RU2519810C1 - Measurement method of synchrophasor of operating condition of power system, and device for its implementation - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: current frequency of a power system is determined as per sampling of digitised values of an operating condition. Parameters of a synchrophasor of the operating condition are determined as per parameters of a pair of vectors. Parameters of vectors are calculated by means of a discrete Fourier transformation method. Calculation of one of the vectors is made using the frequency equal to the whole part of the current frequency value of the power system, and the other one - using frequency that is higher by 1 Hz and using cosine and sine harmonic functions with these frequencies. A phase of these functions is calculated starting from the moment of the last 1PPS. A synchrophasor module is determined by means of linear interpolation as per frequency of modules of the above vectors, and an angle is determined by linear interpolation of angles of vectors and by adding to the obtained values of difference of current and nominal frequencies of the power system, which is multiplied by 2π and by time interval that passed from the time mark of the synchrophasor to the last second mark, 1PPS. A device for implementation of the above method is proposed. The device includes an analogue signal input unit, a receiving unit of signals of the common-timing system, an analogue-to-digital converter (ADC), a discretisation synchronising pulse oscillator, two generation units of cosine signals, two calculation units of vectors of the operating condition, a transfer unit of measurement results to a data gathering centre, as well as a measurement unit of current frequency of the power system, a frequency interval calculation unit and a vector parameter interpolation unit.

EFFECT: improving accurate measurement of operating conditions in a wide range of variation of current frequency of a power system.

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Description

The invention relates to measuring equipment, in particular to a technology for measuring the operational parameters of an electric power system - voltage and current. The invention can be used in monitoring and maintaining the regime of the power system, as well as in devices for preventing instability of the power system.

A known method of measuring the operational parameters of the power system, voltage and current, in the form of vectors, is used in microprocessor devices [V. G. Narovlyansky, A. B. Vaganov. The use of the ALAR-M device for identifying and eliminating the asynchronous mode of the electric power system. // Energetik, No. 5, 2011, pp. 17-21]. In this case, the digitized values of the operating parameters are obtained and their vectors are calculated by the method of discrete Fourier transform using a cosine harmonic function with a nominal frequency, the phase of which is always counted from zero on the sample of digitized values of the operating parameter used to calculate. Based on the calculation results, the need and conditions for influencing the power system mode are determined. The assumption that the frequency of the operating parameter is equal to the nominal frequency of the power system leads to a noticeable measurement error of the operating parameters. In addition, since the measurements of such devices are not synchronized with each other, it is impossible to share the values of operating parameters obtained at different nodes of the power system.

These disadvantages are largely overcome in the method described in [A.G. Phadke and J.S. Thorp. Synchronized Phasor Measurements and Their Applications. ISBN 978-0-387-76535-8, Springer Verlag, 2008].

Measurements are synchronized by second world time marks (1PPS), which form with an accuracy of not more than a few tens of nanoseconds and transmit by GPS / GLONASS satellite positioning system to the measurement device. Using the microcontroller, the digitized values of the mode parameter, voltage or current are obtained and the vector of the mode parameter is calculated at the nominal frequency of the power system using the time counted from the last 1PPS second mark. This vector is associated with a time stamp corresponding, as a rule, to the moment of the middle of the sample of digitized values. This representation of the vector measurement of the operational parameter is called the synchrophasor [IEEE Standard for Synchrophasor Measurements for Power Systems IEEE Std C37.118.1 ™ - 2011].

It is significant that in this case the phase of the cosine harmonic function of the nominal frequency is equal to zero at each moment of 1PPS. The synchrophasor can be used in the measurement node and transmitted via the communication system to the computer of the control center for sharing with synchrophasors from other nodes to control the power system.

On the basis of synchrophasors, the state of the power system is determined, the operation parameters of emergency control systems of the energy system, and the operation of emergency equipment is configured. The advantages of this method consist in obtaining synchronized vector data — synchrophasors — from the nodes of the power system. The disadvantages of the method are the synchrophasor calculations carried out at the nominal frequency of the power system. When the frequency of the power system is different from the nominal one, it is necessary to adjust the obtained synchrophasor parameters with the use of additional information. Therefore, the application of this method is possible only in a limited frequency range of the measured operating parameter [IEEE Standard for Synchrophasor Measurements for Power Systems IEEE Std C37.118.1 ™ - 2011].

