KR102645551B1 - Apparatus for controlling inverter in forming machine system - Google Patents

Abstract

An inverter control method for a forging machine system is disclosed. The control method of one embodiment of the present invention is to control the frequency to decrease according to the result of proportional integral (PI) control of the difference between the reference level and the output current when the output current of the inverter exceeds a predetermined reference level, and the inverter's When the output current is less than the reference level and exceeds a predetermined ratio of the reference level, the frequency is reduced with a constant first slope.

Description

Inverter control device of forging machine system {APPARATUS FOR CONTROLLING INVERTER IN FORMING MACHINE SYSTEM}

The present invention relates to an inverter control device for driving a forging system.

In general, a forging machine is a machine that creates a certain shape by hitting a metal material with a hammer or applying pressure. In this forging machine, the inverter performs inching operation (clutch operation). During inclining operation, a large load is applied, and at this time, a large current is output. If this inching operation continues repeatedly, the speed does not reach the normal command speed and stops.

Figure 1 is an example diagram for explaining the inching operation of the forging machine inverter. In Figure 1, the yellow channel represents the output current, the green channel represents the frequency, and the pink channel represents the DC link voltage.

It can be seen that when the current rises above the suppression level during inching operation, the frequency falls at a certain speed, and when inclining operation is not performed, the frequency recovers slowly. If this inching operation continues continuously, there is a problem in that the frequency decreases and the return response time slows down, eventually leading to the operation stopping.

The technical problem to be solved by the present invention is to provide an inverter control device for a forging machine system that improves speed responsiveness when a large current is continuously applied during constant speed operation.

In order to solve the above technical problem, an inverter control method according to an embodiment of the present invention, which controls the frequency of the voltage output by an inverter including a DC link capacitor and a plurality of switching elements, includes the inverter. When the output current of is higher than a predetermined reference level, controlling the frequency to decrease according to the result of proportional integral (PI) control of the difference between the reference level and the output current; And when the output current of the inverter is less than the reference level and is more than a predetermined ratio of the reference level, it may include reducing the frequency with a constant first slope.

The inverter control method of one embodiment of the present invention may further include increasing the frequency with a constant second slope when the output current of the inverter is below a predetermined ratio of the reference level.

In one embodiment of the present invention, the step of controlling the frequency to decrease may reduce the frequency according to a limit set for the decrease time.

The inverter control method of one embodiment of the present invention may further include maintaining the frequency when the direct current link voltage rises above a predetermined reference voltage in the step of controlling the frequency to decrease.

The inverter control method of one embodiment of the present invention includes the steps of accelerating the inverter to increase the frequency at a constant third slope; And when the output current of the inverter is greater than a predetermined ratio of the reference level, the step of controlling the frequency to increase according to the result of proportional integral (PI) control of the difference between the reference level and the output current may be further included. there is.

An inverter control method according to an embodiment of the present invention includes operating the inverter at a constant speed at a constant frequency; and maintaining the constant frequency when the output current of the inverter exceeds a predetermined ratio of the reference level.

In one embodiment of the present invention, in the controlling step, when the output current of the inverter is above a predetermined reference level, the speed may be controlled to decelerate at a plurality of slopes.

The present invention as described above has the effect of improving speed responsiveness by reducing the frequency according to the PI control result of the difference between the output current and the reference level.

Figure 1 is an example diagram for explaining the inching operation of the forging machine inverter.
Figure 2 is a configuration diagram schematically explaining a forging system to which an embodiment of the present invention is applied.
Figure 3 is a configuration diagram schematically explaining an inverter according to an embodiment of the present invention.
Figure 4 is a graph for explaining current suppression when an overcurrent occurs during acceleration according to an embodiment of the present invention.
Figure 5 is a graph of an embodiment to explain current suppression when an overcurrent occurs during constant speed according to an embodiment of the present invention.
Figure 6 is a flowchart for explaining a conventional inverter control method when overcurrent occurs during acceleration.
Figure 7 is a flowchart illustrating an inverter control method when an overcurrent occurs during acceleration according to an embodiment of the present invention.
Figure 8 is a flowchart for explaining a conventional inverter control method when overcurrent occurs during constant speed.
Figure 9 is a flowchart illustrating an inverter control method when an overcurrent occurs during constant speed according to an embodiment of the present invention.
Figure 10 is for explaining the output waveform by the inverter control method of one embodiment of the present invention.

