JPH11167976A - Electric power control method for electric furnace and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and inexpensively improve a power factor to a common power source by cyclically controlling an electric current of a plurality of resistance heating elements connected in parallel to a common AC power source, so that an integral valve of electric power consumption in respective current carrying cycle positions is uniformized as much as possible. SOLUTION: A heating rate of resistance heating elements R. to R4 is adjusted by cyclically controlling switching units SW1 to SW4 by a common control device CTR by outputting a control signal from temperature controllers TR1 to TR4 in accordance with this measured value by measuring a temperature of electric furnaces F1 to F4 having the resistance heating elements R1 to R4 connected in parallel to, for example, an ST phase of an AC power source by temperature sensing elements TC1 to TC4 . In that case, current-carrying/current-noncarrying of the respective resistance heating elements is decided by respective basic control periods, so that the integrated electric power level is uniformized as much as possible over the cycle number N by integrating electric power consumption in the resistance heating elements up to 1l to (n)-th in respective cycle positions I in the cycle number N, corresponding to the basic control periods.

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 electric power of electric furnace equipment when a plurality of resistance heating elements in one or more electric furnaces are connected in parallel to the same phase of a power supply. An apparatus for performing the method is provided.

[0002]

2. Description of the Related Art As is well known, the amount of heat generated in an electric furnace as described above is adjusted according to the value of power supplied from a power supply to a resistance heating element via a semiconductor switching element. In that case, the supplied power is determined according to the ratio of conduction / non-conduction of the semiconductor switching element. A thyristor is usually used as this semiconductor switching element. There are two types of thyristor control: a phase control method for controlling the energization phase angle, and a cycle control method for energizing / de-energizing each power supply cycle. In the former method, since the amount of heat generation is adjusted by varying the energization phase angle, it is suitable for fine heat generation adjustment. However, the voltage applied to the resistance heating element is often turned on and off at a considerably large phase angle, so that an undesired high-frequency disturbance voltage and a disturbance current associated with the power supply line are generated, It generates unwanted disturbing radio waves to electronic devices around electric furnaces and power lines. In the latter method, since the switching element is turned on and off at the zero cross point of the power supply potential, the effect of the generated disturbance factor is extremely weak, which is desirable for surrounding electronic devices. However, in order to finely adjust the heat generation amount, the latter cycle control method is not easy because the control output is discrete compared to the former phase control method.

[0003] From such a viewpoint, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 63-44214 that the electric power of an electric furnace is controlled based on a cycle control method capable of reducing the occurrence of disturbance. In this case, a pair of half-waves adjacent to each other in which the voltage of the commercial power supply is positive and negative is defined as one cycle, and a cycle in which the resistance heating element is energized and a cycle in which the resistance heating element is not energized are distributed as uniformly as possible over a time axis. It is proposed to control the heating value of the electric furnace in the state.

In a large electric furnace, a large number of resistance heating elements are used, and these resistance heating elements are distributed and connected so as to have a substantially uniform load distribution among three single phases among three phases. Have been. Therefore, usually two or more resistance heating elements are connected in parallel to each phase.
It is not always possible to achieve as uniform a current intensity as possible from the viewpoint of a common input power supply by simply energizing such a resistance heating element in an evenly distributed conduction cycle. This is because, for example, if the energization output rate to the two resistance heating elements is 50%, that is, the voltage is applied for one cycle, and the repetition without voltage is continued during the next cycle. There are cases where the waveforms of the applied voltages are the same, that is, when the voltages having the same waveform having the same phase are applied to both the heating elements, and there are cases where the applied voltages to both are energized with a shift of one cycle from each other. In the former case, when viewed from the common power supply, the current flowing to the common power supply is twice as large as the current for a single load in the first cycle, and no current flows in the next cycle. Assuming that there is no inductance component of the circuit, there is no delay in the current generated with respect to the applied voltage.) On the other hand, in the latter case, the current flowing through a single load flows continuously over all cycles. Therefore, even if the power consumption is the same, the imbalance at the time of energization can be prevented by appropriately selecting the mutual phase position of the energization cycle.

[0005] When a load current equally distributed as seen from the common power supply flows, imbalance of the current flowing through the line can be prevented, and the power factor of the load power can be improved. From this point of view, the present applicant has proposed an efficient power control method and a device advantageous for implementing the method, as disclosed in Japanese Patent Application No. 9-90980.
No. 92254.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for supplying current to a plurality of loads connected in phase, based on a different technical idea from the above-described method. The power factor for the common power supply can be improved by controlling the current flowing to each load so that the cycle in which the individual resistance heating elements are energized and the cycle in which the individual resistance heating elements are not energized are uniform over time. And a method for performing cycle control of electric power supplied to an electric furnace facility, and an apparatus for performing the method.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a rated heating value R connected in parallel to the same phase of an AC power supply is provided.
So as to realize the desired heat rate S _h respectively relative to the total number H of the resistive heating element R _{h (h} = 1~H) having a P _h, each cycle position I of the number of cycles in N which corresponds to the basic control cycle
Integral power TA THAT the power to determine the energization and non-energization of the resistance heating element R _h In the method for cycle control, by integrating the power dissipated by the resistance heating element 1 at the cycle position I through n (I, n) the power level of, each time starting with the resistance heating element 1 sequentially integrated until the resistance heating element H, so that uniform as possible over the number of cycles n, the energization and non-energization of the resistance heating element R _h Is determined in each basic control cycle, and energization / non-energization of all the resistance heating elements is executed in accordance with this determination in the next basic control cycle.

Furthermore, the above problem is by the invention, the heat sensitive element TC _h via a switching unit SW _h in parallel to the phase of the AC power supply connected to the resistive heating element R _h, corresponding to a heating target product, a temperature detection signal of the thermal element TC _h,
In an electric furnace installation comprising a temperature regulator TR _h of the PID calculation from the target temperature to form a desired heating value signal of the resistance heating element R _h of the heating target product, desired amount of heat supplied from the temperature controller TR _h Switching unit SW according to signal
_h is a common control device CTR that outputs a trigger signal for determining the energization / de-energization of _h , wherein the common control device CTR includes:
Positive and negative zero cross point of the power t _+, t _- zero cross point generation circuit for generating a trigger signal to specify a ZC, temperature controller TR
_The analog-to-digital converter A / D which receives the desired heating value signal of _h and outputs it as a digital signal, a storage ROM,
Microprocessor unit MP including RAM, interface, interrupt management unit and central processing unit
And an output control signal from the microprocessor unit be composed of an electrically insulating and individually insulated circuit outputs individually switching control signals to the respective switching unit SW _h in the pulse signal of predetermined width ISO, the micro the storage device ROM of the processor unit MP in response to the interrupt signal of a program and zero crossing point determining energization or non-energization of the resistance heating element by the above method, the opening and closing control signal to the switching unit SW _h The problem is solved by storing the program to be transmitted.

Further advantageous configurations according to the invention are set out in the dependent claims.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
The present invention will be described in more detail with reference to FIG. In FIG.
The arrangement of the electric furnace equipment according to the invention of the invention is shown. This electricity
The furnace equipment is provided, for example, by using a resistance heating element R₁~
R_FourConstant temperature electric furnace F consisting of₁
~ F_FourIt is for passing through. Such an electric furnace
Are appropriately distributed among the phases R, S, T of the three-phase power supply.
You. In the case of FIG. 1, the electric furnace F₁~ F_FourDuring ~
Resistance heating element R₁~ R_FourAre connected in parallel. this
Resistance heating element R₁~ R_FourThe corresponding switching
Unit SW₁~ SW_FourPower from ST phase via
Is done. Each electric furnace F₁~ F_FourThe temperature inside is TC₁
~ TC_FourAnd the detected temperature signals are
The corresponding temperature controller TR₁~ TR_FourWas introduced to
Other parameters stored in it, such as the target temperature,
From the temperature gradient, duration, etc. and the measured temperature signal,
Set temperature calculated based on the programmed formula
Generates a temperature control signal to give
No. for each conductor LS₁~ LS_FourThrough one common
Send to control device CTR. According to the present invention, this common
The controller CTR receives and receives data as described in detail below.
Load R based on the temperature control signal₁~ R_FourEnergized / not energized
In order to conduct electricity at an appropriate cycle position, the conductor LC₁~ L
C_FourSwitching unit SW via₁~
SW_FourTo each of the open / close control signals. each
In the load circuit, a transformer is usually provided with a switching unit S
W₁~ SW _FourIs provided before or after
Since they are not directly related, they are omitted and only voltage and current are
Voltmeter to detect (so-called PT) V₁~ V_FourAnd ammeter (so-called
CT) A₁~ A_FourOnly is implicitly shown.

As shown in FIG. 2A, the switching unit SW comprises two switching elements TH ₁ and TH ₂ connected in anti-parallel between an input terminal T _I1 and an output terminal T _O1 , and an input terminal T _I2 and an output terminal T _I2. And a conducting wire directly passing between the terminals T _O2 . In this case, the switching elements TH ₁ , T
H ₂ is usually composed of a thyristor element. Gate G _1, G ₂ and the corresponding cathode of the thyristors TH _1, TH ₂
Predetermined gate signals SG 1 _between, the SG ₂ is energized, as shown in the upper part of FIG. 2b, thyristors TH _1, TH ₂ is respectively positive and negative as shown in the lower part of Figure 2b conductive Half waves flow. That is, the gate signal SG ₁ supplies a conduction signal at the time of the positive half-wave zero crossing point t ₊ between _one gate and the cathode of _one thyristor, for example, TH ₁ to make this thyristor TH ₁ conductive. Further, the gate signal SG ₂ outputs the conduction signal at the time of the zero cross point t ₋ of the negative half wave to the thyristor TH.
₂ thyristor TH ₂
Is made conductive. According to the present invention, a pair of a positive half wave and a succeeding negative half wave is always conducted as one cycle, and a cycle in which the thyristor is conducted per time (cycles of C ₁ and C ₃ shown in the center of FIG. 2B). , and it determines the power for making and breaking the thyristors, i.e. the heating element by controlling the percentage of the cycle to be paused (cycle C ₂ shown in the middle of FIG. 2b). Such control is the cycle control employed in the present invention. Note that the gate signals SG1 _, SG1, shown in FIG.
The reason why SG ₂ has a relatively long time interval t _s is set to about 60% of the half cycle time so as to follow the delay of the thyristor current due to the inductance component in the circuit.

