SU756576A1 - Self-sustained series inverter - Google Patents

Description

The invention relates to the field of converting technology and is intended for induction heating of metals.

There are known circuits of consecutive 5 autonomous inverters with recovery of excess reactive energy from the commutation of a throttle through the opposite gate to capacitors charged up to half of the supply voltage [1].

The closest to the proposed is an inverter containing two thyristor bridges with commutating LC circuits in diagonals, the anodic 15 groups of which are connected through one of the input pins through the filter chokes and the cathode interconnected through each other and filter capacitors [2]. 20

The drawback of the circuit is that the excess reactive energy stored in the switching circuit is discharged by means of counter-parallel-switching valves 25, therefore, a small reverse voltage is applied to the valves in the time interval provided for restoring controllability.

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equal to the voltage drop on the oncoming valves, which leads to a decrease in the resorption rate of minority carriers in direct valves, and to an increase in the time required to restore their controllability, and, consequently, to a decrease in reliability.

The purpose of the invention is to increase reliability.

To achieve this goal in a serial autonomous inverter containing two thyristor bridges with commutating SC circuits in the diagonals, the anode groups of which are connected through filter chokes to one of the input pins, and the cathode connectors are interconnected through a choke, as well as filter capacitors, the choke is equipped with an additional winding, one end of which is connected to the anode group of the first bridge through one of the filter capacitors and through a series-connected diode connected in the forward direction, and The additional filter capacitor is with the cathode group of the second bridge, and its other end is connected to the first output terminal directly and connected through another filter, a level capacitor with an anode group

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the second bridge, with which through an additional diode connected in the forward direction, is connected a second output terminal, with at least one compensating capacitor connected in parallel with the output terminals, and the connection point of the said diode with an additional filter capacitor is connected with filter chokes.

The inverter is also equipped with an auxiliary choke and a second compensating capacitor included

. in series with the first, with their common point connected to the cathode group of the first bridge, and the auxiliary choke is connected between the second output terminal and the additional diode.

In addition, the inverter is equipped with a second additional filter capacitor and three auxiliary diodes, and the windings of all chokes are made with tapes, and the tap of the filter choke connected to the anode group of the second bridge is connected to the connection point of the said diode with the additional Filter capacitor, and the tap of the filter choke, connected to the anode group of the first bridge, through the second additional filter capacitor connected to the cathode group of the first bridge and through two auxiliary the diode connected in the opposite direction is connected, respectively, with the tap of the main winding of the choke and with the first output terminal, and the tap of the additional winding of the choke through the third auxiliary diode connected in the forward direction is connected with the anode group of the first bridge.

FIG. 1-3 gives an inverter circuit, ’variants.

The inverter contains two bridges consisting of thyristors 1-8, in the diagonal of which are switched commutating circuits consisting of commutating chokes 9, 10 and commutating capacitors 11, 12, filter capacitors 13, 14, additional filter capacitors 15, 16, diode 17 , additional diode 18, auxiliary diodes 19, 20 and 21, choke with main 22 and auxiliary 23 windings, load circuit consisting of compensating capacitors 24, 25. and inductor 26, choke 27, filter chokes 28.

An inverter whose circuit is shown in FIG. 1, operates in steady state as follows.

In the first cycle, the thyristors 1, 2 and 5, 6 are opened and the current flows through the circuits 13-1-9-11-2-24-23-31 and 14-5-10-12-6-22-24-14, t . both currents are summed in the load circuit and flow from the bottom up. The second half of the current half-cycle when the voltage. on the windings 22, 23, the choke adopts the polarity indicated in FIG. 1, and the sum of the voltages on the indicated chokes exceeds the supply voltage to which the additional capacitor 15 is charged, the diode 17 opens. From this moment the current in the inverter bridges stops, the overcharging of the switching capacitors 11, 12 stops at a predetermined level and the current of excess reactive energy flows, stored in the windings of the choke 22, 23 along the contour 22-24-23-17-15-22, i.e. flows along the load circuit in the same direction as the current of the inverter bridges. Since the recovery of excess reactive energy is carried out from two series-connected, common-mode voltages, windings of chokes 22, 23 to a capacitor 15 charged to a full supply voltage, the voltage on each winding is limited to half the supply voltage.

In the second cycle, the thyristors 3, 4 and 7, 8 are opened and the processes in the circuit proceed as described. With an increase in the equivalent load resistance, the voltage on the load circuit also increases, with the amplitude of which, equal to the supply voltage, the diode opens, 18 and the discharge current of the excess reactive energy stored in the load flows through the circuit 24-18-1424. Since the filter capacitors have a finite value, the voltage at the load controller is not sufficiently limited, which leads to a sharp reduction in the time allowed for the restoration of controllability of direct gates and to a breakdown of the inversion process.

