JPH05198366A - Current comparing circuit for induction heating inverter device - Google Patents

Abstract

PURPOSE:To uniform the temperature of a heating target metallic material by stabilizing the output current of an induction heating inverter device. CONSTITUTION:The output signal obtained by amplifying the output of a power regulator 13 by an amplifier 14 is used as a reducing correction value to a current set value, and the value obtained by subtracting the output signal from the set value is used as a comparing standard current value in a comparator 15. When the inverter output current is larger than the comparing standard current, the comparing circuit 15 is laid in operating state to subtract a power proportional value between the inverter output power and its power set value and conduct the reducing compensation of the comparing standard current value to hold the operating state of the current comparing circuit. In this way, the temperature of a heating target material can be stabilized by setting the comparing standard value of the comparing circuit to a fixed value corresponding to the current target value, subtracting the proportional value of the power deviation between the output power of the inverter and the set power value from the current target value to conduct the reducing correction of the comparing standard value, and holding the comparing circuit as it is when laid in the operation state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current control system of an induction heating inverter device which uses an induction heating coil for a metal object as a load and which is related to constant heating temperature control of the metal object. The present invention relates to a current comparison circuit for correcting an output current command value.

[0002]

2. Description of the Related Art The current comparison circuit as described above operates in order to adjust the inverter output current which influences the heating state of the metal object, and operates when the output current increases by a predetermined value or more to reduce the output current. This is for operating a command circuit of a new current command value for control, but in the conventional current comparison circuit of this kind, the reference predetermined value to be compared with the above-mentioned inverter output current is fixed. None, it is known that no correction is made according to the operating state of the comparison circuit.

FIG. 2 is a block circuit diagram of an induction heating inverter device including such a current comparison circuit, and FIG.
It is a heating characteristic view corresponding to. First, the circuit configuration of the induction heating inverter device will be described with reference to FIG. In the figure, 1 is an AC power supply, REC is a rectifier circuit, C _f is a smoothing capacitor, and T _r1 and T _r2 have anti-parallel diodes D ₁ and D ₂ , respectively, and perform switching operation alternately. Power transistors _Cr1 and C functioning as inverters
_r2 is a resonance capacitor, 3 is a heating coil, and each of these elements constitutes a main circuit component of the inverter device. Further, 2 is a metal to be heated, and CT ₁ and CT ₂ are current transformers for detecting the input current and the output current of the inverter device, respectively.

Next, 11 is a power calculator for calculating and detecting the input power of the inverter device by using the detected current of CT ₁ and the terminal voltage of C _f as inputs, and 12 is a power setter.
Reference numeral 13 denotes a power controller that receives a power deviation signal obtained by subtracting the output value of the power calculator from the set value of the power setter,
Reference numeral 16 is a current controller that receives a current deviation signal obtained by subtracting the detected current value of CT ₂ from the output value of the power controller. In addition, 20 is the invertor detected by the CT _2.
The output current value I _o is a constant DC voltage between the busbars P and N and the resistance R ₁
And a comparator for outputting a set value I _so by closing the output path with an operating state if greater than the divided-obtained current setting value I _so by the R _2, wherein the set value I _so
Is a subtraction correction signal for the current deviation signal.

Further, 17 is a phase shifter for calculating a required phase difference of the inverter output voltage based on the detected current of CT ₂ by the output signal of the current regulator 16, and 18 is an output signal of the phase shifter. In response to the frequency ratio calculation of the inverter output voltage and the PWM calculation, the two transistors T
_A pulse distribution circuit for performing a distribution calculation of switching command pulses to _r1 and T _r2 , 19 receives an output signal of the distribution circuit, amplifies it, and outputs it as a switching command to both transistors T _r1 and T _r2 . It is a base drive circuit which is given to the base.

