SU1738550A1 - Power source for resistance arc welding - Google Patents

Abstract

SUMMARY OF THE INVENTION: To ensure trouble-free operation of the source in idle mode, two additional strings of two diodes connected anti-parallel to the thyristors are connected to the DC buses of the series inverter entering the source. The common point of the diodes is connected to the common point of the thyristors, which form one of the inverter arms, and through the series-connected capacitor and choke with the common point, additional thyristors. Two elements are introduced into the control system to control additional thyristors. 2 Il. (L

Description

The invention relates to resistance welding and can be used in the welding part of robots and robot technology complexes.

The aim of the invention is to increase the reliability of the source by preventing its emergency operation when idling.

Figure 1 is a schematic diagram of a power source; Fig. 2 shows voltage plots at various points in the source circuit.

In Fig. 1, the source contains a serial half-bridge inverter on thyristors 1 and 2, a sensor 3 for the current of the primary winding of a welding transformer 4, a control system including a single-oscillator 5, a trigger 6, blocks 7 and 8 for generating inverter thyristor control pulses, two additional chains, one of

which consists of two series-connected thyristors 9 and 10, the other of two series-connected, antiparallel thyristors, diodes 11 and 12, additional ones - a capacitor 13, a choke 14, two two-input control pulse-shaping units that implement the logic 1 function, and elements 15 and 16. Figure 2 shows the current tops of the primary winding of the welding transformer in operating mode 17 and idling mode 18, voltages at the output of current sensor 19, at the direct output of flip-flop 20, at the outputs nyh blocks 21 and 22 forming the control pulses.

The device works as follows.

The welding current is switched on by turning on the thyristor 1 (or 2). Through

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The primary winding of the welding transformer 4 begins to leak the half-wave current of the recharging and switching capacitors of the inverter. An electromotive force (EMF) is induced in the secondary winding of the welding transformer and, under its influence, a welding current flows through the welding circuit connected to the secondary terminals. The parameters of the inverter series circuit are selected so that the primary current of the welding transformer in an operating mode is oscillatory. At the moment of the current transfer from the thyristor 1 to the reverse diode 11, the current sensor 3 issues a pulse to start the one-shot 5 and to the elements 15 and 16. At the direct output of the trigger 6 at this moment a high voltage level corresponding to logical 1, therefore the element 16 forms control pulse to thyristor 9, and it is turned on. The capacitor 13, which is precharged in such a way that there is a positive potential on its right side, is recharged in circuit 13-14-9 through thyristor 1 and reverse diode 11. After a certain time interval, which is specified by the one-vibrator 5, the trigger 6 is transferred to the opposite state, the thyristor 2 is turned on, and the capacitor 13 charges up in circuit 9-14-13-2.

The parameters of the capacitor 13 and the throttles 14 are chosen in such a way that the capacitance charge current is sinusoidal, and the half-wave time of this current is less than the half-life of the source inverter. When the charge current of the capacitor 13 drops to a value less than the holding current of the thyristor 9, the thyristor 9 is turned off. When current is transferred from thyristor 2 to diode 12, current sensor 3 again outputs a signal to block, 15, 16, and element 15 turns on additional thyristor 10. Capacitor 13 recharges through 10, 14, 13, 2 and 12, and

after switching on the thyristor 1 - in the circuit 10-14-13-1.

In idle mode, the current of the primary winding of the welding transformer, after going through zero and until the saturation of the magnetic conductor of the transformer, increases slowly, which slows down the process of the thyristor restoring its locking properties. Current recharge and additional capacitor 13 helps to accelerate the process of turning off the thyristors.

The parameters of the additional elements are chosen so as to ensure reliable shutdown of the thyristors in the required time.

Claims (1)

Claims A power source for resistance welding, comprising a series inverter on thyristors, a current sensor included in the primary winding of a welding transformer, and a control system including a trigger, characterized in that, in order to improve operational reliability by preventing emergency operation at idle, two I elements are introduced into it, a capacitor and a choke, and two additional chains of two series-connected additional are connected to the DC buses of the inverter of the thyristors and two diodes connected in parallel to the additional thyristors, and the common point connected to the common point of the inverter thyristors and through a capacitor and choke - with a common point of additional thyristors, while the outputs of the And elements are connected to the control electrodes of the additional thyristors, the first inputs elements And are connected to the output of the current sensor, and the second inputs - with direct and inverse outputs of the trigger. 15 1B go 2i one 7 Step 7 l