RU2108653C1 - Static converter with quasi-resonant current switching - Google Patents

Abstract

FIELD: power supplies incorporating high-frequency section for loads running at no load for long time, such as welding machines, or equipment requiring no-break power supply. SUBSTANCE: converter that has two series- connected DC power supplies, series resonance-tuned LC circuit connected on one end through controlled valves shorted out by diodes to free poles of power supplies and on other end, to their common point, as well as load connected directly or through matching transformer to resonance-tuned circuit capacitor, is provided, in addition, with choke or series LC circuit connected in parallel with resonance-tuned circuit capacitor to form oscillatory circuit. Choke should be better used for transformerless circuit arrangement, and LC circuit, for circuits using matching transformer. EFFECT: reduced loading of power components and loss under no-load conditions. 4 dwg

Description

 The invention relates to a conversion technique and is intended for use as a power source with a high frequency link.

 The scope of the converter in question is the consumer, where there are long idle modes, such as welding machines, uninterruptible power supply units.

 Known schemes of static converters with a series resonant circuit and quasi-resonant current switching [1, 2].

 The advantages of such converters are the currentless switching of controlled semiconductor switches and natural switching. This provides high switching reliability and significantly reduces loss on shutdown, which is especially important when working at higher frequencies.

 A common drawback of these transformations is the single-cycle design and the output of only constant voltage.

 As a prototype, the converter circuit shown in FIG. 10 [2]. The converter includes a constant voltage source, a series LC resonance circuit connected to the positive pole of the source through a controlled valve shunted by a diode.

 Parallel to the resonator circuit capacitor, a load is connected through a smoothing filter.

 In addition to those already mentioned, the described circuit has a disadvantage in that the power switches and the equipment of the oscillating circuit in idle mode work in almost the same conditions as when the rated load is on.

 The aim of the invention is to reduce the load of the power elements of the converter and losses when operating in idle mode with the extended functionality of the converter due to the combination of the functions of converting a constant supply voltage into a constant or into a variable therein.

 This goal is achieved by the fact that a second DC voltage source, connected in series with the first, and a second controlled valve shunted by a diode through which the resonant circuit is connected to the negative pole of the second source, is introduced into the converter. In addition, in parallel with the capacitor of the resonant circuit, a choke or a series LC circuit is connected, forming a resonant circuit.

 The application of the invention will reduce losses in idle mode and the current load of the power elements of the oscillatory circuit.

 In FIG. 1 shows a diagram of the converter in question; in FIG. 2 a, b - diagrams of currents and voltages on power elements during operation of the circuit without a choke or LC-chain; in FIG. 3 a, b are diagrams of currents and voltages when a choke is connected in parallel to the capacitor; in FIG. 4 a, b are diagrams of currents and voltages when connected in series with a capacitor in series with an LC circuit.

 The converter in question consists of two counter-parallel connected control valves, shunted by diodes 1, 2, connected to two series-connected power sources 3, 4, moreover, the controlled valve 1 is connected to the “+” of the source 3, and the controlled valve 2 to the “-” of the source power supply 4. A resonant circuit consisting of a reactor 5 and a capacitor 6 is placed between the connection points of valves 1 and 2 and power supplies 3 and 4. A matching element 7 is connected to the terminals of the resonant capacitor, which may include matching transformer, rectifier, smoothing filter. The output of the matching element 7 is connected to the load 8.

 To implement the subject of the application, an additional element 9 is introduced, connected in parallel with the capacitor 6. Element 9 can consist of either a choke or a series of chokes and a capacitor.

FIG. 2 - 4 illustrate the operation of the converter with the parameters: E _pit 3.4 = 250 V, R _load 8 = 0.164 Ohm, T _switch. = 480 μs, L5 = 10 μH, L9 = 3 mH (L9 = 8 mH, C9 = 1.27 μF), C6 = 2.1 μF, K _Tr = 6.7.

 The designations in the figures correspond to: I 12 - total current through controlled valves 1 and 2; U 6 is the voltage across the capacitor 6; I 8 - load current 8; U 8 - voltage at load 8.

