J.s. Thorp

• Doctor of Philosophy
• Professor Emeritus at Virginia Tech

Concerning the variation of power system operating condition caused by time-varying factors such as wind generator output power fluctuation and load change, an adaptive control strategy for time-varying power system based on continuous Markov model is proposed in this paper. First, the Lyapunov functional containing the continuous Markov time-varyi...

Utilities across the world are seeing increased penetration of inverter-based RG in their systems. These RGs have ride through curves programmed in them which define operating conditions that need to be satisfied during electrical disturbances. If they are violated, the RGs are tripped offline. In systems with large amounts of RGs tightly coupled e...

In view of the low reliability of traditional protection in the distribution network caused by the massive integration of DGs (distributed generation), an adaptive directional current protection scheme based on fault steady-state component is proposed in this paper. First, by analyzing the fault transient characteristics and fault equalization meth...

Concerning multi-source oscillation scenes, an oscillation centre identification method based on the variation trend of bus frequency is proposed. First, according to the amplitude and phase relationship between voltage and current at any point in the system, the functional expression of the frequency of voltage and current is derived. Then, the va...

Wide area measurement system relies on phasor measurement unit (PMU) data to monitor, protect, and control highvoltage transmission networks. However, errors in instrument transformers (ITs) located at the inputs of a PMU can significantly degrade its output quality. This study proposes two methodologies for voltage and current transformers calibra...

When fault occurs in the grid, the short circuit characteristics of doubly-fed induction generator (DFIG) are more complicated due to the coupling influence of generator electromagnetic transient and converter regulation. In view of this problem, a DFIG stator/rotor short circuit current calculation method considering the transient regulation of bo...

There has been significant increase in penetration of renewable generation (RG) sources all over the world. Localized concentration of many such generators could initiate a cascade tripping sequence that might threaten the stability of the entire system. Understanding the impact of cascade tripping process would help the system planner identify tri...

In view of frequent multi-machine power system oscillations in power grid which may cause traditional oscillation blocking and re-opening schemes to be completely invalid, a distance protection oscillation blocking and re-opening scheme in multi-machine power system oscillation scenes is proposed in this paper. First, the ride-through trajectory of...

An oscillation blocking and re-opening scheme for distance protection in multi-source oscillation scenes is proposed in this paper. First, the expression of measured impedance in multi-source oscillation scenes is derived and the variation characteristic of the trajectory of measured impedance is analyzed. Then, according to the correlation between...

In view of the sensitivity and selectivity problems in DFIG (doubly-fed induction generator) wind farm collector line protection, a new adaptive distance protection scheme is proposed. First, according to the geometric distribution characteristics of the collector line voltage and current, the equation of voltage drop from the relaying point to the...

Traditional Lyapunov based transient stability assessment approaches focus on identifying the stability region (SR) of the equilibrium point under study. When trying to estimate this region using Lyapunov functions, the shape of the final estimate is often limited by the degree of the function chosen, a limitation that results in conservativeness i...

In view of the incorrect operation of local protection caused by multiple distributed generations (DGs) and branches in distribution system, a regional protection scheme for distribution network based on logical information is proposed here. Moreover, a regional centralised protection system in parallel with and independent from the existing protec...

With the wide application of doubly-fed induction generator (DFIG), accurate calculation and analysis of the short circuit currents of DFIG with crowbar protection has become very important key to realizing the low voltage ride through (LVRT) capability of DFIG and establishing the corresponding grid protection scheme. In view of this, a method to...

This paper presents a regional backup protection algorithm based on the adaptive current protection suiting factor, which can be applied to power system with regional centralized backup protection. First, the influence of the adaptive current protection operation status on fault identification is defined as the adaptive current protection effective...

In view of the problem that the detailed model of doubly-fed induction generator (DFIG) considering virtual inertia control is high ordered and difficult to analyse, a reduced-order model for DFIG that is applicable to small-signal stability analysis is presented. First, according to the attenuating speed of each state variable, the dynamic charact...

