The document discusses synchronized phasor measurements in electric power systems and their applications. Precise synchronization of phasor measurements across substations separated by hundreds of miles enables a consistent description of the power system state. GPS provides an ideal synchronization source. Synchronized phasors can improve state estimation algorithms, provide dynamic state estimates, enhance control techniques, and improve protection concepts. The paper describes phasor measurement implementation and several uses including improved state estimation, control, detection of instability, and adaptive relaying.
The document compares different algorithms for detecting voltage sags and swells in power systems. It describes RMS voltage detection, peak voltage detection, and discrete Fourier transform (DFT) methods. RMS detection uses historical data so it can be slow for mitigation. Peak detection requires only single-phase values but DFT is best for steady signals and not fast transients. The paper proposes a novel real-time algorithm to rapidly detect voltage sags and compares it to existing methods.
This document proposes an adaptive scheme for measuring signal parameters for generator monitoring and protection using adaptive orthogonal filters. The algorithm adapts the filter data window length and coefficients according to a coarse estimation of the signal frequency, allowing accurate measurements over a wide frequency band including during generator start-up. Measured signals are also used to train artificial neural networks to classify generator operation modes and detect phenomena like pole slipping and out-of-step conditions. The document describes the adaptive measurement scheme, provides an example using signals from simulations, and discusses using a genetic algorithm to optimize the design of an artificial neural network-based out-of-step protection system.
International Journal of Engineering Research and DevelopmentIJERD Editor
This document compares the performance of a five-level photovoltaic inverter using two different maximum power point tracking (MPPT) algorithms: perturb and observe and incremental conductance. The five-level inverter topology uses a novel pulse width modulation control scheme. Simulation results show that using the incremental conductance MPPT algorithm reduces the total harmonic distortion from 39% to 28% and improves the power factor compared to using the perturb and observe MPPT method under changing atmospheric conditions. The incremental conductance MPPT algorithm can also track maximum power points more rapidly than the perturb and observe method.
Mitigation of Lower Order Harmonics with Filtered Svpwm In Multiphase Voltage...IJERA Editor
Multi-phase machines and drives is a topic of growing relevance in recent years, and it presents many challenging issues that still need further research. This is the case of multi-phase space vector pulse width modulation (SVPWM), which shows not only more space vectors than the standard three-phase case, but also new subspaces where the space vectors are mapped. In the digital implementation, multiphase reference voltages are sampled and fed into the digital modulator to produce gating signals at a constant clock rate f. This means a finite pulse-width resolution because the gating state transition can only occur at some specific time instants depending on frequency. This results in a deviation of produced phase voltages from the desired phase voltages, i.e., increasing harmonic distortion especially for a small modulation index signal. In the present paper a filtered space-vector pulse-width modulation (SVPWM) considering finite pulse-width resolution is proposed to produce a switching sequence with reduced baseband harmonics for multiphase voltage source inverters (VSI). This is achieved by incorporating a pseudo feedback loop regarding weighted voltage difference between desired and produced phase voltages.
This document discusses power density spectrum, which shows how the energy of a signal is distributed over different frequencies. Any signal can be represented as a summation of sinusoids using Fourier analysis. The Fourier transform breaks down a signal into sine and cosine components. A Fourier series represents periodic signals as an infinite sum of sines and cosines. The frequency spectrum shows the frequencies contained in a signal. Each frequency component is obtained from the Fourier transform. The average power of a discrete-time periodic signal can be expressed as the sum of powers of the individual frequency components. The power density spectrum is the distribution of this power as a function of frequency.
This document presents a new method for locating ungrounded faults in underground distribution systems using wavelet analysis and artificial neural networks (ANNs). Voltage and current signals are simulated for different fault types, locations, and conditions using EMTP software. Wavelet analysis is used to extract features from the signals related to fault classification and location. ANNs are then applied to classify fault types based on the extracted features and to determine the fault location for each fault type based on additional extracted features. The results indicate the technique can accurately locate faults under a variety of system conditions.
Transient Monitoring Function based Fault Classifier for Relaying Applications IJECEIAES
This paper proposes Transient monitoring function (TMF) based fault classification approach for transmission line protection. The classifier provides accurate results under various system conditions involving fault resistance, inception angle, location and load angle. The transient component during fault is measured by TMF and appropriate logics applied for fault classification. Simulation studies using MATLAB ® /SIMULINK ™ are carried out for a 400 kV, 50 Hz power system with variable system conditions. Results show that the proposed classifier has high classification accuracy. The method developed has been compared with a fault classification technique based on Discrete Wavelet Transform (DWT). The proposed technique can be implemented for real time protection schemes employing distance relaying.
Basics of Power systems
Network topology
Transmission and Distribution
Load and Resource Balance
Economic Dispatch
Steady State System Analysis
Power flow analysis
Dynamic System Analysis
Transient stability
The document compares different algorithms for detecting voltage sags and swells in power systems. It describes RMS voltage detection, peak voltage detection, and discrete Fourier transform (DFT) methods. RMS detection uses historical data so it can be slow for mitigation. Peak detection requires only single-phase values but DFT is best for steady signals and not fast transients. The paper proposes a novel real-time algorithm to rapidly detect voltage sags and compares it to existing methods.
This document proposes an adaptive scheme for measuring signal parameters for generator monitoring and protection using adaptive orthogonal filters. The algorithm adapts the filter data window length and coefficients according to a coarse estimation of the signal frequency, allowing accurate measurements over a wide frequency band including during generator start-up. Measured signals are also used to train artificial neural networks to classify generator operation modes and detect phenomena like pole slipping and out-of-step conditions. The document describes the adaptive measurement scheme, provides an example using signals from simulations, and discusses using a genetic algorithm to optimize the design of an artificial neural network-based out-of-step protection system.
International Journal of Engineering Research and DevelopmentIJERD Editor
This document compares the performance of a five-level photovoltaic inverter using two different maximum power point tracking (MPPT) algorithms: perturb and observe and incremental conductance. The five-level inverter topology uses a novel pulse width modulation control scheme. Simulation results show that using the incremental conductance MPPT algorithm reduces the total harmonic distortion from 39% to 28% and improves the power factor compared to using the perturb and observe MPPT method under changing atmospheric conditions. The incremental conductance MPPT algorithm can also track maximum power points more rapidly than the perturb and observe method.
