SU888306A1 - Three-phase inverter - Google Patents

Description

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The invention relates to power converter technology and can be applied to power supply at higher frequencies of consumers with drastically changing load.

A three-phase inverter containing a thyristor bridge is known, to the AC terminals of which a reverse diode bridge 13-) is connected through chokes. The external characteristic of such a converter is achieved by large peak currents of the thyristors and diodes in modes close to idle. In addition, the presence of three chokes in the power feedback circuit complicates the device and increases its dimensions.

Also known is an inverter containing an input choke, a bridge of main thyristors and a valve-capacitor bridge mounted at its output closed to the choke 2. The disadvantage of this inverter is a large

the number of controlled valves in the control device, the accidental overlapping of which leads to an inversion.

Connecting the valve-capacitor bridge to the output terminals of the inverter bridge through additional capacitors 31 improves the reliability of the device, but does not eliminate the disadvantage of closing the switching capacitors in a star, which is undesirable in some cases.

The closest to the proposed invention is a three-phase inverter i, which contains a thyristor bridge connected to the input terminals through a filter choke, switching capacitors connected between the alternating current terminals of the thyristor bridge, and a reverse diode bridge, the alternating current terminals of which are connected to the alternating current terminals the current of the thyristor bridge, the current fiocTOflHHoro of the current through the regulating chokes are connected to the output of the direct current of the thyristor bridge. The specified inverter possesses a rigid external characteristic and stability when operating on the motor load. However, the presence of moments of turning the regulating chokes by chains of series-connected diode and thyristor leads to an increase in the average valve current, a decrease in the efficiency of the device and a limitation of its frequency range. The aim of the invention is to increase the efficiency and expansion of the frequency range of the inverter. The goal is achieved by the fact that a three-phase inverter containing a thyristor bridge connected to the input pins, the AC pins of which are connected to the output pins and through the commutating ones to each other, and connected to the AC pins of the reverse dc bridge connected. direct current pins through regulating chokes to the direct current pins of the thyristor bridge are equipped with additional switching capacitors connected in pairs in series between the alternating current pins of the thyristor bridge and the alternating current pins of the reverse diode bridge are connected to the connection points of the additional commutating capacitors of the corresponding pairs . FIG. 1 shows the basic electrical circuit of the inverter; in fig. 2 - vector diagram, graphs of current and voltage, explaining his work; in fig. 3 possible variant of the inverter circuit. A three-phase inverter sodermsite thyristor bridge 1-6 connected to the input terminals through a choke filter 7, switching capacitors 8-16 connected between the AC terminals of the thyristor bridge 1-6, and a reverse diode bridge 17-22, DC terminals through control throttles 23, 2, connected to the DC terminals of the histristic bridge 1-6. Capacitors 8–13 form a capacitive divider for the voltage, containing connected capacitors 8–9, 10–11 12–13 in each phase, the common points of which are connected to the corresponding conclusions of the G | alternating current of the reverse diodes 17–22. The operation of the inverter will be considered on the interval in which thyristors 2 and 3 are flowing. At the beginning of this interval, thyristor 2 turns on and falls on diodes 18, 20, 22 Circassian choke Z voltage, ° responsibly. From the vector diagram (Fig. 2a), it follows that the voltage Id at the time of switching is positive, if the angle is locked, O is positive, if fS, a and | z; positively, if (L 6P Selection of the angle (ig is determined by the ratio of the capacitors of the capacitive divider 8-12, and by varying Ro it is possible to achieve different rigidity of the external characteristics of the inverter under other equal conditions. Since the anodes of the diodes 18, 20, 22 are connected to each other then the diode is turned on, the voltage on the cathode of which is at the moment; the switching moment is minimal. Consider the case when | i is 60 ° and the angle o is so small that at time 0 0, .8 this case the diode 20 turns on and a circuit consisting of Drossel 2, thyristor 2, diode 20 and cond Disconnectors 8, 9, and TO. Under the action of voltage, a regulating choke 2 will develop a current 124 (2.6.). increase when. Then with current ij it will decrease until it becomes zero, it is essential that current i decreases under the action of voltage U in amplitude less than the voltage under which this current accelerates. The proposed inverter circuit favorably differs from the primarily known lack of shorting moments of the regulating chokes, since the diodes and thyristors are connected via capacitors, and therefore, whatever the pair of thyristors and diodes worked, the regulating choke will always be connected through a capacitive circuit formed by a capacitor battery. This makes it possible to increase the efficiency of the device and expand its frequency range. Closing a current pulse through a regulating choke allows, with the same stabilizing effect

improve the current use of the valve, its circuit equipment.

To confirm what has been said, let us compare the current curve of one of the control chokes in the known MHFig device 2, c and in this scheme (Fig.2, b). In the inverter circuit fij, the control choke is connected in parallel with the switching capacitor for the time corresponding to the locking angle | b. In this case, the regulating choke perceives a certain fraction of the reactive power of the capacitor bank. Further, the choke is short-circuited through the thyristor and the diode itself, while the energy accumulated in it is dissipated on the internal resistance of the valves and the active resistance of the throttle itself during the time corresponding to the angle ft. The average current Dejj through the regulating choke is thus connected with its internal resistance RC. M reactive power value q Q to be compensated by the following approximate formula

: SF: - ° From this it follows that stabilization is achieved through active losses in the control chokes.

In this scheme, the regulating throttle current is accelerated and reduced to zero under the action of alternating voltage, taken alternately from different connection points of the capacitor bank. As a result, the average current of the control chokes is determined by the inductance of the throttles, the angle (b, and the magnitude of the reactive power to be compensated

d 0. Therefore, the value of R. can be made arbitrarily small and, therefore, losses in the choke circuit can be made arbitrarily small.

Claims (2)

1. USSR author's certificate No. 156230, cl. H 02 M 7/00, 19b2. 2. USSR author's certificate No. 412660, cl. H 02 M 5 / + 2 1971. So USSR Copyright Certificate № 522537, class. H 02 H 7 / 5.15, 1976. 4, I. Kanter. Static frequency converters Saratov. Izd-vo SSU, 1966. with. 300, fig. 7-3. -i zs " OK: : Ti 3 // i f / zx k 3 / T // / J ( W four //  / Phag. J