JPH10127077A - Motor control method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To avoid tripping of an electric motor due to an increase in internal temperature during rolling and to obtain good thickness accuracy. A motor main circuit current I _M to a step-down motor 3 is provided.
The internal temperature of the electric motor 3 is estimated based on the above, and when the estimated internal temperature T (t) is equal to or higher than the caution temperature T _ALM , the temperature change rate α is obtained from the previous value and the current value of the internal temperature.
When the internal temperature is increasing, the internal temperature T
(T) and the temperature change rate α, the internal temperature is the maximum allowable temperature T
Estimate the allowable time β to reach _MAX, and
Is smaller, the current limit value i _LIM is set smaller.
Then, the current command value i based on the speed deviation ΔV of the electric motor 3
₀ is supplied to the electric motor 3 while being limited by the current limit value i _LIM . Therefore, the supply current to the electric motor 3 is limited and the generated torque is restricted, so that the increase in the internal temperature of the electric motor 3 is suppressed and the maximum allowable temperature T _MAX is avoided, and the electric motor 3 trips during rolling. Is prevented from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a motor used for a step-down motor of an electric screw-down device, for example, and more particularly to a method for controlling a motor when the motor is used in an overloaded state.

[0002]

2. Description of the Related Art Conventionally, in thickness control in hot rolling, a gauge meter type AGC (automatic thickness control) in which a gap between rolls is adjusted by an electric reduction device or a hydraulic reduction device.
Has been done. Generally, the hydraulic pressure reduction device has a higher AGC capability than the electric pressure reduction device. However, the hydraulic pressure reduction device is a technology that has been put into practical use in recent years (15 or 16 years ago) and has a high installation cost. Many rolling mills do not have this.

[0003] In the above-mentioned electric rolling machine, the gap between the rolls is adjusted by controlling the speed of the motor in accordance with the thickness deviation which is the difference between the target thickness and the gauge meter thickness, thereby eliminating the thickness deviation. Is adjusted as follows.

Normally, a rated torque that can always be output is determined for a motor, but it is possible to use the motor beyond the rated torque for a short time. The maximum torque that can be used beyond the rated torque is called an overload tolerance, and is about 250% in the case of a motor used in an electric screw-down device.

[0005] By using this overload capability, a large torque can be generated using a small-capacity motor. However, when the motor is used in an overloaded state, the motor is heated and the internal temperature rises, and the motor's internal temperature rises. The temperature may exceed the allowable temperature, and heating or burning may occur.
In order to avoid this, for example, a protection mechanism for estimating the internal temperature from the generated torque of the motor and tripping, that is, stopping when the value exceeds the allowable temperature of the motor is usually provided. ing.

[0006]

Generally, in AGC,
Feedback control is performed using a value obtained by multiplying a sheet thickness deviation, which is a difference between the target sheet thickness and the gauge meter sheet thickness, by a predetermined control gain as a roll reduction speed command value. Therefore, in order to improve the thickness accuracy, the control gain may be set to a large value within a range where the control does not become unstable. However, if the control gain is increased, the change in the speed command to the step-down motor increases, and as a result, the generated torque of the motor increases, so that the internal temperature of the motor increases and the temperature may exceed the allowable temperature of the motor. Get higher. For this reason, the electric motor trips during the thickness control, so that the thickness control becomes impossible or the rolling becomes impossible.

In order to avoid this, it is necessary to limit the control gain of the AGC to some extent, and there is a problem that the AGC capability is limited because the control gain is restricted.

Further, for example, as shown in a motor control method described in Japanese Patent Application Laid-Open No. 2-70280 proposed by the present applicant, when the speed of the motor is accelerating or decelerating, the range of the overload tolerance is set. And supply a current commensurate with the required torque.When the motor is operating at a constant speed, the motor must be set to a value within the range that does not cause overload even if the load is heavy and requires a large torque. There is a method of avoiding heating or tripping of the motor due to continuous overload of the motor by limiting the supply current of the motor.

However, in this method, at the time of constant speed operation, the current supplied to the motor is limited to a current value within a current range within a rated torque, so that a torque slightly larger than the rated value is generated, for example. Even in the case where a trip does not occur even when operating in an overload state, such as in a state, the current value is limited, so that there is a problem that the motor cannot be used effectively.

Therefore, the present invention has been made in view of the above-mentioned unsolved problem of the related art, and provides a motor control method capable of effectively operating the motor within a range where the motor does not trip. It is intended to be.

