RU187850U1 - MULTI-PHASE RECTIFIER - Google Patents

Abstract

The utility model relates to the field of power electrical engineering and can be used to power DC networks and various industrial consumers and technological processes.

DC power networks are used to supply various kinds of loads, for example, ship networks and to supply specialized consumers and systems, as well as for technological processes in which constant voltage and current are required. For this purpose, as a rule, controlled semiconductor rectifiers are used, which are powered by a three-phase AC network.

One of the main parameters that determine the quality of a constant (rectified) voltage is the number of ripples during the period of the AC mains of industrial frequency. This parameter directly affects the value of the ripple coefficient of the rectified voltage, which gives a numerical estimate of the amplitude and frequency of the ripple. The frequency of output voltage ripples directly depends on the number of rectified phases of alternating current, to increase the number of which the windings of the primary windings of power transformers are used, combining the inclusion of windings according to the star, triangle, zig-zag schemes. The disadvantage is the increase in mass and dimensions, and the drop in the utilization rate of the windings of the power transformer in time.

The proposed solution is aimed at improving the quality of the output voltage of the rectifier, by increasing the number of phases of the rectified alternating voltage, by summing the secondary windings of the power transformer in a different sequence. By combining two or more phases, it is possible to form voltages having a phase shift, and the number of inclusion combinations increases with their number - ensuring the quality of the rectified voltage.

Description

The technical field to which the utility model belongs. The utility model relates to the field of power electrical engineering and can be used to power DC networks and various industrial consumers and technological processes.

The level of technology. The prior art three-phase adjustable AC to DC converter [RF patent for invention No. 2331960], which includes a three-phase converter transformer with a primary winding connected to a "star" and two three-phase secondary windings. One of the windings is connected in a star pattern, the other in a triangle pattern. There is also a booster transformer with one three-phase primary and two three-phase secondary windings connected in each phase to the secondary windings of the converter transformer, and two identical and connected in series three-phase rectifier bridges. A secondary winding of the boost booster transformer is connected to the phases of the secondary winding of the converter transformer connected to the "star", in series with which a controlled reactor is connected, forming together with the secondary winding of the boost transformer a circuit, in parallel with which an uncontrolled reactor is connected, the ends of which are formed with the ends of circuits containing a series-connected secondary winding of a boost booster transformer and a winding of a controlled reactor common points connected a first rectifier bridge. The second secondary winding of the boost transformer is connected in a zigzag circuit and connected to the second secondary winding of the transformer transformer connected in a "triangle". The ends of each phase of the secondary winding of the booster transformer connected in a zigzag circuit are connected to controlled reactors. Uncontrolled reactors are connected in parallel with a circuit consisting of a secondary winding of a boost booster transformer connected in a zigzag circuit and connected in series with a winding of a controlled reactor, while the ends of the windings of a controlled and uncontrolled reactor form a common point in each phase connected to the second valve bridge.

The disadvantages of this solution include the presence of an additional boost booster transformer and smoothing reactors, which increases the weight and dimensions of the installation; in addition, the regulation of the output voltage due to the corresponding controlled reactor leads to a decrease in the efficiency of the converter.

Also known is a static rectifier [RF patent for utility model No. 144830], designed to power industrial power plants and DC power lines, and containing two serially connected three-phase rectifier bridges, one of which is made on uncontrolled valves, the other is made on controlled valves, both rectifier bridges are connected to separate three-phase secondary windings of the transformer. Secondary three-phase windings have transformation ratios that are related to each other as 1: 2.8 and have the same star switching pattern. A controlled rectifier bridge generates 6 ripples of the rectified voltage, consisting of fragments of half-wave fronts, switched at the moments of equality of the fronts of the half-wave modules of voltage of different phases, while the rising and falling edges alternate. As a result of the ripple of the uncontrolled and controlled rectifier bridges, they are shifted by an angle π / 6, and a total voltage is formed at the output of the rectifier, which has 12 symmetrical ripples over the period of the supply network.

The disadvantages of this solution include the low quality of the output voltage for a number of areas due to the presence of twelve ripples of the rectified voltage when powered by a three-phase AC mains.

