RU68809U1 - 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 serial circuit connected to the input terminals of the inverter through the filter chokes 1, 2, containing a switching choke 3, a parallel circuit formed by a compensating capacitor 4 and output terminals with a connected inductor 5, a second switching choke 6 and a controlled valve 7, shunted by filter capacitor 8. 1 ill.

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.

Known self-contained matched inverter containing a serial circuit connected to the input terminals, containing a parallel circuit formed by a compensating capacitor and output terminals with a connected inductor, and a controlled valve (Electromagnetic processes and parametric synthesis of single-fan inverters with a reverse diode for electrothermy / L.E. Roginskaya, A.V. Ivanov, M.M.Mulmenko and others // Electricity. - 2003. - No. 12. - P.42).

The disadvantage of an autonomous matched inverter is its low reliability. This is due to high voltage levels on the controlled valve, which can lead to its failure, as well as stringent requirements for the control system, the need to supply control pulses to the controlled valve simultaneously with the supply of power voltage and precise synchronization of control pulses with the moment of voltage transition on the controlled valve through zero. When starting an autonomous coordinated inverter, direct current surges through a large-amplitude controlled valve are possible due to the charge of the compensating capacitor. Any malfunctions of the control system and violation of synchronization in the supply of control pulses can lead to the failure of the controlled valve due to direct current surges. Interruption of the current of the controlled valve when it is turned off (at maximum value)

and hard switching cause large switching losses, which also reduces the reliability of a stand-alone matched inverter.

Known self-contained matched inverter containing a serial circuit connected to the input terminals, containing a parallel circuit formed by a compensating capacitor and output terminals with a connected inductor, and a controllable valve shunted by the filter capacitor (A.S. 1830642 USSR, MKI Н05В 6 \ 06. Method of regulation output power of the induction heating device \ S.V.Dzliev, E.M. Silkin, S.N. Tazikhin et al. - Announcement 01.10.90, Publ. 30.07.93, B.I. No. 28).

The disadvantage of an autonomous matched inverter is its low reliability. This is due to high voltage levels on the controlled valve, which can lead to its failure, as well as stringent requirements for the control system, the need to supply control pulses to the controlled valve simultaneously with the supply of power voltage and precise synchronization of control pulses with the moment of voltage transition on the controlled valve through zero. When starting an autonomous coordinated inverter, direct current surges through a large-amplitude controlled valve are possible due to the charge of the compensating capacitor. Any malfunctions of the control system and violation of synchronization in the supply of control pulses can lead to the failure of the controlled valve due to direct current surges. An interruption in the current of the controlled valve when it is turned off (at the maximum value) and hard switching cause large switching losses, which also reduces the reliability of the autonomous matched inverter.

A self-contained matched inverter is known, containing a serial circuit connected to the input terminals through a filter choke, containing a parallel circuit formed by a compensating capacitor and output terminals with a connected

an inductor, and a controlled valve shunted by a filter capacitor (A.S. 1800659 USSR, MKI N05V 6 \ 06. Device for induction heating \ S.V.Dzliev, E.M. Silkin, S.N. Tazikhin, etc. - Application 15.10.90, Published 07.03.93, B.I. No. 9).

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

The disadvantage of an autonomous matched resonant inverter is its low reliability. This is due to high voltage levels on the controlled valve, which can lead to its failure, as well as stringent requirements for the control system, the need to supply control pulses to the controlled valve simultaneously with the supply of power voltage and precise synchronization of control pulses with the moment of voltage transition on the controlled valve through zero. When starting an autonomous coordinated inverter, direct current surges through a large-amplitude controlled valve are possible due to the charge of the compensating capacitor. Any malfunctions of the control system and violation of synchronization in the supply of control pulses can lead to the failure of the controlled valve due to direct current surges. An interruption in the current of the controlled valve when it is turned off (at the maximum value) and hard switching cause large switching losses, which also reduces the reliability of the autonomous matched inverter.

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 serial circuit connected to the input terminals of the inverter through the filter chokes, containing a switching choke, a parallel circuit formed by a compensating capacitor and output terminals

with a connected inductor, a second switching choke and a controlled valve shunted by the filter 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 the voltage levels on the controlled valve, reducing switching losses, by excluding the overheating conditions of the controlled valve structure, less critical circuitry to failures in the control system, and the absence of direct surges current through the controlled valve, including, at start-up, by non-rigid switching of the controlled valve.

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 serial circuit connected to the input terminals of the inverter through the filter chokes 1, 2, containing a switching choke 3, a parallel circuit formed by a compensating capacitor 4 and output terminals with a connected inductor 5, a second switching choke 6 and a controlled valve 7, shunted by the capacitor filter 8.