[0011]

According to a first aspect of the present invention, there is provided a method for controlling an electric motor, comprising detecting an increase in the internal temperature of the electric motor, and detecting a rapid rise in the internal temperature. , The current supplied to the electric motor is further limited.

According to the first aspect of the present invention, the rise state of the internal temperature is detected by, for example, detecting the internal temperature of the motor and detecting the rise rate of the internal temperature from the internal temperature at the previous detection. And, for example, when the current internal temperature is equal to or higher than a predetermined value, as the temperature rise of the internal temperature is sharper from the detected rising state, for example, as the rate of increase of the internal temperature is higher,
Assuming that the internal temperature of the motor is likely to reach the maximum allowable temperature, the supply current to the motor is further limited.
Therefore, the generated torque of the electric motor is suppressed, and the increase in the internal temperature of the electric motor is suppressed, so that the internal temperature does not reach the maximum allowable temperature.

According to a second aspect of the present invention, there is provided a method for controlling an electric motor, comprising detecting an internal temperature of the electric motor and a rate of increase of the internal temperature, and requiring caution that the internal temperature is lower than a maximum allowable temperature of the electric motor. When the temperature is within the temperature range, an allowable time until the internal temperature reaches the maximum allowable temperature is estimated based on the internal temperature and the rate of increase, and as the allowable time becomes shorter, the supply current to the electric motor is reduced. Is further restricted.

According to the second aspect of the present invention, the internal temperature of the electric motor is detected. For example, the rate of increase of the internal temperature is detected from the temperature increase per unit time of the internal temperature. And
When the detected internal temperature is within a cautionary temperature range preset as, for example, a value lower than the maximum allowable temperature of the electric motor, the internal temperature reaches the maximum allowable temperature based on the detected internal temperature and the rising rate. The permissible time until the current is estimated is estimated. The shorter the estimated permissible time is, the smaller the current supplied to the electric motor is limited. Therefore, the generated torque of the electric motor is suppressed, and the increase in the internal temperature of the electric motor is suppressed, so that the internal temperature does not reach the maximum allowable temperature.

Further, in the motor control method according to a third aspect of the present invention, the internal temperature is detected based on a current supplied to the motor. According to the third aspect of the invention, since the amount of heat generated by the motor is proportional to the square of the current value, the internal temperature of the motor is detected based on the current supplied to the motor.

[0016]

Embodiments of the present invention will be described below. In this embodiment, the control method of the electric motor according to the present invention is applied to a reduction motor of a finishing stand electric reduction device for hot rolling. FIG. 1 is a schematic configuration diagram illustrating an example of a continuous rolling mill to which the present invention is applied.

This rolling mill includes a pair of upper and lower work rolls 1.
And an upper backup roll 2a and a lower backup roll 2b above and below the work roll, respectively, and the rolling load of the upper and lower work rolls 1 is determined by the upper and lower backup rolls 2a and 2b. The upper and lower backup rolls 2a and 2b are disposed in a reduction mechanism (not shown) that is driven and controlled by a reduction motor 3 capable of normal rotation and reverse rotation. The upper and lower backup rolls 2 are controlled by moving the roll shaft in the vertical direction by rotating the lowering motor 3 forward and reverse.
The gap between a and 2b changes, and the roll gap between the work rolls 1 changes by being pushed by the gap.

The motor 3 is controlled by an AGC unit 4 of a gauge meter type. In the AGC unit 4, a rolling load P by the work roll 1 detected by a load sensor such as a load cell, etc. The thickness deviation ΔH, which is the difference between the gauge meter plate thickness H obtained from the actual speed value V and the preset target thickness h ₀ , is obtained. The reduction is performed so that the thickness deviation ΔH becomes zero. The motor 3 for normal rotation and reverse rotation to control its speed,
The roll gap between the work rolls 1 is adjusted.

