JPH0261044B2 - - Google Patents

Description

[Detailed description of the invention]

This invention connects heaters distributed in an electric furnace to an AC power source via thyristors, and turns on the thyristor at an appropriate number of cycles when the AC power source is at zero voltage, thereby supplying power to each heater. The present invention relates to a cycle control type power adjustment device that adjusts the amount of power supplied. Conventionally, in order to automatically adjust the furnace temperature of an electric furnace used for melting glass, etc., a plurality of heaters distributed within the electric furnace are each connected to an AC power source via a thyristor, and each thyristor's The conduction angle is controlled according to the temperature inside the furnace. To explain this with reference to FIG. 1, the first heater 2 of the electric furnace 1 is connected to an AC power source 6 via a bidirectional thyristor 5 consisting of two thyristor elements 3 and 4 connected in anti-parallel. The second heater 7 of the furnace 1 is a bidirectional thyristor 1 consisting of two thyristor elements 8 and 9 connected in antiparallel.
0 to the AC power source 6. Also,
A first thermoelectric element 12 as a temperature detector installed near the first heater 2 is connected to a signal input terminal of a first gate control circuit 11 for controlling the conduction angle of the thyristor 5. Second gate control circuit 1 for controlling the conduction angle of the thyristor 10
A second thermoelectric element 1 as a temperature detector installed near the second heater 7 is connected to the signal input terminal 3.
4 is connected. In the device configured in this way, the temperature at the location where the thyristors 5 and 10 of the electric furnace 1 are installed is detected by the first and second thermoelectric elements 12 and 14, and the number of power cycles is determined according to the detected temperature. Trigger pulses are supplied to the thyristors 5 and 10 at intervals, and the first
Since the amount of power supplied to the second heaters 2 and 7 is adjusted, the temperature inside the furnace can always be maintained at a predetermined value. However, the thyristors 5 and 10 turn on at any phase of the AC power supply, causing the load current to suddenly show a large value and generating high-frequency noise, which has the disadvantage of adversely affecting other electrical equipment, especially communication equipment. . Therefore, the first and second gate control circuits 1
Thyristors 5, 10 controlled by 1, 13
The turn-on point of the AC power supply 6 is selected at zero voltage of the AC cycle of the AC power supply 6. In this case, the thyristor 5 belonging to the first heater 2
For example, the thyristor 10 belonging to the second heater 7 is conductive only during the period shown by the sine waveform in b of FIG. , the fear of high frequency noise generation as described above is eliminated. However, in such a cycle control type power adjustment device, the thyristor 5 belonging to the first heater 2 and the thyristor 10 belonging to the second heater 7 are related to each other. Since the conduction occurs independently, and the phases match when conduction occurs, the combined load current of both heaters 2 and 7 becomes excessive or becomes 0, as shown in c in Figure 2, and the overall Power consumption varies by number of power cycles. Therefore, the power supply capacity needs to be quite large, which is the sum of the rated power of both heaters 2 and 7. Also, since the load current changes greatly over several cycles, voltage flickers occur.
There are drawbacks that can adversely affect other electrical equipment. This drawback becomes more noticeable as the number of heaters increases. By the way, electric furnaces used for melting glass require a considerable amount of power during the temperature rising period, but during the heat retention period after reaching a predetermined temperature, usually 10 to 50% of each heater's rating is used. All you need to do is supply electricity. Furthermore, in electric furnaces that operate continuously for several tens of days to several months, the temperature rise takes
Since it is acceptable to spend several days, it is not necessary to operate each heater continuously at the rated power even during the temperature rising period. This invention has been made with the above-mentioned points in mind, and includes a temperature disturbance detector that detects temperature changes within an electric furnace, and a system that maintains the overall power consumption almost constant based on the detection results of the temperature disturbance detector. a limit pulse generator that generates a limit pulse for preventing turn-on of each thyristor in a periodic pattern that limits the trigger pulse of each thyristor according to the temperature detected by the temperature detector; The present invention provides a cycle-controlled power regulating device including a trigger control circuit that controls and supplies the gates of each of the thyristors. Therefore, according to the power adjustment device of the present invention, the limit pulse of each thyristor output from the limit pulse generator based on the detection result of the temperature disturbance detector causes the trigger control circuit to adjust the limit pulse according