JP2523991B2 - Control method for induction heating device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of controlling an induction heating device for heating a material to be heated while it is being conveyed.

[0002]

2. Description of the Related Art Generally, the required electric power P (kW) for heating an object to be conveyed by an induction heating device is obtained by the formula (1).

[0003]

[Equation 1]

On the other hand, in the process in which the material to be heated passes through the induction heating device, the amount of heat loss (temperature drop) such as heat dissipation during heating in the coil and heat dissipation during passing through idle parts between the coils. Occurs. In particular, when heating while transferring a thin plate (strip), the strip easily flaps,
Since it is advantageous to make the distance between the strip and the coil as small as possible in order to increase the heating efficiency, the distance between the strip and the coil is only about 50 to 100 mm. It is easy to make contact with and the support roll must be installed between the coils to prevent this. Therefore, the idle running portion between the coils for that purpose is required to be 2 to 3 m, and the heat loss there can not be ignored, which becomes a large cause of the control error. or,
When the existing equipment is modified to install the induction heating device, the same problem may occur due to interference with the existing equipment, resulting in an idle section. Here, taking the induction heating device whose layout is shown in FIG. 1 as an example, a trial calculation of the control error will be made by computer simulation. Table 1 shows the specifications of the induction heating device.

[0005]

[Table 1]

The induction heating apparatus of this example is one of the vertical continuous annealing furnaces.
Three induction heating devices (coils) with a rated output of 1000 kW are arranged in a tandem shape in the path, and No. 1 is sequentially installed from the upstream side in the strip passing direction. 1 induction heating device 33, No. 1
2 induction heating device 34, No. It is called a 3-induction heating device 35. In addition, No. No. 1 induction heating coil 33C.
The above-mentioned strip support roll 36 is installed between the two induction heating coils 34C, and the section is an idle section. (First free-running section) Furthermore, No. of the final stage.
The space from the induction heating coil 35C to the induction heating device outlet plate thermometer 38 for temperature management is also an idle section. (Second
In addition, 37 is an induction heating device inlet plate thermometer for measuring the plate temperature at the induction heating device inlet. Table 2 shows each condition value used for the computer simulation.

[0007]

[Table 2]

The computer simulation divides the span (23 m) from the inlet side plate thermometer to the outlet side plate thermometer at intervals of 1 m, and based on the plate temperature directly below the inlet side plate thermometer, from the upstream side to the downstream side, Immediately below the outlet plate thermometer, add the temperature rise due to induction heating in the section and the temperature drop due to heat dissipation (only the temperature drop when passing through a coil that is not energized or passing through an idle section) Convergence calculation was performed using the heat balance model equation that integrates up to the position, and the setting power value of the coil when the heating target temperature or target heating amount was achieved was obtained. In addition, the power setting distribution to each coil is such that the load factor is uniform with respect to the maximum input power of each induction heating device. Table 3 shows the trial calculation results.

[0009]

[Table 3]

For example, when the temperature of the strip is raised from 300 ° C. to 100 ° C. at a furnace speed of 100 mpm, a total of 1266 (kW) is required considering the heat loss. On the other hand, the required power P _G (k
W) is, as shown in Equation 2 below,

[0011]

[Equation 2]

It can be seen that there is an error of 303 (kW). The temperature error corresponding to this 303 (kW) amount is about 24 ° C. Therefore, when the temperature of the strip is controlled by the induction heating device, unless the electric power value that accounts for these heat losses is set in the induction heating device, that amount becomes an error and control accuracy cannot be secured.

On the other hand, JP-A-51-87836 and JP-A-5-7836.
2-62110, JP-A-52-12941, and JP-A-5-512.
2-122942, JP-A-57-37679, JP-A-SHO-5
In a known induction heating device control method such as 9-59824, a so-called feedback control is used to detect a control error by a plate thermometer installed at the induction heating device outlet and correct the power set value to the induction heating device. In addition, a method of suppressing the control error is adopted, including those caused by changes in various conditions other than those caused by heat loss.

However, since this feedback control system is a control system in which the control operation amount, that is, the electric power value is corrected after detecting the control result, a certain point on the strip passes through the coil and is heated. During that time, of course, it is impossible to control, and there is also a loss time from the point where the coil exits the coil and the temperature is measured by the plate thermometer and the control error is detected until the control is activated and the error is suppressed. Therefore, the strips processed during these may sometimes fall outside the specified temperature error range. That is, this method is effective in the steady part, but immediately after the part where the size of the strip, the target heating temperature or the target heating amount is changed,
The target temperature control accuracy cannot be guaranteed, and therefore it is necessary to set the power value in consideration of the heat loss.

On the other hand, in Japanese Patent Laid-Open No. 54-29141, the electric power value for compensating for the heat loss is derived from the inlet temperature of the material to be heated, the speed, and the target temperature rise amount. However, since the heat loss depends on the size of the material to be heated and the difference between the temperature of the material to be heated and the ambient temperature during heating and the passing time, the inlet temperature of the material to be heated, the speed,
It is not possible to derive a sufficient power setting value for ensuring the target control accuracy with respect to the size of the material to be heated, the target temperature rise amount, or the heating target temperature only from the target temperature rise amount. In particular, in the induction heating device installed in the continuous annealing furnace for strips, the change point of the size of the strip and the target heating temperature or the target heating amount are frequently changed,
In this method, the desired temperature control accuracy cannot be obtained immediately after each change point, and therefore it is useless.