Mitigation of Lower Order Harmonics with Filtered Svpwm In Multiphase Voltage...IJERA Editor
Multi-phase machines and drives is a topic of growing relevance in recent years, and it presents many challenging issues that still need further research. This is the case of multi-phase space vector pulse width modulation (SVPWM), which shows not only more space vectors than the standard three-phase case, but also new subspaces where the space vectors are mapped. In the digital implementation, multiphase reference voltages are sampled and fed into the digital modulator to produce gating signals at a constant clock rate f. This means a finite pulse-width resolution because the gating state transition can only occur at some specific time instants depending on frequency. This results in a deviation of produced phase voltages from the desired phase voltages, i.e., increasing harmonic distortion especially for a small modulation index signal. In the present paper a filtered space-vector pulse-width modulation (SVPWM) considering finite pulse-width resolution is proposed to produce a switching sequence with reduced baseband harmonics for multiphase voltage source inverters (VSI). This is achieved by incorporating a pseudo feedback loop regarding weighted voltage difference between desired and produced phase voltages.
This document discusses power density spectrum, which shows how the energy of a signal is distributed over different frequencies. Any signal can be represented as a summation of sinusoids using Fourier analysis. The Fourier transform breaks down a signal into sine and cosine components. A Fourier series represents periodic signals as an infinite sum of sines and cosines. The frequency spectrum shows the frequencies contained in a signal. Each frequency component is obtained from the Fourier transform. The average power of a discrete-time periodic signal can be expressed as the sum of powers of the individual frequency components. The power density spectrum is the distribution of this power as a function of frequency.
This document presents a new method for locating ungrounded faults in underground distribution systems using wavelet analysis and artificial neural networks (ANNs). Voltage and current signals are simulated for different fault types, locations, and conditions using EMTP software. Wavelet analysis is used to extract features from the signals related to fault classification and location. ANNs are then applied to classify fault types based on the extracted features and to determine the fault location for each fault type based on additional extracted features. The results indicate the technique can accurately locate faults under a variety of system conditions.
Transient Monitoring Function based Fault Classifier for Relaying Applications IJECEIAES
This paper proposes Transient monitoring function (TMF) based fault classification approach for transmission line protection. The classifier provides accurate results under various system conditions involving fault resistance, inception angle, location and load angle. The transient component during fault is measured by TMF and appropriate logics applied for fault classification. Simulation studies using MATLAB ® /SIMULINK ™ are carried out for a 400 kV, 50 Hz power system with variable system conditions. Results show that the proposed classifier has high classification accuracy. The method developed has been compared with a fault classification technique based on Discrete Wavelet Transform (DWT). The proposed technique can be implemented for real time protection schemes employing distance relaying.
Basics of Power systems
Network topology
Transmission and Distribution
Load and Resource Balance
Economic Dispatch
Steady State System Analysis
Power flow analysis
Dynamic System Analysis
Transient stability
MTM (Multitaper Method) is a non-parametric method for spectral estimation that reduces spectral leakage. It involves selecting data tapers within a chosen frequency bandwidth, multiplying the tapers with the signal, and averaging the resulting tapered spectra to estimate the power spectrum. MTM uses orthogonal Slepian tapers to generate multiple tapered versions of the input signal, then averages their periodograms to obtain the spectral estimate. This reduces variance compared to using a single taper. MTM has applications in analyzing atmospheric, oceanic, paleoclimate, geochemical, and seismological time series data.
This document discusses modeling of biomedical signals. It introduces autoregressive (AR) and moving average (MA) modeling techniques. For AR modeling, it describes three methods for computing the model parameters: the least squares method, the autocorrelation method, and the covariance method. The least squares method minimizes the mean squared error between predicted and actual signal samples. The autocorrelation and covariance methods relate the AR model parameters to the autocorrelation function of the signal.
parametric method of power spectrum Estimationjunjer
The document discusses parametric methods of power spectrum estimation. It explains that parametric methods estimate the parameters of a mathematical model that describes the signal generation process. This involves selecting a model such as autoregressive (AR), moving average (MA), or autoregressive moving average (ARMA), estimating the model parameters from the data, and then using the estimated parameters to calculate the power spectrum. The document provides details on how to estimate the power spectrum using AR, MA, and ARMA models. It also discusses maximum entropy spectral estimation and high-resolution spectral estimation based on eigen-analysis.
Three-phase harmonic filters use RLC components to reduce voltage distortion and correct power factors by diverting harmonic currents in low impedance paths. Four common filter types are single-tuned, double-tuned, high-pass, and C-type high-pass filters, which are used individually or together in power systems to filter different harmonic orders. The Three-Phase Harmonic Filter block models these filter types using tunable resistance, inductance, and capacitance values.
non parametric methods for power spectrum estimatonBhavika Jethani
non-parametric methods for power spectrum estimation which includes bartlett method, welch method , blackman and tukey methods and also the comparision of all these methods
This document summarizes a technical seminar on applying a sub-harmonic protection relay. It defines relevant terms like sub-harmonic frequencies and sub-synchronous resonance. It describes loads that can cause sub-harmonic disturbances and the principle of how the protection relay detects sub-harmonics. The relay provides protection for transmission lines and monitors systems for sub-harmonic oscillations. Settings for the relay are determined based on analysis of recorded sub-harmonic current responses during events.
Abstract-This paper presents the novel synchronous frame hysteresis controller for three phase Uninterruptible Power Supply (UPS)based on Z-Source Inverter (ZSI). The proposedsynchronous frame approach minimizes the hysteresis control time delay to onesixthof the fundamental period such that the dynamic response is significantly improved. The hysteresis band currentcontroller determines the switching signals, and the algorithm based onanextension of Synchronous Reference Frame(SRF) Theory (d-q-0) is used to determine thesuitable current reference signals. A filter is applied to further enhance the accuracy of steadystate tracking.Low total harmonic distortion has been achieved under heavilydistorted nonlinear load and unbalanced load.The ZSI provides agreat alternative with lower cost, higher reliability and higher efficiency.
Comparison analysis of shunt active filter and transformerless parallel hybri...csandit
This research work presents the comparison analysis of Shunt Active Filter (SAF) with Parallel
Hybrid Active Filter (PHAF). The performances of SAF and PHAF have been analyzed with PI
controllers based on Synchronous Reference Frame theory. In each case, simulation is carried
out for three phase unbalanced non liner load conditions. The advantages of the designed
system and the proposed current reference calculation methods are verified by simulations
using MATLAB Power system Toolbox.
COMPARISON ANALYSIS OF SHUNT ACTIVE FILTER AND TRANSFORMERLESS PARALLEL HYBRI...cscpconf
This research work presents the comparison analysis of Shunt Active Filter (SAF) with Parallel Hybrid Active Filter (PHAF). The performances of SAF and PHAF have been analyzed with PI controllers based on Synchronous Reference Frame theory. In each case, simulation is carried out for three phase unbalanced non liner load conditions. The advantages of the designed system and the proposed current reference calculation methods are verified by simulations using MATLAB Power system Toolbox.
1) The document discusses power spectrum estimation methods for digital signal processing.
2) It describes five common non-parametric power spectrum estimation techniques: periodogram method, modified periodogram method, Bartlett's method, Welch's method, and Blackman-Tukey method.