to the detected temperature of each temperature detector. The trigger pulses of each thyristor at intervals equal to the number of power supply cycles are limited and output by the periodic pattern of each limit pulse. At this time, in order to keep the overall power consumption almost constant, for example, if two heaters are installed, the AC power supply is cycled to zero voltage in a periodic pattern in which the number of turn-on cycles of the thyristor on the heater side with the lower temperature increases. When four heaters are provided, two thyristors of each heater are alternately turned on in synchronization with the zero voltage in a similar periodic pattern. Therefore, the overall power consumption does not fluctuate suddenly with each power cycle, and the temperature inside the electric furnace can be maintained uniformly during heating and heat retention, preventing high-frequency noise caused by turn-on and voltage flicker caused by load current fluctuations. It is possible to raise and maintain the temperature evenly, and the power supply capacity of the device can be made smaller than before. Next, the power regulating device of the present invention will be explained in detail with reference to the drawings from FIG. 3 onwards showing an embodiment thereof. In FIG. 3, the first heater 2 of the electric furnace 1
is connected to an AC power source 6 via a bidirectional thyristor 5, and the second heater 7 of the electric furnace 1 is connected to the AC power source 6 via a bidirectional thyristor 10. Further, the first thermoelectric element 12 installed near the first heater 2 is connected to the signal input terminal of the first trigger control circuit 15 whose signal output terminal is connected to the gate of the thyristor 5.
A second thermoelectric element 14 installed near the second heater 7 is connected to a signal input terminal of a second trigger control circuit 16 whose signal output terminal is connected to the gate of the second trigger control circuit 16 . Furthermore, temperature disturbance detectors 17 made up of a large number of scattered thermoelectric elements are installed at appropriate locations in the electric furnace 1. The temperature disturbance detector 17 is for detecting changes in the temperature inside the furnace, that is, changes in the temperature inside the furnace that occur when objects to be heated pass through the furnace, etc. The temperature disturbance detector 17 is a temperature disturbance detector. The signal output terminal of the limit pulse generation circuit 18 connected to the trigger control circuit 17 is connected to the first and second trigger control circuits 1
It is connected to another signal input terminal of 5 and 16. The first trigger control circuit 15 has a function of generating a pulse signal at an appropriate number of cycles determined by the output signal of the first thermoelectric element 12 at zero voltage of the AC cycle of the AC power supply 6, and an AND gate function. The second trigger control circuit 16 controls the second thermoelectric element 14 at zero voltage of the AC cycle of the AC power supply 6.
It has a function of generating a pulse signal at an appropriate number of cycles determined by the output signal of , and an AND gate function. On the other hand, the limit pulse generation circuit 18
predicts the heater power required by the electric furnace 1 when there is a disturbance in the temperature inside the furnace, and
A low-level limit pulse is generated to prevent the second trigger control circuits 15 and 16 from simultaneously sending gate trigger pulses to the gates of the thyristors 5 and 10. During the heating period of the electric furnace 1, the temperature inside the furnace is relatively low, so the first and second thermoelectric elements 12, 14 are controlled by the first and second trigger control circuits 15, 16. Requests trigger pulse generation at one cycle period. On the other hand, there is no disturbance in the temperature inside the furnace, so the output signal of the temperature disturbance detector 17 is 0, and the limit pulse generating circuit 18 outputs a 50% response signal as shown in a and b in FIG.
Limit pulses with a two-cycle periodic pattern shifted by one cycle of 50% are sent to the first and second trigger control circuits 15 and 16, respectively. Therefore, the first and second trigger control circuits 15 and 16
are AND gated both input signals and routed to the gates of thyristors 5 and 10 as shown in FIG.
Alternate gate trigger pulses with a two-cycle period as shown in FIG. Power equivalent to 50% of the rating is supplied as shown. During the heat retention period of the electric furnace 1, the temperature inside the furnace rises considerably, so the first and second thermoelectric elements 12 and 14 are operated several cycles with respect to the first and second trigger control circuits 15 and 16. Requests periodic trigger pulse generation. On the other hand, there is no disturbance in the temperature inside the furnace, so the output signal of the temperature disturbance detector 17 is 0, and the limit pulse generation circuit 18 sends out limit pulses with the same 50% vs. 50% periodic pattern as described above. be done. Therefore, both the thyristors 5 and 10 are alternately conductive, and power of approximately 10% of the rated power is supplied to the first and second heaters 2 and 7, respectively. When the object to be heated is inserted into the furnace from the first heater 2 side, the temperature inside the furnace at least in the vicinity of the first heater 2 decreases, so that the first thermoelectric element 12
