JPH06351294A - Crane driving method - Google Patents

Abstract

PURPOSE:To suppress current oscillation when a crane is driven. CONSTITUTION:A driver for crane employing a V/F control inverter 2 is equipped with an oscillation detector 5 for detecting the periodical variation of current of a motor M for driving the crane. An electromagnetic brake Br for the crane driver generates brake force based on an oscillation current detection signal delivered from the detector 5 and increases the load torque of the motor M temporarily. Consequently, slip of the motor is increased and the oscillation of current is suppressed. The current oscillation is suppressed positively by detecting the oscillation current of the driving motor M, generating the brake force from the electromagnetic brake Br based on the detection signal and temporarily increasing the load torque of the motor M thereby increasing the slip of the motor M.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a squirrel-cage induction motor V /
The present invention relates to a crane driving method using an F control inverter, and more particularly to prevention of instability of a drive system (pulsation of electric motor torque, vibration of load) due to vibration of electric motor current during low frequency driving.

[0002]

2. Description of the Related Art FIG. 2 shows a driving procedure of a squirrel cage induction motor using a conventional V / F control inverter. The figure shows the applied voltage V
And rated V / F with constant V / F ratio depending on power supply frequency F
A pattern A is shown, and in a synchronous motor, the pattern is usually preset and the motor is driven.

[0003]

In such V / F constant control driving, it is said that there is an unstable range B shown in the figure, and when an unstable phenomenon appears, the current oscillates, and this oscillation As a result, the torque may also pulsate and the motor and load may vibrate. If the vibration is large and dangerous, there is a drawback that you cannot drive. An example of current oscillation is shown in FIG. The figure is a current-time relationship diagram. When pulsation occurs, the current fluctuates periodically as shown in the figure.

According to the present invention, when the above current oscillation occurs,
It is an object of the invention to suppress the phenomenon and prevent operation failure due to instability of the drive system (electric motor, load, inverter).

[0005]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and in a V / F control inverter drive device, an oscillating current detector for detecting a periodic fluctuation of a current of a driven electric motor. Based on the oscillating current detection signal from this detector, during the oscillating current detection period, a braking force is generated in the electromagnetic brake for deceleration / stop attached to the crane drive device to temporarily increase the load torque of the electric motor. Then, the gist is to suppress the vibration of the current by increasing the slip of the electric motor.

[0006]

When the current vibration occurs, the load of the electric motor is increased by the electromagnetic brake according to the amplitude of the vibration current. As a result, slippage increases, which suppresses current oscillation of the electric motor.

[0007]

[Embodiment] It is known that the current oscillation of the electric motor appearing in the unstable range B in FIG. 2 is smaller in the one having a large secondary resistance of the squirrel-cage induction motor (that is, the one having a large slip) (for example, Naohiko Ueyama) Author "New Drive Electronics" published by P87 Densho Shoin. Since the slip of the electric motor has a characteristic of becoming larger as the load increases, when the current oscillation appears, the load may be temporarily increased to increase the slip. However, in the case of a crane, the load size is constant, and the load size cannot be changed during operation. Therefore, the braking force of the electromagnetic brake for deceleration / stop connected to the electric motor for driving the crane is temporarily used as the electric motor load.

The braking force of this electromagnetic brake has the ability to hold the rated load of the electric motor, but a smaller braking force is required to increase the slip of the electric motor. Therefore, the exciting current of the electromagnetic brake is reduced to reduce the braking force. To adjust the amount of slip increase.

The crane driving method of the present invention applies this principle, and as shown in FIG.
Is equipped with a V / F control inverter 2 and an excitation power supply device 3 for an electromagnetic brake Br coupled to the drive motor M.
An oscillating current detector 5 is provided in the output circuit 4 from the F control inverter 2 to the drive motor M. An output corresponding to the amplitude of the electric vibration by the detector 5 is applied to the exciting power supply device 3 as a control signal. The power supply device 3 emits an exciting current according to the control signal, and changes the braking force for braking the rotating electric motor M according to the magnitude of the exciting current. Suppressing the rotation of the electric motor with an external braking force such as an electromagnetic brake is the same as increasing the load torque for the electric motor, so slippage increases.

