JPH09209949A - Screw compressor, and control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent reduction of discharge pressure even when used air quantity exceeds a rated value in the case where a discharge pressure set value is lowered by determining the number of the highest rotation of a motor in accordance with the discharge pressure set value in a compressor main body. SOLUTION: Compression air compressed to a specified pressure in a compressor main body 3 is discharged from discharge pipings 6. At this time, a pressure sensor 7 detects pressure of the compression air to be fed back to the number of rotation control device 8. The number of rotation control device 8 operates the operation number of rotation in accordance with used air quantity in a demanding apparatus, and an inverter 1 is controlled to control rotation of a motor 2. For a control range of the operation number of rotation in this case, the number of rotation number preliminarily set in the heighest number of rotation control device 9 based on a set pressure by a discharge pressure setting device 10 is taken as the upper limit. In this constitution, in the case where it is set at a lower pressure than a rated pressure, air quantity exceeding rated air quantity can be obtained within a motor load capacity range. Discharge pressure can thus be prevented from lowering even when the rated air quantity is exceeded.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compressor capable of adjusting a discharge pressure and a control method thereof, and in particular,
The present invention relates to a screw compressor suitable for preventing a decrease in discharge pressure and a control method therefor.

[0002]

2. Description of the Related Art As a screw compressor of this type and a method of controlling the screw compressor, there is, for example, a technique described in JP-A-6-200886. A conventional screw compressor includes a compressor body that compresses air, a motor that drives the compressor body, and an inverter that controls the rotation speed of the motor, and further, discharge air discharged from the compressor body. Equipped with discharge air pressure detection means for detecting pressure and information transmission means for returning the detected pressure value to the motor, and controlling the rotation speed of the motor based on the detected pressure value to adjust the discharge air amount of the compressor. It had a function to do.

[0003]

However, in the above-mentioned conventional screw compressor, the maximum rotation speed of the compressor is fixed even if the set pressure value of the discharge air pressure detecting means is changed, so that the output of the compressor is fixed. When the amount of air used on the side exceeds the rated amount of air, there was a situation in which the discharge pressure of the compressor fell below the required set pressure.

For example, the maximum rotation speed of the compressor is the same when the set pressure value of the discharge pressure of the compressor is 0.83 MPa and 0.59 MPa.
For this reason, when the set pressure value of the discharge pressure is lowered, the compressor power is reduced and the motor load has a margin (when the set pressure value is 0.83 MPa and 0.59 MPa, the compressor power is About 20% less),
The maximum values of the amount of air discharged from the compressor are almost the same.

As a result, in the conventional screw compressor, when the amount of air used exceeds a predetermined amount of air, the discharge pressure of the compressor is increased even though the capacity of the motor for driving the compressor has a margin. Has dropped below the set pressure.

Therefore, the present invention maximizes the capacity of the compressor when the set value of the discharge pressure of the compressor is lowered, even if the amount of air used on the output side of the compressor exceeds the conventional rated value. It is an object of the present invention to provide a screw compressor and a method for controlling the screw compressor that can exhibit the above-mentioned effects and prevent a decrease in discharge pressure of the compressor.

[0007]

SUMMARY OF THE INVENTION A screw compressor of the present invention comprises a compressor body for compressing air, a motor for driving the compressor body, and a desired electric power supplied to the motor to rotate the motor. An inverter for controlling the number of discharge air, a discharge air pressure detection means for detecting the pressure of discharge air discharged from the compressor body, and an operation of the inverter based on a pressure detection value of the discharge air pressure detection means. In a screw compressor having a rotation speed control device that adjusts the discharge air amount of the compressor body, a discharge pressure setting that determines a discharge pressure set value that is a desired reference value of the discharge air pressure discharged from the compressor body. It has a device and a maximum rotation speed control device which determines the maximum rotation speed of the motor according to the discharge pressure set value.

Here, it is preferable that the maximum rotation speed control device determines the maximum rotation speed of the motor by making the discharge pressure set value approximately inversely proportional.

Thus, in the present screw compressor, the lower the discharge pressure setting value is set, the higher the maximum rotational speed of the motor, that is, the upper limit of the rotational speed of the motor that drives the compressor main body becomes.