Or the first and second thermoelectric elements 12, 14 are
Requests the trigger control circuit to generate trigger pulses with a shorter cycle period. On the other hand, the temperature disturbance detector 17 detects that the object to be heated has been inserted into the furnace, and transmits this detection result to the limit pulse generation circuit 18. During this period, limit pulses with a periodic pattern of 80% to 20% as shown in c and d of FIG. 4 are sent out. Therefore, both thyristors 15 and 16 are alternately conductive,
As shown in c and d of FIG. 5, power close to 80% of the rated power is supplied to the first heater 2, and power of approximately 10% of the rated power is supplied to the second heater 2. Moreover, when the object to be heated moves toward the second heater 7 side, contrary to the above, the second heater 7
Approximately 80% of the electric power is supplied, and approximately 10% of the rated electric power is supplied to the first heater 2. Note that e and f, c and d, i and j, and k and l in FIG. 4 are the limit pulse generation circuit 1, respectively.
90% vs. 10%, 87.5% vs. 12.5 that can be output from 8
%, 75% vs. 25% and 66.7% vs. 33.3% periodic pattern limit pulses are illustrated, and m in the same figure and e in FIG. 5 show the sine waveform of the AC power source 6. As is clear from the above explanation, in the apparatus having the configuration shown in FIG.
Since power is not supplied to both at the same time, the overall power consumption is kept constant, high frequency noise and voltage flicker are not generated, and the power supply capacity can be small. Next, FIG. 6 shows an embodiment in which the present invention is applied to a large-capacity electric furnace. In this case, the electric furnace 1 is
In addition to the first and second heaters 2, 7 and first and second thermoelectric elements 12, 14, third and fourth heaters 19, 20 and third and fourth thermoelectric elements 21, 22 are provided. , third heater 1
9 is connected to the AC power supply 6 via the bidirectional thyristor 23, the fourth heater 20 is connected to the AC power supply 6 via the bidirectional thyristor 24, and the third
The thermoelectric element 21 is connected to the third trigger control circuit 25
The fourth thermoelectric elements 22 are connected to a fourth trigger control circuit 26, respectively. The heated object position detector 27 is connected to an operation mode determiner 28 that determines the operation mode according to its output signal, and together with this determiner 28 forms a temperature disturbance detector. Further, the signal output terminal of the limit pulse generation circuit 18 connected to the operation mode determiner 28 is connected to the first to fourth trigger control circuits 1
5, 16, 25, and 26. The heated object position detector 27 is composed of a large number of scattered thermoelectric elements or photoelectric switches, and the limit pulse generating circuit 18 is composed of a thyristor 5 belonging to the first heater 2 and a third heater 2. In addition to the limit pulse for preventing the thyristor 23 belonging to the heater 19 from becoming conductive at the same time, the limit pulse is used to prevent the thyristor 10 belonging to the second heater 7 and the thyristor 24 belonging to the fourth heater 20 from becoming conductive at the same time. Generates a limit pulse to prevent this. Then, during the temperature rising period of the electric furnace 1, the first
The output signals of the first to fourth thermoelectric elements 12, 14, 21, and 22 are all small, and the limit pulse generation circuit 18 outputs, for example, 50 as shown in a and b in FIG.
% to 50% limit pulses are sent to the first and third trigger control circuits 15, 25 and the second and fourth trigger control circuits 16, 26. Therefore, the first to fourth heaters 2, 7, 19,
20 each operate with approximately 50% of the rated power supply. Also, during the heat retention period, the first to fourth heaters 2, 7, 19, and 20 operate at 10% of the rated temperature according to the same operating principle as in the above-mentioned embodiment.
It operates with a certain amount of power supplied. When the heated object approaches the electric furnace 1, the heated object position detector 27 starts a detection operation, and the operation mode determiner 28 analyzes the signal from the heated object position detector 27 to determine whether the temperature changes. Detects and selects and determines a predetermined driving mode. Now, assuming that this determination result is A, the limit pulses of the periodic patterns shown in i, a, j, b in FIG. Circuits 15, 16, 25, 26
Each will be sent to. On the other hand, since the first to fourth thermoelectric elements 12, 14, 21, and 22 send their respective detection signals to the trigger control circuit, a gate trigger pulse based on the AND gate output of both signals is applied to the gate of the thyristor. Approximately 75% of the rated power is supplied to the first heater 2, and the second to fourth heaters 7,1
Approximately 10% of the rated power is supplied to 9 and 20, respectively.

