JPH01104482A - Power source for inverter type resistance welding machine - Google Patents

Abstract

PURPOSE:To prevent a G.T.O element from breaking down and to improve productivity of equipment by arranging a reactor between the DC power source output and an electronic switch to restrain di/dt of a short-circuit current. CONSTITUTION:A DC power source 4 is formed of a commercial frequency power source 1, a rectifier 2 and a capacitor 3 and the air-core reactor 5 is connected to a fuse 7 in series and arranged between an inverter bridge 8 and the DC power source 4. When a power source starting switch 13 is pushed, welding sequence is started and the weld time is processed by a microprocessor 14 for controlling. At this time, a PWC conversion circuit 16 outputs a pulse to G.T.O angular gate circuits G1-G4 for the set time. When a cable 12 is short-circuited, the reactor 5 restrains rising of the short-circuit current by inductance of a circuit including the reactor 5. As a result, the G.T.O element is prevented from breaking down and the line down time is reduced and the productivity of the equipment is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to improvement of a power supply for an inverter type resistance welding machine, and more specifically, the present invention relates to the improvement of a power supply for an inverter type resistance welding machine, and more specifically, .

This invention relates to a power supply for an inverter type resistance welding machine that can reliably protect electronic switches such as T elements.

(Prior Art) Resistance welding, such as spot welding and seam welding, is used in many industrial fields including the automobile industry. Most resistance welding machines use a commercial frequency power source, and the welding current is controlled using a thyristor.

These thyristor-type resistance welding machines had limitations in achieving smaller and lighter welding transformers, faster response in current control, and lower power consumption for the robotization of production lines.

l! Recently, inverter-type resistance welding machines have been developed, and the use of inverter-type resistance welding machines is rapidly progressing as the welding transformer is recognized for its smaller size and weight, precise waveform control, and high speed.

(Problems to be Solved by the Invention) However, in the conventional inverter type resistance welding machine, in case of a short circuit between the upper and lower arms or a contact short circuit of the primary cable to the welding transformer,
There was no way to reliably protect the O element (gate turn-off risk) from short-circuit current (at best, the power supply could be protected by blowing the fuse, leaving the G, T, and O elements destroyed.

The present invention relates to G and T constituting an inverter bridge.

The purpose of this is to reliably protect the zero element.

(Means for Solving the Problems) 5 Therefore, in order to achieve the above object, the present invention has the following configuration.

l) Insert an air-core reactor in series with the DC power supply output and the power supply lines to G, T, and O to suppress the current rise di/dt when a short circuit occurs.

2) Insert an overcurrent detector on the positive or negative side of the DC power supply to detect short-circuit current and connect it to G, T, and O.
Insert it into the comparator of the PWC (pulse intermediate division m) circuit that generates the gate signal to , cut off the pulse output of the PWC circuit, and cut off the gate signal to G, T, and O.

(Function) In the present invention, the air core reactor inserted between the DC power supply output and the electronic switch reduces short circuit current di/
By suppressing dt, we can reliably protect expensive G, T, and O from short-circuit accidents.
, T, and O can be shortened, and production efficiency and economic effects can be further improved.

(Example) Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an electrical circuit of the present invention.

In the figure, a commercial frequency power supply 1 forms a DC power supply 4 via a rectifier 2 and a capacitor 3. An air core reactor 5 and a fuse 7 are connected in series to this DC power output a, and the other end of the fuse is connected to C of the inverter bridge 8. This inverter bridge 8 converts it into AC power with a frequency higher than the commercial power frequency (600 to IK, , a direct current is supplied to the electrode 11. A diode 6 is connected in antiparallel to the air core reactor 5.

When the start switch 13 is pressed, the welding sequence is started.

The energization time is processed by the control microprocessor 14, and the PWC conversion circuit 16 is processed for the set time.
Open the gate of G, T, O corner gate circuit (at G
tc, Gm).

The PWC conversion circuit 16 uses a carrier frequency (600 to IK□) predetermined by the inverter carrier oscillator 1B.
This is a circuit that controls the pulse width to control the current according to the current.

The welding current is detected by the current setting signal vS from the control microprocessor and the current detector 20 attached to the electrode 11, and the welding current signal VF converted to a current by the waveform converter 17 is input to the error amplifier 15. P
Through the WC conversion circuit, G, T as the current control pulse width
, O gate drivers (G+ Ga Gs Ga )
is input to.

Pulse signal to each gate driver Sl s Sz s
Ss, Ss, as shown in Figure 2, S, and S,
, S, and S4 are input alternately according to each carrier frequency, and the current flows from d and e of the inverter bridge 8 to the electrode 11 via the welding transformer 9! , is controlled to the set value.

Now, in the above operating state, when the upper and lower arms of the inverter bridge 8 are short-circuited or when the cable 12 to the welding transformer 9 is short-circuited by contact, a short-circuit current flows. if,
When the air core reactor 5 is not inserted, r in Fig. 2
A short circuit current like this flows, and the G of the inverter bridge 8
, T, O elements are destroyed in an instant.

However, as in the present invention, since an air core reactor is inserted between the DC power supply output and the inverter bridge 8,
The rise of short circuit current is di/dt = E/L (A/
I1g) (E: DC power supply voltage.

L: Inductance of the circuit including the air core reactor) The rise of short circuit current is suppressed. That is, the overcurrent detector (21) detects the short circuit current, and the comparator (1)
9) to the p, w, c conversion circuit (16), the time for the short circuit current to reach the current that destroys G, T, 0 is suppressed; , T
, cut off the O gate signal and turn off G, T, and O,
Protects against short circuit currents.

This operation will be explained in more detail with reference to FIG.

In Figure 2, when current ■ is flowing normally, T
Assuming that a short circuit accident occurs at the point in time, if there is no air core reactor, the short circuit current will flow at a rapid di/dt such as f, and at the point in time, the overcurrent detector will reach the detection position 1re.
Even if f is reached, the response delay of the overcurrent detector 1. Due to the response delay t2 between the overcurrent detector and the gate driver (Gr~Ca), the short-circuit current reaches the peak turn-off current of G, T, and O much before these response times.
It exceeds GQM. G, T, and O will be destroyed if the gate is cut off after exceeding the I TGQM of G, T, and O.

However, if an air core reactor with inductance is inserted, the rise of the short circuit current will be di/dt=E/L.
The curve is suppressed by G and the rise becomes gradual. In other words, in consideration of the response delay of the overcurrent detector and the response delay between the overcurrent detector and the gate driver, the inductance L is set so that the point at which the gate signal is cut off does not reach the ITGQM of G, T, and O. If designed in advance, G, T, and O can be reliably protected against short-circuit accidents.

(Effects of the Invention) As explained above, according to the present invention, by inserting an air core reactor into the power supply for an inverter-type resistance welding machine, expensive G, T, and O are reliably protected against short circuit accidents. Since the line can be protected, the line stoppage time required for G, T, and 0 replacement work is short, and the economical effect is extremely large.

[Brief explanation of the drawing]

FIG. 1 is an electric block circuit diagram showing an embodiment of the inverter type resistance welding machine of the present invention. Figure 2 shows the change in the rise of short-circuit current depending on the presence or absence of an air-core reactor.

Claims (1)

[Claims] A power supply for an inverter type resistance welding machine, characterized in that a reactor is inserted between a DC power supply output and an electronic switch to suppress di/dt of short circuit current.