The increasing penetration of inverter based renewable generation (RG) in the form of solar photo-voltaic (PV) or wind has introduced numerous operational challenges and uncertainties. According to the standards, these generators are made to trip offline if their operating requirements are not met. In an RG-rich system, this might alter the system...

A new pilot protection scheme for transmission line based on virtual sequence transition impedance is proposed in this paper. When the out-zone fault occurs, the value of the imaginary part of the virtual sequence transition impedance is greater than the relay setting value of fault location. For internal faults, the current calculated is high as t...

Power system frequency measurement has been in use since the advent of alternating current generators and systems. The speed of rotation of generator rotors is directly related to the frequency of the voltages they generate.

Consider a constant input signal x(t) at the nominal frequency of the power system f 0, which is sampled at a sampling frequency Nf 0. The sampling angle θ is equal to 2π/N, and the phasor estimation is performed using Eqs. (1. 25)–(1. 27).

Prior to the introduction of real-time phasor measurements, power system control was essentially used by local signals. Feedback control with such locally available measurements is widely used in controlling machines. In other situations, control action was taken on the basis of a mathematical model of the system without actual measurement of the s...

As has been mentioned before, phasor is a steady-state concept.

The history of Phasor Measurement Unit (PMU) evolution was discussed in Chapter 1.

Synchronized phasor measurements have offered solutions to a number of vexing protection problems. These include the protection of series compensated lines, protection of multiterminal lines, and the inability to satisfactorily set out-of-step relays. In many situations, the reliable measurement of a remote voltage or current on the same reference...

Several different events connected with the early application of phasor measurements prompted consideration of the propagation of transient events in power systems. The first is typical of what is shown in Fig. 11.1.

Before the advent of state estimation, the power system operator had responsibility for many real-time control center functions including scheduling generation and interchange, monitoring outages and scheduling alternatives, supervising scheduled outages, scheduling frequency and time corrections, coordinating bias settings, and emergency restorati...

Phasors are a steady state concept. In reality, a power system is never in a steady state. Voltage and current signals have constantly changing fundamental frequency (albeit in a relatively narrow range around the nominal frequency) due to changes in load and generation imbalances and due to the interactions between real power demand on the network...

Concerning the stochastic excitation caused by wind power fluctuation and the stochastic parameter of virtual inertia caused by wind speed uncertainty, a power system stability analysis method considering the Wiener noise is proposed in this paper. First, based on the reduced-order model of DFIG retaining virtual inertia control and phase-locked lo...

In view of the jump characteristic of power system, a time-delay stability control strategy that avoids the effect of jump progress is proposed in this study. First, the Newton-Leibniz formula based on the free weighting matrix and the time-delay system model considering Markov jump are introduced to the differential equation of Lyapunov-Krasovskii...

This book builds on the cutting edge research presented in the previous edition that was the first of its kind to present the technology behind an emerging power systems management tool still in the early stages of commercial roll-out. In the intervening years, synchrophasors have become a crucial and widely adopted tool in the battle against elect...

Phase angles of voltage phasors of power network buses have always been of special interest to power system engineers. It is well known that active (real) power flow in a power line is very nearly proportional to the sine of the angle difference between voltages at the two terminals of the line.

Traditional distance protection may mal-operate or refuse to operate in the case of non-metallic faults, endangering the safety of power system. Therefore, a new adaptive distance protection scheme based on the impedance complex plane is proposed in this study. First, by utilising the phase relationship between the negative sequence current at the...

A method to analyze the time-delay stability of stochastic power system with wind power connection is proposed in this paper. First, the reduced-order electromagnetic model of double fed induction generator (DFIG) suitable for time-delay stability analysis is established. Meanwhile, the mechanical power of DFIG is selected as the stochastic excitat...

A new method based on fault chains and the Markov process for analyzing time-delay power system stability is proposed in this article. First, reasonable fault chains are formed using the fault chain generation method based on network power flow. Second, by combining the fault chains and Markov processes, a class of Lyapunov–Krasovskii functionals c...