As described above, the output control system of the inverter device has a current control system as a minor loop in the power control system, and increases the output current of the inverter over a predetermined value. According to the operation of the comparator, the current command value in the current control system is reduced, and the current control according to the reduced command value is performed. Next, FIG. 4 is a heating characteristic diagram of the metal object 2 obtained according to the operation of the inverter device as described above, where P is the output power of the inverter device and T is the surface temperature of the metal object. , T ₁ indicates the temperature at which the resistance of the metal suddenly drops (Curie temperature).

Now, at time t ₁ , if the temperature T reaches the Curie temperature T ₁ and the resistance of the metal object suddenly decreases, the output current I _o and the output power P accompanying it also start to rapidly increase. At t ₃ , the output current I _o is the set value I _so.
If a larger, the output current I _o current command value of the current control system is reduced corrected by set value I _so the operation of the comparator 20 is decreased. As a result, the output current I
_o is the set value I _so from the comparator 20 if the small becomes inoperative again set value I _so correction is eliminated by the output current I _o will start to increase again. Thereafter, the increase / decrease of the output current I _o centered on the set value I _so is repeated according to the circuit time constant, and the output power P also increases / decreases accordingly. In this case, the surface temperature T of the metal object fluctuates as shown in the figure according to the difference between the thermal time constant of the metal object and the time constant of heat radiation to the outside air, which receives the time-integrated value of the electric power P that fluctuates as described above. ..

[0008]

The heating condition of the metal by the induction heating inverter device having the current control system using the conventional current comparison circuit as described above is as shown in the heating characteristic diagram of FIG. The output current of the inverter device and the output power associated therewith, and thus the input power of the metal object, are the fluctuation width and fluctuation period related to the output circuit time constant of the device and the comparison dead band width of the current comparison circuit. Fluctuates.

However, in general, the temperature fluctuation time constant of the metal material is considerably large as compared with the time constant of the output circuit of the inverter device, and thus the input power fluctuates as shown in FIG. The amount of heat input to the metal object is larger than the amount of heat radiated, and the amount of accumulated heat increases and the surface temperature also increases. That is, as long as the inverter device changes its output power as shown in FIG. 4, it is generally very difficult to control the surface temperature of the metal object. This also indicates that unnecessary power is being applied to the metal object.

In view of the above, it is an object of the present invention to provide a current comparison circuit in an induction heating inverter device which can keep the surface temperature of a metal object to be heated constant and prevent unnecessary power application. is there.

[0011]

In order to achieve the above object, the current comparison circuit of the induction heating inverter device according to the present invention provides an output of the inverter device having a metal induction heating coil as a load. It is for correcting the inverter output current command value in the current control system of the control system, and the inverter output current is larger than the comparison reference current value of the comparison circuit, and the comparison circuit is in the operating state. , The proportional value of the power deviation between the inverter output power and its power setting value is subtracted from the comparison reference current value to correct the reduction of the comparison reference current value, and the operating state of the current comparison circuit is changed. Shall be retained.

[0012]

The change in the output power of the inverter as shown in FIG.
This is because the comparator circuit functioning as described above with respect to the output current of the inverter performs a comparison operation with a constant comparison reference value to change the current command value of the output current control system. Further, when the temperature of the metal object to be heated exceeds the Curie temperature, the equivalent resistance of the heating coil having the metal object in its secondary circuit sharply decreases, but the metal object has unstable resistance around the Curie temperature. There is no steady heating operation in the area.

Therefore, if the metal object is heated to a temperature above its Curie temperature and the equivalent resistance of the heating coil is in the stable region, the current value corresponding to the input power that can keep the metal object at the target temperature is set to the target value. By performing the constant current control of the inverter output current having a value, it is possible to stabilize the temperature control of the metal object through the constant value of the input power. Therefore, once again, once the comparator circuit for changing the current command value of the inverter output current control system enters the operating state with the current target value as the reference value for comparison, the operating state is maintained as it is. It is possible to avoid unnecessary fluctuations in the output current and output power of the.

