JPS6358038B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a control device for an electric motor, and particularly to a control device for an electric motor that drives a reversible rolling mill.

[Technical background of the invention]

The DC motor that drives the reversible rolling mill is required to operate under extremely severe conditions, such as rapid acceleration/deceleration, forward/reverse operation, and large load fluctuations due to jamming of rolled material. Therefore, the control device for the electric motor that drives the reversible rolling mill is required to be able to obtain a stable current limit value against repeated loads. For this reason, speed control with current control in a minor loop is generally employed.

FIG. 1 is a system diagram of a conventional control device for a rolling mill drive motor. The rolling roll 1 is driven by an electric motor 2. A tachometer generator 3 is attached to the electric motor 2, and the rotational speed is detected by this.
A field current is supplied to the field 4 for the electric motor 2 from a field current control device 5 . The armature current of the motor 2 is supplied by a thyristor power supply 6 and detected by a current detector 7. The thyristor power supply device 6 is controlled by a current control device 8. The output of the tachometer generator 3 and the speed reference 10 are input to the speed control device 9, and a current reference value is output based on the deviation thereof. This current reference value is limiter 1
1 to the current control device 8. In addition to the current reference value via the limiter 11, the output of the current detector 7 is also input to the current control device 8, and the thyristor power supply device 6 is controlled based on the deviation. Further, the field current control device 5 has a function of weakening the field magnetic flux when the voltage of the electric motor 2 becomes close to the rated value, a so-called automatic field weakening function. The limiter 11 limits the current reference value, which is the output voltage of the speed control device 9, and controls the armature current to be below a permissible value.

In such a conventional control device, if an operation is performed in which the effective value of the armature current exceeds the rated value, the temperature of the motor 2 may exceed the allowable value, and in such a case, the thermal relay 12 A method is adopted in which the temperature of the electric motor 2 is detected and the operation is stopped.

[Problems with background technology]

As mentioned above, conventional control devices protect the motor by stopping operation when it detects that the temperature of the motor exceeds a permissible value. The loss is huge. Therefore, it is desirable that the electric motor that drives the reversible rolling mill be protected without stopping its operation.

Furthermore, an increase in the temperature of the motor adversely affects commutation, causing a local temperature increase in the commutator and brushes. A local temperature increase in the brush causes the brush to become locally red hot, and current is further concentrated in the locally red hot part of the brush made of negative resistance carbon, which further increases the local temperature increase. It will spur you on. In this way, the cause of poor rectification repeats and expands in a vicious cycle, and eventually the brushes end up being locally burnt out. Conventional temperature monitoring of electric motors is
Although methods such as RMS monitoring have been used to monitor the temperature of the entire motor, such methods cannot prevent temperature increases due to local heating. For this reason, in the conventional method, the RMS value has to be kept small, but doing so has the disadvantage that the motor cannot be used near its capacity limit.

[Purpose of the invention]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a control device for a rolling mill driving electric motor that protects the electric motor without stopping operation and allows maximum efficiency of rolling operation.

[Summary of the invention]

The feature of the present invention is that the time required for rolling work is predicted before the rolling work, the motor temperature rise value within that time is predicted and calculated, and if the value exceeds the motor temperature rise allowable value, the actual work is carried out. limits the motor current so that it does not exceed this tolerance, and
The present invention is characterized in that the control device for the rolling mill drive motor is configured to perform control such as changing the rolling schedule using this current limit value.

[Embodiments of the invention]

The present invention will be described in detail below based on illustrated embodiments. In the following figures, the same elements as those shown in FIG. 1 are denoted by the same reference numerals, and their explanations will be omitted.

FIG. 2 is a system diagram showing one embodiment of the present invention. The temperature calculator 13 inputs the motor current value 20 flowing through the motor 2, calculates the current motor temperature _TACT based on this input, and outputs this value as the current motor temperature signal 22. The current motor temperature T _ACT is
Updated every time the motor current value is sampled, the formula
It is obtained using the calculation formula (1).

