JP3015320B2 - Electric furnace power control method and apparatus - 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 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 switching element is often conducted at a phase angle where the voltage applied to the resistance heating element is considerably large, so that an undesirably high frequency disturbance voltage and an associated disturbance current are generated in the power supply line, And undesired disturbing radio waves to electronic devices around the power supply line. In the latter method, since the conduction and interruption of the switching element are performed at the zero cross point of the power supply potential, the generated disturbance factor is extremely weak, which is desirable for surrounding electronic devices. However, in order to finely adjust the calorific value, the latter cycle control method is not as simple as 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.

[0006]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to supply a plurality of loads connected in the same phase with a current as uniform as possible when viewed from a common power supply, and to simultaneously generate individual resistance heating. The power supplied to the electric furnace equipment can be controlled by controlling the current flowing to each load so that the power factor to this common power source can be improved so that the cycle of energizing the body and the cycle of not energizing are uniform over the time axis. It is an object of the present invention to provide a method for controlling a cycle and an apparatus for performing the method.

[0007]

SUMMARY OF THE INVENTION The above problem is by the invention, a plurality of resistance heating element having a rated heat generation amount RP _h R
_h a (h = 1 ~ H) connected in parallel to the phase of the AC power source, gives hope heat rate S _h at predetermined periods for each resistance heating element R _h, the heating value of each resistance heating element R _h Desired calorific value RP _h・ S
_{In the} power control method by cycle control of energizing / de-energizing one cycle at a time so as to satisfy _h , N _h cycles are selected as the basic control cycle of each resistance heating element R _h ,
The number of cycles to be energized from the beginning of the basic control cycle to the _Ih- th cycle is defined as the cumulative energization cycle number J _h (I _h ), and the target energization cycle number ST _h at the end of one basic control cycle and its time The difference from the cumulative energizing cycle number J _h (I _h ) is set as the deviation cycle number ΔS _h , and the target energizing cycle number ST _h for the next basic control cycle is expressed as ST _h = S _h × N _h + ΔS
_h , the plane A with Ih on the horizontal axis and _Jh ( _Ih ) on _the vertical axis
Origin 0 (0,0) and the point on the PL (N _h, ST _h) a straight line connecting the desired heating curve SCV _h, the desired heating curve SCV _h
Upper heating curve U, which were translated upwardly as A _h cycle
A lower limit heat generation curve LCV _h which is shifted downward by CV _h and B _h cycles is determined. If J _h (I _h −1) + 1 ≧ UCV _h (a), the resistance heating element in the I _h- th cycle is determined. R _h
Is de-energized, and if J _h (I _h −1) <LCV _h (b), the resistance heating element R _{h in the} I _h- th cycle
And if neither equation (a) nor (b) is satisfied,
Regarded as an intermediate state of indeterminate, from the sum of the desired calorific value with respect to all the resistance heating element at this time, the resistance heating element is determined for each of I _h is determined as energized by the formula (b) of the resistance heating element R _h The deviation obtained by subtracting the sum of the rated heating values of the above is taken as the target heating value of the entire resistance heating element in the intermediate state, and the sum of the unit cycle outputs of the resistance heating elements in the intermediate state to be energized is closest to the target heating value. In the middle state,
A combination of the resistance heating elements to be de-energized is determined. When a plurality of combinations are present in the determination of the combination, the resistance having a large delay of the cumulative energization cycle number J _h (I _h ) with respect to the desired heating curve SCV _h . a combination heating element R _h are included many adopted, the energization and non-energization of all of the resistance heating element is determined in the previous cycle of the cycle is executed during the cycle, been solved by I have.

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 ROM of the processor unit MP stores the program for determining the energization / de-energization of each resistance heating element according to the above-described power control method and the interrupt signal of the zero cross point,
Program that sends switching control signals to the switching unit SW _h is solved by stored.

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 properly distributed among the three phases R, S, T of the three-phase power supply.
You. In the case of FIG. 1, the electric furnace F₁~ F_Fourof
Resistance heating element R₁~ R_FourAre connected in parallel. These
Resistance heating element R₁~ R_FourThe corresponding switching unit
Knit SW₁~ SW _FourPower is introduced from the ST phase via
It is. Each electric furnace F₁~ F_FourThe temperature inside is TC₁~
TC_FourAnd the detected temperature signals are respectively
Temperature controller TR₁~ TR_FourIntroduced and stored in it
Other parameters such as target temperature, temperature gradient,
Program from duration and measured temperature signals
Gives the set temperature calculated based on the calculation formula
Therefore, a temperature control signal is generated.
Lead wire LS₁~ LS_FourThrough one common control device C
Send to TR. According to the present invention, this common control device C
TR, as will be explained in detail later,
Each load R based on the control signal₁~ R_FourSuitable for energizing and de-energizing
Conductor LC₁~ LC_FourVs through
Corresponding switching unit SW₁~ SW_FourAgainst
One open / close control signal is sent for each. Each load circuit has
Normal transformer is switching unit SW₁~ SW_Fourof
Provided before or after, but not directly related to this invention
So we omit them, just a voltmeter that detects voltage and current
(PT) V₁~ V_FourAnd ammeter (CT) A₁~ A_FourOnly
It is implied.

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.

[0012] To explain the core of the present invention, with reference to FIG. 3, consider the current flowing two load R _1, R ₂ equal resistors connected values in parallel between the same phases. in this case,
Load R ₁ is energized at a rate of 2/3, a load R ₂ is energized at a ratio of 1/3. In the energized state as shown in FIG. 3B load R ₁ is energized in cycles C _1, C _2, the load R ₂ is energized in cycles C _1, are neither energized cycle C ₃ either the load R _1, R _2. Therefore, when viewed from a common power source, through 2 times the current in the current cycle C ₁ in cycle C ₂ is. Contrary to this, the load in the case where the phase of R ₂ to a current flows in Figure 3A are shifted two cycles from the case of FIG. 3B, all the cycle C ₁ has current seen by the common power _supply, C
Flows through the same current in _2, C _3, smooth energization is performed. Therefore, in the energized state as shown in FIG. 3B, the power factor is clearly poor. An object of the present invention is to distribute an energizing cycle of each load so that a predetermined electric power is supplied to each load and a current as smooth as possible when viewed from a common power supply flows. Under normal operating conditions, electric furnace equipment is usually operated so that the power to be supplied to each load is 25 to 75% of the total power. Therefore, providing a smooth common current by distributing the energizing cycles of each load as evenly as possible is extremely effective for the power factor of the power supply.

The electric furnace equipment of FIG.
H resistance heating elements h connected in parallel to each other
(H = 1 to H), the power control method according to the present invention
explain. First, the basic control cycle for each resistance heating element h
Or the basic control cycle number N _hIs determined. Control this
Time t_hWhen converted to_h= T₀・ N_h (1) Where t₀Is the time between one cycle,
If the source frequency is 50 Hz, for example, it is 20 msec.

Furthermore, the amount of heat generated by the energization between the resistance heating element h is 1 cycle with rated capacity PR _h of the resistance heating element h. The desired heating rate ratio of the rated capacity PR _h of heat to be generated the resistance heating element h is S
_h (0 ≦ S _h ≦ 1.0). I _h from the beginning of the basic cycle
Th number of cycles that have been energized by the cycle position J _h (I _h)
It expresses. In this case, it may be simply expressed as J _h (I).

Next, the number of cycles ST _h should energized during the base control cycle N _h a target energization cycles. In the power control method according to the present invention, the target energization cycle number ST _h and the actually energized cycle number J _h at the last time point of the previous basic cycle in the basic cycle (that is, the first time point of the basic cycle). taking the difference between the (N), which represents the deviation cycles [Delta] S _h. That is, ΔS _h = ST _h −J _h (N) (2) Furthermore, target energization cycles ST _h from the fundamental period of the previous deviation cycles [Delta] S _h and the fundamental period of the desired current cycle number _{N h · S h, ST h} = N h · S h + ΔS h (3 ). In the above equation N _h, J _h (N) is an integer, ST _h and [Delta] S _h are real numbers.

If the control method according to the present invention is graphically displayed, it is easy to understand using FIG. That is, taking the number of cycles I _h over time on the horizontal axis, when actually fill in the energized cumulative cycles J _h on the vertical axis, the total output (S h _{= 1.}
0), that is, when energized all cycles, the cumulative number of cycles is moved on a straight line FL _h. If desired heat rate S _h is smaller than 1, linear SCV _h extending from the origin 0 to the determined point P _s by the number of cycles N _h of target energization cycles ST _h and the basic control cycle at this time is determined. This straight line is called a desired heating line. That is, the desired heating line SCV _h is expressed as: SCV _h = ST _h /
_Nh · _Ih (4).

Furthermore, defining the desired heating wire SCV each value from _h A _h and B _h as above and upper heating wire UCV _h and lower heating wire LCV _h moved down. _{That, UCV h = ST h / N} h · I h + A h (5) LCV h = ST h / N h · I h -B h (6)
It is.

