JP3052979B2 - Power supply for induction welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction welding power supply, and more particularly, to applying a high frequency current from an inverter, such as a full bridge inverter, to a work coil, thereby fusing the work coil using a heater made of, for example, a magnetic alloy. The present invention relates to a power supply device for induction welding.

[0002]

2. Description of the Related Art For example, a high-frequency power supply disclosed in Japanese Patent Application Laid-Open No. 63-92277, filed on Apr. 22, 1988, is used as a power supply for this type of induction fusion device. Available. In this prior art, the output of the inverter is controlled by outputting a drive signal whose phase is shifted to each other to the switching element pair of the full-bridge inverter, or the output is controlled by slightly shifting the resonance frequency to follow. It is possible.

[0003]

In the former method, the switching element is turned on when the load current does not become completely zero, so that the switching loss increases. Also,
In the latter method, since the resonance frequency is shifted, there is a problem that the reactive power increases and a switching element having a higher rating is required.

[0004] Therefore, a main object of the present invention is to provide an induction welding power supply device that can more easily control the output of an inverter.

[0005]

SUMMARY OF THE INVENTION The present invention relates to an induction welding power supply device for supplying an output of an inverter driven by an inverter drive circuit to a work coil. Inverter drive signal supply means for supplying an inverter drive signal to the inverter drive circuit, comparison signal creation means for detecting a current flowing through the work coil to create a comparison signal, and phase comparison means for comparing the phases of the inverter drive signal and the comparison signal ,
And a frequency control means for controlling the oscillation frequency of the variable frequency oscillator according to the output of the phase comparison means.

[0006]

The variable frequency oscillator is composed of, for example, a voltage controlled oscillator (Voltage Controlled Oscillator).
e Locked Loop). An output signal from the oscillator is applied as an inverter carrier signal to, for example, an AND gate. The AND gate is supplied with a PWM control signal having a predetermined duty from, for example, a microcomputer. Therefore, the inverter drive signal supply means including such an AND gate supplies the inverter carrier signal to the inverter drive circuit as an inverter drive signal only when the PWM control signal is at a high level, for example. On the other hand, for example, a current transformer (CT) is coupled to the resonance circuit including the work coil, and a current signal flowing through the work coil is detected as a comparison signal. This comparison signal is fed back to the PLL, and the phase is compared with the inverter driving signal output from, for example, an AND gate by the phase comparison means. Therefore, a signal corresponding to the phase difference between the two is output from the phase comparison means, and a frequency control signal corresponding to the phase difference is output from the frequency control means such as a low-pass filter. Therefore, the frequency of the oscillator, that is, the frequency of the inverter drive signal changes following the resonance frequency of the resonance circuit including the work coil.

[0007]

According to the present invention, since the cycle of the inverter drive signal is changed while following the change in the resonance frequency including the work coil while controlling the inverter drive current, temperature fluctuation and load fluctuation (load state change). ) Can reliably cope with variations in circuit constants of the work coil and the like, and thus more stable and reliable fusion can be realized.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG.
0 includes an inverter drive circuit 12, and a switching signal (on / off signal) from the inverter drive circuit 12
Accordingly, the switching element (not shown) of each arm of the full-bridge inverter 14 is turned on or off.
However, the operations of the inverter drive circuit 12 and the full-bridge inverter 14 are well known in, for example, the above-cited Japanese Patent Application Laid-Open No. 63-92277, and a detailed description thereof will be omitted.

A high-frequency output from the full-bridge inverter 14 is supplied to a resonance circuit 18 via a transformer 16. The resonance circuit 18 includes a resonance capacitor 20 and a work coil 22. The work coil 22 is, for example, a fusion heater 2 made of a magnetic alloy body, similar to that disclosed in International Application Publication No. WO92 / 15182.
4 for inducing a high-frequency current.

The resonance circuit 18 has a resonance current path CT26.
The current signal detected by the CT 26 is converted into a voltage signal by the current-voltage conversion circuit 28, and then input to the microcomputer 30.
2 is fed back. As is well known, the PLL 32 includes a phase comparator 34, a low-pass filter 36, and a VCO 38. The output of the VCO 38 is provided to one input of an AND gate 40 as an inverter carrier signal. The other input of the AND gate 40 is supplied with a PWM control signal from the microcomputer 30.

