The present disclosure relates to the field of the smart power grid. The disclosure more
specifically relates to a phasor measurement unit and phasor measurement method using the
NAVIC system for smart grid management.
BACKGROUND OF INVENTION
[0002] A phasor measurement unit (PMU) is a device used to measure voltage and current
synchrophasors of a power system with high accuracy (in order of one microsecond or better).
Resolution of the PMUs is much better than the Supervisory Control and Data Acquisition
(SCADA)technique used earlier. PMU estimates the magnitude and phase angle of an
electrical phasor quantity (such as voltage or current) in the electricity grid using a common
time source for synchronization. Time synchronization is usually provided by GPS or IEEE
1588 Precision Time Protocol, which allows synchronized real-time measurements of multiple
remote points on the grid.
[0003] PMUs can capture samples from a waveform in quick succession and reconstruct the
phasor quantity, made up of angle measurement and a magnitude measurement. The resulting
measurement is known as a synchrophasor. These time-synchronized measurements are
important because if the grid's supply and demand are not perfectly matched, frequency
imbalances can cause stress on the grid, which is a potential cause for power outages.
[0004] PMUs can also be used to measure the frequency in the power grid. A typical commercial
PMU can report measurements with a very high temporal resolution, up to 120 measurements
per second. This helps engineers in analyzing dynamic events in the grid, which is not possible
with traditional SCADA measurements that generate one measurement every 2 or 4 seconds.
Therefore, PMUs equip utilities with enhanced monitoring and control capabilities and are
considered to be one of the most important measuring devices in the future of power systems.
4
[0005] THE existing SCADA system used in the power system has the capability to provide
measurements typically once every 2 or 4 or 10 seconds, which offer only a steady-state view
of the grid. This speed of measurement is not sufficient for monitoring and control of a large
power grid. Synchrophasor measurements using Phasor Measurement Unit (PMU) over a wide
area facilitate better visualization and situational awareness of the grid events such as grid
robustness, oscillations, angle/ voltage instability, system margin, etc. Thus, PMUs make
possible the design of wide-area monitoring, protection, and control (WAMPAC) system for
the smart grid. PMU act as a power quality monitor for an electrical power network, which
measures instantaneous voltage & current phasors in the transmission line. It utilizes the
concept of synchrophasor, by which it can measure timestamped voltage/current magnitudes
at higher reporting rates than the SCADA system. The PMU is the main element of the Wide
Area Management System (WAMS) that permits the measurement of the bus voltages and
current signals.
[0006] At present, a number of manufacturers offer Phasor Measurement Unit (PMU) as a
commercial product, and deployment of PMU on power systems is being carried out in many
countries around the world. Currently, a lot of research is going on in modeling a Synchronized
PMU using simulation software.
[0007] For example, C-DAC has developed a Synchronized PMU, suitable for application in
Power System-Wide Area Measurements and as an interface to the SCADA system under the
ASTeC program, in collaboration with IIT-B and funded by DeitY. Central Power Research
Institute (CPRI) also serves as an independent authority for testing and certification of power
equipment. CPRI has considered PMU and its applications as their major thrust areas of
research. CPRI is developing a Phasor Measurement Unit System Testing and Calibration Lab
for hardware and software products. In order to have a national smart grid, the government of
India has also initiated various projects. One such pilot project was initiated in January 2010
by Power Grid Corporation of India Limited. The project had been implemented in the
Northern Region in India in order to gain firsthand experience in the use of this technology for
monitoring and control of large power grids. Synchrophasor initiative had been successfully
extended to southern, eastern, western, northeastern regions of the country.
5
[0008] However, existing PMUs have several issues. The PMUs are vulnerable to GPS attacks
and cannot mitigate probable GPS spoofing attacks. These PMUs use GPS data for location
and time synchronization. In the event, when GPS data is not able, existing PMUs might not
work.
OBJECT OF INVENTION
[0009] An object of the present disclosure is to provide a PMU for efficient phasor estimation.
[0010] Another object of the present disclosure is to provide a PMU for estimating frequency and
rate of change of frequency in a power grid.
[0011] Another object of the present disclosure is to provide a PMU that uses a non-GPS system
for position and time synchronization.
[0012] Another objective of the present disclosure is to provide modeling of PMU.
[0013] Another object of the present disclosure is to provide a PMU to measure the electrical
parameter in the power system in a frequency band of 44-55 Hz.
