SU951192A1 - Digital meter of voltage symmetrical components in three-phase industrial network - Google Patents

Description

The invention relates to quality control of electric power supply systems.

A device is known that contains three transformers, three rectifier bridges with filters, a three-input functional converter that converts constant voltages proportional to the input voltages into an rms value from the differences, and registers at. boron fl 3.

The disadvantages of this device include a limited frequency range, the presence of a methodological error and insufficient functionality, since this device is designed to measure the component of the reverse sequence. It does not allow the measurement of all symmetrical components, and thus the coefficient of asymmetry.

The closest technical solution to the invention is a device containing a phase switch, an analog-to-code converter, a control unit, two multiplying devices, a sinusoidal function code setter, two reversible counters, a sign identifier, a phase shifting device, a quadrator, two recording devices, a dividing device, and zero organ C23

However, the known device can measure the symmetrical components of a three-phase network in industrial power supply systems under a steady load. Practically in electrical networks, there are always abrupt alternating and shock with non-linear load elements, which leads to a false response of a zero-organ. The latter circumstance leads to a change in the normal operation of the sign meter and, as a consequence, reversible counters. Their order of performing the operations of summation and subtraction is violated, which leads to significant measurement errors. Frequent abrupt alternating current surges in the electric network can lead to an uncertainty in the operation of the null organ and sign determinant, which causes a chaotic mode of operation of the reversible counters. Under such conditions, it is difficult to judge the reliability of the measurement results. In addition, the device does not allow measuring the harmonic spectrum of the components of a three-phase network, which is necessary when compensating for the asymmetry.

The purpose of the invention is the expansion of functionality.

This goal is achieved by the fact that in a digital meter of 5 symmetric voltage components in a three-phase industrial network, it contains a phase switch connected to an analog-code converter, a control unit, two multipliers, two counters, a sign identifier, a quadrator, a registration unit, a unit division and control unit, a scale converter, a memory unit, a read-only memory unit, 15 two multipliers, blocks for realizing the sine, cosine, arc tangent functions, two adder storage units and an adder, three in the meter’s running clamps are connected to the inputs 2θ of the scale converter, the three outputs of which are connected to the three inputs of the switch, the analog-code converter output is connected via the memory block to the first inputs of the second and third multiplier, the outputs of which ^{5 are} connected to the first inputs of the accumulator-accumulator blocks, the block output , control through series-connected counters is connected to the input of the control unit, the second output of the first 30 meter is connected to the first input of the first multiplier, the second input of which is connected to the second m output of the second counter, the second inputs of block adders-accumulators 35 and Bloch com register, the output of the first multiplier is coupled to inputs of blocks implement the cosine and sine trav-. and which are connected to the second inputs of the second and third multiplier 40, respectively, the output of the first block of the adder-accumulator is connected to the first inputs of the division unit and the quadrator, the output of which through the fourth multiplier is connected to the second input 45 of the recorder, the output of the second block of the adder-accumulator is connected to the second inputs a quadrator and a division block, the output of which through the block of realization of the arc tangent function, the sign determinant and the adder is connected to the third input of the recorder, the output of the control unit is connected to the switch rum, an analog-to-code converter, a memory unit, adder-storage units, a quadrator and a recording unit, and the read-only memory output are connected to the third input ^{, the} first multiplier, to the second input of the adder and the second input of the fourth multiplier, respectively.

The drawing shows a diagram of the meter. ^ν

The meter consists of a scale converter 1, a 2-phase switch, 65 analog-code converter (PAC) 3, a memory block 4, counters 5 and 6, read-only memory (ROM) '7, a multiplier 8, block 9 for implementing the cosine function, block 10 the implementation of the sine function of the multipliers 11 and 12, the blocks of the accumulators-accumulators 13 and 14, the quadrator 15, the multiplier 16, the control unit 17, the registration unit 18, the division unit 19, the arc tangent function implementation unit 20, the sign identifier 21, the adder 22.

The meter is based on the following considerations.

The investigated phase voltage can be represented as:

K and (t) = SZj U _m ^ si η (ku) t + 9Ok), (1) where is the amplitude and initial phases of the components of the spec ¹ network;

k = l, 2-k are the harmonic numbers.

Using a PAK, the input voltage U (t) is represented at M equidistant points.