FIG. 2 is a block diagram of the entire control system including the functional configuration of the AGC unit 4. As shown in FIG.
The GC unit 4 includes a speed calculation unit 11 that calculates a speed command value v ₀ of the reduction motor 3 based on a difference between the target plate thickness h ₀ and the gauge meter plate thickness H, that is, a plate thickness deviation ΔH, and a speed calculation unit. And an electric motor drive unit 12 for controlling the drive of the electric motor 3 for reduction based on the speed command value v ₀ from the motor 11.
Then, the speed calculation unit 11 includes a multiplier 21 that multiplies the rolling load P detected by, for example, a load cell or the like, with a control gain that is a ratio of a scale factor Sf to a mill stiffness coefficient K, and that is detected by, for example, a pulse generator. A computing unit 22 for adding the actual position value M of the work roll 1 based on the integrated value of the actual speed value V of the electric motor 3 for reduction and the output of the multiplier 21 to output a gauge meter thickness H; a computing unit 23 for calculating a thickness deviation ΔH from the difference between h ₀ and the gauge meter thickness H, and a thickness deviation ΔH from the computing unit 23
24 multiplied by a control gain [(K + Q) / K], which is set based on the plasticity coefficient Q and the mill stiffness coefficient K of the material L to be rolled, and controlling the automatic thickness control to the output of the multiplier 24 The speed command value v of the step-down motor 3 is multiplied by the gain G _1.
And a multiplier 25 for calculating ₀ .

The motor drive section 12 calculates a speed deviation ΔV from the difference between the speed command value v ₀ from the multiplier 25 and the actual speed value V of the step-down motor 3 detected by, for example, a pulse generator. , A speed controller 32 for calculating a current command value i ₀ to the step-down motor 3 based on the speed deviation ΔV from the calculator 31, and an absolute value of the current command value i ₀ from the speed controller 32 _Limiter 33 limits the current to a predetermined current value i _LIM and outputs it as a current limit command value i _S
And the motor main circuit current (supply current) I _M to the step-down motor 3 based on the current limit command value i _S from the current limiter 33 and
Outputs a current controller 34 for controlling the direction of rotation of the pressure for the motor 3 to estimate the internal temperature of the pressure for the motor 3 based on the motor main circuit current I _M from the current controller 34 current based on this Current limit value i in limiter 33
_And a motor internal temperature estimator 35 for setting the _LIM .

Based on the motor main circuit current I _M from the current controller 34, the motor internal temperature estimator 35 calculates the internal temperature T (t) of the step-down motor 3 based on the following equation (1).
Is estimated.

In the equation, K 'is a proportional coefficient, and τ is a thermal time constant. P (t) is a calorific value of the electric motor, and is calculated by equation (2) based on the current I supplied to the electric motor and the resistance value R. Also, the internal temperature of the motor is determined based on the amount of heat generated and the amount of heat radiation determined by the structure of the motor.
Generally, it can be approximated by a first-order lag equation of the following equation (1).

T (t) = (K ′ / (S + τ)) · P (t) (1) P (t) = I ² · R (2) And calculated based on the above equation (1). Based on the magnitude relationship between the estimated internal temperature value T (t) and the preset caution temperature T _ALM , the allowable time β is calculated based on the following equations (3) to (6).

In the equation, T _MAX is the maximum allowable temperature of the internal temperature of the screw-down motor 3, and T _ALM is the cautionary temperature, for example, when the current value is continuously supplied to the screw-down motor 3. Is the temperature at which the internal temperature is considered to possibly exceed the maximum allowable temperature _TMAX . Also, the allowable time β
Represents the time until the internal temperature of the pressure for the motor 3 reaches the maximum allowable temperature T _MAX. Α is a temperature change rate (a rise state of the internal temperature, a rise rate of the internal temperature), and represents a change amount of the internal temperature per unit time.

Β = (T _MAX −T (t)) / α; T ≧ T _ALM and α> 0 (3) β = previous β value; T ≧ T _ALM and α ≦ 0 (4) β = β ₀ ; T <T _ALM (5) α = (T (t) −T (t−1)) / Δt (6) Then, according to the value of the calculated permissible time β, FIG. The current limit value i _LIM is set based on the control characteristic shown in FIG. As the current limit value i _LIM , when the allowable time β is β = β ₀ , an allowable current value I which is set in advance as a value at which the internal temperature of the electric motor 3 for pressure reduction can operate without _{exceeding the} maximum allowable temperature T _MAX. Set ₀ . Further, when the allowable time β is β = 0, the preset minimum current value I _MIN is set as the current limit value i _LIM , and when 0 <β <β ₀ , I _MIN A value that increases as β increases until I ₀ is set as a current limit value i _LIM . Also, β ₀
If <β, the current limit value I _LIM = I ₀ is set.

Note that I ₀ , T _MAX , T _ALM , β ₀ , I
The value of _{MIN is} a value determined based on the characteristics of the electric motor 3 and the experimental value. Next, the operation of the above embodiment will be described.

