RU2080221C1 - Dc voltage-to-dc voltage converter - Google Patents

Abstract

FIELD: electrical engineering; supply sources for DC arc welding. SUBSTANCE: DC voltage-to-dc voltage converter has main and reverse-conducting thyristors, resonant circuit capacitors, resonant circuit reactors, transformer, rectifier and capacitive ripple filter. Reverse-conducting thyristors are placed in parallel opposition with main thyristors and resonant circuit reactor windings connected in series with main thyristors. EFFECT: improved reliability of welding supply source. 2 dwg

Description

 The invention relates to a conversion technique and can be used in the development of power supplies for DC arc welding.

 Known DC-voltage converter containing a thyristor resonant inverter with reverse diodes, LC circuit, transformer, rectifier and capacitive filter (SU, AS N 1489934, CL B 23 K 9/00, 9/10, 1989). The disadvantages of this converter are: a relatively low conversion frequency, due to the fact that a small reverse voltage is applied to the lockable thyristors, a significant difference between the current and average currents in the transformer windings, and large ripple voltage at the converter output.

 A known converter (SU patent N 1802765, MKI B 23 K 9/00, 9/10, 1993) containing an inverter with main and reverse thyristors connected in parallel with them, a resonant LC circuit, a power transformer, a rectifier, a capacitive smoothing filter and a control system that feeds at regular intervals unlocking pulses to the main and reverse thyristors of the inverter. The frequency of the inverter and the natural frequency of the resonant circuit are selected so that the unlocking of the reverse thyristors occurs with a delay relative to the moment when the current passes through zero in the main thyristors. Due to this, a voltage much higher than the voltage of the conductive valve is applied to the locked main thyristors until the reverse thyristors are unlocked. This allows you to accelerate the shutdown of the main valves and ensure trouble-free operation of the inverter even in such modes when the check valves cannot be turned on due to the high voltage on the filter capacitor.

 The disadvantage of the prototype is that the duration of the current pulse of the reverse thyristor is equal to the duration of the current pulse of the main thyristor, and between these pulses a second pause of the same duration is formed as the first. The presence of a second pause that does not affect the turn off of the thyristors reduces the frequency of the inverter and increases the ripple of the output voltage. The second factor that worsens the frequency properties and overall dimensions of the converter is the relatively large duration of the reverse thyristor current pulse. Since in the nominal mode the amplitude of this current is less than the amplitude of the direct thyristor current, this also increases the ripple of the output voltage and, in addition, contributes to an increase in the effective current in the transformer windings, which leads to an increase in its mass and dimensions.

 The aim of the invention is to increase the frequency of inversion, reducing the dimensions of the reactive elements, reducing the ripple of the output voltage, reducing the amplitude of the current pulse of the main thyristors.

 This goal is achieved by the fact that in the DC-DC converter, containing the main and reverse thyristors forming an inverter, capacitor and reactor of a resonant circuit, a power transformer included in the diagonal of the inverter’s alternating current, a rectifier and a capacitive smoothing filter, the reverse thyristors are turned on in parallel main thyristors and resonant circuit reactor windings connected in series with them.

 In FIG. 1 shows a diagram of a half-bridge version of the proposed Converter. The converter contains the main thyristors 1, 2, resonant circuit capacitors 3, 4, resonant circuit reactors 5, 6, reverse thyristors 7, 8, transformer 9, rectifier 10 and capacitive smoothing filter 11.

где
α коэффициент затухания;
E входное напряжение;

приведенное к первичной обмотке выходное напряжение;
U $\genfrac{}{}{0ex}{}{\text{*}}{\text{c}}$ напряжение на конденсаторе 4 в начальный момент времени;

угловая частота;
L₁ L_p + L_s суммарная индуктивность на интервале включенного состояния тиристора 1;
L_p индуктивность реакторов 5 и 6;
L_s индуктивность рассеяния трансформатора 9;
C емкость конденсаторов 3 и 4.In FIG. 2 is a timing chart explaining the operation of the converter. Suppose that at the initial moment of time a triggering pulse is supplied to thyristor 1. A current pulse of approximately sinusoidal shape is formed in the circuit of this thyristor, reactor 5, in the windings of transformer 9 and capacitors 3, 4

Where
α attenuation coefficient;
E input voltage;

output voltage reduced to the primary winding;
U $\genfrac{}{}{0ex}{}{\text{*}}{\text{c}}$ voltage across capacitor 4 at the initial time;

angular frequency;
L ₁ L _p + L _s total inductance in the on-state interval of thyristor 1;
L _p inductance of reactors 5 and 6;
L _{s the} leakage inductance of the transformer 9;
C capacitance of capacitors 3 and 4.

. Отметим, что в номинальном режиме это напряжение значительно превышает напряжение на открытом диоде.After the end of the current pulse of the first thyristor, the capacitor 3 is charged to the amplitude value V _m , the thyristor 1 is closed and a reverse voltage is applied to it

. Note that in the nominal mode, this voltage significantly exceeds the voltage at the open diode.

где

угловая частота;
U_m амплитуда напряжения на конденсаторе.With a certain delay relative to the end of the current of the first thyristor, a trigger pulse is applied to the thyristor 7 and a reverse polarity pulse is formed in the transformer circuit

Where

angular frequency;
U _{m the} amplitude of the voltage across the capacitor.

Since the angular frequency ω _{2 is} greater than ω ₁ , the duration of the reverse thyristor current pulse is less than the main thyristor pulse duration, and its amplitude is greater than the amplitude of the reverse thyristor current pulse in the prototype.

 After the end of the current in the reverse thyristor 7, the unlocking pulse is supplied to the main thyristor 2 and the processes in the converter are repeated with the participation of thyristors 2 and 8.

 An increase in the inversion frequency is achieved by reducing the interval of conductivity of the check valves and eliminating the pause between the moment of the end of the current pulse of the reverse thyristor and applying the trigger signal to the next main thyristor. A decrease in the current of the transformer windings at a constant average current is possible due to an increase in the amplitude of the reverse current and a decrease in its duration compared to the prototype while reducing the amplitude of the forward current, since the duration of the forward current pulse can be increased due to the duration of the reverse current and a second pause. The reduction in the dimensions of the reactive elements occurs due to several factors: an increase in the frequency reduces the required capacitance of the capacitors 3, 4, and 11, and reduces the dimensions of the transformer and reactors; a decrease in the effective current reduces the cross-section of the wires of the transformer windings; due to the fact that the current of reverse thyristors does not flow through the reactors, the cross-section of the wires of these reactors can be reduced in comparison with the prototype. A decrease in the output voltage ripple occurs due to an increase in the frequency and equalization of the amplitudes of the pulses of the currents of the forward and reverse thyristors.

Claims (1)

 A DC / DC converter containing main and reverse thyristors, a capacitor and a resonant circuit reactor, a power transformer, a rectifier and a capacitive smoothing filter, characterized in that the reverse thyristors are connected in parallel to the main thyristors and the windings of the resonant circuit reactor connected in series with them.

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