SU760341A1 - Thyristorized frequency converter - Google Patents

Description

The invention relates to the field of converter technology and can be used as a power source for ultrasonic magnetostrictive transducers, and 5

also other high frequency consumers.

Known thyristor frequency converters containing inverting bridges with one or several ’θ series-connected commutation capacitors in an AC diagonal, connected in parallel with a chain of series-connected separation capacitor 15 and the load to the rectifier terminals via filter chokes M ·

A thyristor frequency converter is known, which contains an inverting 20 bridge with reverse diodes and a switching serial HC circuit in the diagonal of alternating current connected in parallel with the chain from a series-connected separation capacitor and the load to the output terminals of the rectifier via a filter choke [2], [з].

The rectifier of the known converters is connected to the terminals of the secondary 30

2

Noah winding power supply transformer having a zero point. In known converters, the period of the output current is formed when two thyristors of an inverting ¹ bridge are simultaneously operating.

The closest in technical essence to the proposed thyristor converter is a converter £ 4]. This converter contains a thyristor inverting bridge with three series-connected switching capacitors in an ac diagonal, connected to the output terminals of the rectifier via filter chokes, having average leads and switching chokes, a reverse diode bridge connected by alternating current leads to the middle switching capacitor, and DC outputs current to the middle terminals of the filter chokes, a series of coupling capacitor and output terminals, included I am waiting for the connection points of filter and commutating chokes. The presence of a reverse diode bridge allows you to limit the voltage on the elements of the inverting bridge. However switching

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four

"GGOT'eri in the thyristors of the inverting bridge of this converter are also great when operating at high frequencies, which leads to a decrease in the efficiency of the converter to 0.6-0.7 when operating in the ultrasonic frequency range 22-66 kHz.

The aim of the invention is to increase the efficiency of the thyristor transform "'™ ^;? ^ Telj'" of the part due to the reduction of the total loss of thyristors.

This goal is achieved by the fact that in a converter containing a thyristor inverting bridge with series-connected switching capacitors in an AC diagonal connected via serially connected switching and filter chokes to the DC terminals of a rectifier whose AC terminals are connected to the ends of the secondary windings of the supply transformer, having zero output, a serial chain of coupling capacitor and "output pins, common point commuting x capacitors connected to the zero terminal of the secondary winding of the supply transformer.

Such a connection is the common point of com ¹ mutating capacitors with zero

the output of the secondary windings of the supply transformer allows you to initially turn on one of the two thyristors, forming the period of the output current of the converter. In this case, the thyristor, connected with advance, conducts for a time equal to the turn-on delay time of the second thyristor, a current pulse of small amplitude, which allows it to achieve a conducting state with small switching losses.

On fig. 1 is a schematic diagram of the proposed thyristor frequency converter, ’in FIG. 2, a is an oscillogram of control pulses fed to the inverting bridge thyristors (> ^) in FIG. 2,6 — current waveforms of thyristors (C); in figure 2, in the oscillogram of the load current (ί „).

The thyristor frequency converter contains an inverting bridge, made on thyristors 1-4 with two "series-connected switching capacitors 5.6 in the diagonal of alternating current, connected via switching reactors 7.8 and successively connected filter chokes 9.10 to the DC terminals of the rectifier made on the diodes 11-16, the AC terminals of which are connected to the ends of the secondary windings 17 of the transformer 18, the primary windings 19 of which are connected to the mains, a serial circuit chku razdoli • tion of the capacitor 20 and the load

21, connected between the points of connection of the switching and filter chokes, while the common point of the switching capacitors is connected to the zero output of the secondary windings

5 transformers.

Thyristor Converter hour. Tots works as follows.

In the steady state by the time instant g, the commutating capacitors 5,6 are charged with the polarity shown in Fig. 1. Isolation capacitor 20 is charged to the rectifier output voltage. At the moment of time, a control pulse is applied to the thyristor 1, the thyristor 1 is turned on, and the capacitor 5 is pre-discharged along the circuit: 5-17-11, 12, 13-9-7-1-5. At the same time through the thyristor 1 A current pulse flows, the amplitude and duration of which is determined by

20 capacitor capacitance 5 and choke inductance of 9.7.