The discrete Fourier transform of such a signal has the form m-1 —M ~

W2.W ^(g) or in a trigotometric form

Module and phase spectral density (3) is defined as k ^{= 5} / ^A to ^a ~ * '"

M ^ arctg, (5) k

where S4 and are the modulus and phase of the spectral density, respectively.

Then the amplitude value of the k-th harmonic is determined from expression (6) and the initial phase of the k-th harmonic can be represented as

Thus, in the block 18 registration values of the amplitudes and initial phases of the stresses of the harmonic spectrum for phases A, B, C of the following dependencies are recorded:

^and A (k) = Ufc _m s' ⁿ <kwt + 4 \);

953,192 ^U 6 ( ^k ) ^{= lJ} km ^s ' ⁿ

U £ (к) = и ^ _т 5 i η кu> (t + J) + and

iJimk Μ co It is known that harmonics of order multiple of 3 (.3,6,9, etc.) form a zero-sequence voltage system; harmonics of order k = W _n + 1, where η - any integer number, i.e., with k = 1,4,7,10,13, etc. form a symmetrical direct-sequence stress system;

finally, harmonics at k = 2,5,8,11,14, etc. form a symmetric system of negative sequence stresses. ·

Since in the proposed device, together with the values of U. ^^, and for each phase, the values of K are determined, then it is possible to measure the symmetrical components of the three-phase network.

The meter operates in two stages.

First stage. The phase voltage of the network through a scale converter 1 is supplied to a phase switch 2, 25 which, under the influence of the control unit 17, alternately connects them to the input of the PAK 3. In the converter 3, the analog code converts the analog value to a digital code, which is then written to the memory unit 4. The operation of the PAK 3 and the memory unit 4 is controlled by the control unit 17.

which then go to the adder-accumulator 13 and the adder-accumulator 14, respectively.

Thus, in the blocks of accumulators-accumulators 13 and 14, after the completion of the counter 5 cycle, the values of the real and imaginary parts of expression (3) are formed, i.e. A ^ and. The outputs of the adders-drives 13 and 14 are connected to the inputs of the quadrator 15, which is intended for squaring, summing and extracting the square root of the sum of squares. The output of the quadrator, where the S ^ value is generated, is connected to the multiplier 16. Here, the absolute value is multiplied by a coefficient that comes from the ROM 7. The output value of the multiplier is the amplitude value of the k-th harmonic and it goes to the recording unit 18.

To determine the initial phase • k-th harmonic of the output signals of the adders-accumulators 13 and 14 arrive at the dividing unit 19, which computes the value - A _h kotoI

Second phase. After filling the block 4 of the memory data, the meter goes into processing mode.

Clock pulses from the control unit 17 are supplied to the counter 5 of the current sample and the counter number b to the detected harmonic (formula 3). Counter 6 goes to the next state by the transfer signal of counter 5, i.e. after finishing the calculation of the current harmonic. The output codes of the counters 5 45 and 6, starting from zero values, go to the multiplier 8, where the ROM output of the 7th number is entered and the output of the multiplier 8 forms the value of the current argument of the sine and cosine functions, equal to ‘iJirnk (formula 3).

The signal from the output of the multiplier 8 is fed to the inputs of the block 10 for implementing the sine function and block 9 for the implementation of the cosine function, the output of which is then fed to block 20 for the realization of the arc tangent, the output signal of which is applied to the determinant 21 of the sign.

Depending on the specific sign of the phase of the spectral density Φ ^ in the adder 22, either the addition of the quantity with the quantity (£ coming from ROM 7 or the subtraction in accordance with formula (7) occurs. The output of the adder, which is the phase of the kth harmonic, is received to the registration unit 8. The control unit 17 synchronizes the operation of all the meter blocks. d in memory block 4. After this, the control unit proceeds to Stage 1. That is, the reception of new information begins. Counter 6 also resets the output code of drives 13 and 14 to zero after analyzing the next harmonic.

values are formed

Um to M

Q-iimk

Μ which enter the multipliers 12 and 60 11, respectively. At the other inputs of the multipliers 11 and 12, the current sample value coming from the memory unit 4 is applied, and the values 65 are formed at the outputs of the multipliers 11 and 12

The proposed digital meter, in contrast to the known one, provides increased accuracy, and can be used to continuously isolate the symmetrical voltage components of an industrial network, which significantly increases the efficiency and quality of measurements.

