RU2368909C1 - Metre of harmonic signal parametres - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention is related to electric measurement equipment and is intended for measurement of amplitude, difference of phases and frequency of harmonic signals in different systems, where high efficiency is required, for instance in systems of automatic control. Device consists of squaring circuit, three units of sliding averaging, two linear converters, circuits of square-rooting, clock oscillator, counter of binary pulses, comparator, two multipliers, divider, circuit of nonlinear limitation, trigonometric unit and channel of current amplitude measurement.

EFFECT: reduced time delay from the moment of pickup of discrete counts of inlet signals till production of result (1/4 period), higher accuracy of measurement of difference of phases between current and voltage and possibility to perform assessment of AC parametres with presence of phase and amplitude noise and high order harmonics.

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Description

The invention relates to electrical engineering and is intended to measure the amplitude, phase difference and frequency of harmonic signals with the continuous output of information in stationary modes and during transients, where increased measurement accuracy is required. The invention can be used, for example, in automatic control systems for the excitation of electrical machines for measuring amplitudes of voltage and current, frequency and phase difference between them.

During a short circuit, the measured voltage and current signals are enriched with higher-order harmonics that are multiples of the fundamental frequency, amplitude and phase noise, and a slight deviation from the nominal value is also observed. It is possible to reduce time and reduce voltage surges during the transient process by automatically regulating the excitation of an electric machine by reducing the time it takes to measure the parameters of the input signals (current, voltage, and phase difference).

Currently existing devices for measuring the parameters of low-frequency harmonic signals have a disadvantage, which is significant for the automatic control equipment time delay from the moment of measurement to the issuance of information (0.5-1 period of the measured signal), which reduces the efficiency of their operation, especially during transient conditions, for example network short circuit.

It is known "Device for measuring the amplitude of the signal" (RF patent No. 2280877 from 12/20/2004) of the same purpose as the proposed one, but not having common features with it and consisting of a reference voltage generator, two quadrators, three multipliers, eight integrators, a control unit , computing unit and indicator. Signals generated by the first five integrators are fed to the computing unit, the results of integration of the orthogonal components of the reference signal and the result of integration of the measured signal during the measurement are additionally used, these signals are generated by the sixth, seventh and eighth integrators, respectively. The disadvantage of this device is the large delay in the issuance of the measurement result (for one period of the input signal). The task of measuring the phase difference between current and voltage is not posed or solved; the device loses performance when the frequencies of the reference oscillator and the input signal are mismatched.

The known device "Digital phase meter" (RF patent No. 2207579 from 01/11/2002), which does not have common features with the proposed, but with a similar purpose, consisting of a two-channel converter phase shift - time interval, element "2I / OR", the first element “And”, counter, comparison unit, switch, computing unit, shaper, timing unit, pulse shaper of the end of the first measurement, buffer register, quantizing pulse generator, second element “I”, pulse shaper of the end of the second measurement, ele delay time, the first OR element, RS-trigger, the second OR element, the counter of the number of measurement cycles. The disadvantage of this device is the low accuracy of phase measurement in the presence of additive noise, which is due to the use in this device of a method for determining the phase difference, which consists in measuring the duration of the intervals between the zeros of the input signals.

The known "Device for measuring the amplitude and phase characteristics of harmonic signals" (RF patent No. 2089919 from 05.20.94), which does not have common features with the proposed, but with a similar purpose and consisting of a second division unit, a shaper of control pulses, the first sampling and storage unit , the second sampling-storage unit, the adder, the unit for extracting the square root of the sum of the squares of two values, the first switch, the first division unit, trigonometric converter, the second switch, the unit tions. The disadvantages of this device is the low accuracy of measurement up to the complete impossibility of operation in the presence of phase and amplitude noise in the input signal and harmonics of multiple frequencies, due to the fact that the latter actually performs an instant estimation of the parameters of the input signals; the problem of determining the amplitude is not posed or solved.

The essence of the invention is a device for continuous measurement of the amplitude of the current, voltage and phase difference between them, the algorithm of which is based on estimating the energy and the mutual correlation function of the input signals generated over a half period. The presence of continuously produced integral estimates makes it possible to minimize the influence of additive and phase noise and multiple higher-order harmonics arising from transients in power systems on the accuracy of measuring informative parameters. The frequency of the result is determined by the sampling frequency of the measured signals.

периода), повышении точности измерения разности фаз между током и напряжением и возможности производить оценку параметров переменного тока при наличии фазового и амплитудного шума и гармоник высших порядков.The technical result achieved is a significant reduction in the proposed device time delay from the moment of taking discrete samples of the input signals to the output of the result in comparison with the known solutions (

period), increasing the accuracy of measuring the phase difference between current and voltage, and the ability to evaluate AC parameters in the presence of phase and amplitude noise and higher-order harmonics.