The block diagram of all existing devices for synchronized vector measurements of operational parameters practically coincides with the block diagram of such devices given in the IEEE Standard [IEEE Standard for Synchrophasor Measurements for Power Systems IEEE Std C37.118.1 ™ - 2011]. The device comprises an analog signal input unit, a single-time system signal receiving unit, an ADC, a sampling clock generator, a cosine signal generation unit at a nominal frequency of a power system synchronized by a clock generator, a mode parameter vector calculation unit, a measurement parameter transmission unit to a power system control center and / or to configure relay protection and automation equipment.

An analog signal of a mode parameter is supplied to the input of the input block of analog signals. The output of the analog signal input unit is connected to the ADC signal input, the ADC output is connected to the first input of the mode parameter vector calculation unit. The output of the signal receiving unit of the single-time system is connected to the input of the sampling clock generator, the first output of which is connected to the ADC clock input and to the input of the cosine-signal generation block at the nominal frequency of the power system, and its second output is connected to the first input of the measurement results transmission unit to the power system control center and / or on the settings of the relay protection and automation equipment. The output of the cosine signal generation unit at the nominal frequency of the power system is fed to the second input of the vector calculation unit. The output of the vector calculation unit is fed to the second input of the transmission unit of the measurement results to the power system control center and / or to the setup of the relay protection and automation equipment.

The disadvantage of such a device is a significant dependence of the error of the measurement result on the frequency of the power system, therefore, [IEEE Standard for Synchrophasor Measurements for Power Systems IEEE Std C37.118.1 ™ - 2011] indicates limitations on the frequency range of the device.

The proposed method is aimed at solving the problem of increasing the accuracy of calculating the synchrophasor while removing the restrictions on the frequency range.

The technical solution is based on the fact that the phase of the cosine harmonic function used in the proposed method with a frequency equal to an integer number of hertz is zero at 1PPS.

In the proposed method, with synchronized vector measurements of the operating parameters of a power system operating at a current arbitrary (non-nominal) frequency, the synchrophasor of the operating parameter is calculated by the parameters of a pair of vectors, one of which is calculated at a frequency equal to the integer part of the current frequency of the power system, and the other at a frequency of 1 Hz more. The vector of operational parameters at the current frequency of the power system is obtained by linear interpolation of the parameters of the vectors calculated at these frequencies. The synchrophasor parameters, modulus and angle are obtained using the vector parameters at the current frequency.

The proposed method allows to increase the accuracy of measuring operational parameters in a wide range of changes in the current frequency of the power system.

To implement the method perform the following operations:

- measure the current frequency of the power system (f) from the sample of digitized values of the operating parameter obtained at the time of measurement,

- get the value of the difference between the current frequency and the nominal frequency of the power system,

- determine the frequency interval: the lower boundary of the interval is set as the integer part of the current frequency of the power system (f _floor ), and the upper boundary is 1 Hz greater than the lower boundary (f _ceil = f _floor +1),

и $${\underset{\_}{V}}_{ceil}=A_{ceil}\cdot e^{j{\delta }_{ceil}}$$

с учетом того, что в моменты 1PPS фаза используемых в предлагаемом способе косинусоидальных гармонических функций с частотами, равными целому числу герц, равна нулю, и сохраняют результат в машиночитаемом виде,- according to the sample of digitized values of the operating parameter, the vector of the operational parameter at the boundary frequencies of the interval is calculated by the method of discrete Fourier transform: $${\underset{\_}{V}}_{floor}=A_{floor}\cdot e^{j{\delta }_{floor}}$$

and $${\underset{\_}{V}}_{ceil}=A_{ceil}\cdot e^{j{\delta }_{ceil}}$$

taking into account that at 1PPS moments the phase of the cosine harmonic functions used in the proposed method with frequencies equal to an integer number of hertz is zero, and the result is stored in a machine-readable form,

- take the result of linear interpolation in frequency of the modules of the vectors of the parameter parameter as the synchrophasor module of the mode parameter

, $$A=A_{floor}+\frac{f-f_{floor}}{f_{ceil}-f_{floor}}\cdot (A_{ceil}-A_{floor})$$

,

- determine the phase of the signal as the difference between the current and nominal frequencies of the power system, multiplied by 2π and the time interval that has passed from the last signal of the second mark to the moment of measuring the synchrophasor

δ _s = 2π (ff ₀ ) · Δt,

and storing the signal phase value in a machine readable form,

- take for the angle of synchrophasor the result of linear interpolation in frequency of the stored values of the angles of the vectors of the mode parameter with the addition to the obtained value of the stored value of the signal phase

, $$\delta ={\delta }_{floor}+\frac{f-f_{floor}}{f_{ceil}-f_{floor}}\cdot ({\delta }_{ceil}-{\delta }_{floor})+{\delta }_s$$

,

where f ₀ = 50 Hz is the nominal frequency of the power system, Δt is the interval from the time stamp of the synchrophasor to the last second mark of 1PPS.

