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The paper addresses the problem of decentralized optimization for a power system partitioned into several areas controlled by different transmission system operators (TSOs). The optimization variables are the settings for taps, generators' voltages and compensators', and the objective function is either based on the minimization of reactive power support, the minimization of active power losses, or a combination of both criteria. We suppose that each TSO assumes an external network equivalent for its neighboring areas and optimizes without concern for the neighboring systems' objectives its own optimization function. We study, in the context where every TSO adopts the same type of objective function, the performance of an iterative scheme, where every TSO refreshes at each iteration the parameters of its external network equivalents depending on its past internal observations, solves its local optimization problem, and then, applies its 'optimal actions' to the power system. In the context of voltage optimization, we find out that this decentralized control scheme can converge to nearly optimal global performance for relatively simple equivalents and simple procedures for fitting their parameters. Index Terms--Decentralized control, multi-TSO power system operation, network equivalent, reactive power scheduling, voltage management.

In evaluating the energy-generation potential of a photovoltaic (PV) energy system, the system is usually assumed to work without interruptions over its entire life. PV energy systems are fairly reliable, but as any complex system, they may fail. In PV systems, the inverter is responsible for the majority of failures, and most inverter failures are blamed on the aluminum electrolytic capacitors typically used in the dc bus. This paper investigates the effects of common failure modes on the reliability of PV inverters and suggests a model framework for decomposing the inverter into subsystems for more detailed study. The challenges of statistical analysis based on small data sets are discussed, and simulations are performed to illustrate the proposed model using a simple decomposition into subsystems of the inverter used in the 342-kW PV system at the Georgia Tech Aquatic Center. Index Terms--Photovoltaic (PV) power systems, power-system reliability, power-system simulation, reliability modeling, simulation.

Screening methodology for evaluation of interconnection of distributed generation (DG) to distribution feeder is presented. Applicable regulatory documents are used as guidelines for the approach. DG applications are screened into three categories: those that should be approved without further actions; those which are not acceptable under any circumstances; and those which require further study. Detailed interconnection studies are proposed for further investigation of the proposed interconnection. Additional considerations for siting and capacity allocation of DG are discussed. Application of a screening tool to a realistic feeder model is demonstrated. DOI: 10.1061/(ASCE)0733-9402(2007)133:3(165) CE Database subject headings: Distribution functions; Networks; Utilities; Models.

This paper introduces a concept of a generator coherency-based System Protection Scheme (SPS), addressing interarea oscillation events. The scheme uses wide-area generator speed measurements combined with discrete Fourier transform (DFT) analysis to determine coherency. A test case simulated in the NPCC 68-bus system is used to introduce the scheme's operating principle. The test case is also used to investigate the scheme suitability for different well-established digital signal processing (DSP) methods. Further aspects, such as evolving/sliding window functions, window size, and frequency resolution are analyzed. For the detection of interarea modes, parametric DSP methods turned out to be the most feasible. In general, evolving windows are faster than sliding windows. However, evolving windows require a trigger and were therefore rejected for the design proposed here. A lower frequency resolution may shorten the response time at the expense of the quality of the estimates of the instantaneous speed deviation and the generator coherency. The design proposed here is based on a high-frequency resolution at the cost of a lower response time. Index Terms--Coherency determination, digital signal processing, discrete Fourier transform analysis, interarea oscillations, system protection scheme, transient instability, wide-area protection.

The aim of this paper is to illustrate that wide area generator speed measurements combined with Fourier analysis can be used to determine coherent generator groups. Studies are based on simulations in a 68-bus test system. Three test cases are investigated where the new method is compared to conventional methods based on the generator speed, modal analysis, and phasor angle measurement. The method introduced in this paper has proven to be an interesting alternative for generator coherency determination. It gives almost identical results to the offline methods based on the generator speed or modal analysis. Based on their trustworthiness the test cases indicate that the method reflects a more accurate coherency than the conventional online method based on phasor angle measurement. Moreover, compared with online applications using modal analysis the method supports real-time applications better according to its less extensive computational requirements. Index Terms--Fourier analysis, inter-area oscillations, power system oscillations, transient instability, wide area protection.

