JPH053074A - Induction heating inverter device control method - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the heating temperature control performance of the metal object to be induction-heated by the inverter. A method of controlling an inverter device for induction heating for supplying electric power to a load metal object by electromagnetic induction through an induction heating coil to heat the load metal object, wherein the surface temperature of the metal object is variable. A temperature switch that detects that the temperature is exceeded and outputs the output, and a current setting circuit that can change the set value that is operated by the output of the switch are provided, and the surface temperature of the metal object is equal to or higher than the set temperature. In this state, the output current of the inverter device is set to a value specified by the output of the current setting circuit. Furthermore, instead of the temperature switch, a rapid increase in the output current of the inverter device is increased in magnitude and time. A comparison circuit for the output current, which is detected by the rate and the duration, etc., is provided.

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 an induction heating inverter device for holding a heating temperature of a metal object such as a pan or an iron plate, which is a load to be heated, at a predetermined value.

[0002]

2. Description of the Related Art A conventional control method of this type is shown in FIG.
It is known to perform a heating operation as shown in the heating characteristic diagram shown in FIG. 5 by the block circuit diagram shown in FIG. First, in FIG. 6, 1 is an AC power supply, REC is a rectifier circuit, Cf is a smoothing capacitor, and T _r1 and T _r2 have diodes D ₁ and D _{2 in} antiparallel, respectively, and alternately perform switching operation to form an inverter. The functioning power transistors, C _r1 and C _r2 , are resonance capacitors, 3 is a heating coil, each constituting a main circuit component of the inverter device, and 2 is heated by power feeding by electromagnetic induction from the heating coil. a metallic object, the CT ₁ and CT ₂ is a current transformer for detecting the input current and the output current of each of the inverter device.

Next, 11 is a power calculator, which is the CT.₁of
The detected current and the terminal voltage of the Cf are used as inputs for the input signal.
The input power of the burner device is calculated and detected.
The detected value of the power is calculated from the power set by the power setter 12.
The subtracted value is input to the power controller 13 as a power deviation signal.
Then, from the current signal that forms the output of the controller 13, the C
T₂The value obtained by subtracting the detected current value of is the current deviation signal
The signal is input to the controller 14 and further output to the controller 14.
More CT₂Inverter output based on the detected current of
When the voltage is output, that is, the required phase difference between the current and voltage is
The output signal of the phase shifter 15 is calculated by the phase shifter 15.
Of the inverter output voltage in the pulse distributor 18
Output frequency ratio calculation, PWM calculation, both transistors
T_r1, T _r2The distribution of switching command pulses to the
Further, the command pulse is amplified by the base drive circuit 19.
Applied to the bases of both transistors
To be done.

As described above, the control system of the inverter device is configured by using the power control system as a major loop and the output current control system as a minor loop, and stops the operation of the pulse distributor 18 at the same time. Therefore, the inverter device is in a state in which the inverter operation command signal S ₁ is applied and the temperature signal S ₂ is applied via the temperature switch 20 which is closed when the surface temperature of the metal object is lower than the set temperature. AND element for detecting
The output signal of the start arithmetic circuit 16 which operates under the condition that the output signal S ₃ of No. ₁ is applied and the abnormality detection signal from the protection circuit 17 is not output, the operating state is brought about by the above. Then, the inverter device turns off its output.

Next, FIG. 5 shows the operation of the inverter device as described above.
FIG. 3 is a heating characteristic diagram of the metal object 2 obtained according to a production,
T and P shown by solid lines and dotted lines in the drawing are the metal objects, respectively.
Surface temperature and input power, and T₁Is the resistance of the metal
Anti-depletion point temperature (Curie temperature), T₂Is the set temperature
It Now time t₁Where the temperature T is T₁Has reached
When the electric power P rapidly increases and the rise of the temperature T is accelerated,
t₂At the temperature T₂If the temperature switch reaches
20 operates so that the temperature signal S₂To be cut off
The inverter device also disconnects its output,
The supply of the electric power P is cut off, and the temperature T is delayed by a specific time.
After reaching its maximum temperature, it descends at time t_FourTo
The temperature T₂If it is lower than
t_FourFrom the supply of the electric power P by the inverter device
It will be restarted. After that, similarly, at time t _Four-T_FiveBetween, t₆−
t₇Between, t₈-T₉Intermittent power supply continues as shown between
The temperature T is the set temperature T₂Controlled temperature
It will be kept within the width ΔT.

