JPH07208371A - Inverter-driven screw compressor - Google Patents

Abstract

PURPOSE:To secure emergency operation without an inverter, at the time of abnormality occrrence of the inverter, by providing the inverter with function of abnormality diagnosis and of outputting information notifying abnormality occurrence, and operating a power switch based on the information. CONSTITUTION:A power switch 7 is normally set to the side of supplying power to an inverter, and an electric machine 3 is driven by an output of the inverter 4. When abnormality occurs at the inverter 4, the inverter 4 generates an abnormality occurrence signal, and simultaneously stops its output. Upon reception of the abnormality occurrence signal, the power switch 7 changes over the output connected to the inverter 4 to a bypass power line 8 instantaneously. When inverter operation is disabled, circuit excluding the inverter can be formed to succeed emergency operation in which the electric machine is directly driven by commercial power. It is thus possible to stop supply of compressed gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compressor, and more particularly, to a variable displacement screw compressor having a function of controlling the discharge pressure to a constant value by increasing or decreasing the rotational speed of an inverter even if the consumption of compressed gas increases or decreases. Regarding the machine.

[0002]

2. Description of the Related Art The basic function of a compressor is to inhale, compress, and discharge gas. It is desirable that the discharge pressure of compressed gas (hereinafter referred to as compressed gas. It is often air, but other gases may be compressed for chemical plants, etc.) is constant, but the amount used It is difficult to keep it constant, as described below, because it often changes every moment. That is, for example, when the amount of compressed gas used is constant and the discharge pressure matches the target value, and when the amount of use suddenly increases from the steady state, the discharge capacity of the compressor becomes insufficient and the discharge pressure decreases. However, conversely, when the usage amount decreases, the compressed gas becomes excessive and the discharge pressure becomes high. In the past, the discharge pressure of the compressor was allowed to fluctuate within a certain pressure range even if it was not precisely fixed. However, recently, there is a demand for improvement of discharge pressure accuracy, and there is a tendency that excessive compression is not desirable from the viewpoint of energy saving. Therefore, it is desired that the compressor has the ability to adjust the discharge amount according to the usage amount of the compressed gas, that is, it is possible to control the discharge pressure at a constant value with a variable capacity.

In a conventional compressor, a compressed gas is supplied to the outside via a compressed gas container (in the case where the compressed gas is air, it is called an air tank) provided at the discharge end, and the compressed gas is supplied to the outside. It employs on / off control that starts the compressor when the internal pressure falls below the set lower limit and stops the compressor when it exceeds the set upper limit. Since this method is simple and widely used, the fluctuation range of the discharge pressure is large, so that it is difficult to use for applications requiring a precise discharge pressure. In addition, the compressed gas container generally has a disadvantage that it requires a large space.

In order to keep the discharge pressure constant, it is necessary to make the discharge amount follow the varying usage amount. Therefore, as means for controlling the discharge amount, Japanese Patent Application Laid-Open No. 55-164792 discloses a method of controlling the rotation speed of a screw compressor by an inverter to make the capacity variable. In this known example, a method of detecting a load amount by a load data detection sensor and using it for feedback control is specifically described. However, this known example describes only the normal operation, does not mention the possibility of the abnormality of the inverter, and does not mention the avoidance method or the countermeasure when it occurs.

[0005]

A stable supply of compressed gas is very important, and its interruption or interruption causes serious damage. For example, compressed air in a production plant is an essential energy source as well as electricity, and its interruption means stopping production. Therefore, the technology of the compressor has been cultivated as a machine that requires high reliability.

Inverter-driven screw compressors have been put into practical use in recent years by mounting an inverter on a conventional screw compressor. Compared to compressors and electric motors, which have a long tradition, inverters in the process of development are inferior in terms of reliability. In addition, the inverter is often the first to be damaged in the event of overload or contingency.

Therefore, in the inverter-driven compressor,
Even if there is no problem with the compressor body, there is a possibility that the compressor as a whole will stop due to an abnormality or failure of the inverter.

An object of the present invention is to provide a compressor capable of ensuring emergency operation without using the inverter even when an abnormality occurs in the inverter and supplying the compressed gas with high reliability.

[0009]

In order to achieve the above object, the present invention uses the following means.

The power line input from the outside to the present compressor is connected to the input end of the power switch through a leakage breaker for the purpose of ensuring safety. The power switching device has two output terminals and has a function of connecting one of them to an input terminal according to a command from the outside. One of the output terminals is for normal use and goes through the inverter, and the other one is for occurrence of abnormality and is guided to the electric motor through the bypass power line.

The inverter has an abnormality diagnosing function and can detect an abnormality of the inverter itself, an excessive supply current, a decrease in input voltage, and the like. At the same time, it also has a function of outputting information indicating an abnormality occurrence to the outside of the inverter.

