JPH05144909A - Direct electric heating equipment - Google Patents

Abstract

PURPOSE:To eliminate the necessity of considering the quality of a primary power supply and to control a constant voltage or a constant current stably by causing the output of a switching element to coincide with a command value of a controlling device. CONSTITUTION:This device is provided with a controlling device 1 for controlling the output of main body of the device, a thyristor which is supplied with the primary power Vin, that is, a switching device 3, and a firing angle controlling device 4 which controls a firing angle of the switching device 3 on a basis of a command value output from the controlling device 1. This device also has a constant voltage controlling device 2. When the output of the switching device 3 is detected and the primary power Vin changes, the firing angle controlling device 4 is so controlled as the output of the switching device 3 may coincide with a command signal Sc from the controlling device 1. Therefore, the fluctuation of the primary power Vin is eliminated. Consequently, stable power or stable current is supplied to the load at all times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct electric heating apparatus for heating an object to be processed by directly applying an electric current to perform sintering or heat treatment.

[0002]

2. Description of the Related Art Conventionally, a resistance heating method has been adopted as a heating method in a heating device such as a heat treatment furnace. In this method, since the object to be processed is heated at the ambient temperature, the temperature can be measured and controlled relatively easily.
In addition, since the atmosphere and the heat capacity of the internal member of the object to be processed are large, there is an advantage in that the temperature of the object to be processed does not immediately change due to fluctuations in power during heating.

On the other hand, in addition to the resistance heating method, there is a heating method by direct energization. In the case of the direct current heating method, since it is difficult to measure the temperature of the object to be processed, the heating device is operated by constant power or constant current control, and the temperature of the object to be processed is indirectly controlled by the supplied power. Here, FIG. 6 is a block diagram showing a schematic configuration of the heating power source of the direct current heating device. As shown in this figure, the ignition circuit 1 inputs the output command value Sc output from the controller 2, controls the ignition angle of the thyristor 3 every half cycle based on this value, and adjusts the output. . In this case, the output command value Sc is a signal for changing the output of the thyristor 3 so that the power value or the current value matches the set value when the constant power or constant current control is performed. .

[0004]

By the way, in the above-mentioned direct current heating method, the temperature is controlled based on the electric power or the electric current value being supplied to the object to be processed, but the fluctuation of the electric power to be supplied. However, there is a problem in that it is difficult to maintain its stability due to disturbance factors such as load fluctuations and primary power supply fluctuations, because of the immediate temperature fluctuations. In this case, since the load fluctuation is generally a gradual change, it can be dealt with by the adjustment by the controller 2. However, since the first-order fluctuation is caused by the operating states of equipment that requires a large amount of electric power, such as a welding machine, an electric furnace, and a crane, which are installed in one factory, it is difficult to deal with the controller 2. FIG. 7 shows how the output changes due to the change in the primary power supply. In this figure, the symbol α is the firing angle.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a direct electric heating device which is not affected by fluctuations in the primary power source.

[0006]

According to the present invention, an adjusting means for adjusting the output of the apparatus body, a switching element to which a primary power source is supplied, and a command value output from the adjusting means are used. In a direct current heating device comprising a firing angle control means for controlling the firing angle of the switching element, the output of the switching element is detected, and the point is set so that the detection result matches the command value of the adjusting means. It is characterized by comprising constant voltage control means for controlling the arc angle control means.

[0007]

According to the above construction, when the primary power source fluctuates, the firing angle control means is controlled so that the output of the switching element coincides with the command value output from the adjusting means. Therefore, the fluctuation of the primary power source is removed, so that stable power or current is always supplied to the load.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a direct electric heating apparatus which is an embodiment of the present invention. In this figure, reference numeral 1 is a conventionally used regulator, to which the output (electric power or current) Sh of the heating device main body is supplied. The controller 1 supplies the output of the PID control to the constant voltage control circuit 2 as a command value signal Sc. The constant voltage control circuit 2 performs PID control so that the output Ss of the thyristor 3 matches the command value signal Sc, and supplies the output to the firing angle control circuit 4. In this case, the constant voltage control circuit 2 has a circuit configuration capable of performing control at a higher speed than the response speed of the controller 1.