According to the power control method of the present invention, the cumulative energization cycle number J _h (I _h ) exists in the intermediate region between the upper limit heating line UCV _h and the lower limit heating line LCV _h at all times (cycle I _h ). Control. FIG. 5 is used to explain the control in more detail. The state actually allowed by the control is a point between the upper limit heating line UCV and the lower limit heating line LCV (in this case, the subscript of the resistance heating element h is omitted for simplicity). That is, at the time of i-1, P ₀₁ , P ₀₂ , P ₀₃
, And at time i, P ₁₂ and P ₁₃ , and i + 1
At the time of it is allowed _{P 22, P 23, P 23} . When shifting from cycle i-1 to cycle i, P
When ₀₁ of the state does not perform power shifts to P _11, this state is not allowed. P and to energize in the state of P _01
A transition is made to state ₁₂ , which is allowed. _{Additionally,} the process proceeds to _{P 12} in a non-energized from the state of _{P 02,} the process proceeds to _{P 13} in conduction. All of these states are allowed. The process proceeds to P ₁₃ in a non-energized from the state of P _03, this transition is not allowed because the P ₁₄ is energized. For the transition from i to i + 1, the transition between energized and de-energized can be determined from similar considerations.

[0019] By mathematically express this situation, as I _h a common time t is in the resistance heating element h for all loads, cumulative cycles in the cycle time of I _h -1 of the resistance heating element h If the number J _h satisfies the following condition J _h (I _h −1) + 1 ≧ UCV _h (7), the resistance heating element R in the I _h- th cycle
_h is de-energized. This state corresponds to P ₀₃ → P in FIG.
₁₄ is not allowed, meaning only P ₀₃ → P ₁₃ is allowed. If you do not meet the equation (7), then examine the following condition _{J h (I h -1) <} LCV h (8), satisfies the equation (8), said at I _h-th cycle The resistance heating element _Rh is energized. This condition, in the case of FIG. 5 is not permitted P ₀₁ → P _11, means that it must be P ₀₁ → P _12.

[0020] Equation (7) is also the formula (8) is not satisfied, that is, as the transition state was determined to be indefinite from both equations (7, 8), the case of FIG. 5, or P ₀₂ → P ₁₂ , P ₀₂ → P ₁₃ are possible. Such a resistance heating element h ^′ is energized (P ₀₂
→ P ₁₃₎ or, or de-energized (P ₀₂ → P ₁₂₎ or is further determined by the following determination conditions. Since desired heating rates of the resistance heating element h is a S _h, the original total heating value P all of the resistance heating elements connected in parallel to the phase to be generated during one cycle ₀ of the resistance heating element h with rated capacity RP _h, is required to be _{P 0 = Σ h = 1,} H RP h · S h (9).

On the other hand, the calorific value P ₁ generated from the resistance heating element in the transition state determined by the two equations (7, 8) is P ₁ = Σh _″ RP (h ^″ ) (10). Here, h ^″ denotes a resistance heating element that satisfies Expression (8), and Σh _″ denotes that the sum of all such resistance heating elements is obtained. Therefore, according to the power control method of the present invention, δ (h ^′ ) is introduced as an index indicating whether the above-mentioned indeterminate transitional resistance heating element h ^′ is energized or deenergized, δ (h ^′ ) = 1, energized δ (h ^′ ) = 0, non-energized, and ΔP = P ₀ −P ₁ (11), then | ΔP−Σ _{h ′} RP _{h ′} · δ ( h ^′ ) | is equivalent to finding a set of δ (h ^′ ) that minimizes (12). First, it is assumed that the total number of h ^′ is K. Then, there are no energized states, only one energized state, two energized states,... K cases, and the number of combinations of the states is 2 ^K. For each of these combinations, calculate Eq. (12) and find the one that gives the minimum value.

