RU2373628C1 - Variable-to-constant voltage converter - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: proposed converter is intended for supplying loads with higher requirements to quality of rectified voltage, electromagnetic compatibility and smaller sizes and weight. It comprises two three-phase transformers each with magnetic core accommodating one-phase primary and two-phase secondaries, and two six-phase gate bridges. Phase primaries in one transformer are connected into star, while second transformer primaries are connected into triangle. Ratio of the number of turns of primary phase windings,

, connected in a star, to that of primary phase windings connected in a triangle is equal to i, ratio of the number of turns of secondary phase windings in pairs of turns arranged on each of cores is equal to

where ∀ µ=∈ [6,∞], while phase secondaries have equal number of turns. Note here that six phase secondaries in every transformer feature anti-parallel interconnection to form semi regular hexagon. Note here there is a tap of central point of every phase secondary. Note also that taps of central points of phase secondaries of one transformer are connected with AC leadouts of the six-phase bridge, while taps of central points of phase secondaries of another transformer are connected to appropriate AC leadouts of the second six-phase gate bridge. Note here that six-phase gate bridges are connected via a pair of unlike-pole DC leadouts in series, and that free unlike-pole bridge leadouts form output terminals of the device.

EFFECT: higher quality of conversion.

10 dwg, 1 tbl

Description

The invention relates to electrical engineering and power converting equipment and can be used as an AC to DC converter for supplying consumers with increased requirements for the quality of the rectified voltage, electromagnetic compatibility and overall dimensions.

где m - фазность преобразования (Яценко А.А. Применение схемы «скользящего треугольника» в многофазных преобразователях. // Электричество. - 1982. - №7. - С.17-24).Known AC to DC converters with increased phase conversion, built on the basis of three-phase valve bridges, which are powered from autonomous symmetric three-phase EMF systems, angled relative to each other

where m is the phase transformation (Yatsenko A.A. Application of the "moving triangle" circuit in multiphase converters. // Electricity. - 1982. - No. 7. - P.17-24).

Regardless of the construction schemes of these converters, their main drawback is the reduction in conversion quality with asymmetry of the supply voltage, constructive and parametric asymmetries of the transformers, which impairs electromagnetic compatibility and even, sometimes, limits the possibility of using multiphase converters.

, считается от одноименного зажима каждой обмотки, причем первичные обмотки одного трансформатора соединены в звезду, а второго в треугольник, а выходы всех выпрямителей включены параллельно.A known converter of alternating voltage to DC, providing twenty-four times the frequency of the ripple of the rectified voltage (US Pat. RF No. 2219647, MKI N02M 7/08, publ. 12/20/2003), containing two three-phase transformers, the secondary phase windings of each transformer are connected in a triangle, each secondary the phase winding is equipped with two internal taps that are connected to the diagonals of the alternating current of two bridge rectifiers connected in parallel in the input, while these taps from the phase windings are made parts from the ratio

, is counted from the same clamp of each winding, with the primary windings of one transformer connected to a star, and the second to a triangle, and the outputs of all rectifiers are connected in parallel.

The disadvantages of this converter are the large overall dimensions of the transformers and the use of secondary windings performed using three values of the number of turns. With small numbers of turns, which is typical, for example, in the manufacture of high-power and heavy-duty transformers, this limits the ability to provide the required design ratios between these numbers and thereby reduces the efficiency of electric energy conversion.

, причем k-я и (n+1-k)-я пара обмоток (k=1, 2, 3, 4) образуют одну шестилучевую звезду, а оставшаяся пара другую, при этом фазы одной шестилучевой звезды подключены к входам переменного тока одного моста, фазы второй к входам другого моста, а крайние анодная и катодная группы мостов образуют выходные выводы устройства.Also known is an AC to DC converter (AS USSR No. 817923, MKI N02M 7/06, published March 30, 1981), which provides twenty-four times the frequency of the rectified voltage ripple, containing two six-phase valve bridges connected in series, and a three-phase transformer with four secondary windings (n = 4) connected to stars with the ratio of the number of turns of the secondary windings determined by the function

and the kth and (n + 1-k) -th pair of windings (k = 1, 2, 3, 4) form one six-pointed star, and the remaining pair is another, while the phases of one six-pointed star are connected to the AC inputs of one bridge, the second phase to the inputs of another bridge, and the extreme anode and cathode groups of bridges form the output terminals of the device.

