SU780119A1 - Three-phase ac-to-dc voltage converter - Google Patents

Description

(54) THREE PHASE ALTERNATING VOLTAGE CONVERTER

one

The invention relates to a converter technique and can be used as a source of direct current, designed for a high current and relatively low to the input voltage.

Three-phase AC / DC converters are widely known, in which to increase the duration of the conductivity of valves up to 120 e. hail and improving the shape of the curve of the current flowing through the diodes and the secondary windings of the transformer, used two reverse star circuit with equalization reactor.

The disadvantage of such converters is the necessity of introducing an equalizing reactor, which creates unstable operation when the control pulse is unbalanced. In addition, the amplitude through the diode

equals only 3d / 2.

Also known is a three-phase AC-to-constant voltage converter, which is the prototype of the present invention and the bridge-controlled rectifier, according to a bridge circuit, whose output is PERMANENT

shunted by a smoothing choke, and a transformer, to the three-phase primary winding of which the input of the controlled rectifier is connected, and the secondary windings are connected to a star, the zero point of which is connected to one output terminal, and each of its ends the circuit diode is connected to another output pin

10 2. This form of current is not yet optimal.

The disadvantage of such a converter is that it has an amplitude. current through the diode and secondary o1 4toki:

five

also makes only Jd P. at DPS

120 el.gra.Gak formK current is not yet optimal in connection with which the power transformer has a significant overall

20 power.

The aim of the invention is to improve the energy performance of the converter.

This goal is achieved by

25 that into a three-phase converter of a voltage into a constant voltage containing a controlled rectifier assembled according to a bridge circuit, the output of which is bridged smoothed 30

and a transformer, to the three-phase primary winding of which a controllable rectifier input is connected, and the secondary windings are connected to a star, the zero point of which is connected to one output terminal, and each of its ends is connected via a diode to another output terminal, an additional three-phase input a group of windings connected to the transformer primary winding according to a zigzag scheme, each of the free ends of an additional group of windings connected to the input of a controlled rectifier made about dvenadtsatiplechevoy moetovoy s.heme.

In addition, in order to reduce the magnetizing current, the transformer is group-made.

FIG. 1 a-c shows a converter circuit and embodiments of the transformer magnetic cores; in fig. 2 ak - diagrams of linear voltages on the primary winding of the transformer, anode currents i. through the thyristors, the phase currents through the main d and additional 1d windings, the currents through the uncontrolled (-) -th / diodes.

Scheme 1a contains a three-phase transformer 1 with two groups of primary windings 2, connected in a zigzag, and in Toplichn me windings 3, which are connected into a six-phase star. Terminals A, U, Cj, and X., Oy, Zy, additional secondary winding are connected to the input of a controlled twelve-arm bridge on thyristors 4-15; A smoothing choke 16 is connected to the output of this bridge. Secondary windings 3 are connected to diodes 17-22. The load 23 is connected to the star zero point and the common connection point of the cathodes (anodes) of the diodes. The principle of operation of the circuit is considered in the case when the magnetic core of the transformer is made three-core in accordance with FIG. sixteen.

Starting from the moment of time t, the current conducts phase A and the phase B continuing. In this case, the current passing circuit will be qyldyukd: phase A of the network, backing X of the first group of primary winding, thyristor 8, smoothing choke 16, thyristor 12, phase C, 2 and XB. In accordance with such current flow, diodes 18, 20 and will conduct on the secondary side. 22 {FIG. 2Д, 5К, к), because for each pair of primary and secondary windings located on the same rod, the amperages L w, (if you ignore the no-load currents) are equal, at kbmmutatsiya current from phase B to phase C, is preto. At this moment, the thyristors 5 and 13 must be simultaneously turned on. At the same time, the current will flow through the circuit: power supply terminal A, phase AH, phase 5 V, thyristor 5 smoothing choke 16, thyristor 13, phase ZC. In the secondary windings, the current will pass through phase x, diode 20, phase c and diode 19, phase b and diode 18. At time tj, the current switches from phase A to phase B, for which the thyristors 9 and 10 turn on. the current after turning on the thyristors 9 and 10 will be: the phase of the WU, the thyristor 9; smoothing choke 16, thyristor 10, phase A | X ,,, phase ZC. On the secondary side, the current will be carried out: phase X and diode 20, phase Y and diode 21, phase C and diode 19. Subsequently, the switching of the current by the heaters occurs in accordance with the diagram of figure 2b. In this diagram, the current flow through the diodes 17 and the associated winding windings are shown in FIG. 2d As can be seen from these diagrams, the average value of the load current pd at any non-switching moment of time is divided between the tres of simultaneously conducting phases of the secondary windings and the associated windings. Therefore, the amplitude of the current through the uncontrolled valve

dd

will be equal to

. The duration of the passage of current through the diodes and windings is half the period, and the average

the value of the current through the valve is 3 ,,

Thus, the shape factor of the anode current through the diode with a current amplitude equal to. and the duration of T / 2 will be better than PB compared with the known converter, in which the duration

ness is equal to

and amplitude

Current amplitude through primary phases

Noah winding is equal to "p

where K is KOiH.

. OK

transformation efficiency of the main or additional group of primary syncope by b wearing to secondary. The duration of the positive half-wave of the current of the nepBH4Htax windings for each main and additional group of windings is respectively equal to T / 3 (Fig. 2c) and T / 6 (Fig. 2d).

Thus, the overall power of the transformer of the proposed device is less than that of the known transducers, which is equal to it. 1.26 Pd,

The output voltage curve at load 13 corresponds to the six-pulse rectifying mode in the general case with the control angle 0.

Since the implementation of the first Kirchhoff law for the magnetic circuit of FIG. 16 requires transforming part of the magnetic flux through the air and increasing the magnetizing current; it is advisable to make the magnetic system in the form of three groups in accordance with FIG. 1c.

Claims (2)

1. A three-phase AC-DC converter, containing a controlled rectifier assembled in a bridge circuit, the output of which is bridged by a smoothing choke, and a transformer, to the three-phase primary winding of which the input of the controlled rectifier is connected, and the secondary windings are connected in a star, the zero point of which is connected to one output terminal, and each of its ends through a diode is connected to another output terminal, characterized in that, in order to improve the energy performance, additional sweetheart a three-phase group of windings connected to the indicated primary winding of the transformer according to a zigzag scheme, each of the free ends of an additional group of windings connected to the input of a controlled rectifier that is complete according to a twelve-arm bridge circuit. 2. Three-phase AC to DC converter according to claim 1, characterized by 0 in order to reduce the magnetizing current, the transformer is made as a group transformer. Information sources, 5 taken into account in the examination 1. Kaganov I.L. Electronic and Ion Converters, Part G., Gosenergoizdat, 1956. 2. USSR author's certificate on the application 2460404 / 24-07, 0 cl. H 02 M 7/12, 1977 (prototype). 1