JP2003003975A - Control method of screw compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screw compressor which can control pressure and a delivery amount in a wide range of compressed air while maintaining a delivery pressure of prescribed value or more. SOLUTION: The highest rotational speed Nmax capable of operating a drive motor 6 with fixed power is calculated from a delivery pressure Pd input by a controller 11, for making a deviation zero between an input prescribed pressure Pc and the delivery pressure Pd, a rotational speed NPID is calculated by PID calculation, relating to an inverter 12 controlling the drive motor 6 driving a compressor main unit 2 in the case of rotational speed NPID < rotational speed Nmax, the rotational speed NPID is output as a rotational speed command N, in the other hand, in except the case, the rotational speed Nmax is output as the rotational speed command N.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a screw compressor, and more particularly, to a method for controlling a wide range of compressed air pressure while maintaining a discharge pressure equal to or higher than a specified pressure. The present invention belongs to the technical field of a screw compressor control method capable of controlling a discharge amount. 2. Description of the Related Art As a compressor control method for controlling the drive of a compressor by inverter / PID control,
For example, a compressor can be operated in the most efficient and energy-saving state in accordance with a use state.
No. 69486, “Inverter / PI
A method of driving a compressor by D control "is known. Less than,
The outline of the “method of driving a compressor by inverter / PID control” according to this conventional example will be described. [0003] Hereinafter, referring to FIG. 3 of a block diagram showing the entire configuration, the same name and the same reference numeral described in the publication will be described. P1 and the air amount Q1 are obtained by the detecting means. The inverter / PID control unit 4 has a target value (P0, P0,
Q0, Qmax) are input. And the inverter P
As a basic operation of the ID control, the amount of compressed air is
The rotation speed control to increase to x is performed. That is, the magnitude of the amount of air Q1 of the compressed air on the use side 3 and the amount of 100% air Q0 at the compressed pressure P0 of the compressed air at the rated horsepower are compared. When Q1> Q0, the compressed air pressure P1 on the use side 3 is usually lower than the compressed pressure P0. Here, the inverter / PID control operates to control the rotation speed of the drive motor 1 that drives the compressor 2, and the air amount Q2 discharged from the compressor 2 is increased toward Q1 and Qmax. To be increased. Accordingly, the compressor 2
The compression pressure P2 discharged from the pressure increases to point to P0, which is higher than P1. As a result, compressed air having a compression pressure of P2 ≒ P0 and Qmax can be discharged, and the use side 3 uses the compressed air in the most efficient and energy-saving state. On the other hand, when Q1 ≦ Q0, Q2 remains Q1 and the compression pressure P2 discharged from the compressor 2 is P0 <P1.
, And the compressed air of P0 and Q1 can be discharged from the compressor 2. Similarly, the use side 3 uses the compressed air in the most efficient and energy-saving state. That is, the rotation speed of the drive motor 1 is controlled so as to increase the discharge air amount up to 100% or more Qmax by the rotation speed control, and the compressed air having a compression pressure corresponding to the rated horsepower in that state is automatically discharged. Controlled. According to the "method of driving a compressor by inverter / PID control" according to the above conventional example, the maximum air amount Qm within the rated horsepower of the compressor is always maintained.
Control for adjusting the discharge air amount up to ax is performed. Therefore, the "inverter / PID"
The method of driving the compressor by control "has economical and functional problems as described below. In order to detect the discharge air amount, it is necessary to prepare an expensive flow rate sensor which is not required to be provided in a normal compressor, so that it is economically disadvantageous with respect to the initial cost of the compressor control device. The inverter / PID control unit receives a target value of the required horsepower and the air amount for each type of compression pressure to be subjected to inverter / PID control. (If the discharge pressure is reduced, the value of Qmax changes. Conversely, if Qmax is increased, the discharge pressure will be significantly lower than the rated pressure.) There is no method for obtaining the maximum air amount Qmax within the rated horsepower, and it is difficult to control with high accuracy. Further, the discharge air amount is increased every time based on the rated horsepower. That is, although it is sufficient to discharge the air amount according to the usage amount, always increasing the discharge air amount does not save energy. In this conventional example, the discharge air amount Q2 is controlled to be equal to the user's use air amount Q1, but the discharge pressure P2 at this time is also set to the rated pressure P0. Discharge pressure P2 ≒ rated pressure P0 and discharge air amount Q2
= Qmax, rated pressure P0 100 of rated horsepower
Qmax is realized by overloading from the% air amount Q0. That is, in order to discharge a larger amount of air than the rated value, a certain amount of power is required, which is contradictory. In this case, Qmax = Q0 must be satisfied in order not to overload the drive motor, and there is no energy saving effect. Originally, if the discharge pressure equal to or higher than the required pressure can be maintained, it is not always necessary to increase the rotation speed until the air amount reaches Qmax, and it is sufficient to control the rotation speed to the maximum rotation speed according to the discharge pressure. In addition, inverter-driven compressors of all manufacturers are currently selling the distinctive function of inverter-driven compressors, which "controls the discharge pressure consistent with the user's specifications". There is no characteristic function as a machine. The prior art focuses on how to increase the discharge air volume near the rated pressure, but there is almost no increase in the discharge air volume near the rated pressure. That is, since the rated pressure and the amount of air discharged at the same output cannot increase, in the conventional example, when the compressor is operated at the rated pressure or higher, the compressor having the higher specified pressure rank is used. When operating at or below the specified pressure, a compressor with a lower specified pressure rank was selected, and when operating at a lower pressure, the compressor with the lowest pressure specification was selected. Accordingly, an object of the present invention is to provide a wide range of compressed air discharge pressure while maintaining a discharge pressure equal to or higher than a specified pressure.