FIG. 3 shows the control device CT used in FIG.
Indicates the contents of R. Is supplied to the temperature controller TR ₁ to Tr temperature is supplied from the _fourth control signal LS ₁ ~LS ₄ is first converted to the corresponding analog-to-digital circuit _{A / D 1 ~A / D 4} , where the digital equivalent to the temperature control signal A control signal is formed. These control signals are introduced into the microprocessor unit MP. Also, the loads R _{1 to} R ₄ used are
1, the voltage signal of the AC power supply between ST in FIG. 1 is introduced into a zero cross point generating circuit ZS to form interrupt signals S _{Z +} and S _Z− corresponding to positive and negative zero cross points, These interrupt signals are also introduced into the microprocessor unit MP. Microprocessor unit MP is ROM, RA
M, an interface, a synchronization control unit, an interrupt management unit, a large-scale integrated circuit including an arithmetic processing unit, etc., for example, HD643180 manufactured by Hitachi. Microprocessor unit M
P is a parameter to be used, the basic control period N _h of the resistance heating element h which is the load already described, the rated capacity RP of each load.
_h and programs necessary for the arithmetic processing are stored in the corresponding storage ROM in advance. In this calculation process, the first determination condition and the second determination condition described above are checked, and the load, that is, the resistance heating element is energized in an optimal cycle. That is, during each cycle I _h −1, a load to be energized and a load not to be energized in the next cycle I _h are determined, and the load is appropriately determined at the first zero cross point t _+, t ₋ of the pair of positive and negative cycles. closing control signal SG _1, SG ₂ (see Figure 2) occurs in a time width t _s, the insulating circuit ISO ₁ ~I corresponding to each load R ₁ to R ₄
Switching control signal SG ₁ of this like the SO _4, and supplies the SG _2. The insulating circuits ISO _{1 to} ISO ₄ are composed of, for example, a light emitting diode and a phototransistor, and an AC power supply and a rectifier circuit. A light emitting diode is disposed on the primary side, and a phototransistor is disposed on the secondary side. In addition, an insulation coupling circuit that simply uses a pulse transformer can be considered. Each load R ₁ -R from the secondary side of the insulation circuits ISO ₁ -ISO _4
4 switching control signal for firing the switching unit SW ₁ to SW ₄ is output to. Each load h is turned on / off in response to the control signal.

The electric furnace equipment shown in FIG. 1 is further expanded to include a total of H resistance heating elements h connected in parallel with each other in the same phase.
The power control method according to the present invention will be described for (h = 1 to H). First, define a common basic control period or basic control cycle number N _s for all of the resistance heating element. Converting this to the control time t _s , t _s = t ₀ · N _s (1). Here, t ₀ is the time during one cycle of the power supply, and is 20 msec when the power supply frequency is, for example, 50 Hz.

Furthermore, the amount of heat generated by energizing between the resistance heating element h is 1 cycle with rated capacity PR _h of the resistance heating element h. The desired heat rate S _h (0 the ratio of rated capacity PR _h of heat to be the resistance heating element h is generated
≦ S _h ≦ 1.0). An integrated value of the number of cycles which is energized during the cycle position to I-th from the beginning of the base period N _s represents a J _h (I).

Next, a certain basic control cycle N_sResistance between
Number of cycles ST to which heat body h should be energized _hThe target energizing cycle
, ST_h= [N_sS_h] (2) Where [X] means the integer part of the real number X
You. That is, the above condition is the basic period N_sTarget energization
Number of cycles ST_hThe more the energizing cycle
Show.