As the specific method, the following two methods can be considered. A. Equation (12) is calculated for all the sets, and if there is only one set that gives the minimum value, it means that the energization / de-energization of the indeterminate transition state has been determined in that set. However, if there are a plurality of sets, the difference DEV _{h '} between the number of accumulated cycles between the desired heating line SCV and the state after the transition is calculated. _{That, DEV h '= SCV h'} - (J h (I h ') +1) (13) This difference DEV _h' deemed energization larger the delayed. That is, in FIG. 5, for example, undefined transition state at i cycle time is the _{P 12} and _{P 13.} Proceeds to _{P 23} the state of the P ₁₂ is _energized, the state of the _{P 13} is energized _{P 24}
Move to When P ₁₂ → P ₂₃ and P ₁₃ → P ₂₄ are compared, the difference between P _{24 and} β from the desired heating line SCV is negative, and it can be said that the lead is advanced. On the other hand, the difference between the β point in P ₂₃ is positive, it can be said that delayed. Based on such an idea, the largest DEV among the plurality of sets is described.
Select the set containing _{h '} . In that case, if there are a plurality of pairs, the pair containing the second largest difference is selected. Furthermore,
If there are a plurality of the same sets, the set is determined by the same procedure. B. First, the difference DEV _{h ′} in the equation (13) is calculated for all the undefined transitional resistance heating elements h ′, and the difference DEV _{h ′} is calculated.
Rearrange in ascending order of _{h '} . In this order, the number k (k =
1 to K) are newly added, and all possible combinations of energized and de-energized are prepared in a table so that the one with the smallest sequential number appears first. For example, FIG. 6 shows a table when K = 4. In this table, the symbol e is the serial number of the combination (1-2
⁴ = 16), and the symbol D ₀ is the number of resistance heating elements that are energized. Symbols d _{1 to} d ₄ indicate a k-th resistance heating element to be energized. For example, when e = 4, the number of energized loads is three, k = 1, 2, and 3 are energized, and k = 4 is non-energized. When e = 12, the number of energized loads is three, k = 2, 3, and 4 are energized, and k = 1 is non-energized. The total value of the rated heating value of the resistance heating element in accordance with the combination table 2 ^k number calculated, closest, moreover determines the energization and non-energization of all undefined state in combination appeared earliest combination table to the target heating value I do. It is reasonable to prepare such a table in advance for K = 1, 2,... H (total number of loads).

In summary, in the power control method according to the present invention, the energization / de-energization of the resistance heating element h in each cycle is determined by the first condition for determining whether or not the equations (7) and (8) are satisfied. When,
For the unsettled state that is not satisfied, it is determined by the second judgment condition that minimizes the equation (12). Next, a few explanations will be given for the parameters used in the method described above. (a) Relationship between the movement amounts A and B and the degree of freedom of the energization cycle distribution Regarding the movement amounts A and B in Expressions (5) and (6), m ≦ A + B ≦ m
+1; if (m an integer), between the upper heating wire UCV _h and the lower limit heating wire LCV _h there are m or m + 1 integers. However, when the realized heating curve is RCV, 0
Since .ltoreq.RCV (I) .ltoreq.I, at the beginning of the basic control cycle, the dashed line in FIG. 7a is meaningless, and the number of existing integers is reduced accordingly. Δ in the basic cycle before and after
Assuming that S is 0, the desired heating rate S is used (hereinafter, the index h of the resistance heating element is omitted unless it is necessary), SCV is J = S ・ I UCV is J = S ・ I + A LCV is J = S ・ I −B.

Number of cycles N that can be continuously de-energized
_off is a value obtained by subtracting the horizontal coordinate I ₁ of the intersection of the J ₀ and the upper limit heating wire UCV from the abscissa I ₂ at the intersection of any cumulative cycles J ₀ and lower heating wire LCV. From J ₀ = S · I ₂ -B J ₀ = S · I ₁ + A, N _off = I ₂ −I ₁ = (A + B) / S

Similarly, the number of cycles N _on that can be continuously energized is the abscissa I ₂ of the intersection of the straight line J = I-α of the number of cycles having a 45 ° gradient _on the APL surface and the upper limit heating line UVC.
From a value obtained by subtracting the horizontal coordinate I ₁ of the intersection of the cycle number J = I-alpha and lower heating wire LCV. That is, from I ₂ −α = S · I ₂ + A I ₁ −α = S · I ₁ -B, N _on = I ₂ −I ₁ = (A + B) / (1−S).

In the temperature control of the electric furnace, S = 0.2 in a steady state.
Since it is often operated at 5 to 0.75, S = 0.25, 0.
When N _off and N _on are obtained for 50 and 0.75, N _off = 4 (A + B) and N _on = 4 (A +
B) / 3 S = 0.50 and N _off = 2 (A + B), N _on = 2 (A +
B) When S = 0.75, N _off = 4 (A + B) / 3, N _on = 4 (A +
B).

In general, when S <0.5, there are more non-energized cycles than energized cycles, so N _on = 1 in an ideal distribution for energized and de-energized, and when S> 0.5, energized from non-energized cycles. Since there are more cycles, N _off = 1 in an ideal distribution. By giving the degree of freedom to the energizing cycle position, deviation occurs. However, when the deviation rate is γ, the maximum energizing cycle number (maximum continuous non-energizing cycle number) when S = 0.5 is defined as γ = 2 (A + B). For example, the distribution of the actual energization cycle is as follows.