In order to fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described with reference to the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and various changes can be made. However, the description of this embodiment is provided to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the present invention of the scope of the invention. In the attached drawings, components are shown enlarged in size for convenience of explanation, and the proportions of each component may be exaggerated or reduced.

When a component is described as being ‘on’ or ‘adjacent to’ another component, it should be understood that it may be in direct contact with or connected to the other component, but that another component may exist in between. something to do. On the other hand, if a component is described as being 'right above' or 'in direct contact' with another component, it can be understood that there is no other component in the middle. Other expressions that describe the relationship between components, such as 'between' and 'directly between', can be interpreted similarly.

Terms such as 'first' and 'second' may be used to describe various components, but the components should not be limited by the above terms. The above terms may be used only for the purpose of distinguishing one component from another. For example, a 'first component' may be named a 'second component' without departing from the scope of the present invention, and similarly, a 'second component' may also be named a 'first component'. You can.

Singular expressions include plural expressions unless the context clearly dictates otherwise. Terms such as 'include' or 'have' are used to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, including one or more other features or numbers, It can be interpreted that steps, operations, components, parts, or combinations thereof can be added.

Unless otherwise defined, terms used in the embodiments of the present invention may be interpreted as meanings commonly known to those skilled in the art.

Hereinafter, the present invention will be described in detail by explaining preferred embodiments of the present invention with reference to the accompanying drawings.

Figure 2 is a configuration diagram schematically explaining a forging system to which an embodiment of the present invention is applied.

As shown in the drawing, in the forging system of one embodiment of the present invention, when the operation terminal is turned on at the control panel (not shown), the inverter 1 drives the motor 2, and the motor 2 The belt 3 rotates by driving, and the flywheel 4 connected to the belt 3 rotates accordingly.

In this state, when the control panel starts the inclination operation, the wheel 6 engaged with the gear disposed in a position opposite the clutch 5 operates to process the screw or bolt.

During inclining operation, a large load is applied to the inverter (1), which causes a large current to flow in the inverter (1). As a result, the inverter 1 performs a protection operation, so the frequency slowly decreases as shown in 1A in FIG. 1, and as a result, the current gradually decreases. Afterwards, as in 1B, the frequency gradually increases again and restarts. However, there was a problem in that the response time for frequency reduction and recovery became slow due to continuous inching operation, making driving itself impossible after the inching operation continued.

One embodiment of the present invention is intended to solve this problem and improve speed responsiveness even when a large current is applied during constant speed operation in a forging machine system.

Figure 3 is a configuration diagram schematically explaining an inverter according to an embodiment of the present invention.

As shown in the figure, the inverter 1 receives three-phase AC power, the rectifier 10 converts this AC power into DC voltage, and the DC link capacitor 20 smoothes the DC voltage to produce a DC link voltage. After saving, the inverter unit 30 can convert the direct current link voltage into an alternating current voltage of a predetermined size and frequency and apply it to the electric motor 2.

The control unit 40 usually controls the inverter 1 using the Variable Voltage Variable Frequency (VVVF) method or vector control method. In one embodiment of the present invention, the control unit 40 controls the inverter 1 using the VVVF method. It will be possible to control the inverter unit 30 of the inverter 1.

That is, the control unit 40 can control the magnitude and frequency of the voltage output by the inverter 1 by controlling the on or off of a plurality of switching elements.

Figure 4 is an example graph for explaining current suppression when overcurrent occurs during acceleration according to an embodiment of the present invention. Figure 4 (a) is based on the prior art, and (b) is an embodiment of the present invention. It is according to example.

As shown in (a) of FIG. 4, during acceleration of the inverter where the frequency increases at a constant slope (4A), when the current increases to a range of 90% or more of the reference level, the PI of the difference between the reference level and the output current It accelerates to the frequency (4C) corresponding to the control output, and when it exceeds the standard level, the frequency decreases at a certain slope (4C). As a result, when the output current becomes smaller than the reference level and is more than 90% of the reference level, it decelerates to the frequency (4D) corresponding to the PI control output of the difference between the reference level and the output current, and when the output current becomes less than that, It accelerates at a constant slope (4E).

