RU2458449C1 - Eight-phase voltage converter - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: in a converter there is one three-phase transformer with a double set of main secondary windings, with two auxiliary windings on a rod of one of phases and eight valves; main secondary windings of all transformer phases are connected in bundles into a single circuit in the form of a "hexagon" so that voltages between bundles form a six-phase system of voltages; each auxiliary winding with its one output is connected to a bundle of the "hexagon", with which main secondary phases of the phase, on the rod of which auxiliary windings are located, are not connected; the other output of each additional winding together with six taps from coils of main secondary windings represents one of outputs of the eight-phase voltage system. Two valves are always in operation - one of four valves of a cathode group, potential on the anode of which is highest, and one of four valves of the anode group, potential on the cathode of which is lowest. Each valve during the period is switched once.

EFFECT: higher efficiency, reduced value of rectified voltage pulsations and reduced content of higher harmonics in an AC curve.

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Description

The present invention relates to a conversion technique and can be used to create adjustable voltage converters for DC electric drives for machines to increase their speed, as well as in converter substations for supplying electrified railways, in the electrometallurgical and chemical industries to reduce the ripple of the rectified voltage and decrease the content of higher harmonic components in the AC curve.

The closest solution from the prior art to the proposed one adopted as a prototype is a constant voltage source with an 8-fold ripple frequency [Utility Model Patent No. 53082. A constant voltage source with an 8-fold ripple frequency [Vorfolomeev G.N., Schurov N.I., Neiman L.A., - Application. No. 20055132895; declared 10/25/2005; publ. 04/27/2006; bull. No. 12], containing two transformer sources of variable EMF shifted in phase orthogonal to each other, and sixteen valves; each source has two secondary windings equipped with additional taps connected to each other and with valves connected to four four-valve bridges. Thus, the prototype requires for its implementation a three-phase network, two single-phase transformers, the primary windings of which are connected to the three-phase network according to Scott's scheme, and sixteen valves.

The disadvantage of this device is the presence of a rather large number of valves, which greatly complicates the design of the converter, since each valve must be accompanied by a unit that generates a signal that controls the valve.

The objective of the invention is the creation of a constant voltage source with eight times the ripple frequency, having half the number of valves and a fairly simple design and technology of the device.

The problem is solved by the fact that in an eight-phase converter containing a three-phase transformer with a double set of coils of the main secondary windings with two coils of auxiliary windings on the rod of one of the phases and eight valves, the main secondary windings are connected by nodes in one circuit in the form of a "hexagon" in this way that the voltages between the vertices of the “hexagon” form a six-phase voltage system, while one of the terminals of the auxiliary winding is connected to the circuit node “hexagons” ka ”, which is not connected with the main secondary windings of that phase, on the rod of which there are auxiliary windings, and each other of the outputs together with six tap-offs from the coils of the main secondary windings is one of the outputs of the eight-phase voltage system, and the valves are connected in two groups - the anode and cathode, while in the anode group of valves the anodes are connected to one node, which is one pole on the DC side, and in the cathode group of valves, the cathodes are connected to one node, representing the other pole on the DC side, in addition, each valve of the cathode group is connected by its anode to the even phase of the eight-phase voltage system, and each valve of the anode group is connected by its cathode to the odd phase of the eight-phase voltage system.

The invention is illustrated by graphic materials, where:

- figure 1 presents a diagram of an eight-phase voltage Converter;

- figure 2 is a vector diagram of the potentials on the valves;

- figure 3-10 - presents equivalent circuits generated in the Converter for each of the eight time intervals.

The eight-phase voltage converter consists of a three-phase transformer having three coils 1, 2, 3 of the primary winding, connected by a star circuit and connected to a three-phase network, six interconnected coils 4, 5, 6, 7, 8, 9 of the main secondary windings having tap from the turns 10, 11, 12, 13, 14, 15, connected to the valves of the Converter, and two auxiliary coils of the secondary winding 16 and 17, also connected to the valves. The same clamps (beginning) of all coils are marked with an asterisk (*). The beginning of the secondary coil 4 is connected to the beginning of the secondary coil 9, the end of the secondary coil 9 to the end of the secondary coil 6, the beginning of the secondary coil 6 to the beginning of the secondary coil 5, the end of secondary coil 5 to the end of the coil 8 of the secondary winding, the beginning of the coil 8 of the secondary winding - with the beginning of the coil 7 of the secondary winding, the end of the coil 7 of the secondary winding - with the end of the coil 4 of the secondary winding, closing the loop circuit of the secondary windings. Each coil of the main secondary windings of the transformer is a side of the "hexagon". Auxiliary secondary windings are each connected to one vertex of the "hexagon", to which the main secondary windings of the same rod, on which the auxiliary windings are located, are not connected.

