SU1522364A1 - Method of controlling direct thyristor frequency converter with delta connection of load phases - Google Patents

Abstract

The invention relates to electrical engineering and can be used to control a converter. The purpose of the invention is to increase the reliability of work. In the converter control method, the thyristors of the anodic and cathodic groups of the two phases of the converter are switched on in accordance with the polarity and the value of the formed phase modulating voltages of the converter, and with positive polarity of the phase modulating voltage the thyristors of the cathode group are included with negative polarity anode group. At the moment of time when the phase modulating voltage of the converter reaches zero, the generation of thyristor control pulses of the converter's rectifying mode is prohibited, and at the time of passing through zero, the line voltage applied to the load is switched according to the polarity of the phase modulating voltages of the converter thyristors from the anodic and cathodic groups of the two phases of the converter, which commute two consecutive linear supply voltages, after passing through zero of the second in order of the linear voltage of the power supply, the prohibition of the formation of control pulses is removed and the converter provides a rectifying mode of operation by turning on the thyristors of the two phases of the converter in accordance with the polarity and the value of their phase modulating voltages. 3 il.

Description

The invention relates to electrical engineering and can be used to control a converter in an adjustable AC drive.

The purpose of the invention is to increase the reliability of the direct frequency converter.

FIG. 1 shows a converter circuit; Fig. 2 shows time diagrams of its voltages and currents; on

FIG. 3 is a control circuit implementing the proposed method.

The thyristor converter includes a power unit and a thyristor control unit 2. The power unit I contains 18 thyristors 3 - 20, forming three-valve anodic and cathodic groups in each phase of the converter and interconnected counter-parallel. Three transducer outputs are connected to active.

ductive load, the phases 21, 22 and 23 of which are connected by a triangle.

The control method is implemented using a device (Fig. 3), which contains a generator of 24 modulating (leading) signals, a control unit 25, a phase shifter unit 26 and a driver-distributor 27. Unit 25 I consists of an indicator 28 for the modulating voltage of the modulating voltage, unit 29 inverting linear voltage, separate control unit 30, zero linear voltage indicator 31, power supply 31..

The method is carried out as follows.

From the given linear modulating voltages and „,.: They disconnect. with phase modulating voltage

MAs Ms defined as

between the respective two linear modulating voltages (Fig. 2). In rectification mode

the resistor 15, the thyristor 16 is then switched off, the voltage U. is applied to the load. Further, the switching process of the linear supply voltages using the thyristors of the two phases of the converter -B and C continues until the instant value of the phase modulating voltage is changed. The considered method of switching on thyristors in the accelerating operation mode of the converter increases by two times the pulse frequency of the converter, which in turn improves the harmonic composition of the output voltages and currents.

After changing the instantaneous value of the PD value, the formation of thyristor control pulses is prohibited, and then the load current is inverted.

The instantaneous values of and and jvjy change at cot o (.4 (Fig. 2). Control pulses in the interval ci

work of the converter is included - 25 are formed and the load is 35

the resistors of the two phases of the converter with the locked thyristors of the third phase, and with positive polarity of the phase modulating voltage, the thyristors of the cathode group are included,, and for the negative polarity - the anode thyristors.

Consider the process of forming the output voltage, starting from the time tO t LI 5 on the time diagrams (Fig. 2). In accordance with the polarity of the phase modulating voltages and, and include a fistor 12 of phase B and a thyristor 16 of phase C of the converter. Since VfAa is equal to the purchase, then the thyristors of phase A of the converter will be in the locked state. Linear voltage Ug is applied to load phase 22 and to a parallel branch formed by the series connection of phases 21 and 23. At the time point cot Nc. corresponding to the specified thyristor switching angle, the next linear supply voltage is switched, for which the thyristor 14 is turned on, while the thyristor 12 is turned off under the action of the reverse anode voltage. Through conductive thyristors 14 and 16, the line voltage Uga applies 40

45

50

is connected to the current linear voltage id,., until it reaches zero.

The inversion current dp at the time of the cot includes, in accordance with the polarity of the phase modulating voltages, and thyristors 4 and 14 belonging to the A and B phases of the converter and the switching voltage UBA, which contains the voltage of the phase A (U () of the power supply) to which the load is connected via a conductive thyristor 17 of a converter C phase with zero phase modulating voltage. A linear voltage Uc / is applied to phases 21 and 23, and phase 22 is short-circuited through conductive thyristors 14 and 17 (Fig. 1 and 2). The current ij is directed against the applied linear voltage, as a result of which it decreases sharply.

At time point cot 06, corresponding to the specified thyristor switching-on angle, the thyristor 3 is turned on, the thyristor 4 is switched off by the action of the reverse anode voltage V c, the conducting thyristors 3, 14 and 17 apply to the phases 21 and 23 a linear voltage UCA containing

c to the phase 22 of the load and to parallel- 55 in its composition the voltage of the phase A of the yen branch, formed by the series connection of phases 21 and 23, In the MOMeHt time cot include

„

0

five

0

is connected to the current linear voltage id,., until it reaches zero.

The inversion current dp at the time of the cot includes, in accordance with the polarity of the phase modulating voltages, and thyristors 4 and 14 belonging to the A and B phases of the converter and the switching voltage UBA, which contains the voltage of the phase A (U () of the power supply) to which the load is connected via a conductive thyristor 17 of a converter C phase with zero phase modulating voltage. A linear voltage Uc / is applied to phases 21 and 23, and phase 22 is short-circuited through conductive thyristors 14 and 17 (Fig. 1 and 2). The current ij is directed against the applied linear voltage, as a result of which it decreases sharply.

At time point cot 06, corresponding to the specified thyristor switching-on angle, the thyristor 3 is turned on, the thyristor 4 is switched off by the action of the reverse anode voltage V c, the conducting thyristors 3, 14 and 17 apply to the phases 21 and 23 a linear voltage UCA containing

5 includes the voltage of phase A of the power supply source, while phase 22 will be short-circuited. The current is again directed towards the voltage and

at some point in time he is. passes through a zero value and changes its direction (inverted), at the moment

0.7 when J2 thyristor

2E

becomes

Qt time

with i22 equal, the thyristor 17 is locked by disconnecting the phase converter C from the load.

Thus, the process of inverting the current in the load is carried out automatically without the use of special devices, which simplifies the control of the converter and increases the reliability of its operation,

At time G3t, when the sign of the linear voltage changes, the prohibition on the formation of control pulses is removed and the converter provides rectifier mode of operation, the thyristors of the two phases of the converter are turned on in accordance with the polarity and value of the phase modulating voltages.

The device that implements the method works as follows.

The three-phase system of linear modulating voltages U, formed by the generator 24, enters the block 26 and the distributor 27. In the distributor block 27, a three-phase system of phase modulating voltages U, 11 ,, is formed.

After changing the instantaneous value of the phase modulating voltage, the inverter operation mode of the converter begins and the device 25 comes into action, by which the formation of thyristor control pulses of the rectifying operation mode is prohibited. With the help of the indicator 28 and the block 29, two linear supply voltages are allocated, which ensure the inverter mode of operation of the converter. The converter is controlled by block 30. The device provides higher reliability of the converter by eliminating the operation of switching the current in the phases of the converter from one thyristor group to another, causing emergency modes of through short-circuiting.

Claims (1)

Invention Formula The control method of the thyristor direct frequency converter when connecting the phases of the load three 0 five the square, which sets three linear modulating voltages, corresponding to the phases of the voltage on the load, the frequency of which is determined by the frequency of the modulating voltage, the output voltage is formed by separating the anodic and cathodic groups of the thyristors in each phase, the anode and the cathode thyristor groups set the value of the modulating voltage, characterized in that, in order to increase the reliability of the operation of the converter, linear supply voltages are measured and fixed the sequence of their alternation, form three linear phase modulating voltages from the given linear modulating voltages; each of these three voltages is formed as the difference between the corresponding two linear modulating voltages, the indicated inclusion of the thyristors of the anodic and cathodic groups of the two phases of the converter is produced in accordance with polarity and the value of the formed phase modulating voltages, with a positive polarity of the phase modulating voltage include the thyristors of the cathode group, and with a negative th polarities include thyristors of the anode group, at the moment of time when the phase modulating voltage of the converter reaches zero, the formation of control pulses of the corresponding group is prohibited, the thyristors belonging to the Q-thyristors belong to fixed at the moment of zero crossing of the linear voltage applied to the load The power supply terminals include, in accordance with the polarity of the phase modulators of the mea- sure voltage of the converter, thyristors from the anode and cathode groups of the two phases of the converter, They do not commute two successive linear supply voltages, which include the voltage of the phase of the power source connected to the load through a conductive thyristor of the phase converter with zero phase modulating voltage, after passing through the second 5 in order of the linear voltage of the power supply, remove the ban on the formation of control pulses and provide for the operating mode of the converter, producing five five This includes the inclusion of two phase thyristors by the brightness and the value of their phase converter modules in accordance with the polarized voltages. - b cjifI iii I rm rm yy 1L 1 ± 12 13 " 2 Fff nineteen go Well 1 23 .Z BUT  MO evt 0) 1