3) Each method has different tradeoffs between frequency resolution, variance, and bias that make some techniques better for certain applications like feature extraction.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Determining Multiple Steady State Zcs Operating Points Of A Switch Mode Conta...tchunsen
The document presents a new method for determining all possible steady-state zero current switching (ZCS) operating points of a switch-mode contactless power transfer system. It uses a stroboscopic mapping model and calculates fixed points corresponding to circuit ZCS conditions. This allows identifying four steady-state operating points for an inductor-capacitor-inductor type system. Parameter influences on ZCS periods are studied using bifurcation diagrams. Both simulations and experiments verified the proposed method, providing opportunities for a practical system to operate at different soft switching frequencies.
A review of Wireless Information and Power Transfer in Multiuser OFDM SystemsIJERA Editor
We study the resource allocation algorithm design for multiuser orthogonal frequency division multiplexing
(OFDM) downlink systems with simultaneous wireless information and power transfer. The algorithm design is
formulated as a non-convex optimization problem for maximizing the energy efficiency of data transmission
(bit/Joule delivered to the users). In particular, the problem formulation takes into account the minimum
required system data rate, heterogeneous minimum required power transfers to the users, and the circuit power
consumption. Subsequently, by exploiting the method of timesharing and the properties of nonlinear fractional
programming, the considered non-convex optimization problem is solved using an efficient iterative resource
allocation algorithm. Recently, simultaneous wireless information and power transfer (SWIPT) becomes
appealing by essentially providing a perpetual energy source for the wireless networks. For the TDMA-based
information transmission, we employ TS at the receivers; for the OFDMA-based information transmission, we
employ PS at the receivers. Under the above two scenarios, we address the problem of maximizing the weighted
sum-rate over all users by varying the time/frequency power allocation and either TS or PS ratio, subject to a
minimum harvested energy constraint on each user as well as a peak and/or total transmission power constraint.
Wavelet energy moment and neural networks based particle swarm optimisation f...journalBEEI
In this study, a combined approach of discrete wavelet transform analysis and a feed forward neural networks algorithm to detect and classify transmission line faults. The proposed algorithm uses a multi -resolution analysis decoposition of three-phasecurrents only to calculate the wavelet energy moment of detailed coefficients. In comparison with the energy spectrum, the energy moment could reveal the energy distribution features better, which is beneficial when extracting signal features. Theapproach use particle swarm optimization algorithm to train a feed forward neural network. The goal is the enhancement of the convergence rate, learning process and fill up the gap of local minimum point.The purposed scheme consists of two FNNs, one for detecting and another for classifying all the ten types of faults using Matlab/Simulink. The proposed algorithm have been extensively tested on a system 400 kV, 3 phases, 100 km line consideringvarious fault parameter variations.
Hybrid Time-power Switching Protocol of Energy Harvesting Bidirectional Relay...TELKOMNIKA JOURNAL
In this paper, we investigate system performance in term of throughput and ergodic capacity of the hybrid time-power switching protocol of energy harvesting bidirectional relaying network. In the first stage, the analytical expression of the system throughput and ergodic capacity of the model system is proposed and derived. In this analysis, both delay-limited and delay-tolerant transmission modes are presented and considered. After that, the effect of various system parameters on the proposed system is investigated and demonstrated by Monte-Carlo simulation. Finally, the results show that the analytical mathematical and simulated results match for all possible parameter values for both schemes.
A Modified Novel Approach to Control of Thyristor Controlled Series Capacitor...IOSR Journals
1) The document presents a modified control system for a Thyristor Controlled Series Capacitor (TCSC) based on instantaneous power (PQ) theory. Using instantaneous current and voltage measurements, the control system can instantaneously calculate the active and reactive power flow to control the TCSC thyristor firing angle.
2) Simulations show the control system using instantaneous power values responds faster and more accurately to disturbances compared to a control system using RMS power values. The instantaneous power control stabilized the power flow within 0.4 seconds after a disturbance, while the RMS control took 0.46 seconds.
3) The control system was able to accurately control the power flow through a transmission line
Implementation of Instantaneous Reactive Power Theory for Current Harmonic Re...IOSR Journals
This document discusses implementing the instantaneous reactive power theory (IRP theory) for current harmonic reduction and reactive power compensation in a three phase four wire power system. The IRP theory defines instantaneous power components in the α-β-0 coordinate system. It can calculate the reference compensating currents required by a shunt active power filter to inject into the network. Simulations show the power filter can reduce current harmonics and reactive power, improving the power factor by making the source current sinusoidal and in phase with the voltage. The IRP theory provides a flexible way to select the undesirable power components for compensation to minimize pollution from nonlinear loads.
State Estimation of Power System with Interline Power Flow ControllerIDES Editor
This document summarizes a research paper on state estimation of power systems with Interline Power Flow Controllers (IPFCs). The key points are:
1) A new state estimation method is proposed that incorporates an IPFC power injection model into the conventional state estimation algorithm.
2) The IPFC is modeled as injecting both real and reactive power at the buses it connects. This power injection model represents the effect of the IPFC on power flows.
3) The proposed method is tested on the Anderson and Fouad 9-bus system and results are presented. The method allows state estimation of power systems that include FACTS devices like the IPFC.
International Journal of Engineering Research and DevelopmentIJERD Editor
Electrical, Electronics and Computer Engineering,
Information Engineering and Technology,
Mechanical, Industrial and Manufacturing Engineering,
Automation and Mechatronics Engineering,
Material and Chemical Engineering,
Civil and Architecture Engineering,
Biotechnology and Bio Engineering,
Environmental Engineering,
Petroleum and Mining Engineering,
Marine and Agriculture engineering,
Aerospace Engineering.
A Simulink Model for Damping Power System Oscillations Using Fact DevicesIOSR Journals
This document presents a Simulink model for damping power system oscillations using FACTS devices. It describes a hybrid series compensation scheme using a single-phase thyristor controlled series capacitor (TCSC) and fixed capacitors on the other two phases. The TCSC is equipped with a proportional-integral controller to modulate its reactance based on stabilizing signals. Case studies on a test power system show the hybrid scheme provides better damping than fixed compensation alone. The best damping was achieved using local generator angle differences as stabilizing signals.
MTM (Multitaper Method) is a non-parametric method for spectral estimation that reduces spectral leakage. It involves selecting data tapers within a chosen frequency bandwidth, multiplying the tapers with the signal, and averaging the resulting tapered spectra to estimate the power spectrum. MTM uses orthogonal Slepian tapers to generate multiple tapered versions of the input signal, then averages their periodograms to obtain the spectral estimate. This reduces variance compared to using a single taper. MTM has applications in analyzing atmospheric, oceanic, paleoclimate, geochemical, and seismological time series data.