SUMMARY
[0014] A phasor measurement system for power system wide-area measurement and method for
calculating phasor values are described. The system includes one or more phasor measurement
units (PMU) installed at disperse locations in a power distribution network and a computing
device configured to receive phasor value from each of the one or more PMU to estimate
abnormal conditions. Each PMU is configured to measure phasor value from a specific location
in the power distribution network, store the phasor value in local storage, and send the
measured phasor value to the computing device through a communication module. The
computing device receives phasor values from the one or more PMUs, synchronizes the phasor
6
values received from the one or more PMUs using a common time source of a Navigation with
Indian Constellation (NAVIC) radio clock, correlates the synchronized phasor values to
determine the abnormal condition in the power distribution network, and alerts one or more
concerned person for preventive action.
[0015] In an embodiment, the system synchronizes the phasor values received from the one or
more PMUs integrated with NAVIC. The system is configured to calculate voltage phasors,
current phasors, frequency, rate of change of frequency (ROCOF), positive sequence, negative
sequence, and zero sequence components to improve the reliability of the power distribution
network by early detection of the abnormal condition.
[0016] In an embodiment, the PMU is configured to estimate amplitude value using any of a zerocrossing technique, Discrete Fourier Transform (DFT), or to slide DFT and estimate phasor
value and frequency using the least square technique.
[0017] In an embodiment, the system calculates the positive sequence, negative sequence, and
zero sequence components using Taylor Weighted Least Square (TWLS) technique.
[0018] A PMU can be a dedicated device, or the PMU function can be incorporated into
a protective relay or another device.
[0019] The PMU is used in smart grids for automation of the power system, to detect isolated
networks and prevent total system blackout, to maintain real-time power system stability, and
in power system monitoring, protection and control.
[0020] These and other aspects of the embodiments herein will be better appreciated and
understood when considered in conjunction with the following description and the
accompanying drawings. It should be understood, however, that the following descriptions,
while indicating preferred embodiments and numerous specific details thereof, are given by
way of illustration and not of limitation. Many changes and modifications may be made within
the scope of the embodiments herein without departing from the spirit thereof, and the
embodiments herein include all such modifications.
7
BRIEF DESCRIPTION OF FIGURES
[0021] The inventive concepts are illustrated in the accompanying drawings, throughout which
like reference letters indicate corresponding parts in the various figures. The embodiments
herein will be better understood from the following description with reference to the drawings,
in which:
[0022] FIG. 1 illustrates a block diagram of a phasor estimation system based on the NAVIC
system in accordance with an embodiment of the present disclosure.
[0023] FIG. 2 illustrates navigation with Indian Constellation (NAVIC) used in the phasor
estimation system in accordance with an embodiment of the present disclosure.
[0024] FIG. 3 illustrates an exemplary block diagram of a power distribution network monitoring
system configured to use the PMU in accordance with an embodiment of the present disclosure.
[0025] FIG. 4 illustrates an example process flow estimating abnormal conditions using phasor
measurement in accordance with an embodiment of the present disclosure.
DETAILED DESCRIPTION OF INVENTION
[0026] The embodiments herein and the various features and advantageous details thereof are
explained more fully with reference to the non-limiting embodiments that are illustrated in the
accompanying drawings and detailed in the following description. Descriptions of well-known
components and processing techniques are omitted so as to not unnecessarily obscure the
embodiments herein. Also, the various embodiments described herein are not necessarily
mutually exclusive, as some embodiments can be combined with one or more other
embodiments to form new embodiments. The term "or" as used herein refers to a non-exclusive
or unless otherwise indicated. As used herein, the term "and/or" includes any and all
combinations of one or more of the associated listed items. Expressions such as "at least one
of," when preceding a list of elements, modify the entire list of elements and do not modify the
individual elements of the list.The examples used herein are intended merely to facilitate an
understanding of ways in which the embodiments herein can be practiced and to further enable
those skilled in the art to practice the embodiments herein. Accordingly, the examples should
not be construed as limiting the scope of the embodiments herein.
8
[0027] As is traditional in the field, embodiments may be described and illustrated in terms of
blocks that carry out a described function or functions. These blocks, which may be referred
to herein as units or modules or the like, are physically implemented by electronic devicessuch
as mobile, laptop, mini-tablets, or the like and may optionally be driven by firmware and
software. The modules may, for example, be embodied in one or more electronic devices, or
on any other communication devices and the like. The modules constituting a block may be
implemented by dedicated hardware, or by a processor (e.g., one or more programmed
microprocessors and associated circuitry), or by a combination of dedicated hardware to
perform some functions of the block and a processor to perform other functions of the block.