Gates 18, 19, 20, 21 of the anode group are connected by their cathodes to the outputs of the eight-phase voltage system (tap from the turns of the coils of the main secondary windings) 12, 13, 14, 15, respectively. Gates 22, 23, 24, 25 of the converter cathode group are connected by their anodes to the outputs of the eight-phase voltage system, respectively 16, 10, 17, 11.

The vector diagram shows the potential vectors on the anodes of the valves of the cathode group and on the cathodes of the valves of the anode group relative to the center of the "hexagon" and "octagon" - point 0, whose potential is taken equal to zero.

The eight-phase voltage Converter operates as follows.

The eight-phase voltage converter can operate in two modes: in rectifier mode and in inverter mode. Operation in an uncontrolled rectifier mode when using semiconductor diodes as valves is as follows: two valves always work - one of the four valves of the cathode group, the potential at the anode of which is the largest, and one of the four valves of the anode group, the potential at the cathode of which is the smallest (Fig. 3, Fig. 4). Therefore, the average value of the current flowing through the valve - Iv, is equal to one fourth of the average value of the load current - Io: Iv = 1 / 4Io. Each valve for a period turns on once.

In time, the potentials on the valves change according to a harmonic law determined by the change in the projection of the potential vector on the ordinate axis when the vectors rotate counterclockwise with an angular velocity ω = 2πf ₁ , where f ₁ is the frequency of the supply voltage converter. A vector diagram of the potentials of the converter nodes is presented for the point in time when the valve 19 of the anode group changes the valve 21 of the anode group that worked before that time, since the potential at the cathode of the valve 21 has become less. Thus, the voltage at the rectifier output, determined by the projection of the segment 22-21 (see Fig. 2) on the ordinate axis, changes to the voltage equal to it, determined by the projection of the segment 22-19, and will be determined by this projection until the valve 22 the cathode group will be replaced by another valve 25 of the cathode group - at that time when the potential at the anode of the valve 25 becomes greater than the potential at the anode of the valve 22 of the cathode group.

In an eight-phase voltage converter, each period of the supply voltage is divided into eight time intervals. In each subsequent time interval, the law of voltage change at the output repeats the law of voltage change of the previous interval. We introduce the following notation: Ni — sequence number of the interval; Ti is the time moment of the beginning of the i-th interval (ms); Ba - working valve of the anode group; VK is a working valve of the cathode group. The cycle diagram of the valves of the cathode and anode groups is shown in table 1.

We express the value of the average rectified voltage at the output of the converter through the amplitude of the phase voltage at the output of the six-phase converter of the number of phases U _6m , equal to the amplitude of the voltage on the coil of the main secondary phase winding.

Table 1 Ni one 2 3 four 5 6 7 8 Ti 0 2.5 5 7.5 10 12.5 fifteen 17.5 Ba 19 19 twenty twenty eighteen eighteen 21 21 Bk 22 25 25 24 24 23 23 22

Within the same time interval of an eight-phase rectifier, its output voltage varies in harmonic law. Denote the amplitude of the output voltage by U _0m . It can be represented by segment 19-22 in the vector diagram as the hypotenuse of the right triangle E-19-22 with legs: E-19 and E-22, respectively equal to U _6m Sin60 ° Sin45 ° and U _6m (1 + Sin60 ° Sin45 °). Then U _0m = 1,6U _6m

Within the time interval -T / 16 <t <T / 16, where T is the period of change of the three-phase voltage of the supply network, the voltage at the converter output changes according to the law

U ₀ (t) = U _0m Cosωt

Therefore, the average rectified voltage at the output of the converter U ₀ is determined by the average value of a certain integral of the function U ₀ (t) in the range from -T / 16 to + T / 16 for one eighth of the period: U ₀ = 1.56U _6m .