When the material L is caught in the finishing stand and rolling is performed, a rolling load P calculated by a load cell or the like is supplied to the multiplier 21 as shown in FIG. The gauge meter plate thickness H is estimated based on the actual value M of the rolling position of the work roll 1 based on the actual value V of the motor speed of the electric motor 3. Then, a control gain [(K + Q) / a control gain set based on the plasticity coefficient Q and the mill stiffness coefficient K of the material L to be rolled so that the estimated gauge thickness H and the target thickness h ₀ match. K] or the like, is multiplied by the sheet thickness deviation ΔH to set a speed command value v ₀ for driving and controlling the electric motor 3 for pressure reduction.
Then, a speed deviation ΔV between the speed command value v ₀ and the actual speed value V of the reduction motor 3 is obtained, and the speed deviation ΔV
In the speed controller 32 on the basis of the current command value i ₀ which drives the reduction electric motor 3 so that the speed deviation ΔV becomes zero it is calculated.

Then, the motor main circuit current I _M according to the current command value i ₀ is supplied to the step-down motor 3, and the step-down motor 3 is rotated in a specified rotation direction and its rotation speed is controlled. is the motor torque TR ₁ is generated in accordance with the characteristics K _T of the pressure for the motor 3, the motor generated torque TR ₁ and the rolling mill characteristic of the deviation ΔTR and pressure electric motor 3 and the load torque TR ₂ of mILL K _K / (GD ²・
s), the roll gap is adjusted, and the thickness of the material bitten into the finishing stand is controlled to be constant.

At this time, the motor internal temperature estimator 35 estimates the internal temperature T of the step-down motor 3 based on the motor main circuit current _IM and the above equations (1) to (6), and based on this, The current limit value i _LIM is set.

For example, when the current internal temperature T (t) is lower than the caution temperature T _ALM , that is, when the possibility of the electric motor 3 tripping is low even when the current value is continuously supplied. , The allowable time β is set as the reference value β ₀ . Therefore, from the control characteristic of FIG.
_LIM is set to a permissible current value I _0. That is, the allowable current value I ₀ the internal temperature of the pressure for the motor 3 is set in advance as an operating possible values without exceeding the maximum allowable temperature T _MAX is set as the current limit i _LIM.

Therefore, a current whose absolute value is equal to or _smaller than the allowable current value I ₀ is supplied to the step-down motor 3, and the maximum torque that can be generated by the step-down motor 3 is limited. However, the torque control is performed up to the maximum torque that can be generated in the electric motor 3 for rolling-down, and the roll gap is controlled so that the desired gauge meter plate thickness H is obtained.

From this state, if the speed command value v ₀ changes suddenly due to, for example, a sudden increase in the plate thickness deviation ΔH, or if the load torque is large and the speed deviation ΔV does not decrease, the current command value i ₀ becomes large. becomes, there may reach the allowable current value I _0, even if it be permissible current value I ₀ as a motor main circuit current I _M is supplied for a short time, the internal temperature of the pressure for the motor 3 because not significantly increased The reduction motor 3 does not trip.

However, for example, when the control gain of the speed calculation unit 11 is set large, the ratio of the change in the speed command value v _{0 to} the change in the plate thickness deviation ΔH becomes large. When i ₀ increases and the plate thickness deviation ΔH fluctuates frequently, the number of times of reaching the allowable current value I ₀ increases. Therefore, the allowable current value I ₀ is frequently supplied to the step-down motor 3, and the step-down motor 3 is in a heating state and its internal temperature rises. As a result, the internal temperature reaches the maximum allowable temperature T _MAX , The reduction motor 3 trips. Further, when the operation is performed for a long time in an overload state, the internal temperature T of the screw-down motor 3 gradually increases, and the screw-down motor 3 eventually trips.

However, the motor internal temperature estimator 35
Then, based on the motor main circuit current I _M , the internal temperature T and the temperature change rate α of the step-down motor 3 are estimated. When the internal temperature T rises and exceeds the caution temperature T _ALM , the internal temperature T
The temperature change rate α is calculated based on (t) and the previously estimated internal temperature T (t−1). Then, when the internal temperature is rising, the temperature change rate α is α> 0.
The allowable time β is calculated from the ratio between the difference between the maximum allowable temperature T _MAX and the internal temperature T (t) and the temperature change rate α.
The current limit value i _LIM is set based on the control characteristics shown in FIG.

