user through the discharge pipe 15. On the other hand, the oil cooler 8 cools the oil and sends it to the bearing of the screw compressor 1 through the oil pipe 16.

A suction throttle valve 10 has one end connected to the suction side of the screw compressor 1 and is installed in the middle of a suction pipe 12 having a suction filter 9 at the other end. 11
Is an electromagnetic valve, which is installed at an end of an operation pipe 18 branched from the discharge pipe 14, and opens and closes the suction throttle valve 10 by compressed air from the discharge pipe 14 according to a signal from an inverter 19.

Reference numeral 19 denotes an inverter, which previously obtains the relationship between the load starting torque and the rotational speed of the ordinary screw compressor 1 as shown by the solid line in FIG. outputs a signal for closing the suction throttle valve 10 to the solenoid valve 11, then activating the screw compressor 1, the lower starting torque than the rotational speed N ₁ of the peak value indicated by the solid line in FIG. 3 upon reaching the rotational speed N _2, and outputs a signal for opening the front Symbol suction throttle valve 10
Input to the solenoid valve 11. Incidentally, before Symbol rotational speed of the screw compressor 1, for example, obtained from such peripheral speed of the rotor 2.

Reference numeral 20 denotes a PID control device, as shown in FIG.
The current or voltage signal output corresponding to the detected pressure value A of the compressed air detected by the above is compared with the current or voltage signal corresponding to the preset set pressure value B, and the change in the pressure difference between the two is minimized. Inverter 19 to become
The output rotation speed is calculated and output to the inverter 19 to rotate the motor 5. The set pressure value B is:
For example, it can be changed by turning a knob (not shown) according to the use condition of the compressed air.

Next, the operation will be described. Before the screw compressor 1 is started, the suction throttle valve 10 is completely closed from the inverter 19 via the electromagnetic valve 11.
When the motor 5 is rotated in this state, the drive-side rotor 2 and the driven-side rotor 3 rotate via the coupling 4, so that the suction side of the screw compressor 1 becomes vacuum, and the discharge side of the oil separator 6 And discharges compressed air.

For this reason, the starting torque of the screw compressor 1 is, as shown by the dashed line in FIG.
The smaller than the starting torque indicated by dashed line starting torque and the inverter 19 indicated by the solid line in the case of performing normal load operation to open.

Thereafter, the rotation speed obtained from the frequency of the rotors 2 and 3 is the rotation speed N ₂ shown in FIG.
The rotation speed N _{2 of} the startup torque sufficiently lower than the rotation speed N ₁ of the peak value during the normal startup operation shown by the solid line in FIG.
, The suction throttle valve 10 is opened via the solenoid valve 11 in response to a signal from the inverter 19, and outside air is sucked into the suction side of the screw compressor 1 through the suction filter 9 and the suction pipe 12 to perform a load operation. Therefore, the screw compressor 1 can be started smoothly.

The air compressed by the screw compressor 1 is sent to an oil separator 6 through a discharge pipe 13, and the oil separator 6 separates the compressed air from the oil contained in the compressed air. The separated oil is sent to an oil cooler 8 through an oil pipe 17,
After being cooled by the oil cooler 8, the oil is supplied to a bearing portion and the like in the screw compressor 1 through an oil pipe 16.

On the other hand, the compressed air is sent to the aftercooler 7 through the discharge pipe 14, is cooled by the aftercooler 7, and is supplied to the user through the discharge pipe 15. A part of the compressed air from the oil separator 6 is branched from the discharge pipe 14 and passes through the operation pipe 18 to the electromagnetic valve 1.
1 and is used as air for opening and closing the suction throttle valve 10.

When the amount of air used by the user becomes larger than the amount of compressed air sent from the discharge pipe 15 to the user, the pressure of the compressed air sent from the discharge pipe 15 to the user gradually decreases from the set pressure value B. This is always detected by the pressure sensor 21 installed in the discharge pipe 15 and a detection signal is output to the PID control device 20.