The performed numerical experiments confirm the stated positions. For example, for a harmonic signal in the frequency range from 35 to 65 Hz at a sampling frequency of 12800 Hz, the error of the synchrophasor module calculated by the proposed method did not exceed 0.025%, and the angle error did not exceed 0.03 degrees. The [IEEE Standard for Synchrophasor Measurements for Power Systems IEEE Std C37.118.1 ™ - 2011] specifies requirements for synchrophasor accuracy. According to the standard, it is necessary that in the range from 45 to 55 Hz the error does not exceed 1%. The experimental results showed that in the studied range, expanded with respect to the requirements of the standard [IEEE Standard for Synchrophasor Measurements for Power Systems IEEE Std C37.118.1 ™ - 20 II], the error does not exceed 0.1%.

Special cases of using this method of measuring the operating parameters of the power system are voltage measurements in the power system node or current along the line leaving the power system node.

The inventive method can be implemented in a device with a block diagram shown in Fig. 1. In contrast to the prototype, the proposed device uses two blocks for calculating the vectors of the operational parameter. This is due to the fact that in the prototype the calculation of the vector of the operational parameter is always carried out at the nominal frequency of the power system (50 Hz), and in the proposed device, the calculation of the vectors of the operational parameter is carried out at two frequencies and their values depend on the current frequency of the energy system. In addition, in comparison with the prototype, a unit for measuring the current frequency of the power system, a unit for calculating the frequency interval f _floor and f _ceil , a block for interpolating vector parameters and a second block for generating cosine signals synchronized by a sampling clock generator are added to the device, while the first block for generating values of cosine signals equipped with a second entrance.

In Fig. 1, the following notation is accepted:

1 - block input analog signals; 2 - analog-to-digital converter (ADC); 3 - sampling clock generator; 4 - a unit for receiving signals of a single time system; 5 - block generating cosine signals at a frequency of f _floor ; 6 - block generating cosine signals at a frequency f _ceil ; 7 - unit for transmitting measurement results to a data collection center; 8 - unit for measuring the current frequency of the power system; 9 - block calculation of the vectors of the operational parameter at a frequency f _floor ; 10 - block calculation of the vectors of the operational parameter at a frequency f _ceil ; 11 - block calculation of the frequency interval; 12 - block interpolation of parameters of vectors.

The output of the input unit for analog (1) signals is connected to the ADC signal input (2), the ADC output (2) is connected to the first input of the vector parameter block of the parameter mode f _floor (9), with the first input of the second vector block of the parameter parameter calculation on the frequency f _ceil (10) and with the input of the unit for measuring the current frequency of the power system (8), the output of the signal receiving unit of the single-time system (4) is connected to the input of the sampling clock generator (3), the first output of the sampling clock generator (3) is connected to the ADC synchronization input (2 ), with the input of the first of the second cosine signal generating unit at the frequency f _floor (5) and with the first input of the second cosine signal generating unit f _ceil (6), the second output of the sampling clock generator (3) is connected to the first input of the measurement results transmission unit to the data collection center (7) , the output of the unit for measuring the current frequency of the energy system (8) is connected to the input of the unit for calculating the frequency interval (11), the first output of the unit for calculating the frequency interval (11) is connected to the second input of the first cosine signal generation unit f _floor (5), the second output is and the calculation of the frequency interval (11) is connected to the second input of the second block of cosine signals generation f _ceil (6), the output of the first block of cosine signals generation f _floor (5) is connected to the second input of the first block of vector calculation of the mode parameter f _floor (9), output the second block of cosine-signal generation f _ceil (6) is connected to the second input of the second block of vector calculation of the mode parameter f _ceil (10), the output of the first block of vector calculation of the mode parameter f _floor (9) is connected to the first input of the block of interpolation of vector parameters (1 2), the output of the second block of calculation of vectors of the operational parameter f _ceil (10) is connected to the second input of the block of interpolation of parameters of vectors (12), the output of the block of interpolation of parameters of vectors (12) is connected to the second input of the block of transmission of measurement results to the data collection center (7) .

