SU1411899A1 - Device for controlling direct three-phase frequency converter - Google Patents

Abstract

The invention relates to electrical engineering and can be used in electrothermal thyristor converters. The aim of the invention is to increase the transmission coefficient of the converter when one of the phases of the load is broken. For the expense of. the introduction of two key blocks is adjustable, with the energy supply of the load when it is transferred from a three-phase mode to a two-phase one in the accident of one of the furnace electrodes. At the time of the accident, due to the proposed connection scheme, another valve set is added to the working valve set, assembled from parts of the non-working valve sets. In this case, the power of the network is transmitted to the furnace through two valve sets, which allows maintaining the power introduced by the furnace at a level close to the worker. 5 ill., 1 tab. a & cl

Description

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The invention relates to electrical engineering, in particular, to converting technology, and can be used in electrical installations containing a three-electrode. An electric furnace that is powered from a three-phase direct conversion of the main current often into a low-frequency current.

The purpose of the invention is to increase the coefficient |) of the transfer of the converter of the break of one of the phases of the load

FIG. 1 is a block diagram of the device; in fig. 2 shows an example of the implementation of a converter control unit; in fig. 3 - communications between three control units; in fig. 4 and 5 are timing diagrams of valve set currents and phase load currents for a symmetrical mode, when the power of the casting network is transferred to three phases A, B, C of the load by three valve sets (Fig. 4), and asymmetrical mode, when the power of the supply network is transmitted to two phases loads in the first set and parts of the second and third sets in the emergency state of phase C of the load, when the GOK is equal to zero (Fig. 5).

The device (Fig. 1) contains a three-phase supply transformer 1 with two secondary windings, three vengative sets 2-4, each of which contains two three-phase bridges connected in an anti-parallel circuit. The output pins A, x; B, T with, Z valve sets are interconnected in a triangle, to the ver- itaHHM A, B, C from which Yagruzki 5, connected in a star, are connected. You 1zoda network frequency of three-phase mono-Ltov, forming the valve current set one direction, sub-: | connected to one of the two secondary windings of the supply transformer 1.; (each valve set contains your own 6-8 control unit, which 1Is pulses from valve control: | complete sets. Each control unit with, holds serially connected control locks 9–11, blocks. 12–1: (switches and blocks 15–17 of output amplifiers, whose outputs are connected to equal transitions of their own sets .

In addition, the device contains, per chipboard, for four grams of a reload: a slider 18, each board of which

ten

20

25

jj

thirty

five

0

five

0

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belongs to one of the control units of the valve sets. Each switch board 18 contains one mobile and four fixed contacts 19.1-19.4, 20.1-20.4, 21.1-21.4. The movable contact of each switch board is connected to the second input of blocks 9-11,

The first fixed contacts 19.1, 20.1 and 21.1 of the boards of the switch 18 are each connected to the corresponding output of the three-phase master oscillator 22. The fixed contacts 19.2 and 19.4 are connected to the fixed contact 21.4 and the first output of the two-phase master oscillator 23, the second output of which is connected to the fixed : mi 20.2 and 20.3 and still 21.4 contacts. The remaining fixed contacts are connected to the output of block 24 of the inhibit signal,

Each block 9-11 (Fig. 2) contains a series-connected current regulator 25, a phase shifter 26, a pulse distributor 27, the input of which is intended to connect the current frequency reference signal. Each b, pok 12-14 consists of two groups of 28 and 29 keys. The outputs of a group of 28 switches are connected via output amplifiers 30-33 to the control electrodes of the valves of the set. In addition, the group of outputs that is connected to the odd valves of one bridge kit is connected to the output 34 of the block, and the group of leads that is connected to the valves 4, 3 and 2 of the other bridge is connected to you, stroke 35 of the block.

The outputs of the key group 29 for connecting to the even valves of the first bridge and the second bridge are connected to the corresponding terminals of the key group 28. Output groups-. Key switches 29, intended for connection to even-numbered valves of the second bridge kit, are connected to output 36 of the unit, and outputs intended for connection to odd-numbered valves of the first bridge, to output 37 of the block, Valve sets control units 6–8 are interconnected in accordance with the scheme shown in FIG. 3. In this case, the view ports 34 and 35 of each block are connected respectively to the outputs 36 and 37 of the other block connected to the outputs 34 and 35 of the third block.

