SU913529A1 - Three-phase ac-to-dc voltage converter - Google Patents

Description

The invention relates to a conversion technique and can be used in power supply systems with adjustable rectified voltage, where higher quality of the output and input currents is required. *

Known three-phase AC to DC converter with improved quality of the output and input currents, made by parallel connection of three-phase "bridge. Circuits, and supplying them from a voltage system with an increased number of phases [1].

The disadvantage of this converter is the need for a special transformer to increase the number of phases.

Closest to the proposed is a three-phase AC to DC converter containing a controlled valve bridge and a chain of two series-connected valves connected in parallel with the specified bridge, with the middle • point of the valve chain connected to the zero point of the supply system. This converter is characterized by the fact that for the cathode and anode groups of controlled valves there are separate zero diodes. As a result of this, it becomes possible to independently and alternately control the valves of the cathode and anode groups, which makes it possible to reduce the ripple of the output rectified current and improve the shape of the AC consumed from the mains as compared to a bridge rectifier both without shunt diodes and with one shunt diode [2].

The disadvantage of the converter is that it can only work in

3-pulse and 6-pulse modes. As a result of this, the 3rd and 6th harmonics appear in the output rectified current, and the 5th and 7th harmonics of the power frequency appear in the alternating current supply, which makes it difficult to smooth the input and output currents.

913529 4

The purpose of the invention is the improvement of form | current consumed from the network and reducing ripple of the output rectified voltage.

The goal is achieved by the fact that the three-phase inverter ₅ AC to DC comprising a controlled main valve bridge and a chain of two series-connected valves, the connected parallel to the main w hydrochloric controlled veytilnomu bridge, the combined output terminals formed anodes and cathodes of said bridge is provided with two additional controllable 15 valve bridges connected in parallel at the input to the main controlled valve bridge, as well as a current divider otka which is arranged on one core and has two ₂ 0 consistently according connected sections with approach from the point sections a compound, wherein the outlet is connected to the point valves connecting said chain, the beginning of the winding is connected to 25 combined anodes and cathodes of the additional control valve bridge, and end of the winding is connected to the combined anode and cathode of another additional managed the Vienna _W d threshing bridge.

In addition, to completely eliminate the higher harmonics below the 11th in the current consumed from the network, the ratio of the number of turns of the sections of the windings of the current divider is chosen to be 0.7 32: 0.268.

In FIG. 1 shows a schematic diagram of a three-phase AC to DC converter; in FIG. 2 is a time diagram of the supply voltage of one phase, the supply current of one phase and the load voltage with a completely smoothed current, as well as a table of the on state of the controlled valves. ⁴⁵

The three-phase AC to DC converter (see Fig. 1) contains the main controlled valve bridge with controlled valves 1-6, two additional controlled ⁵⁰ valve bridges with controlled valves 7-12 and 13-18, respectively, the three-phase inputs of these bridges are connected to the terminals power supply 19 - 21, the output terminals of the converter 22 and ⁵⁵ 23, the load 24, a chain of series-connected diodes 25 and 26, a current divider 27, the winding of which is located on one core and has a beginning 28, end 29 and branch 30. Branch 30 is connected to then junction of the diodes 25 and 26, the beginning 28 of the winding is connected to the combined anodes and cathodes of the additional controlled valve bridge 7 - 12, and the end 29 of the winding is connected to the combined anodes and cathodes of the additional controlled valve bridge 13 - 18.

The device operates as follows.

At each moment in time, only three valves are located in different phases and in different three-phase bridges. Moreover, when the valve of the cathode group is turned on in the main valve bridge 1 6, then in the additional valve bridges

-12 and 13-18 the included valves are in the anode group and vice versa.

As a result of this, the current of the main valve bridge 1-6 is equal to the sum of the currents of the additional valve bridges 7 -12 and 13 - 18. The ratio of currents is determined by the ratio of the number of turns of the sections of the winding of the current divider. Since the currents in the current divider winding are variable and energy storage in the current divider is not required, its core can be made without a non-magnetic gap, which allows the magnetizing current to be neglected when analyzing the operation. Accordingly, the total magnetizing force of the two sections is zero and the currents in the sections (and, therefore, in the corresponding additional valve bridges) are inversely proportional to the number of turns of the sections.

In order to exclude higher harmonics from the supply current below the 11th, it is advisable to choose the ratio of the number of turns of sections of the winding of the current divider equal to 005 45 °: co5 75 ° = 2.73, which corresponds to the number of turns of sections 0.732 and 0.268 of the total number of turns of the winding of the current divider .