The functions of the present invention can be increased by using the following means together.

A suction throttle valve is provided at the compressed gas suction port of the screw compressor body. The suction throttle valve can control the discharge amount by limiting the inflow amount of the compressed gas according to a command from the outside.

Furthermore, when the inverter supplies a frequency higher than the commercial power to the electric motor during normal operation, the electric motor is an induction motor having a pole number switching function,
It is advisable to provide a circuit for reducing the number of poles according to the information indicating the occurrence of abnormality.

[0015]

In normal operation, the power switch selects the inverter side to supply power. The inverter converts the input commercial power frequency and voltage and supplies it to the electric motor. The frequency is a value instructed by the control means to match the discharge pressure with the target value.

When an inverter malfunction or an abnormality such as an excessive current occurs and the operation by the inverter becomes difficult, the abnormality diagnosis function of the inverter judges and outputs the information that the abnormality has occurred. When the power switch receives the information, it switches the power supply destination from the inverter to the bypass power line and simultaneously stops the inverter. Since the electric motor is directly driven by commercial power without passing through the inverter, the operation of the compressor is maintained even if the inverter stops.

In the case of a screw compressor having an intake throttle valve that opens and closes according to an external command, the power switch is switched, and at the same time, an abnormality occurrence signal is sent to the intake throttle valve. The suction throttle valve is opened in a steady state where the rotation speed is stable during normal operation. On the other hand, at the time of abnormality, the intake throttle valve control is performed which opens and closes according to the discharge pressure to limit the suction amount and bring the discharge pressure close to a constant value. The suction throttle valve control is a conventional discharge amount control method and operates reliably and reliably.

When the inverter is supplied with high-frequency electric power during normal operation, when the electric motor is directly driven by commercial electric power, the rotation speed is reduced and the compressor capacity is not fully utilized. Therefore, if the motor is provided with a pole number switching function and a circuit that reduces the number of poles by a signal indicating the occurrence of an abnormality is provided, the reduction in the drive frequency is compensated by the reduction in the number of poles, and the rotation speed is not reduced or reduced. However, the degree is small. Therefore, the capacity of the compressor body can be effectively utilized. Further, when the frequency is reduced by the inverter and supplied in the normal state, the rotation speed is suppressed by the opposite action.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a system diagram of an inverter-driven screw compressor for air of this embodiment. The compressor 1 is composed of a compressor body 2 and some auxiliary machines. Since the compressor body 2 is a screw type compressor which is a kind of positive displacement type compressor,
The discharge capacity can be increased or decreased in proportion to the rotation speed. The compressor body 2 operates by the rotation power supplied by the electric motor 3 and the rotation of the screw rotor, and the air is sucked into the suction port 11
It is sucked in from the nozzle, compressed, and then discharged from the discharge port 12.
The electric motor 3 is an induction motor and is rotated by being supplied with a three-phase alternating current from the inverter 4. The inverter 4 receives the speed command from the control device 5, converts the commercial AC power 6 supplied from the outside into the commanded frequency and voltage, and outputs the commanded frequency and voltage.

The commercial AC power 6 is introduced into the compressor 1 from the outside and reaches an input terminal of the power switch 7 via a leakage breaker (not shown) for safety. The power switch 7 has two output terminals, and has a function of selecting one of the output terminals according to a signal from the outside and connecting it to the input terminal. One of the output terminals is wired to the primary side terminal (power input terminal) of the inverter 4, and further wired from the secondary side terminal (power output terminal) of the inverter 4 to the terminal of the electric motor 3. Power switch 7
The other output terminal is directly connected to the same terminal of the electric motor 3 via the bypass power line 8 without passing through the inverter 4. In this figure, the power line is shown by a single white arrow, but since it is a three-phase alternating current, it forms three lines.

A signal line 9 connects the abnormal signal output terminal of the inverter 4 and the switching signal input terminal of the power switch 7.

A suction throttle valve 14 is provided on the upstream side of the suction port 11 of the compressor main body 2, and a discharge pressure feedback pipe 15 is led from a discharge pipe 16. The suction throttle valve 14 opens and closes according to the discharge pressure, and has a function of reducing the suction amount as the discharge pressure is higher, and preventing the discharge pressure from rising too high. An air cleaner 13 is provided on the upstream side of the intake throttle valve.

The air compressor of this embodiment operates as follows. The power switch 7 is normally set on the side that supplies power to the inverter 4, and the electric motor 3 is driven by the output power of the inverter 4.

