SU941093A1 - Welding current control method - Google Patents

Description

(54) WELDING CURRENT CONTROL METHOD

one

The invention relates to electrical resistance welding equipment and can be used in machines containing a power controlled rectifier.

A current control manual for single-phase resistance welding machines is known, according to which each controlled valve (thyristor) of the interrupter on the primary side of the welding transformer is switched on with adjustable delay relative to the extinction time of the previous valve 1.

The disadvantage of this method when using it in machines with a three-phase rectifier is the asymmetric turning on of controlled gates (thyristors) in different phases of the rectifier, since the moment of turning off the previous thyristor depends on the magnetising current of the transformer phase, which conducts the previous thyristor, and the magnitude of the magnetizing currents of different phases are different.

The closest in technical essence to the invention is a method of controlling the welding current with thyristors in the primary circuit of the welding transformer, based on the generation of the turn-on signals of the thyristors in accordance with

in order to follow the phases of the supply voltage and turn on the thyristors 2.

The disadvantage of this method is that it is possible to skip switching on the next thyristor when operating in near-phase modes, in case of a previous shutdown delay by a time greater than the angle of the rectangular pitch relative to the step-like saw.

The purpose of the invention is to reduce the mass of the welding transformer and improve the quality of welding by eliminating gaps in the inclusion of thyristors.

15

The goal is achieved by the fact that, in the method of controlling the welding current, mainly in three-phase machines for resistance welding with thyristors in the primary circuit of a welding transformer,

20 based on the formation of a thyristor turn-on signal in accordance with the order of the phases of the supply voltage and the turn-on of the thyristors, form a second control signal on the basis of the voltage on the switched on thyristor and turn on the next thyristor by the presence of both signals simultaneously.

The drawing shows diagrams illustrating the formation of these

There are 30 signals for a shielded zero rectifier controlled by three thyristors, which are connected by a star to the primary winding of a three phase transformer. The method is carried out as follows.

The required moment of switching on each thyristor is determined depending on the target current magnitude, supply voltage and other factors, and from this moment on a single input of the thyristor turn on pulse generator a signal of a certain duration. To the second input of the pulse shaper, a signal is supplied that a voltage is present at this thyristor, and the control pulse is formed at the thyristor at the instant of the coincidence of these two signals. In the diagram: / - time;

Uc is the linear voltage of the network; f / y is the control signal that sets the thyristor turn-on phase;

f / T is the voltage across the thyristor; and os - feedback signal, existing at non-zero voltage on thyristor; bf is the pulse supplied to the control electrode of the thyristor by the driver.

The voltages are shown in two modes of operation of the rectifier — at an adjustment angle a oi and at a 0. In both modes, the voltage on the switched-on thyristor appears after a certain time, determined by the angle Skr, after passing through zero the corresponding linear voltage of the network. At the same time, a signal is given (A wash is one of the inputs of the output device of the pulse former.

The control signal t / y, which specifies the thyristor turn-on phase, is applied to the second input of the output device of the driver in the first mode via a and at the same time a pulse t / f is applied to the control electrode of the thyristor. Thus, the moment of turning on the thyristor in this mode is determined by the front of the control signal t / y. When operating in full phase mode with,

and O, the control signal Uy is input to the output device of the pulse driver earlier than the feedback signal t / oc. Therefore, the coincidence of the signals and the switching on of the next thyristor occurs at the moment of arrival of the feedback signal, which corresponds to the real mode of full-phase operation taking into account the magnetizing current of the transformer.

This method can be used in resistance welding machines, in which the welding current is controlled by thyristors, turn ON

primary side of the welding transformer. Turning on the thyristors ensures reliable operation of the maschine in all modes up to full phase at various ratios of the magnetizing current of the transformer and the load component of its primary current, including idling. This removes restrictions on choosing the maximum induction in the transformer magnetic core.

Claims (2)

1. USSR author's certificate L 541616 cl. In 23 K 11/24, 1975. 2. Japanese Patent No. 48-21187, cl. In 23 K 11/24, 1973 (prototype).