SU1347036A1 - Device for measuring frequency characteristics of industrial electric mains - Google Patents

Abstract

The invention relates to a pulse technique. A device for measuring the frequency response of an industrial electric network contains a nonlinear load 1, a multiplier 3, a shaper of 4 pulses of the mains frequency, a controlled pulse generator 5, a shaper of 6 quadrature signals, a synchronous quadrature detector 7 and a recording unit 8. The device improves accuracy measuring the frequency response of the circuit. 2 hp f-ly, 8 ill. Network 1 (LC, 15 CO 42: O with Pha9.3

Description

The invention relates to a pulse technique and can be used to study the frequency characteristics of the input impedance of the power supply systems of industrial enterprises.

The purpose of the invention is to simplify a device for measuring the frequency response of an industrial electrical network.

Fig. 1a shows an equivalent replacement circuit for the network under investigation in Fig. 16 — a network replacement circuit at a measurement frequency; Fig. 2 is a timing diagram of the formation of the modulating signal; on fig.Z - functional diagram of the device; 4 is a circuit diagram of a multiplier; Fig. 5 is a schematic diagram of a quadrature signal driver; figure 6 is a functional diagram of the synchronous HOi o quadrature detector; 7 is a timing diagram of the output signals of the quadrature face shaper; Fig. 8 is a functional circuit of the voltage converter - voltage.

 The proposed device, in contrast to the known, has a single-channel structure of the measuring part, i.e.

By means of a voltage channel including a voltage converter - voltage, a synchronous quadrature detector and a recording unit, only the measuring component of the voltage in the network node under investigation is analyzed. By analyzing this component, the complex frequency response of the input impedance of the network can be measured with high accuracy (tenths of a percent).

Figure 1a shows an equivalent circuit for replacing the network under study at an arbitrary measurement frequency S. The electrical network being analyzed with respect to the branch with non-linear load R (t) can be represented as a equivalent source of sinusoidal voltage E, frequency-dependent resistance Z.

Fig. 16 shows the replacement circuit of the network under study at the frequency of the measuring signal, where the non-linear load is replaced by an equivalent current generator Igg with internal resistance Kd, and the input resistance of the network at the measurement frequency Zc.

The magnitude of the current 1 and the resistance R are determined mainly by the magnitude of the voltage U at the network node under study (Fig. I a) and the law of variation of the non-linear load conductivity g (t) l / R (t).

In practical measurements, the nonlinear load power is much less than the short circuit mode in the network node under study, or, equivalently, the R value is much larger

The network impedance module at the main network frequency. This is due to the following reasons. The input impedance of the network is preferably measured at frequency intervals located between the frequencies of the neighboring harmonics, where the main noise of the electrical network takes place. To generate a sufficiently useful level, i.e. measuring signal at the indicated frequency gaps requires a non-linear load with a power several orders of magnitude smaller than the short-circuit power at the network node under study. In addition, the required non-linear load power also depends on the sensitivity of the measuring part of the device for measuring the frequency response of the electrical network. In order to separate out the measuring signal against the background of the yoBi-no components of fundamental frequency and harmonics of the network, the measuring part, as a rule, contains a synchronous filter (or a device similar in characteristics) that is characterized by high selectivity with

the ability to adjust its tuning frequency over a wide range. In addition, such filters are highly sensitive. So, their sensitivity reaches

120 dB, i.e. a signal can be filtered, the amplitude of which is ten times smaller than the level of the other harmonic components of the signal being studied,

the sensitivity of the measuring part should be 140-150 dB (for example, by pre-suppressing the fundamental frequency component of the network, followed by amplification of the resulting signal). However, such a high sensitivity cannot be realized due to the fact that the network noise level is about 10 (80 - 100 dB),

and, therefore, the level of the measuring signal must exceed the specified value of the noise level. Thus, the required power of the non-linear load, and hence the required value of the ratio Hp / iZ I, is approximately equal to

, Yu - (1)

 to measure current component

I (Fig. 1b), leaked; its equivalent network resistance Z at the measurement frequency S is equal to

R s so o (2)

OS

so, as the network input impedance module at the measurement frequency is also much less than the nonlinear load resistance R.

According to practical research, in industrial power supply networks, the highest value of network resistance is within the frequency range 50, which is the voltage channel, which is used to analyze the measurement component of the voltage, which is sufficient to measure the complex frequency response of the industrial impedance electric network.

In the proposed device, ka

10 in a known manner, a non-linear load is used, comprising a successively connected resistive load electronic key. In a special way, the generated pulse mode

15, the modulating signal controls the state of the key, as a result of which the non-linear load being conducted changes according to a law that coincides with the modulating signal. Time

20, a diagram explaining the process of the modulating signal is shown in FIG.