According to the present invention, under the condition that the distribution of the energizing cycle and the non-energizing cycle of each resistance heating element h itself is made as equal as possible, the current flowing to the common power supply is also uniform over all the cycles of the power supply. The energization / non-energization of all the resistance heating elements h (h = 1 to H) is determined so that a current, that is, a substantially constant current flows. The first condition, that is, the distribution of the energizing cycle and the non-energizing cycle of each resistance heating element h itself is made as equal as possible as follows. Here, for the sake of simplicity, the distinction between the individual resistance heating elements is omitted and the symbol h is omitted unless necessary. Further, a target energization cycle number ST and M, represents the basic control period N _s and K. That is, the first condition is that M cycles are energized during K, KM cycles are de-energized, and M cycle positions are distributed as evenly as possible within the basic period K. . A method for determining the equal distribution will be described for the case where K = 10 and M = 6 as shown in FIG. In the graph display, the horizontal axis represents each cycle position I of the power supply, and the vertical axis represents the integrated energizing cycle J energized to the resistance heating element.
A straight line (PQ) is drawn between (0, 0) and a point (10, 6) indicated by a square symbol determined by K = 10, M = 6, and the straight line PQ is drawn by -α (α is an appropriate real number). A shifted straight line PP, J = M / K / I-α (3) is drawn, and an integer value J (I) on the vertical axis closest to the straight line PP is examined at each cycle position I. And this integer value J
A case where (I) is above the straight line PP is indicated by a white circle 、, and a case where it is below the straight line PP is indicated by a black circle ●. It is assumed that the white circle 白 thus determined is the non-energized position and the black circle で is the energized position. When the integer J (I) is on the straight line PP, one of them is determined in advance as the non-energized position or the energized position. As is apparent from FIG. 4, there are M energization cycles of the black circles in the basic control cycle K, and the distribution of non-energization and energization on the horizontal axis is substantially uniform. FIG. 4 also shows, for reference, a relational expression FP in the case of full-power operation, that is, energization at all cycle positions. Of course, when energization is not performed at any cycle position, the horizontal axis (J = 0)
Is itself.

FIG. 5 shows patterns indicating the energized / de-energized cycle positions determined in this way for possible values of M for K = 2 to 10. In this case, the obvious outputs (M = K) and no outputs (M = 0) are omitted from the drawing. In the pattern of FIG. 5, a white circle indicates energization, and a horizontal bar indicates non-energization. Various changes and improvements can be considered for determining the pattern of the energized / deenergized cycle position. For example, when the basic control cycle K is relatively short, the original target calorific value K · S is obtained, but the allowable cycle is a positive integer.
Rounding was performed as in (2). This difference, that is, the difference Δγ between the target heat generation amount K · S in the immediately preceding basic control cycle and its integer value M, Δγ = KS− [KS] = K · S−M, is calculated as the next target heat generation amount. In other words, M in the next basic control cycle is changed to M
= M + Δγ increases control accuracy. But,
If the basic control cycle K is considerably long, for example, if K ≧ 15, the effect of such correction is extremely weak. Also,
It is advantageous to use an appropriate numerical value of 0 to 1.0 for α in equation (3) so that the calculation is easy.

As another modification, the pattern of the energized / deenergized cycle position can be determined empirically, not by calculation, but visually. At this time, the number of cycles M to be energized during the basic control cycle K may be evenly distributed.
For example, with respect to K = 0 and M = 8 in FIG. 5, the calculation of equation (3) determines ○ -−- ○-○, which is empirically determined as ○ -−- ○. ○○○ － can also be determined. The power control method according to the present invention can be realized by preparing in advance the patterns determined empirically for all necessary K and M, as in FIG.

Next, under the second condition, that is, under the condition that the pattern of the energized / de-energized cycle position of each resistance heating element is made as uniform as possible, the current flowing through the common power source also extends over all the cycles of the power source. In order to determine the energization / de-energization of all the resistance heating elements so that a uniform current flows, the following procedure is performed. For simplicity of explanation, as one specific example, as shown in FIG. 6, the basic control cycle K is 10 cycles, and the loads connected in-phase in parallel, that is, five resistance heating elements (h
= 1 to 5), the rated heat generation amount of each load as shown PR _h
Are 10, 9, 8, 7, and 6, respectively. The number of cycles M to be energized is set to 7, 5, 4, 5, and 6, respectively. Then, the energized / deenergized cycles are distributed in descending order of the rated calorific value.

First, as a step (I), M = 7 is equally distributed for the cycle of K = 10.
The arrangement of M = 7 columns of 10 patterns applies. That is, the non-energized cycle positions are I = 2, 6, 9, and the energized cycle positions I = 1, 3, 4, 5, 7, 8, 10. In addition,
The length in the vertical direction is displayed so as to be proportional to the magnitude of the calorific value.

Next, in step (II), since M = 5, the load is energized at the non-energized cycle positions I = 2, 6, and 9. In addition, it is necessary to energize for two cycles. To perform this energization in an evenly distributed state,
Except for the previously compensated cycle positions of I = 2, 6, 9 it is necessary to energize for about two cycles of I = 1, 3, 4, 5, 7, 8, 10 cycles. That is, the basic control cycle K
Considers the possible cycle as K = 7 and replaces I = 1,3,4,5,7,8,10 with the new cycle I = 1,2,3,4,5,6,7 Regard it. Two cycles are equally distributed to this arrangement. This includes M = 7 of the K = 7 pattern in FIG.
Apply the second column pattern. According to this pattern, since the distribution is-○ -−- ○-, the current is supplied at the cycle position of I = 2, 6 and is not supplied at the other 5 cycle positions. When the energization cycle position is converted into the original cycle position, both cycle positions are I = 3, 8 (see the second energization distribution from the bottom in FIG. 6).

