RU2143701C1 - Process determining energy consumption in a c circuits and device for its implementation - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: process provides for conducting of two series, direct and reverse, of samples of momentary values of current and voltage in examined circuit that periodically change one another. Momentary values of current and voltage are converted to digital signals, are memorized and momentary values of power are computed with subsequent averaging in the course of preset time interval in accord with calculation formulas. Device for implementation of process has current and voltage pickups which outputs are connected to analog inputs of analog commutation multiplexer whose output is connected to input of analog-to-digital converter which output is linked to input of processor, register of parity of samples having direct and reverse coupling with processor and connected with its output to address input of analog commutation multiplexer and frequency meter connected with its input to output of voltage pickup and with output to input of processor. EFFECT: increased accuracy of measurement of energy consumption. 5 cl, 3 dwg, 1 tbl

Description

 The invention relates to measuring technique and can be used to determine energy consumption in alternating current circuits with the periodic nature of changes in current and voltage.

 A known method of determining energy consumption in AC circuits [1].

The method provides for the simultaneous sampling of instantaneous values of current and voltage in the circuit under study, which is periodically repeated at a time interval corresponding to a phase angle of 90 ^° , converting the samples into digital signals proportional to the selected instantaneous values of current and voltage, storing these signals and calculating instantaneous power values.

 To determine the energy consumption, the obtained power values are averaged over a given time interval.

 The main disadvantages of this method are low speed, since the shortest energy measurement time is 1/4 of the input signal period, and low accuracy, since only four samples of current and voltage are produced during the input signal period. In addition, when determining the energy consumption in multiphase circuits, measurements of instantaneous currents and their corresponding voltages are required to be performed simultaneously in all circuits, which complicates the implementation of the method.

 A device for implementing this method contains current and voltage sensors connected to the inputs of analog-to-digital converters connected through a multiplexer and an operation unit to a processor.

 In addition, the reference frequency generator, key and integrator are connected to the control unit [1].

 Samples of instantaneous values of current and voltage are supplied by sensors to analog-to-digital converters that convert them into digital signals. The signals are processed in the processor, after which the instantaneous power values are calculated in the operating unit and averaged in the integrator to obtain the total energy consumption in the circuit under study for a given time interval.

 The main disadvantage of the known device is that to determine the energy consumption in multiphase circuits according to the known method [1], which provides for simultaneous measurements of instantaneous values of current and voltage in all studied circuits, the number of analog-to-digital converters equal to the number of studied circuits is required, which complicates calculation algorithm and control scheme.

 The consequence of this is a decrease in speed and reliability.

 A known method of determining energy consumption in AC circuits [2].

 This method is the closest to the claimed combination of essential features and is selected as a prototype.

 A prototype, similar to the claimed invention, includes sequentially sampling, at certain time intervals, the instantaneous values of current and voltage in the circuit under study, converting the samples into digital signals proportional to the selected values, storing them in memory, and calculating the instantaneous power values, followed by averaging over a given time interval.

 In contrast to the claimed technical solution in the known method, the voltage signal is considered as a sinusoid, integrate and determine the maximum. The voltage corresponding to the moment of measurement of the current signal is calculated by interpolation according to a sinusoidal curve obtained by integration. The possibility of alternately sampling the instantaneous values of current and voltage simplifies the procedure for implementing the known method, however, to compensate for the measurement error arising from non-simultaneous sampling, it is necessary to perform complex computational operations, which reduces speed and accuracy.

 In addition, the prototype does not have procedures to compensate for the error arising due to the presence of constant components in the measured current and voltage signals, as well as the procedure for setting the time interval between current and voltage samples taking into account nonlinear distortions in the circuit under study, which negatively affects the accuracy of determination energy consumption.

 To implement the prototype, a device is used that contains current and voltage sensors, the outputs of which are connected to the input of an analog switching multiplexer, connected through an analog-to-digital converter with a processor, similarly to the claimed one. A memory device and an operation unit [2] are also connected to the processor.

 The device [2] is the closest to the claimed combination of essential features and is selected as a prototype.