For example, if the permissible time β is larger than the reference value β ₀ , there is a margin before the internal temperature of the electric motor 3 reaches the maximum permissible temperature T _MAX.
LIM is set to the allowable current value I _0. Therefore, the electric motor 3 for pressure reduction is controlled within the range of the allowable current value I ₀ ,
The maximum torque that can be generated by the reduction motor 3 is not limited, and the torque control is performed within a range up to the maximum torque that can be generated by the reduction motor 3. Therefore, the roll gap is controlled so as to have a desired gauge meter plate thickness H.

When the internal temperature T of the screw-down motor 3 further increases and approaches the maximum allowable temperature T _MAX , the allowable time β decreases, and the internal temperature T of the screw-down motor 3 reaches the maximum allowable temperature T _MAX . The time to do it is shorter. Therefore, the current limit value i _LIM is set to a value smaller than the allowable current value I _{0 as} the allowable time β decreases, and finally, the minimum current value I _MIN is set as the current limit value i _LIM. Is done.

Therefore, the reduction motor 3 has the allowable current value I ₀
As a result, the maximum torque that can be generated by the reduction motor 3 is limited. Therefore, since the maximum torque is limited, the responsiveness of the control of the roll gap decreases, but the rise in the internal temperature of the electric motor 3 is suppressed, so that the internal temperature does not reach the maximum allowable temperature T. Is done.

At this time, for example, the motor main circuit current I _M
When the internal temperature of the screw-down electric motor 3 tends to decrease due to the restriction of the temperature, the temperature change rate α becomes α ≦ 0. Configure _LIM . And the internal temperature is T
(T) <until the T _ALM, limits the motor main circuit current I _M to the current limit value i _LIM on hold, T (t)
<When a T _ALM, releases the restriction of the motor main circuit current I _M with increasing temperature, it sets the motor main circuit current I _M in the range up to the allowable current value I _0.

Therefore, the internal temperature T of the screw-down motor 3
And the rate of temperature rise, the internal temperature T becomes the maximum allowable temperature T
The time to reach _MAX , that is, the permissible time β is estimated, and if the permissible time β is large, there is still room for the internal temperature T to reach the maximum permissible temperature T _MAX , and the current motor main circuit current Even if I _M is continuously supplied to the step-down motor 3, current is not limited because the possibility of trip is low. If the allowable time β is short, the internal temperature T is close to the maximum allowable temperature T _MAX and the internal temperature T Since it is necessary to suppress the rise of T, by setting the current limit value i _LIM to a small value and performing the current limit, the generated torque of the step-down motor 3 is limited, and the rise in the internal temperature thereof can be suppressed. .

At this time, since the current limit value i _LIM is set based on the current internal temperature, for example, the current limit value i _LIM is low despite the low internal temperature.
Is set unnecessarily small so as not to limit the generated torque of the screw-down motor 3, and the screw-down motor 3 is set to the extent possible according to the current internal temperature of the screw-down motor 3.
And the electric motor 3 can be operated effectively.

Further, not only the current internal temperature but also the temperature change rate α is calculated, the allowable time until the reduction motor 3 trips is determined from the temperature rise rate, and the current limit value i _LIM is calculated accordingly. Because it is set, for example,
As shown in S ₁ and S ₂ in FIG. 4, even when the internal temperature is the same, the temperature rise rate is higher, in this case, the allowable time β is shorter in S ₁ (β ₁ <β ₂ ). Although a trip occurs, the current limit value i _LIM is set based on the allowable time until the step-down motor 3 trips, so that the step-down motor 3 is effectively operated within a range where the step-down motor 3 does not trip. be able to.

Further, for example, when increasing the control gain of the automatic gauge control for thickness deviation [Delta] H, the variation amount of the motor main circuit current I _M to the pressure for the motor 3 is increased,
Frequently, when the allowable current value I ₀ is reached, the reduction motor 3 generates heat and its internal temperature rises. At this time, the current internal temperature of the reduction motor 3 is estimated, and the motor is controlled based on the estimated temperature. Since the motor main circuit current _IM is adjusted, the maximum operation of the screw-down motor 3 is performed within a range where the screw-down motor 3 does not trip according to the current internal temperature of the screw-down motor 3. And high-accuracy plate thickness control can be performed.