Each block of the embodiments may be physically separated into two or more interacting and
discrete blocks without departing from the scope of the invention. Likewise, the blocks of the
embodiments may be physically combined into more complex blocks without departing from
the scope of the invention.
[0028] The accompanying drawings are used to help easily understand various technical features,
and it should be understood that the embodiments presented herein are not limited by the
accompanying drawings. As such, the present disclosure should be construed to extend to any
alterations, equivalents, and substitutes in addition to those which are particularly set out in the
accompanying drawings. Like numbers refer to like elements throughout.Thus, the same or
similar numbers may be described with reference to other drawings even if they are neither
mentioned nor described in the corresponding drawing.Also, elements that are not denoted by
reference numbers may be described with reference to other drawings.Although the terms first,
second, etc., may be used herein to describe various elements, these elements should not be
limited by these terms. These terms are generally only used to distinguish one element from
another.
[0029] Accordingly, embodiments herein disclose a phasor measurement system for power system
wide-area measurement, and the method for calculating phasor values is described. The system
includes one or more phasor measurement units (PMU) installed at disperse locations in a
power distribution network and a computing device configured to receive phasor value from
each of the one or more PMU to estimate abnormal conditions. Each PMU is configured to
9
measure phasor value from a specific location in the power distribution network, store the
phasor value in local storage, and send the measured phasor value to the computing device
through a communication module. The computing device receives phasor values from the one
or more PMUs, synchronizes the phasor values received from the one or more PMUs using a
common time source of a Navigation with Indian Constellation (NAVIC) radio clock,
correlates the synchronized phasor values to determine the abnormal condition in the power
distribution network, and alerts one or more concerned person for preventive action.
[0030] In an embodiment, the system synchronizes the phasor values received from the one or
more PMUs integrated with NAVIC. The system is configured to calculate voltage phasors,
current phasors, frequency, rate of change of frequency (ROCOF), positive sequence, negative
sequence, and zero sequence components to improve the reliability of the power distribution
network by early detection of the abnormal condition.
[0031] In an embodiment, the PMU is configured to estimate amplitude value using any of a zerocrossing technique, Discrete Fourier Transform (DFT) or sliding DFT, and estimate phasor
value and frequency using the least square technique.
[0032] In an embodiment, the system calculates the positive sequence, negative sequence, and
zero sequence components using Taylor Weighted Least Square (TWLS) technique.
[0033] A PMU can be a dedicated device, or the PMU function can be incorporated into
a protective relay or another device.
[0034] The PMU is used in smart grids for automation of the power system, to detect isolated
networks and prevent total system blackout, to maintain real-time power system stability, and
in power system monitoring, protection and control.
[0035] FIG. 1 illustrates a block diagram of the phasor estimation system based on the NAVIC
system in accordance with an embodiment of the present disclosure. The proposed system
uses NAVIC satellites (for simplicity of FIG. only one satellite is shown) to time
synchronization between multiple PMUs. A PMU includes an IRNSS receiver 102used to
receive a signal from the NAVIC satellite 116. The receiver 102 providesa primary
synchronization signal (PSS) to phase-locked oscillator 104, which provides a sampling
signal to A/D converter 106. The PMU includes an analog filter 112 configured to receive
10
3 phase electrical signal from power transmission lin2 114.The analog filter provides a
filtered signal to the A/D converter 106. The A/D converter 106 generates sample data
from the filtered signal based on the sampling signal. The PMU includes a microcontroller
108 that receives the sample data, adds the timestamp based on the time counter received
from the IRNSS receiver 102. IRNSS receiver 102 provides a very accurate time counter
in microsecond scale. The "second of century counter" provided by the IRNSS receiver is
used to tag the phasor value output. The microcontroller 108 of the PMU determines the
phasor value, tag it with the timestamp and store the phasor value in local memory (Not
shown in FIG.). The PMU may include a model 110 for transmitting the phasor value along
with the measurement timestamp to a central or cloud-based computing device. The PMU
system receives phasor values from other PMU in a similar manner and synchronizes the
phasor values to perform analysis to determine any abnormal behavior.