A comparative analysis with the listed meters shows that the proposed device is characterized by the presence of new elements: series-connected squaring circuits, the first block of moving averaging, the first linear converter and the square root extraction circuit; a series-connected clock, a binary pulse counter, a second block of moving averaging, a second linear converter, as well as a comparator, the output of which is connected to the reset input of the binary pulse counter; connected in series to the first multiplier, the third block of moving averaging, the divider, the nonlinear limiting circuit, the trigonometric block, and the second multiplier, the output of which is connected to the input of the divider of the divider, and the inputs are connected to the outputs of the channels for measuring the voltage and current amplitudes, respectively, as well as to a constant source quantities α, where α = 2; the first, second and third blocks of moving averaging consist of an adder and two delay lines, the first input of the adder connected to the input of the first delay line, the output of the adder connected to the input of the second delay line, and the outputs of the first and second delay lines connected to the second and third inputs of the adder respectively, the second input being inverse.

Therefore, the device meets the criterion of "novelty."

Comparison with other technical solutions shows that the performance is doubled and the noise immunity of the device is significantly improved with respect to harmonics of multiple frequencies, amplitude and phase noise in the input signals.

The invention is illustrated by the following graphic material:

figure 1 is a General functional diagram of the meter parameters of the harmonic signal;

figure 2 is a structural diagram of a block of moving averaging.

The device consists of four channels (Fig. 1): a channel for measuring the amplitude of the voltage, a channel for measuring the frequency, a channel for measuring the difference in phase of the current and voltage, and a channel for measuring the amplitude of the current.

The channel for measuring the voltage amplitude consists of series-connected squaring circuits 1, the first block of moving averaging 2, the first linear converter 3 and the square root extraction circuit 4. The channel for measuring the current amplitude 16 is similar to the channel for measuring the voltage amplitude. The phase measurement channel consists of a series-connected first multiplier 10, a third block of moving averaging 11, a divider 12, a non-linear constraint 13, a trigonometric block 14, and a second multiplier 15, the output of which is connected to the input of the divider 12, and the output signals are supplied the channel for measuring the amplitude of the voltage and the channel for measuring the amplitude of the current 16, and a constant value α, where α = 2.

The frequency measurement channel consists of a series-connected clock generator 5, a binary pulse counter 6, a second moving averaging block 7, a second linear converter 8, and a comparator 9, the output of which is connected to the reset input of the binary pulse counter 6.

The first, second and third blocks of moving averaging (figure 2) consist of the first and second delay lines 18, 19 and the adder 17, and the first input of the adder 17 is combined with the input of the first delay line 18, and the output of the adder 17 is connected to the input of the second delay line 19, and the outputs of the first and second delay lines 18 and 19 are connected to the second and third inputs of the adder 17, respectively, and the second input of the adder is inverse. In the first 2 and third 11 blocks of moving averaging, the first delay line 18 has a depth N, where N is the number of discrete samples in the half-cycle. In the second block of moving averaging 7, the first delay line 18 has a depth K, where K is the number of averaging periods when measuring the frequency.

Consider the principle of operation of the meter. Imagine the input voltage and current signals in the form of a fundamental harmonic with a frequency f ₀ and a set of higher-order harmonics arising from transients:

,

,

where n is the harmonic number, φ is the phase difference between current and voltage.

In energy systems during transients, the odd harmonics prevail, especially the third and fifth. We find the signal energy at n = 2p + 1, where p = 0,1,2 .... Due to the orthogonality of the harmonic components of the signal for odd harmonics, we have:

where <U ² > is the estimate of the root mean square amplitude of the signal,

- период основной гармоники.

- period of the fundamental harmonic.

Then the estimate of the rms amplitude of the voltage:

By analogy, to evaluate the mean square amplitude of the current, the expression is satisfied:

The cross-correlation function of the current and voltage signals, taking into account the assumptions made, provided that there is a high correlation between current and voltage, can be calculated as:

From where we get the expression for the cosine of the phase difference:

The principle of operation of the voltage amplitude measurement channel is based on algorithm (1), implemented in a discrete approximation:

where U _k = U [kT _∂ ] are the discrete samples of the input voltage signals taken at time kT _∂ , where T is the sampling period.

