SU1458926A1 - Arrangement for controlling a higher-harmonic filter in power supply system - Google Patents

Abstract

The invention relates to power engineering and can be used, but in industrial power supply systems containing loads with non-linear current-voltage characteristics (valve-driven electric, electrical installations, electrified transport). The aim of the invention is to reduce the loss of electrical energy. The invention makes it possible to improve the power quality by adjusting a high-harmonic filter, which provides the minimum value of the input resistance module of the power supply system external to the branch with non-linear load. To do this, in each control cycle, the quadrature components of the voltage harmonics on the non-linear load supply buses, the current harmonics in the power supply circuit of this load, and the current harmonics in the highest harmonic circuit are measured simultaneously. The total input impedances of the filter and the power supply system supplying the non-linear load are determined and the new reactive resistance of the filter is determined, calculated using the formula indicated in the description text. 7 il. easm bliB :::

Description

SD

00

one

The invention relates to electric power industry and can be used in industrial power supply systems containing loads with non-linear current-voltage characteristics (valve electric drive, electro-technological installations, electrified transport, etc.).

The aim of the invention is to reduce the loss of electrical energy.

FIG. 1 shows a simplified diagram of the power supply system; in fig. 2 is a replacement circuit; on. FIG. 3 is a functional diagram of the device for implementing the method; in fig. 4 - scheme of fixing analog signals; in fig. 5 is a diagram of a matching device; in fig. 6 is a control block diagram; in fig. 7 is a control signal driver circuit. The invention is explained as follows.

at

In accordance with the replacement scheme (Fig. 2), the total input resistance of the electrical network, external to the branch with non-linear load, at the harmonic frequency is

about

Tf; L с.л) - ф. with }

(ABOUT

Where

 impedance resonant filter;

L (.rc,; + JXj, is the impedance of the supply system.

The input impedance module at the frequency of the harmonic can be written as the following expression (index) omitted)

h

() (r -4-xl)

t; + g; 7 + tx; + hf7

(2)

If we determine the value of the reactance of the resonant filter (X,), at which the value of the input impedance modulus of the network external to the branch with nonlinear load is minimal at the harmonic frequency, then

x; l; (2r, r. + R + x jV4x r

- (2гггг- г х). (3).

Introduce the designation A 2gfgs + Gs + Xs, the formula (G) is defined as

x; -one- ().

(four)

The minimum of electric power losses in the filter elements and the power supply system takes place with a minimum value of the residual voltage level of the harmonic on the non-linear load supply buses.

In turn, the minimum value of the residual voltage occurs when the minimum input module is withstand of the entire electrical network external to the branch with non-linear load. Therefore, formula (4) determines the optimal filter setting.

From formula (4), it follows that in order to determine the desired value of filter reactance, it is necessary to know the impedance of the feed system.

Its value is conveniently obtained from /, the measurement results of the input impedance of the electrical network and the LOL resistance of the power filter in accordance with the formulas:

UK + JU

. ".

iri + jlj ..

Kn Uk + jUc

(5) (6)

where r xjx is active and reactive impedance components;

and. a pair of quadrature component harmonics, respectively, of the voltage on the supply buses of the non-linear load, the current in the power supply circuit of this load, and the current in the resonant filter circuit; Gf, X f - active and reactive

filter impedance components. Using (1), we obtain the components of the impedance of the supply system:

five

Xc 5 (X ,, / Gf / -Hf / L.U);

(Lf / -f / vm,

(7)

(eight)

0

0

AT

where B () + (). In these formulas

(L4 (M + xV,

where the components r and hf are obtained by measuring the values of voltage and current. In each control cycle, in accordance with the basic formula (4), a new filter reactance value is set.

A device for implementing the method (Fig. 3) contains a non-linear load current transformer 1, a voltage transformer 2 connected to a non-linear 5 load power bus, a current filter circuit current transformer 3, analog signal fixing circuit 4, a unit 5 controls, an analog-to-digital converter 6, a computing device 7, a power filter control signal generator 8 and a reactance control element 9 of the power filter 10, a non-linear load 11.

The device works as follows.

