RU2249294C2 - Current inverter - Google Patents

Abstract

FIELD: converter engineering; power supplies for induction heaters.

SUBSTANCE: proposed current inverter built in the form of single-phase bridge around transistors with series-connected diodes and transistor shunting diodes is provided with newly introduced series circuits of which one incorporates voltage limiter and two resistors, other circuit has voltage limiter, and third one, two resistors, two diodes, and two capacitors. Each series circuit shorts out single-phase bridge built around transistors and connected to input leads through filter chokes. Third series circuit is connected to collector and emitter groups of single-phase bridge transistor through fourth and fifth series circuits, each incorporating diode, resistor, and choke. In case of open circuit in induction heater thyristor is turned on to short out single-phase bridge through capacitor that limits input voltage of inverter in response to thyristor failure. Input voltage of inverter is limited by limiting voltage across first series circuit.

EFFECT: enhanced operating reliability and noise immunity of current inverter; reduced switching loss and voltage surges.

1 cl, 1 dwg

Description

The invention relates to a conversion technique and can be used as a power source for an induction heater.

A known current inverter containing a single-phase bridge on transistors, the collector group of which is connected to the positive input terminal through a filter inductor, with a capacitor shunting the output terminals of the current inverter, the emitter group of the single-phase bridge on transistors is connected to the negative input terminal of the current inverter (Glazenko T.A. , Senkov V.I. Circuit and constructive methods for ensuring electromagnetic compatibility of transistor DC-DC converters // Electricity. - 1989. - N 2. - C.37-43).

The disadvantage of the current inverter is the low reliability due to the high values of switching losses in transistors, high overvoltages on the elements of the current inverter circuit when the load circuit breaks.

A current inverter containing a single-phase bridge on transistors is known, the collector group of which is connected to the positive input terminal through a filter choke, with a capacitor shunting the output terminals of the current inverter, the emitter group of a single-phase bridge on transistors is connected to the negative input terminal of the current inverter (P. 2155433, Russia MKI N 02 M 5/451. Frequency converter / Silkin EM - Announcement 13.04.99, Publ. 27.08.00. - Bull. N 24).

The disadvantage of the current inverter is the low reliability due to the high values of switching losses in transistors, high overvoltages on the elements of the current inverter circuit when the load circuit breaks.

The closest in technical essence to the invention is a current inverter (Ruzsamyi T., Baesanyi C. Transistor-wechelrichter fur Induktiwe Erwarmung // Period. Polytechn. Mech. Engineering. - 1986. - N 1. - S.99-122) and is considered as a prototype.

The prototype contains a single-phase bridge on transistors with series diodes, the collector group of which is connected to the positive input terminal through a filter inductor, with a capacitor shunting the output terminals of the current inverter, a thyristor, the anode of which is connected to the collector group of a single-phase bridge on transistors with series diodes, a second capacitor , diode, emitter group of a single-phase bridge on transistors with series diodes connected to the negative input terminal.

The disadvantage of the prototype is the low reliability due to high values of switching losses in transistors and diodes, overvoltages on the elements of the current inverter circuit, possible thyristor overloads when turned on, possible overloads of the emitter group transistors when the induction heater fails.

The invention is aimed at solving the problem of improving the reliability of the current inverter, which is the purpose of the invention.

This goal is achieved by the fact that in a current inverter containing a single-phase bridge on transistors with series diodes, the collector group of which is connected to the positive input terminal through a filter inductor, with a capacitor shunting the output terminals of the current inverter, a thyristor, the anode of which is connected to the collector group of a single-phase bridge on transistors with serial diodes, the second capacitor, diode, thyristor cathode is connected to the emitter group of a single-phase bridge on transistors with serial diodes through the second capacitor, the diode cathode is connected to the thyristor control electrode, the emitter group of the single-phase bridge on transistors with serial diodes is connected to the negative input terminal of the current inverter through the second filter choke, and the AC terminals of the single-phase bridge on transistors with serial diodes are connected to the output terminals of the current inverter through switching chokes, transistors are shunted by counter diodes, serial diodes are shunted by serial circuits, containing they have a resistor and a capacitor, a single-phase bridge on transistors with serial diodes is shunted by a serial circuit containing a voltage limiter, a resistor and a second resistor, a common connection point of a voltage limiter and a resistor is connected to the diode anode, a common connection point of a resistor and a second resistor is connected to the thyristor cathode, single-phase the bridge on transistors with series diodes is shunted by a second voltage limiter, a second series circuit containing a third voltage limiter and a second diode, the anode of which is connected to the third voltage limiter, and the cathode is connected to the collector group of a single-phase bridge on transistors with series diodes, a third series circuit containing a third resistor, a third diode, a third capacitor, a fourth diode, a fourth resistor, a cathode connection point the third diode and the third capacitor is connected to the collector group of a single-phase bridge on transistors with series diodes through a fourth series circuit containing a fifth diode, fifth re History and throttle point of the fourth diode anode connection and the third capacitor is connected to the emitter group of single-phase bridge based on transistors with successive diodes through the fifth series circuit comprising a sixth diode, the sixth resistor and a second inductor.

