SU1262626A1 - Device for increasing voltage quality of polyphase a.c.network - Google Patents

Abstract

The invention relates to the field of electrical engineering and can be used in secondary power supplies, which are subject to increased requirements for the quality of the output voltage. The purpose of the invention is to increase the efficiency of balancing multiphase mains voltages. With an increase in voltage at one of the phases, for example at phase A, the output of two integrators 15 and 17, whose inputs through the diodes 18, 20, 21, 23 are supplied with linear voltages corresponding to this phase voltage, appears constant component of negative and positive polarity, which changes the amplification factors of amplifiers 10 and 12. This leads to a change in the resulting capacitance of the filters of the respective Two phases, which causes a change in the current flowing through the inductors I and 3 installed in the phases, the voltage drops (L on which s decreases its voltage in phase A and increases in phase C. This causes a change in the d.c. negative polarity at the output of the integrator 16, which leads to povpieniyu voltage in phase B and phase symmetry voltages .. 2 yl. SH

Description

The invention relates to electrical engineering and can be used in secondary power sources that meet the requirements of the quality of the output voltage, in particular, can be used as a network filter for synchronous converter control systems.

The purpose of the invention is to increase the efficiency of balancing multiphase mains voltages.

FIG. 1 is a schematic diagram of the proposed device; in fig. 2 - diagrams on the operation of the device.

The device (Fig. 1) contains pos; and in the corresponding phases of the asymmetrical network are connected chokes -3, to the outputs of which are connected capacitors 4-6 of L-shaped LC filters connected in a star. Additional capacitors 7-9 are connected to the mains phases and the outputs of amplifiers 10-12 with coefficients and gains adjustable by inputs 13. Input 14 of each amplifier is connected to the corresponding phase of the network. The inputs 13 of the amplifiers are connected to the outputs of the respective integrators 15-17, the first inputs of which are connected respectively to phases A, B, C through the diodes 18–20 connected in the forward direction, and the second through the diodes 21–23 connected in the opposite direction, to the output of the subsequent phase filter

The operation of the device is illustrated by the diagrams shown in FIG. 2. Asymmetrical voltages ∆P,,, and, Up are passed through L-shaped LC filters, consisting of chokes 1-3 and capacitors 4-6. With variations in the parameters of chokes 1-3 and capacitors 4-6, the currents flowing through these elements are unequal, which leads to a different drop in voltage across chokes x 13 filters. The latter, even in the case of the Ideal symmetry of the supply voltages and, vi, and,, leads to the asymmetry of the voltages at the output of the filters UQ, Ir, Up. Only with real variations in the parameters of capacitors 4-6 the complex asymmetry coefficient introduced by the filters, defined by the formula

1/7 1aa

-y (VO (,) where

e

,/WITH,,".-,

1x) „- frequency of supply voltage

network,

reaches a few percent.

In general, the asymmetry is food-. ha; their voltages and ,, and ,, and, and introduced by the spread of filter parameters create an asymmetrical system of output voltages and, and, Uf (Fig. 2a). Consider the particular, but obvious, case when the asymmetry of the voltages of the phases a, b, c is manifested in the fact that the amplitude of one of them, for example, the voltage UQ, exceeds the tonal ones by a certain amount (Fig. 2a). In the absence of a neutral wire, some phase asymmetry is observed with this. The kesymmetric system of voltages and, and,, and through diodes 18-23 is applied to the inputs of the integrator (Fig. 2S-r) with the accepted character of voltage unbalance at the input of the integrator 15 and 5 and 1 are not equal in amplitude, due to which large integrator time constant T

t - 2TT

0

at its output is formed

constant component of voltage u, j. The input voltages of the integrator 16 are the same, so at its output of the integrator 17 there is a constant component of negative polarity.

The output voltages of the integrators are applied to the inputs 13 of the amplifiers 10-12 and change their gain factors. As a result, when the input voltage 13 of the amplifier 10 is positive, its gain factor k increases. The gain of the amplifier 1 1 to remains unchanged, and the gain of the amplifier 12

decreases. Coefficient change

amplification of the amplifier leads to a change in the equivalent capacitance c.

Claims (1)

chains consisting of series-connected additional capacitors Co 7-9 and outputs of amplifiers 10-12 in accordance with the formula c, c (l + k). With a change in c, the resulting capacitance Cp of the filter of the corresponding phase changes accordingly. In addition, an increase in the resulting capacitance of the Asr phase filter capacitors leads to an increase in the current through the choke 1 and an increase in the voltage across it, which leads to a decrease in the voltage and. At the same time, a decrease in the resultant capacitance of phase C leads to a decrease in the current through the inductor 3 and a slight decrease in the voltage drop, which does not lead to a corresponding increase in voltage and. The latter, in turn, (Fig. 2b) leads to the appearance of a constant negative polarity component at the output of integrator 16. This leads to a decrease in the gain of amplifier II and a decrease in the resulting capacitance of the phase B filter and, by analogy with the above, increases Uj .. As a result, the voltage and, a (,, goat Loop become the same, and the asymmetry factor is zero. The proposed device allows for a high degree of stress balancing at its output and can be successfully used as a network A filter that is frequency-invariant for supplying power to 26 synchronous semiconductor converter control systems. Formula of the Invention A device for varying the voltage quality of a multiphase AC network containing L-shaped LC filters in each phase, the capacitors of the parallel legs of which are interconnected in A star, characterized in that, in order to increase the efficiency of balancing multiphase mains voltages, it is equipped with three additional capacitors, three amplifiers having additional terminals for adjusting the gain, and three integrators, the input terminal of each amplifier connected to its output terminal through an additional capacitor and connected simultaneously to the output of the L-shaped IjC filter of the corresponding phase, the ground of the terminals of each amplifier connected to the connection point of the filter capacitors the additional input terminal of each amplifier is connected to the output of one of the integrators, while one of the inputs of the integrator is connected via a diode connected to the ohm direction corresponding to the output phase of the filter and another input of the integrator is connected via a diode connected in the reverse direction to the output of a subsequent phase filter. phi2.2