Consider the operation interval when valves 4.9 and 14 are turned on. In this case, the beginning 28 of the winding of the current divider 27 is connected through valve 9 and the terminal to phase C of the power system, the end 29 of the winding is connected through valve 14 and the terminal to phase B, and branch 30 windings through diode 25, load 24, valve 4 and terminal 21 with phase A of the power system. Neglecting the voltage drops on the On valves, the voltage on the winding of the current divider is equal to the linear supply voltage. Denoting the number of turns and the voltage of the winding between the terminals 28, 29 and 30, respectively, through ^ 00'EO ^AND 00-19 '% -30 ^{AND 5 For} EO-0.9, we can write ^ OV-ZO _ Che-lo. y ^ 10-19, ^and 10-19 ^ ΐθ-19 _ ^υ 30-19 ^ 00-19 ^υ 10-Ί9 15

Given that the interval ⁼ C &^{"and the} load voltage equal to ^the voltage ^and 114th ^{= and} A-ao ^'and Ag ^{+ and!} 19-LP * based optimal ratio of numbers of turns of the sections" aa-sc-Chotm- ⁰ · ⁷³²¹⁰ · ²⁶⁸ · we obtain for the instantaneous value of the load ^υ «% ^{+ and} 09 -?) 0 ^{= and} A6 ^{+ O |, 2b8 and} bS ·

2.73, strains. If the linear voltages and zo are sinusoidal, then in the considered interval the instantaneous voltage at the load changes along a section of a sinusoid.

For the 12-pulse rectifier operation mode ₃₅ is necessary to load voltage rectifier formed of identical segments of sinusoids that are shifted between themselves by 30 °. The required shifted sinusoidal ₄₀ half-waves for the formation of a 12-pulse rectified voltage can be obtained by choosing suitable combinations of the included valves. The sequence of closure of valves 1-18, providing. ₄₅ 12-pulse mode of operation of the circuit (see Fig. 1, is shown in the table in Fig. 2).

The rectified voltage is changed by shifting the closing phase of the given valve combinations, $ ₀ and thereby the phase of the supply current relative to the phase of the supply voltage. Moreover, regulation is possible both with lagging and with leading feed current. Timing diagrams of the supply voltage and d, supply current (d and load voltage of 9 C (see Fig. 2) | correspond to a completely smoothed 1 output current Zo equal to the current amplitude (d, and phase shift C d “60® between voltage and power supply current.

The phase shift in all phases is the same, i.e. 1 {deC> ^ r g. On fit. 2 also shows the time diagram of the maximum load voltage '0 corresponding to the phase shift = 0 °. The regulation of the output voltage from maximum to zero corresponds to a phase change <<within · from 0 ° - 90 ^e . With a fully smoothed load current Y _{0, the} shape of the supply current remains unchanged in the entire control range. Accordingly, the spectral composition of the supply current does not change. As a result of the fact that the current in the windings of the current divider is rigidly connected to the supply current, its shape also does not change, moreover, this current has a rectangular shape and a triple frequency. The amplitude of the rectangular current through the outlet 30 is equal to the load current ЗО · Under the action of the current divider, the rectangular current through the branch of the ЗО is distributed into two rectangular currents with amplitudes inversely proportional to the number of turns of the sections of the winding of the current divider. Under active load, the shape of the output current coincides with the shape of the output voltage, and the primary current has a shape typical of a 12-pulse operation mode.

A positive property of the converter is a significant improvement in the spectral composition of both the AC consumed from the network and the rectified output current. This is achieved by the fact that two additional three-phase controlled valve bridges and an inductive current divider with a tap shifted from the center of the winding are used in the converter circuit, as a result of which a 12-pulse operation mode can be carried out without the need for a phase converter or a special input transformer. The operation of the inductive current divider at the tripled 'Frequency helps to reduce its mass-dimensional indicators.

Claims (2)

Claim 1. A three-phase AC-to-DC converter, containing the main - controlled valve bridge and a chain of two series-connected valves connected in parallel with the main controlled one. valve bridge, while the output of water 913529, formed by the combined anodes and cathodes of the specified bridge, characterized in that, in order to improve the shape of the current consumed from the network and reduce ripple you are direct. voltage, it is equipped with two additional controlled valve bridges connected in parallel along the main drive valve bridge, as well as a current divider, the winding of which is located on one core and has two series-connected sections with a tap from the connection point of the sections, moreover this tap is connected to the point of connection of the valves of the specified chain, the beginning of the winding is connected to the combined anodes and cathodes of one additional controlled valve bridge, and the end of the winding and is connected _to? combined anodes to the cathodes of another additional controlled valve bridge. 2. The converter according to π. 1, due to the fact that, in order to completely eliminate the higher harmonics below the 11th in the current consumed from the network, the ratio of the number of turns of the sections of the winding of the current divider is set equal to b, 732: 0.268.