Accordingly, the reduction motor 3 can be effectively operated within a range in which the reduction motor 3 does not trip, and accordingly, it is impossible to control the thickness of the plate or to disable the rolling. Can be avoided and processing efficiency can be improved.

FIG. 5 shows the variation of the exit side sheet thickness deviation and the internal temperature of the draft motor 3 due to the hot rolling finish rolling in the present invention. FIG. 6A shows a conventional motor control method in which the reduction motor 3 is tripped when the current command value i ₀ exceeds the allowable current value I ₀ , and the control gain in the AGC is increased. FIG. 6 (b) shows the state of change in the output side plate thickness deviation and the internal temperature of the screw-down motor 3 in the above case. FIG. 6 (b) shows the output side plate thickness deviation when the control gain in the AGC is reduced in the conventional motor control method. And the state of change of the internal temperature of the electric motor 3 for pressure reduction.

As shown in FIGS. 5 and 6, in the electric screw-down device, when the outlet-side plate thickness deviation becomes positive and the outlet-side plate thickness becomes larger than the target plate thickness, the pressing-down motor 3 is controlled according to the plate thickness deviation, for example. By making a forward rotation, the roll gap between the work rolls 1 is narrowed. Then, when the roll gap becomes narrower, the outlet plate thickness becomes smaller than the target plate thickness, and the outlet plate thickness deviation becomes negative, the roll-down motor 3 is rotated in reverse according to the plate thickness deviation to increase the roll gap, It is adjusted so that the exit side plate thickness is increased. At this time, the sheet thickness deviation becomes large, and particularly when the delivery side sheet thickness is larger than the target sheet thickness, a load from the material L is applied to the screw-down motor 3, so that the supply current to the screw-down motor 3 is large. When a current exceeding the permissible current value I ₀ is supplied, the electric motor 3 generates heat, and the internal temperature of the electric motor 3 increases accordingly. Therefore,
As shown in FIG. 5 and FIG. 6, when the exit side plate thickness deviation frequently becomes positive and the supply current to the reduction motor 3 frequently increases,
As a result, the electric motor 3 generates heat, and the internal temperature of the electric motor 3 gradually increases.

At this time, if the exit side sheet thickness deviation is negative, the reduction motor 3 is controlled to rotate in the reverse direction to widen the roll gap. In this case, the material L applied to the reduction motor 3 5 is reduced, the screw-down motor 3 may not generate heat. However, as shown in FIGS. 5 and 6, since the outlet-side sheet thickness deviation frequently becomes positive or negative,
Even if the rolling motor 3 does not generate heat, the roll gap is controlled to be narrowed again before the internal temperature decreases. By repeating this state, the internal temperature of the rolling motor 3 decreases. It will rise gradually.

However, as shown in FIG. 5, in the above-described embodiment, the motor main circuit current _IM is limited so as to become smaller as the internal temperature of the electric motor 3 for pressure reduction rises. As the temperature increases, the rate of increase of the internal temperature is suppressed, and the maximum allowable temperature T _MAX is not reached.

In contrast, as shown in FIG. 6A, when the control gain in the AGC is increased in the conventional motor control method, the responsiveness of the roll gap to the exit side sheet thickness deviation is good. Therefore, good thickness control can be performed. However, since the current command value i ₀ for the thickness deviation ΔH, that is, the motor main circuit current I _M is large, this frequently exceeds the allowable current value I ₀ , and the internal temperature increases, and the rolling reduction occurs during the rolling. The electric motor 3 trips, and subsequent plate thickness control becomes impossible.

As shown in FIG. 6B, when the control gain in the AGC is reduced, the sheet thickness deviation ΔH
Since the amount of variation of the current command value i ₀ is small relative to, but is not the internal temperature of the pressure for the motor 3 is tripped without much increase, due to poor responsiveness of the roll gap with respect to thickness deviation [Delta] H, gauge control Performance has deteriorated considerably.

On the other hand, as shown in FIG. 5, according to the control method of the present invention, since the motor main circuit current I _M is suppressed, the thickness controllability is somewhat poor, but the step-down motor 3 is tripped. Therefore, there is no possibility that the thickness control becomes impossible during the rolling or the rolling becomes impossible. Therefore, good plate thickness control performance can be obtained as a whole.

In the above embodiment, the case where the control method of the electric motor according to the present invention is applied to the electric motor for the reduction of the electric rolling device of the finishing stand for the hot rolling has been described. However, the present invention is not limited to this. The present invention can be applied to a temper rolling mill or the like, and is not limited to a rolling mill, and can be applied to any electric motor used in a state where a peak load is repeatedly applied to the electric motor.