(I) When S = 0.5, the energizing cycle and the non-energizing cycle are ideally realized alternately one by one.
In the worst case, it is possible that the γ-cycle is continuously energized and the γ-cycle is continuously de-energized. (ii) Ideally, one cycle of energization and three cycles of non-energization are alternately realized when S = 0.25. In the worst case, 2γ / 3
It is possible that continuous energization for 2 cycles and continuous non-energization for 2γ cycles may occur. (iii) When S = 0.75, ideally, three cycles of energization and one cycle of non-energization are alternately realized, but in the worst case, continuous energization of 2γ cycles and continuous energization of 2γ / 3 cycles may occur. possible.

(B) Tolerance of the bias rate γ The relationship between the amount of heat generated in the resistance heating element, the temperature of the resistance heating element, and the temperature of the object to be heated greatly differs depending on the heat capacity and the heat conduction characteristics, respectively. Γ for temperature control of electric furnace
Over 25 cycles (0.5 seconds at 50 Hz commercial frequency). However, the generated power of the resistance heating element,
In measuring the voltage and current, the larger the value of γ, the greater the delay in measurement and the lower the measurement accuracy when extracting the average value (or the effective value) as a DC signal. The smaller the value of γ, the better. Is practically up to 10 or so.

The total number H of the target resistance heating elements and the bias ratio γ
From the viewpoint of the uniformity of the power supply current for the purpose of the present invention, the effect increases as H increases, but the "intermediate state" of the H resistance heating elements (Equations (5) and (6) The effect does not increase if the number of resistive heating elements that are not satisfied) is increased. Ideally, if γ = H or more, the average S
When H is large, when か な り is large, there is a considerable effect at about γ = H / 2.

In consideration of the above circumstances, when H = 6, it is realistic that γ = 3 to 6 and A + B = 1.5 to 3 are the average of the values of A and B of each resistance heating element. is there. (c) About the values of A and B When the value of A + B is determined in the above description,
The distribution to B will be described. Desired heating line SCV
A = B in order to realize an actual heat generation curve close to.
Since the vertical axis of the APL plane cannot be reduced by the cumulative amount, going too far upward is a problem. For example, A ≧ 1.0
In this case, even if S = 0, power is supplied. As a method for solving such a problem, (i) A = 0.99 and the rest are B. (ii) A = B, but when A ≧ 1.0, the upper limit heating line UCV
Is set to [ST] +1 as shown in FIG. 7B ([ST] means an integer value obtained by removing the number below the decimal point of ST). In addition, the lower limit heating line L
For CV, correction is made as shown in FIG. 7c in order to approach the desired value ST as much as possible within the basic control cycle N when B ≧ 1.0 (the straight line portion having a large gradient instead of the broken line is shown in FIG. 4).
Is the same slope as the maximum output straight line FL).

(D) The mutual interval Z of the control cycle The resistance heating element to be used usually has its resistance value and corresponding electric current.
Since the thermal characteristics of the furnace differ, the basic control cycle N_hIs resistance
It differs for each heating element h. But several things are the same as each other
When the resistance value and the thermal characteristics of the surroundings are almost the same,
Basic control cycle N _h7b, and FIGS. 7b and 7c
Is corrected, A + at the final stage of the basic control cycle
Since B is substantially smaller, the degree of freedom is reduced and the power supply
There is a high possibility that uniformity of current cannot be achieved. H resistors
Among the anti-heating elements, the same basic control cycle N_hWith resistance
For the heating element, the basic control cycle is Z cycle (Z ≒ 2 (A
+ B)) are desirably shifted from each other.

(E) Relationship between basic control period _Nh and _Ah , _Bh The above considerations (a) to (d) are valid only when N is sufficiently larger than A + B. When N is large enough, A <N / 4, B
It is meaningless if it is not <N / 4, and in fact, A <N / 20, B <
It must be N / 20. However, since it is necessary that A + B> 1.0, it is appropriate to use A = B ≒ 1.0 when 1 ≦ N ≦ 10 (the minimum value is A = B ≒ 0.5).

