JPS6318971A - Power source circuit for inverter control arc - Google Patents

Abstract

PURPOSE:To control to stably feed back an inverter by providing a current transformer in the output AC circuit of an inverter frequency. CONSTITUTION:A current transformer 7 is provided in a current path between a transformer 3 and an output side rectifier 4, a converter 8 converts its AC output voltage to a DC voltage, and applies it through a switching circuit 9 for switching synchronously with the switching of an inverter 2 to a capacitor 10. The voltage of the capacitor 10 is fed back as a feedback signal to the inverter 2 to control as required, e.g., a constant current.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a power supply circuit for an inverter-controlled arc used in an inverter-controlled arc welding machine or an inverter-controlled plasma cutting machine.

[Background of the invention]

The inverter-controlled arc power supply circuit is an epoch-making system that is significantly smaller and has higher performance than the conventional thyristor system, and is configured as shown in Figure 2.

In other words, the input side rectifier circuit 1 converts the commercial AC power supply into DC, and the inverter circuit 2 converts it into DC from several kilohertz to several tens of kilohertz.
It converts into AC voltage and applies it to the transformer 3, converts it into a voltage suitable for welding and cutting, and then applies it to the output side rectifier circuit 4. The DC output is supplied to a load (not shown), and is used for arc welding and plasma. It is used for cutting. In this case, the inverter circuit 2 is feedback-controlled by the output current detection signal, but conventionally, as shown in the figure, a shunt 5 is provided on the output side (output DC circuit) of the output side rectifier circuit 4, and the voltage is transferred to the amplifier. 6 and gives it to the inverter circuit 2 as the output current detection signal (feedback signal), which is then feedback-controlled to obtain desired characteristics (mainly constant current characteristics).
I was trying to get it.

However, in the conventional circuit described above, the output current detection signal is obtained by providing the shunt 5 in the output DC circuit. Therefore, the shunt 5 has the advantage of being able to detect a smoothed DC current, but on the other hand, the shunt 5 does not detect a noisy signal, and the detection signal is very small. Since it is amplified, the resulting output current detection signal is susceptible to noise. In particular, since this type of power supply circuit is used in welding and cutting sites where there is a lot of noise and rough handling, noise countermeasures were an important improvement item.

Furthermore, when the pulse width due to inverter control changed, the output current could not be detected stably, and the control became unstable.

[Purpose of the invention]

The present invention was made in view of the above-mentioned circumstances.
An object of the present invention is to provide an inverter-controlled arc power supply circuit that is less susceptible to noise and is capable of stable inverter feedback control.

[Summary of the invention]

The circuit of the present invention has a current-carrying path between the transformer on the output side of the inverter circuit and the rectifier circuit on the output side, that is, the inverter frequency (
By installing a current transformer in the output AC circuit (several kHz to several tens of kHz), the output current can be isolated from the output AC circuit and detected, and by taking advantage of the high operating frequency and large reactance, the current transformer can be By increasing the output voltage, no amplification is required to obtain a feedback signal to the inverter circuit, and by detecting the peak value of the output voltage of the current transformer and providing a feedback signal based on this, the influence of pulse width changes due to inverter control is reduced. This eliminates the problem and achieves the above purpose.

[Embodiments of the invention]

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an embodiment of an inverter-controlled arc power supply circuit according to the present invention. In FIG. 1, the same or equivalent parts as in FIG. 2 are given the same reference numerals and will be described. First, a commercial AC power supply (not shown) (3-phase 200 V) is converted to DC by the input side rectifier circuit 1, and this is converted to 520kHz by the inverter circuit 2.
z to alternating current, and further transformer 3 converts it to about 50 V.
The voltage is stepped down to the output side rectifier circuit 4 and supplied to the arc as a DC output. The following is the same as the conventional circuit, but in the present invention, the current-carrying path (
A current transformer 7 is connected to the secondary output AC circuit of the transformer 3.
The AC output voltage is converted to DC voltage by a conversion circuit 8, and the capacitor l is connected via a switch circuit 9 that switches in synchronization with the switching of the inverter circuit 2.
Apply to O. The voltage of this capacitor 10 is then fed back to the inverter circuit 2 as an output current detection signal (feedback signal) to perform necessary control, such as constant current control.

According to the circuit of the present invention described above, the output current is detected using the current transformer 7 in the output AC circuit.

Therefore, the current transformer 7 is not easily affected by noise, and generally the current transformer 7 is required to have an extremely small resistance component compared to the output winding reactance component, but in this example, the operating frequency is as high as 20 kflZ, and the reactance component is extremely small. It's getting bigger. Therefore, by using a ferrite core and setting the output winding to 500 turns, a voltage of several tens of V can be achieved.
A sufficient output voltage can be obtained, and no amplification is required to provide it to the inverter circuit 2 as an output current detection signal (feedback signal).

In addition, the waveforms of the AC voltage and current output from the inverter circuit 2 are positive and negative rectangular waves/4' pulse, and the wave width is 4' to obtain the output DC voltage corresponding to the load.
Varies by pulse width control. Therefore, the output DC is 1 regardless of the output DC voltage! In order to detect the current, it is necessary to detect the peak value of the AC output/Grus waveform of the current transformer 7.

Therefore, the DC voltage obtained by the conversion circuit 8 needs to have a time constant corresponding to the operating frequency (inverter frequency), and in this embodiment, the time constant is about 100 μ5. As a result, the DC voltage obtained by the conversion circuit 8 fluctuates depending on its time constant, so in order to pick up the level, in this embodiment, the analog switch 9
is turned on, and the 0.01 μF capacitor 10 is charged and discharged to generate an output current detection signal.

〔Effect of the invention〕

As described above, according to the present invention, the inverter frequency is generally relatively high, and therefore a current transformer with a high operating frequency can be used, so a large output current detection signal can be obtained, and there is no need for signal amplification as in the conventional case. In addition, the output current is detected using a current transformer in the output AC circuit, and the output current detection circuit up to the inverter circuit is insulated from the main current circuit, and the circuit impedance is low, so it is resistant to disturbances such as noise. Furthermore, since the method detects the peak value of the output voltage of the current transformer, the output current can be detected stably even if there are changes in the width of 9 pulses due to in-cooper control, resulting in stable control. It has the effect of transforming

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the circuit of the present invention, and FIG. 2 is a diagram showing a conventional circuit. 2... Inverter circuit, 3... Transformer, 4... Rectifier circuit, 7... Current transformer, 8... Conversion circuit,
9... Switch circuit, 10... Capacitor.

Claims (1)

[Claims] 1. An inverter circuit that is feedback-controlled by the output current detection signal converts the rectified AC power output into AC of the desired frequency and feeds it to the transformer, converts it to a voltage suitable for welding and cutting, feeds it to the rectifier circuit, and In an inverter-controlled arc power supply circuit that supplies DC output to a load, a current transformer provided in a current-carrying path between the transformer and the rectifier circuit, a conversion circuit that converts the output voltage of the current transformer into a DC voltage, and the A switch circuit that switches in synchronization with the switching of the inverter circuit, and a capacitor to which a DC voltage from the conversion circuit is applied via the switch circuit, and the voltage of the capacitor is used as the output current detection signal to connect the inverter circuit to the inverter circuit. An inverter-controlled arc power supply circuit characterized in that it provides: