JPH033670A - Method of controlling induction heating inverter - Google Patents

Abstract

PURPOSE:To perform stable operation of an induction heating inverter by controlling a value responsive to the rising value from a predetermined value of temperature of an electrolytic capacitor to reduce an output current as a new limiting current set value in a current control system, thereby suppressing the temperature rise of the capacitor. CONSTITUTION:A temperature detecting sensor 10 of an electrolytic capacitor 2 and a converter 6f for calculating a variable or constant limiting current set value upon reception of the output of the sensor 10 to apply its output to a current regulator 6c are provided. If the detected temperature of the capacitor 2 exceeds its predetermined value, a limiting current set value automatically corrected at its value in suitable relationship in response to the difference between the detected temperature and its predetermined value is output to suppress the temperature rise of the capacitor 2. Thus, an inverter can be stably operated without special countermeasure against heat for the capacitor 2 itself.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a series resonant induction heating voltage source inverter device having a direct current intermediate circuit composed of an electrolytic capacitor, etc., in which the temperature rise of the electrolytic capacitor is suppressed. This invention relates to a method of controlling a device.

[Conventional technology]

As a conventional voltage source inverter device for series resonant induction heating of this type, one illustrated in the circuit diagram of FIG. 2 is known.

In FIG. 2, 1 is a three-phase full-wave rectifier consisting of a diode bridge, 2 is an electrolytic capacitor, 3 is a switching transistor 3b, a diode 3c connected in antiparallel to the transistor 3b, and a BDU 3a which is a base drive circuit of the transistor 3b. 4 is a resonant capacitor, and 5 is an induction heating work coil. Here, the rectifier 1 and electrolytic capacitor 2 form a DC intermediate circuit between the inverter 3 and the AC power source.

Next, 6 is a control circuit that outputs a control signal for each BDU 3a of the inverter 3, and inputs the combined output of the input end current transformer CT of the DC intermediate circuit and C70 and the output DC voltage of the intermediate circuit. a power calculator 6a, which receives as input the deviation between the power detection value by the calculator 6a and the power setting value by the setting device 7; a current regulator 6c whose input is the deviation from the output of the current transformer CT; and the current transformer CT.
, and the current transformer C receives the output of the converter 6f and the output of the current regulator 6c.
A sawtooth wave is generated which is reset at the zero cross point of the output current of the inverter 3 detected by T4 and is synchronized with the output current, and the sawtooth wave and the current regulator 6c are generated.
A phase shifter 6d for phase adjustment determines a required control phase angle for each half wave of the output current by comparing the output of
The control element includes a pulse distributor 6e that distributes and outputs control signals for the power supply, and has a current control system as a minor loop within a power control system as a major loop.

The control circuit 6 includes a protection circuit 6 which receives as input the output of the current transformer CT for detecting the current flowing in the electrolytic capacitor 2, the terminal voltage of the capacitor, and the output of the current transformer CT. A DC power supply 6h for supplying control DC power is included.

In addition, the equivalent circuit including the object to be heated by the work coil 5 is a series circuit of the reactance of the reactance and the resistance of the resistance value R. Therefore, the load circuit of the inverter 3 consists of the work coil and its capacitance of C. This becomes a series resonant circuit with a certain resonant capacitor 4.

Figure 3 shows the characteristics of the load circuit of the inverter 3. Figure (A) is its equivalent circuit diagram, and Figures (B) and (C) are impedance vector diagrams corresponding to Figure (A). be. Note that the impedance angle φ1 or φ2 shown in both figures
also indicates the phase angle between the voltage and current of the circuit whose load is the impedance, and therefore the inverter 3
It can be controlled by adjusting the timing of applying the power supply voltage in accordance with the zero-cross point of the output current, and is subject to phase adjustment by the phase shifter 6d in the control circuit 6. Figure 3 (b)
and Figure (c) means that under a constant condition of the resistance value R of the total equivalent impedance Z of the inverter load circuit, the phase angle φ is adjusted as φ1 and φ2, and the angular velocity ω(ω 2πf) is set to ω1 minus ω2, and the impedance Z is set to satisfy IZll<IZll.