Further, in JP-A-55-78490, the effect of cooling (heat loss) between the coils is corrected by adjusting the target temperature setting. In addition to having the same reasons as described for 29141, there is heat loss between the coils as well as heat loss between the coils while the strip is passing through the induction heating device. The part that is not taken into account is the control error. Therefore, this method is also disclosed in JP-A-54-29.
Similar to 141, particularly for an induction heating apparatus installed in a continuous annealing furnace for strips, such as an induction heating apparatus in which the size of the strip is changed and the heating target temperature or the target heating amount is frequently changed, It does not provide a method of deriving a power set value for obtaining a desired temperature control accuracy.

[0017]

On the other hand, the present invention has flexibility and quick response to changes in the heating conditions such as the size of the strip, the target heating temperature or the target heating amount, and idle running between the coils. Provided is a method for deriving a power set value to an induction heating device for obtaining a heating target temperature or a target temperature rise amount in consideration of a heat loss amount not only in a coil portion but also in a coil portion.

[0018]

That is, according to the present invention, a plurality of heating coils are arranged in tandem and at least one heating coil is arranged.
A method for controlling an induction heating device, in which a support roll is installed between coils at a place and an induction heating device having a free running portion is used to heat a strip while being transported to secure a predetermined heating temperature or a predetermined temperature rise amount. When the strip heating target temperature or target heating amount change part or the strip size change part reaches the inlet of the induction heating device, the strip size and the ambient temperature installed in each coil part and inter-coil feeding part Based on the temperature value detected by the meter,
Induction that achieves the target heating temperature or target heating amount by performing convergence calculation using the heat balance model equation that takes into account the heat loss (temperature drop) that occurs while the strip passes from the inlet to the outlet of the induction heating device. It is a control method for an induction heating device, characterized in that a required optimum power set value for the heating device is obtained and set.

[0019]

According to the method of the present invention, the atmospheric temperature, which is an important factor in deriving the heat loss amount, is actually measured and used when obtaining the electric power set value in consideration of the heat loss amount. , Calculate the amount of heat given to the strip in each process and the amount of heat lost by the strip by a heat balance model formula, and generally derive the required power value that can obtain the desired heating target temperature or target heating amount. Therefore, it is possible to flexibly and accurately respond to a change in the heating target temperature or the target temperature rise amount. Further, since the size of the strip is taken into consideration in the heat balance model formula, it is possible to flexibly and accurately respond to the size change. Therefore, as a result, the desired temperature control accuracy can be obtained even if the strip size is changed or the heating target temperature or the target temperature rise amount is changed frequently.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A concrete method of carrying out the present invention is shown in FIGS. In FIG. 2, 1 is a strip, 2 is a heating coil and a coil cover, 3 and 4 are matching capacitors connected to the heating coil 2, and an inverter device. 5 is a thermometer for measuring the ambient temperature inside the heating coil, 6 is a thermometer for measuring the temperature of the idle portion between the coils, 7 is a thermometer for measuring the strip temperature at the inlet of the heating device, and 8 is for the outlet of the heating device. A thermometer for measuring the strip temperature, 9 a speedometer for measuring the processing speed of the strip, 10 an arithmetic / judgment processing device, and 11 a host computer. 10 and 11 may be realized by the same computer.

Further, FIG. 3 shows an arithmetic / judgment processing device 10.
The processing flow inside is shown. When the size changing part of the strip 1 or the changing part of the target heating temperature or the target heating amount reaches the induction heating device inlet thermometer 7, the processing flow starts (12), and the strip processing speed meter 9 indicates the strip 1 The measured speed, the actual temperature at the inlet of the heating device of the strip 1 from the plate thermometer 7 at the inlet of the heating device, and the measured value of the atmospheric temperature at the coil part and the idle running part between the coils from the thermometers 5 and 6 respectively. Is taken into the calculation / judgment processing device 10, and the cross-sectional area of the strip is also calculated from the host computer 11.
Each data such as the surface area per unit length is taken into the arithmetic / judgment processing device 10 (13).

Next, at 14 the initial value T0 of the temperature integration calculation is set to the induction heating device inlet temperature TE, and at 15 the initial value of the temperature integration calculation number N is set to 0, and the a-expression calculation unit 1
7. After calculating the temperature rise amount (temperature drop amount) in the first section by the b formula calculation unit 18 and the c formula calculation unit 19, the number of integration calculations N
Is increased by 1 (20). Here, in the processing of the c-expression calculation unit 19, the ambient temperature TG measured by the thermometers 5 and 6 loaded into the calculation / judgment processing device 10 at 13 is used. In addition, the following formula 3 is used as the calculation formula in each of the calculation units 17, 18, and 19 described above.