The firing angle control circuit 4 generates a gate signal Sg based on the output of the constant voltage control circuit 2 and supplies it to the gate of the thyristor 3 as a switching element. In this embodiment, the output Sh of the heating device main body and the output Ss of the thyristor 3 are shown separately because the output Sh of the heating device is not necessarily the output Ss of the thyristor 3 in an actual direct current heating device. This is not possible. For example, when a large current is taken out through the step-down transformer after the thyristor 3, the output Sh of the heating device and the output Ss of the thyristor 3 obviously do not match.

In the direct current heating device having such a configuration, when the primary power source Vin fluctuates, the fluctuation is detected by the constant voltage control circuit 2, and the output Ss of the thyristor 3 is set to match the command value signal Sc. The firing angle of the thyristor 3 is controlled by the arc angle control circuit 4. Here, the relationship shown in FIG. 2 is established between the command value signal Sc and the output Ss of the thyristor 3 regardless of the disturbance of the fluctuation of the primary power source Vin. In this case, the command value signal Sc and the thyristor 3
The relationship of the output Ss of does not need to be a straight line shown in
It may be a curved relationship such as. That is, if the command value signal Sc is a constant value even if the primary power source Vin changes,
It is sufficient that the output Ss of the thyristor 3 is kept constant.

As described above, since the constant voltage control circuit 2 is provided and the output Ss of the thyristor 3 is controlled so as to reach the set value of the controller 1, the power value detected at the output end (load end) of the main body of the apparatus. Alternatively, the control based on the current value (control by the controller 1) is not adversely affected by the fluctuation of the primary power source Vin, and stable heating is possible.

Here, FIG. 3 shows AC200V, 50Hz.
Input the single-phase primary power supply of
It is a direct current heating device that outputs C10V, 3500A, and 50Hz, and the output power is controlled to a constant power. In this figure, the output of the thyristor is converted into a DC signal of the same level as the command value signal output by the controller by the voltage converter, and PID control is performed by the constant voltage control circuit so that these signals match. .

FIG. 4 is a waveform diagram showing the output voltage of this heating device, and FIG. 5 is a waveform diagram showing the output voltage of the conventional heating device. As can be seen from these figures, the heating device is not affected by the fluctuation of the primary power source as compared with the conventional heating device. In this case, since the dummy resistor is used as the load, the load does not change.

[0014]

As described above, according to the direct current heating device of the present invention, the firing angle of the switching element is controlled so that the output of the switching element matches the command value of the adjusting means. The following effects are achieved. (B) Stable constant power control or constant current control can be performed, and reproducible heat treatment of the object to be processed can be performed at all times. (B) It is not necessary to consider the quality of the primary power supply, and it is not necessary to prepare expensive equipment such as a stabilized power supply on the primary side. (C) It is possible to make additional improvements to the conventional heating device and obtain good quality heating control at a low cost and additional cost. (D) It can be applied to a wide variety of power supply circuits.

[0015]

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a direct electric heating apparatus which is an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between an output command signal and a thyristor output voltage.

FIG. 3 is a block diagram showing a configuration of an actual direct current heating device.

FIG. 4 is a waveform diagram showing an output of the direct current heating device in FIG.

FIG. 5 is a waveform diagram showing the output of a conventional direct current heating device.

FIG. 6 is a block diagram showing a schematic configuration of a conventional direct current heating device.

FIG. 7 is a waveform diagram for explaining problems of the conventional direct current heating device.

[Explanation of symbols]

 1 Controller 2 Constant voltage control circuit 3 Thyristor (switching element) 4 Firing angle control circuit

Claims (1)

[Claims] 1. An adjusting means for adjusting an output of an apparatus body, a switching element to which a primary power source is supplied, and an ignition angle of the switching element is controlled based on a command value output from the adjusting means. In the direct current heating device including the ignition angle control means, the output of the switching element is detected, and the ignition angle control means is controlled so that the detection result matches the command value of the adjusting means. A direct electric heating device comprising a voltage control means.