In view of the maloperation problem in traditional distance protection zone-III caused by overload in lines, an adaptive overload identification method based on the complex phasor plane is proposed in this paper. First, according to the geometric distribution of the measured phasors under different operating conditions, the virtual voltage drop pha...

A phasor measurement unit placement scheme is developed in this article that ensures complete observability of large systems while reducing the computational burden of optimization. Redundancy in measurement of the critical buses of the network that are identified based on system studies and/or topologies is also provided by the proposed methodolog...

When grid fault occurs, the doubly fed induction generator short-circuit currents are very complex due to the interaction between the doubly fed induction generator and the grid. As the capacity of wind power generation increases, it has become vital to analyze and evaluate the doubly fed induction generator stator/rotor short-circuit currents corr...

Concerning the difficulty in quantitatively describing the influence of different disturbances on power system stability, a novel composite energy stability region (ESR) is proposed in this study based on the dynamic damping theory. First, considering the influence of time-variant factors in the oscillation process on the dynamic characteristics of...

In this chapter, we study the consequences of an improvised nuclear detonation (IND) to the sub-transmission and distribution systems of Washington D.C. in the Eastern Interconnection (EI). We briefly discuss the geographical location of the blast and the interconnection of the power utility serving this area, with the neighboring power utilities....

A new method to analyze the stability of power system with multiple operating conditions considering the stochastic characteristic of wind speed is proposed in this study. First, the parameter Weibull model is used to do fitting prediction of the wind speed variation trend in the short term. Second, the wind speed is divided into different interval...

A method to analyze the angle stability of power system with multiple operating conditions considering cascading failure is proposed in this paper. First, considering stochastic events such as uncertain operation of protection/breaker and system hardware failure, the system operating condition set is determined based on the flow transfer theory and...

Doubly fed induction generator (DFIG) wind turbines with virtual inertia control are coupled to power system in dynamic characteristics, and the control input of virtual inertia control is directly affected by the tracking ability of phase-locked loop (PLL). Thus, it is urgent to study the impact of DFIG wind turbines with virtual inertia control o...

An adaptive control scheme based on the convexity property of polytopes for damping interarea oscillations is developed here. A polytopic control guarantees requisite damping when the current operating point lies inside it. Multiple polytopes increase the robustness of the control provided the polytope inside which the operating point lies after a...

A day dispatch strategy for the integrated system (IS) of wind/photovoltaic/pumped-storage/gas-turbine-power/energy-storage plant is proposed in this paper based on the time-frequency scales of power of wind/photovoltaic (PWP). Based on the day-ahead dispatch strategy, the day dispatch optimization model of the IS is first established, and then acc...

This paper takes advantage of wide-area measurements to propose a centralized nonlinear controller that acts on power system stabilizers (PSSs), to cooperatively increase the damping of problematic small-signal oscillations all over the system. Details are given to utilize existing stabilizers while causing minimum changes to the equipment and warr...

Abstract—Current research on short-circuit currents of the doubly fed induction generator is all based on the traditional flux analysis theory. In this article, a novel method to calculate the doubly fed induction generator stator and rotor short-circuit currents is proposed based on the fault equivalent network. First, the fault network is decompo...

In order to improve the performance of the conventional distance protection scheme under high-resistance fault, an adaptive distance protection scheme is proposed in this paper. First, according to the geometric distribution characteristics of voltage and current in the system, the equation of voltage drop from the relaying point to the fault point...

An adaptive damping control scheme based on classification and regression tree (CART) using wide-area signals is proposed in this paper. Different polytopes are chosen using classification trees. Next, a family of robust polytopic controllers is designed off-line. Finally, using regression trees and PMU data, the desired polytopic controller is ide...

In this paper we analyze the response of the electric power grid to a hypothetical nuclear attack inside a major city in the US. We assume that the protective devices of the power system located within a given distance of the attack will be affected by the resulting radiation and hence will not work. A probabilistic examination of the resulting pow...