The disadvantages of this converter are the relatively large typical power of the transformer (S _T = 1,165 P _d , where P _d is the load power) when executed on a single transformer; the need to use four values of the number of turns for the secondary windings, which complicates the manufacturing technology and complicates the limitation of structural asymmetry at an acceptable level; the presence of forced magnetization flows in the transformer rods, which, in aggregate, reduces the quality of the conversion.

, а два вывода первичной обмотки одного из трансформаторов присоединены к трехфазной сети с транспозицией по отношению к присоединению идентичных выводов первичной обмотки другого трансформатора, при этом из частей вторичных обмоток, имеющих по две вторичные фазные обмотки на каждом стержне магнитопроводов трансформаторов, в каждом трансформаторе сформирован источник шестифазной системы ЭДС, образованный звездой и обратной звездой, соединенными нулевыми точками, причем части обмоток звезды и части обмоток обратной звезды находятся в соотношении

, а из шести вентилей сформировано вентильное кольцо, вентили которого соединены между собой только одноименными электродами, при этом каждая из трех точек соединения, образованных электродами одного наименования, подключена к одному из выводов звезды одного источника, а каждая из трех точек соединения, образованных электродами другого наименования, подключена к одному из выводов звезды другого источника, причем каждая точка соединения вентилей кольца, подключенная к выводу звезды одного из источников, подключена также к точке соединения разноименных электродов двух вентилей, образующих вентильную ячейку, один крайний электрод которой, имеющий наименование, отличное от наименования электродов вентилей кольца в точке соединения с кольцом данной ячейки, соединен с выводом обратной звезды другого источника, причем этот вывод имеет наименование, аналогичное наименованию вывода звезды источника, подключенного к данной точке кольца, а второй крайний электрод ячейки подключен к соответствующему выходному выводу устройства, при этом каждый из выводов обратных звезд, к которому присоединен электрод вентиля ячейки, соединен с электродом другого наименования незадействованного вентиля, второй электрод которого присоединен к соответствующему выходному выводу, причем выводы звезд, имеющие одинаковое наименование, подключены к диаметрально противоположным точкам соединения вентилей кольца.Closest to the invention adopted as a prototype is an AC to DC converter (RU No. 2321149, PMK Н02М 7/08, published March 27, 2008), containing twenty-four valves connected to twelve valve cells with two valves in each cell, connected by opposite electrodes, of which two groups of valves are formed, six valve cells each, and free electrodes of one name of half the valves in each of the groups are connected, and an anode gear is formed in one group of valves yl star, while in the other group cathodic shestiventilnaya star and two trehsterzhnevyh three-phase transformer, the primary windings are connected in a "sliding triangles" winding ratio of parts constituting the triangles in which the parts of the windings constituting extensions of sides is 1:

and the two leads of the primary winding of one of the transformers are connected to a three-phase network with transposition with respect to the connection of identical leads of the primary winding of the other transformer, while from the parts of the secondary windings having two secondary phase windings on each core of the transformer magnetic circuits, a source is formed in each transformer a six-phase EMF system formed by a star and a reciprocal star connected by zero points, and parts of the windings of the star and parts of the windings of the reverse star are ratio

and a valve ring is formed from six gates, the gates of which are interconnected by electrodes of the same name, with each of the three connection points formed by the electrodes of the same name connected to one of the terminals of the star of one source, and each of the three connection points formed by the electrodes of the other names connected to one of the star terminals of another source, and each connection point of the ring valves connected to the star terminal of one of the sources is also connected to the connection point the opposite electrodes of two valves forming a valve cell, one extreme electrode of which, having a name different from the name of the valve electrodes of the ring at the connection point with the ring of this cell, is connected to the reverse star terminal of another source, and this terminal has a name similar to the name of the star terminal a source connected to this point of the ring, and the second extreme electrode of the cell is connected to the corresponding output terminal of the device, with each of the conclusions of the reverse stars to the cat The cell valve electrode is connected to each other, connected to the electrode of another name for the idle valve, the second electrode of which is connected to the corresponding output terminal, the star terminals having the same name are connected to diametrically opposite points of connection of the ring valves.