, а далее на схему извлечения квадратного корня 4, откуда снимается оценка амплитуды входного сигнала напряжения, выраженная в масштабе величин входных дискретных отсчетов XUi.The channel for measuring the amplitude of the voltage operates as follows. Discrete samples of the voltage signal XU _i go to the squaring circuit 1 (Fig. 1), where they undergo non-linear transformation, and then to the first block of moving averaging 2, where the energy characteristic of the input signal is calculated. Then the result is fed to the first linear converter 3, implemented as a constant factor multiplier

and then to the square root 4 extraction scheme, from which the estimate of the amplitude of the input voltage signal, expressed in the scale of the values of the input discrete samples XUi, is taken.

The algorithm of the frequency measurement channel is based on counting the number of clock intervals (pulses) between the zeros of the input voltage signal. The counting result is continuously averaged over K periods. In practical applications, the choice of K depends on the required accuracy; K≥8 recommended. Since the change in frequency in power systems is slower than the change in current, voltage and phase difference, the requirements for high speed are not imposed on the frequency measurement channel.

. Оценка частоты выдается в единицах количества дискретных отсчетов тактового генератора на половину периода входного сигнала.The frequency measurement channel operates as follows. Rectangular signals from a clock generator 5 (Fig. 1) are input to a binary counter with a reset 6, where the number of clock pulses is calculated over a duration of K periods. Once every half-time, at the time of the difference between the reset signal supplied from the output of the comparator 9 (the threshold value γ ₀ selected depending on the noise level in the input signals), the value accumulated by the counter is fed to the second block of moving averaging 7, where it is continuously averaged over By periods and then scaled by a second linear converter 8, implemented as a constant factor multiplier

. The frequency estimate is given in units of the number of discrete samples of the clock generator for half the period of the input signal.

The algorithm of the channel measuring the amplitude of the current 16 is similar to the algorithm of the channel measuring the amplitude of the voltage.

The principle of operation of the channel for measuring the phase difference between current and voltage is based on the algorithm (2) in a discrete approximation:

where I _k = [kT _∂ ] - discrete samples of current input signals taken at the moment kT _∂ ;

<I _i > - discrete samples of the mean square estimate of the current amplitude;

<FI _i > = φ [iT _∂ ].

The phase measurement channel operates as follows. Discrete samples of current and voltage are supplied to the first multiplier 10, which performs the function of a phase detector. From the output of the first multiplier 10, the result is fed to the third block of moving averaging 11, from which the samples of the cross-correlation function between the signals calculated over the half-period are taken. Then the latter are fed to the input of the divider 12, where they are normalized to the product of the product taken from the output of the second multiplier 15, the inputs of which are fed with discrete samples of the voltage amplitude <U _i > and current <I _i > 16, and a constant value α, where α = 2. The output signal from the divider 12 is fed to a nonlinear restriction circuit 13, operating in accordance with the rule:

From the output of the nonlinear constraint 13, the result is sent to the trigonometric block 14, which calculates the function arccos (x). The output of the trigonometric block 14 is taken discrete samples of the evaluation of the phase difference between the current and voltage <FI _i >.

The proposed device allows to evaluate the parameters of alternating current in the presence of amplitude and phase noise, higher-order harmonics that are multiples of the fundamental frequency with a delay of a quarter of the period from the moment of taking the discrete samples to the output of the result.

Based on practical studies of the performance characteristics of the proposed device for measuring alternating current parameters of an industrial frequency of 50 Hz at a reference oscillator frequency and a sampling frequency of input signals of 20 kHz and a harmonic coefficient of 15%, the following indicators are obtained: accuracy of measuring current and voltage amplitudes - 0.1%; accuracy of phase difference measurement - 0.1%; frequency measurement accuracy (at K = 8) - 0.02%; the delay in measuring parameters from the moment of taking discrete samples to the output of the results is 5 ms.

Claims (1)

A harmonic signal parameter meter comprising a channel for measuring the amplitude of the current, a series-connected squaring circuit, a first moving averaging unit, a first linear converter and a square root extraction circuit; a series-connected clock, a binary pulse counter, a second block of moving averaging, a second linear converter, and a comparator, the output of which is connected to the reset input of the binary pulse counter; connected in series are the first multiplier, the third block of moving averaging, the divider, the nonlinear limiting circuit, the trigonometric block, and the second multiplier, the output of which is connected to the input of the divider, and the inputs of the second multiplier are connected to the outputs of the voltage amplitude measurement channel and the current amplitude measurement channel, as well as with a constant value source, characterized in that a divider, a non-linear restriction circuit and a trigonometric block are connected in series to the third block of moving averaging ; the square root extraction circuit is connected to the first linear converter, and the first, second, and third moving averaging units consist of an adder and two delay lines, the first adder input connected to the input of the first delay line, the adder output connected to the input of the second delay line, and the outputs of the first and the second delay lines are connected to the second and third inputs of the adder, respectively, and the second input is inverse.

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