According to one embodiment of the present invention, as shown in Figure 4 (b), during inverter acceleration where the frequency increases at a constant slope (4A), when the current increases to a range of 90% or more of the reference level, the reference level and output It accelerates to the frequency (4G) corresponding to the PI control output of the difference in current, and when the reference level is exceeded, the frequency is reduced to the frequency (4I) corresponding to the PI control output of the difference between the reference level and the output current. That is, according to one embodiment of the present invention, when the output current becomes greater than the reference level, the frequency is not controlled to decrease at a constant slope, but the frequency is reduced according to the PI control output of the difference between the reference level and the output current, By this, the frequency can be lowered much faster.

At this time, in order to prevent overvoltage tripping during deceleration, the control unit 40 in one embodiment of the present invention may set a standard for the DC link voltage. In other words, when the DC link voltage rises above the reference voltage, the control unit 40 temporarily increases the deceleration to keep the decelerated frequency constant, and when it falls below the reference voltage, the control unit 40 returns the PI of the difference between the reference level and the output current. The frequency can be reduced to the frequency (4I) corresponding to the control output.

Afterwards, if the output current becomes smaller than the standard level and is more than 90% of the standard level, the frequency can be decelerated at a certain slope (4J), and if the output current becomes lower than that, it can be accelerated up to the command frequency at a certain slope (4K). there is.

Figure 5 is a graph for explaining current suppression when an overcurrent occurs during constant speed according to an embodiment of the present invention. Figure 5 (a) is based on the prior art, and (b) is an embodiment of the present invention. It is according to example.

As shown in Figure 5 (a), during operation of the inverter with a constant frequency (5A), when the current increases to a range of 90% or more of the reference level, the frequency is maintained constant (5B), If the reference level is exceeded, the frequency is reduced at a certain slope (5C). As a result, when the output current becomes smaller than the reference level and is more than 90% of the reference level, it decelerates to the frequency (5D) corresponding to the PI control output of the difference between the reference level and the output current, and when the output current becomes less than that, It accelerates to the command frequency at a constant slope (5E).

According to one embodiment of the present invention, as shown in Figure 5 (b), when the current increases to a range of 90% or more of the reference level during operation of an inverter with a constant frequency (5F), the frequency remains constant. It is maintained (5G), and when it exceeds the reference level, the frequency is reduced to the frequency (5I) corresponding to the PI control output of the difference between the reference level and the output current. That is, according to one embodiment of the present invention, when the output current becomes greater than the reference level, the frequency is not controlled to decrease at a constant slope, but the frequency is reduced according to the PI control output of the difference between the reference level and the output current, By this, the frequency can be lowered much faster.

At this time, in order to prevent overvoltage tripping during deceleration, the control unit 40 in one embodiment of the present invention may set a standard for the DC link voltage. In other words, when the DC link voltage rises above the reference voltage, the control unit 40 temporarily increases the deceleration to keep the decelerated frequency constant, and when it falls below the reference voltage, the control unit 40 returns the PI of the difference between the reference level and the output current. The frequency can be reduced to the frequency (4I) corresponding to the control output.

Afterwards, if the output current becomes smaller than the standard level and is more than 90% of the standard level, the frequency can be decelerated at a certain slope (5J), and if the output current becomes less than that, it can be accelerated up to the command frequency at a certain slope (5K). there is.

Hereinafter, the operations of FIGS. 4 and 5 above will be described in more detail with reference to the drawings.

Figure 6 is a flowchart for explaining a conventional inverter control method when overcurrent occurs during acceleration.

The control unit of a conventional inverter continuously outputs the result (delFreq) of proportional integral (PI) control of the difference between the reference level and the output current (S61), and when accelerating at a frequency of a certain slope (4A), the output current is at the reference level. If it exceeds 90% (S62), the frequency is increased according to the PI control result (delFreq) (4B) of the difference between the reference level and the output current (S63).

If the output current continues to rise and becomes greater than the reference level (S64), the control unit controls the frequency to decrease at a certain slope (4C) (S65), and due to the decrease in frequency, the output current is below the reference level and more than 90% of the reference level. When this happens (S66), the frequency is reduced according to the PI control result (delFreq) (4D) of the difference between the reference level and the output current (S67).