FIG. 2 shows an inverter circuit in which the main switching processes proceed as described, and the voltage on the inductor 26 is twice as high as in the circuit in FIG. 1, due to the inclusion in series with it of an additional compensating capacitor, equal in magnitude to the first. Since only the compensating capacitor 24 flows around the high-frequency current of the inverter bridges, only half of the voltage on the inductor will be applied to them, the critical value of the voltage applied to the inverter bridges is 0.8-0.9 of the supply voltage, and at the same time voltage amplitude is 1.6-1.8 of the supply voltage. This level of voltage limitation on the load circuit is achieved by regulating

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the inductor 27, in the discharge circuit of excess reactive energy stored in the load (26-27-18-14-26), and the discharge circuit covers the entire inductor, and the control range ^{- the} amplitude of the voltage on the inductor is in the range from the level equal to the supply , to which the filter capacitor 14 is charged with the minimum inductance of the choke 27 and above - with an increase in the inductance of the choke 27. Accordingly, the range of voltage regulation on the load applied to the inverter bridges lies in the range from half the supply . Since there is a constant component in the current of the inverter bridges, it is bridged by a filter choke 28 to eliminate the one-sided recharge of the compensating capacitor 24.

With an increase in the power and frequency of the converters, the parasitic inductances that are not covered by the fault circuit and the parasitic inductance connected to the circuit of the excess reactive power circuit have a significant influence on the voltage buildup on the switching capacitors. FIG. 3 shows an embodiment of the circuit of the proposed inverter, in which the effectiveness of voltage limiting on the elements is increased. This scheme works as follows.

In the first cycle, the thyristors 1, 2 and 5, 6 are opened. First, due to the energy stored in the switching capacitors, the current flows through the circuits 11-2-24-23-21-1-1-9-11 and 12-622-20-16 -24-14-5-10-12, and then, when the voltage on the taps of the windings of the choke is lower than the supply voltage, to which the capacitors 13 and 16 are charged, the current flows through the circuits 13-1-9-11-2-24 -23-13 and 14-5-10-12-6-22-24-14. In the second half of the current half-cycle, as in the first case, the diode 17 opens and the reset current flows along the circuit 22-24-23-17-15-24. In this case, the excess reactive energy stored in the switching capacitors is discharged in the first half of the current half-cycle, and the excess reactive energy stored in the windings of the choke is discharged in the second half of the current half-period. Reset of excess reactive energy stored in the load circuit is carried out in both the first and second half-periods of the output voltage along the circuits 24-18-14-24 and 24-29-16-24.

To eliminate the uneven distribution of voltage on the windings of the choke 22, 23 when dumping excess

reactive energy in the second half of the current half-cycle, and therefore, for equal voltage limiting on the inverter bridge elements, the windings 22, 23 of the choke are magitically coupled.

Claims (3)

Claim 1. Serial autonomous inverter containing two thyristor bridges with switching 1C-circuits in the diagonals, the anode groups of which are connected through filter chokes with one of the input terminals, and the cathode are connected to each other through a choke, as well as filter capacitors, characterized in that, in order to increase the reliability, the choke is provided with an additional winding, one end of which through one of filter capacitors connected to the anode group of the first bridge and through a series-connected diode connected in the forward direction, and an additional filter capacitor to the cathode group of the second bridge, and its other horse C is connected to the first output terminal directly and connected through another filter condensate. with the anode group of the second bridge, to which a second output terminal is connected via an additional diode connected in the forward direction, with at least one compensating capacitor connected in parallel with the output terminals, and the connection point of the said diode with an additional filter capacitor is connected to filter chokes. 2. Inverter on π. 1, which is equipped with an auxiliary choke and a second compensating capacitor connected in series with the first, with their common point connected to the cathode group of the first bridge, and an auxiliary choke connected between the second output terminal and the auxiliary diode. 3. Inverter on π. 1, characterized in that it is equipped with a second additional filter capacitor and three auxiliary diodes, and the windings of all chokes are made with tapes, and the filter choke, connected to the anode group of the second bridge, is connected to the connection point of the diode with an additional filter capacitor, and the tap of the filter choke connected to the anode group of the first bridge through the second additional filter capacitor connected to the cathode 7 the group of the first bridge and through two auxiliary diodes connected in the opposite direction are connected, respectively, with the tap of the main winding of the choke and with the first output terminal, and the tap of the additional winding of the Choke through the third auxiliary diode included in 756576 8 forward direction connected to anode group of the first bridge.