The control system operates as follows with respect to fluctuations in the amount of air used during normal compressor operation. When the amount of air used increases from the steady state where the amount of air used is constant, the pressure inside the discharge pipe 16 decreases. The discharge pressure is constantly monitored by the pressure sensor 21, and the information is sent to the control device 5 as soon as a pressure drop occurs. Based on the received information, the control device 5 judges the increase of the compressor discharge amount and the amount to be increased, and commands the inverter 4 to perform the acceleration corresponding to the increase of the discharge amount. As the frequency of the output power of the inverter 4 increases according to the command, the rotation speeds of the electric motor 3 and the compressor main body 2 interlocked therewith increase, and the discharge amount increases in proportion thereto.
Since the amount of air flowing into the discharge pipe 7 increases, the internal pressure rises and recovers the target value.

On the contrary, when the amount of air used decreases from the steady state, the operation is controlled in the reverse manner. When the discharge pressure rises above the target value, the rotation speed of the compressor body 2 and the discharge amount are suppressed, and the temporarily exceeded discharge pressure decreases and the target value is restored. When the amount of decrease in the amount of air used is large and the deviation of the discharge pressure from the specified value is large, the rotation speed does not decrease in time, so the suction throttle valve 14 temporarily limits the suction amount, and the discharge pressure becomes abnormal. Control the rise.

When an abnormality occurs in the inverter 4 or when it becomes difficult to continue the operation of the inverter 4 due to a cause other than the inverter 4, the inverter 4 outputs an abnormality occurrence signal and stops the output almost at the same time. In response to this abnormality occurrence signal, the power switch 7 instantly switches the output connected to the inverter 4 to the bypass power line 8. By this switching, the commercial power 6 is directly sent to the electric motor 3. Electric motor 3
Rotates depending on the frequency of the power supply frequency regardless of the inverter 4. Since the frequency is fixed, the rotation speeds of the electric motor 3 and the screw rotor inside the compressor main body 2 are substantially constant.

Therefore, it becomes impossible to control the discharge amount for changing the rotation speed as in the normal state. Therefore, instead of the rotation speed control, the discharge amount control by the suction throttle valve, which is performed in the conventional air compressor without the inverter, is performed. This suction throttle control is performed as follows. When the amount of air used decreases and the pressure inside the discharge pipe 16 rises, the discharge pressure reaches the suction throttle valve 14 via the feedback pipe 15. When the discharge pressure is equal to or higher than the specified value, the suction throttle valve 14 closes the flow passage in accordance with the excess amount to suppress the discharge amount,
Prevents rise in discharge pressure. The suction throttle control is inferior to the inverter variable speed control in terms of energy efficiency and accuracy of discharge pressure, but the demand can be satisfied for emergency operation.
Further, since the discharge pressure regulation value at which the suction throttling is performed is higher than the set pressure at the time of variable speed control, the suction throttle valve normally remains open, which does not hinder the variable speed control.

According to this embodiment, with a relatively simple structure,
The object of the present invention can be achieved. Further, the suction throttle valve can compensate for a portion of the rotational speed control that cannot be followed in response to a sudden increase in discharge pressure that normally occurs, and can function to prevent generation of abnormally high and dangerous pressure. In addition, even if the rotation speed reaches the maximum value even when the air usage amount is small due to the runaway of the control device, the suction throttle valve limits the suction amount, so that a dangerously high discharge pressure may be generated. Absent. Therefore, a highly safe compressor can be realized.

The second embodiment of the present invention will be described below with reference to FIG. It should be noted that description of parts and functions common to those of the first embodiment will be omitted.

FIG. 2 is a system diagram of the inverter-driven screw compressor for air of this embodiment. The feedback pipe provided in the first embodiment is not provided, and the suction throttle valve 14 is a solenoid valve and has a function of opening and closing according to a command value of the control device 5. The control unit 5 comprises a microcomputer, an input / output interface and a storage unit, and performs operations such as data reading, judgment, storage, and instruction output according to a program incorporated in advance. The display device 22 is means for transmitting the operating state of the compressor 1 to the user according to the instruction of the control device 5,
It is a liquid crystal or light emitting display device.

This embodiment operates as follows. That is, normally, while the discharge pressure is monitored by the pressure sensor as in the first embodiment, the control device 5 instructs the rotation speed to the inverter 4 and controls the discharge pressure to be constant.

When an abnormality occurs in the inverter 4 or when it becomes difficult to continue the operation of the inverter 4 due to a cause other than the inverter 4, the inverter 4 outputs an abnormality occurrence signal to the control device 5 and stops the output almost at the same time. To do. In response to this abnormality occurrence signal, the control device 5 instructs the power switching unit 7 to instantly switch the output connected to the inverter 4 to the bypass power line 8, and the power switching unit 7 immediately executes. By this switching, the commercial power 6 is directly sent to the electric motor 3. The electric motor 3 rotates according to the frequency of the power supply frequency without depending on the inverter 4. Since the frequency is fixed, the rotation speeds of the electric motor 3 and the screw rotor inside the compressor body 2 are constant values.