Next, in step (III), step (I
Four powers with the third power ratio 8 are evenly distributed and stacked on the distribution of current I). The energized power after step (II) is completed can be divided into three types of integrated power groups. That is, the first group, the five cycle positions with the power ratio of 9 that is energized at the three cycle positions 2, 6, and 9
Divided into three groups: a second group with power ratio 10 energized at 1, 4, 5, 7, 10 and a third group with power ratio 19 energized at two cycle positions 3, 8 . Three of the four cycles with power ratio 8 are first allocated to the first group of cycle positions, i.e., I = 2,6,9. The remaining one cycle is allocated to the second group of cycle positions I = 1, 4, 5, 7, and 10. For this, the distribution of K = 1 and M = 1 in FIG. 5 is adopted. That is,
The energization cycle position is I = 3, which corresponds to I = 5 when converted to the original cycle position. Therefore, at the end of step (III), the power having a power ratio of 3 is supplied to the cycle positions of I = 2, 5, 6, and 9 (see the distribution of power in the center of FIG. 6).

Steps (IV) and (V) can be performed in a similar procedure. In the final step (V), the integrated power is made uniform as shown in the uppermost part of FIG. That is, assuming that all the loads h = 1 to 5 happen to be energized at the cycle position I = 8, the power level P indicated by a broken line in FIG.
_The power consumption is extremely high like ₀ (corresponding to 40 in the power ratio). Further, when all the loads are energized at this cycle position, there is a possibility that all the loads are not energized at other cycle positions, or that the power consumption is significantly lower than the average level. Such irregular power consumption naturally results in a lower power factor. However, the power control method according to the present invention can completely prevent such undesired distribution of energized power, and can provide a substantially uniform power consumption distribution over the entire cycle position of the basic control cycle.

In order to program the above procedure using mathematical formulas, the following quantities are introduced. First, all loads h are ordered. Although this order is not particularly specified, for example, the order may be larger in the order of the rated heating value RP, or vice versa. Assuming that the integrated power output from the first load to the h-th load by energization at the I-th cycle position in the basic control cycle K is TA (I, h), TA (I, h) = Σ _{k = 1, h} RP _k ε (I, k) (4) Here, ε (I, k) changes depending on whether or not the k-th load is energized at the I-cycle position. That is,

[0025]

[Outside 1] It is. Further, those having the same size of TA (I, h) are sequentially grouped from small to large. Each group is distinguished by a symbol g, and the total number of the groups g is expressed as GN (g). M out of the total number K of cycles in group g
A pattern for energizing the number of cycles is represented as GNT (g; K / M). Actually, K corresponds to the total number GN (g) of the group g, and GNT (g; K / M) corresponds to the column of M where K = GN (g).

A program of a procedure for deciding the energization / non-energization of the load for each cycle position I under such preparation will be described with reference to the flowchart of FIG. Step S
_{At 0} , no load is set, and h = 0 (set to the state before step I in FIG. 6). Then, at this time of the TA (I, h) in step S ₁ obtained. In this case, the electric power is 0 at all the step positions. The total number of groups is only one, and GNT (g; K / M) is K = 10 and M = 0 under the conditions of FIG. The operation under this condition is simple, so it is omitted, and the further advanced case of h> 1 will be described.

In step S ₃ , the number of cycles M corresponding to the amount of heat to be generated by the next load is obtained from the above-described equation (2). In step S ₄ , this is calculated by K = the number GN of the first group. Compare with (1). If M is less than K, it is possible to allocate all the M cycle into K cycle in step S _5. Equal distribution can be achieved by looking up a pattern as shown in FIG. 5, which is prepared in advance and allocates M cycles to the basic cycle of K. Or the expression
By using the reference line of (3), the energized and de-energized patterns can be determined. Converting the cycle position of the pattern S ₆ to the actual cycle position corresponding thereto.

[0028] If M is greater than K, the K-number of cycles at this time to all energized at step S _7, obtains the MM = total number of M-K-number of cycles and the next group KK = GN (2), step compared thereto at S _8, if MM ≦ KK, determined the pattern of rows of M = MM in Table K = KK step S _9, converts the corresponding cycle position in step S ₁₀ based on the cycle position . If MM> KK,
And energizing all cycles location of the group 2 in step S _11, the group and the remaining MM-KK number of cycles of the following 3
Allocate evenly. At this time, similar to the previous step S ₄ and S _8, the cycle number GN (3) Group 3 investigate whether accommodating any remaining MM-KK number of cycles in step S _12. Subroutines for repeating such arithmetic processing are sequentially executed, and finally, energization / non-energization of all loads h can be determined at all cycle positions in the basic control cycle.

[0029] in the calculations for the next load h + 1 back to the original step S ₁ in step S _13, the energization and non-energization of loads h at every cycle position determined. All loads h =
H to examine whether this calculation is performed in step S _14, After computation is complete energization and non-energization pattern is determined, the load power or the corresponding current seen from a common power source of the uppermost 6 Pattern TA (I, H) (I = 1,
K).