Distributed generation (DG) reduces losses and eliminates some of the transmission and distribution costs. It may also reduce fossil fuel emissions, defer capital costs, and improve the distribution feeder voltage conditions. The calculation of the effects of small residential photovoltaic and wind DG systems on various feeder operating variables is complicated by both the probabilistic nature of their output and the variety of their possible spatial allocations. A method based on a combination of clustering techniques and a convex hull algorithm is proposed that may reduce the computational burden by an order of magnitude, while still allowing accurate estimation of DG-enhanced feeder operation. Index Terms--Dispersed storage and generation, photovoltaic power systems, power distribution planning.

This paper proposes a strategy for placing capacitors at multiple locations on a distribution feeder to allow: 1) deeper levels of substation voltage reduction for peak load reduction; 2) power factor correction; and 3) power loss reduction. By reducing peak demand, a utility can avoid paying high prices when purchasing power or it may sell excess generation at high prices. By minimizing system losses, savings are obtained through reduced demand and energy charges. Besides a positive economic response, load reduction associated with improved power factor at the substation has a beneficial effect on voltage stability by increasing the system stability limit margin. Index Terms--Capacitor placement, load reduction, nondominated sorting genetic algorithm (NSGA), voltage reduction.

This paper presents a concept for local monitoring of the onset of voltage collapse, protective, and emergency control in the presence of voltage-sensitive loads. The onset of voltage collapse point is calculated based on the load characteristics and simulated voltage and current phasors measurements, which are provided by a network of phasor-measurement units. If the stability margin is small and the reactive-power reserves are nearly exhausted, then controls to steer the power system away from the critical point will be activated. Index Terms--Emergency control, load modeling, protective relaying, voltage stability, voltage-stability index.

This paper considers a phasor measurement unit (PMU) placement problem requiring simultaneous optimization of two conflicting objectives, such as minimization of the number of PMUs and maximization of the measurement redundancy. The objectives are in conflict since the improvement of one of them leads to the deterioration of another. Instead of a unique optimal solution, it exists a set of best tradeoffs between competing objectives, the so-called Pareto-optimal solutions. A specially tailored nondominated sorting genetic algorithm (NSGA) for a PMU placement problem is proposed as a methodology to find these Pareto-optimal solutions. The algorithm is combined with the graph-theoretical procedure and a simple GA to reduce the initial number of the PMU's candidate locations. The NSGA parameters are carefully set by performing a number of trial runs and evaluating the NSGA performances based on the number of distinct Pareto-optimal solutions found in the particular run and distance of the obtained Pareto front from the optimal one. Illustrative results on the 39- and 118-bus IEEE systems are presented. Index Terms--Genetic algorithm (GA), multiobjective optimization, nondominated sorting, Pareto-optimal solutions, phasor measurement unit (PMU), topological observability.

Estimating the proximity of power systems to voltage collapse in real time still faces difficulties. Beside the data-management and computational issues, any central-control method is subject to the reliability of long-distance data communications. In the paper, we describe a new data-processing method to estimate the proximity to voltage collapse. The method (code-named SMARTDevice, for Stability Monitoring And Reference Tuning Device) employs only local measurements - bus voltage and load current - and calculates the strength of the transmission system relative to the bus. The collapse occurs when the local load approaches this value. The method is simple enough so that it can be implemented in a numerical relay. The performance of SMARTDevice is compared against the conventional undervoltage relay. It is shown that the latter can misoperate while the new device does not. SMARTDevice is in fact a new breed of voltage relays whose setpoint is automatically tuned to the system condition. Keywords: Voltage Stability, Local Measurements, Voltage-Stability Margin, SMARTDevice, Thevenin equivalent, load shedding.

Multi-inverter microgrid systems, particularly those with loop topology, offer higher power supply reliability and robustness compared to conventional radial distribution systems. In meshed systems, communication-less protection schemes have proved to be ineffective for multi-inverter microgrids due to bidirectional power flow, and limited and controlled fault currents generated by the voltage source converters interfacing the energy source to the network. This makes communication-assisted line protection schemes preferable for such systems despite the necessity for communication means. While these protection schemes are effective, their reliability depends much on the communication availability. This requires a back-up communication path in case the main one fails bringing up the cost issue that hinders their uptake. This paper proposes a novel and low-cost line protection based on directional blocking strategy that can operate as a main as well as a back-up protection to any protection scheme using communication means between the line terminals. As the main, it requires low-bandwidth communication system. As a back-up, it would share the same communication means with the main one and use those of the healthy lines when the faulted line's fails. Thus saving the cost of back-up communication system. [ABSTRACT FROM AUTHOR]