 The sensors sample instantaneous values of current and voltage in the circuit under study. An analog switching multiplexer, connected to the outputs of the sensors, sets the sampling sequence, the time interval between samples and provides analog signals to the input of an analog-to-digital converter, where they are converted into digital signals proportional to the selected current and voltage values. The processor reads and processes the output of the analog-to-digital converter and transfers it to the storage device, after which the instantaneous power values are calculated in the operation unit and the energy consumption is determined by averaging the instantaneous power values over a given time interval.

 The presence in the prototype of an analog switching multiplexer allows alternately sampling the instantaneous values of current and voltage in all the circuits under study, which makes it possible to include one analog-to-digital converter in the device circuit even if the energy consumption in multiphase circuits is determined.

 However, in the known device there are no nodes necessary for determining the energy consumption in alternating current circuits with non-linear distortions. In addition, a disadvantage of the known device is the presence of a complex node (high-speed operating unit) that compensates for errors arising from the simultaneous reading of current and voltage signals.

 The basis of the invention is the task to improve the method of determining energy consumption in AC circuits by introducing a procedure for changing the sampling sequence, taking into account the constant components of the current and voltage signals and setting the time interval between current and voltage samples, which will improve the accuracy of determining energy consumption, as well as improve the device to implement this method by including nodes that control the sampling sequence and specify the initial data to compensate for errors arising from the simultaneous reading of current and voltage signals, which will improve the accuracy of determining energy consumption.

где W_а - потребление активной энергии;
W_р - потребление реактивной энергии;
K - масштабный коэффициент;
Δt - период изменения последовательности выборки;
α = 2n-1 - номера нечетных выборок тока и напряжения;
u(t) - мгновенные значения напряжения;
t_α - моменты времени нечетных выборок тока и напряжения;
i(t) - мгновенные значения тока;
τ - интервал времени между выборками тока и напряжения;
β = 2n - номера четных выборок тока и напряжения;
t_β - моменты времени четных выборок тока и напряжения;
W - угловая частота переменного тока,
при этом последовательность выборки мгновенных значений тока и напряжения изменяют на обратную четное число раз.The problem is solved in that in a method for determining energy consumption in alternating current circuits, including alternately sampling, at predetermined time intervals, the instantaneous values of current and voltage in the circuit under study, converting the samples into digital signals proportional to the selected values, storing the received digital signals, calculating instant values power, followed by averaging over a given time interval, according to the invention, a sampling sequence of instantaneous current and voltage stresses are periodically reversed, and energy consumption is determined by the formulas:

where W _a - active energy consumption;
W _p - reactive energy consumption;
K is the scale factor;
Δt is the period of changing the sequence of the sample;
α = 2n-1 - numbers of odd samples of current and voltage;
u (t) - instantaneous voltage values;
t _α - time instants of odd samples of current and voltage;
i (t) - instantaneous current values;
τ is the time interval between samples of current and voltage;
β = 2n are the numbers of even samples of current and voltage;
t _β are the time instants of even samples of current and voltage;
W is the angular frequency of the alternating current,
wherein the sampling sequence of instantaneous values of current and voltage is reversed an even number of times.

где μ - номер наивысшей гармоники в исследуемой цепи;
δ_a - относительная погрешность определения потребления активной энергии;
K_ниа - коэффициент нелинейных искажений по активной мощности;
δ_{a доп} - допустимая относительная погрешность определения потребления активной энергии;
δ_p - относительная погрешность определения потребления реактивной энергии;
K_нир - коэффициент нелинейных искажений по реактивной мощности;
δ_{p доп} - допустимая относительная погрешность определения потребления реактивной энергии.In addition, the time interval between the current and voltage samples is adjusted taking into account the non-linear distortion factors and the highest harmonic numbers in the circuit under study so that the errors in determining the consumption of active and reactive energies do not exceed acceptable values in accordance with the inequalities:
wτ <π / 2μ; (4)

where μ is the number of the highest harmonic in the circuit under study;
δ _a is the relative error in determining the consumption of active energy;
K _nia is the coefficient of nonlinear distortion in active power;
δ _{a add} - permissible relative error in determining the consumption of active energy;
δ _p is the relative error in determining the consumption of reactive energy;
K _nir is the coefficient of nonlinear distortion in reactive power;
δ _{p add} - permissible relative error in determining the consumption of reactive energy.