FIG. 4 shows the output voltage of the inverter 3 using the impedance Z as a parameter. and output current■. It is an output characteristic diagram showing the relationship between ■. , is the required operating voltage, ■. ,
indicates a limit current appropriately determined for the operation of the inverter 3. In Figure 4, do ■. -The voltage ■ in the v0 characteristic. , the output current corresponding to ■. is the aforementioned current ■. This would result in exceeding the construction limit.

When the load impedance decreases as described above, the inverter 3 automatically increases the phase angle of the load impedance and therefore the phase angle between the output voltage and current of the inverter 3 by the phase shifter 6d in the control circuit 6 in order to continue its normal operation. This is intended to reduce the output current due to the increase in load impedance. FIG. 5 shows an operating waveform diagram during the phase angle control described above.

As shown in Figures (A) and (B) of Fig. 5, the output voltage of the DC intermediate circuit (■). is cut out into a rectangular wave by the conduction of one of the two pairs of upper and lower arm switching elements in the inverter 3 and is applied to the series resonant circuit of the load, and the voltage application causes a current . is applied to the load.

Further, at an appropriate phase angle φ1 or φ2 before the current I0 becomes zero, the conducting pair of switching elements is cut off, and another pair of upper and lower arm switching elements is made conductive. The direction of voltage application to the load is reversed. Such a switching operation is carried out by the current ■.

By repeating this every half wave, the output voltage (2) has the phase relationship shown in the figure in the inverter 3. and output current I0 can be obtained. As shown in the figure, by setting the phase angle φ to φ2, the cut-off current (■) at the time of commutation of each switching element becomes 1. +< 1.
It increases like 2.

Incidentally, the quantities of each part of the inverter 3 obtained as a result of controlling the phase angle φ as described above are as shown in the following equation (1).

However, Po is the high frequency output power of the inverter 3, and ω. is the resonant angular frequency of the load resonant circuit, and the coefficient 0.9 in the relational expression of the power P0 is the voltage (2). This is the waveform rate for waveform correction by applying in the form of a rectangular wave.

[Problem to be solved by the invention]

However, in the operation of the voltage source inverter device for series resonant induction heating using the conventional method as described above, the control to increase the phase angle φ as described above for limiting the output current simultaneously increases the cutoff current at the time of commutation of the inverter switching elements. As a result, the ripple current flowing out from the electrolytic capacitor in the DC intermediate circuit of the inverter device increases, increasing the heat generation of the capacitor, and there is a risk of impeding stable operation of the inverter device. It was necessary to take measures such as using an electrolytic capacitor that can withstand the above or limiting the reduction in inverter load impedance in advance.

In view of the above, an object of the present invention is to provide a control method that enables stable operation of the inverter device without taking special heat resistance measures for the electrolytic capacitor itself.

[Means for Solving the Problems] In order to achieve the above object, in the control method of the inverter device for induction heating of the present invention, series resonance is used to control the output power by controlling the phase between the output voltage and the output current. In an inverter device for induction heating, a sensor for detecting the temperature of an electrolytic capacitor in a DC intermediate circuit of the inverter device, and a minor loop in the output power control system of the inverter device when the detected temperature of the sensor exceeds a predetermined value. and a converter that outputs a fixed limit current setting value for an output current control system constituting the inverter, and when a temperature rise of a predetermined value or more occurs in the electrolytic capacitor, the output current of the inverter device is controlled to limit and the output power is accordingly reduced. or suppress the temperature rise of the electrolytic capacitor, or alternatively, instead of using a converter that outputs a certain limit current setting value for the output current control system, the detected temperature of the electrolytic capacitor exceeds a predetermined value. In this case, a converter is provided to output a limiting current set value whose value is automatically corrected in an appropriate relationship according to the difference between the detected temperature and its predetermined value, thereby suppressing the temperature rise of the electrolytic capacitor.

[Function] As described above, the inverter device has an output current control system as a minor loop within the power control system of its control circuit.