FIG. 8 shows the control device CT used in FIG.
Indicates the contents of R. Temperature controller TR₁~ TR_FourSupplied by
Temperature control signal LS₁~ LS_FourIs the corresponding analog first
Digital converter A / D₁~ A / D_FourSupplied to
Here, a digital control signal corresponding to the temperature control signal is formed.
It is. These control signals are sent to the microprocessor unit.
To MP. Also, the load R used₁~ R_Four
1 and the voltage signal of the AC power supply between ST in FIG.
Positive and negative zero crosses are introduced to the loss point generation circuit ZS.
Interrupt signal S corresponding to point_{Z +}, S_Z-To form
Signal to the microprocessor unit MP
You. Microprocessor unit MP is ROM, RA
M, interface, synchronization control unit, interrupt management unit
Large-scale integrated circuits that include
HD 643180. Microprocessor unit M
P is the parameter to be used,
Basic control period N of anti-heating element h_h, Rated capacity RP of each load
_hAnd the programs that are necessary for
It is stored in the memory ROM. This operation is explained above
The first judgment condition and the second judgment condition are checked, and the load,
Apply the optimal cycle current to the anti-heating element. That is, each cycle
Le I_h-1 during the next cycle I_hShould be energized with
Load that is not to be changed
Zero cross point t at the beginning of the cycle_+,t_-Suitable time width
t_sSwitching control signal SG with_1,SG_Two(See Figure 2)
Generated, each load R₁~ R_FourInsulation circuit ISO corresponding to₁
~ ISO_FourOpen / close control signals SG of these_1,SG_TwoSupply
I do. The insulation circuit includes, for example, a light emitting diode and a photo
It is composed of a transistor, an AC power supply, and a rectifier circuit.
LED on the secondary side and phototransistor on the secondary side
There is a star. Isolation circuit ISO ₁~ ISO_FourFrom the secondary side of
Each load R₁~ R_FourSwitching unit SW for
₁~ SW_FourAn open / close control signal for firing is output. this
Each load h is turned on / off in response to the control signal.

FIGS. 9, 10 and 11 show flowcharts of a processing program including the above-described first determination condition and second determination condition. The content of this program has been described in detail for the main components above, so it is only briefly mentioned here. First, the required parameters H in _{preparation, RP h, N h, A} h, put a B _h in a predetermined storage device, previously housed a required calculation program in the ROM memory device. Further, all tables used in the second determination condition are also stored in the ROM storage.

Next, in the process FA, all the circulation parameters ΔS _h, I _h, J _H (I _h ), OUT _{h, and} ROU are initialized.
Set _Th to zero. Then, the interruption prohibition of the zero cross point signal is released. Here, OUT _h represents either de-energized or the final energization in the determination condition. OUT = 0 is not energized,
OUT = 1 means an energized state. ROUT _h the trigger signal an interrupt signal (SG _1, SG ₂₎ the isolation circuit ISO
In memory to output to, it is a copy of the OUT _h.

In the processing step FB, the zero cross point is observed, and a wait is performed for calculating the energization / non-energization of the next cycle. Next, the first determination condition (Equation (5) and
Check whether (6)) is satisfied. At this stage, the one determined to be non-energized has OUT = 0, and the one determined to be energized has OUT = 1. In the case of an undetermined one, OUT = 0 is set and the process F of the next second determination condition is performed.
Sent to D.

In the process FD of the second determination condition, the following equation (1)
By finding a set of undefined resistance heating elements that minimizes the value of 2), the method B described above is employed in this flowchart. In this processing step FD, energization / non-energization of all the resistance heating elements is determined. In other words, OU without electricity
T = 0 and OUT = 1 when energized. Process F
F starts by interrupting a positive zero crossing point during FB processing,
Outputs the previous result OUT _h calculated in the cycle to SG1 insulating circuit with copy to ROUT _h, passing a positive half-wave by a thyristor switch. After the end of the FF, calculations FC to FE in the next cycle are performed.

The process FG operates by interruption of a negative zero crossing point, which occurs during the calculation of the next cycle (FC to FE) or after the calculation is completed (FB), and energizes the negative half wave by the thyristor switch. I do. The SG2 to output the insulating circuit by the preceding ROUT _h. This process is shown in the time chart of FIG. Symbols FA, FB, FC, FD, F in the figure
E indicates the processing shown in FIGS. 9 and 10, and symbols FF and FG indicate the interrupt processing shown in FIG. Time sequence of the process determines the energization and non-energization of all the loads in the previous cycle, positive and negative zero cross point detected by the zero cross point generating circuit in the next cycle t _+, t _- in applying The time is extended for a predetermined period, and energization or non-energization is performed for about one cycle depending on the state (energization / non-energization) corresponding to the load.

In this time chart, the FA block operates only once when power is supplied to the microprocessor.
Next, initial processing of the FB block, initial setting of required parameters and release of interrupt prohibition are performed, and an interrupt after completion of the initial processing is accepted. The FB block waits for calculation of energization / non-energization in the next cycle.
As described above, the FC block determines energization / non-energization according to the first determination conditions of FC1 to FC10, and prepares to send an undefined one under the conditions to the processing of the next FD block. For the FD block, the energization
The non-energized state is finally determined based on the second determination condition. FE
1 to 6 are preparations for performing calculations in the next cycle.