Here, T _ACT (n): Current temperature of the motor (at the time of n-th sampling) T _ACT (n-1): Current temperature of the motor at the time of previous calculation I: Motor current value K: Temperature conversion coefficient T: Time constant ts : Temperature calculation sampling time T _AMB : Ambient temperature.

Next, the allowable current limit calculator 15
3 and the predicted rolling time signal 21 from the rolling schedule calculator 17.
and a motor temperature rise permissible value 23 as inputs, and outputs a motor permissible current limit signal 24. The calculations performed by this allowable current limit calculation unit 15 will be described below. First, the motor temperature T _co at the end of rolling
is expressed by equation (2).

Here, T _ACT : Current temperature of the electric motor K ₁ : Temperature conversion coefficient i _K : Allowable current limit value of the electric motor T ₁ : Time constant t ₁ : Predicted rolling time. If the allowable value of motor temperature rise is T _R , then
The condition for ensuring that the motor temperature T _co at the end of rolling does not exceed this allowable value is expressed by equation (3).

T _R > T _co ...(3) By substituting equation (2) into equation (3) and considering i _K , equation (4) is obtained.

The allowable current limit calculator 15 performs a calculation based on equation (4), and determines whether the rated current limit value of the motor exceeds the value on the right side of equation (4). If it exceeds the limit, the allowable current limit signal 24 is set to the limiter 1 in order to limit the allowable current limit value i _K to satisfy equation (4).
Output to 1. Note that a temperature sensor may be used instead of the temperature calculator 13 to capture the current temperature of the temperature-wise weakest part of the motor, and the output signal from the temperature sensor may be used as the motor current temperature signal 22.

Since the armature current is limited by the allowable current limit value i _K , the motor torque is also limited. The rolling schedule calculator 17 is an element provided to deal with such torque limitations, and changes the motor rotation speed based on the relationship between motor torque, armature current, and motor rotation speed, and changes the motor rotation speed to achieve the highest This is a device that controls the rolling schedule to achieve an economical rolling schedule. In the case of a shunt-wound DC motor, the relationship between motor torque, armature current, and motor rotation speed is expressed by equation (5).

T=K ₂ I _a /N ...(5) Here, K ₂ : Coefficient T: Motor torque [Kg・m] I _a : Armature current [A] N: Motor rotation speed [rpm] (Base speed above).

Now using a shunt-wound DC motor as a drive motor,
The operation of the embodiment when the speed standard is also compensated by the rolling schedule calculator 17 will be described with reference to FIG. For example, assume that the current rolling schedule is set to motor rotation speed N ₁ , motor torque T ₁ , and predicted rolling time t ₁ . The allowable current limit calculator 15 calculates the allowable current limit value in this state, and this calculated value i _K1 is input to the limiter 11 and the rolling schedule calculator 17. Limita 1
1 gives upper and lower limit values to the current reference given from the speed controller 9 to the current controller 8 based on i _K1 . Also, the rolling schedule calculator 17
is a calculation that corrects the motor rotation speed N to an appropriate value using equation (5) so that the necessary rolling torque can be obtained even when the armature current is limited by the calculation value i _K1 . Do the following. As a result, the motor rotation speed is changed from the value K ₁ set in the initial schedule to the value N ₂ calculated using Equation 5.
Next, the rolling schedule calculator 17 calculates and obtains the predicted rolling time t ₂ corresponding to the new motor rotation speed N ₂ using the relational expression between the motor rotation speed N and the rolling time t shown in equation (6). , this value is fed back to the allowable current limit calculator 15.

t=K ₂ /N・f(l) ...(6) Here, K ₂ : Coefficient N : Motor rotation speed (rpm) t : Rolling time f(l) : Correction of predicted rolling length l to predicted rolling time It is a term.

By repeating the same process thereafter, it is possible to suppress the motor temperature T _co at the end of rolling to below the motor temperature rise allowable value T _R and to select a motor rotation speed N that is sufficient to always provide the necessary rolling torque. become. In this way, efficient rolling can be achieved without damaging the electric motor.