This document discusses modeling of biomedical signals. It introduces autoregressive (AR) and moving average (MA) modeling techniques. For AR modeling, it describes three methods for computing the model parameters: the least squares method, the autocorrelation method, and the covariance method. The least squares method minimizes the mean squared error between predicted and actual signal samples. The autocorrelation and covariance methods relate the AR model parameters to the autocorrelation function of the signal.
parametric method of power spectrum Estimationjunjer
The document discusses parametric methods of power spectrum estimation. It explains that parametric methods estimate the parameters of a mathematical model that describes the signal generation process. This involves selecting a model such as autoregressive (AR), moving average (MA), or autoregressive moving average (ARMA), estimating the model parameters from the data, and then using the estimated parameters to calculate the power spectrum. The document provides details on how to estimate the power spectrum using AR, MA, and ARMA models. It also discusses maximum entropy spectral estimation and high-resolution spectral estimation based on eigen-analysis.
Three-phase harmonic filters use RLC components to reduce voltage distortion and correct power factors by diverting harmonic currents in low impedance paths. Four common filter types are single-tuned, double-tuned, high-pass, and C-type high-pass filters, which are used individually or together in power systems to filter different harmonic orders. The Three-Phase Harmonic Filter block models these filter types using tunable resistance, inductance, and capacitance values.
non parametric methods for power spectrum estimatonBhavika Jethani
non-parametric methods for power spectrum estimation which includes bartlett method, welch method , blackman and tukey methods and also the comparision of all these methods
This document summarizes a technical seminar on applying a sub-harmonic protection relay. It defines relevant terms like sub-harmonic frequencies and sub-synchronous resonance. It describes loads that can cause sub-harmonic disturbances and the principle of how the protection relay detects sub-harmonics. The relay provides protection for transmission lines and monitors systems for sub-harmonic oscillations. Settings for the relay are determined based on analysis of recorded sub-harmonic current responses during events.
Abstract-This paper presents the novel synchronous frame hysteresis controller for three phase Uninterruptible Power Supply (UPS)based on Z-Source Inverter (ZSI). The proposedsynchronous frame approach minimizes the hysteresis control time delay to onesixthof the fundamental period such that the dynamic response is significantly improved. The hysteresis band currentcontroller determines the switching signals, and the algorithm based onanextension of Synchronous Reference Frame(SRF) Theory (d-q-0) is used to determine thesuitable current reference signals. A filter is applied to further enhance the accuracy of steadystate tracking.Low total harmonic distortion has been achieved under heavilydistorted nonlinear load and unbalanced load.The ZSI provides agreat alternative with lower cost, higher reliability and higher efficiency.
Comparison analysis of shunt active filter and transformerless parallel hybri...csandit
This research work presents the comparison analysis of Shunt Active Filter (SAF) with Parallel
Hybrid Active Filter (PHAF). The performances of SAF and PHAF have been analyzed with PI
controllers based on Synchronous Reference Frame theory. In each case, simulation is carried
out for three phase unbalanced non liner load conditions. The advantages of the designed
system and the proposed current reference calculation methods are verified by simulations
using MATLAB Power system Toolbox.
COMPARISON ANALYSIS OF SHUNT ACTIVE FILTER AND TRANSFORMERLESS PARALLEL HYBRI...cscpconf
This research work presents the comparison analysis of Shunt Active Filter (SAF) with Parallel Hybrid Active Filter (PHAF). The performances of SAF and PHAF have been analyzed with PI controllers based on Synchronous Reference Frame theory. In each case, simulation is carried out for three phase unbalanced non liner load conditions. The advantages of the designed system and the proposed current reference calculation methods are verified by simulations using MATLAB Power system Toolbox.
1) The document discusses power spectrum estimation methods for digital signal processing.
2) It describes five common non-parametric power spectrum estimation techniques: periodogram method, modified periodogram method, Bartlett's method, Welch's method, and Blackman-Tukey method.
3) Each method has different tradeoffs between frequency resolution, variance, and bias that make some techniques better for certain applications like feature extraction.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Determining Multiple Steady State Zcs Operating Points Of A Switch Mode Conta...tchunsen
The document presents a new method for determining all possible steady-state zero current switching (ZCS) operating points of a switch-mode contactless power transfer system. It uses a stroboscopic mapping model and calculates fixed points corresponding to circuit ZCS conditions. This allows identifying four steady-state operating points for an inductor-capacitor-inductor type system. Parameter influences on ZCS periods are studied using bifurcation diagrams. Both simulations and experiments verified the proposed method, providing opportunities for a practical system to operate at different soft switching frequencies.
A review of Wireless Information and Power Transfer in Multiuser OFDM SystemsIJERA Editor
We study the resource allocation algorithm design for multiuser orthogonal frequency division multiplexing
(OFDM) downlink systems with simultaneous wireless information and power transfer. The algorithm design is
formulated as a non-convex optimization problem for maximizing the energy efficiency of data transmission
(bit/Joule delivered to the users). In particular, the problem formulation takes into account the minimum
required system data rate, heterogeneous minimum required power transfers to the users, and the circuit power
consumption. Subsequently, by exploiting the method of timesharing and the properties of nonlinear fractional
programming, the considered non-convex optimization problem is solved using an efficient iterative resource
allocation algorithm. Recently, simultaneous wireless information and power transfer (SWIPT) becomes
appealing by essentially providing a perpetual energy source for the wireless networks. For the TDMA-based
information transmission, we employ TS at the receivers; for the OFDMA-based information transmission, we
employ PS at the receivers. Under the above two scenarios, we address the problem of maximizing the weighted
sum-rate over all users by varying the time/frequency power allocation and either TS or PS ratio, subject to a
minimum harvested energy constraint on each user as well as a peak and/or total transmission power constraint.
Wavelet energy moment and neural networks based particle swarm optimisation f...journalBEEI
In this study, a combined approach of discrete wavelet transform analysis and a feed forward neural networks algorithm to detect and classify transmission line faults. The proposed algorithm uses a multi -resolution analysis decoposition of three-phasecurrents only to calculate the wavelet energy moment of detailed coefficients. In comparison with the energy spectrum, the energy moment could reveal the energy distribution features better, which is beneficial when extracting signal features. Theapproach use particle swarm optimization algorithm to train a feed forward neural network. The goal is the enhancement of the convergence rate, learning process and fill up the gap of local minimum point.The purposed scheme consists of two FNNs, one for detecting and another for classifying all the ten types of faults using Matlab/Simulink. The proposed algorithm have been extensively tested on a system 400 kV, 3 phases, 100 km line consideringvarious fault parameter variations.
