SU1067574A1 - Method of adjusting three-phase direct frequency converter - Google Patents

Abstract

METHOD OF THREE PHASE direct frequency converter by simultaneously and a cyclic connecting the output of its conclusions alternately to all input terminals through a fully actuated AC semiconductor switches, wherein laws connecting output terminals of adjacent phases are different between a phase shift to one-third of the switching cycle of t This is due to the fact that, in order to improve the quality of the output current by reducing its harmonic coefficient, to form a voltage to Each output phase connects the corresponding output pins to the input pins in such an order that the connection of one of the output pins to only one of the input pins is carried out in the continuation of the twenty-fourth, twelfth, twelfth and twenty-fourth parts of the commutation circuit. }, separated by intervals, respectively, on the twelfth, twenty-fourth, twenty-fourth and twelve parts of the switching cycle of these semi-proprietary keys.

Description

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4 The invention relates to electrical engineering, to a section of frequency converters. There is a known method of controlling a fully controlled direct frequency converter by connecting a phase to an input phase, the instantaneous value of which is close to the instantaneous value of the drive voltage. According to this method, at each moment of time, the difference between the input and the input voltages is measured, they are integrated and, upon receiving a positive integral, they produce a signal to connect the output output to the input output of that phase, the difference of the voltages of which the driving voltage is the least negative L 11 The disadvantages of this method are the relative complexity of this control topic, due to the need to use the input voltage transformer block, the voltage setting blocks for each input phase, for detecting at each moment of time the input phase, the voltage difference of which with the voltage setting is minimal, the integration unit of the difference between the output voltage and the voltage setting voltage matching blocks, etc., the uncertainty of the spectral composition of the output voltage of the converter controlled in such a way that does not exclude occurrence of such components of the output voltage that are capable of substantial:; to worsen the energy performance of both the frequency-controlled asynchronous motor and the system of predominantly - load. There is also known a method of controlling a three-phase direct frequency converter by cyclically simultaneously connecting the output pins alternately over all input pins using fully controlled AC semiconductor switches, so that the output pins of the other phases are connected to one of the phases by shifting one and two TpjSTKx of the common switching cycle C21. This control method, adopted as a prototype, is designed for a cyclically monotonous abrupt change in the initial phase of the output voltage by degrees of two to two degrees. The spectral composition of the output voltage of the frequency converter, in which the sophisticated C 21 control method is implemented, has a well-defined character and may be; described by an analytical expression. This is one of the advantages of this method of controlling til. Along with that. It is desirable to develop such a control method which, with active inductive load, would provide an improvement in the quality of the output current as compared with the known control method 2. The purpose of the invention is to improve the quality of the output current by reducing its harmonic coefficient. This goal is achieved in that according to the method of controlling a three-phase direct frequency converter, it is that simultaneously and cyclically using fully controlled semiconductor switches of alternating current alternately connected to all input pins, and the laws for connecting the output pins of adjacent phases differ from each other to phase shift one third of the total voltage of a 1 d switch, for forming the voltage of each of the output phases, connect the corresponding output terminals to the input with such an order that the connection of one of the output conclusions only and one of the input turns out to be only during the twenty-fourth, twelfth, twelfth and twenty-fourth parts of the common switching cycle, separated by the twelfth, twenty-fourth, twenty the fourth and twelfth parts of the switching cycle of these semiconductor Keys. I. . FIG. Figure 1 shows an idealized transducer circuit diagram. Key switching algorithms 1-9 in the course of one switching cycle with indication of the corresponding values of the switching functions are presented in Table 1. In FIG. 2o - the output converter output curve for one of the load phases, composed of pieces of sinusoids of the three phases of the mains supply as a result of switching, set by switching functions K-t) (Hg. C-h) iVitt); in fig. 2 сГ, в, г.- epures of these fNuHs; in fig. 3 is a block diagram of a device implementing the proposed method. The direct frequency converter is controlled in the form of fully controlled AC semiconductor switches 1-9, connected to both the input terminals 10-12 and the output terminals 13-15. The control system of such a frequency converter contains an oscillator (CV) 16, redefined distribution

device 17 and shapers 18 32 pulses.