Afterwards, when the output current decreases below 90% of the reference level (S68), the frequency is increased at a constant slope (4E) until the command frequency is reached (S69).

However, according to this prior art, when the output current exceeds the reference level, it decreases at a certain slope, so there was a problem in that speed responsiveness was deteriorated.

FIG. 7 is a flowchart for explaining an inverter control method when an overcurrent occurs during acceleration according to an embodiment of the present invention, and shows a control method by the control unit 40 of the inverter 1 of FIG. 3.

As shown in the figure, the control unit 40 of one embodiment of the present invention can continuously receive the result (delFreq) of PI control of the difference between the reference level and the output current (S71). According to one embodiment of the present invention, it is shown that the result (delFreq) of temporarily controlling the difference between the reference level and the output current by PI is output in S71, but the control unit 40 of the present invention is not limited thereto. The result (delFreq) of PI control of the difference between the reference level and the output current can be continuously received.

PI control is a control method that outputs a magnitude proportional to the difference between the target level (reference level in one embodiment of the present invention) and the current position (output current in one embodiment of the present invention), and the current position is at the target level. This is a control method that operates by accumulating the residual deviation between the current position and the target level when approaching, thereby eliminating the deviation. The detailed description of PI control will be obvious to those skilled in the art to which the present invention pertains.

When the output current of the inverter 1 becomes 90% or more of the reference level when accelerating at a frequency of a certain slope (5A) (S72), the control unit 40 performs PI control on the difference between the reference level and the output current ( The frequency can be increased (S73) according to delFreq (5B). Referring to (b) of Figure 4, since the output current is constantly increasing (4P), it can be seen that the result (delFreq) of PI controlling the difference between the reference level and the output current gradually increases to a smaller size ( 4G). Meanwhile, in one embodiment of the present invention, it is explained as an example that the control unit 40 operates at 90% of the reference level, but it is not limited to this, and the operation level of the control unit 40 may be determined depending on the setting. There will be. Hereinafter, the level at which the control unit 40 operates will be described as 90% of the reference level.

If the output current continues to rise and becomes greater than the reference level (S74), the control unit 40 can control the frequency to decrease as a result of PI control (delFreq) (4I) of the difference between the reference level and the output current (S75). Referring to (b) of FIG. 4, it can be seen that the output current is slightly changing in the area where it becomes larger than the reference level, so the result (delFreq) of PI controlling the difference between the reference level and the output current is also changing somewhat ( 4I). At this time, the control unit 40 can set a limit for the reduction time.

At this time, although not shown, the control unit 40 may check the DC link voltage and, if the DC link voltage rises above a predetermined reference voltage, stop deceleration and maintain the frequency. Thereby, overvoltage tripping can be prevented.

Thereafter, when the output current is below the reference level and above 90% of the reference level due to a decrease in frequency (S76), the control unit 40 can reduce the frequency at a certain slope (4J) (S77).

Thereafter, when the output current is reduced to 90% or less of the reference level (S78), the control unit 40 can increase the frequency at a constant slope (4K) until it reaches the command frequency (S79). At this time, the control unit 40 can set the acceleration time upon frequency recovery, and the slope (4K) can be determined accordingly.

Figure 8 is a flowchart for explaining a conventional inverter control method when overcurrent occurs during constant speed.

The control unit of a conventional inverter continuously outputs the result (delFreq) of proportional integral (PI) control of the difference between the reference level and the output current (S81), and at constant speed at a constant frequency (5A), the output current is 90% of the reference level. If an abnormality occurs (S82), the frequency (5B) is maintained (S63).

If the output current continues to rise and becomes greater than the reference level (S84), the control unit controls the frequency to decrease at a certain slope (5C) (S85), and due to the decrease in frequency, the output current is below the reference level and more than 90% of the reference level. When this happens (S86), the frequency is reduced according to the PI control result (delFreq) (5D) of the difference between the reference level and the output current (S87). At this time, the control unit 40 can set a limit for the reduction time.

Afterwards, when the output current decreases below 90% of the reference level (S88), the frequency is increased at a constant slope (5E) until the command frequency is reached (S89).

However, according to this prior art, when the output current exceeds the reference level, it decreases at a certain slope, so there was a problem in that speed responsiveness was deteriorated.