The details of the program of the ROM storage in the microprocessor MP (FIG. 3) for actually performing the above-described arithmetic processing will be described here. In addition to the codes described so far, the contents of the main variables or status symbols used in the program are listed below. N: Basic control cycle or cycle, K until now
And what. H: The serial number of the load, which has been set to h so far.

STS: Specifies the start-up state.
When = 0, it indicates a state of waiting for completion of the first calculation, and when = 1, it indicates a state in which a result exists. CEND: Specifies a calculation completion notification. When = 1, the completion of the calculation of the energized position for N cycles of the basic control cycle at the program level is notified to the t ₊ zero interrupt program. The t ₊ zero interrupt program confirms that CEND = 1 at the timing when the output of the first cycle of the next basic control cycle is completed and the output of the N cycles of the basic control cycle currently being output is completed, and calculates Result OUT (H,
N) is copied to MOUT (H, N), and CEND = 0.

S (H): Desired heat rate. ΔS (H): The heat generation rate that can be generated within the basic control cycle is 0.0,
1 / N, 2 / N,..., 1.0, there is a difference between the target heat rate and the realized heat rate in the basic control cycle. ΔS (H) = target heat rate−realized heat rate, and the target heat rate of the basic control cycle is S (H) + ΔS (H) immediately before. OUT (H, N): Calculation result at program level, expression
In the symbol of the quantity corresponding to the factor (Equation (5)) used in (4), 0
Or a value of 1. MOUT (H, N): a stored value for controlling the thyristor at the interrupt level, which is transferred from OUT (H, N) once every N cycles. After OUT (H, N) is copied to MOUT (H, N), the calculation result of the next basic control cycle is stored.

CY: has a value of 1 to N, and MOUT (H, N)
Of which cycle is output to the thyristor. M: the number of cycles to be energized within the basic control cycle for one load (0 ≦ M ≦ N). The initial value is N × (S (h) + ΔS (h) of the immediately preceding basic control cycle), and M energization cycle positions are determined by a plurality of DC routines and at most one DB subroutine (DC and The DB subroutine will be described later). TA (N): In the middle of deciding the load energizing cycle position in the order of the rated capacity, the total value of the calorific values of the load (which may be considered as current values) determined so far is within the basic control cycle. Is the total value for each cycle position. It is equivalent to TA (I, h) in equation (4), but D for I and H
These values are omitted because the exponent in the O-loop is not used directly. At the stage when the energization cycle positions of the h loads are determined, the values of the N TAs can take only (h + 1) kinds of values at the maximum.

G: A symbol for designating a group determined from TA. G: Total number of groups g. GN (g): Total number of cycle positions belonging to group g. GNT (G, GN (G)): The cycle position belonging to the group g is stored. FLG (N): = 0 means that the i-th cycle position has not been grouped, and = 1 means that the grouping has been completed.

CNT: means the total number of cycle positions of the group for which grouping has been completed. Next, the operation of the flowchart shown in FIG. 7 is performed under the following conditions: (1) The desired heat generation rate S (h) is defined as
Use the more accurate one with. (2) The energized / de-energized pattern corresponding to FIG. 5 is determined from the reference line of equation (3).

(3) The cumulative heating value is determined for each of the resistance heating elements h having a higher rated power value and a smaller rated power value. 8 to 10 show programs executed under the following conditions. Here, since the principle procedure of the present invention has already been described in detail with reference to FIG. 7, detailed description of the program is omitted, but it is composed of the following main parts. FC1 to FC3: Preparation stage for arithmetic processing FC3B: Reads the desired calorific value from the temperature controller FC4: Initializes the integrated power TA and the factor that expresses energization / deenergization FC6: Determines target cycle number M FC7 (DA) : Subroutine for determining grouping and arrangement of energization patterns corresponding to FC9: Judgment whether target cycle number M can be filled with the number of cycles of group FC10 (DB): Subroutine for equally distributing energization cycle positions FC11 (DC): Subroutine for determining the energizing cycle position of group g FC12: Calculate the number of cycles that could not be processed in group g FC13: Preparation for transition to group (g + 1) FIG. 9 shows the processing contents of subroutines DA, DB, and DC among these. And FIG. Since the principle of the processing of each step has already been described above, it can be easily understood from symbols and mathematical expressions implicitly shown in the frame of the step.
Therefore, the detailed description is omitted here. This FC
In the flow, the energization / non-energization of the resistance heating element h at the i-th cycle position is finally determined as OUT (h, i).

Next, in FIG. 11, the energized / de-energized OUT (h, i) of the resistance heating element h at the determined cycle position i and the positive / negative signal detected by the zero cross point signal generator ZC (FIG. 3). zero cross point t _{+ a,} t _- based on the time of performing the energization and non-energization of the positive voltage portion and a negative voltage portion of the cycle. Flow FA for positive zero cross point t _+, also flow FB is negative zero cross point t _- a program to be executed for. In both the FA and FB flows, OUT (h, i) obtained by the FC flow is replaced with MOUT (h, i), and the energized / non-energized determination result MOUT (h, i) is used as an insulation circuit ISO. The trigger signal S is applied to the gates of the corresponding thyristors TH ₁ and TH ₂ (FIG. 2a) via (FIG. 3).
It is supplied as G ₁ and SG ₂ .