At the time when the structure of the circuit changes due to the changed potentials on the valves, the voltage at the rectifier output is minimal. We determine its value by the example of the time instant of transition to the first time interval for which a vector diagram is constructed. The magnitude of the output voltage will be minimal and will be determined by the difference between the projections of the potential vectors of the valves 22 and 19 on the ordinate axis, i.e. the length of the segment E-22:

U _0min = U _6m (1 + Sin60 ° Sin45 °) = 1,478 U _6m

The rectified voltage pulsates with an eight-fold frequency in the voltage span of 1.488U _6m <U ₀ (t) <1.6U _6m with an average value of U ₀ = 1.56U _6m with an amplitude of 0.0265U _6m , which is below 1.5% of the average value .

We now determine the position of the tap from the turns of the main secondary windings. In the coils of the main secondary windings (4 and 5) located on the rod, on which there are additional secondary windings (16 and 17), the tap is removed from half the turns. In coils of other phases, the soldering divides the turns of the coils into two parts with a ratio of turns (2Sin22.5 ° Sin67.5 °) :( 1-2Sin22.5 ° Sin67.5 °). The position of the tap in relation to the beginning of the winding is shown in the vector diagram (Figure 2). For coils 7 and 8, the number of turns counted from the beginning of the coil to the soldering is 0.707W ₂ , from the soldering to the end of the coil is 0.293W ₂ . For coils 6 and 9, on the contrary: from the beginning to the soldering - 0.293W ₂ , and from the soldering to the end - 0.707W ₂ . The geometric analysis of the vector diagram (Figure 2) gives the following number of turns of the auxiliary secondary windings: W ₁₆ = W ₁₇ = 0,134W ₂ . Here W ₂ is the number of turns of one coil of the main secondary winding.

The magnitude of the currents flowing along the coils of the secondary windings is determined based on the fact that the load current in the hexagon of the secondary windings is divided into two parallel branches, consisting of a different number of turns, which is different at different time intervals. We take the resistance of one full coil of the secondary winding per unit. Then the resistance of its part to the branch can be represented by the numbers given above, and the resistance of each branch can be represented by one of the four numbers obtained below: 1 + 1 + 1 + 0.707 = 3.707; 1 + 1 + 0.293 = 2.293; 1 + 0.707 + 0.5 = 2.207; 1 + 1 + 1 + 0.5 + 0.293 = 3.793. The composition of parallel branches for each time interval can be determined by Figure 3 for the first four intervals and Figure 4 for the remaining intervals. The currents in the coils in fractions of the load current I ₀ with an ideal filter at the output of the converter are shown in table 2.

Here Nk is the coil number, Ik / Io is the coil current in fractions of the load current,

Thus, the proposed technical solution allows to reduce the number of valves of the Converter, which ultimately allows to reduce the size, weight and cost of the Converter.

The analysis of the claimed technical solution for compliance with the requirements of patentability showed that the characteristics indicated in the independent claim are interrelated with each other with the formation of a stable set of necessary features, unknown at the priority date from the prior art, sufficient to obtain the required synergistic (over-total) technical result.

The properties regulated in the claimed compound by individual features are well known in the art and require no further explanation.

Thus, the above information indicates the fulfillment of the following set of conditions when using the claimed technical solution:

- the object embodying the claimed technical solution, in its implementation is intended for use in the creation of adjustable DC electric drives;

- for the claimed object in the form described in the independent claim, the possibility of its implementation using the means and methods known from the prior art on the priority date on the priority date has been confirmed;

- the object embodying the claimed technical solution, when implemented, is able to ensure the achievement of the technical result perceived by the applicant.

Therefore, the claimed object meets the requirements of patentability “novelty”, “inventive step” and “industrial applicability” under applicable law.

Claims (1)

An eight-phase converter containing a three-phase transformer with a double set of coils of the main secondary windings with two coils of auxiliary windings on the rod of one of the phases and eight valves, characterized in that the main secondary windings are connected by nodes in one circuit in the form of a “hexagon” so that the voltage between the vertices of the “hexagon” form a six-phase voltage system, while one of the terminals of the auxiliary winding is connected to the node of the “hexagon” circuit, which is not connected to the main toric windings of that phase, on the rod of which there are auxiliary windings, and each other of the terminals together with six tap-offs from the coils of the main secondary windings is one of the outputs of the eight-phase voltage system, and the valves are connected in two groups - anode and cathode, while in the anode group of valves, the anodes are connected in one node, which represents one pole on the DC side, and in the cathode group of valves, the cathodes are connected in one node, representing another pole on the DC side ka, in addition, each valve group cathodic its anode connected to the even vosmifaznoy phase voltage system, and each gate group by its anode connected to the cathode of odd vosmifaznoy phase voltage system.

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