The signal from block 5, synchronized with the network via transformer 2, circuit 4 remembers the three (three)

0

five

instantaneous values of the signals that occur on the secondary windings of transformers 1, 2 and 3. After this, unit 5 generates three identical series of two pulses successively in time. The first is controlled by circuit 4, at the output of which the instantaneous value of the first of the three signals stored in the memory of circuit 4 appears (for example, the instantaneous value of the signal from the output of the transformer is 2, and B f the third is transformer 3). All of the processes described are cyclically repeated N times at regular intervals over a period of time in one period of the fundamental network frequency. As a result, 3N samples (samples) of three continuous analog signals are fed to the computing device during one period of the network frequency. The calculating device 7 produces counting samples up to 3N. After that, it calculates the quadrature components.

UK Uc,, ICH

TSF formula

discrete Fourier transform, i.e. ..

iv-t --liilli X (K) 1x (n) -e (9)

BY

where X (K) is the complex value of K.

harmonics;

x (n) is a sequence of equivalent samples (samples) of instantaneous values of a continuous curve (in our case, current or voltage); N is the number of samples per

one period of the curve; and

11- l ,, ... ji4, -J-I 1

in which samples of the corresponding curve are used instead of the numbers x (n). Then the calculating device 7 calculates the values of L

(and

and bf, respectively, according to formulas and (6) and the value of the desired parameter Hf according to formula (4). After that, the computing device 7 transmits the calculated value X to the input of the generator 8, which simultaneously performs proportional HF control of the controlled element of the power filter and generates a start pulse for unit 5. This pulse is the signal for the next cycle of the device to control the external harmonic filter

с14589266

in the power supply system. The next cycle is identical to the previous one. The control cycle durability with moderate demands on the speed of the computing device is 0.2-0.5 s.

Scheme 4 of fixing analog signals (Fig. 6) contains matching

0 devices 12, 13 N filters. frequencies, sampling-memory circuits 14 and analog switch 15. Device 12 consistency is needed in order to convert:

5 secondary current transformers 1 and 3 to a voltage that is more convenient for further processing.

The matching device is implemented according to the scheme of a1stitive transformer

0 current (Fig. 5). This circuit, consisting of a transformer TP and an op-amp operational amplifier, provides galvanic isolation and has a linear amplitude-phase-frequency characteristic in a wide frequency band. Low-pass filters 13 are needed to limit the spectrum of signals arriving at their inputs. Restriction is necessary in order to

0 eliminate errors due to the effect of superposition of frequencies upon further processing and calculating the quadrature components of a higher harmonic by the calculating device 7, Cp5 frequency for F filters 13 should be chosen from the ratio

FS2Vfc,

0 where fc.50 Hz is the frequency of the first harmonic of the network.

Scheme 4 fixation works as follows

The signal from block 5 work

5 of the circuit 14 and the instantaneous values are stored. Then, the control input of the analog switch from block 5 receives three signals in series, and the switch in turn passes the analog values to the output of circuit 4.

The control unit 5 (Fig. 6) contains a comparator 16, a multiplier I7 frequency, one-shot 18, logic gates And 19, 20, binary counters

5 21 and 22, triggers 23-25, button 26 and logic element OR 27. Comparator 16 is required to form square impulses at times of a petrol zero crossing voltage.

Frequency multiplier 17 multiplies the frequency of the input pulse sequence J generated at the first output clock signal with a frequency of N times the frequency of the network, and at the second output, the auxiliary pulse frequency sequence is greater than clock frequency, for example, 8. times (N is as before , the number of instantaneous values of the analog signal on the period of the main network frequency).

Block 5 works as follows.

The initial position of the block is set by pressing button 26. At the same time, trigger 23 through element 27 resets counter 2 to O, sets trigger 24 to a position in which it creates an enabling potential at the input of element 19, and prohibits the passage of pulses through element 19. When the button is released 23 generates a signal that permits the passage of pulses through element 9 and through element 27 generates a signal enabling the counter to be counted 21, Counter 21 counts the pulses to K, and counter 22 to the three. At the output of the one-shot 18, delayed pulses with a frequency of 8N take place. The first three pulses from this one-shot output, passing through elements 19 and 20J, change the state of counter 22, the code word of which controls the analog switch 15 and is the output signal of block 5. The overflow pulse of counter 22 changes the state of trigger 25 to the opposite , - which locks the element 20, prohibiting the passage of signals to the input of the counter 22. The trigger 25 produces a detuning for the passage of the next three pulses into the counter 22 only by the time of the next clock’s clock — output from the transmitter 17. O the bottom of the vibrator 18 with a time delay relative to each input pulse of the counter 22 generates pulses for starting the analog-digital converter 6,

After N clock pulses have elapsed, an overflow signal appears at the output of counter 21, changing the state of flip-flop 24 to the opposite. The trigger 24 locks the element 19 This completes one cycle of operation of block 5, the next cycle of operation

five

0

The block 5 starts when a pulse is detected at the input of the element 27 coming from the former 8. Thus, the button 26 is necessary only for the initial start-up of the block 5, and all further work is carried out automatically. Frequency multiplier 17 is designed as a phase locked loop (PLL) with a frequency divider in the feedback circuit.