An object of the present invention is to provide a screw compressor capable of controlling a discharge amount. If the power of the motor is controlled to be constant regardless of the discharge pressure of the compressed air, for example, if the discharge pressure of the compressed air becomes low, the required power becomes small. The present invention has been made on the assumption that since the rotation speed of the motor automatically increases and the discharge amount of the compressed air increases, the pressure and discharge amount of the compressed air can be controlled over a wide range. . Therefore, in order to solve the above-mentioned problems, the means adopted by the control method of the screw compressor according to the first aspect of the present invention controls the number of rotations of the drive motor for driving the screw rotor of the compressor body. In the method for controlling a screw compressor, a first rotation speed for keeping a power of a drive motor constant according to a discharge pressure of compressed air discharged from the compressor body is obtained, and a predetermined rotation speed between a predetermined pressure and a discharge pressure is determined. A second rotation speed of the drive motor, which is determined based on a PID calculation, that reduces the deviation, is obtained, and the magnitudes of the first rotation speed and the second rotation speed are compared. The rotation speed of the drive motor is controlled so that the rotation speed becomes the second rotation speed when the rotation speed is smaller than the first rotation speed, and to the first rotation speed otherwise. is there. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A screw compressor for realizing a screw compressor control method according to an embodiment of the present invention will be described below with reference to FIG. 1 of a block diagram including a control system. . That is, the screw compressor according to the present embodiment comprises a suction filter 1, a compressor body 2 for sucking air in the atmosphere through an air inlet 21, and a discharge port 2 of the compressor body 2.
2 is provided with a compressed air supply path 3 for supplying the compressed air discharged from 2 to an air supply destination (not shown). The compressed air supply passage 3 removes oil from the compressed air containing oil discharged from the discharge port 22 and sends out the compressed air from which the oil has been removed to the air supply side. And an oil separation and recovery device (not shown) for sending out oil stored in a lower oil sump portion to the compressor main body 2 through an oil supply path. The oil sent from the oil separation and recovery unit to the compressor body 2 is compressed by a pair of male and female screw rotors meshing with each other, a compression space formed between a casing accommodating the screw rotors, a bearing portion for supporting the rotor shaft, And a shaft sealing portion for sealing the rotor shaft. A screw rotor (not shown) of the compressor body 2 is rotated by a drive motor 6 via a coupling. The rotation of the drive motor 6, that is, the operation of the compressor body 2, is controlled by a controller 11 having a function to be described later and a rotation speed command from the controller 11, and the rotation speed based on the input rotation speed command. The motor control unit 10 includes an inverter 12 for rotating the drive motor 6. Reference numeral 7 denotes a power supply that supplies power to the inverter 12 to rotate the drive motor 6 at a rotation speed based on a rotation speed command. The controller 11 of the motor control unit 10
Is provided between the compressor main body 2 of the compressed air supply path 3 and the oil separation and recovery device, is compressed in a compression space of the compressor main body 2, and is discharged from a discharge port 22 of the compressor main body 2. The discharge pressure is input from a pressure detection sensor 13 that detects the discharge pressure of the compressed air. The controller 11 detects the pressure by the pressure detection sensor 13 and, based on the compressed air discharge pressure Pd input from the pressure detection sensor 13, operates the drive motor 6, which has a constant power, at the highest operable level. Rotational speed Nma
The value of x (first rotation speed) is calculated, and the deviation between the specified pressure (preset pressure) Pc specified by the user and the discharge pressure Pd of the compressed air discharged from the compressor body 2 is calculated by PID calculation. Speed NPID (second rotation speed) that tries to make 0 zero
Is calculated. Further, the magnitudes of the respective rotation speeds obtained by the calculation are compared and calculated, and a rotation speed command is output to the inverter 12 for controlling the rotation speed of the drive motor 6 based on the comparison result. Has a function.