The above operation will be explained using the graph shown in FIG. 3 showing an example of calculation by the allowable current limit calculation unit. The upper graph in Figure 3 shows the motor rotation speed N and motor torque T when the allowable current limit value is taken as a parameter.
Indicates the relationship between Here, TN1, TN2, …TN5
shows the relationship when the allowable current limit values are i _K1 , i _K2 , ... i _K5 , respectively. Furthermore, T _A indicates the torque value required for rolling. The lower graph in FIG. 3 shows the relationship between the motor rotation speed N and the allowable current limit value. For example, if the current rolling schedule is motor rotation speed N ₁ ,
Assume that the motor torque T ₁ and the predicted rolling time t ₁ are set. The allowable current limit calculator 15 calculates the allowable current limit value i _K1 in this state. The torque value when limited by this i _K1 is the curve
This is the vertical coordinate value of point T ₁ corresponding to horizontal axis N ₁ on TN1. In order to increase the torque to the torque T _A required for rolling, the motor rotation speed N is the curve TN1 and the straight line T = T _A
is updated to N ₂ , which corresponds to the abscissa value of the intersection with
(Calculated by equation (5)) Next, the predicted rolling time _t1 is also updated (calculated by equation (6)), and this value is fed back to the allowable current limit calculator 15, so the allowable current limit value is also changed to _iK2. Updated. As a result, the torque becomes the ordinate value of point T ₂ , so the motor rotation speed increases again to the torque T _A required for rolling _.
will be updated. Similar operations are repeated thereafter.

In this example, common techniques for rolling operations are used, such as fixing the allowable current limit value at the time when the rolled material is caught in the rolling mill, and avoiding automatic rolling near the current limit value limit. It is necessary to create a system that reflects this.

Next, FIG. 4 shows a system diagram of an embodiment in which the speed reference and the reduction amount are also compensated.
In addition to the embodiment shown in FIG.
A rolling reduction control device 18 is provided, the predicted rolling time which is the output of the rolling schedule calculator 17 is inputted, and a control signal is outputted to the rolling roll 1 based on this,
Perform rolling control. In addition, the predicted rolling time which is the output of the rolling schedule calculator 17 is set to the speed standard 1.
It is input to the speed control device 9 as 0.

The operation of the embodiment having such a configuration will be explained using the graph shown in FIG. 5 showing an example of calculation by the allowable current limit calculation unit. Note that the symbol in Figure 5 is the third
It is similar to the figure. For example, assume that the initial setting rolling schedule is motor rotation speed N ₁ , predicted rolling time t ₁ , allowable current limit value i _K1 and set rolling amount △h ₁ , and the necessary rolling torque for the set rolling amount △h ₁ is T _A. . In this case, the motor torque calculated by the calculation becomes the ordinate value of point T _1. Therefore, since it also corresponds to the required rolling torque T _A , the motor rotation speed is changed from N ₁ to N ₂ by the rolling schedule calculator 17. will be updated to. Subsequently, the predicted rolling time t ₂ and the allowable current limit value i _K2 are calculated as updated values. Since the allowable current limit value is i _K2 , the motor torque is limited to the ordinate value T _B of point T ₂ . Here, when looking at the relationship between the rolling reduction amount Δh and the required rolling torque T _A to realize the rolling reduction, it becomes as shown in equation (7).

T _A = F(H)・P√・△ ...(7) F(H)=γ ₀ + γ ₁ H Here, T _A : Required rolling torque P : Load R : Roll radius H : Inlet side plate thickness △h : Reduction amount γ ₀ , γ ₁ : Constants. Therefore, the rolling schedule calculator 17 uses the relationship of equation (7) to calculate the rolling reduction amount Δh ₂ that makes the motor torque T _B the required rolling torque. This rolling reduction amount Δh ₂ is input to the rolling reduction control device 18, and the rolling roll 1 is controlled.