The quality of converting AC voltage to DC by this converter is significantly reduced with asymmetry of the supply voltage, structural asymmetry of the phase voltages of the secondary windings and parametric asymmetry of the transformers. Typical power transformers are relatively large.

The objective of the invention is the creation of an AC to DC converter with the best conversion quality with asymmetry of the supply voltage, structural asymmetry of the phase voltages of the secondary windings and parametric asymmetry of the transformers having a lower typical power transformers.

, отношение чисел витков вторичных фазных обмоток в парах обмоток, размещенных на каждом из стержней, равноThis problem is achieved by the fact that the AC to DC converter contains two three-phase transformers, on each of the magnetic core rods of which there are one primary and two secondary phase windings, as well as twelve valve cells with two valves in each cell connected by unlike electrodes from valve cells two valve groups are formed, six valve cells in each, and free electrodes of one name of half of the valves in each group are connected, and in one g in this case, an anode six-star star is formed in the valve group, and in the other group a cathode six-star star is formed, the primary phase windings in one transformer are connected to a star, and in the second to a triangle, the ratio of the numbers of turns of the primary phase windings connected to the star to the numbers of turns of the primary phase windings connected in a triangle equals

, the ratio of the number of turns of the secondary phase windings in pairs of windings placed on each of the rods is

where ∀ µ = ∈ [6, ∞],

and the secondary phase windings corresponding in relative sizes are made with the same number of turns, while six secondary phase windings in each transformer are interconnected in series, topologically forming a semi-regular hexagon, and a tap is made from the midpoint of each secondary phase winding, with each of of taps from the midpoints of the secondary phase windings of one transformer is connected to an unused point of connection of unlike valve electrodes in the valve cells ah of one group of gates, and each of the taps from the midpoints of the secondary phase windings of the second transformer is connected to an unused point of connection of dissimilar electrode electrodes in the valve cells of the second group of valves, with the same free electrodes of the second half of the valves in each of the groups of valves connected, and in one group at the same time, a cathode six-star star is formed in the valves, and in the other group an anode six-star star is formed, and from the valve groups, respectively, two hex valve gates with direct current leads from common points of connection of gates in six-star stars; moreover, six-phase gate bridges are connected in series with unipolar DC leads in series and free bipolar leads of the bridges form the output terminals of the device.

Figure 1 shows a circuit diagram of the proposed Converter with a serial connection of six-phase valve bridges and with primary windings connected in one transformer to a star, and in the second to a triangle; figure 2 for converters with different parameters µ shows the vector voltage diagrams presented in the form of amplitude-phase portraits of the voltage of the secondary windings and the resulting rectified voltage vectors that form ripples s _i relative to each other; figure 3 shows the expanded vector diagrams explaining the principle of formation of the vectors of the resulting stresses on the example of the Converter with parameter µ = 8; figure 4 shows the timing diagram of the output voltages of six-phase valve bridges (a) and the curve of the rectified voltage of the Converter with µ = 24 (b); figure 5 gives examples of the topological implementation of the EMF systems of the secondary windings of the transformers of the Converter; figure 6 shows the dependence of the mismatch of the amplitudes of adjacent vectors of the resulting rectified voltage of the Converter from the number µ in percent; figure 7 shows the timing diagrams of the anode currents and reverse voltages of the gate valves of the Converter with the parameter µ = 24; Fig. 8 shows a time diagram of the rectified voltage of the converter with the parameter μ = 24 with structural asymmetry of the phase voltages of the secondary windings K _H = 10%; figure 9 shows the alternating components of the rectified voltages of the proposed Converter with µ = 24 (a) and a prototype, the EMF system of the secondary windings of the transformers which are shifted relative to each other by 15 el. hail. (b) at K _H = 10%; Also shown are the alternating components of the rectified voltages of the proposed converter (c) and the prototype (d) with asymmetry of the network voltage αU = 2%; figure 10 - shows the curve of the mains phase A current consumed by the Converter with µ = 24.