Also known semiconductor rectifier [RF patent for the invention No. 2673250], containing two three-phase rod transformers, the primary three-phase windings of which are connected to the mains. The primary three-phase winding of one transformer has a star connection, the three-phase winding of the second transformer has a triangle connection. All secondary windings are connected to rectifier bridges, and are connected according to the scheme by a star. Each mentioned three-phase rod transformer has two secondary windings, with the ratio of the number of turns between the secondary windings in each transformer approximately equal to the product of the natural number e and the square root of two. The secondary windings of transformers having an equal number of turns are combined into a pair of windings equipped with a common neutral. Three-phase rectifier bridges connected to the said pairs of secondary windings with an equal number of turns are combined in parallel and according to a common neutral. The outputs of three-phase rectifier bridges, paired and connected to pairs of secondary windings with an equal number of turns, between two such pairs of rectifier bridges are connected to each other in series and in accordance.

The disadvantages of this solution include the ratio of the number of turns of the windings, equal to the base of the natural logarithm (number 2.72) - the observance of the exact proportion of which can be difficult in powerful transformers. Four secondary three-phase windings are used to form the output voltage - which worsens the mass and dimensions.

This technical solution is the closest prototype in its technical essence.

Disclosure of a utility model. DC power networks are used to supply various kinds of loads, for example, ship networks and to supply specialized consumers and systems, as well as for technological processes in which constant voltage and current are required. For this purpose, as a rule, controlled semiconductor rectifiers are used, which are powered by a three-phase AC network.

One of the main parameters that determine the quality of a constant (rectified) voltage is the number of ripples during the period of the AC mains of industrial frequency. This parameter directly affects the value of the ripple coefficient of the rectified voltage, which gives a numerical estimate of the amplitude and frequency of the ripple. The frequency of the output voltage ripples directly depends on the number of rectified phases of alternating current, to increase the number of which the primary windings of power transformers are used, according to the star, triangle, zig-zag schemes in various combinations. The disadvantage is the increase in mass and dimensions, and the deterioration in the use of turns of the secondary windings of the power transformer in time.

The simplest version of a multiphase AC network is the vector diagram of a three-phase system shown in Figure 1. It can be seen here that the angle between the phase stress vectors is 120 °, which gives a completely symmetric system of stresses [1]. Any phase is symmetric with respect to the other two, while there is only one phase shift value. Another distinctive property of the three-phase voltage system is the equality of the sum of the voltages of the three phases to zero, which explains the absence of surge currents in the triangle windings [1].

There are multiphase electrical circuits having a six-phase voltage, as shown in figure 2, which presents a vector diagram of a six-phase system. It is such a voltage system that is used in twelve-pulse semiconductor rectifiers, using star and delta type windings [1, 2, 3].

The use of an additional shift between the phases is necessary to obtain a larger number of ripples of the rectified voltage, which gives a lower ripple amplitude. Most often, various combinations of primary winding switching circuits [3] are used for this (such as a star, a triangle, a zigzag). However, existing industrial plants use separate three-phase windings that do not have a common neutral connection. This scheme allows you to use double the number of phases. However, as follows from figure 2, in a six-phase system with a common neutral, it is possible to obtain a larger number of combinations of phases.

Figure 3 shows a vector diagram of the sum of two phases with a shift of 150 electrical degrees, figure 4 shows a vector diagram of the sum of two phases with a shift of 120 electrical degrees, figure 5 shows a vector diagram of the sum of two phases with a shift of 90 electrical degrees, figure 6 shows a vector diagram of the sum of two phases at a shift of 30 electrical degrees. The resulting stress vectors are characterized by an additional phase shift.

The figure 7 presents the electrical circuit diagram of a three-phase rectifier, providing 6 ripples at the output. Such a circuit is characterized by simplicity, however, the magnitude (amplitude) of the ripple of the rectified voltage exceeds the maximum allowable for many DC consumers. The figure 8 presents the electrical circuit diagram of a six-phase rectifier, with a serial connection of two semiconductor switches (three-phase bridges), and providing 12 ripples at the output. The primary winding of one of the two transformers used to power the bridges is connected according to the triangle scheme to obtain a phase shift of 30 electrical degrees between the secondary windings of the transformers. The number of output voltage ripples in such a circuit is determined by the number of phases of the secondary windings of the supply transformers. Since the circuit does not have a common neutral for two three-phase windings, the number of ripples is 12.

However, as shown above, in a six-phase winding with a common neutral, it is possible to obtain a larger number of phase shifts, which makes it possible to increase the number of ripples at the output of the rectifier.

Such an increase in the number of pulsations becomes possible due to the combinatorial connection of phases to each other, with various combinations of the summed phases and their number. For example, it is possible to sum two, three, four and five phases, which gives a greater number of combinations of phases with each other, accompanied by an additional phase shift.