The magnitude of the exciting current has an upper limit set in advance depending on the motor current due to the increase in load torque, that is, the allowable overcurrent of the inverter current and the allowable overload of the motor.

In the above structure, as an example, as shown in FIG. 4, the operation is performed at a frequency fa (for example, 10HZ), the output torque at that time is T1, and the slip generated with respect to the load torque Ta is S1. At this time, it is assumed that the electric current to the electric motor M is vibrated. This oscillating current is detected by the detector 5 in FIG. 1 and a control signal corresponding to the amplitude is applied to the exciting power supply device 3. The power supply device 3 applies a corresponding exciting current to the electromagnetic brake, whereby a required braking force is generated in the electromagnetic brake, and when the torque is Tb, it overlaps with the load torque Ta for the electric motor M. Torque increases, and the motor slip increases from S1 to S2.
This suppresses the current oscillation.

Next, the increase in load torque during acceleration will be described with reference to FIG. Motor drive frequency (f)
If current oscillation occurs during operation at fa (for example, 10 HZ) while increasing according to the pattern A in which V / F is constant in FIG. 2, the torque Tb due to the electromagnetic braking force becomes the load torque Ta as described above. In addition, increasing the slip from S1 to S2 is the same.

Since this current oscillation is expected to continue during the unstable range B in FIG. 2, the torque Tb generated by the electromagnetic braking force is generated until the frequency reaches a preset frequency such as Fb (for example, 20HZ). The acceleration frequency Fb (20H
When Z) is reached, the excitation current supply to the electromagnetic brake is stopped and the torque Tb generated by the braking force is released. The output torque when operating at this frequency Fb is indicated by T2, and a slip S4 occurs with respect to the load torque Ta, and a slip when the brake torque Tb due to the electromagnetic brake is overlapped is S3.

As a result, the torque applied to the electric motor M becomes only the load torque Ta, and it decreases from the slip S3 to S4, and the slip (S) corresponding to the original load torque Ta (S
It is operated in 4). If current oscillation is still detected at this time, the electromagnetic brake is excited again to increase the load torque and increase the slip.

At this time, the maximum limit of the frequency for generating the braking force is set to f = 30HZ, and f = 30HZ
The load torque is increased according to the current oscillation up to, but the electromagnetic brake is not excited when the frequency is higher than that.

[0016]

As described above, according to the present invention, the periodic fluctuation of the electric current of the drive motor is detected by the oscillating current detector, and the braking force is generated in the electromagnetic brake based on the detection signal to cause the load torque of the electric motor. Temporarily increase
As a result, the slip of the electric motor is increased, so that the oscillating current can be surely suppressed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an inverter drive device for implementing the method of the present invention.

FIG. 2 is an explanatory diagram of an unstable range in which current oscillation occurs in motor operation according to a rated V / F ratio.

FIG. 3 is an explanatory diagram showing an example of current oscillation.

FIG. 4 is a graph showing a torque-slave relationship.

[Explanation of symbols]

 1 Crane drive circuit 2 V / F control inverter 3 Excitation power supply device 4 Output circuit 5 Vibration current detector M Electric motor Br Electromagnetic brake

Claims (1)

[Claims] 1. A drive device for a crane driven by using a V / F control inverter, comprising an oscillating current detector for detecting a periodic fluctuation of a current of a driven electric motor, and detecting an oscillating current from this detector. During the oscillating current detection period based on the signal, the load torque of the electric motor is temporarily increased by generating a braking force in the electromagnetic brake for deceleration / stop attached to the crane drive device, thereby increasing the slip of the electric motor. A method of driving a crane by a V / F control inverter, characterized in that the current vibration is suppressed by doing so.