CS253353B1 - Connection of rectifier power circuits - Google Patents

Abstract

Current semiconductor rectifiers of peak power do not allow full use of the rectifier elements. The solution lies in the parallel cooperation of several elements. According to the invention, each element of the parallel-connected group is separately connected by an electrode to its own secondary winding of the transformer. The second electrodes of the elements are connected to the common bus of the respective rectifier pole. This arrangement allows the use of the magnetic coupling between the transformer windings as a means for comparing the currents flowing through the individual rectifier elements. There is no need for preliminary selection of elements according to the loss groups at the rated rectifier current.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to the connection of power circuits of a rectifier, in particular for resistance welding machines.

One of the basic conditions of realization of outgoing welding machines with welding current rectification is realization of rectifying block for DC currents in the range of several tens to hundreds of kilo-amps. Current peak power semiconductor valves do not allow the rectifier of said current dimensioning to be solved with one semiconductor valve in each rectifier branch, and the transmission of said current must be solved by the parallel cooperation of several valves. The same reasons lead to the need to design machine transformers with multiple secondary turns in the same rectifier branch. In addition, at the currents and low transformer secondary voltage values (units of volts), deviations in the voltage drop across the valves in the forward direction are also significant. The design of the rectifier block and the transformers is also of great importance, since the transient voltage must be minimized

the resistance between the transformer and the rectifier block, the transient resistors in the rectifier block, and all the line resistances of the outlets, ensuring the water cooling of the secondary threads of the machine and the rectifier semiconductor valves.

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Connections are known where parallel valve operation in each rectifier branch is solved by direct parallel sequencing of these valves so that all the anodes and all cathodes of the valves of the same rectifier branch are connected and the outlets of said parallel combination are connected to a common secondary output of the transformer of the same branch. This solution has some disadvantages. First of all, it is necessary to ensure the choice of semiconductor valves so that at the nominal value of the output current of the rectifier, all valves of the same branch have as much as possible a leakage in the forward direction. This requirement is very difficult to realize due to the fact that the current load of each valve at the rated output current of the rectifier reaches several tens of kilos.

Standard measuring techniques cannot be used for this area and the preliminary determination of losses in the downstream direction is very problematic. In addition, there are variations in the transition resistances between the diode and the heatsink and various path resistances of the supply conductors. It is also necessary to solve the connection of parallel valves either by an additional bus, which increases the transition and displacement resistance, or to solve a special pressure system allowing uniform pressure of several valves in the common cooler, which is very demanding design problem. The unequal magnetic coupling of the individual threads leads to the generation of circular currents between the threads, and thus to an increased load on the transformer windings and higher losses in the transformers. Unequal valve losses, transient and field resistances cause uneven loading of the rectifier diodes.

The above-mentioned disadvantages are overcome by the invention of the connection of the power circuits of the rectifier, the principle being that each rectifier element of the parallel connected group is separately connected by an electrode on its own.

253 353 transformer secondary thread. The second rectifier element electrodes are connected to a common bus of the respective rectifier pole. This solution according to the invention allows the use of a magnetic coupling between the transformer coils as a means of comparing the currents flowing through the individual rectifying elements, eliminating the equalizing circuit currents between the coils, resulting in a lower required current dimensioning of the transformer secondary coils.

Further advantages of the solution according to the invention are the elimination of the necessity of preselecting valves according to the drop groups at the nominal current of the rectifier, the simple design of the radiators and the thrust valves, the design of the interconnecting bus design for the valves of this group.

The attached drawing shows an example of wiring. It represents a general solution of a six-pulse node rectifier. The input three-phase network is connected to terminals ΙΑ, 1B, 1C, from there it is led to thyristor switches of phase control SI and primary transformers B12. B34. B56. The secondary side of the rectifier is represented by six groups of threads All - Aln * A21 - A2n! A31-A3nt A41-MnJ A51-A5nl A61-A6 &. Each group contains n turns connected so that the beginning of the thread All is connected to the anode of the rectifier element Vil and the end of the thread is connected to the ends of the threads of group AI, ie A12 - Aln V12 - Vln. All rectifier element cathodes in

of this group are connected to the positive rectifier output bus, all winding ends are connected to the negative rectifier bus. In the group of windings A2 (counter-phase), the origins of all windings A21 - A2n are connected to the negative bus, the ends of the windings A21 - A2n to the anodes of the respective rectifier elements V21 - V2n. The cathodes of the rectifiers V21 - V2n are connected to a common positive output bus. Similarly, the other phases of the windings A31-A ^ n with the rectifying elements VJ1-V ^ n, A ^ 1-A £ n are arranged.

- 4 253 353 with rectifier elements V41 - V4n. windings A51 - A5n with rectifier elements V51 - V5n and A61 - A6n with rectifier elements V61 V6n.

In the single-phase rectifier, transformers B34 and B56 with the respective valve groups are then omitted.

Claims (1)

SUBJECT OF THE INVENTION Wiring of rectifier power circuits, especially for resistance welding machines, characterized in that each rectifier element (V1 to Vln, V21 to V2n, ..) of the parallel connected group is separately connected by an electrode to its own secondary thread (All to Alri, A21 to A2n, ...) the transformer and the other rectifier element electrodes (V1 to Vln, V21 to V2n, ..) are connected to the common bus of the respective rectifier pole.