SU1376199A1 - Three-phase inverter with quasi-sine output voltage - Google Patents

Abstract

The invention relates to electrical engineering, in particular, to converter technology, and can be used in power supply systems. The purpose of the invention is to improve the quality of the output voltage. The converter contains a control unit, a main three-phase bridge of key elements with a shunt three-phase bridge of reverse current diodes, To additional three-phase bridges of key elements with a three-phase bridge bridge of key elements of a reverse current. The output three-phase transformer contains the main and an additional windings of each phase on the primary side. The outputs of the first additional three-phase bridge are connected through the first additional phase windings to the outputs of the main three-phase bridge. The outputs of each subsequent additional three-phase bridge are connected via successive additional phase windings to the outputs of each previous additional three-phase bridge, and the inputs of additional three-phase bridges are connected in parallel to the input of the main three-phase bridge. The selection of the ratio of the number of turns is carried out in such a way as to ensure the formation of a multi-stage voltage curve with a minimum coefficient. harmonics for a given number of steps of a quarter period. 1 hp f-ly, 2 ill. -1 (L with O5 with so

Description

The invention relates to electrical engineering and can be used in secondary power supply and electric drive systems to convert a DC voltage to a three-phase AC voltage of quasi-sinusoidal form.

The purpose of the invention is to improve the quality of the output voltage of the inverter.

Fig. 1 shows a block diagram of the proposed three-phase inverter with a quasi-sinusoidal output voltage with three steps at a quarter of a period; Fig. 2 shows time diagrams of output phase voltages with an algorithm of included states of key elements (in the form of a table) over a period of one period.

The three-phase inverter (FIG. 1) contains a three-phase transformer with taps and leads 141-1.6 of the primary windings, a main three-phase bridge on controlled key elements 2-7 shunted by return diodes 8-13, an additional three-phase bridge on controlled key elements 14-19, shunt counter-controlled key elements 20-25; and a control block 26.

The three-phase transformer contains three phase windings on the primary side, which are connected in a star, and three phase windings on the secondary side. Each primary phase winding consists of a series-connected main (with the number of turns W and an additional (with the number of turns Wj-W) sections. By means of controlled key elements 2-7 and 14-1) the primary windings are connected to the input terminals forming the output voltage of all three phases simultaneously. Each secondary phase winding of the transformer has a fixed number of turns W, j and serves as a dp to obtain the specified value of the output EMF from the phases

  - BS

The magnetic core of the output transformer is made three-phase.

The three-phase inverter works as follows.

The control unit 26 switches the key elements in accordance with the given algorithm. In this case, the inclusion of elements 2-7 provide5

0

50

5 0 5 0

five

There is a connection to a positive or negative input terminal of the tap 1.1 and. primary windings of a transformer with the number of turns W ,, and switching on, elements 14–19 - taps 1.2, 1.4 and 1.6 of the primary windings of the transformer with the number of turns Wj. The return diodes 8-13 and controlled key elements 20-25 ensure the operation of the transducer on the active-inductive load. The use of controlled key elements 20-25, rather than diodes, is caused by the need to eliminate short circuits of the additional phase windings of the primary side of the transformer when connecting the corresponding taps 1.1, 1.3 and 1.5 to the power source.

When forming the output phase voltages, for example, in the time interval from zero to T / 12, key elements 14, 4, 7 and 20 are included. A tap 1.2 of the primary windings of a transformer with a number of turns W is connected to the negative input terminal of the key. With the active element 14 or with the key element 20 with the active-inductive load, the output 1.3 and 1.5 of the primary windings of the transformer with the number of turns W ,, are connected respectively to the negative and poloskitelny input output. do key elements 4 and 7. The closed key elements of the reverse current 22 and 25 exclude short-circuiting of additional windings of phases B and C of the primary side of the transformer through elements 4 and 22, 7 and 25, respectively. In this time interval 1d + + Ig + (- o (Fig. 2), which confirms the fact of the synthesis of three-phase voltage.

The formation of the output phase voltages on the remaining time intervals is carried out similarly.

The selection of the ratio of the sections of the number of turns of the primary windings of a three-phase transformer is made so as to ensure the formation of a multi-stage voltage curve with a minimum harmonic coefficient for a given number of steps per quarter period. So, for a specific example of the implementation of the proposed inverter with K 1, the ratio Wj / W is 2.73. output phase voltage

there are only higher harmonics with the number 12 N ± 1, where N 1, 7 H

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Claims (2)

1. A three-phase inverter with quasi-sinusoidal output voltage, containing the main and K additional three-phase bridges of controlled switches connected in parallel to the input, and the output connected to the extreme terminals and intermediate taps of the primary winding of the three-phase output transformer, which differs from In order to improve the quality of the output voltage, the main three-phase bridge is made on controlled keys of one-sided driveability, shunted by return diodes, additional three-phase bridges are made Enes are on controlled AC switches, the output transformer is made on a three-phase magnetic circuit, and its primary windings are connected by a star and have Q. intermediate taps in each phase, the first, closest to the common point of the star, the intermediate tap connected to the output pins of the main three-phase the bridge of controlled keys, and the subsequent intermediate taps and the extreme terminal of the primary winding are connected to the output terminals of the respective additional three-phase bridges of the controlled keys. 2. The inverter according to claim. At K 1, the intermediate primary tap in each phase of the output transformer is positioned so that the ratio of the number of turns of the section between this tap and the common point of the star to the number of turns of the section between this tap and the extreme output is 1 -: 1.73. Oa C 0 FIG. 2