Processing of the FC, FD, and FE blocks must be completed within one cycle time (20 msec at 50 Hz). FF block interrupt 1 during processing of FB block
(T ₊ interrupt) initiated by outputs a result OUT _h calculated in the previous cycle as SG1 with copies to MOUT _h. After the end of the FF block, the calculation of the next cycle (FC to FE block) is started. The FG block is operated by the interrupt 2 (t _- interrupt), during the calculation of the next cycle (FC-FE block) or after the completion of the calculation (F
Occurs B), and outputs it as SG2 by MOUT _h.

Note that the timing of occurrence of the interrupt 2 (t _- interrupt) is not always during the processing of the FD block, but may be during the processing of the FC to FE blocks or during the FB block. In the control method described above, energization or non-energization of all the resistance heating elements is determined for the next cycle i + 1 during a certain cycle i, and the positive and negative zero cross points t _+, When t _- is detected, energization / de-energization is performed for each corresponding half-wave, and energization / de-energization for one cycle is performed.

Finally, based on FIG. 3 shown above, the desired heating rates are given to two resistance heating elements R ₁ and R ₂ having the same rated capacity and connected in parallel to the common power supply in the same phase. The current situation when S (1) = 2/3 and S (2) = 1/3 is determined by the cycle control method (A) according to the present invention, the conventional cycle control method (B), and the control method using the phase angle control ( C) will be described in comparison.

The effective current values I ₁ and I ₂ of the resistance heating elements R ₁ and R ₂ can be calculated as follows: I ₁ = √ (S (1)) = √ (0.667) ≒ 0.82 A I ₂ = √ (S (2)) = √ (0.333) ≒ 0.58 A However, in the case of the control method of the present invention, the waveform of the combined current I ₁ + I ₂ is a continuous sine wave having the same amplitude as shown in FIG. Therefore, the effective value of the combined current I ₁ + I ₂ is 1.0 A.

On the other hand, in the control method (C) using the phase angle control, the effective value of the combined current I ₁ + I ₂ is 1.29 A from the calculation of the effective value. Further, in the conventional cycle control method (B), the situation of FIG. 3B and the situation of FIG. 3A occur with a probability of 2: 1. Because it is because, if the phase relationship between the current flowing through the resistance heating element R ₁ is any case the same, if the period of the current flowing in R ₂ is only C _1, C ₂ or C _3, respectively occurs at the same frequency There is (the first case corresponds to FIG. 3B, the last case corresponds to FIG. 3A according to the invention, and the middle case is not shown). And R ₂
There when energized only during the period C ₁ or C _2, the effective value of the composite current I ₁ + I ₂ of the conventional cycle control method since the effective value of the same synthetic current and phase angle control method (B) is √ ( (2 × 1.29 ² +1.0 ² ) / 3) = 1.2A.

As a result, the effective current value seen on the common power supply side by the method (A) of the present invention is 1/1/50 of the effective current value of the phase angle control method (C) or the conventional method (B).
Reduce to 1.29 or 1 / 1.2. In the description of FIG. 3, a special case in which the number of resistance heating elements is two and the desired heating rates are 2/3 and 1/3 is used. The present invention is also generally applicable and effective. Therefore, the effective current value can be effectively reduced even in an actual continuous furnace or batch furnace.

Such a reduction in the effective current value means that the reactive current can be reduced, and the power factor can be significantly improved. Therefore, the electric power is used more effectively. In particular, considering that the electric power consumed in an electric furnace is usually very large, even a small reduction rate of the reactive current significantly improves the power utilization. When the total number of resistance heating elements connected in parallel in the same phase increases, a uniform current flows from the common power supply side, which is advantageous for improving the power factor.
If there is a particularly large load (small resistance) in the resistance heating element, the load can be divided into a plurality of parts and connected in parallel in the same phase via one switching unit for control. it can. In this case, the temperature controller and the thermal element are commonly used. Such an arrangement increases costs due to the increased number of connecting wires and their terminations, but reduces the cost of the thyristor elements of the switching unit, so that the manufacturing costs are reduced overall or almost as compared to the case of individual loads. Can be equivalent. Such division of the resistance heating element is particularly advantageous for improving the power factor.

The power control method according to the present invention and the apparatus for implementing the method can be variously modified and modified in addition to the method described above. However, it goes without saying that all the structures defined in the claims belong to the category of the present invention.

[0049]

As described above, the power cycle control method according to the present invention and the apparatus for executing the control method according to the present invention make the power sources as uniform as possible from a common power supply for a plurality of resistance heating elements connected in parallel in the same phase. High current can flow. Therefore, the power factor for the common power supply can be improved by optimally controlling the current flowing through each load.