According to the present invention, the comparison reference value of the comparison circuit is not a constant value corresponding to the current target value, and the proportional value of the power deviation between the output power of the inverter and its power setting value is the current target value. Is performed to reduce the comparison reference current value, that is, the correction amount for the target value is adjusted to be smaller as the output power becomes larger, and the operating state of the comparison circuit once entered into the operating state. The control circuit is configured so as to hold the same.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to a block circuit diagram of an induction heating inverter device of FIG. 1 and a heating characteristic diagram of FIG. 3 corresponding to FIG. In FIG. 1, constituent elements having the same functions as those in the embodiment of the prior art shown in FIG. 2 are designated by the same reference numerals.

First, FIG. 1 is provided with an amplifier 14 to which the output signal of the power controller 13 in FIG. 2 is input, and the output signal ΔI _{s of the} amplifier is not used as a reduction correction value for the current setting value I _so . it is obtained without the comparative reference current value in the comparator 15 with a value I value by subtracting the output signal [Delta] I _s than _so I _s. Next, FIG. 3 is a heating characteristic diagram of the metal object 2 obtained in accordance with the operation of the inverter device as shown in FIG. 1 and corresponds to FIG. 4 described above.
It shows a state in which each of the output current I _o , the output power P, and the temperature T is stably controlled by providing the reduction correction value ΔI _s as described above.

That is, if the temperature T reaches the Curie temperature T ₁ at time t ₁ and the resistance of the metal material suddenly decreases, the output current I _o and the output power P associated therewith also start to rapidly increase. _{If the} output current I _o becomes larger than the corrected set value I _s as described above at 2, then the comparator 15
The current command value of the current control system is reduced and corrected by the operation of, and the output current I _o decreases, and at the same time, the output power P
Also decreases. Therefore, after the time t ₂ , the set value I _s of the comparator 15 also decreases simultaneously with the decrease of the output current I _o due to the decrease of the output power P, so that the magnitude relationship between the two values does not change, and The comparator 15 continues its operating state, so that the current command value in the inverter output current control system also becomes constant, and the output current I _o , the output power P, and the temperature T are stabilized as described above. Will be planned.

[0018]

According to the present invention, the present invention relates to a current comparison circuit for correcting the inverter output current command value in the current control system of the output control system of the inverter device having the induction heating coil as a load. If the inverter output current becomes larger than the comparison reference current value and the comparison circuit enters the operating state, the comparison reference current value is inverted.
Output of the inverter by subtracting the proportional value of the power deviation between the output power of the inverter and its set value to correct the reduction of the comparison reference current value to maintain the operating state of the current comparison circuit. The surface temperature of the metal object to be heated can be made constant through stable constant control of current and output power, and at the same time, energy saving operation of the inverter device can be achieved by preventing unnecessary power application. ..

[Brief description of drawings]

FIG. 1 is a block circuit diagram of an induction heating inverter device showing an embodiment of the present invention.

FIG. 2 is a block circuit diagram of an induction heating inverter device showing an embodiment of the prior art.

FIG. 3 is a heating characteristic diagram corresponding to FIG.

FIG. 4 is a heating characteristic diagram corresponding to FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Metal object 3 Heating coil 11 Power calculator 12 Power setting device 13 Power regulator 14 Amplifier 15 Comparator 16 Current regulator 17 Phaser 18 Pulse distribution circuit 19 Base drive circuit C _f Smoothing capacitor C _r resonance Capacitor (C _r1 , C _r2 ) CT Current transformer (CT ₁ , CT ₂ ) D Diode (D ₁ , D ₂ ) REC Rectifier circuit T _r Power transistor (T _r1 , T _r2 )

Claims (1)

[Claims] 1. A current comparison circuit for correcting an inverter output current command value in a current control system of an output control system of an inverter device using a coil for induction heating of a metal object as a load,
When the inverter output current becomes larger than the comparison reference current value of the comparison circuit and the comparison circuit enters the operating state, the inverter output power and its power setting value are changed from the comparison reference current value. A current comparison circuit for an inverter device for induction heating, wherein a proportional value of a power deviation is subtracted to reduce and compare the comparison reference current value to maintain the operating state of the current comparison circuit.