A new capstone design course, which combines elements of power electronics and power systems analysis, has recently been introduced at Georgia Tech as part of the newly revised curriculum. The paper explains the relationship of the new course with respect to the rest of the power curriculum, and how the course material and teaching style respond to various ABET requirements for an integrated design experience. Keywords: Power Engineering Education, Power Quality, Harmonics, Electric Vehicle Charging Infrastructure, ABET 2000.

The control of a nonlinear system with delayed inputs and measurements is illustrated on the example of transient excitation control of a generator. Through simulated studies, the direct feedback linearization approach is found to yield unsatisfactory results in the presence of large measurement processing delays. An effective way to compensate for the delay using prediction is demonstrated. Keywords: Phasor Measurements, Time Delay, Real-Time Generator Control, Prediction.

Three new techniques for frequency measurement are proposed in the paper. The first is a modified zero crossing method using curve fitting of voltage samples. The second method is based on polynomial fitting of the DFT quasi-stationary phasor data for calculation of the rate of change of the positive sequence phase angle. The third method operates on a complex signal obtained by the standard technique of quadrature demodulation. All three methods are characterized by immunity to reasonable amounts of noise and harmonics in power systems. The performance of the proposed techniques is illustrated on several scenarios by computer simulation.

Power electronics interface of renewable energy to system is now the trend in both transmission and distribution segments of power network. Unlike synchronous generators, the fault feeding and control characteristic of these renewable generators are different and mostly influenced by the topology, switching, and control deployed in power electronics interface. So, the network protection design and operational requirements are now challenged in the absence of large fault current. Although the differential current principle still works, its implementation is limited by the significant cost associated to its communication system. This paper proposes a differential line protection scheme based on local fault detection and comparing binary state outputs of relays at both ends of the line thus requiring a simple, flexible and low bandwidth communication system. The performance of the proposed scheme is assessed through simulation of an example system with several scenarios. [ABSTRACT FROM AUTHOR]

Islanding of a utility-interactive photovoltaic (UIPV) system occurs if the UIPV system continues to power a section of the utility system after that section has been disconnected from the utility source. Since islanding creates hazards for personnel and equipment, UIPV systems are required to detect and prevent it. It is desirable to have a simplified method of determining which islanding detection methods (IDM's) are most effective. In this paper, a previously described method for finding the nondetection zones (NDZ's) of IDM's is experimentally verified. This method is used to determine the NDZ's of several common IDM's. These results indicate that, of the IDM's discussed in this paper: 1) Sandia Frequency Shift (SFS) is most effective; 2) the worst-case loads are low-power loads that are near resonance at the line frequency and have a large capacitance and small inductance (a high value of the quality factor Q).

Reports on the activities of the PES society and assesses its outlook for the future. [ABSTRACT FROM PUBLISHER]

Presents information regarding changes planned to PES Technical Committee. [ABSTRACT FROM PUBLISHER]

Conservation voltage reduction (CVR) and distributed-generation (DG) integration are popular strategies implemented by utilities to improve energy efficiency. This paper investigates the interactions between CVR and DG placement to minimize load consumption in distribution networks, while keeping the lowest voltage level within the predefined range. The optimal placement of DG units is formulated as a stochastic optimization problem considering the uncertainty of DG outputs and load consumptions. A sample average approximation algorithm-based technique is developed to solve the formulated problem effectively. A multiple replications procedure is developed to test the stability of the solution and calculate the confidence interval of the gap between the candidate solution and optimal solution. The proposed method has been applied to the IEEE 37-bus distribution test system with different scenarios. The numerical results indicate that the implementations of CVR and DG, if combined, can achieve significant energy savings. [ABSTRACT FROM AUTHOR]

