RU68812U1 - AUTONOMOUS AGREED INVERTER WITH RESONANT COMMUTATION - Google Patents

Abstract

The utility model relates to a conversion technique and can be used in power supplies for induction heaters. The utility model improves the reliability of a stand-alone matched inverter with resonant switching. The self-contained matched inverter with resonant switching contains a single-phase bridge connected through the inductors of the filter 1, 2 to the input terminals of the inverter, two serially connected arms of which contain controllable valves 3, 4 with counter-parallel diodes 5, 6, and two other series-connected arms contain capacitors 7, 8, AC terminals of a single-phase bridge through series-connected saturable reactors 9, 10 and switching reactors 11, 12 are connected to the output terminals of the inverter ora shunted by compensating capacitor 13. To the output terminals of the inverter 1 is connected inductor 14. Fig.

Description

The utility model relates to a conversion technique and can be used in the design of power supplies for induction heaters and other electrotechnological loads. The utility model improves the reliability of a stand-alone matched inverter with resonant switching.

A self-contained coordinated inverter with resonant switching is known, which contains a single-phase bridge connected to the inverter output terminals with a single-phase bridge, two series-connected arms of which contain controlled valves with counter-parallel diodes, and two other series-connected arms contain capacitors, single-phase bridge alternating current leads through series connected switching inductor and switching capacitor are connected to the output terminals of the inverter (Thyristor frequency browsers / A.K. Belkin, T.P. Kostyukova, L.E. Roginskaya, etc. - M .: Energoatomizdat, 2000. - P.37)

The disadvantage of a stand-alone matched inverter with resonant switching is the low reliability. This is due to high levels of currents through controlled gates and counter-parallel diodes in the inverter, made at a given power, which can lead to their failure due to overheating of semiconductor structures of controlled valves and anti-parallel diodes. The inverter does not provide a symmetrical limitation of the current of the power source during emergency closures of the output terminals to the load housing due to filter chokes.

A self-contained matched inverter with resonant switching is known, which contains a single-phase bridge connected to the input terminals of the inverter with a DC link, the two shoulders of which are connected in series

valves with counter-parallel diodes, and the other two series-connected arms contain capacitors, the AC terminals of a single-phase bridge are connected to the output terminals of the inverter (P. 2024177 of the Russian Federation, MKI N02M 7 \ 538. AC converter for powering the inductor \ EM Silkin , G.V. Mizin, A.I. Pakhalin and others - Declaration 04.07.91, Pub. 30.11.94, B.I. No. 22).

The disadvantage of a stand-alone matched inverter with resonant switching is the low reliability. This is due to high levels of currents through controlled gates and counter-parallel diodes in the inverter, made at a given power, which can lead to their failure due to overheating of semiconductor structures of controlled valves and anti-parallel diodes. The inverter does not provide a symmetrical limitation of the current of the power source during emergency closures of the output terminals to the load housing due to filter chokes.

A self-contained coordinated inverter with resonant switching is known, which contains a single-phase bridge connected to the inverter output terminals with a single-phase bridge, two series-connected arms of which contain controllable valves with counter-parallel diodes, and two other series-connected arms contain capacitors, single-phase bridge AC terminals are connected to inverter output terminals (P. 2025881 RF, MKI Н02М 7 \ 538. AC converter for inductor power supply \ E.M. Silkin, G.V. Mizin, A.I. Pa Khalin et al. - Declaration 03.09.91, Publ. 30.12.94, B.I. No. 24).

The specified autonomous matched inverter with resonant switching is the closest in technical essence to a utility model and is selected as a prototype.

The disadvantage of a stand-alone matched inverter with resonant switching is the low reliability. This is due to high current levels through

controlled gates and anti-parallel diodes in an inverter made at a given power, which can lead to their failure due to overheating of semiconductor structures of controlled valves and anti-parallel diodes. The inverter does not provide a symmetrical limitation of the current of the power source during emergency closures of the output terminals to the load housing due to filter chokes. There are large levels of overvoltage on controlled valves and on-parallel diodes and high levels of electromagnetic interference due to high levels and rates of rise and fall of current of controlled valves and on-parallel diodes.

The utility model is aimed at solving the problem of improving the reliability of a stand-alone coordinated inverter, which is the purpose of the utility model.

This goal is achieved by the fact that a self-contained matched inverter with resonant switching contains a single-phase bridge connected to the input terminals of the inverter through filter inductors of the inverter, a single-phase bridge, two series-connected arms of which contain controlled valves with on-parallel diodes, and two other series-connected arms contain capacitors, AC terminals of a single-phase bridge through series-connected saturable reactors and commutating reactors are connected to the output with the inverter outputs shunted by a compensating capacitor.