Hybrid Time-power Switching Protocol of Energy Harvesting Bidirectional Relay...TELKOMNIKA JOURNAL
In this paper, we investigate system performance in term of throughput and ergodic capacity of the hybrid time-power switching protocol of energy harvesting bidirectional relaying network. In the first stage, the analytical expression of the system throughput and ergodic capacity of the model system is proposed and derived. In this analysis, both delay-limited and delay-tolerant transmission modes are presented and considered. After that, the effect of various system parameters on the proposed system is investigated and demonstrated by Monte-Carlo simulation. Finally, the results show that the analytical mathematical and simulated results match for all possible parameter values for both schemes.
A Modified Novel Approach to Control of Thyristor Controlled Series Capacitor...IOSR Journals
1) The document presents a modified control system for a Thyristor Controlled Series Capacitor (TCSC) based on instantaneous power (PQ) theory. Using instantaneous current and voltage measurements, the control system can instantaneously calculate the active and reactive power flow to control the TCSC thyristor firing angle.
2) Simulations show the control system using instantaneous power values responds faster and more accurately to disturbances compared to a control system using RMS power values. The instantaneous power control stabilized the power flow within 0.4 seconds after a disturbance, while the RMS control took 0.46 seconds.
3) The control system was able to accurately control the power flow through a transmission line
Implementation of Instantaneous Reactive Power Theory for Current Harmonic Re...IOSR Journals
This document discusses implementing the instantaneous reactive power theory (IRP theory) for current harmonic reduction and reactive power compensation in a three phase four wire power system. The IRP theory defines instantaneous power components in the α-β-0 coordinate system. It can calculate the reference compensating currents required by a shunt active power filter to inject into the network. Simulations show the power filter can reduce current harmonics and reactive power, improving the power factor by making the source current sinusoidal and in phase with the voltage. The IRP theory provides a flexible way to select the undesirable power components for compensation to minimize pollution from nonlinear loads.
State Estimation of Power System with Interline Power Flow ControllerIDES Editor
This document summarizes a research paper on state estimation of power systems with Interline Power Flow Controllers (IPFCs). The key points are:
1) A new state estimation method is proposed that incorporates an IPFC power injection model into the conventional state estimation algorithm.
2) The IPFC is modeled as injecting both real and reactive power at the buses it connects. This power injection model represents the effect of the IPFC on power flows.
3) The proposed method is tested on the Anderson and Fouad 9-bus system and results are presented. The method allows state estimation of power systems that include FACTS devices like the IPFC.
International Journal of Engineering Research and DevelopmentIJERD Editor
Electrical, Electronics and Computer Engineering,
Information Engineering and Technology,
Mechanical, Industrial and Manufacturing Engineering,
Automation and Mechatronics Engineering,
Material and Chemical Engineering,
Civil and Architecture Engineering,
Biotechnology and Bio Engineering,
Environmental Engineering,
Petroleum and Mining Engineering,
Marine and Agriculture engineering,
Aerospace Engineering.
A Simulink Model for Damping Power System Oscillations Using Fact DevicesIOSR Journals
This document presents a Simulink model for damping power system oscillations using FACTS devices. It describes a hybrid series compensation scheme using a single-phase thyristor controlled series capacitor (TCSC) and fixed capacitors on the other two phases. The TCSC is equipped with a proportional-integral controller to modulate its reactance based on stabilizing signals. Case studies on a test power system show the hybrid scheme provides better damping than fixed compensation alone. The best damping was achieved using local generator angle differences as stabilizing signals.
The document describes a power system model used to obtain training data for an artificial neural network (ANN) to detect high impedance faults. The power system model includes two radial distribution feeders with linear and nonlinear loads, voltage correction capacitor banks, and an equivalent high impedance fault arc model. Digital simulations were performed using an electromagnetic transient program to generate training data for different fault types, locations, and contingencies like capacitor switching. The proposed ANN module processes current and voltage signals at the beginning of the distribution line. Its six inputs are the second and third harmonics of residual current and voltage, as well as the second and third harmonics of residual apparent impedance. The ANN is trained to detect high impedance faults based
IJCER (www.ijceronline.com) International Journal of computational Engineeri...ijceronline
This document summarizes a study on using a Thyristor Controlled Series Capacitor (TCSC) to reduce power system oscillations. Key points:
1) A hybrid series compensation scheme is proposed using fixed capacitors on two phases and a TCSC on the third phase to maintain phase balance at power frequency but create imbalance at other frequencies.
2) Time domain simulations were conducted on a benchmark power system model using EMTP-RV software to evaluate the effectiveness of the hybrid scheme in damping oscillations.
3) Results showed the hybrid scheme has potential for enhancing power system dynamics by damping power swings and subsynchronous resonance oscillations.
This document summarizes research determining the optimal location for installing a unified power flow controller (UPFC) in an electric transmission system using particle swarm optimization (PSO) to minimize oscillations. The UPFC regulates voltages and controls power flows. PSO is an efficient method for solving nonlinear optimization problems with constraints. By varying parameters like power angle and incorporating time delays, the approach presents an innovative control scheme to apply UPFC beneficially for economical operation with reduced costs. Sensitivity analysis on the UPFC controller finds the optimal buses to place it and regulate flows.
This document proposes using continuous wavelet transform (CWT) with a complex Morlet wavelet to detect low frequency oscillations in a power system. CWT is applied to signals measured from a two-area four-machine power system model. The results extract the frequency and damping of inter-area oscillations, which closely match those obtained from eigenvalue analysis. This demonstrates CWT as an effective technique for identifying low frequency oscillations in power systems.
This document discusses the application of synchronized phasor measurement in real-time wide-area monitoring. It provides an overview of phasor and synchrophasor measurement techniques using Fourier transforms. It also discusses power system stability and transient stability. The document demonstrates the monitoring of a multi-machine system using synchronized phasor measurements by simulating various fault conditions and load changes on a 3-machine, 9-bus system and observing the results with a phasor measurement unit to analyze stability.
Enhancement of power quality by DVR using "ANN Technique" under unbalanced an...ijceronline
The paper discusses the voltage control of a critical load bus using dynamic voltage restorer (DVR) in a distribution system. The critical load requires a balanced sinusoidal waveform across its terminals preferably at system nominal frequency of 50Hz .It is assumed that the frequency of the supply voltage can be varied and it is different from the system nominal frequency. The DVR is operated such that it holds the voltage across critical load bus terminals constant at system nominal frequency irrespective of the frequency of the source voltage. In case of a frequency mismatch, the total real power requirement of the critical load bus has to be supplied by the DVR. Proposed method used to compensate for frequency variation, the DC link of the DVR is supplied through an uncontrolled rectifier that provides a path for the real power required by the critical load to flow .A simple frequency estimation technique is discussed which are Discrete Fourier transform (DFT), ANN controller. The present work study the compensation principle and different control strategies of DVR used here are based on DFT, and ANN Controller .Through detailed analysis and simulation studies using MATLAB. It is shown that the voltage is completely controlled across the critical load.