The AC to DC Converter (Figure 1) contains two three-phase transformers: a transformer 1 with primary windings connected to a star, and a transformer 2 with primary windings connected to a triangle. The corresponding secondary windings of the transformers are made in the form of semi-regular hexagons 3 and 4, and the corresponding phase taps from the midpoints a, z, b, x, c, at the sides of the semi-regular hexagon 3 and taps from the midpoints a ′, z ′ b ′, x ′ , c ′, y ′ of the sides of the hexagon 4 are connected to the AC inputs of the six-phase valve bridges 5 and 6 connected in series. The common point 7 of the anode group of valves of the bridge 5 and the common point 8 of the cathode group of valves of the bridge 6 are connected to the load 9.

The principle of operation of the device (Figure 1) is illustrated by vector diagrams of the voltage of EMF sources, presented in the form of amplitude-phase portraits of the voltage of the secondary windings moved relative to each other at various values of the parameter μ (Figure 2), and by detailed vector diagrams explaining the principle of formation of the resulting vectors rectified voltages (Figure 3) on the example of a Converter with parameter µ = 8. In any phase of the conversion cycle, the rectified voltage ripples s _i are formed as a result of the addition of the maximum linear EMF at the moment in each of the six-phase EMF systems formed between the midpoints of the secondary phase windings (sides) of the hexagons. In accordance with the polarity of the linear EMF, the pair of valves that connects to the branches from the phases between which the linear EMF is currently maximum is open in each six-phase bridge. A feature of the converter is that adjacent linear EMFs between phase taps in hexagons differ in amplitude (except when µ = 12). As a result of this, at the output of each of the six-phase valve bridges, non-canonical 12-pulse rectified voltages u _{d (5)} and u _{d (6)} are formed in shape (Figure 4, a). Since these voltages are phase shifted relative to each other by 30 el. hail., as a result of adding their instantaneous values to the load, a voltage u _d (b) is formed with a canonical curve shape having 24 ripples over a period of mains voltage. Figure 4 shows the voltage curves for the Converter with µ = 24 when close to the ideal ratio of the number of turns of small and large secondary phase windings of transformers.

The table below shows the relative topological dimensions of small secondary phase windings (for large sizes taken as 1.0), calculated for different values of µ and the angular topological parameter ε.

The canonical 24-pulse form of the rectified voltage (for non-canonical forms, the phase of the conversion in the table is shown in italics) is provided only with topological parameters µ = 8 and µ = 24. For µ = 6, a triangle is obtained. With two shifted relative to each other by 30 e. hail. amplitude-phase portraits of this type provides a 12-phase conversion mode. As μ → ∞, a symmetric six-phase EMF system (regular hexagon) is obtained. With two shifted by 30 el. hail. amplitude-phase portraits of this type also provides only a 12-phase conversion mode. Recent topologies are well known.

The topological dimensions given in the table can be converted into the topological dimensions of six-phase stars (the expression of the length of a small ray of a star l _{M in} terms of the length of a large ray l _B ) by the formula

(Figure 5, a). Here we used the angular topological parameter ε, the values of which are given in the table.

The converter topology with μ = 12 allows one to obtain a canonical 24-phase conversion only on the basis of two EMF systems shifted relative to each other by Δφ = 15 e. city., i.e. according to the known scheme with the disadvantages inherent in the prototype. With a shift of Δφ = 30 e. hail. the mismatch of the amplitudes of adjacent vectors of the resulting stresses K _S in the proposed version of the Converter with µ = 12 exceeds 3% (Fig.6).