[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), and the actual flowing current waveform (b)
Below),

FIG. 3 shows waveforms of a combined current obtained by various control methods: a cycle method (a) according to the present invention, a conventional cycle control method (b) and a phase angle control method (c),

FIG. 4 is a diagram showing possible energization states according to the invention for cycle control,

FIG. 5 is a diagram for explaining a determination condition of energization / non-energization,

FIG. 6 is a table for specifying various sets of energized states;

FIG. 7 is a diagram showing various deformations of the heating wire;

FIG. 8 is a block diagram of an internal circuit of the control device;

FIG. 9 is a flowchart of a calculation process for determining energization / non-energization,

FIG. 10 is a flowchart following FIG. 9;

FIG. 11 is a flowchart of a zero crossing point interrupt process;

FIG. 12 is a time chart of a calculation process for determining energization / non-energization.

[Explanation of symbols]

F electric furnace R resistance heating elements (load) h individual index TR temperature specifying the resistance heating element controller TC thermal element (thermocouple) SW switching unit TH _1, TH ₂ SCR CTR controller MP microprocessor unit ZC Zero cross point signal generator A / D analog / digital converter ISO isolation circuit

Continuation of front page (56) References JP-A-6-335234 (JP, A) JP-A-4-235613 (JP, A) JP-A-2-23036 (JP, A) JP-A 64-9510 (JP) JP-A-62-233814 (JP, A) JP-A-63-122818 (JP, U) JP-B 8-3762 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB Name) G05F 1/45

Claims (5)

(57) [Claims] 1. A plurality of resistance heating element having a rated heat generation amount RP _h; connected in parallel with (R _{h h} = 1~ _H) in phase of the AC power supply, for each resistance heating element (R _h) gives hope heat rate S _h in a given time period, the amount of heat generated desired heating value RP _h · S of each resistance heating element (R _{h)
In the} power control method by cycle control of energizing / de-energizing one cycle at a time so as to satisfy _h , N _h cycles are selected as the basic control cycle of each resistance heating element (R _h ), and the start of the basic control cycle is selected. I _h-th the number of cycles until the performing energization cycle and cumulative energization cycles J _h (I _h), 1 basic control cycle before target energization cycles ST of the end from
As _h the difference the speed deviation cycles [Delta] S _h between the cumulative energization cycles J _h (I _h) at that time, and the target energization cycles ST _h of the next basic control cycle and _{ST h = S h × N h} + ΔS h A straight line connecting the origin 0 (0, 0) and the point (N _h, ST _h ) on the plane APL in which I _{h is} plotted on the horizontal axis and J _h (I _h ) is plotted on the vertical axis is a desired heat generation curve SCV _h . defines the lower limit of heating curve LCV _h moved parallel downward to the desired heating curve SCV _h as upper heating curve UCV _h and B _h cycles were translated upwardly as a _{h cycle, J h (I h -1)} + 1 ≧ UCV if _h (a), the resistance heating element in the I _h-th cycle (R
The _h) a non-energized, if _{J h (I h -1) <} LCV h (b), the resistive heating element in the I _h-th cycle (R
_h ) is energized, and if neither of equations (a) and (b) is satisfied, it is regarded as an indeterminate intermediate state, and each resistance heating element (R _h ) The difference obtained by subtracting the sum of the rated heating values of the resistance heating elements determined to be energized by equation (b) for each I _{h in} the determination is the target heating value of the entire resistance heating element in the intermediate state, and energized. The combination of the resistance heating elements to be energized and de-energized in the intermediate state is determined so that the sum of the unit cycle outputs of the resistance heating elements in the intermediate state should be closest to the target heating value. If the combination is present, employing a combination that contains many large resistance heating element R _h delay cumulative energization cycles J _h (I _h) with respect to desired heating curve SCV _h, energization of all of the resistance heating element・ De-energize Power control method determined in the previous cycle of Le, run during that cycle, characterized in that. Wherein A _h ≧ 1.0 in the upper heating curve UCV _h
, The upper limit value of UCV _h is set to [ST _h ] +1.
2. The power control method according to claim 1, wherein [ST _h ] denotes an integer obtained by removing a number of decimal places of ST _h or less. Wherein B _h ≧ 1.0 at the lower heating curve LCV _h
, The gradient is 1 through the point (N _h, [ST _h ]) on the APL plane.
The power control method according to claim 1, wherein a straight line above and the LCV _h are used. 4. For a resistance heating element (h) having the same basic control cycle N _h , the start of the cycle is set to 2 (A + B)
3. The method according to claim 1, wherein the phase is shifted by about one cycle.
3. The power control method according to 1. 5. 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 whether to energize
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)
The OM has the power control method according to any one of claims 1 to 4.
Program to determine the energization / de-energization of each resistance heating element
And each switching signal according to the interrupt signal of
Unit (SW _h) Program that sends an open / close control signal to
A common control device characterized by storing a program.