[0006]

However, in the conventional control method as described above, in order to perform the intermittent power supply of the electric power P before and after the set temperature T ₂ , that is, the metal material having a thermal time constant is used. In order to carry out the maximum input fluctuation with respect to the surface temperature, the vertical overshoot amount in the control of the surface temperature, that is, the temperature width ΔT as described above is inevitably large. In view of this, it is an object of the present invention to provide a control method of an induction heating inverter device capable of reducing the temperature width ΔT.

[0007]

In order to achieve the above object, a control method for an induction heating inverter device according to the present invention comprises:
A method for controlling an inverter device for induction heating, which supplies electric power to a load metal object by electromagnetic induction through an induction heating coil to heat the load metal object, wherein the surface temperature of the metal object is equal to or higher than a variable set temperature. A temperature switch that detects that the output of the metal is output and a current setting circuit with a variable set value that is operated by the output of the switch, and the surface temperature of the metal object is equal to or higher than the set temperature. Then, the output current of the inverter device is made to be a value designated by the output of the current setting circuit, and instead of the temperature switch, a rapid increase in the output current of the inverter device is made to have a magnitude, a temporal increase rate and a duration time. It is assumed that a comparison circuit for the output current that is detected by, for example, is provided.

[0008]

In general, the temperature of a metal object as an object to be heated is determined as a value that is proportional to the difference between the input heat amount including the surface temperature of the metal object and the heat radiation amount thereof. Therefore, the temperature control of the metal object whose heat dissipation characteristic is fixed can be performed by controlling the supply amount of the electric power per unit time, that is, the supplied power. Therefore, when the resistance value of the energizing path can be regarded as constant, the current control corresponding to the electric power can be applied.

According to the present invention, when the heating target temperature of the metal to be heated is higher than the Curie temperature of the metal, the control state switching temperature is set to an appropriate value between the heating target temperature and the Curie temperature. In the state above the switching temperature detected by a temperature switch or the like, a current corresponding to the input power that can maintain the target temperature for the metal object whose resistance value in the energizing path is in the stationary state is set. It is intended to perform continuous constant current control with the target value, and by the constant current control, a constant required power is supplied to the metal object to bring the heating temperature of the metal object to the vicinity of the target temperature. It is to keep the input power to the metal object intermittently as compared with the intermittent control of the input power, and by further reducing the input fluctuation, the temperature range given as the deviation between the maximum value and the minimum value of the heating temperature of the metal object is further reduced. It is those in which an attempt is made to reduce.

During the heating of the metal material from a low temperature, the function of the temperature switch is changed by detecting the rapid increase of the current due to the rapid decrease of the resistance in the vicinity of the Curie temperature based on the rate of increase, duration and the like. Is possible.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.
1 and 2 are block circuit diagrams showing first and second embodiments of the present invention, respectively, and FIGS. 3 and 4 are heating characteristic diagrams corresponding to FIGS. 1 and 2, respectively. 1 and 2, components having the same functions as those in the embodiment of the prior art shown in FIG. 6 are designated by the same reference numerals.

First, in FIG. 1, the operation command signal for the start arithmetic circuit 16 is obtained as a signal S obtained in the state where the inverter operation command signal S ₁ and the temperature signal S ₂ when the temperature switch is not operating are simultaneously established as shown in FIG. ₃ together form only the signals S ₁ instead of the _{(S 3 = S 1 · S} 2), the output end of the current setter 1 21 is provided and the setting device in order to perform a constant current control of the inverter output current It is connected to the reference potential point M via the temperature switch 20, and the current setting device 1 of 21 is further provided as compared with the case where the input signal of the current controller 14 is shown in FIG.
The current setting signal is added. Therefore, the constant current control of the inverter output current according to the current setting signal is performed only when the temperature switch is operating.