The input block of analog signals (1) is used to enter into the device a mode parameter in the analog representation and to coordinate the signal level for the ADC (2). Depending on the type of operating parameter, voltage or current, the analog signal input unit (1) is a voltage or current transformer. The ADC (2) converts the analog input signal to digitized values synchronized by clock pulses from the sampling clock generator (3). The sampling clock generator (3) is synchronized by timestamp systems with a single time. The frequency of clock pulses determines the frequency of data sampling in the ADC (2) and the frequency of generation of the values of cosine signals in the block of generation of cosine signals at the frequency f _floor (5) and the block of generation of cosine signals at the frequency f _ceil (6). The signal receiving unit of the single time system (4) receives second marks of the single time system. Reception can be carried out either directly from the GPS / GLONASS navigation satellite systems, or from the means of the local single-station substation system using the IRIG-B or RTR protocols with a synchronization error of not more than 1 μs. In addition, the signal receiving unit of the single time system (4) generates a time stamp for measuring the synchrophasor. The unit for measuring the current frequency of the power system (8) measures the current frequency of the power system.

In the block for calculating the frequency interval (11), the lower and upper boundaries of the frequency interval f _floor and f _ceil are obtained from the value of the current frequency. The block generating cosine signals at a frequency f _floor (5) and the block generating cosine signals at a frequency f _ceil (6) generate values of cosine signals at these frequencies with a clock frequency discreteness. In the block for calculating the vectors of the regime parameter at the frequency f _floor (9) and the block for calculating the vectors of the regime parameter at the frequency f _ceil (10), the vectors at the frequencies f _floor and f _{ceil are} calculated, respectively. In the block of interpolation of the parameters of the vectors (12), the parameters of the obtained vectors are converted into the module and the synchrophasor angle. The unit for transmitting measurement results to the data collection center (7) serves to transfer the synchrophasor to the power system control center or to the relay protection and automation equipment.

The device operates as follows. The analog mode parameter is input to the analog input block (1). From the output of the analog input block (1), the analog values are sent to the signal input of the ADC (2). The ADC synchronization input (2) receives clock pulses from the first output of the sampling clock generator (3). They are rigidly tied to second marks of the single time system received by the signal receiving unit of the single time system (4). Clock pulses from the first output of the sampling clock generator (3) also go to the second inputs of the cosine signal generation unit at frequency f _floor (5) and the cosine signal generation unit at frequency f _ceil (6). Therefore, the values of cosine signals at frequencies f _floor and f _ceil , in particular their phase, correspond to the same time instants as the digitized values of the input signal of the mode parameter. From the second output of the sampling clock generator (3), the time stamp of the synchrophasor is received at the first input of the measurement results transmission unit to the data collection center (7).

From the output of the ADC (2), the digitized values of the mode parameter go to the current system frequency measuring unit (8) for measuring the current system frequency and to the first inputs of the mode parameter vector calculation unit at the frequency f _floor (9) and the mode parameter vector calculation unit at the frequency f _ceil (10). The value of the current frequency from the output of the unit for measuring the current frequency of the power system (8) is fed to the input of the unit for calculating the frequency interval (11). From the first output of the block for calculating the frequency interval (11), the value of the frequency f _{floor is} supplied to the second input of the block generating cosine signals at a frequency f _floor (5). From the second output of the block for calculating the frequency interval (11), the value of the frequency f _{ceil is} supplied to the second input of the block generating cosine signals at a frequency f _ceil (6).

From the output of the block generating cosine signals at a frequency of f _floor (5), its values are fed to the second input of a block for calculating the vectors of a regime parameter at a frequency of f _floor (9) to calculate a vector at a frequency of f _floor .

From the output of the block generating cosine signals at a frequency f _ceil (6), its values are fed to the second input of the block for calculating the vectors of the regime parameter at a frequency f _ceil (10) to calculate the vector at a frequency f _ceil .