A significant difference characterizing the utility model is an increase in the reliability of an autonomous matched inverter with resonant switching, which is achieved by lowering current levels through controlled valves and counter-parallel diodes, reducing switching losses, overvoltage and electromagnetic interference, with the exception of overheating modes of the structure of controlled valves and counter parallel diodes, providing a symmetrical limitation of the current of the inverter power source during emergency closures of output dov to the load housing due to filter chokes.

Improving the reliability of an autonomous matched inverter with resonant switching is a technical result due to new elements in the circuit of an autonomous matched inverter, the order in which they are turned on, and new connections, that is, the hallmarks of a utility model. Thus, the distinguishing features of the claimed autonomous matched inverter with resonant switching are essential.

The figure shows a diagram of an autonomous matched inverter with resonant switching.

The self-contained matched resonant inverter contains a single-phase bridge connected through the inductors of the filter 1, 2 to the input terminals of the inverter, the two in series connected arms of which contain controlled valves 3, 4 with counter-parallel diodes 5, 6, and the other two series connected arms contain capacitors 7, 8, the AC terminals of the single-phase bridge through series-connected saturating reactors 9, 10 and switching reactors 11, 12 are connected to the output terminals of the inverter, shunt en compensating capacitor 13. To the output terminals of the inverter 14 is connected inductor.

Autonomous matched inverter with resonant switching in steady state operates as follows. The control pulses to the controlled valves 3, 4 are supplied alternately at the moments when the voltage across the compensating capacitor 13 passes through zero. The parameters of saturation chokes 9, 10, switching chokes 11, 12, the capacitance of the compensating capacitor 13 and capacitors 7, 8 are selected from the condition for ensuring the oscillatory nature of the current in the circuits: 7-3 (5) -10-12- (13, 14) -11 -9-7 and 8-9-11- (13, 14) -12-10-4 (6) -8, formed when the controlled valves 3, 4 and counter-parallel diodes 5, 6 are turned on. The natural frequency of the circuits is approximately twice the output frequency of the device. For a full cycle of work

controlled valves 3, 4 and counter-parallel diodes 5, 6 in the load (13, 14) we obtain the full period of the output AC voltage. The inductance values of the filter chokes 1, 2 are selected sufficient for high-quality filtering of the current at the input of a single-phase bridge containing controlled valves 3, 4 with two parallel connected diodes 5, 6, and capacitors 7, 8 in two other series-connected shoulders. Compensating capacitor 13 provides parallel compensation of the reactive power of the induction heater (inductor or load) 14 and sequential compensation, together with capacitors 7, 8 (at the final value their capacitance), reactive power of saturation reactors 9, 10 and commutating reactors 11, 12. Saturation reactors 9, 10 have a large inductance at low initial currents in the switching circuits. With increasing current, the inductance of saturation chokes 9, 10 decreases to a small value, and they further do not affect the electromagnetic processes in the inter-switching interval. Switching chokes 11, 12 can be made in the form of independent elements or represent inductance of the load (part of the load) and (or) connecting outlet busbars (cables). Saturation chokes 9, 10 and switching chokes 11, 12, respectively, can be structurally combined into one element with a non-linear characteristic. The output signal period of a self-contained matched inverter with resonant switching consists of six time intervals corresponding to various combinations of on and off state of controlled valves 3, 4 and counter-parallel diodes 5, 6. As single-operation or two-operation valves with reverse conductivity (with anti-parallel diodes) or without reverse conductivity. In this case, the electromagnetic processes in the circuit of an autonomous matched inverter with resonant switching are qualitatively similar. Consider an embodiment of a circuit based on controlled two-operation valves (transistors)