Autonomous matched inverter with resonant switching in steady state operates as follows. Control impulses to a controlled valve

7 are applied at the moments when the voltage across the compensating capacitor 4 passes through zero to the positive range of values (+ on the left-sided circuit of the compensating capacitor 4). The parameters of the commutating chokes 3, 6, the capacitance of the compensating capacitor 4 and the filter capacitor 8 are selected from the condition of providing the oscillatory nature of the current in the circuit: 8-3- (4, 5) -6-8, which is formed when the controlled valve 7 is turned on. The natural frequency of the circuit is approximately 4 times the output frequency of the device. The inductance values of the filter chokes 1, 2 are selected sufficient for high-quality filtering of current and voltage at the input of a serial circuit containing a switching choke 3, a parallel circuit formed by a compensating capacitor 4 and output terminals with a connected inductor 5, a second switching choke 6 and a controlled valve 7. Compensating the capacitor 4 provides parallel compensation of the reactive power of the induction heater (inductor or load) 5 and sequential compensation, together with filter capacitor 8 (at the final value of the capacitance), reactive power of switching reactors 3, 6. Switching reactors 3, 6 can be made in the form of independent elements or represent inductance of the load (part of the load) and (or) connecting discharge busbars (cables). The full cycle (period) of the output signal of an autonomous matched inverter with resonant switching consists of three time intervals corresponding to various combinations of the on and off state of the controlled valve 7. As a controlled valve, both single-operation and two-operation valves without reverse or reverse conductivity can be used ( with anti-parallel diode). Moreover, the electromagnetic processes in the circuit are qualitatively similar. Consider an embodiment of a circuit based on a controlled two-operation valve (transistor) with

anti-parallel diode. The main (first) interval corresponds to the direct conduction interval of the controlled valve 7. When the controlled valve 7 is turned on, an oscillating charge begins with the positive polarity of the compensating capacitor 4 along the circuit: 8-3- (4, 5) -6-7-8 from the filter capacitor 8 and power source of an autonomous matched inverter. At the same time, the discharge of the compensating capacitor 4 occurs through the inductor 5 in the circuit: 4-5-4. After the oscillatory decrease in current in the circuit: 8-3- (4, 5) -6-7-8 to zero, the compensating capacitor 4 is charged to the maximum positive voltage that exceeds the voltage on the filter capacitor 8. The discharge (second interval) of the compensating capacitor 4 begins along the chain: (4, 5) -3-8-7-6- (4, 5). A reverse current flows through an anti-parallel diode of the controlled valve 7. In the second interval, the control pulse is removed from the controlled valve 7. At the same time, the compensating capacitor 4 is also discharged through the inductor 5 in the circuit: 4-5-4. After the oscillatory decrease in current in the circuit: (4, 5) -3-8-7-6- (4, 5) to zero, the counter-parallel diode of the controlled valve 7 is turned off. In this case, the voltage at the compensating capacitor still remains positive and its value is less than the voltage at the filter capacitor 8. At the third time interval, the compensating capacitor 4 continues to recharge in the circuit: 4-5-4 to a voltage of negative polarity (+ on the right-hand side wiring diagram) for account of the energy stored in the electromagnetic fields of the compensating capacitor 4 and inductor 5. At the maximum negative voltage on the compensating capacitor 4 on the controlled valve 7 there is a maximum Noe positive voltage equal to the sum of voltages at the filter capacitor 8 and the compensating capacitor 4 (about twice the supply voltage). The third interval in the operation of the self-contained matched inverter ends when the compensating capacitor 4 is completely discharged. At the time of the transition of the voltage across the compensating

capacitor 4 through zero in the positive range of values ends the period in the work of an autonomous matched inverter, the next control pulse is applied, the controlled valve 7 is turned on and the next period in the operation of an autonomous matched inverter starts. When using a two-operation controlled valve 7, the second interval, it is advisable to set a short duration by selecting the parameters of the circuit elements, which provides higher energy performance of the device. In the conduction interval of the counter-parallel diode, a small reverse (negative) voltage equal to the voltage drop across the counter-parallel diode is applied to the turned-off controlled valve 7, and the controlled valve can restore its control properties (when using single-operation valves). In this case, the duration of the second interval is set based on the required shutdown time of the used single-operation controlled valve 7.

Controlled valve 7 when implementing an autonomous matched inverter with resonant switching, as described above, can be performed as single-operation symmetrical or without reverse blocking ability (thyristors of various types, reversibly-switched dynistors, gas-discharge valves), and two-operation, that is, fully controlled symmetric or asymmetric (lockable thyristors, transistors of various types, combination keys).

Compared with the prototype, the reliability of the autonomous coordinated inverter with resonant switching is significantly increased. This is achieved by reducing the voltage on the controlled valve (by more than two times), the levels of overvoltage on the controlled valve that occur when it is turned off, the levels of electromagnetic interference that occur when the controlled valve and counter-parallel diode are turned off, by non-rigid switching of the controlled valve, ensuring symmetrical limitation inverter power supply during fault

inverter output terminals to the load housing due to filter chokes. The stability of the autonomous coordinated inverter with resonant switching is increased and the likelihood of inversion failures (execution on a single-operation controlled valve) when operating at a widely varying electrotechnological load (induction heater), as well as failures in the inverter control system, is reduced. Possible inrush currents of large amplitude through the controlled valve during start-up or failures in the control system are excluded.

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 additionally increased by reducing switching energy losses in controlled valves and counter-parallel diodes (lowering levels of switching overvoltages, initial rise and fall rates of currents when turning on and off controlled valves and counter-parallel diodes, recovery parts of the overvoltage energy into the load).

Additionally (in comparison with the prototype), the design of the energy (power) part of the inverter can be significantly simplified and the field 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, the possibility of using single-operation valves.

Claims (1)

A self-contained matched inverter with resonant switching, containing a serial circuit connected to the input terminals of the inverter through the filter chokes, containing a switching choke, a parallel circuit formed by a compensating capacitor and output terminals with a connected inductor, a second switching choke and a controlled valve shunted by the filter capacitor.