с выхода блока расчета векторов режимного параметра на частоте f_floor (9) поступают на первый вход блока интерполяции параметров векторов (12), а параметры векторов $${\underset{\_}{V}}_{ceil}$$

с выхода блока расчета векторов режимного параметра на частоте f_ceil (10) попадают на второй вход блока интерполяции параметров векторов (12).To calculate the parameters of the synchrophasor parameters of the vectors $${\underset{\_}{V}}_{floor}$$

from the output of the block for calculating the vectors of the operational parameter at the frequency f _floor (9), they arrive at the first input of the block of interpolation of the parameters of the vectors (12), and the parameters of the vectors $${\underset{\_}{V}}_{ceil}$$

from the output of the block for calculating the vectors of the operational parameter at the frequency f _ceil (10), they go to the second input of the block of interpolation of the parameters of the vectors (12).

The values of the synchrophasor parameters from the output of the vector parameter interpolation unit (12) are sent to the second input of the measurement results transmission unit to the data collection center (7) to transmit the synchrophasor parameters and its time stamp to the power system control center or to relay protection and automation equipment.

Application of the proposed method allows more efficient use of the results of synchronized vector measurements by improving the accuracy of determining the parameters of synchrophasors.

This increases the accuracy of both assessing the power system mode when transmitting operating parameters to the power system control center via communication lines, and setting the operating parameters of the power system control devices in the mode parameter measuring unit.

Claims (3)

1. A method for measuring the synchrophasor of a power system mode parameter, including obtaining a sample of digitized values of a mode parameter signal, receiving a second mark signal from a single time system, obtaining a mode parameter vector by a discrete Fourier transform method, characterized in that the current system frequency is determined from a sample of digitized mode signal values parameter, determine the frequency interval, the lower limit of which is set as an integer part of the current frequency of the power system, and the upper Itsu - 1 Hz more than the lower boundary, receive the parameter vector at the frequencies of the upper and lower boundary of the interval, save the obtained vector values in a machine-readable form, take the result of linear interpolation from the frequency of the stored values of the vector parameter modules of the parameter parameter as the synchrophasor module, determine the signal phase as the value of the difference between the current and nominal frequencies of the power system, multiplied by 2π and the time interval that has passed from the last signal of the second mark to the moment of measurement hrofazora and maintain it in machine-readable form is taken as the angle synchrophasor result of the linear interpolation frequency values stored angles modal parameter vectors with the addition to the resulting value of the stored signal phase values. 2. The method according to claim 1, characterized in that the voltage in the node of the power system or the current in the branch connected to the node of the power system is used as the operating parameter. 3. A device for measuring the synchrophasor of a power system mode parameter, comprising an analog signal input unit, a single-time system signal receiving unit, an analog-to-digital converter (ADC), a sampling clock generator, cosine signals generating unit, a mode parameter vector calculation unit, a measurement result transmission unit to the data collection center, and the output of the analog signal input unit is connected to the ADC signal input, the ADC output is connected to the first input of the mode vector calculation unit ameter, the output of the signaling unit of the single-time system is connected to the input of the sampling clock generator, the first output of which is connected to the ADC clock input and to the input of the cosine-signal generation block, the second output of the sampling clock generator is connected to the input of the measurement results transmission unit to the data center, output the cosine-signal generation unit is connected to the second input of the mode parameter vector calculation unit, characterized in that it further comprises a unit measuring the current frequency of the power system, the unit for calculating the frequency interval, the second unit for generating cosine signals, the second unit for calculating the vectors of the mode parameter, the unit for interpolating the parameters of the vectors, while the first unit for generating the cosine signals is equipped with a second input, the ADC output being additionally connected to the first input of the second unit of calculation vectors of the operating parameter and with the input of the unit for measuring the current frequency of the power system, and the first output of the sampling clock generator is additionally connected with the first input of the second cosine signal generation unit, the output of the current system frequency measurement unit is connected to the input of the frequency interval calculation unit, the first output of the frequency interval calculation unit is connected to the second input of the first cosine signal generation unit, the second output of the frequency interval calculation unit is connected to the second input of the second block generating cosine signals, the output of the second block generating cosine signals is connected to the second input of the second block calculating the mode vectors parameter, the output of the first block of calculation of the vector of the parameter of the parameter is connected to the first input of the block of interpolation of the vectors of the parameters, the output of the second block of the calculation of the vectors of the parameter of parameters is connected to the second input of the block of interpolation of the vectors, the output of the block of interpolation of the parameters of the vectors is connected to the second input of the block of transmission of measurement results to the collection center data.