This means that in the present screw compressor, when the discharge pressure set value is set low, when the demand for the low pressure discharge air increases, the rotation speed of the motor becomes higher than that of the conventional screw compressor. Means that you can. That is, the screw compressor,
The discharge amount of low-pressure discharge air can be increased more than that of the conventional one without increasing the rating of the motor, and the capacity of the motor can be maximized.

Further, the screw compressor control method of the present invention comprises a motor for driving the compressor body, an inverter for supplying desired electric power to the motor to control the rotation speed of the motor, and the compressor body. Discharge air pressure detecting means for detecting the pressure of discharge air discharged from the discharge air pressure control means, and control the operation of the inverter based on the pressure detection value of the discharge air pressure detecting means to adjust the discharge air amount of the compressor body. In a method for controlling a screw compressor having a rotation speed control device, control for determining a maximum rotation speed of the motor according to a discharge pressure set value that is a desired reference value of discharge air pressure discharged from the compressor body. It is characterized by doing.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a system diagram of a screw compressor according to an embodiment of the present invention. The present screw compressor includes a compressor body 3 that compresses air, a motor 2 that drives the compressor body 3, and an inverter 1 that supplies desired electric power to the motor 2 to control the rotation speed of the motor 2. And a pressure sensor 7 which is a discharge air pressure detecting means for detecting the pressure of discharge air discharged from the compressor body 3, and the operation of the inverter 1 is controlled based on the pressure detection value of the pressure sensor 7 to control the compressor. A rotation speed control device 8 for adjusting the amount of air discharged from the main body 3 is provided.

Further, the present screw compressor has a discharge pressure setting device 10 for setting a discharge pressure setting value which is a desired reference value of the discharge air pressure discharged from the compressor body 3, and a discharge pressure setting device 10 according to the discharge pressure setting value. A maximum rotation speed control device 9 that determines the maximum rotation speed of the motor 2 is provided. The screw compressor also includes an oil separator, an air cooler 5, and a discharge pipe 6 described below.

Next, the operation of the present screw compressor will be described. First, electric power is supplied from the inverter 1 to rotate the motor 2, and the rotation of the motor 2 drives the compressor body 3.

The air compressed to a predetermined pressure by the compressor body 3 enters the oil separator 4 together with the lubricating oil mixed in the compression process. The compressed air separated from the lubricating oil here is discharged to the outside through the air cooler 5 and the discharge pipe 6.

The pressure sensor 7 provided in the discharge pipe 6 is
The pressure of compressed air is detected and the detected value is used as the rotation speed control device 8
Feedback to. The rotation speed control device 8 calculates an operation rotation speed according to the amount of compressed air demand equipment used air,
The inverter 1 is controlled based on the value to control the rotation speed of the motor 2.

Here, the control range of the operating rotational speed is based on the pressure set by the discharge pressure setting device 10 and has the upper limit of the rotational speed preset in the maximum rotational speed control device 9.

FIG. 2 is a graph showing the operable range of the present screw compressor by the discharge pressure set value and the rotation speed ratio. The inside of the trapezoid shown on this graph is the operable range. For example, the discharge pressure setting value is 0.8
Assuming that the maximum rotation speed at 3 MPa is 100%, the upper limit of the maximum rotation speed is increased as the discharge pressure setting value is lowered.

That is, the maximum rotation speed control device 9 determines the maximum rotation speed of the motor by making it approximately inversely proportional to the discharge pressure set value.

In this example, the discharge pressure set value is lowered to 0.
When it is set to 59 MPa, the maximum rotation speed is 0.8 above.
The rotation speed is 120% of that at 3 MPa.

On the other hand, in the conventional screw compressor, the maximum rotation speed of the compressor is fixed even if the set pressure value of the discharge air pressure detecting means is changed. Therefore, for example, the discharge pressure set value of the compressor is 0. The maximum rotation speed of the compressor is the same value at 0.83 MPa and 0.59 MPa,
When the set pressure value is 0.59 MPa, the maximum rotation speed of the motor 2 is suppressed to a value 20% lower than that of the present screw compressor.