That is, the VCO 38 outputs an inverter carrier signal as shown in FIG. 2 (A), which is ANDed together with the PWM control signal as shown in FIG. 2 (B).
Input to gate 40. Therefore, an inverter drive signal as shown in FIG. 2C is output from AND gate 40 and applied to inverter drive circuit 12. The inverter drive signal is supplied to the PLL 3 together with the current signal detected by the CT 26 (FIG. 2D).
2 of the phase comparator 34.

Therefore, the phase comparator 34 compares the phases of the inverter drive signal and the current signal, and outputs a signal corresponding to the phase difference. From the low-pass filter 36, a voltage signal having a level corresponding to the phase difference is output.
It is provided as a control voltage for CO38. Therefore, VC
The output of O38, that is, the cycle or frequency of the inverter carrier signal is controlled to be equal to the current signal corresponding to the load current flowing through the resonance circuit 18. Therefore, the frequency of the inverter drive signal supplied to the inverter drive circuit 12 follows the change in the resonance frequency of the resonance circuit 18.

Next, a method of controlling the output of the full-bridge inverter 14 by the microcomputer 30 will be described with reference to FIG. In the first step S1 of FIG. 3, the initial value of the duty of the PWM signal is D =
Set d ₀ . At the same time, in step S3, the microcomputer 30 outputs a PWM signal having an on / off period corresponding to the duty d ₀ set in this manner. As a result, the inverter drive signal is supplied from the AND gate 40 to the inverter drive circuit 12, the full-bridge inverter 14 operates, and the high-frequency current is supplied to the work coil 22 forming the resonance circuit 18 as described above.

[0015] In the subsequent step S5, the microcomputer 30 based on the voltage value from the current / voltage conversion circuit 28, detects the load current I _L is detected by CT26. Then, by comparing the load current I _L and a predetermined reference current I ₀ detected at the next step S7, in step S9, the difference between both "I _L -I _0" determines whether "0". If the two current values I _L and I ₀ are equal, that is, if “YES” is determined in step S9, the process returns to step S3 to continue the operation.

On the other hand, when the difference between the two current values I _L and I ₀ is not “0”, that is, in step S9, “N
When it is determined to be O ", the microcomputer 30
Determines in the next step S11 whether the difference is positive or negative. When the difference is positive, that is, when “YES” is determined in step S11,
In the next step S13, the microcomputer 30 decrements the duty of the PWM signal (−
1) Then, the process returns to step S3. Conversely, if the difference is negative, that is, if “NO” is determined in step S11, the microcomputer 30 proceeds to the next step S15
In step (1), the duty of the PWM control signal is incremented (+1), and the process returns to step S3.

In this manner, the load current I _L is compared with the predetermined reference current I ₀ , thereby controlling the duty of the PWM control signal to control the output of the full bridge inverter 14. Is much simpler than that of the prior art.
Note that, in the above-described embodiment, an example in which the full-bridge inverter 14 is used as an inverter has been described, but it is a matter of course that any other type of inverter may be used.

[Brief description of the drawings]

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

FIG. 2 is a waveform chart showing signals of respective units in the embodiment of FIG.

FIG. 3 is a flowchart showing an operation of controlling the output of the inverter in the embodiment of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Induction fusion power supply device 12 ... Inverter drive circuit 14 ... Full bridge inverter 18 ... Resonance circuit 22 ... Work coil 24 ... Magnetic alloy heater 26 ... CT 30 ... Microcomputer 32 ... PLL 34 ... Phase comparator 36 ... Low pass filter 38 ... VCO 40 ... AND gate

──────────────────────────────────────────────────続 き Continuing from the front page (72) Kozo Nishikawa 1-1-1, Hama, Amagasaki-shi, Hyogo Prefecture Inside Kubota Research Institute of Technology (72) Inventor Masayuki Kanda 1-1-1, Hama, Amagasaki-shi, Hyogo Shares (58) Investigated field (Int. Cl. ⁷ , DB name) H02M 7/48 B29C 65/32

Claims (1)

(57) [Claims] 1. An induction welding power supply device for supplying an output of an inverter driven by an inverter driving circuit to a work coil, comprising: a frequency variable oscillator; and an inverter driving the inverter driving circuit based on an output of the frequency variable oscillator. An inverter drive signal supply unit that supplies a signal; a comparison signal creation unit that creates a comparison signal by detecting a current flowing through the work coil; a phase comparison unit that compares a phase between the inverter drive signal and the comparison signal; A power supply for induction welding, comprising: frequency control means for controlling the oscillation frequency of the variable frequency oscillator according to the output of the phase comparison means.