[0036] FIG. 2 illustrates navigation with Indian Constellation (NAVIC) used in the phasor
estimation system in accordance with an embodiment of the present disclosure. The system
uses the NAVIC system for timestamping the phasor values measured by PMU. The PMU is
configured to use a NAVIC timing system instead of a GPS timing system for better timing
accuracy. Accuracy of timing improves the accuracy of wide-area monitoring of power grids.
The NAVIC system is an independent Indian satellite-based positioning system for critical
National applications. The main objective is to provide Reliable Position, Navigation, and
Timing services over India and its neighborhoods202, to provide fairly good accuracy to the
user. Indian Space Research Organization (ISRO) has built a total of nine satellites in the
IRNSS series, of which eight are currently in orbit. Three of these satellites (e.g., satellite 206a,
satellite 206b, and satellite 206c) are in geostationary orbit (GEO) while the remaining (e.g.,
satellite 204a, satellite204b, satellite204c, and satellite204d) in geosynchronous orbits (GSO)
that maintain an inclination of 29° to the equatorial plane. The PMU system uses the time
service of the NAVIC. In an embodiment, the PMU may use other satellite-based timing
services that have equal or better accuracy.
[0037] FIG. 3 illustrates an exemplary block diagram of a power distribution network monitoring
system configured to use the PMU in accordance with an embodiment of the present disclosure.
11
PMU system 302 implemented on a central server or cloud-based computing device may
receive phasor values from one or more PMUs (e.g., PMU 308a, PMU 308b, PMU 308c, and
PMU 308d). A data concentrator and collector 304 of the system 302 collects phasor values
from the PMU 308a-d. Each of these PMUs receivesan electrical signal sample from the
respective location in the power transmission line and forward the phasor values to the PMU
system 302. Application software 306 of the system 302 may synchronize the phasor values
received from the one or more PMUs using a common time source of a Navigation with Indian
Constellation (NAVIC) radio clock, correlates the synchronized phasor values to determine
the abnormal condition in the power distribution network, and alerts one or more concerned
person for preventive action.
[0038] In an embodiment, the system synchronizes the phasor values received from the one or
more PMUs integrated with NAVIC system. The system is configured to calculate voltage
phasors, current phasors, frequency, rate of change of frequency (ROCOF), positive sequence,
negative sequence, and zero sequence components to improve the reliability of the power
distribution network by early detection of the abnormal condition.
[0039] In an embodiment, the PMU is configured to estimate amplitude value using any of a zerocrossing technique, Discrete Fourier Transform (DFT) or sliding DFT, and estimate phasor
value and frequency using the least square technique.
[0040] In an embodiment, the system calculates the positive sequence, negative sequence, and
zero sequence components using Taylor Weighted Least Square (TWLS) technique. The
application software 306 may generally signal for other systemsand provide a signal to control
protection functions to take preventive and corrective actions, whenever required. The
application software 306 may archive the phasor value and other measured values in a
database.
[0041] System 302 implements an efficient algorithm as described above for phasor estimation,
frequency, and rate of change of frequency estimation. System 302 usage an anti-aliasing filter
to measure electrical parameters in the power system frequency band of 45-55 Hz. The system
302 is designed to use a phase-locked oscillator circuit to generate pulses having a pulse rate
of 60 kHz and its integration with a NAVIC system. The system 302 provides a timing
12
accuracy of less than a microsecond (e.g., 50 ns or better) and better and measurement accuracy
with a potential error of +/- 1 %.
[0042] FIG. 4 illustrates an example process flow estimating abnormal conditions using phasor
measurement in accordance with an embodiment of the present disclosure. Method 400 for
Power System-Wide Area Measurements includes steps of measuring, using each phasor
measurement unit (PMU) of a one or more PMUs of a power distribution network, phasor
value from a specific location in the power distribution network as shown at block 402. Method
400 further includes steps of storing, at each PMU of the one or more PMUs, the phasor value
in local storage as shown at block 404, and sending, by each PMU of the one or more PMUs,
the measured phasor value to a computing device through a communication module as shown
at block 406. Method 400 includes further steps performed on a central system or cloud-based
system. The steps include receiving phasor values from the one or more PMUs as shown at
block 408, synchronizing the phasor values received from the one or more PMUs using a
common time source of a Navigation with Indian Constellation (NAVIC) radio clock as shown
at block 410, correlating the synchronized phasor values to determine the abnormal condition
in the power distribution network as shown at block 412, and alerting one or more concerned
person for preventive action as shown at block 414.