with counter-parallel diodes. The main (first, fourth) interval corresponds to the direct conductivity interval of controlled valve 3 (4). When the controlled valve 3 is turned on, an oscillatory charge begins with the positive polarity of the compensating capacitor 13 in the circuit: 7-3-10-12- (13, 14) -11-9-7 from the capacitor 7 and the power supply of an autonomous matched inverter. At the same time, the discharge of the compensating capacitor 13 occurs through the inductor 14 in a parallel circuit: 13-14-13. After the oscillatory decrease in current in the circuit: 7-3-10-12- (13, 14) -11-9-7 to zero, the compensating capacitor 13 is charged to the maximum positive voltage, which exceeds the voltage on the capacitor 7. The discharge begins (second interval) compensating capacitor 13 in the chain: (13, 14) -12-10-5-7-9-11- (13, 14). A reverse current flows through an anti-parallel diode 5 of the controlled valve 3, which is added with a constant charge current of the capacitor 7. Through the load circuit 13, 14, the current also flows in the opposite direction. In the second interval, the control pulse is removed from the controlled valve 3. At the same time, the compensating capacitor 13 is discharged through the inductor 14 in the circuit: 13-14-13. After the oscillatory decrease in current in the circuit: (13, 14) -12-10-5-7-9-11- (13, 14) to zero, the counter-parallel diode 5 of the controlled valve 3 is turned off. In this case, the voltage at the compensating capacitor 13 continues to decrease and after a pause interval (third interval) becomes negative. At the third time interval of the pause, the compensating capacitor 13 continues to be recharged in the circuit: 13-14-13 to a voltage, as indicated, of negative polarity (+ on the right-facing circuit of the compensating capacitor 13). The third interval in the operation of the self-contained matched inverter ends when the compensating capacitor 13 is completely discharged. At the moment the voltage across the compensating capacitor 13 passes through zero to the negative range of values, the half-cycle in the operation of the self-matched inverter ends, the next control pulse is applied, and the controlled

gate 4 and the next half-cycle (fourth to sixth time intervals) begins in the operation of the autonomous matched inverter. Electromagnetic processes during operation of the controlled valve 4 and the counter-parallel diode 6 are completely similar to those considered. The currents through the diagonal elements of the alternating current of the single-phase inverter bridge in the second half-cycle have the opposite direction. When using two-operation controlled valves 3, 4, it is advisable to set the third interval of short duration by choosing the parameters of the circuit elements, which ensures higher energy performance of the device. In the conduction intervals of counter-parallel diodes 5, 6, a small reverse (negative) voltage equal to the voltage drop across the counter-parallel diode 5, 6 is applied to the switched-off controlled valves 3, 4, and the controlled valves 3, 4 can restore their control properties (when using single-operation valves). In this case, the duration of the second interval is set by selecting the parameters of the circuit elements based on the required shutdown time of the used single-operation controlled valves 3, 4.

Controlled gates 3, 4 when implementing an autonomous matched inverter with resonant switching, as described above, can be performed either as single-operation symmetrical or without reverse blocking ability (thyristors of various types, reversibly-switched dynistors, gas-discharge valves), and two-operation, i.e. fully controlled symmetric or unbalanced (lockable thyristors, transistors of various types, combination keys).

Saturation chokes 9, 10 work at the moments of turning on and off the controlled valves 3, 4 and counter-parallel diodes 5, 6 limiting (decreasing) the rate of rise and fall of currents, which significantly reduces switching losses and overvoltages

on the elements of the inverter circuit and controlled gates 3, 4 and counter-parallel diodes 5, 6.

Compared with the prototype, the reliability of the autonomous coordinated inverter with resonant switching is significantly increased. This is achieved by reducing the magnitude of the currents through the controlled valves (more than twice) by changing the compensation scheme, the levels of overvoltage on the controlled valves that occur when they are turned off, the levels of electromagnetic interference that occur when the controlled valves and counter-parallel diodes are turned off, providing a symmetrical limitation the current of the inverter power source in case of emergency circuits of the inverter output terminals to the load casing due to filter chokes.

Improving the reliability of a stand-alone coordinated inverter with resonant switching is estimated by the time between which the device fails. According to experimental studies and expert estimates, the time between failures of the claimed inverter can be increased by 30-40%.

Compared with the prototype, the inverter’s efficiency is further increased by reducing switching energy losses in controlled gates and counter-parallel diodes (lowering levels of switching overvoltages, initial rise and fall rates of currents when turning on and off controlled gates and anti-parallel diodes.

Additionally (in comparison with the prototype), the design of the energy (power) part of the inverter can be greatly simplified and the scope of application can be expanded by providing the possibility of using controlled valves and counter-parallel diodes with reduced requirements for their parameters and lower price.

Claims (1)

A self-contained matched inverter with resonant switching, comprising a single-phase bridge connected through a filter choke to the input terminals of the inverter, two serially connected arms of which contain controlled gates with counter-parallel diodes, and two other series-connected arms contain capacitors, single-phase bridge AC terminals through series-connected saturable reactors and switching reactors are connected to the output terminals of the inverter, shunted annymi compensating capacitor.