The device works as follows.

The supply voltage through the transformer 1 is supplied to the inputs of the valve sets 2-4, which are controlled by the corresponding blocks 6-8 of the control. In addition, each control unit 6-8 sets the rectangular shape of the current of the valve set group in accordance with FIG. 4 with a three-phase load 5 and in accordance with FIG. 5 under two-phase load. The current pulses of the positive-polarity valve assembly are formed by the first-bridge valves, and the negative-polarity current pulses by the second-bridge valves. The pulses for unlocking the gates are formed by blocks 9-P. The phase shifting unit 26 and the regulator 25 allow the valve set current to be varied and stabilized. The pulse frequency of the output current of the valve set is set by generators 22 and 23 depending on the position of the switch 18.

Using the distributor 27, the inputs of which receive pulses from the output of the phase-shifting unit 26 and pulses to set the square-shaped current frequency from the generators 22 and 23, generate pulses to control the forward current direction valves and pulses to control the reverse current direction valves. The pulses at the output of the distributor 27 appear when the pulse of the phase-shifting unit 26 and the pulses coincide: the current frequency is set, and if there is a separate ventilator control unit, even if they coincide with the enable signal of the separate control unit. The pulses from the output of the distributor 27 arrive at the input of the blocks 12-14 of keys, depending on the state of the groups 28 and 29, go through the output amplifiers 15-17 only to the gate control valves of their valve set or part of them through the amplification blocks and the distribution of the pulses of the next set enters the control electrodes of the valves of the adjacent set.

The switch 18 with the appropriate state of groups 28 and 29 and blocks 12-14 set the operation mode

0

five

0

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..

ravovatel at three-phase and at two-phase loading. The first position of the switch corresponds to the three-phase load mode, when the power of the supply network is transferred to the three load phases by the three valve sets of the converter. In this mode, each of the 6-g8 units receives signals for setting the current from the generator 22 s, three-phase output.

The second, third and fourth positions of the switch 18 correspond to the two-phase load mode, when the mains supply is transmitted to the two phases of the load by one valve M with a set of converter and parts of two other valve kits. In this mode, two of the three control units receive a signal for setting the current frequency from the generator 22 with a two-phase output, and the input signal of the third control unit is the inhibit signal from. block 24.

The position of the switch 18 and the state of the blocks 12-14 depending on which phases of the load are working are given in the table.

With a three-phase load (Fig. 4), each valve set forms: positive and negative current pulses of substantial polarity with the help of second-bridge valves. The duration of current pulses in one direction is 2U / 3. In each phase of the load, linear currents flow, determined from the expressions

where i, ijj, i - currents in the phases of the load;

- currents valve kits.

The actual value of the current in the load phase is equal to

T ito P G2

Where

2E 3

E is the voltage at the outlet of the valve set when one of its valve groups conducts current;

g is the phase load resistance (we take the load symmetric).

The power consumed by the three phases of the load in this mode is determined by the formula

H

from -I g 2e

FROM

Suppose that it is necessary to disconnect the phase C of the load (for example, for technological reasons or as a result of an emergency). To do this, set the switch 18 to the second position, at which bipolar rectangular control pulses with a duration equal to half the output frequency period are fed from the generator 23 to the inputs of blocks 6 and 7. The pulses of the frequency setting, arriving at the inputs of blocks 6 and 7, are shifted relative to each other by half the period of the output frequency. The input of block 8 from block 24 receives a prohibitory signal, which prohibits pulses at its output. The impulse sequences formed by blocks 9 and 10 are received by blocks 12 and 13, respectively. According to the table, block 12 is set to a position where its group 28 is closed, and group 29 is open, and 13 group 28 is open and group 29 is closed.

Thus, in block .6, the pulses of block 9 through block 15 are passed to control transitions of the valve set. 2. In block 7, part of the pulses of block 10 through block 16 passes to the valves of kit 3, connected to the phase B of the load, and the other part passes through block 17 to the valves of kit 4, connected to phase A of the load.