A significant difference that characterizes the invention is to increase the reliability of the current inverter to the induction heater by reducing switching losses in transistors and diodes, switching overvoltages, limiting the currents of the thyristor and transistors of the emitter group.

Improving the reliability of the current inverter to the induction heater is a technical result due to the introduction of new elements and connections, i.e. distinguishing features. Thus, the distinguishing features of the inventive current inverter are essential.

The drawing shows a diagram of a current inverter.

The current inverter contains a single-phase bridge on transistors 1-4 with series diodes 5-8, the collector group of which is connected to the positive input terminal through the filter inductor 9, with a capacitor 10, shunting the output terminals 11 of the current inverter, thyristor 12, the anode of which is connected to the collector group single-phase transistors with series diodes, the second capacitor 13, diode 14, the thyristor cathode is connected to the emitter group of a single-phase bridge on transistors with serial diodes through the second capacitor, cathode d the ode is connected to the thyristor control electrode, the emitter group of the onophase bridge on transistors with serial diodes is connected to the negative input terminal of the current inverter through the second filter choke 15, and the AC terminals of the single-phase bridge on transistors with serial diodes are connected to the output terminals of the current inverter through switching chokes 16 , 17, transistors are shunted by counter diodes 18-21, serial diodes are shunted by serial circuits containing a resistor 22-25 and a capacitor OP 26-29, a single-phase bridge on transistors with serial diodes is shunted by a serial circuit containing a voltage limiter 30, a resistor 31 and a second resistor 32, a common connection point of the voltage limiter and resistor is connected to the diode anode, a common connection point of the resistor and the second resistor is connected to the cathode thyristor, a single-phase bridge on transistors with series diodes is shunted by a second voltage limiter 33, a second series circuit containing a third voltage limiter 34 and a second d iodine 35, the anode of which is connected to the third voltage limiter, and the cathode is connected to the collector group of a single-phase bridge on transistors with series diodes, a third series circuit containing a third resistor 36, a third diode 37, a third capacitor 38, a fourth diode 39, a fourth resistor 40, the connection point of the cathode of the third diode and the third capacitor is connected to the collector group of a single-phase bridge on transistors with series diodes through a fourth series circuit containing a fifth diode 41, fifth side 42 and inductor 43, the connection point of the anode of the fourth diode and the third capacitor is connected to the emitter group of a single-phase bridge on transistors with series diodes through a fifth series circuit containing a sixth diode 44, a sixth resistor 45 and a second inductor 46.

The current inverter operates as follows. The transistors of the diagonals of the inverter bridge 1, 4 and 2, 3 are switched on alternately with a frequency determined by the natural frequency of the parallel oscillatory circuit formed by the induction heater 11 and the capacitor 10. Moreover, the next pair of transistors 1, 4 or 2, 3 is turned on ahead of the time the voltage goes to loop capacitor 10 through a zero value. The specified circuit has a high quality factor, as a result of which the voltage across the induction heater 11 and the capacitor 10 is close to a sinusoidal shape. The inductance of the filter chokes 9, 15 has a large value. Therefore, the input current of the current inverter is smoothed, and the current flowing through the transistor 1-4 and the serial diodes 5-8, has a shape close to rectangular. At the time of turning on the transistors 2,3, the voltage across the capacitor 10 is conditionally negative ("+" on the left in FIG. 1). The voltage level (module) on the capacitor 10 is equal to:

u = v · E · cosb · sinb;

u <E,

where v is the constant circuit coefficient, E is the constant voltage at the input of the current inverter, b is the lead angle (the angle between the moment the next pair of transistors is turned on and the moment the voltage across the capacitor 10 passes through the zero value). The capacitor 10 begins to discharge in the circuits: 10-16-5-1-3-7-17-10 and 10-16-6-2-4-8-8-17-10. Inductors 16, 17 limit the rate of discharge of the capacitor 10 and the rate of decline (rise) of the current through the consecutive diodes 5, 8 (6, 7). The current of transistors 1, 4 and serial diodes 5, 8 decreases from the maximum value to zero, and the current of transistors 2, 3 and serial diodes 6, 7 increases from zero to maximum. When the reverse current of the sequential diodes 5, 8 is interrupted, the discharge current of the capacitor 10 closes through the capacitors 26, 29 in the following circuits: 10-16--26-22-18-3-7-17-10 and 10-16-6-2-21 -25-29-17-10. The energy stored in the electromagnetic field of the chokes 16, 17 (as well as the busbars) is partially transferred to the capacitors 26, 29 and partially dissipated in the resistors 22, 25 and the induction heater 11. Switching losses in transistors and series diodes, as well as switching voltage levels on the elements of the inverter circuit, the current decreases. When the voltage at the capacitors 22, 29 rises above the voltage E at the input of the current inverter, the diodes 37, 39 are turned on and the overvoltage energy is directed to the charge of the capacitor 38. In the initial state, the capacitor 38 is charged to a voltage close to the voltage at the input of the current inverter E. After the energy is consumed overvoltage diodes 37, 39 are turned off. The energy transferred to the capacitor 38 is then returned (recovered) to the induction heater 11, where it is consumed through serial circuits: 41-42-43 and 44-45-46. Partially, the energy is dissipated in resistors 42, 45. If in the switching interval the voltage on the capacitor 38 exceeds the voltage level of the voltage limiter 34 (a sharp change in the parameters of the induction heater or failure of the diodes 37, 39), the diode 35 is turned on and the voltage at the input of a single-phase bridge on transistors with serial diodes it is limited at the level of the rated voltage of the voltage limiter 34 (about 1.1 E). When the transistors 2, 3 are operated, after the end of the switching interval, the energy stored in the capacitors 26, 29 is returned (recovered) to the induction heater 11 until they are completely discharged. The electromagnetic processes in the current inverter when the transistors 1.4 are turned on proceed similarly. The next inclusion of transistors 2, 3 ends the period. In the induction heater 11, a full wave of alternating voltage is formed.