Claims (2)

phase network, which is necessary for the compensation of asymmetry. The purpose of the invention is the expansion of functional capabilities. The goal is achieved by the fact that in a digital meter of symmetric components of voltages in a three-phase industrial network, containing a phase switch, connected analog-code converter, control unit, two multipliers, two counters, sign determinant, quad, registration block, division block and a control unit, a scale converter, a memory block, a permanent memory unit, two multipliers, blocks implementing the functions of sine, cosine, arctangent, two blocks of adders and accumulators, and three in One meter terminals are connected to the inputs of a large-scale converter, three outputs of which are connected to three switch inputs, the analog-code converter output is connected to the first inputs of the second and third multiplier, the outputs of which are connected to the first inputs of accumulators-accumulators, the output of the block control through serially connected counters is connected to the input of the control unit, the second output of the first counter is connected to the first input of the first multiplier, the second input of which is connected to the second in the output of the second counter, the second inputs of the blocks adders-drives and the registration unit, the output of the first multiplier is connected to the inputs of the blocks of the implementation of cosine and sine, output-. The ports of which are connected to the second inputs of the second and third multipliers, respectively, the output of the first block of the accumulator adder is connected to the first inputs of the division block and the quadrator, the output of which is connected through the fourth multiplier to the second input of the recorder, the output of the second block of the accumulator adder and a division block, the output of which is connected to the third input of the recorder through the block of realization of the arctangent function, the determinant of the sign and the adder, the outputs of the control unit are connected to the switch Hur, analogue code converter, unit memory blocks for storage ring-adders, .kvadratorom and recording unit, and outputs constant memory coupled to a third input of the first multiplier, the second input of the adder and the second multiplier WMOs fourth house respectively. The drawing shows a diagram of the meter. The meter consists of a scale converter 1, a switch of 2 phases. Converter 3 analog-code (PAK), memory block 4, counters 5 and 6, permanent storage devices (ROM) 7, multiplier 8, junction box 9 for the cosine function, block 10 for the sine function of the multipliers 11 and 12, blocks adders- drives 13 and 14, quad 15, multiplier 16, control block. 17, a registration unit 18, a division unit 19, an arctangent function realization unit 20, a sign determiner 21, an adder 22. The following considerations are based on the meter operation. The phase voltage under investigation can be represented as: K U (t) U.j, sin (ku) t + 4Uk), (1) where. - amplitude and initial phases of the network spectrum components; , 2-k - harmonic numbers. With the help of PAK, the input voltage U (t) is represented at M equal points. The discrete Fourier transform of such a signal has the form or in the trigotometric form iM-S, () J S .. Z. and .COS W f The module and phase of the spectral density (3) are defined as follows: arctant where Si, and, is the module and the phase of the spectral density, respectively. Then the amplitude value of the k-th harmonic is determined from the expression and the initial phase of the k-th harmonic can be represented as n1. t-r) Thus, in block 18 of registration, the values of the amplitudes and initial phases of the harmonic spectrum stresses for the phases A, B, C of the following dependencies are recorded: I (); Ue (k) ka) (t- I) 4i, C () UvniSn kiu (t +) + 4 It is known that harmonics of the order of a multiple of 3 (.3,6,9, etc.) form a system of voltages zero sequence; harmonics on the order of k- 3 | + 1, where n is any integer, i.e. at, 4,7,10,13, etc. form a symmetrical voltage system of direct sequence; finally harmonics at, 5, 8,11,14, and so on. form a symmetric system of negative sequence voltages. Since, in the proposed device, together with the values and H for each phase, the values of -k are determined, it is thus possible to measure the symmetrical components of the three-phase network. The meter works in two stages. First stage. The phase voltage of the network through the scale converter 1 is fed to the switch 2 of the phases which, under the influence of the control unit 17, alternately connects them to the input of the ACK 3. In the converter 3 analog-code, the analog value is converted into a digital code, which is then written to the memory block 4. The operation of the PAK 3 and the memory block 4 is controlled by the control block 17. Second phase. After filling the block 4 memory data, the meter goes into processing mode. The clock pulses from the control unit 17 are fed to the sequentially switched on counter 5 of the current sample and the counter b of the defined harmonic k (formula 3). Counter b enters the next state by the transfer signal of counter 5, i.e. after the end of the current harmonic calculation. The output codes of the counters 5 and b, starting with zero values, go