FIG. 12 shows a microprocessor unit M
12 is a timing chart of the arithmetic processing sequence shown in FIGS. In this case, the cycle number N of the basic control cycle is shortened to 5 in order to make the drawing easy to see. The time lapse of the flow of FC, FA, and FB is attached to the time axis t on the horizontal axis, and the solid arrow α and the broken arrow β shown on the time axis indicate the positive and negative zero cross points, respectively. Show.

In the first control cycle shown in the figure, since the power is turned on, CY = 0 is set and the thyristor is not fired. Actual control starts from the second control cycle, and CY increases by one for each cycle. At the end of the control cycle, the calculation completion notification signal CEND, which has been low (0), becomes high (1). The FC 3A is waiting for a time adjustment, during which time the microprocessor unit MP is not performing any calculations. The control output signal of the temperature controller TR attached to each resistance heating element is read by the FC 3B, and a calculation for equally distributing the energization / de-energization of all the resistance heating elements is performed by the FC 4 to 17 following this.

The basic control cycle N _S (or K) is usually selected to be about 20 cycles. This value is determined in relation to the response speed of the electric furnace. In a normal case, the control output signal of a commercially available temperature controller is XXX according to the response speed.
Output every msec . Therefore, it is advantageous to select the sampling rate (ie, corresponding to N _S ) for receiving the desired heating value _Sh to be this output cycle, that is, about 20 cycles.

The programs shown in FIGS. 7 to 11 show a preferred embodiment of the power control method according to the present invention, but various modifications and improvements are possible. For example, longer and 20 about as basic control cycle N _S stated above, the deviation of the heat generation rate of the previous basic control cycle as the target heat rate _{S h Δγ (= NΔS (h} ); FC 6 in FIG. 8 ) Are not included in the next basic control cycle. That is, even if Δγ is always regarded as 0, almost no error occurs.

The cycle pattern of energization / de-energization of each resistance heating element can be determined not by the equation (3) but by a look-up table method using a pattern obtained empirically. However, in any case, it goes without saying that all the methods and apparatuses defined in the claims fall within the scope of the present invention.

[0043]

As described above, according to the power cycle control method of the present invention, the energization / de-energization of the individual resistance heating elements connected in parallel to the same phase of the power supply is made as uniform as possible over a continuous predetermined period. At the same time, the total power consumed by the total resistance heating element or the total current flowing through the total resistance heating element can be maintained substantially constant over a continuous predetermined period. Therefore, the power factor for the common power supply can be improved.

Further, the common control device for the power control device according to the present invention, whether it is a cycle control system or a phase angle control system, can be easily introduced without significantly modifying existing electric furnace equipment. . Then, the method according to the present invention can be executed only by storing a program which can apply the above-described power method to various electric furnace facilities in the ROM storage of the microprocessor unit. Above all, the common control device proposed in the present invention has a simple structure and can be manufactured at low cost, and the number of working steps can be significantly reduced as compared with ordinary electric furnace equipment.

According to the power cycle control method of the present invention, the thyristor is ignited at the zero-crossing point, so that the original excellent characteristic, that is, the disturbance of the power supply line can be reduced to a minimum, and the surrounding electronic devices can also be affected by radio waves Is maintained, and power control with high adjustment accuracy is enabled.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of an electric furnace facility,

FIG. 2 shows the connection of the switching unit (a), the trigger signal of the switching element corresponding to a pair of energized cycles (above b), and the current waveform actually flowing (b)
Below),

FIG. 3 is a block circuit diagram of a main part of a common control circuit,

FIG. 4 is a graph showing a relational expression for determining energization / de-energization in each cycle,

FIG. 5 is an even distribution cycle pattern of energization / de-energization for various control periods K and energization rates M,

FIG. 6 is a diagram showing a distribution of integrated power at each cycle position by sequential excitation of a resistance heating element,

FIG. 7 is a flowchart for calculating an equal distribution of energization and non-energization;

FIG. 8 is a flowchart showing FIG. 7 in further detail;

FIG. 9 is a detailed flowchart of a DA subroutine for grouping,

FIG. 10 is a detailed flowchart of a DB subroutine for equal distribution and a DC subroutine for cycle position conversion;

[11] zero cross point t ₊ a t _- a subroutine for generating a firing signal,

FIG. 12 is a timing chart showing a control flow.