The base voltage voltage of the fundamental frequency of the network with an arbitrary

Uu, 31П (-ХХ),

2000 Hz, i.e. the pole of the frequency characteristic phase 25 (fig. 2a) is equal to the resistance characteristic with the highest: the resistance practically does not exceed the value (10 - 20) Z.

Thus, the approximation (2) with regard to (1) is valid with high accuracy.

In the proposed device, in contrast to the known, there is no current measurement channel, namely, the measuring component 1. However, in the proposed device there is a signal in phase with current I (Fig. 16). As follows from (2) with regard to (I), the phase of current I also coincides with high accuracy with the phase of current 1, and, thus, the specified in-phase signal can be used to measure the impedance angle of the network Zg at an arbitrary measurement frequency S .

According pig and the relation (1) we have

45

where is the voltage amplitude of the mains frequency. As a result of the selection of this next node of the network, which receives voltage from the spectrum, it receives which phase error dC (Fig. 26):

and sin (2 jia) t + 4 + ah).

Its amplitude in this case does not matter and is equal to one (ind This signal is used to form a modulating signal of a non-linear load.

Let a certain sinusoidal signal be used to control the frequency of the measuring signal with an arbitrary frequency S and phase

and.

sin (23 (St + 45).

As a result of the multiplication, the signals (FIG. 26, c) can receive a signal and (FIG. 2d) having two pressing with frequencies S + OL) and S-u 1 2

7 R tt t f-j t 7

 R + Zs.

(3)

so

Consequently, the amplitude of the measuring component of the voltage Uj and its phase shift relative to the current I with high accuracy (tenths of a percent or less) describe the network impedance at the measurement frequency S.

Thus, the single-channel structure of the measuring part, i.e. the presence of a voltage channel only, by means of which the measuring component of the voltage is analyzed, is sufficient to measure the complex frequency characteristic of the input resistance of an industrial electric network.

In the proposed device, as well as

in a known manner, a non-linear load is used, comprising a series-connected resistive load and an electronic key. In a special way, the generated pulse modulating signal controls the state of the key, as a result of which the conductivity of the non-linear load changes in time according to a law that coincides in shape with the modulating signal. A timing diagram explaining the process of forming a modulating signal is presented in FIG.

The mains voltage of the main frequency of the network with a random onU, 31P (-ХХ),

initial phase H (figa) is equal to

(four)

where is the voltage amplitude of the main network frequency. As a result of the separation of this component from the voltage spectrum in the network node under study, it receives some phase error dC (Fig. 26):

and sin (2 jia) t + 4 + ah). (five)

Its amplitude in this case is irrelevant and equal to one (index. This signal is used to form the modulating signal of a non-linear load.

Let a certain sinusoidal signal with an arbitrary frequency S and phase 4j be used to control the frequency of the measuring signal:

and.

sin (23 (St + 45).

(6)

As a result of multiplying the signals (Fig. 26, c), a signal can be obtained and (Fig. 2d) having two components with frequencies S + OL) and S-u): 1 2

and.

iG

4 {cosl2ir (S-u)) t -% - t-4-AV

(S + uJt- -4 + tf.

(7)

From the received signal (Fig. 2d) a sequence of pulses is formed (Fig. 2d), in the spectrum of which, besides the high-frequency components, there are also components with frequencies S-tOn S + u) according to (7), this pulse sequence is modulating signal nonlinear load. When a non-linear load is connected, the conductivity of which in time has the form (Fig. 2d), which takes only positive for

 С „and, Gj - I (S-2cJ) t - -2, + I sint2Ji (St-2a)) t + 2tf + yg + + I sin (.. V cos.4 r. I,. ,, - ,, (eight)

where i

the main components of the current nonlinear load;

: ,,:: I

 + 2ix

current components, respectively, with frequencies S-2a), S + 2a, S; GO - constant coefficient

having dimensionality of conductivity-. From (8) it follows that the component

current

,

Ig coincides in phase with the signal (G (6), by means of which the frequency of measuring the resistance of the network is specified, and, therefore, the signal U can be used to read the angle of resistance H (with Zg

- IZ,.

Thus, if the non-linear load conductance g (t) l / R (t)

(fig.la) varies in time with the law having the shape of a curve (fig.2d). shifted to the region of positive values, the signal U used in the formation of the modulating signal (fig.2d) of the nonlinear load R (t) , in phase with the measuring component of the current (Fig. 16), where -r-ok Tj (jecTb too, as the current 1, t ,,; However, since taking into account (2) U

Z

Iso

SO

TO complies

 - 1U)

-y-y

so

-so

COSH, -fj

so

(9)

- the amplitude of the measuring component of the voltage.