As the computing device 7 can be used serial microcomputer or microcontroller.

The constructive implementation of the driver may be different depending on the design of the controlled reactance element 9 of the power filter.

The signal conditioner can be configured as shown in FIG. 7. The circuit contains a register 28, a digital-to-analog converter 29 and a power amplifier 30. Shaper works 25 like that. A signal 28 arrives at one of the data output lines of the computing device 7 (the same signal is the second output of the imaging unit 8 arriving at the first input of block 5), and a register 28 is activated. stores the code of the output word of the computing device 7. At the same time, this code is fed to the input of the converter 29, which converts it into analog voltage. The amplifier 30 is proportional to. It amplifies this voltage in terms of power (current) and, thus, regulates the magnitude of the inductive resistance of the 40

harmonics.

The proposed: method of controlling the high harmonic filter in the power supply system has the following

45 main advantages: .. the electric power losses are reduced due to the harmonic current in the filter circuit and in the elements of the system, which supply power to the non-linear: load; power quality rises as mini. The level of residual voltage of the harmonic on the non-linear load power buses is measured; the reliability of the filter is increased, which is due to a decrease in the non-sinusoidal voltage applied to the capacitor bank, and a decrease in the effective value of the non-sinusoidal current in the filter circuit.

thirty

35

50

91458926

Form u ;; l.; And iso-shadow where

A method of controlling a higher harmonic filter in an electrical supply system containing a non-linear load, which consists in controlling the reactance of a resonant filter, characterized in that, in order to reduce power losses, control is performed by identical independent cycles, and in each control cycle simultaneously quadrature components U, U of the harmonic voltage on the non-linear load power supply buses, quadrature components of the harmonic in the non-linear load power circuit and quadrature component yursche 1c, guar MONIKI..v current resonant filter circuits determined electrical impedance network external to the branches with a nonlinear load using the formula.

 Ux + jUc

-at

-

ten

active and reactive impedance components;

and impedance of the resonant filter by the formula

p -i; 7n:

,

where gf, hf is active. and reactive

composes the filter impedance, and sets the new value of the reactive resistance of the resonant filter to the one calculated by the formula

x; (/ GYh 4-A),

where B (r4x-r, j) ()

Hc with Yo (GVH

,

one,..

A 2g GS + GSHs

fiAtr yar, harmonics.

figure 1

1458926

Input resistance of the power supply system

Pitanland wednesday

K trannorornatar K troms1rormat) p2 K tratss (rornator

5

Claims (2)

A method of controlling a higher harmonic filter in a power supply system containing a non-linear load, namely, that the reactance of the resonance filter is different, characterized by gem, which, in order to reduce losses - [θ of electric power, is controlled by identical independent cycles, and in each control cycle simultaneously measured quadrature components U _K, U _c jg harmonic voltage busbar power of nonlinear force, quadrature components I _m, 1 _cN harmonic current in the circuit of the nonlinear power n Booting, quadrature components _K 1 f, guar Stream 20 moniki..v resonant filter circuit, determine an impedance electrical network, external to the branches with a nonlinear load of formula 25 ₌ Uk + jUc _ 2P “+ P _SN T ^g ” * ^ΰΛ 8 * 'where r _6K , X _gJf - active and reactive components of the input impedance; ΰ = / - ϊ7 and the total resistance of the resonance filter according to the formula _m _ Uk + JUc * -r _k ; + l :; = Γφ + _ν 1Χφ, where Γφ, Χφ are the active and reactive components of the filter impedance, and a new value of the reactance of the resonant filter is set equal to that calculated by the formula Xf = ₂ 1- (7n ^g + 4X ^ 4-A), where B = (g » _x -Γφ) ¹ + (Χ _ίχ -Xp) ¹ ; X _c = 1 (X _6x / bp / ^ - Xp / ^ / ² ); c = ^g / L ^ / ² -Gf / L _/ ^d); A = 2tfH _s + GcHc