When the circuit of the induction heater 11 (or turning off the current inverter) is cut off, the voltage at the input of a single-phase bridge on transistors with serial diodes increases. If the voltage exceeds the limit level of the voltage limiter 30, the current increases through it and the thyristor 12 is turned on. The input current of the current inverter is closed by the circuit: "+" - 9-12-13-15 - "-" "+". In the initial state, the capacitor 13 is not charged. The voltage at the input of a single-phase bridge on transistors with series diodes is limited at the voltage level on the capacitor 13. The charge on the capacitor 13 reduces the input current of the current inverter. The energy accumulated in the electromagnetic field of the chokes of the filter 9, 15 at previous intervals of operation, passes into the capacitor 13. The thyristor 12 is turned off. Next, the capacitor 13 is discharged through the resistor 32. If, for some reason, the voltage across the capacitor 13 exceeds the voltage level of the voltage limiter 33, and also in case of failure, for example, thyristor 12, the voltage limiter 33 will turn on and limit the voltage (about 2, 1 E) at the input of a single-phase bridge on transistors with series diodes. The diode 14 and resistor 31 prevent the discharge of the capacitor 13 through the control electrode of the thyristor 12 and increase the noise immunity of the thyristor 12.

Compared with the prototype, the reliability of the current inverter is significantly increased by reducing switching losses and overvoltages. This is ensured by a rational set and mutual redundancy of protective circuits. Surge voltages on transistors are absent. Reliability is also increased by limiting the thyristor currents when charging the second capacitor and the currents of the transistors of the emitter group when the induction heater fails. The MTBF of the inventive current inverter compared with the prototype increases for the above reasons by 2-3 times.

Compared with the prototype increases the efficiency of the current inverter by reducing losses in the circuit elements.

Compared with the prototype, the cost of the inverter elements is reduced due to the possibility of using elements (transistors, diodes, etc.) for lower permissible currents.

Claims (1)

A current inverter containing a single-phase bridge on transistors with series diodes, the collector group of which is connected to the positive input terminal through a filter inductor, with a capacitor shunting the output terminals of the current inverter, a thyristor, the anode of which is connected to the collector group of a single-phase bridge on transistors with series diodes, the second capacitor, diode, characterized in that the thyristor cathode is connected to the emitter group of a single-phase bridge on transistors with series diodes through a second con The sensor, the cathode of the diode is connected to the thyristor control electrode, the emitter group of the single-phase bridge on transistors with serial diodes is connected to the negative input terminal of the current inverter through the second filter choke, and the AC terminals of the single-phase bridge on transistors with serial diodes are connected to the output terminals of the current inverter via commuting chokes, transistors are shunted by counter diodes, serial diodes are shunted by serial circuits containing a resistor and to capacitor, a single-phase bridge on transistors with serial diodes is shunted by a serial circuit containing a voltage limiter, a resistor and a second resistor, a common connection point of a voltage limiter and a resistor is connected to the diode anode, a common connection point of a resistor and a second resistor is connected to the thyristor cathode, a single-phase bridge on transistors with serial diodes is shunted by a second voltage limiter, a second series circuit containing a third voltage limiter and a second diode, the anode of which is connected to the third voltage limiter, and the cathode is connected to the collector group of a single-phase bridge on transistors with series diodes, a third series circuit containing a third resistor, a third diode, a third capacitor, a fourth diode, a fourth resistor, a junction point of the cathode of the third diode and the third capacitor connected to the collector group of a single-phase bridge on transistors with series diodes through a fourth series circuit containing a fifth diode, fifth resistor and inductor , the connection point of the anode of the fourth diode and the third capacitor is connected to the emitter group of a single-phase bridge on transistors with series diodes through a fifth series circuit containing a sixth diode, a sixth resistor and a second inductor.