The present invention performs reduction control of the inverter output current by the output current control system in accordance with a temperature rise value from a predetermined value of the temperature of an electrolytic capacitor in the DC intermediate circuit of the inverter device. A new limiting current set value is given to the current regulator in the control system, and the set value is automatically changed in an appropriate relationship with the temperature rise value, or alternatively, the rise value is changed upon the occurrence of the temperature rise. Correspondingly, the sensor for temperature detection of the electrolytic capacitor and the output of the sensor are set to a variable or constant limiting current as described above. A converter that calculates a value and provides the output to the current regulator is provided.

〔Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and components having the same functions as those in the prior art embodiment shown in FIG. 2 are given the same reference numerals.

FIG. 1 shows the circuit diagram shown in FIG. 2, which includes a temperature sensor 10 for detecting the temperature of the electrolytic capacitor 2, and a device that receives the output of the sensor and calculates a limit current setting value that specifies the output current reduction value of the inverter 3. A converter 6m is provided to supply the current to the current regulator 6c.

The present invention determines the limiting current setting value in the converter 6II+ by calculating an appropriate relational expression such as calculating the square of the deviation between the temperature detection value by the temperature sensor 10 and its predetermined value, that is, the temperature rise equivalent value. The present invention is intended for both the case where the temperature rise is performed and the case where the temperature rise value is kept constant regardless of the temperature rise value itself when the temperature rise occurs.

In any of the above cases, as the temperature rises in the electrolytic capacitor as described above, the output current of the inverter 3 is reduced according to a predetermined relationship, and the temperature of the electrolytic capacitor is maintained within the predetermined value.

〔Effect of the invention〕

According to the present invention, in a series resonant induction heating voltage source inverter device having a direct current intermediate circuit including an electrolytic capacitor or the like, the current of the inverter device is set to a value corresponding to an increase in temperature of the electrolytic capacitor from a predetermined value. By performing output current reduction control of the inverter using a new limiting current setting value in the control system, a temperature rise in the electrolytic capacitor caused by harmonic current is suppressed, and stable operation of the inverter device is possible. .

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing an embodiment of the prior art, Fig. 3 is an equivalent circuit diagram and impedance vector diagram of an inverter load circuit, and Fig. 4 is an inverter output The voltage/current output characteristic diagram, FIG. 5, is an operating waveform diagram during inverter phase angle control. 1... Rectifier, 2... Electrolytic capacitor, 3... Inverter, 3a... BDU (base drive circuit), 3
b...Transistor, 3c...Diode, 4...
- Resonance capacitor, 5... Work coil, 6... Control circuit, 6a... Power calculator, 6b... Power regulator, 6C... Current regulator, 6d... Phase shifter, 6e・・・
・Pulse distributor, 6f...V/F converter, 6g...
Startup calculation circuit, 6h...DC power supply, 6k...protection circuit, 6m...converter, 7...(power) setting device, 10
・・・Temperature sensor, CT, ~CT4me box - town evening w 2 (a) (b) (c) Fig. 3 V○ Fig. 4

Claims (1)

[Scope of Claims] 1) A sensor for detecting the temperature of an electrolytic capacitor in a DC intermediate circuit of the inverter device in a series resonant induction heating inverter device that controls its output power by controlling the phase between its output voltage and output current. and a converter that outputs a certain limit current setting value for an output current control system that constitutes a minor loop in the output power control system of the inverter device when the detected temperature of the sensor exceeds the predetermined value, An inverter device for induction heating, characterized in that when a temperature rise of a predetermined value or more occurs in the electrolytic capacitor, the output current limit control of the inverter device and the accompanying reduction in output power are performed to suppress the temperature rise of the electrolytic capacitor. Control method. 2) In the method for controlling an inverter device for induction heating according to claim 1, in place of the converter that outputs a fixed limit current setting value for the output current control system, the detected temperature of the electrolytic capacitor exceeds a predetermined value. A converter is provided to output a limiting current set value whose value is automatically corrected in an appropriate relationship according to the difference between the detected temperature and its predetermined value when the detected temperature and the predetermined value are different, thereby suppressing the temperature rise of the electrolytic capacitor. A method of controlling an inverter device for induction heating.