FIG. 9 is a flowchart for explaining an inverter control method when an overcurrent occurs during constant speed according to an embodiment of the present invention, and shows a control method by the control unit 40 of the inverter 1 of FIG. 3.

As shown in the figure, the control unit 40 of one embodiment of the present invention can continuously receive the result (delFreq) of PI control of the difference between the reference level and the output current (S91). According to one embodiment of the present invention, it is shown that the result (delFreq) of PI control of the difference between the reference level and the output current is temporarily output in S91, but the control unit 40 of the present invention is not limited thereto. As already explained, the result (delFreq) of PI control of the difference between the reference level and the output current can be continuously received.

The control unit 40 can maintain a constant frequency (5G) when the output current during acceleration at a constant frequency (5F) becomes 90% or more of the reference level (S92).

If the output current continues to rise and becomes greater than the reference level (S94), the control unit 40 can control the frequency to decrease as a result of PI control (delFreq) (5I) of the difference between the reference level and the output current (S95). Referring to Figure 5(b), it can be seen that the output current is slightly changing in the area where it becomes larger than the reference level, so the result (delFreq) of PI controlling the difference between the reference level and the output current is also changing somewhat ( 5I).

At this time, although not shown, the control unit 40 may check the DC link voltage and, if the DC link voltage rises above a predetermined reference voltage, stop deceleration and maintain the frequency. Thereby, overvoltage tripping can be prevented.

Thereafter, when the output current is below the reference level and above 90% of the reference level due to a decrease in frequency (S96), the control unit 40 can reduce the frequency at a certain slope (5J) (S97).

Thereafter, when the output current is reduced to 90% or less of the reference level (S98), the control unit 40 can increase the frequency at a constant slope (5K) until it reaches the command frequency (S99). At this time, the control unit 40 can set the acceleration time upon frequency recovery, and the slope (5K) can be determined accordingly.

Figure 10 is for explaining the output waveform by the inverter control method of an embodiment of the present invention. In the figure, the yellow channel represents the output current, the green channel represents the frequency, and the pink channel represents the DC link voltage.

As shown in the figure, when the output current rises above the reference level, the frequency is quickly reduced, and even when the output current decreases below the reference level, the frequency is quickly recovered.

As such, according to one embodiment of the present invention, speed responsiveness can be improved by reducing the frequency according to the PI control result of the difference between the output current and the reference level.

Although embodiments according to the present invention have been described above, they are merely illustrative, and those skilled in the art will understand that various modifications and equivalent scope of embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention should be determined by the following claims.

1: Inverter 2: Motor
10: Rectifier 20: DC link capacitor
30: inverter unit 40: control unit

Claims (7)

A voltage output by an inverter including a rectifier unit that converts AC power to DC voltage, a DC link capacitor that smoothes the DC voltage and stores it as a DC link voltage, and an inverter unit that converts the DC link voltage by consisting of a plurality of switching elements. In the inverter control method for controlling the frequency of
When the output current of the inverter exceeds a predetermined reference level, controlling the frequency to decrease according to a result of proportional integral (PI) control of the difference between the reference level and the output current; and
An inverter control method comprising reducing the frequency with a constant first slope when the output current of the inverter is less than the reference level and is more than a predetermined ratio of the reference level.
According to paragraph 1,
The inverter control method further includes increasing the frequency with a constant second slope when the output current of the inverter is below a predetermined ratio of the reference level.
The method of claim 1, wherein the controlling step includes:
An inverter control method that reduces the frequency according to a limit set for the reduction time.
According to paragraph 1,
In the controlling step, when the direct current link voltage rises above a predetermined reference voltage, the inverter control method further includes maintaining the frequency.
According to any one of claims 1 to 4,
accelerating the inverter to increase frequency at a constant third slope; and
When the output current of the inverter is greater than a predetermined ratio of the reference level, the inverter further includes controlling the frequency to increase according to a result of proportional integral (PI) control of the difference between the reference level and the output current. Control method.
According to any one of claims 1 to 4,
Operating the inverter at a constant speed without slope; and
An inverter control method further comprising maintaining the constant frequency when the output current of the inverter exceeds a predetermined ratio of the reference level.
The method of claim 1, wherein the controlling step includes:
An inverter control method characterized in that when the output current of the inverter is above a predetermined reference level, the inverter is controlled to decelerate at a plurality of slopes.

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