This document discusses model-in-the-loop real-time simulation using phasor models. It describes how to integrate power system components with voltage source converters (STATCOMs and PV arrays) into a phasor-domain simulation. Various applications are mentioned, including testing wide area control systems and integrating renewable energy. It also presents simulation results comparing ePHASORsim to SimPowerSystems for a test system with STATCOM voltage control.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Wavelet based detection and location of faults in 400kv, 50km Underground Po...ijceronline
This document presents a method for detecting and locating faults in underground power cables using wavelet transforms. A 400kV, 50km underground cable system is modeled in MATLAB Simulink. Various single-phase, two-phase, and three-phase faults are simulated at distances of 25km and 50km from the measurement point. Voltage and current signals are analyzed using continuous wavelet transforms to detect and locate faults. Simulation results show the method can accurately estimate fault locations, with errors generally under 7%. The method is capable of determining fault type and location for both transmission and distribution cables.
This document discusses the implementation of instantaneous reactive power theory (IRP theory) for current harmonic reduction and reactive power compensation in three phase four wire power systems. IRP theory is used to calculate reference compensating currents that are injected by a shunt active power filter (SAPF) to compensate for non-linear and reactive loads. Clarke's transformation is used to convert voltages and currents to the α-β-0 reference frame for IRP calculations. Hysteresis current control with a constant switching frequency is used to generate PWM signals to control the SAPF inverter. Simulations show the SAPF reducing current harmonics and reactive power, improving the power factor by making the source current sinusoidal and in phase with
A mho type phase comparator relay guideline using phase comparison technique ...IJECEIAES
This paper presents a mho distance relay simulation based on the phase comparison technique using a typical electrical power systems analysis software for two cases: when the operation state is close to the static voltage limit and during a dynamic perturbation in the system. The paper evaluates the impedance variations caused by complex voltage values, the mho polarization, and the comparator operating region into the complex plane. In addition, the paper found the information for the dynamic perturbations from the outputs considering a mid-term stability program. The simulation of the mho-phase comparator in the static voltage proximity limit detects unit distance elements with impedance measured close to reach the threshold in the steady-state. Dynamic mho simulations in the complex plane are successfully tested by plotting time phase difference curves on the comparator input signals. Relay programmers can use these curves to analyze other phase comparators applications and the corresponding models in the complex plane.
The Need for Enhanced Power System Modelling Techniques and Simulation ToolsPower System Operation
This document discusses power system modeling techniques and simulation tools. It covers:
1) Static models like power flow and fault level studies that represent steady-state network behavior using phasor/sequence models.
2) Dynamic RMS models that simulate time-domain performance for stability studies using positive or three-phase representation.
3) Emerging needs for more advanced tools due to the increasing complexity of power systems with high renewable penetration, requiring electromagnetic transient models to capture sub-cycle dynamics.
This document summarizes a paper that presents a novel method for determining the optimal location of Flexible AC Transmission System (FACTS) controllers in a multi-machine power system using a Fuzzy Controlled Genetic Algorithm (FCGA). The proposed algorithm aims to simultaneously optimize the location, type, and rated values of FACTS controllers while minimizing the overall system cost, which includes generation and investment costs. The algorithm is tested on IEEE 14-bus and 30-bus test systems, incorporating thyristor-controlled series compensator (TCSC) and unified power flow controller (UPFC) devices. Simulation results show the obtained solution is feasible and accurate for solving the optimal power flow problem.
Best Power Surge Using Fuzzy Controlled Genetic TechniqueIOSR Journals
This document presents a novel method for optimizing power surge in a multi-machine power system using a fuzzy controlled genetic algorithm. The algorithm simultaneously optimizes the location, type, and rating of Flexible AC Transmission System (FACTS) controllers to minimize overall system cost, which includes generation and investment costs. Thyristor Controlled Series Compensator (TCSC) and Unified Power Flow Controller (UPFC) are considered as FACTS controllers. The algorithm uses a genetic algorithm and fuzzy logic to determine optimal FACTS controller placements and settings while satisfying power flow and voltage constraints. Simulation results on IEEE 14-bus and 30-bus test systems show feasible and accurate solutions are obtained for optimal power flow problems when incorporating
This paper proposes a hybrid series capacitive compensation scheme using a thyristor controlled series capacitor (TCSC) to damp power system oscillations. The scheme uses a single-phase TCSC in one transmission line phase along with fixed capacitors in the other two phases. This creates a phase imbalance that can dampen both power swings and sub-synchronous resonance oscillations. MATLAB simulations show the scheme effectively dampens generator load angle oscillations compared to a fixed compensation scheme following a fault. The hybrid scheme has potential for industrial application as it provides damping benefits while reducing costs versus a full three-phase TCSC installation.
Line Losses in the 14-Bus Power System Network using UPFCIDES Editor
Controlling power flow in modern power systems
can be made more flexible by the use of recent developments
in power electronic and computing control technology. The
Unified Power Flow Controller (UPFC) is a Flexible AC
transmission system (FACTS) device that can control all the
three system variables namely line reactance, magnitude and
phase angle difference of voltage across the line. The UPFC
provides a promising means to control power flow in modern
power systems. Essentially the performance depends on proper
control setting achievable through a power flow analysis
program. This paper presents a reliable method to meet the
requirements by developing a Newton-Raphson based load
flow calculation through which control settings of UPFC can
be determined for the pre-specified power flow between the
lines. The proposed method keeps Newton-Raphson Load Flow
(NRLF) algorithm intact and needs (little modification in the
Jacobian matrix). A MATLAB program has been developed to
calculate the control settings of UPFC and the power flow
between the lines after the load flow is converged. Case studies
have been performed on IEEE 5-bus system and 14-bus system
to show that the proposed method is effective. These studies
indicate that the method maintains the basic NRLF properties
such as fast computational speed, high degree of accuracy and
good convergence rate.
This document summarizes various regulator collections that can be used to control a parallel active power filter. It discusses fuzzy logic, PWM, space vector PWM (SVPWM), new space vector PWM (NSVPWM), and hysteresis regulators. It provides block diagrams and equations to describe how each regulator works. The document also proposes a new method of using NSVPWM with hysteresis control to regulate harmonic currents injected by the active filter while maintaining a fixed switching frequency.
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1) Precise synchronization of phasor measurements across wide areas of the electric grid is important for monitoring system state, control, and protection. GPS provides an ideal synchronization source with accuracy of 1 microsecond or better.
2) Synchronized phasor measurements directly measure the system state vector and dynamic conditions, providing faster response than traditional state estimation. They can improve control schemes and adaptive relaying by providing real-time feedback across the entire system.
3) Detection of instability between two interconnected regions can be achieved using synchronized phasor measurements to predict angular stability based on the equal area criterion for a two-machine system.