In order to have a reliable N-1 contingency ranking, the analysis must be based on the current power system topology. Load model composition plays a crucial role in the effects of particular contingencies; and this can change the ranked lists used by the Energy Management System. Modern devices such as Phasor Measurement Units (PMUs) allow us to be...

With growing penetration of renewable energy sources in power grids, it is increasingly important to reduce the renewable power forecasting error and variability to maintain balance of grid load and supply and participate in wholesale energy markets. Power from weather-dependent renewable sources like wind and solar are particularly subject to vari...

A phasor measurement unit (PMU) only state estimator is intrinsically superior to its SCADA analogue with respect to speed, performance, and reliability. However, ensuring the quality of the data stream which enters the linear estimator is crucial before establishing it as the front end of an EMS or other network applications. One approach is to pr...

The development of large inter-connected power grid poses an urgent need for better adaptability of the backup protection. In this paper, a wide area backup protection tripping strategy based on directional weighting is proposed, on the premise that the fault component has been identified by the limited wide area centralized backup protection. Firs...

In view of the requirement for instantaneity on power system topology analysis, a novel power system topology analysis method is proposed in this paper. For the plant-station topology method, the nodes that represent the circuit breakers are numbered according to the graph theory. On this basis, combining the main wiring characteristics and the swi...

This paper presents the idea of a partitioned linear state estimator (PLSE) as an alternative to the classical linear state estimator (LSE). PLSE is found to be especially useful for performing state estimation in large systems comprising of multiple entities. The best example of this is different utilities functioning under an independent system o...

Abstract—This article presents a fault-classification method for transmission lines based on voltage phasors using classification and regression trees. The proposed method is intended to aid system operators in understanding the outputs of a phasor measurement unit only state estimator. Faults are classified into four categories when the estimator...

Uncalibrated instrument transformers present at the inputs of phasor measurement units (PMUs) can significantly degrade their outputs. This also causes problems in downstream applications that use PMU data. This paper presents a method for calibrating voltage transformers online using synchrophasor measurements. The proposed approach aims to find t...

In view of the time delay and potential information loss problem in wide-area data acquisition, a wide-area backup protection algorithm based on the distance protection fitting factor is proposed in this paper. First, the contribution of the distance protection operating information to fault identification is defined as the distance protection cont...

Concerning the maloperation or operation-rejection problem caused by the fault resistance, a novel line protection scheme for a single-phase-to-ground fault based on voltage phase comparison is proposed. First, according to phase relationship between the negative-sequence current at the relaying point and the negative-sequence current at the fault...

This study concerns the misoperation of differential protection of long distance UHVDC transmission line under external faults. The two main factors that have effect on the sensitivity of differential protection long distance UHVDC transmission line are discussed in this study: transient harmonic currents and shunt branch currents. With the improve...

In this paper, we study the consequences of an improvised nuclear detonation (IND) to the sub-transmission and distribution sys-tems in Washington D.C. in the Eastern Interconnection (EI). We briefly discuss the geographical location of the blast and the interconnection of the power utility serving this area, with the neighboring power utilities. A...

An adaptive damping control scheme based on classification and regression tree (CART) using wide-area signals is proposed in this study. A family of robust controllers is designed off-line and are used in real-time after the corresponding operating point is retrieved from phasor measurement unit (PMU) data with CART interpolation. When the power sy...

In view of the potential problems in the system such as sustained oscillation and low damping ratio, which are not considered in traditional small-signal stability region (SSSR), an improved SSSR (ISSSR) calculation method based on the guardian map is proposed. First, according to the map theory, the system is mapped from the ISSSR to the negative...

An adaptive damping control scheme based on the dual Youla parameterization is proposed in this paper for inter-area low frequency oscillations. First, a set of observer-based feedback controllers are pre-designed using ${rm H}_{2} /{rm H}_{infty}$ robust control method for a set of nominal operating conditions. Second, the power system and control...