 We consider the operating principles of the converter according to the circuit shown in FIG. 1. First, we consider the operation of the circuit without element 9. When the controlled valve 1 is turned on, the capacitor 6 first charges, and when the charging current passes through zero, the capacitor 6 discharges through the inductor 5 and diode 1, a half-wave of voltage forms on the capacitor 6, which is transformed through 7 to the load 8. Similarly, the process occurs when the control valve 2 is turned on, and a half-wave of voltage of opposite polarity is formed on the capacitor 6.

,
Частота переключения двухтактного преобразователя F_упр<F_p/2 с целью обеспечения паузы между рабочими состояниями переключателя.Natural frequency of the oscillatory circuit formed by the inductor 5 and the capacitor 6

,
The switching frequency of the push-pull converter F _control <F _p / 2 in order to ensure a pause between the operating states of the switch.

 In FIG. 2a shows currents and voltages in the short-circuit mode, and in FIG. 2, b in load connection mode.

When the element 9 is connected in parallel to the capacitor 6 (a choke is connected separately), an additional oscillatory circuit is formed, formed by the choke 9 and the capacitor 6. The natural frequency of the newly formed circuit F _rdp is the frequency F _xx to which the converter should switch in xx mode

F_xx<<F_p/2.

F _xx << F _p / 2.

The physics of the process is as follows (the xx mode is considered). When the controlled valve 1 is turned on, the oscillatory charge of the capacitor 6 occurs through the inductor 5 ( _because F _p >> F _pdop ), and then the natural oscillations develop at a frequency F _xx in the circuit L9 and C6. If the frequency F _CPR = F _xx , then the charge of the capacitor 6 from the power source 3 occurs in antiphase with the voltage across the capacitor 6 from its own oscillations at a frequency F _{p add} , i.e. power supply 3 is turned on to counter EMF, while the current 13 from the power source is reduced in accordance with the formula
I ₃ = (U ₃ - U _C6 ) / Z _in
Where
U ₃ - voltage power supply 3;
U _C6 is the voltage across the capacitor 6;
Z _I - input circuit resistance, relative to the terminals of the power source.

 A decrease in the current of the power supply also means a decrease in the current in elements 1, 2, 5 and a decrease in power consumption. In FIG. 3, a shows the processes in the circuit when connecting the inductor 9.

 When using an additional serial connection L9, C9, the nature of the process is similar to that described above (see Fig. 4, a). A qualitative difference is to increase the quality factor of the oscillating circuit formed by the L9, C9, C6 and L transformer from the matching element 7.

By selecting the parameters L9 or L9, C9, you can select the optimal frequency F _xx .

When the load is connected, the quality factor of the circuit L9, C6 or L9, C9, C6 changes sharply, the natural oscillations (at the frequency F _rdop ) quickly decay, in addition, F _control >> F _xx and there is practically no initial voltage to U C6 at the moment of switching on the controlled valves 1, 2. Therefore, on the working parts (F _control ) in the presence of load, the inventive converter operates as a prototype (see Fig. 2, b, 3, b, 4, b).

 The use of inductor 9 is advisable for transformerless circuits in element 7, and the serial connection of inductor 9 and capacitor 9 is advisable for circuits using a matching transformer.

Sources of information
1. KH Ziu et al. Quasi-resonant converters - topology and characteristics, - IEEE Fransaction on Power Electronics, vol. PE-2, N 1, 1987, p. 62 - 71.

 2. Lee Quasi-resonant zero-current switching converters operating in half-wave mode. U.S. Patent 4,720,667, cl. 323 - 271.

 3. Application N 5068591/07 of the Russian Federation. Static converter with quasi-resonant current / V switching. A. Chvanov, V.I. Sidorov / Priority from 6.10. 1992, H 02 m 7/519.

Claims (1)

 A static converter with quasi-resonant current switching, containing a constant voltage source, a serial resonant circuit connected to the positive terminal of the constant voltage source through a controlled valve shunted by a diode, and a matching element with a load connected in parallel to the series capacitor of the resonant circuit, characterized in that he introduced a second source of constant voltage, a second controlled valve, shunted by a diode, and a choke and a series circuit of a choke and a capacitor, wherein the DC voltage sources are connected in series, the series resonant circuit is connected by the first terminal to the negative terminal of the second power source through a second controlled valve, the choke or the series circuit of the choke and capacitor is connected in parallel with the series resonator circuit capacitor, and the second the output of the series resonant circuit is connected to a common point of constant voltage sources.

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