The maximum operable rotational speed Nmax of the drive motor 6
Is obtained from the relationship between the compressed air pressure discharged from the compressor main body 2 and the rotation speed of the compressor main body 2. Next, a control method of the screw compressor according to the present invention will be described below with reference to FIG. When a specified pressure Pc specified by the user is input to the controller 11, the controller 11 recognizes the input specified pressure Pc. However, if the specified pressure Pc is not changed, the input is previously input. The specified pressure is recognized as the specified pressure Pc. In parallel with the input of the designated pressure Pc, the discharge pressure Pd of the compressed air detected by the pressure detection sensor 13 is input to the controller 11. The controller 11 performs the following calculations based on the discharge pressure Pd input from the pressure detection sensor 13 and the recognized specified pressure Pc, respectively, and controls the drive motor 6 for driving the compressor body 2. A rotation speed command N described later is output to the inverter 12 that controls the rotation speed. a. First, in step 1, the maximum operable rotational speed Nmax (first rotational speed) of the electric motor 6 at which the power is constant is calculated from the discharge pressure Pd. b. Similarly, in step 1, in parallel with the calculation of the maximum rotation speed Nmax, the rotation speed NPID (second rotation speed) is calculated by PID calculation in order to reduce the deviation between the specified pressure Pc specified by the user and the discharge pressure Pd to zero. Number). c. Then, in step 2, it is determined whether or not the rotation speed NPID is smaller than the highest rotation speed Nmax. That is, in Step 2, when the rotation speed NPID <the rotation speed Nmax and Yes, the inverter 12 that controls the rotation speed of the drive motor 6 that drives the compressor body 2
The rotation number NPID is output as the rotation number command N. On the other hand, in step 2, the rotational speed NPID is larger than the rotational speed Nmax and
In the case of, the rotation speed command N is sent to the inverter 12 that controls the rotation speed of the drive motor 6 that drives the compressor body 2.
Is output as the rotation speed Nmax. At this time, if the rotation speed NPID is output to the inverter 12 without outputting the rotation speed Nmax as the rotation speed command N, the rotation speed of the drive motor 6 exceeds the maximum rotation speed Nmax at which the constant operation is possible. Therefore, the driving motor 6 is overloaded. The inverter 12 controls the rotation speed of the drive motor 6 based on the rotation speed NPID or the rotation speed Nmax output from the controller 11 as the rotation speed command N such that the rotation speed of the drive motor 6 becomes the rotation speed NPID or the rotation speed Nmax. . Therefore, compressed air of a pressure and amount required by the user is discharged from the compressor body 2 driven by the drive motor 6. Then, the above is repeated such that the discharge pressure of the compressed air discharged from the compressed air supply passage 3 is detected by the pressure sensor 13 and is input to the controller 11 again. According to the method of controlling a screw compressor according to the present invention, as described above, only the normally provided pressure sensor is required, and the user need only specify the specified pressure Pc. Therefore, as in the conventional driving method of the compressor,
Since there is no need to provide an expensive flow sensor, it is economically advantageous with respect to the initial cost of the screw compressor equipment. Since it is not necessary to obtain the maximum air amount Qmax within the rated horsepower which is difficult to obtain as in the conventional method of driving a compressor, it is necessary to control the pressure and air amount of the discharge air with high accuracy. Can be. Further, according to the screw compressor control method of the present invention, the maximum air amount Qm
ax, but supplies compressed air in an amount commensurate with the amount used by the user, and does not perform control to adjust the discharge air amount to the maximum air amount Qmax within the rated horsepower. In terms of energy saving, it is superior to the conventional compressor driving method. According to the conventional driving method of the compressor,
Despite having to discharge the air amount according to the usage amount, the maximum air amount Qmax within the rated horsepower of the compressor
The control for adjusting the discharge air amount is performed until this time. On the other hand, according to the screw compressor control method of the present invention, when the amount of compressed air used is smaller than the amount of compressed air discharged, the rotational speed of the compressor body 2 is controlled by the rotational speed NPID. Therefore, the compressed air having the specified pressure Pc according to the usage amount is discharged, so that the method of controlling the screw compressor according to the present invention is more excellent than the conventional example in terms of energy saving. Further, according to the conventional compressor driving method, the discharge air amount Q2 is controlled to be equal to the user's use air amount Q1, but the discharge pressure P2 at this time is set to the rated pressure P0. The discharge pressure P2 ≒
If the rated pressure P0 and the discharge air amount Q2 = Qmax,
Since Qmax is realized by overloading from the rated pressure P0 and the 100% air amount Q0 of the rated horsepower, there is a risk of overloading. However, according to the method for controlling the screw compressor according to the present invention, since the maximum operable speed is determined by the discharge pressure, there is no possibility that the drive motor 6 is overloaded. In the above embodiment, the case where the screw compressor is oil-cooled has been described as an example.
