SU1758809A1 - Independent current inverter - Google Patents

Abstract

The invention relates to a converter equipment and can be used in thyristor frequency converters designed to power asynchronous traction motors of direct and alternating current electric trains. The purpose of the invention is to increase reliability by ensuring the restoration of valve properties of thyristors in the switching process. The device contains main thyristors (T) 5-10, recharged T 22, 23 and commuting T 24, 25. Accelerator T 26, 27 are connected to the bridge distribution diodes 14-19. T 22-27 are shunted by chains of diodes 28-35, 40-43 connected to capacitors 36-39, 44, 45. Capacitors can be charged in a direction consistent with the direction of the thyristors turned on, up to a voltage equal to the voltage drop on the diodes . 3 il. WITH S

Description

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The invention relates to converter technology and can be used in thyristor frequency converters intended for powering induction traction motors (ATD) of direct and alternating current electric trains, as well as for powering ADT of general industrial mechanisms.

The purpose of the invention is to increase reliability by ensuring the restoration of valve properties of thyristors in the switching process.

Figure 1 is a schematic diagram of the power circuits of an autonomous current inverter; Fig. 2 is a control pulse diagram explaining the principle of operation of the proposed device and the process of converting a DC voltage to a three-phase AC; Fig. 3 is a diagram of currents and voltages, explaining the principle of operation and electromagnetic processes occurring in the device.

The standalone current inverter (FIG. 1) contains DC busbars 1 and 2 for connecting to power supply 3, a smoothing reactor 4 connected to the power supply bus, a three-phase main thyristor bridge 5-10 connected by direct current leads to a smoothing reactor lead 4 and to the DC bus 2, and the AC leads to a three-phase load 11,12,13 (where 11 is a phase A, 12 is phase B and 13 is phase C), a three-phase distribution diode bridge 14-19 connected by AC leads current to AC leads of a three-phase bridge thyristors, a commutating LC circuit, consisting of a series-connected commutating capacitor 20 and a reactor 21, two recharging thyristors 22 and 23 connected by the same anode and cathode to the anodes and cathodes of the three-phase main thyristors and other anode and cathode to the outputs of the commutating LC - circuits, switching thyristors 24, 25, connected by one anode and cathode to the anodes and cathodes of a three-phase bridge distribution diodes and other anodes and cathodes to another output of the switching LC circuit, accelerator thyristors 26,27, connected by the corresponding pins between the direct current pins of the three-phase bridges of the main thyristors and distribution diodes, the chains consisting of two diodes 28 and 29.30 and 31.32 and 33.34 and 35, connected in anti-successive cathodes and free ends connected in parallel to the switching and recharge

thyristors, capacitors 36, 37, 38. 39, one output connected to the common connection point of the cathodes of the diode chains, and the other ends to the anodes of the commuting and rechargeable thyristors, chains consisting of two diodes 40 and 41, 42 and 43 connected opposite anode and other free ends connected in parallel to the accelerator thyristors 26 and 27, capacitors 44 and 45, some of the leads connected to common points of the anodes, and the other leads to the cathodes of the thyristors 26 and 27, the control system 46 connected

its outputs to the input terminals of the control thyristors 5-10, 22-27,

Autonomous current inverter according to the diagrams of Fig.2 and 3 works as follows.

Suppose that in the time interval tcrti the thyristors 8, 9 are turned on, as a result of which the load current flows from the plus of the power source 3 through bus 1, reactor 4 through circuit 9, phase C, phase B, 8, bus 2, minus

power supply 3. In this case, the capacitor 20 is charged with the polarity of the voltage indicated in Fig. 1. At time ti according to the diagram of FIG. 2, the thyristors 22 and 24 are turned on, as a result of which the capacitor 20 is recharged around the circuit 20, 21, 24, 16, 9, 22, 20, and the current in the thyristor 9 decreases to zero (FIG. ).

At the moment of turning off the thyristor 9, the load current of phase C is closed along the circuit: 3, 1,

4, 22, 20, 21, 24, 16, phase C, phase B, 8, 2, 3, as a result of which the capacitor 20 is recharged by the load current, and the voltage of the capacitor 20 is applied to the switchable thyristor 9 for the duration of the restoration of the valve properties.

At time t2 with a time delay equal to t, the accelerator thyristor 26 is turned on, and the switching capacitor 20 is recharged in the oscillating mode to the opposite polarity along the contour 20, 21, 24, 26, 22, 20.

At the instant of time r3, the voltage across the switching capacitor reaches the voltage of the input power source 3,

as a result, the process of current decline in phase C and growth in phase A begins, since a control pulse is applied to the input of the thyristor 5. In the interval t3-t4, the current in phase C drops to zero and the capacitor 20 is charged to a voltage higher than the input voltage of source 3. At the same time, the thyristors 22, 26, 24 are restored by the reverse recovery current (lrr) along the contour 20, 22, 26 , 24, 21, 20. Consider the possible

options for combining charge parameters

reverse thyristor recovery: 1)

Qrr, 22 Qrr.26 Qrr, 24; 2) Qrr, 24 Qrr, 26 Qrr, 22;

3) Qrr, 26 Qrr, 24 Qrr, 22, where the subscripts 22, 24, 26 denote the thyristors in FIG.

In the first variant, the thyristor 24 is restored to its first valve properties, as a result of which all the reverse voltage of the recharging of the switching capacitor is applied to it. As a result, the thyristors 22 and 26 remain without the reverse voltage necessary to restore the valve properties. It should be emphasized that in this case the reverse current flow circuit is interrupted in the prototype device.

As a result, when switching on at the next moment of switching the thyristor 23 along the circuit of switching thyristors, a short-circuit of the power source will occur.

In the proposed device, when the thyristor 24 is turned off, the reverse recovery thyristor 22 current flows along the contour 20, 22, 26, 28, 39, 21, 20. When the thyristor 26 is turned off, the reverse recovery thyristor 22 current flows along the circuit 20, 22, 45, 43, 28 , 39, 21, 20.

In the second variant, thyristor 22 is first switched off, as a result of which there is no circuit in the prototype for the flow of reverse restoration thyristors 26 and 24. As a result, when the thyristor 25 is switched on at the next switching point 25, the prototype device short-circuits the load (11, 12, 13 ), (17-19), 25, 24, 14-16 (11, 12, 13). In the proposed device, the reverse recovery thyristor 24, 26 current flows through the circuit 20, 33, 37, 26, 24, 21, 20. Then, when the thyristor 26 is turned off, the reverse recovery current of the thyristor 24 flows through the circuit 20,33,37,45, 43 , 24, 21, 20. As a result, when the thyristor 24 is turned off, a reverse voltage is applied to it and it restores its valve properties over the time specified in the thyristor passports.

In the third variant, the thyristor 24 restores its valve properties to the second, as a result of which the thyristor 26 is restored along the circuit 20, 33,37,26, 28, 39,21,20.

In order to limit the switching voltages associated with the rapid fall of the current and reverse recovery, the characteristics of the diodes are avalanche. For example, when a reverse voltage is applied to the thyristor 22 exceeding the avalanche voltage of diode 32, diode 32 is turned on and the surge of reverse voltage across the thyristor is limited at the level of diode voltage of the diode.

At the next moment of switching (the moment of time ts), the recharge

thyristor 23 and commuting 25, and then delayed thyristor 27 with a time delay, as a result of which thyristor 8 of phase B is turned off. Electromagnetic processes in a switching circuit are similar to those considered earlier. At the same time, if for example Qrr, 23 Qrr, 27 and Qn-, 25, then it restores its valve properties along the contour 20.21, 30, 36, 44, 40, 23, 20, etc.

The initial charge of the switching capacitor to the voltage of any polarity can be made from a separate source of charging voltage or from the power source 3 by switching on the rechargeable switching and main

0 thyristors. For example, to charge a compensator to the original polarity indicated in Fig. 2, include thyristors 5, 25, 23, as a result of which the capacitor is charged along circuit 3, 1, 4, 5, 17, 25, 21, 20, 23, 2, 3.

5It should be noted that the connection in parallel to the thyristors of capacitors without diode strings does not allow to solve the problem, since the capacitors are chosen from

 AQrr (Qg + 3 srgg) - (Qr-3aQ, r)

About

7G

AU

where Qrr is the mathematical expectation of thyristor reverse recovery charge: OQn standard deviation; Au is the maximum voltage to which a capacitor can charge, l can amount to several microfarads. In the process of restoring the valve properties and in the process of switching, the capacitors can be charged in the consonant direction with the thyristors and when the thyristors are turned on, the capacitor without the limiting resistor can be discharged through the control junction circuit and cause the thyristor to fail. Connection parallel to the thyristors of an RC circuit, in which the resistor is selected on the order of 20 ohms and has an inductance of the order of 0.1

Mr. 1 does not allow bursts to be limited.

switching voltages and to create a loop for the flow of the reverse reconstruction current. In the device (Fig. 1), capacitors are connected in parallel to the diodes, as a result of which they can be charged in a direction consistent with the direction of switching on the thyristors only up to the voltage,

equal to 1.5-2 V, i.e. voltage drops on the diodes. In addition, the indicated capacitor connection eliminates the damped oscillatory process from one voltage sign to another and vice versa and reduces the effect on the process in the switching circuit. Thus, the device improves reliability by limiting switching voltages and

guaranteed restoration of thyristor valve properties,

Claims (2)

1. Autonomous current inverter auth. St. No. 1683157, characterized in that, in order to increase reliability by ensuring that the valve properties of the thyristors are restored during the switching process, six chains consisting of two diodes connected back-to-back and six capacitors connected by a single output to the common points of the diodes are added each chain, the free terminals of the diode chains are connected in parallel to each of the switching, recharging and accelerator thyristors, and to the switching and recharging thyristors The diode chains with common points of connection of cathodes, the capacitors of these chains are connected to the anodes of commuting and recharging thyristors, the chains of diodes having common points of connecting anodes are connected in parallel to the accelerator thyristors, and the capacitors of these chains are connected by other leads to the cathodes of accelerating thyristors. 2. The current inverter according to claim 1, differs from the fact that the chain of diodes included counter-consistent, made with the avalanche characteristic. FIG 2 L / gZ