In the above embodiment, since the internal temperature of the step-down motor 3 is estimated based on the motor main circuit current I _M , it is not necessary to newly provide a temperature sensor or the like. Although it is possible to estimate the internal temperature, for example, a temperature sensor or the like may be provided to directly detect the temperature. In this case, since the internal temperature can be detected with higher accuracy, the temperature can be more accurately detected. The current limit value i _LIM can be set.

In the above embodiment, the internal temperature T (t) at the time of the previous detection and the internal temperature T (t) at the time of the current detection are set.
-1), the temperature change rate α is detected. However, the present invention is not limited to this. For example, the temperature change rate α may be detected based on a change state of the internal temperature at a plurality of past times.

In the above embodiment, the allowable time β until the internal temperature reaches the maximum allowable temperature T _MAX is estimated based on the temperature change rate α and the current internal temperature T (t). The case where the current limit value i _LIM is set based on this is described. For example, when the internal temperature exceeds the caution temperature T _ALM , as the current internal temperature T (t) becomes higher, The current limit value i _LIM may be set smaller as the temperature change rate α increases, and in this case, the same effect as in the above embodiment can be obtained. Further, the current limit value i _LIM may be set according to, for example, the difference between the internal temperature at the time of the previous detection and the internal temperature at the time of the current detection, without being limited to the temperature change rate α.

[0055]

As described above, according to the first aspect of the present invention,
The motor control method according to the present invention detects a rise in the internal temperature and, based on this, based on this, assumes that the more rapidly the internal temperature rises, the higher the possibility that the internal temperature of the motor will reach the maximum allowable temperature is In addition, since the supply current to the motor is further limited, it is possible to suppress the torque generated by the motor to suppress an increase in the internal temperature of the motor, and to prevent the internal temperature from reaching the maximum allowable temperature. Can be.

According to a second aspect of the present invention, there is provided a method for controlling a motor, comprising detecting an internal temperature of the motor and a rate of increase thereof.
When the internal temperature is within the caution temperature range, the allowable time until the internal temperature reaches the maximum allowable temperature is estimated based on the detected internal temperature and the rising rate. Since the supply current to the motor is limited to a smaller value, the generated torque of the motor can be suppressed, the rise in the internal temperature of the motor can be suppressed, and the internal temperature can be prevented from reaching the maximum allowable temperature. it can.

Further, in the motor control method according to the third aspect of the present invention, since the internal temperature of the motor is detected based on the current supplied to the motor, the method can be easily performed without newly providing a temperature sensor or the like. Internal temperature can be detected.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a continuous rolling mill to which the present invention is applied.

FIG. 2 is a block diagram illustrating a configuration of an AGC unit in FIG.

FIG. 3 is a control characteristic diagram showing a correspondence between a current limit value i _LIM and an allowable time β.

FIG. 4 is an explanatory diagram for explaining the operation of the present invention;

FIG. 5 is an explanatory diagram illustrating a change state of a deviation of a delivery side thickness of a material accompanying a change in an internal temperature when rolling is performed by an electric rolling device to which the present invention is applied.

FIG. 6 is an explanatory diagram showing a change state of a deviation of a sheet thickness at an outlet side of a material accompanying a change in an internal temperature when rolling is performed by an electric rolling device to which a conventional motor control method is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Work roll 2a, 2b Backup roll 3 Reduction motor 4 AGC unit 11 Speed calculation unit 12 Motor control unit 35 Motor internal temperature estimator α Temperature change rate β Allowable time

Claims (3)

[Claims] An internal temperature rise of the electric motor is detected,
A method for controlling an electric motor, wherein the current supplied to the electric motor is further limited as the temperature of the internal temperature rises more steeply. 2. An internal temperature of the electric motor and a rise rate of the internal temperature are detected, and when the internal temperature is within a cautionary temperature range lower than a maximum allowable temperature of the electric motor, the internal temperature and the rise rate are detected. And estimating a permissible time until the internal temperature reaches the maximum permissible temperature on the basis of the above, and as the permissible time becomes shorter, the current supplied to the motor is further restricted. Control method. 3. The apparatus according to claim 2, wherein said internal temperature is detected based on a current supplied to said electric motor.
The control method of the electric motor according to the above.