The conduction angles of six-phase bridge valves depend on the topological implementation (µ). In this case, the valves of either of the two bridges (Fig. 1) connected to the midpoints of the large secondary phase windings have a smaller conduction angle than the valves connected to the midpoints of the small secondary phase windings. So, with µ = 24, all the valves in the bridges connected to the large secondary phase windings conduct a current of 45 el. hail., and valves connected to small secondary phase windings - 75 el. hail. (Fig.7). In the case of the implementation of the Converter with µ = 8, the angles of conductivity of the valves are equal, respectively, 15 el. hail. and 105 email hail. The maximum reverse voltages (Fig. 7) applied to the valves of six-phase bridges are in all cases equal to U _{OBR MAX} = 0.512 U _d0 (U _d0 is the average value of the rectified voltage at idle).

The average value of the rectified voltage of the Converter (Figure 1) at idle when shifting between six-phase systems Δφ = 30 e. hail. is determined by the formulas (for pu, the effective voltage value of half of the large secondary phase winding is taken):

for converters with µ ∈ [6, 12] - U ^* _d0 = 1,664 · ϖ + 2,678;

for converters with µ more than 12 - U ^* _d0 = 2,143 · ϖ + 2,495, where

The difference of the above formulas is associated with a change in the positions of the mutual arrangement of the amplitude-phase portraits of the secondary windings when the parameter µ passes through the value µ = 12, which is shown by the example of the values µ = 48 and µ = 9 in FIG. 2, a; g.

The converter maintains a relatively good conversion quality even with large structural asymmetry of the phase voltages of the secondary windings, especially with the parameter μ = 24. On Fig shows a curve of the rectified voltage of the Converter with µ = 24 with structural asymmetry of the secondary windings To _H = 10%. It is characteristic that structural asymmetry does not lead to the appearance of the sixth harmonic in the rectified voltage curve. The graph shown in Fig.6 shows the dependence (in percent) of the amplitude asymmetry of adjacent vectors (ripple s _i-1 , s _i ; s _i , s _{i + 1} ; s _{i + 1} , s _{i + 2} , etc. ) resulting rectified voltages in the converter for various numbers µ. For µ = 8 or µ = 24, adjacent vectors have the same length, i.e. the rectified voltage is canonical. However, the converter constructed according to the topology µ = 24 is more stable, since the slope of the dependence curve at the point µ = 24 is much smaller than at the point µ = 8, i.e. the effect of structural asymmetry is minimal. Therefore, in the vicinity of the point µ = 24 (FIG. 6), it is possible to choose those topological sizes of the secondary windings of the transformers of the converter for which the specified level of structural asymmetry will not be exceeded (note that the mismatch in the lengths of adjacent vectors of the resulting rectified voltages (K _S ) even with a significant constructive asymmetry is significantly less than the last in percentage terms).

Figures 9 (a) and (b) compare the alternating components of the rectified voltage of the proposed converter with μ = 24 and the prototype, the six-phase systems of which are shifted relative to each other by an angle Δφ = 15 e. hail. The mismatch of the lengths of the vectors of the resulting voltages of the proposed converter amounted to only K _S = 0.77% with structural asymmetry of the phase voltages of the secondary windings K _H = 10%, while in the prototype such asymmetry practically leads to six-pulse rectification. In this case, the amplitude of the variable component of the rectified voltage of the prototype is 2.25 times greater than the corresponding distortion of the proposed converter.

A similar effect is manifested with asymmetry of supply voltages. When the asymmetry of the supply voltage αU = 2%, the alternating component of the rectified voltage of the proposed Converter does not contain the sixth and multiple harmonics to it. Figure 9 compares the distortion of the rectified voltage in the proposed Converter (b) and distortion in the prototype (d).

These effects are explained by a non-standard way of forming a rectified voltage curve. The output voltage of each of the rectifier sections is not canonical 12-pulse (Figure 4). It is as if modulated by the sixth harmonic, and the nature of the modulation does not change with an increase in structural asymmetry, since the power systems are six-phase and the angle of shift between the conditional phases (rays of a six-phase star inscribed in the hexagon (Figure 5, a)) is 60 e. city., i.e. period of the sixth harmonic. However, the output voltage of the rectifier sections of the proposed Converter is shifted relative to each other by an angle Δφ = 30 el. hail. (half the period of the sixth harmonic), and not the angle Δφ = 15 e. hail. (used in the prototype and known circuits with four three-phase rectifier sections). Therefore, the sixth harmonics of adjacent sections are mutually compensated for any reasons that give rise to them, including parametric asymmetry of current circuits in the phases of transformers during the formation of resulting rectified voltages and differences in switching angles. As for the prototype, then, even with a small structural asymmetry, the sixth harmonic appears in its rectified voltage, and with an asymmetry of the supply voltage 2, 4, 6, ... harmonics.