Therefore, it becomes impossible to control the discharge amount by changing the rotation speed as in the normal state. Therefore, instead of the rotation speed control, the discharge amount control by the suction throttle valve 14 is performed. The control device 5 compares the pressure data read by the pressure sensor 21 with a preset target value of the discharge pressure,
When it is insufficient, the suction throttle valve 14 is opened, and when it is excessive, it is controlled in the closing direction so that the discharge pressure is controlled to be constant.

The display device 22 normally displays the set value of the discharge pressure, the actual discharge pressure measured by the pressure sensor 21 at that time, the ratio of the load to the compression function force, and the like.
Further, when an abnormality occurs, the type of the abnormality, countermeasures, and when the emergency operation that bypasses the inverter 4 is automatically switched, the fact is displayed.

According to the present embodiment, all the information and instructions on the condition of the compressor are concentrated in the control device, so it is possible to change the characteristics of the compressor only by changing the operating program and the set values. . In addition, since feedback piping is unnecessary, the piping system can be simplified. Furthermore, the user can immediately know the operating condition of the compressor and the response when an abnormality occurs on the display device.

The third embodiment of the present invention will be described below with reference to FIG. It should be noted that description of parts and functions common to the first and second embodiments will be omitted.

FIG. 3 is a system diagram of the inverter-driven screw compressor for air of this embodiment. The electric motor 3 is an induction motor having a pole number switching function, and has a function of changing the pole number according to an instruction from the control device 5. Control device 4 for switching the number of poles
Is transmitted to the electric motor 3 by the pole number indicating wiring 23. Note that, in FIG. 3, the electric motor 3 includes an electric power device and an auxiliary device such as a relay necessary for switching the number of poles in the electric motor main body.

As a property of the induction motor, the rotation speed is determined by the drive frequency and the number of poles, except for a slight change in the rotation speed due to the increase / decrease in the slip caused by the change in the load torque. Normally, the drive frequency is changed by the inverter 4 to change the rotation speed of the electric motor 3 to control the discharge amount. When obtaining the maximum discharge amount of the compressor, the rotation speed also becomes the highest. Due to the nature of the compressor body 2, the drive frequency at that time is often higher than the frequency of the commercial power 6 (50 or 60 Hz in Japan). Therefore, when the electric motor 3 is directly driven by the commercial electric power 6 without passing through the inverter 4 during the emergency operation, the rotation speed does not reach the maximum value, and there is a problem that the full capacity of the compressor cannot be used. .

Therefore, in this embodiment, the following operation is performed to solve this problem. The control device 5 makes a determination to switch to the emergency operation, sends an instruction to the power switch 7 and the suction throttle valve 14, and at the same time instructs the electric motor 3 to switch the number of poles (for example, from 4 poles to 2 poles). . Then, the frequency of the electric power supplied to the electric motor is reduced, but the number of poles is reduced, so that the reduction of the rotation speed can be prevented.

According to the present embodiment, in a model in which the electric motor is rotated by the inverter at a frequency higher than the commercial power at the maximum output of the compressor, even when the operation is performed without the inverter during the emergency operation. , The compression function power can be fully used.

[0042]

The inverter-driven screw compressor according to the present invention constitutes a circuit without an inverter even when the inverter, the compressor body, or the operating condition cannot be maintained and the inverter cannot be continuously operated. The operation can be continued by an emergency operation by directly driving the electric motor. Therefore, the supply of the compressed gas is not interrupted.

[Brief description of drawings]

FIG. 1 is a system diagram of a first embodiment of the present invention.

FIG. 2 is a system diagram of a second embodiment of the present invention.

FIG. 3 is a system diagram of a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Compressor, 2 ... Compressor main body, 3 ... Electric motor, 4 ... Inverter, 5 ... Control device, 6 ... Commercial AC power, 7 ... Power switching device, 8 ... Bypass power line, 9 ... Signal line, 11 ... Suction port ,
12 ... Discharge port, 13 ... Air cleaner, 14 ... Suction throttle valve, 15 ... Feedback pipe, 16 ... Discharge pipe, 21
… Pressure sensor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyuki Matsuda 390 Muramatsu, Shimizu City, Shizuoka Prefecture Hitachi Ltd. Air Conditioning Systems Division

Claims (1)

[Claims] 1. A screw compressor having a screw compressor main body, an electric motor for driving the screw compressor, an inverter for supplying frequency-variable electric power to the electric motor, and a control means for instructing an output frequency to the inverter. A bypass power line that directly supplies commercial power to the electric motor without passing through the inverter, and a power switch that selects one of the inverter and the bypass power line as a power supply unit to the electric motor, The inverter-driven screw compressor is characterized in that the inverter has a function of diagnosing an abnormality and a function of outputting information indicating occurrence of an abnormality, and means for operating the power switching device according to the information.