In the PID controller 20, as shown in FIG. 2, a signal of a detection value A from the pressure sensor 21 and a set value B
And the pressure value A detected by the pressure sensor 21.
Is smaller than the set pressure value B, the inverter 1 such that the difference between the detected pressure value A and the set pressure value B is minimized.
Nine output rotation speeds are calculated, and an output rotation speed signal based on the calculation result is sent to the inverter 19.

The inverter 1 9 increases the rotational speed of the motor 5 based on the output speed signal from the PID controller 20. For this reason, the discharge amount of the compressed air of the screw compressor 1 increases, and the compressed air sent to the user from the discharge pipe 15 becomes an amount corresponding to the air amount used by the user. It is kept at the set pressure value B.

The amount of air used by the user is
From the amount of compressed air sent to the user from
The pressure gradually increases from the pressure set value B of the compressed air sent from the discharge pipe 15 to the user. This is detected by the pressure sensor 21 and a detection signal is output to the PID control device 20.

The PID control device 20 calculates the output rotation speed to the inverter 19 so that the difference between the set pressure value B and the detected pressure value A from the pressure sensor 21 is minimized, and based on the calculation result. The output rotation signal is sent to the inverter 19.

[0026] Inverter 19 reduces the rotational speed of the motor 5 based on the output rotational speed from the PID controller 20. For this reason, since the discharge amount of the compressed air of the screw compressor 1 is decreased, the pressure of the compressed air delivered from the discharge pipe 15 to the user is maintained at the set pressure value B.

The set pressure value B can be changed according to a user's request within the pressure range of the screw compressor 1, so that high-quality compressed air can be supplied with ease, and If the pressure is set, useless pressure is not consumed, so that there is a great energy saving effect. Further, as shown in FIG. 4, it is possible to configure a front SL PID controller 20 a and the front Symbol inverter 19 a on one body.

[0028]

Since the present invention is configured as described above, the following effects can be obtained. According to the present invention, by controlling the suction side by the rotation speed signal of the inverter, the starting torque of the screw compressor can be controlled so as not to exceed the generated torque of the inverter, so that the screw compressor can be started smoothly. can do.

Further, since the required pressure can be easily set in accordance with the use state of the compressed air, high-quality compressed air can be easily supplied and the required minimum pressure can be set. Because it does not consume unnecessary pressure,
There is a great energy saving effect.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a PID control device according to the present invention.

FIG. 3 is a diagram showing a starting torque of a screw compressor.

FIG. 4 is a perspective view showing a case where a PID control device and an inverter are integrated.

[Description of Signs] 1 ... screw compressor, 2 ... drive side rotor, 3 ... driven side rotor, 4 ... coupling, 5 ... motor, 6 ... oil separator, 7 ... after cooler, 8 ... oil cooler, 9
... Suction filter, 10 ... Suction throttle valve, 11 ... Solenoid valve, 1
9 ... Inverter, 20 ... PID control device, 21 ... Pressure sensor.

Continuation of the front page (56) References JP-A-2-264190 (JP, A) JP-A-61-79943 (JP, A) JP-A-62-29867 (JP, A) JP-A-63-310385 (JP) , A) Fully open 1987-36269 (JP, U) Fully open 1987-40290 (JP, U) Fully open 1984-11,189 (JP, U) Fully open 56-77677 (JP, U) (58) Field surveyed (Int.Cl. ⁷ , DB name) F04C 29/10 311 F04C 29/10 321 F04C 18/16

Claims (2)

(57) [Claims] 1. A method of operating an inverter-driven screw compressor, comprising: operating a motor after closing a suction throttle valve according to an inverter command; When the rotation speed of the screw compressor is reached, a start-up operation mode in which the suction throttle valve is opened by the command of the inverter, and after the start-up operation mode, based on the pressure of the compressed air discharged from the screw compressor after the screw compressor is started smoothly. A load operation mode in which the rotation speed of the compressor is controlled by an inverter to a rotation speed based on an output rotation speed signal from a PID control device.
A method for operating an inverter-driven screw compressor, wherein the torque generated by a bar is not exceeded . 2. The method according to claim 1, wherein the pressure of the compressed air used for controlling the number of revolutions of the compressor is a pressure detected downstream of an oil separator provided on a discharge side of the compressor. An operating method of the inverter-driven screw compressor according to the above.