[0023]

(Equation 3)

Thereafter, N is the length of the induction heating device path length L (the distance from the heating device inlet temperature measuring point to the heating device outlet temperature control point-usually, the heating device outlet temperature measuring point) is the length of one temperature calculation section. 15,16,17,18,19,20,21,29 until the integer divided by l becomes NMAX or more.
The calculation process is repeated in the order of. However, here, when calculating a section that is not the heating coil section, that is, a section that corresponds to the idle running section, the heating coil section determination unit 16 branches to
T0 is replaced by T2 (28), bypassing 17,18 and connected to 19.

On the other hand, the power simple calculation unit 25 obtains the rough value of the total electric power required to obtain the heating target temperature or the target heating amount by the above-mentioned formula 1 and distributes the electric power to each induction heating device. Accordingly, the temporary power distribution unit 26 calculates the rough power set value P _PRO for each induction heating device. And
In the calculation process of the section corresponding to each induction heating device (coil), the corresponding coarse power set value P _PRO is used. Needless to say, various data other than the crude power set value P _PRO used in each calculation process are also those of the corresponding section, and the specific heat C in each section is a function of the average temperature in that section.

When N reaches NMAX, the above temperature integration calculation processing (integration calculation of the amount of temperature rise or the amount of temperature drop) is terminated (21), and the final calculated value is set to TD (2
2) Calculate the difference ERR between TD and the set TD (23).
Here, if ERR exceeds the control deviation allowable value A (2
4) modify the amount corresponding required total power roughness value corresponding to the ERR by the power correcting section 27 performs re-power the temporary distributed with (26), again using the crude power setting P _PRO revised above The temperature calculation process is performed. In this way, the above processing is repeated until ERR becomes A or less. If ERR becomes less than A,
The rough power set value P _PRO to each induction heating device at that time is set as a formal power set value P _SET (30), output to each induction heating device (inverter device) (31), and the process ends (32).

The above is a concrete implementation method of the present invention. If supplemented with NMAX and control deviation allowable value A used in the processing, NMAX takes into account the required control accuracy and the load on the computer. It is desirable to decide by
Furthermore, unknown parameters such as the heating efficiency in the coil section and the overall heat transfer coefficient in the coil section and the idle section, which greatly affect the control accuracy, can be determined by the Kalman filter in each zone such as the coil section and the idle section. It can be effectively obtained by using, estimating and learning.

The control deviation allowable value A is preferably set smaller than the actual control deviation allowable value in consideration of the error of various data used in the temperature calculation formula and the accuracy of the temperature calculation formula itself. If it is too small, there is a high risk that the calculations will not converge, and there will be adverse effects such as an increase in the load on the computer, so these must be taken into consideration when setting.

In the case of deriving the electric power set value for the target temperature rise amount, ERR = (TD-
TEJ) -ΔT _SET . In addition, TD is a calculated heating temperature, TEJ is an induction heating device inlet actual measurement plate temperature, and ΔT _SET is a target heating amount.

[0030]

According to the method of the present invention described above, in determining the power set value in consideration of the heat loss, the ambient temperature, which is an important factor in deriving the heat loss, is actually measured and used, and Electric power required to obtain a desired heating target temperature or target heating amount by calculating the amount of heat given to the strip and the amount of heat lost by the strip in each process while passing through the heating device, using the heat balance model formula. Therefore, it is possible to flexibly and accurately respond to changes in the heating target temperature or the target temperature rise amount, and the heat balance model formula considers the strip size. Similarly, since it is possible to flexibly and accurately respond to size changes, it is necessary to frequently change the strip size or the heating target temperature or target heating amount. It is possible to obtain the desired temperature control accuracy even when the crack.

[Brief description of drawings]

FIG. 1 is a layout diagram of an induction heating device.

FIG. 2 is a diagram illustrating a specific implementation method of the present invention.

FIG. 3 is a control flow chart of the method of the present invention.

[Explanation of symbols]

 1 Strip 2 Heating Coil 3 Matching Capacitor 4 Inverter 5-8 Thermometer 9 Speedometer 10 Arithmetic / Judgment Processing Device 11 High-end Computer

Claims (1)

(57) [Claims] 1. An induction heating apparatus having a plurality of heating coils arranged in tandem and having a idler section in which at least one coil is provided with a support roll, and heating is performed while the strip is being conveyed to a predetermined temperature. In a method for controlling an induction heating device that secures a heating temperature or a predetermined heating amount, when the heating target temperature of the strip or the target heating amount changing unit or the strip size changing unit reaches the inlet of the induction heating device, Based on the size of the strip and the temperature value detected by the atmospheric thermometers installed in each coil section and the inter-coil air feeding section, the heat loss (temperature drop) that occurs while the strip passes from the induction heating device inlet to the outlet )
Control of an induction heating device characterized by performing a convergence calculation using a heat balance model equation that takes into account the temperature, and finding and setting the necessary optimum power set value for the induction heating device that achieves the heating target temperature or the target heating amount. Method.