JP2001016884A - Method for controlling prevention of overcurrent accident in motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent tripping of a motor and continue its operation without causing damages to the motor or machines by, if it is predicted that the speed will be reduced abruptly, lowering the current target value given to the motor to prevent produced torque from exceeding an allowable value. SOLUTION: A current regulator 30 calculates a target voltage Vt to match an actual current Ia, detected through a current converter 28 with a target current It' outputted from a current limiter 26. The result of calculation is inputted to a power converter 34 via a gate pulse generator 32, and a motor terminal voltage V as a target is produced. Such a side guide drive device 20 is further provided with a load torque estimator 40, which estimates a load torque from the produced torque and speed of a motor 14 and a current target interrupter 42, which when the load torque estimated by the load torque estimator 40 exceeds a prescribed value, interrupts the target current It' inputted to the current regulator 30 and to set it to zero.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent accident prevention control method for a motor, and more particularly to a method for preventing a motor power supply from tripping when a load torque suddenly increases due to a collision with a material or the like. The present invention relates to an overcurrent accident prevention control method for a motor.

[0002]

2. Description of the Related Art When a machine such as an extractor of a heating furnace or a guide of a rolling mill is driven by an electric motor, the speed of the electric motor is controlled in order to drive these at a desired speed.

In normal speed control, the target speed of the motor is compared with the actual speed, and if there is a difference, the target speed of the motor is adjusted and the target value of the generated torque of the motor is compared with the actual value. And a torque (current) control system that adjusts the generated voltage of the power supply and the like so that both become equal.
When the load torque increases, the actual speed decreases. Therefore, the torque target is increased to match the speed with the target. When a load torque exceeding the allowable torque is generated, a limiter is provided to protect the electric motor and the mechanical device so as not to generate an excessive torque (current).

However, if the load torque increases suddenly due to a collision with a material or the like, a so-called overcurrent accident occurs, in which the limiter cannot completely suppress the load torque and the generated torque of the electric motor exceeds an allowable value. When such a situation occurs, the motor power supply is forcibly shut down (called a trip) to protect the motor and the machine.

[0005]

Therefore, it takes time to investigate the cause and restart the operation again. Further, in the worst case, there is a problem that the electric motor or the machine may be damaged by a sudden stop due to a trip.

In order to solve such a problem, Japanese Utility Model Registration No. 2522769 discloses that when controlling a strip winding motor, the motor current value is fed back to calculate the current degree of overload. Determines whether the strip can be wound within the motor's maximum overload capacity and, if possible, winds the strip at the current set tension and speed, while winding the strip within the maximum overload capacity If it is determined that it is not possible, the tension at which the maximum overload capacity is calculated at the end of the winding of the strip is calculated, and the set tension is automatically corrected, so that the motor is not tripped. It is described that the performance of the motor is maximized, but it could not be applied to anything other than tension control during strip winding.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and it is an object of the present invention to prevent a trip of an electric motor and to continue the operation without damaging the electric motor or the machine. And

[0008]

SUMMARY OF THE INVENTION According to the present invention, a load torque is estimated from a generated torque and a speed of an electric motor, and when the estimated load torque is expected to increase rapidly and the speed is suddenly decreased, the motor is connected to the motor. The object of the present invention is to solve the above problem by lowering the target current value to prevent the generated torque from increasing beyond an allowable value.

The load torque is estimated from the total moment of inertia of the motor and the load, the rate of change in speed, and the actual current.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings.

In this embodiment, as shown in FIG.
Side guide driving device 2 for driving a side guide 12 for guiding a horizontal position of the motor 0 by a DC motor 14.
0 applies the present invention.

In the side guide driving device 20, a torque (current) target It necessary for matching the speed target St with the actual speed Sa detected by the speed sensor 22 is calculated by the speed adjuster 24. The result is the current target It
Output as This current target It is input to the current regulator 30 via the current limiter 26 so as not to generate a torque exceeding a limit value determined by the characteristics of the drive system and the load (side guide 12). In the current regulator 30, the current record Ia detected by the current converter (CT) 28
To the current target It 'output from the current limiter 26 to calculate the voltage target Vt. The result is input to the power converter 34 via the gate pulse generator 32, and the target motor terminal voltage V is generated.

In the present invention, a load torque estimator 4 for estimating the load torque from the generated torque and speed of the electric motor 14 is provided for the side guide drive device 20 in the present invention.
0, a current target breaker 42 for interrupting the current target It 'input to the current regulator 30 to zero when the load torque estimated by the load torque estimator 40 exceeds a predetermined value; It has.