The document discusses the Entergy Phasor Project which aims to modernize Entergy's electricity grid using phasor measurement units (PMUs). The project is part of a larger Eastern Interconnection Phasor Project involving multiple organizations. Entergy has installed 11 PMUs so far with benefits including improved wide-area visibility, monitoring tools for operators, and ability to monitor grid dynamics and stability. Future phases aim to install more PMUs across North America and realize additional benefits like automatic control applications.
This document describes a lab activity to characterize fuel cells by measuring their current output at different voltages. Students will measure the current produced by a miniature fuel cell using graphite electrodes, and then compare it to fuel cells using platinum electrodes and operating in a buffered water solution. The goal is to determine which conditions and materials produce the best fuel cell performance as indicated by higher current output.
The document discusses a fuel cell characterization system from LXinstruments that uses Agilent Technologies equipment. The system allows for multi-channel electrochemical impedance spectroscopy (EIS) measurements of fuel cells in both stacked and segmented configurations. It utilizes an Agilent L4534A digitizer with four channels for measurements and Agilent electronic loads modulated by a function generator to provide variable load conditions. Proprietary software implements a lock-in amplifier algorithm to accurately measure frequency and phase responses from individual fuel cells. The system provides an affordable solution for comprehensive fuel cell testing and analysis.
The document summarizes experimental testing of a proton exchange membrane fuel cell system for electric vehicle applications. Key findings include:
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1. I
I PRECISE SYNCHRONIZATION OF PHASOR
MEASUREMENTS IN ELECTRIC POWER SYSTEMS
Dr. A.G. Phadke
Virginia Polytechnic Institute and State University
Blacksburg, Virginia 240614111. U.S.A.
Abstract
Phasors representing positive sequence voltages and currents ih a power network are the most
important parameters i n several monitoring, control, and protection functions i n inter-
connected electric power networks. Recent advances i n computer relaying have led t o very
efficient and accurate phasor measurement systems. When the phasors to be measured are
separated by hundrea of miles, it becomes necessary t o synchronize the mesurement processes,
so that a consistent description of the state of the power system can be established. GPS
transmissions offer an ideal source for synchronization of phasor measurements. The paper
describes the concept and implementation of this technique. Several uses of synchronized
phasor measurements are also described. Among these are improved state estimation algo-
rithms, state estimator enhancements, dynamic state estimates, improved control techniques,
and improved protection concepts.
INTRODUCTION
Computer relaying is a well established field by now, and it has furnished a new insight into
the technique of measuring power system quantities in real-time from sampled data. Voltage
and current phasors in a three phase power system can be measured from waveform samples,
and the measurement process can be made to be responsive to dynamically changing system
conditions. For many new applications of phasor measurements now under consideration,
measurement response times of 1-5 periods of the power frequency seem desirable. This paper
will examine the concept of phasor measurements, and describe some practical considerations
in achieving synchronous sampling of currents and voltages in different substations in a power
system. We will also describe research now under way in the development of a phasor based
protection and control system.
PHASORS FROM SAMPLED DATA
A phasor is a complex number which represents the fundamental frequency component of a
waveform. Consider the samples xk obtained from a signal (voltage or current) x(t). The
phasor representation of the signal x(t) is related to the fundamental frequency component
calculated by the Discrete Fourier Transform (DFT). If the phasor is X, and the fundamental
frequency calculated by the DFT is XI, then +,
k=l
where K is the total number of samples (usually a multiple of the fundamental frequency
period), and At is the sampling interval. One could drop the constant in front of the
2. summation sign in equation (I), and instead use cosine and sine sums of the sampled data to
represent the phasor:
X = Xc-JX, (2)
where
K K
X, = C xk cos k w ~ t , X, =
Cxk sin k w ~ t
If the actual frequency of the power system differs from the nominal frequency used in the
sampling process, the phasor calculated by equation 2) is in error. For all practical frequency
are given by X,, Xb, and Xc, h e ~ o s i t i v e
t
deviations, the error in the phasor calculation is neg igible. If the phasors of the three phases
sequence quantity Xi (not to be confused with the
-
fundamental frequency component computed by the DFT) is given by
x~=x,+ ax,,+ dxC (4)
where (I! and a 2 are the usual phase shift operators of 120" and 240" respectively at the
nominal frequency. An important use of the positive sequence voltage is the measurement of
the power system frequency. If we write the positive sequence phasor in its polar form, the
phase angle of the positive sequence phasor can be differentiated to obtain the incremental
frequency of the input waveform over the nominal frequency. If cp is the phase angle of XI,
and wo is the nominal frequency, then the actual frequency of the input signal is given by
d
w=wo+i;e (5)
Equation (5) is one of the most sensitive methods of measuring power system frequency.
SYNCHRONIZATION OF THE SAMPLING PROCESS
1
The phasor given by equation (1 uses the sampling instant of the first sample as the refe-
rence. The necessary accuracy o synchronization may be specified in terms of the prevailing
phase angle differences between buses of a power network. Typically, these angular diffe-
rences may vary between a few degrees, to perhaps 60" under extreme loading conditions.
Under these circumstances, a precision corresponding to 0.1" seems to be desirable to measure
angular differences corresponding to lightly loaded systems. Allowing for other sources of
error in the measurement system, it seems certain that a synchronizing accuracy of about 1
pecond would meet the needs of this measurement technique. A superior and satisfying solu-
tion to the synchronization problem is to use the 1 pulse-per-second (pps) transmission
provided by the Global Positioning System (GPS) satellites.
IMPLEMENTATION FOR FIELD TFUALS
A typical phasor measurement system is shown in Figure 1. The GPS receiver is designed to
provide the standard 1 pps, a phase-locked sampling pulse at the desired sampling frequency,
and a time-stamp corresponding to the 1 pps. The three signals from the GPS receiver are
connected to a microprocessor, which acquires the power system current and voltage input
signals through the si nal conditioning units and the Analog-to-Digital converter. The
B
microprocessor chosen or the task is a 16-bit processor with a sufficient instruction speed to
accommodate between 1000 and 2000 instructions within the sampling period. The AID con-
verters are typically 12-bit converters, and with careful design of the computation algorithms,
provide measurements with very good precision. The measured phasor, its associated time-
stamp, and other message codes of interest are communicated to the next hierarchical level
3. i over a communication channel. The local display port and the connected terminal is used to
provide a graphic and alphanumeric display of the measured phasors, the reference phasor, the
local frequency, and the rate of change of frequency. The system time error can be calculated
by counting the rotations of the measured
I
GPS Satellite positive sequence voltage phasor with
I respect to the true time reference
provided by the GPS receiver.