The figure 9 presents a schematic diagram of the proposed solution, made on the basis of two rod three-phase transformers, with a phase shift of 30 electrical degrees between the windings of the mentioned transformers. All phases of the secondary windings are interconnected in series, and the sum of the voltages of all six phases in this case is zero. The semiconductor switches shown in figure 9 are divided into 2 groups according to their purpose. One group of keys provides the connection of the phases of the windings, the other shunts the phases of the windings - providing a current flow around the unused phases of the windings.

Thus, in the proposed solution, the control of an arbitrary sequence of winding phases is implemented - it is possible both to exclude phases from the sequence and sequential summation of phases. This made it possible to combine phases, and to obtain the sum of the voltages of any number of phases. The summation of all six phases of the windings does not make sense, since it will give a voltage equal to zero, but it is possible.

Presented in figure 9, the circuit diagram uses to connect the primary winding of one of them according to the triangle to obtain a symmetric phase shift between two transformers. However, any other options for the formation of a phase shift are possible, for example, the zig-zag version shown in figure 10, proposed in the patent for utility model of the Russian Federation No. 182989. Providing a phase shift between the transformer windings is achieved by the prior art.

In figures 11-13 shows the state of the circuit and the path of the currents during operation of two, three and four phases of the windings, respectively. The bold line indicates the part of the electric circuit through which current flows, closed contacts show the included keys (transistors). To implement the proposed solution, it is necessary to use fully controllable semiconductor switches (transistors), for example IGBT.

Also, the proposed solution allows the use of single-phase windings, which will correspond to the normal mode of operation with 12 ripples of the rectified voltage. However, when summarizing a larger number of phases, it is possible to obtain both a larger number of ripples at the output of the rectifier and a better voltage quality.

The proposed solution is aimed at improving the quality of the output voltage of the rectifier, by increasing the number of phases of the rectified alternating voltage, by summing the secondary windings of the power transformer in a different sequence. By combining two or more phases, the formation of voltages having a phase shift is possible, and the number of switching combinations increases with increasing number of phases - ensuring the quality of the rectified voltage.

The inventive utility model is a new solution having the following fundamental differences from the prototype:

- all phases of the secondary windings of three-phase transformers are connected in series;

- each of the phases of the secondary windings is equipped with a semiconductor key connected in series with it;

- parallel to all phases of the secondary windings are connected bypass semiconductor switches.

Thus, the set of essential features of the solution leads to a new technical result - an increase in the number of ripples of the output voltage.

A brief description of the drawings. The figure 1 shows a vector diagram of a three-phase voltage system. The figure 2 shows a vector diagram of a six-phase voltage system. The figure 3 shows a vector diagram of the sum of the stresses of two phases with a shear angle of 150 electrical degrees. Figure 4 shows a vector diagram of the sum of the stresses of two phases with a shear angle of 120 electrical degrees. Figure 5 shows a vector diagram of the sum of the stresses of two phases with a shear angle of 90 electrical degrees. Figure 6 shows a vector diagram of the sum of the stresses of two phases with a shear angle of 30 electrical degrees. The figure 7 shows a schematic diagram of a three-phase rectifier. The figure 8 shows a schematic diagram of a six-phase rectifier with a second primary winding according to the triangle diagram. The figure 9 shows a schematic diagram of the proposed multiphase rectifier with a second primary winding according to the triangle. The figure 10 shows a schematic diagram of the proposed multiphase rectifier with primary windings according to the zig-zag circuit. The figure 11 shows a schematic diagram of a switch when operating two phases. The figure 12 shows a schematic diagram of a switch when operating three phases. The figure 13 shows a schematic diagram of a switch with four phases.

List of used literature.

1. Frumkin A.M. Theoretical foundations of electrical engineering. - M.: Higher School, 1982. - 407 p.

2. Kartashov R.P., A.K. Kulish, E.M. Case Thyristor frequency converters with artificial switching. / Kiev: TECHNOLOGY, 1979. - p. 152.

3. Dmitriev B.F., Ryabenky V.M., Cherevko A.I., Music M.M. Marine semiconductor converters: a textbook. - Arkhangelsk: Publishing House of NArFU, 2015 .-- 556 p.

Claims (1)

A multiphase rectifier containing three-phase transformers, the windings of which have a mutual phase shift, characterized in that all phases of the secondary three-phase windings of the said transformers are connected in series with each other, each of which is equipped with a semiconductor switch connected in series and a shunt switch connected in parallel.

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