The technical idea of the present invention can be applied to an air-cooled screw compressor, and is not limited to an oil-cooled screw compressor. As described above, according to the method for controlling a screw compressor according to the present invention, unlike the conventional example, there is no need to provide an expensive flow sensor, and only the normally provided pressure detection sensor is used. Good is economically advantageous in terms of initial costs associated with oil-cooled screw compressor equipment. Then, unlike the conventional example, there is no need to find the maximum air amount Qmax within the rated horsepower, which is difficult to find,
It is possible to accurately control the pressure and the amount of the discharge air. Further, in the control method of the screw compressor according to the present invention, the maximum air amount Qmax is always constant as in the conventional example.
Rather than supplying compressed air in an amount commensurate with the amount of use by the user, and not performing control to adjust the discharge air amount to the maximum air amount Qmax within the rated horsepower, It is superior to the conventional example in energy saving. In the conventional example, control is performed to adjust the discharge air amount to the maximum air amount Qmax within the rated horsepower of the compressor, although the air amount according to the usage amount may be discharged. On the other hand, according to the control method of the screw compressor according to the present invention, when the usage amount of the compressed air is smaller than the discharge amount of the compressed air, the rotation speed of the compressor body is controlled by the rotation speed NPID. For this reason, the compressed air having the specified pressure Pc according to the usage amount is discharged, so that the method for controlling the screw compressor according to the present invention is superior to the conventional example also in terms of energy saving. Further, in the conventional example, when the discharge air amount Q2 is controlled to be equal to the user's use air amount Q1, the discharge pressure P2 is set to the rated pressure P0.
Discharge pressure P2 ≒ rated pressure P0 and discharge air amount Q2 = Qm
If ax is reached, Qmax is realized by overloading from the rated pressure P0 and 100% air volume Q0 of the rated horsepower, and there is a risk of overloading. In the method, since the maximum number of rotations that can be operated is determined by the discharge pressure, there is no possibility that the drive motor is overloaded.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a screw compressor including a control system according to the present embodiment. FIG. 2 is a control flowchart of a screw compressor according to the embodiment. FIG. 3 is a block diagram showing an overall configuration of a compressor driving method by inverter / PID control according to a conventional example. [Description of Signs] 1 ... Suction filter 2 ... Compressor body, 21 ... Air inlet, 22 ... Discharge port 3 ... Compressed air supply path 6 ... Drive motor 7 ... Power supply 10 ... Motor control unit, 11 ... Controller, 12 ... Inverter , 13 ... Pressure detection sensor

Continuation of front page    (72) Inventor Masamichi Minamiyashiki             41 Niijima, Harima-cho, Kako-gun, Hyogo Pref.             Kobe Steel, Harima general-purpose compressor plant (72) Inventor Makoto Tomizawa             41 Niijima, Harima-cho, Kako-gun, Hyogo Pref.             Kobe Steel, Harima general-purpose compressor plant (72) Inventor Kazuo Komura             41 Niijima, Harima-cho, Kako-gun, Hyogo Pref.             Kobe Steel, Harima general-purpose compressor plant F term (reference) 3H029 AA03 AA18 AB02 BB53 BB57                       CC02 CC07 CC27 CC54 CC58                       CC60 CC62                 3H045 AA05 AA12 AA26 BA20 BA28                       CA03 CA09 CA29 DA07 EA13                       EA17 EA26 EA34

Claims (1)

Claims 1. A method of controlling a screw compressor for controlling the number of revolutions of a drive motor for driving a screw rotor of a compressor body, the method comprising controlling a discharge pressure of compressed air discharged from the compressor body. A first rotational speed that keeps the power of the drive motor constant in accordance with the first rotational speed is determined, and a second rotational speed of the drive motor that is determined based on the PID calculation to reduce a deviation between a predetermined specified pressure and a discharge pressure is calculated. And calculating the first rotation speed and the second rotation speed. If the second rotation speed is smaller than the first rotation speed, the second rotation speed becomes the second rotation speed. And controlling the rotational speed of the drive motor so that the rotational speed is equal to the first rotational speed.