From the shape of the curve in the diagram (Figure 10) it is seen that the composition of the higher harmonics in the current consumed by the proposed Converter (for example, the network current of phase A) is low. This ensures a high level of electromagnetic compatibility of the converter with the mains and its consumers.

It is important that the parts of the secondary phase windings of the transformers of the converter are symmetrical with respect to the midpoints (phase taps), and the wires of all parts of the windings have the same cross section. Since in the manufacture of windings according to the schemes of semi-regular hexagons for each phase of the transformer, there are two windings with taps from midpoints, the manufacturing technology is simplified. If necessary, the secondary windings of the transformers of the Converter can be made according to other schemes, for example, shown in Figure 5, and the primary windings according to the schemes of sliding triangles. The use of primary windings, connected according to the schemes of moving triangles or non-equilateral zigzags, providing a phase shift between secondary systems Δφ = 30 e. hail., contributes to the unification of the converter equipment, but with a certain increase in the typical power of transformers.

With the parallel connection of six-phase bridges, the use of a surge reactor is a prerequisite. At the load connected to the midpoint of the surge reactor winding, relative to the other output terminal of the converter, a half-sum of instantaneous values of phase-shifted voltages generated at the outputs of the valve bridges is allocated. Without the use of a surge reactor, the conversion mode as a result of superposition of the curves u _{d (5)} and u _{d (6)} (Figure 4) will be only 12-phase.

In the transformers of the converter (Figure 1) there are no flows of forced magnetization and the typical power of the transformer equipment of the converter at µ = 24 is S _T = 1,1394 · P _d , and at µ = 8 it is equal to S _T = 1,078 · P _d . These indicators are better than the prototype, a typical transformer power of which S _T = 1,217 · R _d .

Thus, the proposed AC to DC converter has, in comparison with the prototype, a higher conversion quality with asymmetry of the supply voltage, structural asymmetry of the phase voltages of the secondary windings and parametric asymmetry of the transformers and lower typical power of the transformers.

Claims (1)

An AC to DC converter containing two three-phase transformers, on each of the six terminals of the magnetic cores of which one primary and two secondary phase windings are located, as well as twelve valve cells with two valves in each cell connected by unlike electrodes, two groups of valves are formed from valve cells , six valve cells in each, and the free electrodes of the same name half of the valves in each of the groups are connected, and in one group of valves the image An anode six-valve star is delineated, and a cathode six-star star is formed in another group, characterized in that the primary phase windings in one transformer are connected to a star, and in the second to a triangle, the ratio of the number of turns of the primary phase windings connected to the star to the numbers of turns of the primary phase windings connected in a triangle is

, the ratio of the number of turns of the secondary phase windings in pairs of windings placed on each of the rods is

Where

and the secondary phase windings corresponding in relative sizes are made with the same number of turns, while six secondary phase windings in each transformer are interconnected in series, topologically forming a semi-regular hexagon, and a tap is made from the midpoint of each secondary phase winding, with each of of taps from the midpoints of the secondary phase windings of one transformer is connected to an unused point of connection of unlike valve electrodes in the valve cells ah of one group of valves, and each of the taps from the midpoints of the secondary phase windings of the second transformer is connected to an unused point of connection of dissimilar electrode electrodes in the valve cells of the second group of valves, with the same free electrodes of the second half of the valves in each of the valve groups connected, and in one group at the same time, a cathode six-star star is formed in the valves, and in the other group an anode six-star star is formed, and two hexes are respectively formed from the valve groups valve bridges with DC leads from common points of connection of gates in six-star stars, moreover, six-phase valve bridges are connected in series by bipolar DC leads, and free bipolar leads of the bridges form the output terminals of the device.

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