USES OF SYNCHRONIZED PHASORS
Antenna n
sig. State Estimation with Phasors
PP ; A/D - Cond. The collection of all positive sequence
Unit
bus voltages of a power system is known
as its state vector. A knowledge of the
state vector is essential in many of the
From CT and VT
central control functions associated with
Comm. Port power system operations. The present
practice is to obtain measurements of
various system quantities such as real and
reactive power flow over transmission
-
Flaure I. lines. real and reactive power injections,
Phasor Measurement System Block Diagram
voltage magnitudes at system buses, line
current magnitudes, et c., and estimate
the state of the power system with a non-linear state estimator. The measurement vector z is
a non-linear function of the state vector:
z = h(x) + E (6)
where c is the measurement noise with a covariance matrix W. One could obtain the
weighted-least-square (WLS) estimate of the st ate with an iterative algorithm:
rn 4 m 4
where H x is the Jacobian matrix of the measurement functions:
()
l
a
H(x) = h(x) (8)
I The iterations are continued until the measurement residual [z - h(xk)]becomes smaller than
a pre-selected tolerance. A state estimation procedure such as that described above can never
represent the dynamic phenomena occurring on the power system during transient power
swings. The data scan rates in use at present are rather slow, and the non-linear iterative
algorithm also contributes to the slow response time of the estimation process.
The synchronized phasor measurement technique provides the system state with direct mea-
surements. Let the complete measurement set consist of positive sequence voltages at buses,
and currents in transmission lines and transformers. These measurements are linear functions
of the state vector:
The measurement matrix B now consists of tk6 sub-matrices, the unity matrix, and a matrix
relating the currents and the system state. This latter sub-matrix is similar to the familiar
admittance matrix of the power system. In any case, the important point is that equation (9)
is linear. Since B is a complex matrix, the WLS solution is now given by
4. Equation (10) can be much simplified by using the known structure of the admittance matrix
elements.
An interesting distinction of the phasor measurement technique is that a complete system-
wide data scan is not needed to complete the estimation process. The measured positive
sequence voltages, with appropriate data validation done at the source, can be used directly.
Thus, if the partial state vector is useful is some applications, it can be put to use imme-
diately. For example, the phase angle between two regions of a network may be measured
directly, in order to assess the inter-regional power transfer, without having to measure the
connecting network, and then estimating the phase angle. In the next two sections, other
examples of uses of partial state vector measurements will be discussed.
Improved Control with Phasors
It is possible to improve post-disturbance power system performance using control schemes
based on real-time phasor measurements. Present day controllers which act in such situa-
tions are restricted by the limited (local) nature of the measurements available to the
controller. If synchronized phasor measurements from throughout the system are available,
the quality of the control can be improved considerably. Such controllers for dynamic
st ability enhancement of AC/DC systems, and the application of real-time phasor measure-
ments in generator exciter and speed governing system control has been reported in the
technical literature. The key idea is to replace the non linear differential equation describing
power system dynamics
x(t> = f(x(t),u(t>> (11)
by an equation that linearizes f, and then collects the remainder as a correction term
Note that this equation (12) is not an approximation, it is in fact the same as equation (11).
One may treat the term in the bracket
r(t) =f(x + x , u ) - A x - B u = x - A x - B u
0 (13)
as a correction term, which is some unknown function of time. If sufficient observations of
x(t) are available, r(t) can be predicted, and an optimal control law determined for the
original system of equation (11). The resulting control law has several interesting properties,
and it has been shown that the computational burden in the real-time control function can be
accommodated in modern microcomput er based implement ation.
In summary, we may say that real-time phasor measurements provide highly beneficial feed-
back to various controllers in use in power systems. Although a complete state vector
feedback would be ideal, even partially observed states can help. With currently available
communication channel speeds, the feedback can be obtained in a continuous data stream
with state vector sampling periods of between 50 and 100 milliseconds. This makes the
feedback most appropriate for controlling power system transients which lie in the frequency
band of 0-5 Hz. Thus, most phenomena associated with electromechanical oscillations on
power systems can be controlled with state vector feedback.
Protection with Phuors
Protection is a form of control. Phasors play an important role in protection system design.
In fact, modern phasor measurement techniques originated in the field of computer relaying.
5. It has now become clear that synchronized phasor measurements can be of great use in many
of the protection applications. Although phasars may be used in many relaying tasks, their
full impact is felt in the new field of adaptive relaying. Adaptive Protection is a protection
philosophy which permits and seeks to make adjwtrnents in various protection findions auto-
matically in order to make them more attlrned to prevailing power system conditiotls. The idea
of adaptive relaying is an old one. Thus, existing protection systems try to adapt to changing
system conditions in a limited manner. However, the advent of computer relaying has added
a new dimension to this idea. For the first time, it is possible to imagine protection systems
which can have dynamic settings, in order to provide the best protection possible in a chan-
ging environment. Of course, not all relay characteristics are amenable to adaptive adjust-
ments. And, one must take care that in case of failures of the adaptive features, the relays
revert to their pre-adaptive mode of operation. A number of studies of adaptive relaying
have appeared in the technical literature in recent years. We will consider one example to
give the flavor of this new and exciting development.
Detection of Instability
This problem impacts many protection and control applications. As the power system under-
goes oscillations of synchronizing power following a disturbance, it would be extremely useful
to know in real-time whether the swing under development is going to lead to an instability.
At present, this problem cannot be solved for a completely general system, but progress can
be made in case of systems with two areas of concentrated load-generation complexes, con-
nected together by somewhat weak interconnections. These systems behave like the classical
two-machine system. The detection of instability for such a problem is equivalent to an
evaluation of the balance between the accelerating and decelerating powers using the equal
area criterion. If 6(t) is the angle between the two equivalent machines, the set of obser-
vations {&;k = 1. . - n ) can be used to predict the balance between the accelerating and dece-
lerating areas on the P-6 plane. It has been observed that observations made over one quar-
ter of the period of the electromechanical oscillation are sufficient to provide a reliable
estimate of the outcome of a power swing.
As mentioned before, no such results for the general case of multi-machine oscillations exist
at this time. Several promising approaches to this problem - such as the method of Potential
Energy Boundary Surface, and Extended Equal Area - are currently under investigation,
SUMMARY AND CONCLUSIONS
Synchronized measurement of power system parameters is now achievable with the time
transmissions of the GPS satellites. The hardware costs associated with such a measurement
system are comparable to those of other relays and measurement systems in general use at
present. The synchronized phasor measurement systems are likely to have a significant
impact on all aspects of power system operations in the coming years, and will usher in an era
of electric power networks operating with greater efficiency and security.
FOR FURTHER READING
Transactions of IEEE on Power Apparatus and Systems contain many of the research results
described above. The book, "Computer Relaying for Power Systems", by A. G . Phadke and
J, S. Thorp, gives a coherent account of some of these developments,