Based on measured ring-down signals from the power systems, this paper introduces the Ibrahim time domain (ITD) method for estimating the inter-area electromechanical modes, including the frequencies, damping ratios and the mode shapes. A zero-phase low-pass filter is utilized to improve the performance of the ITD method in the presence of measurem...

This paper presents a phasor measurement unit (PMU) placement scheme that provides real-time monitoring of key buses of the network. High-voltage lines, substations relevant for transient and dynamic stability of the network, and buses with high connectivity are given the highest priority while placing the PMUs. Binary integer programming and “dept...

We present a synthetic information and modeling environment that can allow policy makers to study various counter-factual experiments in the event of a large human-initiated crisis. The specific scenario we consider is a ground detonation caused by an improvised nuclear device in a large urban region. In contrast to earlier work in this area that f...

A power system consists of generators which convert energy from some primary form – such as coal, wind, gas, sunlight, or water flow – into electric power. Most generators in modern power systems produce alternating currents and voltages (AC) which are then transmitted over appropriate distances to supply loads. It is economical to transmit power a...

The post-mortem analysis of few blackouts in US and Europe has revealed that the Zone 3 of step-distance protection is one of the primary causes of blackouts in power systems. In order to provide the Zone 3 relays with situational awareness and prevent its undesirable tripping, we propose a non-intrusive agent based relay supervised distance protec...

Traditional methods for predicting transient stability of power systems such as the direct method, the time domain approach, and the energy function methods, do not work well for real-time stability predictions. The use of Phasor Measurement Units (PMUs) appears to alleviate this problem by providing information in real-time for transient stability...

Classification and regression trees (CART) has been used for various applications in power systems. In most of these applications, phasor data obtained from phasor measurement units are used for building the decision tree. However, the splits in CART are based on a single attribute or a combination of variables chosen by CART itself rather than the...

We analyze the actual commuting profiles of vehicles in the US and develop a statistical model to fit the observed data. Subsequently, this model is leveraged in a simulation framework to simulate the behavior of fleets of Plug-in Electric Vehicles (PEV), analyze their impact on the grid and, compute the effective load carrying capacity (ELCC) cont...

In this paper, we describe our global event-driven co-simulation framework GECO that we developed to co-simulate power systems dynamics with data network activities. The GECO framework utilizes global event scheduling across two different simulators with distinct simulation disciplines --to eliminate common synchronization errors often found in fed...

The application of phasor measurement unit (PMU) measurements and adaptive wide-area damping control based on federated Kalman filters are investigated. The Kalman filters used for estimating the operating conditions are federated using chi-square variables and a confidence interval. When the power system is operating precisely at a preselected ope...

The effect of integrating intermittent renewable generation such as wind and solar, as well as plug-in electric vehicles (PEVs) on a grid is an important area of study. Renewable generation depends on weather. Energy consumption, storage, and emergency usage of battery-stored power in PEVs are dependent on the spread of such vehicles in a geographi...

Conventional active islanding detection approaches are devastating to distributed generation, while passive islanding detection methods have the disadvantage of a non-detection zone. To solve these two problems, a novel islanding detection method employing positive feedback of voltage harmonic distortion is presented. By introducing a positive feed...

Historical data indicate that protection system hidden failures contribute to cascading power system disturbances. There are many types of hidden failures in protection systems, including in instrument transformers, primary equipment such as breakers, secondary system hardware and firmware, and relay settings. Most of the hidden failures can be tra...

This paper demonstrates the application of a robust technique for damping low frequency oscillations in the WECC. The control is designed by extending the logic of SMA and integrating it with the LMI technique to develop a single-gain feedback controller that is capable of damping oscillations in large systems. It is an integrated form of control b...

We study the impacts of a hypothetical improvised nuclear detonation (IND) on the electrical infrastructure and its cascading effects on other urban inter-dependent infrastructures of a major metropolitan area in the US. We synthesize open source information, expert knowledge, commercial software and Google Earth data to derive a realistic electric...