In this case, the masculinity of the mains is transmitted to two phases L and B of the load by valve set 2 and parts of power sets 3 and 4 connected to the remaining phases of the load. If, however, it is necessary to disconnect the phase A or B of the load, then the reversal switch 18 is set to the second or fourth position, respectively, and the blocks 12-14, according to the table, distribute the control pulses so that in the case of the test, the set 3 remains and the parts of the sets 2 and 4, which are not associated with the phase A of the load, but in the main case there is a set of 4 and parts

valves sets 2 and 3, not connected to the phase of the load.

Thus, in the two-phase load mode, two ventilation sets are connected in parallel to the load, each of which is designed to generate a current of amplitude 1; / 2. Slegp

Indeed, they can provide a current with amplitude 1 in the load (figure 5).

PP

The power consumed by the two phases of the load is determined by the formula

4E BE

R ,, 21

t

-2 5-1 9,

2E

-D 5

Consequently, the load power, if it is possible to maintain the current amplitude of the valve set, can be somewhat greater than in the symmetric three-phase mode. If the voltage at the output of the transformer remains unchanged when switching from a three-phase load to a two-phase load, then the amplitude of the current of the valve set with a constant load phase resistance remains equal to

I - 2g

Then the total load power is

1 E

„O / m-X 1 Ji

, 2 (1 5--.

in this case, the load power is 1.33 times less than in the symmetric three-phase mode. In order for the power in the load to remain the same, it is necessary to increase the voltage E by 17%, for example, by switching the transformer voltage levels.

In the proposed device, in the emergency state of one of the three electrodes, the power of the power supply network is transferred to the furnace through two electrodes by re-engineering the power source control algorithm, which allows reducing the simple furnace until the end of the technological cycle.

In the known device, in an emergency condition of one of the electrodes, for example, when the electrode is broken, the power of the network transmitted by the furnace decreases sharply, since one valve set remains in operation. AT

7141

The proposed technical solution adds to the working kit one more kit assembled from parts of non-working sets. In this case, the power of the network is transmitted to the furnace through two sets, which allows to maintain the power introduced into the furnace at a level close to the worker.

Claims (1)

Invention Formula A device for controlling a direct three-phase frequency converter, consisting of three valve kits in the form of two three-phase bridges oppositely connected in parallel in each phase of the converter, with outputs connected in and four fixed contacts on each board, a two-phase master oscillator, the first output of which is connected to the second and fourth fixed contacts of the first board and the third fixed contact of the third board, and the second output to the second and the third fixed contacts of the second board and the fourth fixed The contact of the third board, the third, fourth and second fixed contacts of the first, second and third boards, respectively, are connected to the output of the inhibit signal unit, characterized in that, in order to increase the transmission coefficient of the converter when one of the load phases is broken, it is provided in each unit a triangle containing three control units with two key blocks, each with each series-connected current regulator, a phase-shifting unit and a pulse distributor with pairs of three-phase output groups corresponding to two three-phase bridges of this phase of the converter, and a block of output amplifiers, Two pairs of three-phase groups, the outputs of which are intended for connection to the control inputs of the corresponding-valves of this phase converter, are common to the entire device three-phase An admitting generator whose outputs are connected to the first fixed contacts of the respective boards of a three-board switch with one movable Emergency Position Electrode Switch Switch Position 12 (28) 1 12 (29) 1 13 (28) | 13 (29) 1 14 (28) 14 (29) First Second Third Fourth Note: (+) - the switch is on (closed); () switch off (open). The first of which contains four groups of three keys, the outputs of the pulse distributor through the first block of keys are connected to the corresponding inputs of the block of output amplifiers, the first three-phase group of outputs of the first pair and the second three-phase group of the second pair of outputs of the pulse distributor are connected via the second block of keys to the corresponding outputs of the first block keys, the second three-phase group of the first pair and the first three-phase group of the second pair of outputs of the first key block of each control block are connected to the corresponding r control outputs of the next control unit. Switch Position . rltp .2 ..- .: one g /. lg / d / # one g II 25 I , t isa. L- .. u% r 7 g /. lg / d / # one g Ijfft v four 1 I "V i. FIG. 2 J Fshl .five