【table】

[Table] When the object to be heated moves to the vicinity of the first heater 2, the operation mode determiner 28 makes the determination B in the previous table, and the first heater 2 is given approximately 80% of the rated power. but,
Approximately 75% of the rated power is supplied to the second heater 7, and approximately 10% of the rated power is supplied to the third and fourth heaters 19 and 20, respectively. Further, when the object to be heated moves to the vicinity of the second heater 7, determination C in the previous table is made, and the third heater 19
By moving to the vicinity of
By moving to the vicinity of the heater 20, E is determined, and by escaping from the furnace, F is determined.
Judgments are made for each. Further, when the first heated object is near the fourth heater 20 and the second heated object approaches the inside of the furnace, a G judgment is made because the first heated object has escaped outside the furnace. When the second heated object is near the first heater 2, the judgment is H, and the first heated object escapes from the furnace and the second heated object approaches the inside of the furnace. The program is such that sometimes a determination of I is made for each, thereby alleviating the disturbance in the temperature inside the furnace caused by the passage of the object to be heated inside the furnace. Further, the amount of power supplied to the first to fourth heaters 2, 7, 19, 20 does not become excessive even momentarily, and voltage flicker is prevented from occurring. Moreover, the power supply capacity can be relatively small. Note that the operation mode determiner 28 can be configured by a logic circuit, but a microcomputer may also be used.

[Brief explanation of drawings]

Figure 1 is an electric circuit diagram of an electric furnace to which a conventional power adjustment device is applied; Figures a, b, and c in Figure 2 are waveform diagrams of the current supplied to the heater of the electric furnace; Figures 3 to 5; shows one embodiment of the power adjustment device of the present invention, FIG. 3 is an electric circuit diagram, and FIG. 4 a, b,
c, d, e, f, g, h, i, j, k, l are limit pulse waveform diagrams, m in Figure 4 is a sine waveform diagram of AC power supply, a, b, c, d in Figure 5 are A waveform diagram of the current flowing through the heater, e in FIG. 5 is a sine waveform diagram of the AC power supply, and FIG. 6 is an electric circuit diagram of another embodiment of the present invention. 1... Electric furnace, 2, 7, 19, 20... Heater, 5, 10, 23, 24... Thyristor, 6...
...AC power supply, 15, 16, 25, 26...Trigger control circuit, 18...Limit pulse generation circuit, 1
7...Temperature disturbance detector, 27...Heated object position detector, 28...Operation mode determiner.

Claims (1)

[Scope of Claims] 1. A plurality of heaters distributed in an electric furnace are each connected to an AC power source via a thyristor, and an interval of the number of power supply cycles is determined according to the temperature detected by a temperature detector near each of the thyristors. In the cycle control type power adjustment device that controls turn-on of each thyristor by supplying a trigger pulse to the gate of each thyristor in synchronization with the zero voltage of the AC power supply, a temperature change in the electric furnace is detected. a temperature disturbance detector; and a limit pulse for preventing turn-on of each of the thyristors in a periodic pattern that limits the trigger pulse of each of the thyristors so that the overall power consumption is kept approximately constant according to the detection result of the temperature disturbance detector. A cycle control type power adjustment device comprising: a limit pulse generator that generates a limit pulse; and a trigger control circuit that gate-controls each of the trigger pulses using each of the limit pulses and supplies the gates to the gates of each of the thyristors.