Here, if T _A > T _B , the required rolling torque is
The reduction amount △h corresponds to the change from T _A to T _B.
is reduced. For this reason, the predicted rolling extension decreases, and the predicted rolling time t ₂ becomes shorter than the predicted rolling time _{t 1} before the reduction in rolling reduction, and as a result, the allowable current limit value changes from i _K2 to i Increases to _K3 .
In this state, the motor rotation speed N ₂ , the reduction amount △h ₂ ,
For predicted rolling time t ₂ and permissible current limit value i _K3 ,
As shown in FIG. 5, the electric motor torque has a value on the ordinate of point T ₂ ', which is greater than the required rolling torque T _B and is ready for rolling. Therefore, in this example, the reduction amount △
By changing h once, rolling can be performed with the motor temperature T _co within the predicted rolling time being equal to or less than the motor temperature rise allowable value T _R .

Conversely, if T _A < T _B , rolling can be performed as is, so there is no need to make any changes.

〔Effect of the invention〕

As described above, according to the present invention, control is performed to change the rolling schedule when the predicted motor temperature rise value within the predicted rolling time exceeds the motor temperature rise allowable value. It is possible to perform control that protects the rolling stock and allows maximum efficiency of rolling operation.

Further, by adding an element for controlling the rolling speed and the amount of reduction according to the rolling schedule, changes in the rolling schedule for performing the above control can be minimized.

[Brief explanation of drawings]

Fig. 1 is a system diagram of a conventional control device for a rolling mill drive motor, Fig. 2 is a system diagram of an embodiment of a control device for a rolling mill drive motor according to the present invention, and Fig. 3 is an allowable current limit calculation. FIG. 4 is a system diagram of another embodiment of the control device for a rolling mill drive motor according to the present invention, and FIG. It is a graph showing another example. DESCRIPTION OF SYMBOLS 1... Roll roll, 2... Electric motor, 3... Tachometer generator, 4... Field, 5... Field current control device, 6... Thyristor power supply device, 7... Current detector, 8... ...Current control device, 9...Speed control device,
10... Speed standard, 11... Limiter, 12...
Thermal relay, 13...Temperature calculator, 15...
Allowable current limit calculator, 17... Rolling schedule calculator, 18... Rolling down control device, 20... Motor current value, 21... Predicted rolling time signal, 22... Motor current temperature signal, 23... Motor temperature rise Allowable value, 24...Motor allowable current limit signal.

Claims (1)

[Claims] 1. A current control device that controls an armature current of a motor for driving one of a pair of rolling rolls, a speed control device that outputs a current control signal according to a set speed standard, A control device for a rolling mill driving electric motor, comprising a limiter that inputs the current control signal, applies a limit to it, and outputs it to the current control device, wherein the temperature of the electric motor during rolling operation is controlled based on the current of the electric motor. A temperature calculator that predicts and calculates
an allowable current limit calculator that receives the temperature, predicted rolling time, and allowable motor temperature rise value obtained by the predictive calculation and outputs a current limit signal to the limiter; a rolling schedule calculator for calculating a predicted rolling time and feeding it back to the allowable current limit calculator; A control device for an electric motor for driving a rolling mill, characterized in that the limiter is controlled so that the temperature thus obtained does not exceed the allowable temperature rise value of the electric motor. 2. A current control device that controls the armature current of a motor for driving one of a pair of rolling rolls, a speed control device that outputs a current control signal according to a set speed standard, and inputs the current control signal. and a limiter that outputs a limiter to the current control device, the control device for a rolling mill driving electric motor comprising: a temperature calculation for predicting and calculating the temperature of the electric motor during rolling operation based on the electric current of the electric motor; The vessel and
an allowable current limit calculator that receives the temperature, predicted rolling time, and allowable motor temperature rise value obtained by the predictive calculation and outputs a current limit signal to the limiter; a rolling schedule calculator that calculates a predicted rolling time by calculation and feeds it back to the allowable current limit calculator; and a roll-down control device that controls the amount of roll-down, and the current limit signal output from the allowable current limit calculator indicates that the temperature obtained by the predictive calculation during the predicted rolling time is the permissible rise in temperature of the electric motor. The electric motor for driving a rolling mill is characterized in that the limiter is controlled so as not to exceed a value, and the predicted rolling time, which is the output of the rolling schedule calculator, is inputted to the speed control device and used as a speed reference. control device.