Gain scheduling applications begin by creating a set linear parameter varying (LPV) systems for many operating points in the non-linear system. In this paper, the load and line reactance are used as parameters. The scheduling variables are power flows in tie lines because they provide useful information about the power system state and are availabl...

Given the ability of the Phasor Measurement Unit (PMU) to directly measure the system state and the increasing implementation of PMUs across the electric power industry, a natural application of PMUs to state estimation techniques would be one that employed the exclusive use of PMU data. Virginia Electric and Power Company aims to implement a three...

Traditional state estimators require longer scan time, leading to delayed, and inaccurate state estimation. Given the increased deployment trend of phasor measurement units (PMUs), it is expected that all-PMU state estimation will eventually replace traditional or mixed state estimators at the control centers of power utilities. Due to the repeated...

This book demonstrates the application of a robust technique for damping low frequency oscillations. The control is designed by extending the logic of SMA and integrating it with the LMI technique to develop a single-gain feedback controller that is capable of damping oscillations in large systems. It is an integrated form of control because it com...

Power systems measurements are often performed with current and voltage signals derived from instrument transformer secondary circuits. Errors introduced by these transformers are a recognized component of input data errors in supervisory control and data acquisition and phasor measurements. Correcting these errors by {in situ} calibration is an ex...

Based on the boundary characteristic of a dc transmission line, the response of transient harmonic current in the line-commutated converter HVDC transmission system is analyzed under various fault conditions in this paper. A new transient harmonic current protection scheme is proposed. The discrete Fourier transform is used to extract transient har...

The vision of a smart grid is predicated upon pervasive use of modern digital communication techniques to today's power system. As wide area measurements and control techniques are being developed and deployed for a more resilient power system, the role of communication network is becoming prominent. Power system dynamics gets influenced by the com...

A method for computing interval eigenvalues of closed-loop system is proposed using interval theory for low-frequency oscillation in power system. Firstly, the closed-loop system state matrix based on interval parameters is deduced, then, the algorithm for estimating the lower and upper bounds of the interval complex eigenvalues using matrix pertur...

With the advent of the concept of smart-grid, the power system infrastructure is being equipped with high-bandwidth data communication and embedded computing infrastructure. The communication infrastructure has gained importance in the transmissions subsystems due to increasing use of the wide area measurement and monitoring using Phasor measuremen...

We have developed a model for analyzing the system imbalance with different mixes of renewable generation (solar photovoltaic and wind) including in the presence of large pools of plug-in electric vehicles (PEVs) that participate in vehicle-to-grid and grid-to-vehicle operations. Our proposed model also identifies optimal compositions of renewable...

Inter-area oscillation modes could be changed with the parameters of large scale power system varying. Therefore, complex modal perturbation is proposed to make modal analysis of inter-area oscillations considering uncertainties in this paper. The 1st order perturbation is applicable for the case of small modification of the parameter. However, if...

Observations from synchronized phasor measurements (PMUs) have confirmed the fact that real power disturbance propagate over the power network with a speed well less than that of light. By treating an electric power network as a continuum system, a nonlinear partial differential equation in the form of a wave equation has been derived to describe t...

We have developed a model to identify optimal sizes of aggregate solar PV capacity in a region that maximizes the effective load carrying capacity (ELCC) of the grid in the presence of increasing number of plug-in electric vehicles (PEVs) participating in vehicle-to-grid operations. The model has been implemented using a simulation-based framework...

The book has three introductory chapters about the need for tools, techniques, and issues involved in disturbance analysis ranging from the functioning of digital fault recorders to symmetrical components and COMTRADE. The chapters contain more than 80 larger case studies based on the author¿s 40 years of experience organized by disturbances involv...

This paper presents a systematic design procedure for a wide-area damping controller (WADC) employing Energy Storage Systems (ESSs). The WADC is aimed at enhancing the damping of multiple inter-area modes in a large scale power system. Firstly, geometric measures of controllability and obsevability are used to select the control locations for ESSs...