But com I

toSO

IU is component and proportional

 Conveniently have in-phase with

active component R of the input impedance of the network at the frequency. Accordingly, lUji-sin, is quadrature relative,

as well as u, the component voltage is proportional to

In this case, the non-sinusoidal current flowing through the non-linear load will have dominant components caused by the multiplication of the side-frequency components R + u) and S-uj (7) with the voltage (3) of the main network frequency):

reactive component Xj of the desired resistance of the network Z, From here

s

20

25

thirty

35

40

45

50

55

iUsL t

J V.

SO

Conscious

 x sin 4- ,, RS + jXs.

(ten)

Thus, the amplitude of the measuring component of the current I (8) depends on the phase error angle & if (5) and - (FIG. 2) and, therefore, this error should be properly compensated (i.e. it is necessary to provide soy, and correspondingly ).

In the proposed device, the modulating signal of a nonlinear load is formed from two pulse sequences having the form of a meander. One of them is formed from the filtered and phase-adjusted voltage of the main network frequency (indicated in dotted lines in Fig. 26), and the other is formed by a quadrature signal generator, to the input of which a controlled frequency generator output signal is supplied. As a result of the multiplication of these signals (sequences of pulses) by the multiplier, the output signal of the multiplier is shown in Fig. 2e and is used as a modulating signal of a non-linear load. The above analysis (expressions (4) - (8)) describes the transformation of the main harmonics of the indicated pulse signals. The injection (filtering) of the in-phase and quadrature components of the measuring signal in the voltage spectrum of the network node under investigation is carried out by means of a synchronous quadrature detector controlled by a pair of pulse signals connected by a quadrature ratio. At the corresponding outputs of the synchronous quadrature detector, constant voltages are proportional to the active and reactive components of the input impedance of the network. These voltages can be measured, for example, by means of a voltmeter included in the recording device. Using the parameters of the nonlinear load and the magnitude of the voltages in the network node under study, the absolute values of the components of the sought resistance of the network, as well as its module and phase (angle) can be determined.

The device (FIG. 3) contains non-linear load 1, converter 2 voltage - voltage, multiplier 3,

The shaper of 4 pulses of the frequency of 20 l 16 is connected via a switch 21 (C), the controlled generator 5 of the pulse is a common point of the circuit, the control input of the coppers, the driver of 6 quadrature switches of the 21 (C) is connected to the output of the input signals , a synchronous quadrature converter 20, whose input is a vector 7, a recording unit B, a driver 9, a phase correction unit 10 and a network frequency filter 11, a rejection filter 12 and an amplifier 13. Nonlinear load 1 contains resistive connected series 14 (R) and power switch 15

the second input of the multiplier 3.

Shaper 6 quadrature signals (figure 5) contains the first 22 and second 23 D-flip-flops and inverter 24. The synchronization input of the first D-flip-flop is connected to the input of the inverter 24 and is inserted into the first input of the shaper 6 d-quadrant signals. The inverse output Q of the first D-flip-flop 22 is connected to its data input, and the direct output Q is connected to the data input of the second

30 is the first input of a 6 dwatt signal generator. The inverse output Q of the first D-flip-flop 22 is connected to its data input, and the direct output Q is connected to the data input of the second D-flip-flop 23 and is the first output of the quadrature signal generator 6. The output of the inverter 24 is connected to the synchronization input of the second D-flip-flop, the direct output Q of which is (K).

Nonlinear load 1 connected

one output with the network node under study, and the other with the earth bus. The input of the voltage converter 2 is the voltage connected to the network node under study, and the output is connected to the third input of the synchronous quadrature detector 7 and the input of the driver 4 of the network frequency, the output of which 40 is connected to the second output of the driver four connected to the first input of the multiplier 3 whose output is connected with power switch control input 14

Routine signals.

The synchronous-quadrature detector 7 (FIG. 6) contains two identical pi circuits containing series-connected shreds 25 (K), a resistor 26 (R) and a capacitor 27 (C), the free terminal of which is connected to the common point of the circuit. The free pins of keys 25 (K) of the quadrature detector 7, the outputs of a 50 IOT common connection point, which are connected to the inputs recorded by the third input of the synchronous

quadrature detector, and the control inputs of the keys 25 (K) are the first and second inputs of the synchronous

(K) nonlinear load 1. The output of the controlled generator of 5 pulses is connected to the input of the former 6 quadrature signals, the first and second outputs of which are connected to the corresponding inputs, synchronous

common block 8; the second input of the multiplier 3 is connected to the first output of the quadrature signal generator 6.