At time _{2, the} thyristor 3 is turned on and an oscillatory overcharge of the switching capacitors 5, b and the discharge of the coupling capacitor 20 occur along the circuit: 5-6-3-8-21-207-1-5. Thereby, through the load in the direction indicated in FIG. 1 by an arrow, a current impulse flows, the amplitude there and the duration of which is determined by the inductance of the commutating chokes of 7.8 th capacity of the commutating capacitors of 5.6. At the moment of time, the current pulse of the recharge of the switching capacitors 5.6 passes through zero, the thyristors 1.3 are turned off, and there is a pause in the nag current, ruzy. Switching capacitors

5.6 to the time point ί _{3 are} recharged to a voltage with polarity, reverse indicated in FIG. 1. At the moment of time, the thyristor 2 is turned on and the capacitor 6 is pre-discharged along the circuit: 6-17-11,

12, 13-9-7-2-6. At time ι ₅

45, the thyristor 4 is turned on and oscillatory overcharge of capacitors 5,6 and discharge of the coupling capacitor 20 along the circuit occurs: 5-4-3-21-20-72-6-5. A current impulse flows through the load. At time moment g _{6, the} current pulse of the recharging of capacitors 5.6 passes through zero, the thyristors 2.4 turn off and a pause occurs in the load current. Capacitors

5.6 are recharged to a voltage with the polarity indicated in FIG. one.

By the time of turning on the next thyristor, the first half-cycle of the inverting bridge operation ends.

The second half-cycle of the inverting bridge starts at the moment of time, ΐγ with the switching on of the thyristor 3. When ₍ this happens the preliminary discharge of the capacitor 6 along the circuit: 6-3-8-1014,15,16-17-6. At the moment of time

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the thyristor 1 is turned on and the capacitors 5.6 are recharged and the capacitor 20 is discharged and the next current pulse is generated in the load. At the moment of time, the thyristors 1.3 are turned off, there is a pause in the load current, the capacitors 5.6 are charged to a voltage with the opposite polarity indicated in FIG. one.

At the moment of time _{ί ι0 the} thyristor 4 is turned on, thus a preliminary discharge of the capacitor 5 along the circuit occurs: 5-4-8-10-14 ^ 15,16-17-5. At the time point c _{d the} thyristor is switched on.2 and the oscillatory overcharge of capacitors 5.6 and discharge of the capacitor 20 along the circuit occurs: 2-6-5-4-8-21-20-7-2 and the next current pulse in the load is formed. At time, thyristors 2.4 turn off, there is a pause in the load current, capacitors

5.6 are charged to the voltage with the polarity indicated in FIG.

By the time g _{| E of the} next switching on of the thyristor 1, the full cycle of the inverting bridge is completed.

The separation capacitor 20 is continuously recharged from the mains through a rectifier and filter inductors 9,10.

Thus, in the first half-cycle of the inverting bridge, thyristors 1,2 are switched on with respect to thyristors 3,4, and in the second half-cycle, thyristors 3,4 are switched on ahead of thyristors 1,2.

'Thyristors, turned on with advance, conduct pulses of current of preliminary discharge of switching capacitors 5,6, the amplitude and duration of which are determined by the capacity of switching capacitors,

5.6 and the inductance of the filter chokes 9,10. The inductance of the filter chokes is 10-30 times the inductance of the switching chokes. Consequently, the amplitude of the current pulses of the preliminary discharge of the switching capacitors is several (3-5) times lower than the amplitude of the current pulses of the overcharging of the switching capacitors during the formation of the current in the load. Accordingly, the duration of the current pulses of the preliminary discharge of switching capacitors increases.

The delay in the inclusion of thyristors 3,4 in the first half cycle of thyristors 1,2

in the second half-cycle of operation, the inverting bridge should be less than the duration of the current pulse of the preliminary discharge of switching capacitors 5.6 so that the thyristors connected ahead of them remain in the conducting state by the moment the next thyristors are turned on.

In the thyristors switched on with advance, a conducting state is established at a small current amplitude, which leads to a decrease in switching losses in them and to an increase in the efficiency of the frequency converter.

Claims (1)

Claim A thyristor frequency converter containing an inverting bridge with series-connected switching capacitors in an AC diagonal, connected through series-connected switching, and filter chokes to the rectifier DC terminals, the AC terminals of which are connected to the ends of the secondary windings of the supply transformer, having a zero output, a series from section- capacitor and output pins connected between switching and filter chokes, characterized in that, in order to increase efficiency, two switching capacitors are included in the inverting bridge AC diagonal, the common point of which is connected to the zero output of the secondary windings of the supply transformer.