[Explanation of symbols]

F _1-4 Electric furnace R _1-4 Resistance heating element (load) h Index to designate each resistance heating element TR _1-4 Temperature controller TC _1-4 Thermal element (thermocouple) SW _1-4 Switching unit TH _1, TH ₂ SCR CTR controller MP microprocessor unit ZC zero cross point signal generator A / D _1-4 analog-to-digital converter ISO _1-4 insulated circuit

Claims (8)

[Claims] 1. A total number H of resistance heating elements (R _h ; h = 1) having a rated heating value RP _h and connected in parallel to the same phase of an AC power supply.
Each so as to realize the desired heat rate S _h respect to H), and determines the energization and non-energization of the resistance heating element (R _h) at each cycle position I of the number of cycles in N which corresponds to the basic control cycle The power level of the integrated power TA (I, n) obtained by integrating the power consumed by the first to n-th resistive heating elements at the cycle position I is changed from the resistance heating element 1 Each time the heating element H is successively integrated, the energization / de-energization of each resistance heating element (R _h ) is determined in each basic control cycle so as to be as uniform as possible over the cycle number N, and in the next basic control cycle. A power control method, characterized in that energization / non-energization of all resistance heating elements is executed according to this determination. 2. A case where the resistance heating element energized M _h number of cycles located in the number of cycles N in order to achieve a desired heating rate S _h of (R _h), the previous step n at each integrated step n cumulative energization power TA (I, n-1) at -1 were classified according to the size of the power level, starting from a low power level group, the number of cycles M _h is the power level to be energized (a) If less than the number of groups g are allocated evenly distributed so as to be uniform as much as possible conduction cycle position relative cycle position of the group g, (b) the number of cycles M _h should energization the power If it is larger than the number of groups of the level, all the cycle positions are energized, and (c) the number of remaining cycles is the group g + of the next power level.
If the number of cycle positions is smaller than 1, the allocation procedure (a) is performed by changing the group g to the group g + 1, and (d) the number of remaining cycles is equal to the group g + of the next power level.
If it is larger than the number of cycle positions of 1, the allocation process (c) is performed by changing the group g to the group g + 1, and the above allocation procedure (a) is performed until all the cycle numbers M _h are filled.
The method according to claim 1, wherein (d) is performed. 3. The method according to claim 1, wherein K = K
The number of energization cycles is m for each of N to K = 2, and a pattern indicating an even arrangement of energization cycle positions is prepared by empirically obtaining in advance all possible m (1 to K). 3. The method according to claim 2, wherein K and m are specified, and an optimum arrangement of the energization cycle positions in that case is found. 4. When the number of energizing cycles is m with respect to the number of continuous K cycles, the arrangement of the energizing cycle positions is determined by setting the horizontal axis to the cycle position I and the vertical axis to the integrated cycle number J. = M / K ・ I-α When the integer value closest to the straight line at the cycle position I is greater than or equal to J, the current is determined to be non-energized, and when the integer value is smaller, the current is determined to be energized. The method of claim 2, wherein the real number is between 0 and 1.0. The number M _h of cycle position to realize a desired heat rate S _h of 5. A resistive heating element (R _h) is the product of the values of the total number of cycles N corresponding to the rated heat generation amount RP _h and the basic control period 5. The method according to claim 2, wherein the value is an integer value or a value obtained by adding one to this value. The number M _h of cycle position to realize a desired heat rate S _h of 6. resistive heating element (R _h) is rated heating value RP _h and the basic control of the basic control period of the previous one of the basic control cycle integer value of this product from the product of the total number of cycles N corresponding to the period or by subtracting the plus 1 to the integer value, corresponding subtraction value to the rated heat generation amount RP _h and the basic control period of the basic control cycle The method according to any one of claims 2 to 4, wherein an integer value of a value added to a product of the total number of cycles N to be performed or one obtained by adding 1 to the integer value. 7. To determine the integrated energizing power TA (I, n),
The method according to any one of claims 1 to 6, characterized in that use a set of resistive heating elements h chosen in descending order of rating calorific RP _h. 8. Switching in parallel with an AC power supply in phase.
Unit (SW_h) Through the resistance heating element (R_h) Connect
And a heat-sensitive element (TC_h) And heat
Element (TC_h) And the target temperature of the object to be heated
The resistance heating element (R_h) Hope
Temperature controller (TR _h)
In the furnace, the temperature controller (TR_hHope) supplied by
Switching unit (SW) according to heat generation signal_h)
Common system that outputs a trigger signal to determine the energization / de-energization of
In the control device (CTR), the common control device (CTR) includes a positive / negative zero clock of a power supply.
Point (t_+,t_-) To generate a trigger signal
Loss point generation circuit (ZC), temperature controller (TR_h) Hope
An analyzer that accepts the calorific value signal and outputs it as a digital signal
Log / digital converter (A / D), storage ROM, RA
M, interface, interrupt management unit and central performance
A microprocessor unit (M
P), and from this microprocessor unit
Output control signals are electrically insulated and pulse signals of a certain width
Each switching unit (SW_hOpening and closing control individually
It consists of an individual insulation circuit (ISO) that outputs signals.
And a memory R of the microprocessor unit (MP)
Each resistance is set to OM by the method according to any one of claims 1 to 7.
Program to determine whether to turn on and off the heating element
Each switching unit responds to the loss point interrupt signal.
(SW_h) Stores a program that sends an open / close control signal to
A common control device characterized in that: