RU176542U1 - Device for generating control pulses of a diode-thyristor bridge - Google Patents

Abstract

The utility model relates to electrical engineering, in particular to converter technology, and can be used to turn on thyristors when transferring a diode-thyristor bridge to a diode mode. The proposed circuit is a synchronization system with mains voltages, assembled on optocouplers without the use of a neutral wire and transformer isolation. Upon receipt of an input enabling signal, the device generates three sequences of galvanically decoupled powerful control pulses shifted by 120 electrical degrees, which allows the previously closed diode-thyristor bridge to be switched into a diode bridge mode with natural switching.

Description

A useful model of a device for generating control pulses of a three-phase diode-thyristor bridge relates to electrical engineering, in particular to converter technology, and can be used to turn on thyristors when transferring a diode-thyristor bridge to a diode mode.

Known devices for converting AC voltage to DC, in which it is most rational to use diode-thyristor bridges, and the output voltage control functions by changing the opening angle of the thyristors are not used.

The most typical example of such an application can be a widespread input rectifier circuit for a two-link frequency converter [1], consisting of an input diode power bridge and a separate circuit including additional low-current diodes, a low-current relay, and a charging current limiting resistor. When supplying the mains voltage to the input of the converter to eliminate shock currents through the rectifier bridge, the preliminary charge of the filter capacitors is made through this separate circuit.

After a smooth charge of the capacitors to some voltage close enough to the maximum, you can turn on the thyristors of the diode-thyristor bridge. Obviously, in this application, the output voltage control function is not needed and the diode-thyristor bridge will operate in the diode bridge mode with natural switching.

This solution allows you to abandon the use of unreliable and volumetric power contactors to power the inverter, and also allows you to quickly disconnect the rectifier from the DC link filter in case of accidents, closing all thyristors of the diode-thyristor bridge. The cost of diode-thyristor modules exceeds the cost of diode modules by approximately 10%, therefore, the use of such a solution is quite justified.

Recently, in the circuits of frequency converters, the neutral wire of the input network is usually not used, therefore, the pulse-phase control system (SIFU), which generates control pulses to turn on the thyristors, should use only linear input voltages.

The most widely used are vertical-controlled SIFUs [2], which contain a reference voltage generator, usually made with the use of isolation transformers, a zero-organ, and a pulse shaper.

With the vertical control principle, the thyristor unlocking angle is determined by the moment of equality of the reference voltage, for which sawtooth pulses are most often selected, synchronized with the transitions through zero of the input network voltages and the control voltage specified by the regulator. These SIFU are made on the elements of analog circuitry and are actively used in a variety of converters.

The disadvantages of such SIFUs include rather cumbersome circuits, the use of expensive and low-tech transformers for galvanic isolation and synchronization with the network, the instability of analog cascades, the requirements for tuning elements, the need for components with exact ratings.

The objective of the proposed utility model is to simplify the thyristor control circuit, exclude the isolation transformer for synchronization with mains voltages in the absence of a neutral wire, increase the operational reliability of the opening pulse generators for thyristors, and the absence of accuracy requirements for components — it is solved using a device for generating three-phase diode-thyristor control pulses a bridge containing three synchronization optocouplers with linear mains voltages, a control optocoupler, form high-frequency pulse generators, three bridges on MOSFET transistors and capacitors, three high-frequency isolation transformers and three rectifiers supplying opening pulses to the thyristors; in this case, three chains with optocouplers connected to the line voltage of the network without a neutral wire and an isolation transformer are used to synchronize with the network , and optocoupler receivers run three generators of high-frequency rectangular pulses, which are amplified by bridges made on field-effect transistors, and through transformers are transferred to the shapers to control the thyristors, and wide pulses are formed on the thyristor control electrodes, which allow reliably transfer the diode-thyristor bridge at the right time to the diode mode with natural switching ..

In FIG. 1 shows the proposed circuit, containing three synchronization optocouplers with linear mains voltages (LEDs 5, 7 and 9 and optoelectronic receivers 11, 12 and 13, respectively), a control optocouple 4, high-frequency pulse shapers 14, 15 and 16, three bridges on MOSFET transistors 17 and 18, 19 and 20, 21 and 22, three isolation transformers with primary windings 23, 24 and 25 and secondary windings 32, 33 and 34, respectively, and three rectifiers 35, 36 and 37, which supply opening pulses to the thyristors.

The input line voltages L1, L2, and L3 are supplied to a star consisting of resistors 1, 2, and 3 and LEDs of optocouplers 6, 8, and 10. It can be seen that these circuits do not need a zero input network wire, which is an advantage of such a circuit. Concurrently with the LEDs of the optocouplers, conventional LEDs are installed to control the presence of mains voltages.

The transistors of the optocoupler optocouplers 11, 12 and 13 open and start the pulse shapers 14, 15 and 16. These shapers produce high-frequency meanders and control half-bridges consisting of field-effect transistors 17 and 18, 19 and 20, 21 and 22.

Half-bridges work in pairs of capacitors 26 and 27, 28 and 29, 30 and 31, and the load of these bridges are the primary windings of transformers 23, 24 and 25. The secondary windings of the decoupling transformers 32, 33 and 34 are loaded on the control driver circuit 35, 35 and 37, which convert the modulated alternating voltage into direct current pulses supplied to the control electrodes of the thyristors.

The power to the receivers of the synchronizing optocouplers 11, 12 and 13 is supplied by another optocouple 4, the inclusion of which allows the transmission of clock pulses and the operation of the pulse shapers, the first to open the thyristor, which created the conditions for inclusion. Next, the thyristors will turn on in turn, and the bridge will operate in a diode bridge mode with natural switching.

The resistors from which the control voltage is removed to start the pulse generators are shunted by capacitors to increase the noise immunity of the start of the generators.

Transformers operate at a high frequency, can be performed on small-sized cores and are used for galvanic isolation of the control system and power circuit. LEDs 6, 8 and 10 signal the correct operation of the circuit.

A timing diagram of the operation of the circuit is shown in FIG. 2. The upper diagram shows the input line voltages supplied to the inputs L1, L2, and L3, and the lower ones show the sequence of pulses synchronous with the voltages of the input network, triggering the pulse shapers supplied to the thyristors. It is seen that the control pulses occupy 180 el. with positive values of the linear voltage of each phase, therefore, by the time the conditions for switching on appear on the thyristor, a trigger voltage will already be applied to its control electrode.

For example, when a diode bridge is operating on a purely active load, the conduction interval of each diode begins after 30 degrees. from the moment the zero voltage crosses the line voltage, and the entire conduction interval takes 120 el. degrees.

During the operation of the diode-thyristor bridge and a purely active load, the proposed circuit will generate a trigger voltage for 30 el. until the moment of natural switching, which guarantees the inclusion of the corresponding thyristor at the right time.

Information sources:

1. IGBT Modules Technologies, Driver and Application / Andreas Volke, Michael Hornkamp, Published by Infineon Technologies AG, Second Edition, 2012.

2. Electric drives of direct current with valve converters / E.N. Zimin, V.L. Katsevich, S.K. Kozyrev. - M.: Energoizdat, 1981 - 192 pp.

Claims (1)

A device for generating control pulses of a three-phase diode-thyristor bridge, containing three synchronization optocouplers with linear network voltages, controlling an optocoupler, high-frequency pulse shapers, three bridges on MOSFET transistors and capacitors, three high-frequency isolation transformers and three rectifiers, which supply opening pulses to the thyristors, characterized in that for synchronization with the network, three chains are used with optocouplers connected to the line voltage of the network without neutral an ode and a decoupling transformer, and optocoupler receivers trigger three generators of high-frequency rectangular pulses, which are amplified by bridges on field-effect transistors and transmitted through transformers to the shapers to control the thyristors, and wide pulses are formed on the thyristor control electrodes, which allow reliable transfer of the thyristor-diode bridge at the right time in diode mode with natural switching.

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