SU446935A1 - Control voltage forming method for frequency converter - Google Patents

Description

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The invention relates to valve converter technology and can be used in a three-phase valve frequency converter to obtain a control voltage.

In the known method of forming a symmetric three-phase voltage to control a three-phase valve-frequency converter, three unipolar voltages are formed, having the form of a half-wave sinusoid and shifted relative to each other by 120 (in the output frequency), followed by modulation and demodulation.

The disadvantage of this method is the asymmetry of the resulting three-phase system of voltages due to the difficulty of forming three completely identical voltages.

Celting symmetry improvement in three-phase sinusoidal output, ipro voltage is formed by two j

I circuits, one of which at any I moment of time is equal to the smallest in modulus, and the other to the greatest (or average) in modulus of the voltages of a three-phase symmetric voltage system, and modulated generated voltages and their difference (or amount) alternately demodulate on each of the three outputs.

Due to this, the symmetry of the voltage system is improved, since the same areas of the three output voltages are formed from

5 common to all. Three output voltage phases

In Fig. 1 (a, b, c, d, d, e), voltage drills are given to clarify the proposed method; Fig.2 0 diagram of the device that implements this method.

Fig. 1a shows a three-phase symmetric system of voltages 1EDSi11is1is1 shown.

5 | Which has negative half-waves ,. replaced by their mirror-positive images, iia of Figs 1, 6, shows two generated voltages, one of which and (figl, o) B any moment of time is the smallest in modulus and the other U (figl, c) - the greatest ( or. as shown by a dotted line, medium) modulo the voltages of a three-phase symmetrical voltage system (figl, a), figl, d, e, e shows modulated (square shorm) and demodulated (monotone sinusoid) / output voltages . The essence of the invention is as follows. Any of the known methods (for example, techniques of discrete technology) form two voltages, one of which (FIG. 1.6) at any time is equal to the smallest value, and the other U (FIG, in) is the largest value depicted in absolute value ( Fig. 1, a) a three-phase symmetric voltage system. In a symmetric system of sinusoidal voltages, the average (in modulus) value of three waves is equal to the difference between the maximum P11n: which is maximally mix (but modulus) and minimum (modulo) voltages. For example, in Itirvale I UftUIUcl-lUgl, in the interval tg-tj lUcl 1id} - | iv1. Therefore, at each time point, it is sufficient to have two values (the smallest and the largest), and the third value (average) can be obtained by subtracting the smallest of its largest. Modulated naprsson, two of which form, and the third receive, alternately demodulate at each output. For example, in section O - t, demodulation is performed in (.Aza A: modulated HUQ voltage luH, in phase B voltage U, and in phase. From the voltage difference (Uj-Ua) e part of the t.-ta demodulated in phase A The difference in the values of (and - Ua) in Phase B 11a11r-Kenyu Ua, in phase C - for example; 1b1; ie, the output voltage is necessary, provided by phase-sensitive demodulators controlled by k1, -: mutator - distributor, which also sets the order of the generated and: stress voltage at the output of each phase. Instead of the largest one can be formed on the middle one (modulo; from the voltages of a three-phase symmetric voltage system (as shown in a) ig.1, in dashed lines). In this case, the third voltage is obtained by summing the voltages U (and Ua. Device contains I, 2 voltage drivers, transurers 3-5, key modulators 6-14, switch distributor 15. phase sensitive demodulators IC-I8 and master oscillator 19. To the outputs of two driver I and. ipspshy pbshchy POINT, and to the outputs of these drivers, which are not common, through the primary windings of transformers 3, 4. 5 connected modulators-keys 6-14 Switch-distributor 15 controls the driver g-sh I and 2, modulators-keys 6-14 and the phase-sensitive demodulators 16, 17, 18 connected to the secondary windings of transformers 3, 4, 5. A master oscillator .19 determining the frequency of the output voltage is connected to the distribution switch 15, the Formers I and 2 form voltage U and Uj (Fig.1,6, c), which are equal, respectively, the smallest it modulo and the largest absolute value of voltage three-phase symmetric system NAAL zheNII. In the interval 0-t, the voltage of the driver I is modulated and connected with the help of modulator keys 6 to the primary windings of the transformer 3, the voltage of the driver 2 is modulated and connected with 1. short wires to the key 10 to the primary windings of transformer 4, the voltage difference is two (1; normalizers I and 2 are modulated and connected by means of modulator keys 14 to the primary windings of the transformer 5; In the interval, the direction of the driver I is modulated and connected by means of modulator keys 12 to the primary transformers Ator 5, the driver of modulator 2 is modulated and connected with moduli keys 10 to the primary windings of transformer 4, the ionization difference between the two formers I and modulated and connected with modulators 8 to the primary windings of transformer 3. Thus, to the primary windings transformers are connected alternately the voltage of the formers I and 2 and their difference. On the secondary windings of transformers 3, 4, 5 modulated voltages are transformed (figl, d, e, e) which are deodulated by phase-sensing The demodulators 16, 17, 18 controlled by the co-mutator distributor 15 to obtain the desired polarity of the output voltage (for fIgL, G, d, e are solid smooth sinusoids).

In the particular case, a device for controlling a three-phase valve-frequency converter, in addition to the above-mentioned unipolar shaper sections of sinusoids, modulators, switch-distributor and phase-sensitive demodulators, is equipped with a three-phase transformer. , and the secondary windings are connected to phase-sensitive demodulators, the key modulators are controlled by a switch-distributor so that the primary windings are alternately de-energized. The formers are designed so that at any moment of time one of the generated voltages is equal to the smallest in modulus, and the other to the greatest in modulus of the voltages of a three-phase symmetric system of sinusoidal voltages. Instead of the largest one, it is possible to form a voltage that is an average (modulo) of

voltages of a three-phase symmetric system of sinus-halogen stresses; in this case, the moduli of the key switches must be connected so that the rod, whose primary windings are de-energized, runs through; magnetic flux, which is the sum of the magnetic fluxes of the other two rods. Then, on the winding of this rod, e, d, s, windings of the other two rods are output.

It should be noted that in order to obtain the desired polarity of the output voltage U /, OB "Uc (Fig. 2, d, e, e), you can not change the phase of the demodulator control signal, but change the phase of the control signal of the modulator keys,

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SUBJECT OF INVENTION

The method of forming a control voltage for a frequency converter from a unipolar voltage 5, followed by modulation and demodulation, is characterized in that, in order to improve the symmetry of the output voltage, two voltages are generated, one of which at any time

0 is the smallest in modulus, and the other is the greater in modulus of the voltages of the three-phase symmetric system of voltages, and the modulated voltages and their algebraic sum are alternately demodulated.

ig.1