According to the diagrams in FIG. 2 connection of the load by a group of keys 1, 5 and 9 occurs during that time interval, when YD-b) 1, keys 2, 6 and 7 when 1 (1 and keys 3, 4 and 8 - when tfc) 1.

The PRU switchboard 17 carries out the division into twenty-four pulses coming from SG 16, as well as their distribution between 18-32 PI pulse makers. The sequence of numbers of the pulse former 18-32 is shown in FIG. 3 is the same. with a sequence of pulses from the PRU to these formers, which also corresponds to the sequence of pulses of switching functions (Fig. 2) related to unlocking. three different combinations of fully controlled AC semiconductor switches 1-9. At the same time, the next unlocking of one combination of fully controlled AC semiconductor switches should correspond to the simultaneous locking of another combination of these previously open AC keys, and the duration of the open state of the keys is unequal and corresponds to the switching functions (Fig. 2).

For example, the unlocking of the semiconductor switches 3, 4 and 8 is performed by applying to the control inputs the silent keys of the unlocking pulse formers FI 22, 24, 26, 28 and 30 In this case, as follows from FIG. 2i. after the supply of unlocking pulses from PHI 22, the open state of the keys 3, 4 and, 8 takes place in the continuation of the twenty-fourth part of the switching cycle, after the impulse is supplied from FI 24 - the continuation of the twentieth part of this cycle, after the impulse is applied from FI 26 to the twelfth, s FI 28 - the twelfth, with FI 30 - twenty-fourth part of the switching cycle. The open state of the keys 3, 4 and 8, due to the supply of unlocking pulses from FI 22, is followed by their locking due to unlocking another combination of keys 2, 6 and 7 from FI 23, and after the twelfth part of the switching cycle - the newly discovered state of the keys 3 4 and 8 and closed klnzchey 2,6

and 7 and md. Thus, the open state of the keys 3, 4 and 8 alternates at intervals of their keys 2, 6 and 7, and so on. Thus, in accordance with the plots of switching functions in FIG. 2, the indicated open state intervals of keys 3, 4, and 8 alternate with the next closed state intervals: the twelve, twenty-fourth, and twelve parts of the switching cycle j at these closed state intervals of keys 3, 4, and 8 are turned on twice, first, keys 2, 6, and 7, and then {also twice) - keys 1, 5 and 9.

According to FIG. With 2 diagrams of kbm1 function corresponding to the proposed method of controlling a direct frequency converter, the output voltage can be represented as

.l) l.

bSeosCae llfivniH-Caa i li,

where tOx and -TL are the network and switching frequencies, respectively, the amplitude of the phase voltage of the network.

The output voltages of the other phases differ by a third part of the period.

From C1), it follows that among the components of the output voltage of a frequency converter controlled by the proposed method, there are no frequencies ii) + 251 and Oijt - 451, which are in the output voltage of a similar converter controlled by a known method L21.

This is where the advantages of the proposed method over the known one lie. At the same time, the ratios of the amplitudes of the other components in the output 1 of the voltage of the converter controlled by the known and proposed methods turn out to be unequal.

The calculation results (see Table 2) show that the proposed control method ensures the quality of the output current is better than the known one.

The data from the table. 2 are calculated for the ratio of the inductive cOjL and the active R of the load resistances to 2.

T a b l and c

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1D 0.0910 / POTOTIP; The proposed method 0,0868

Table 2

1.5 1.75

2.0

1.3 0.0938 0.0966 0.1083 0.1200 0.0888 0.0908 0.0975 0.1045

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Claims (1)

METHOD FOR CONTROL OF A THREE-PHASE DIRECT FREQUENCY CONVERTER by simultaneously and cyclically connecting its output terminals alternately to all input terminals using fully controlled semiconductor switches of alternating current, and the laws of connecting the output terminals of adjacent phases differ by one third of the commutation phase shift by one third of the comm cycle and. characterized in that, in order to improve the quality of the output current by reducing its harmonic coefficient, to form the voltage of each and From the output phases, the corresponding output terminals are connected to the input ones with such a sequence that the connection of one of the output terminals with only one input is carried out in the continuation of the twenty-fourth, twelfth, twelfth and twenty-fourth parts of the general switching cycle, divided by intervals of twelfth, twenty the fourth, twenty fourth and twelfth parts of the switching cycle of these semiconductor switches. _na SU 1067574 control converters full direct