When the heating characteristic corresponding to FIG. 1 is compared with FIG. 5 corresponding to FIG. 6 with respect to FIG. 3, the time t at which the temperature T of the metal object 2 to be heated reaches its Curie temperature T ₁ is shown.
₁ and the time t _{2 at} which the temperature T is equal to or higher than the operation setting temperature T ₂ of the temperature switch 20 and the switch is in the open state, are the same in both FIGS. 3 and 4, but in the case of FIG. After time t ₂ , the control shifts to constant current control according to the set value of the current setting device 1 of 21 and the electric power corresponding to the current also becomes substantially constant. Therefore, the temperature T is also substantially constant except for the transient fluctuation immediately after the time t _2. Will change to.

FIG. 2 also shows the current regulator 14 in FIG.
Is a modification of the current setting signal generating section for the comparator 22, which detects the Curie temperature T ₁ passing state of the temperature T and substitutes the function of the temperature switch 20.
And a current setting device 2 of 23 which operates by the operation of the comparator and outputs the required current setting signal. The comparator 22 judges and detects the rapid increase state of the inverter output current due to the sudden decrease in resistance of the metal material when passing the Curie temperature, based on the time increase rate, duration time, etc. of the current. The detection signal of the inverter output current by CT ₂ is input.

Referring to the heating characteristics corresponding to FIG. 2 in comparison with FIG. 3 corresponding to FIG. 1 with respect to FIG. 4, the Curie temperature passing state is entered after time t _{1 and the} inverter output current indicated by the alternate long and short dash line is shown. When I _o rapidly increases, a predetermined confirmation calculation is performed to confirm the completion of the passing state. After time t ₃ , constant current control of the current I _o is performed to perform the electric power P and temperature T as in the case of FIG. And are almost constant.

[0016]

According to the present invention, there is provided a method of controlling an induction heating inverter device for supplying electric power to a load metal object by electromagnetic induction through an induction heating coil to heat the load metal object, wherein the surface of the metal object is controlled. A temperature switch that detects that the temperature has risen above a variable set temperature and emits its output, and a current setting circuit with a variable set value that is operated by the output of the switch are provided. When the surface temperature is equal to or higher than the set temperature, the output current of the inverter device is not the value designated by the output of the current setting circuit, and the output current of the inverter device is increased rapidly instead of the temperature switch. By providing a comparison circuit for the output current that is detected based on its size, the rate of temporal increase, the duration, etc. It is possible to achieve a significant improvement in heating control performance with no small temperature fluctuation range before and after temperature, and improvement of reliability of the control system operation according to an alternative in the current comparison operation of the high-temperature detection temperature switch function.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a block circuit diagram showing a second embodiment of the present invention.

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

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

FIG. 5: Heating characteristic diagram according to conventional technology

FIG. 6 is a block circuit diagram showing an embodiment of the prior art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Metal object 3 Heating coil 11 Electric power calculator 12 Electric power setting device 13 Electric power controller 14 Current controller 15 Phaser 16 Start arithmetic circuit 17 Protection circuit 18 Pulse distributor 19 Base drive circuit 20 Temperature switch 21 Current setting device 1 22 Comparator 23 Current setting device 2 C _r1 Resonant capacitor C _r2 Resonant capacitor CT ₁ Current transformer CT ₂ Current transformer T _r1 Power transistor T _r2 Power transistor

Claims (2)

[Claims] 1. A method of controlling an inverter device for induction heating, which supplies electric power to a load metal object by electromagnetic induction through an induction heating coil to heat the load metal object, wherein the surface temperature of the metal object is variable. A temperature switch that detects when the temperature exceeds a set temperature and outputs the output, and a set value variable current setting circuit that is operated by the output of the switch are provided, and the surface temperature of the metal object is the set temperature. In the above condition, the output current of the inverter device is set to a value designated by the output of the current setting circuit, and the method for controlling an induction heating inverter device is characterized. 2. The method for controlling an induction heating inverter device according to claim 1, wherein instead of the temperature switch, a rapid increase in the output current of the inverter device is detected by its magnitude, rate of temporal increase, duration and the like. A method for controlling an inverter device for induction heating, comprising: a comparison circuit for the output current.