 In addition, in a device for implementing the above method, comprising current and voltage sensors, the outputs of which are connected to the analog inputs of an analog switching multiplexer, the output of which is connected to the input of an analog-to-digital converter, the output of which is connected to the processor input, according to the invention, a parity register of samples and a frequency meter, moreover, the parity register of samples has a direct and feedback connection with the processor, and its output is connected to the address input of an analog switching mult of the multiplexer, the input of the frequency meter is connected to the output of the voltage sensor, and the output to the processor input, and the parity register of samples includes a reversible counter, two decoders and an RS-trigger, while the input of the reverse counter is connected to the output of the processor and RS-trigger, and the output is connected to the address input of the analog switching multiplexer and the outputs of the decoders, the outputs of which are connected to the inputs of the RS-trigger, and the output of the RS-trigger is to the input of the processor.

 In FIG. 1 and 2 graphically display a sequence of samples of instantaneous values of current and voltage, implemented respectively by the prototype and the claimed method.

 Moreover, the presence of a time interval τ between the current and voltage samples introduces an additional error in determining the energy consumption. The magnitude of this error is equivalent to the phase shift created by unaccounted impedance in the circuit under study.

 In the present invention, to compensate for this error, it is proposed to periodically change the sampling sequence of instantaneous values of current and voltage to the opposite (Fig. 2). In this case, the entire set of samples can be divided into two sequences - direct and reverse. Direct sequence samples are indicated by dots, and reverse sequence samples are indicated by crosses on current and voltage curves. As can be seen from FIG. 2, changing the sequence of samples is equivalent to alternating positive and negative shear angles between adjacent instantaneous values of current and voltage.

где t₁ и t₂ - начальный и конечный моменты времени выборки на интервале времени усреднения.Carrying out the passage to the limit Δt _ → 0, n _ → ∞ in expressions (1) and (2), we obtain:

where t ₁ and t ₂ are the initial and final moments of the sampling time on the averaging time interval.

где T = t₂ - t₁ - величина интервала усреднения;
m - номер гармоники;
P_m - истинная активная мощность m-й гармоники на интервале усреднения;
Q_m - истинная реактивная мощность m-й гармоники на интервале усреднения.Expanding the functions u (t), i (t) in Fourier series on the interval (-kπ, + kπ) taking into account the orthogonality of the system of trigonometric functions, we obtain:

where T = t ₂ - t ₁ - the value of the averaging interval;
m is the number of harmonics;
P _m is the true active power of the mth harmonic in the averaging interval;
Q _m is the true reactive power of the mth harmonic in the averaging interval.

Последние выражения можно преобразовать к виду:

В реальных электрических цепях энергетический спектр ограничен гармоникой с номером μ ≠ ∞, коэффициенты нелинейных искажений по активной K_ниа по реактивной K_нир мощностям также ограничены требованиями к качеству электроэнергии

Интервал времени τ между замерами токов и напряжений настраивается так, чтобы при определении энергии в исследуемой цепи учитывались все гармоники до μ включительно wτ < π/2μ. (4)
Следовательно, с ограниченной точностью вторыми слагаемыми в формулах (13) и (14) можно пренебречь:

При этом относительные погрешности δ_a и δ_p не превысят

Таким образом, определенные по формулам (1) и (2) значения энергии равны истинным с точностью, определяемой неравенствами (5), (6):

где W_а - истинное значение потребления активной энергии;
W_р - истинное значение потребления реактивной энергии.Since Sin x = - Sin (-x), Cos x = Cos (-x), then expressions (9) and (10) are reduced to the form:

Recent expressions can be converted to:

The actual electric connections is limited harmonic energy spectrum with a number μ ≠ ∞, the coefficients for nonlinear distortion active _NIA K K _nir reactive power is also limited by the requirements for power quality