to multiplier 8, where you get the output ROM of the 7th number, and the output of the mind of the knife 8 generates the value of the current argument of the sine and cosine functions equal to (formula 3). M The signal from the output of the multiplier 8 is fed to the inputs of block 10 of the sine function realization and block 9 of the cosine function realization, at the output of which IJTrnV i llm, the values of - r; - and cos-J -; - JA I M are received at the multipliers 12 and 11 respectively. The other inputs of the multipliers 11 and 12 are applied to the current sampling value, coming from the memory block 4, and the outputs of the clever inhabitants 11 and 12 form the values "V, -, 4.", which then go to the accumulator 13 and the accumulator 14 respectively. Thus, in the blocks of accumulators 13 and 14, after the completion of the cycle of operation of the counter 5, the values of the real and imaginary parts of expression (3) are formed, i.e. A and B. The outputs of the accumulators 13 and 14 are connected to the inputs of the quad 15, which is intended for squaring, summing and extracting the square root of the sum of squares. The output of the quadrant, where the value of Sj is formed, is connected to the multiplier 16. Here, the absolute value of Sj is multiplied by a factor n, which comes from ROM 7. The output value of the multiplier is the amplitude value of the k-th harmonic and goes to the recording unit 18. For determining the initial phase of the ith harmonic, the output signals of the accumulators 13 and 14 are fed to the division block 19, where the calculation of the value -li- is made, which is then fed to the arc tangent realization block 20, TC to the determinant of 21 characters. Depending on the determined sign of the phase of the spectral density 4 in the adder 22, either the addition of the value of F with the value coming from the ROM 7 or the subtraction in accordance with formula (7) occurs. The output information of the adder, which is the phase of the k-th harmonic, arrives at block 8 of registration. The control unit 17 synchronizes the operation of all the units of the meter. The harmonic number counter 6 indicates on the registration unit 18 the number of the harmonic to be analyzed and on the control unit a signal that the analysis of the implementation of the signal recorded in memory block 4 is finished. After that, the control unit proceeds to the first stage, i.e. reception of new information begins. Counter 6 also resets the output code of drives 13 and 14 to zero state after analyzing the next harmonic. The proposed digital meter, in contrast to the known, provides increased accuracy, and can be used to continuously isolate the symmetrical components of industrial network voltages, which significantly increases the efficiency and quality of measurements. DETAILED DESCRIPTION OF THE INVENTION A digital symmetric voltage meter in a three-phase industrial network, comprising a phase switch connected to an analog-code converter, a control unit, two multipliers, two counters, a sign determinant, a quadrant, a registration unit, a division unit, and a control unit characterized by that, in order to expand its functionality, a large-scale converter, a memory block, a permanent memory block, two multipliers, and blocks implementing the functions of sine, cosine, arctangent, d The block of adders and accumulators, the three input terminals of the meter are connected to the inputs of the scaler, the three outputs of which are connected to the three inputs of the switch, the output of the analog-code converter is connected to the first inputs of the second and third multipliers, the outputs of which are connected to the first inputs of the accumulator accumulators, the output of the control unit through serially connected counters is connected to the input of the control unit, the second output of the first counter is connected to the first input of a second multiplier, the second input of which is connected to the second output of the second counter, the second inputs of the accumulator adders and the recording unit, the output of the first multiplier is connected to the inputs of cosine and sine realization blocks, the outputs of which are connected to the second inputs of the second. and the third multipliers, respectively, the output of the first block of the accumulator is connected to the first inputs of the division unit and the quadrator, the output of which through the fourth multiplier is connected to the second input of the recorder, the output of the second block of the accumulator of the accumulator is connected to the second inputs of the quadrant and the division block, which output through the implementation unit the arctangent functions, the sign determinant and the adder are connected to the third input of the recorder, the outputs of the control unit are connected to the switch, the analog-code converter, the memory block, Locks summatorovgnakopiteley, quad and recording unit, and outputs constant memory coupled to the third inputs of the first multiplier, a second input of the adder and a second input of the fourth multiplier, respectively. Sources of information taken into account in the examination 1. The author's certificate of the USSR 481859, cl. G 01 R 29/16, 11.05.73. 2. USSR author's certificate number 737882, cl. G 01 R 29/16, 21.02.77 (prototype).