The torque load estimator 40 calculates a load torque T
Using the relationship of the following equation (1) or (2) between load, the rotation speed N, and the motor generated torque Tmot, the estimated torque actual value T to load is obtained by an observer, a differential filter, or the like.

J · (dN / dt) = Tmot−Tload = K1 · I−Tload (1) Tload = J · (dN / dt) + K1 · I (2)

Here, J is the total moment of inertia of the motor and the load, and K1 is a constant.

The reason why the observer and the differential filter are used is that the equation (1) or (2) has a differential term of the speed N, and cannot be used as it is due to noise or the like.

When the following relationship is established, the current target breaker 42 sets the current target It to zero.

T〜load> K 2 · T〜mot (3)

Here, K2 is a constant determined by the estimation accuracy of T to load, and T to mot is the upper limit of the torque of the motor.

The operation will be described below with reference to FIG.

FIG. 2A shows a time change of the speed and the current when the slab 10 collides while the opening degree of the side guide 12 is changed in the closing direction. At time t1, it collides with the slab 10, and the rotational speed of the motor rapidly decreases.

FIG. 2B shows a current change when the present invention is not used. Although the speed is reduced by the collision of the slab 10, the current target It does not change immediately due to the response delay of the current regulator 30. However, the current result Ia increases according to the following equation.

N = K 3 · (VIR) (4)

Here, K3 is a constant, and R is the electric resistance of the motor circuit.

More specifically, the current target It starts to rise from time t2, reaches the current limit value Im at time t3, and becomes constant. On the other hand, the actual current Ia is expressed by the terminal voltage V
Rise, and the rotation speed N is zero, so that it keeps rising. The current regulator 30 is used to reduce the current performance.
Although the terminal voltage V is lowered, the normal response cannot be made in time, and finally reaches the overcurrent value In at the time t4. For protection, the power supply is forcibly shut off and a trip state occurs.

FIG. 2C shows a current change when the present invention is applied. At time t2, the current target It slightly increases, but at time t3, the current target It is cut off, and the current result Ia also decreases. As a result, even when a collision occurs, an overcurrent accident does not occur and a trip is eliminated.

In this embodiment, when the load torque suddenly increases, the current target value is set to zero by the current target circuit breaker 42, so that the configuration is simple. In addition, it is also possible to reduce the current target to a small value other than zero. Further, instead of the current target circuit breaker 42, the current regulator 3
The output of 0 may be cut off, or the pulse of the gate pulse generator 32 may be stopped.

In the present embodiment, a DC motor is used. However, the application of the present invention is not limited to this, and the present invention can be similarly applied to a variable speed device using an AC motor.
It is apparent that the present invention can be similarly applied to a drive device of another machine other than the side guide drive device, such as an extractor of a heating furnace.

[0030]

According to the present invention, an overcurrent accident can be prevented and damage to the motor and mechanical system can be prevented even when the load torque suddenly increases and cannot be suppressed by a torque limiter of the motor. It is possible to continue the operation without causing any trouble.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a side guide driving device to which the present invention is applied.

FIG. 2 is a diagram showing a comparison of a time change of a speed and a current when a slab collides while the opening degree of a side guide is changed to a closing direction in a conventional example and an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Slab 12 ... Side guide 14 ... DC motor 20 ... Side guide drive device 22 ... Speed sensor 24 ... Speed adjuster 26 ... Current limiter 28 ... Current converter (CT) 30 ... Current adjuster 32 ... Gate pulse generator 34 ... power converter 40 ... load torque estimator 42 ... current target breaker

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02P 5/00 H02P 5/00 UXP F term (Reference) 5G004 AA05 AB02 BA04 DA01 EA01 5G044 AA01 AA07 AC02 AE01 CA01 CA07 CA11 CE08 5H550 AA03 AA20 BB08 DD01 GG03 GG05 JJ04 JJ11 JJ23 JJ26 LL01 LL22 LL32 MM02 MM04 5H571 AA05 AA20 BB07 GG02 GG04 HA11 HB01 HD03 JJ04 JJ23 JJ26 JJ28 LL28

Claims (2)

[Claims] A load torque is estimated from a generated torque and a speed of a motor, and when the estimated load torque is expected to increase rapidly and the speed is suddenly reduced, a target current value to be applied to the motor is reduced. And preventing the generated torque from exceeding an allowable value, thereby preventing an overcurrent accident of the motor. 2. The method according to claim 1, wherein the load torque is obtained by calculating a total moment of inertia of a motor and a load, a rate of change in speed, and
An overcurrent accident prevention control method for an electric motor, characterized by estimating from an actual current.