The time interval τ between measurements of currents and voltages is adjusted so that when determining the energy in the circuit under study, all harmonics up to μ inclusive wτ <π / 2μ are taken into account. (4)
Therefore, with limited accuracy, the second terms in formulas (13) and (14) can be neglected:

In this case, the relative errors δ _a and δ _p will not exceed

Thus, the energy values determined by formulas (1) and (2) are equal to true with an accuracy determined by inequalities (5), (6):

where W _a is the true value of active energy consumption;
W _p - the true value of the consumption of reactive energy.

 Thus, the energy consumption determined according to the claimed method corresponds to the true value of energy consumption in the circuit.

 Changing the sampling sequence of the instantaneous values of current and voltage by an even inverse number of times eliminates the error due to the presence of an unpaired term in expressions (1) and (2), which improves the accuracy of determining energy consumption.

Наличие в заявляемом устройстве для осуществления предложенного способа регистра четности выборок позволяет осуществлять изменение последовательности выборки мгновенных значений тока и напряжения на обратную. Выход регистра четности выборок подключен ко входу аналогового коммутирующего мультиплексора, задающего последовательность выборки. Регистр четности выборок имеет также прямую и обратную связь с процессором, подающим на его вход импульсные управляющие сигналы. В свою очередь, с выхода регистра четности выборок на вход процессора поступают данные о количестве четных и нечетных выборок.In special cases, in the presence of interference in the measuring channels, to compensate for minor errors due to a shift in the average values of current and voltage, the active energy consumption W _na can be determined by the formula:

The presence in the inventive device for implementing the proposed method of register parity of samples allows you to change the sequence of samples of instantaneous values of current and voltage to the opposite. The output of the parity register of samples is connected to the input of an analog switching multiplexer that sets the sampling sequence. The parity register of samples also has a direct and feedback connection with a processor supplying pulse control signals to its input. In turn, from the output of the parity register of samples, the processor receives data on the number of even and odd samples.

 The frequency meter takes the voltage signal from the output of the voltage sensor, converts it and transfers it to the central processor, which determines the angular frequency of the alternating current, which is the initial value for determining energy consumption.

 An example of a specific embodiment of the inventive device is shown in FIG. 3.

 The device contains current sensors 1 and voltage 2. Their outputs are connected to the input of the analog switching multiplexer 3, the output of which is connected to the input of the analog-to-digital converter 4, the output of which, in turn, is connected to the input of the processor 5. The processor 5 has direct and feedback with a parity register of samples 6, including a reverse counter 7, decoders of the first and second switching addresses 8 and 9, respectively, and an RS-trigger 10. The impulse input of the reverse counter 7 is connected to the output of the processor 5, and the output encoding the address of the measuring channel, with the address input of the multiplexer 3 and with the inputs of the decoders 8 and 9, the outputs of which, in turn, are connected to the paraphase inputs of the RS-flip-flop 10, connected by its output to the control inputs of the counter 7 and processor 5.

 The input of the frequency meter 11 is connected to the output of the voltage sensor 2, and the output to the input of the processor 5.

 The inventive method is as follows.

 At predetermined time intervals, the processor 5 generates a pulse signal at its output. The reversible counter 7 sums or subtracts these signals depending on the level 1 / ⌀ of the signal at its control input. The counter 7 has 2n + 2 stable states, two of which, corresponding to the addresses "⌀" and "2n + 1", are not mapped to any of the addresses 1, 2, 3,., 2n of the measuring channels. The addresses "⌀" and "2n + 1" are recognized by the decoders 8 and 9, respectively. When the decoder recognizes the corresponding address, a signal appears at its output, which changes the state and output of the RS-trigger 10 to the opposite. In this case, the counter 7 changes the direction of counting pulses to the opposite.

 This achieves a periodic change in the sampling sequence of instantaneous values of current and voltage to the opposite.

 The signal from the output of the RS-trigger is fed to the input of the processor 5, where it is set according to the signal level "1" or "⌀" sign "+" or "-" when calculating reactive energy.