Shaper 4 impulses frequency gg quadrature detector. The common points of the network (FIG. 3) contain a series of connections of the resistor 26 (R) and the connected frequency filter 1I of the sensor 27 (C) of both circuits, phase correction block 10 and for- mats with synchronous quadrature outputs - the globalizer 9, the output of which is an e-detector 7.

with the output of the mains frequency pulse generator, and the input of the mains frequency filter is the input of the mains frequency pulse.

The multiplier 3 (FIG. 4) contains an operational amplifier 16, resistors 17-19 (R), an inverter 20 and a switch 21 (C). The common connection point of resistors 18 and 19 (R) is the first input of the multiplier, other outputs of resistors 18 and 19 are connected respectively to the inverting and non-inverting inputs of the operational amplifier.

16, the output of which is the output of the switch {3, and connected via a resistor 17 (R) to the inverting input of the operational amplifier 16; the non-inverting input of the operational amplifier 16 is connected via a switch 21 (C) to the common point of the circuit; the control input of the switch 21 (C) is connected to the output of the inverter 20, whose input is

the second input of the multiplier 3.

Shaper 6 quadrature signals (Fig. 5) contains the first 22 and second 23 D-flip-flops and the inverter 24. The synchronization input of the first D-flip-flop is connected to the input of the inverter 24 and is the first input of the shaper 6 of the wedding signals. The inverse output Q of the first D-flip-flop 22 is connected to its data input, and the direct output Q is connected to the data input of the second D-flip-flop 23 and is the first output of the quadrature signal generator 6. The output of the inverter 24 is connected to the synchronization input of the second D-flip-flop, the direct output Q of which is the second output of the quadrature shaper.

913

Voltage converter 2 - voltage (Fig. 8) contains a wideband transformer 28 and voltage follower 29, the high voltage inputs of the voltage converter - voltage being the outputs of the primary winding of the wideband transformer 28, and the secondary winding is connected to a common terminal point of the circuit, another output of the secondary winding is connected to the input of the voltage follower 29, the output of which in the output of the voltage converter is voltage.

The device works as follows.

After turning on the power source, the controlled pulse generator 5 (Fig. 3) generates square pulses that are fed to the input of the quadrature signal generator 6, at the output of which a periodic signal is generated.

from the first and second outputs of the formiros with the following frequency S, interconnected by the quadrature ratio. The pulse signal from the first output of the quadrature signal generator is fed to the second input of the multiplier 30 of the body 3. The first input of the multiplier 3 receives a bipolar sequence of pulses formed from the network frequency voltage by means of the driver of the 4 network frequency pulses. As a result of multiplying the pulse sequences arriving at the inputs of multiplier 3, our output will have a pulse sequence (fig.2d), containing 40 dominant components with frequencies S + CO and S-CO (7). The pulses from the output of the multiplier 3, the key state control 15 (KN) nevotel 6 quadrature signals, respectively, in-phase and quadrature signals. As a result of the flow of current I, the measuring component of the voltage arises in the network node under study

and.

35

„1 UsI sin (2llSt + 4 U, X X sin (St + H),

where is izsi

(12)

input impedance module at frequency; and "" is the amplitude of the voltage measuring component; network resistance angle at frequency S.

The voltage in the network node under study, through the voltage converter 2 - the voltage goes to the third input of the synchronous quadrature detector,

am

torus 7. Elementary RC integrators

.. 26 (Yu and 27 (About the synchronous quadrature detector 7 (Fig. 6)), at its respective outputs, constant voltages proportional to the amplitudes of the in-phase and quadrature components of the voltage U. (12). Blue conductivities of a non-linear load according to the law which has a waveform (Fig. 2d) that is shifted to the region of positive values relative to the time axis. As a result of multiplying the line frequency voltage (4) in the node under study and the nonlinear load conductivity I, a non-sinusoidal current is generated, which dominate orogo have frequencies

S + 2t "i, S-2a) and S according to (8). Composition T1CH

50

the phase signal controlling the state of the key 25 (K) at the first input of the synchronous quadrature detector 7, causes a constant voltage at the corresponding output equal to

I

Uj sin (2JiSt + 4.j),

S

ten

A current with a frequency S is used as a measuring component in the process of measuring the frequency response of the network.