That is, the operating range of the present screw compressor is a trapezoidal range surrounded by points a, b, c and d in FIG. 2, whereas the operating range of the conventional screw compressor is shown in FIG. There is only a rectangular area surrounded by points a, j, c, d.

As a result, the present screw compressor sets the maximum rotation speed according to the discharge pressure set value in the screw compressor in which the rotation speed of the compressor body is controlled according to the amount of air used by the demand equipment. As a result, when a pressure lower than the rated pressure is set, an air volume equal to or higher than the rated air volume is obtained within the load capacity range of the motor, and the discharge pressure drop that occurs when the rated air volume is exceeded is reduced. Can be prevented. The rated value is a typical value in product specifications.

FIG. 3 is a graph showing an example of operating characteristics of the maximum rotation speed control device 9 in the present screw compressor. As shown in this graph, the relationship between the discharge pressure setting value P and the maximum rotation speed ratio x can be expressed by the equation P = ax + b. Here, the constant a is a value determined according to the rated value of the set pressure, and the constant b is a value determined according to the lower limit of the set pressure value.

Further, the discharge pressure set value P and the maximum rotation speed ratio x
Is not limited to the above mathematical expression, and for example, data indicating the relationship between various discharge pressure setting values P and the corresponding maximum rotation speed ratio x is preset in a memory or the like. You may stay.

FIG. 4 is a graph showing a specific example of the operating characteristics of the maximum rotation speed control device 9, in which the rated value of the set pressure is 0.
83 MPa and the lower limit value is 0.59 MPa. From this, the relationship between the discharge pressure setting value P and the maximum rotation speed ratio x can be expressed by the equation P = -0.0125x + 2.08.

[0028]

As described above, according to the present invention, since the operating range of the compressor is wide, when the discharge pressure set value of the compressor is lowered, the amount of air used on the output side of the compressor is the same as the conventional rating. It is possible to provide a screw compressor capable of maximizing the capacity of the compressor even when the value exceeds the value and preventing a decrease in the discharge pressure of the compressor.

[Brief description of drawings]

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

FIG. 2 is a graph showing an operable range of the screw compressor according to the embodiment of the present invention.

FIG. 3 is a graph showing an example of operation characteristics of the maximum rotation speed control device according to the embodiment of the present invention.

FIG. 4 is a graph showing a specific example of operation characteristics of the maximum rotation speed control device according to the embodiment of the present invention.

[Explanation of symbols]

 1 Inverter 2 Motor 3 Compressor body 4 Oil separator 5 Air cooler 6 Discharge pipe 7 Pressure sensor 8 Rotation speed control device 9 Maximum rotation speed control device 10 Discharge pressure setting device

Claims (4)

[Claims] 1. A compressor body that compresses air, a motor that drives the compressor body, and an inverter that supplies desired electric power to the motor to control the rotation speed of the motor.
Discharge air pressure detecting means for detecting the pressure of discharge air discharged from the compressor body, and discharge air of the compressor body by controlling the operation of the inverter based on the pressure detection value of the discharge air pressure detecting means. In a screw compressor having a rotation speed control device that adjusts the amount, a discharge pressure setting device that determines a discharge pressure set value that is a desired reference value of the discharge air pressure discharged from the compressor body, and the discharge pressure setting device. A maximum rotation speed control device that determines the maximum rotation speed of the motor according to a value, and a screw compressor. 2. The screw compressor according to claim 1, wherein the maximum rotation speed control device determines the maximum rotation speed of the motor in approximately inverse proportion to the discharge pressure set value. 3. A motor for driving the compressor body, an inverter for supplying desired electric power to the motor to control the rotation speed of the motor, and a pressure of discharge air discharged from the compressor body. A discharge compressor having a discharge air pressure detection means and a rotation speed control device for controlling the operation of the inverter based on the pressure detection value of the discharge air pressure detection means to adjust the discharge air amount of the compressor body. In the control method, according to the discharge pressure set value that is a desired reference value of the discharge air pressure discharged from the compressor body,
A control method for a screw compressor, characterized in that control is performed to determine a maximum rotation speed of the motor. 4. The method of controlling a screw compressor according to claim 3, wherein the maximum rotation speed of the motor is determined by making it approximately inversely proportional to the discharge pressure set value.