[0043] The various actions, acts, blocks, steps, or the like in the FIGS. 1-4 may be performed in
the order presented, in a different order, or simultaneously. Further, in some embodiments,
some of the actions, acts, blocks, steps, or the like may be omitted, added, modified, skipped,
or the like without departing from the scope of the invention.
[0044] The embodiments disclosed herein can be implemented using at least one software program
running on at least one hardware device and performing network management functions to
control the elements.
[0045] The foregoing description of the specific embodiments will so fully reveal the general
nature of the embodiments herein that others can, by applying current knowledge, readily
modify and/or adapt for various applications such specific embodiments without departing
from the generic concept, and, therefore, such adaptations and modifications should and are
intended to be comprehended within the meaning and range of equivalents of the disclosed
13
embodiments. It is to be understood that the phraseology or terminology employed herein is
for the purpose of description and not of limitation. Therefore, while the embodiments herein
have been described in terms of preferred embodiments, those skilled in the art will recognize
that the embodiments herein can be practiced with modification within the spirit and scope of
the embodiments as described herein.
ADVANTAGE OF INVENTION
[0046] The present disclosure provides a PMU for efficient phasor estimation.
[0047] The present disclosure provides a PMU for estimating frequency and rate of change of
frequency in a power grid.
[0048] The present disclosure provides a PMU that usesa non-GPS system for position and time
synchronization.
[0049] The present disclosure provides modeling of PMU.
[0050] The present disclosure provides a PMU to measure an electrical parameter in the power
system in a frequency band of 44-55 Hz.

CLAIMS
We Claim:
1. A phasor measurement system (302) for Power System-Wide Area Measurements, the
system (302) comprisingone or more phasor measurement units (PMU) (308a-d) installed at disperse
locations in a power distribution network, wherein each of the one or more PMUs
is configured to measure phasor value from a specific location in the power
distribution network, store the phasor value in local storage, and send the measured
phasor value to a computing device through a communication module (110); and
the computing device configured to
receive phasor values from the one or more PMUs(308a-d);
synchronize the phasor values received from the one or more PMUs using
a common time source of a Navigation with Indian Constellation (NAVIC) radio
clock;
correlate the synchronized phasor values to determine the abnormal
condition in the power distribution network; and
alerting one or more concerned persons for preventive action.
2. The system of claim 1, wherein the phasor values received from one or more PMUs are
synchronized using a NAVIC timing system.
3. The system of claim 1 configured to calculate voltage phasors, current phasors,
frequency, rate of change of frequency (ROCOF), positive sequence, negative
sequence, and zero sequence components to improve the reliability of the power
distribution network by early detection of the abnormal condition.
15
4. The system of claim 1, wherein each PMU is configured to estimate phasor values and
its sequence components using any of a zero-crossing technique, Discrete Fourier
Transform (DFT) or sliding DFT, and Taylor Weighted Least Square (TWLS)
technique.
5. The system of claim 4, wherein sequence components comprise positive sequence,
negative sequence, and zero sequence components.
6. A method for Power System-Wide Area Measurements, the method comprisingmeasuring, using each phasor measurement unit (PMU) of a one or more PMUs of
a power distribution network, phasor value from a specific location in the power
distribution network;
storing, at each PMU of the one or more PMUs, the phasor value in local storage;
sending, by each PMU of the one or more PMUs, the measured phasor value to a
computing device through a communication module;
receiving phasor values from the one or more PMUs;
synchronizing the phasor values received from the one or more PMUs using a
common time source of a Navigation with Indian Constellation (NAVIC) radio
clock;
correlating the synchronized phasor values to determine the abnormal condition in
the power distribution network; and
alerting one or more concerned persons for preventive action.
7. The method of claim 6, wherein the phasor values received from the one or more PMUs
are synchronized using a NAVIC timing system.
8. The method of claim 6 is further configured to calculate voltage phasors, current
phasors, frequency, rate of change of frequency (ROCOF), positive sequence, negative
16
sequence, and zero sequence components to improve the reliability of the power
distribution network by early detection of the abnormal condition.
9. The method of claim 6, wherein each PMU is configured to estimate phasor values and
its sequence components using any of a zero-crossing technique, Discrete Fourier
Transform (DFT) or sliding DFT, and Taylor Weighted Least Square (TWLS)
technique.
10. The method of claim 9, wherein sequence components comprise positive sequence,
negative sequence, and zero sequence components.