The measuring component of the current of the nonlinear load 1 with the frequency S is in phase with the pulse sequence supplied to the other input of the multiplier 3, i.e. The measuring component of the current has the same phase as the first harmonic of the pulse sequence from the first output of the 6 quadrature signal generator (Fig. 76).

Let the measurement component of the current with frequency S be

Is where 1 „- amplitude

current supply

and its phase shift relative to the pulse sequence from the first output of the quadrature signal generator 6 is zero. Let's call the signals

2Mst (11) measuring co0

O 0

A rotary 6 quadrature signals respectively in-phase and quadrature signals. As a result of the flow of current I, the measuring component of the voltage arises in the network node under study

and.

five

„1 UsI sin (2llSt + 4 U, X X sin (St + H),

where is izsi

(12)

input impedance module at frequency; and "" is the amplitude of the voltage measuring component; network resistance angle at frequency S.

The voltage in the network node under study, through the voltage converter 2 - the voltage goes to the third input of the synchronous quadrature detector,

am

The horizontal detector 7 (Fig. 6) at its respective outputs exhibits constant voltages proportional to the amplitudes of the in-phase and quadrature components of the voltage U. (12). Syn

a phase signal that controls the state of the key 25 (K) at the first input of the synchronous quadrature detector 7, causes a constant voltage at the corresponding output equal to

(13)

Taking into account (12), we obtain Uc4.Isn. IZsl; Cos 2 Isn, RS.

where is the active component of the input impedance of the network at frequency S.

ST / 4

    T / 4 sin (25fSt-if) sin4, I X,, (15)

where X - is a reactive component

input impedance of the network at frequency S.

The constant voltages allocated at the output of the synchronous quadrature detector are fed to the input of the recording unit 8.

Thus, by changing the frequency of the controlled generator 5 pulses, the frequency dependences of the active and reactive components of the input resistance of the electrical network under study can be measured. According to the measurement results, the frequency characteristics of the module and the angle of the sought resistance of the network can be constructed.

The accuracy of measuring the frequency response of the network can be improved by introducing into the device additionally connected in series notch filter 12 and amplifier 13 (FIG. 3) connected between the output of the voltage converter 2 - voltage and the input of the synchronous quadrature detector 7. The notch filter 12 is implemented suppression of the maximum amplitude component of the fundamental frequency of the network in the voltage spectrum of the network node under investigation. The amplifier 13 provides amplification of the remaining spectral components up to. the dynamic range of the input voltages of the synchronous quadrature detector 7 and, accordingly, increases the level of the measuring signal at the input of the block 7.

Thus, by introducing the notch filter 12 and amplifier 13, the signal-to-noise ratio at the input of the synchronous quadrature detector 7 is increased, and thus the accuracy of measurements of the frequency response of the network is increased.

Thus, the in-phase component of Ugq, the voltage of the measuring signal U is proportional to the active resistance of the network.

The quadrature component U of the KS measuring signal is

Claims (3)

1. A device for measuring the frequency response of an industrial electrical network, comprising a controlled pulse generator, a recording unit, a pulse frequency network driver, a multiplier and a nonlinear load, one of which is connected to the earth bus and another to the network node under study and the input of the converter voltage - voltage, the control input of the nonlinear load is connected to the output of the multiplier, the first input of which is connected to the output of the mains frequency generator, characterized in that, for the purpose of simplification, The quadrature signal former and the synchronous quadrature detector are configured, the output of the controlled pulse generator is connected to the input of the quadrature signal generator, the first and second outputs of which are connected to the corresponding inputs of the synchronous quadrature detector, and the first output of the quadrature signal former is connected to the second multiplier input, the output of the converter voltage - the voltage is connected to the input of the mains frequency pulse generator and the third input synchronous quadrature detector, the outputs of which are connected to the inputs of the recording unit. 50 2. The device POP.1, which is different from the fact that the driver of the frequency of the network frequency contains a network frequency filter connected in series, the phase correction unit and gg the driver, the output of which is the output of the driver of the frequency of the network frequency, and the input of the filter mains frequency is the input of the mains frequency pulse generator. 13 3. The device according to n.lj is different in that, in order to measure the measurement accuracy, a notch filter and an amplifier are additionally introduced, and the output of the voltage converter is the voltage of the connection 13D7036 It is connected with the input of the pulse frequency generator and, through a series-connected notch filter and amplifier, is connected to the third input of the synchronous quadrature detector. 1 "A (.,. Srrrirrr Phage.2 Vmd f / f block 6) 5 Input 3 (to §2 (13) t-- x: 7 Exit 1 € (to jioKi / 8) ig.6 rlH ST / if 5G / Y Fy entrance IK researched d§l network)