 Sensors of current 1 and voltage 2 at time intervals specified by the processor 5, select the instantaneous values of current and voltage in the circuit under study. The analog switching multiplexer 3, which receives the control signals of the reverse counter 7, sets the sampling sequence and supplies analog signals to the input of the analog-to-digital converter 4, where they are converted into digital signals proportional to the selected current and voltage values.

 The output signals of the analog-to-digital Converter 4 and the frequency meter 11 are read, processed and stored in the internal memory by the processor 5, which calculates the energy consumption in accordance with the claimed method.

Using a personal computer, a device model was created that implements the inventive method with the following parameters:
circuit of the circuit under study - three-phase four-wire;
load mode - symmetrical;
frequency of alternating current in a circuit, Hz - 50;
time interval between current and voltage samples, τ, μs - 30;
the period of the sample sequence change, Δt, ms - 2.5.

 The values of relative errors in comparing the results of calculations obtained using the model and calculated analytically in the chains of sinusoidal and non-sinusoidal currents and voltages are presented in the table.

 The results of digital modeling of the proposed method confirm that with an increase in the averaging interval, the error in determining energy tends to zero.

Sources of information:
1. Patent of Russia N 2039358, G 01 R 21/06, 09/09/95.

 2. Accepted application of Japan N 5075269, G 01 R 21/133, 10.20.93.

Claims (5)

1. A method for determining energy consumption in alternating current circuits, including alternately sampling at instant intervals the instantaneous values of current and voltage in the circuit under study, converting the samples into digital signals proportional to the selected values, storing the received digital signals, calculating the instantaneous power values, followed by averaging in a predetermined time interval, characterized in that the sampling sequence of instantaneous values of current and voltage is periodically reversed energy consumption is determined by the formulas

where W _a - active energy consumption;
W _p - reactive energy consumption;
K is the scale factor;
Δt is the period of changing the sequence of the sample;
α = 2n-1 - numbers of odd samples of current and voltage;
u (t) - instantaneous voltage values;
t _α - time instants of odd samples of current and voltage;
i (t) - instantaneous current values;
τ is the time interval between samples of current and voltage;
β = 2n are the numbers of even samples of current and voltage;
t _β are the time instants of even samples of current and voltage;
w is the angular frequency of the alternating current.  2. The method according to p. 1, characterized in that the sampling sequence of instantaneous values of current and voltage is reversed an even number of times. 3. The method according to claim 1, characterized in that the time interval between the current and voltage samples is adjusted taking into account the non-linear distortion coefficients and the highest harmonic number in the circuit under study so that the errors in determining the consumption of active and reactive energies do not exceed allowable in accordance with the inequalities

where μ is the number of the highest harmonic in the circuit under study;
K _nia - the relative error in the determination of active energy;
δ _{a add} - the coefficient of nonlinear distortion of the active power;
δ _{a add} - permissible relative error in determining the active energy;
δ _p is the relative error in the determination of reactive energy;
K _nir is the coefficient of nonlinear distortion of reactive power;
δ _{p add} - permissible relative error in the determination of reactive energy.  4. The device for implementing the method according to claim 1, containing current and voltage sensors, the outputs of which are connected to the analog inputs of an analog switching multiplexer, the output of which is connected to the input of an analog-to-digital converter, the output of which is connected to the input of the processor, characterized in that it additionally contains a register of parity of samples and a frequency meter, moreover, the register of parity of samples has a direct and feedback connection with the processor, and its output is connected to the address input of an analog switching multiplex pa frequency meter input connected to the output voltage of the sensor and an output - to an input of the processor.  5. The device according to claim 4 for implementing the method according to claim 1, characterized in that the parity register of the samples includes a reversible counter, two decoders and an RS-trigger, while the input of the reverse counter is connected to the output of the processor and the RS-trigger, and the output is with the address input of the analog switching multiplexer and the inputs of the decoders, the outputs of which are connected to the inputs of the RS-trigger, and the output of the RS-trigger is to the input of the processor.

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