Discusses the need for PES technical committees and technical councils to restructure and improve the reach, quality, and efficiency of the many technical activities of each group. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel control strategy for coordinated operation of networked microgrids (MGs) in a distribution system. The distribution network operator (DNO) and each MG are considered as distinct entities with individual objectives to minimize the operation costs. It is assumed that both the dispatchable and nondispatchable distributed generators (DGs) exist in the networked MGs. In order to achieve the equilibrium among all entities and take into account the uncertainties of DG outputs, we formulate the problem as a stochastic bi-level problem with the DNO in the upper level and MGs in the lower level. Each level consists of two stages. The first stage is to determine base generation setpoints based on the load and nondispatchable DG output forecasts and the second stage is to adjust the generation outputs based on the realized scenarios. A scenario reduction method is applied to enhance a tradeoff between the accuracy of the solution and the computational burden. Case studies of a distribution system with multiple MGs of different types demonstrate the effectiveness of the proposed methodology. The centralized control, deterministic formulation, and stochastic formulation are also compared. [ABSTRACT FROM PUBLISHER]

This paper proposes a hybrid voltage/var control (VVC) architecture for distribution systems with a high PV penetration. The architecture consists of two control loops: coordinated normal control loop and uncoordinated transient cloud movement control loop. In the first loop, hourly dispatches are scheduled for on-load tap changer (OLTC), capacitor banks (CBs), and static var compensators (SVCs) based on forecasted load and PV power output so as to minimize power losses and voltage deviations. The second loop is triggered when large variations of PV power output caused by rapid cloud movement happen. All SVCs and CBs become self-controlled based on local voltage measurements with the single control objective to minimize voltage deviations. SVCs will operate firstly to flatten the voltage profile. If SVCs fail, CBs will switch to provide reactive power support. A time-adaptive delay is applied to each CB to avoid overcompensation. Case studies show the proposed method can optimize the system operation and is effective in voltage regulation with PV generators. [ABSTRACT FROM PUBLISHER]

This paper proposes a model predictive control (MPC)-based voltage/var optimization (VVO) technique considering the integration of distributed generators and load-to-voltage sensitivities. The paper schedules optimal tap positions of on-load tap changer and switch statuses of capacitor banks based on predictive outputs of wind turbines and photovoltaic generators. Compared with previous efforts on VVO which used constant-power load model, the exponential load model is used to capture the various load behaviors in this paper. Different customer types such as industrial, residential, and commercial loads are also considered. The uncertainties of model prediction errors are taken into account in the proposed model. A scenario reduction technique is applied to enhance a tradeoff between the accuracy of the solution and the computational burden. The MPC-based VVO problem is formulated as a mixed-integer nonlinear program with reduced scenarios. Case studies show the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel Microgrid (MG) planning methodology to decide optimal locations, sizes and mix of dispatchable and intermittent distributed generators (DGs). The long-term costs in the proposed planning model include investment, operation and maintenance (O&M), fuel and emission costs of DGs while the revenue includes payment by MG loads and utility grid. The problem is formulated as a mixed-integer program (MIP) considering the probabilistic nature of DG outputs and load consumption, wherein the costs are minimized and profits are maximized. The model is transformed to be a two-stage robust optimization problem. A column and constraint generation (CCG) framework is used to solve the problem. Compared with conventional MG planning approaches, the proposed model is more practical in that it fully considers the system uncertainties and only requires a deterministic uncertainty set, rather than a probability distribution of uncertain data which is difficult to obtain. Case studies of a MG with wind turbines, photovoltaic generators (PVs) and microturbines (MTs) demonstrate the effectiveness of the proposed methodology. [ABSTRACT FROM PUBLISHER]

Wood poles comprise a portion of the power utility's aging infrastructure that make a significant impact on customer's reliability. A large number may fail under the influence of severe wind storms and hurricanes, sometimes resulting in millions of dollars in replacement costs per year to the utilities. A holistic approach to risk assessment of wood poles in power distribution networks would therefore consider the simultaneous effects of decay and natural hazards on the failure probability of the poles. Toward this goal, this paper presents a framework for the development of age-dependent fragility curves of utility wood poles that relies on age-dependent probabilistic capacity models of wood poles and wind induced demand models. The framework considers uncertainties in the initial fiber strength of the wood poles, the age-dependent capacity loss model, the geometric features of wood poles of different classes, and the applied wind loads. The results of this study show that the decay process in wood poles may increase the fragility of the poles significantly as the age of the poles increase. The fragility curves provided in this research may constitute a major component of risk assessment approaches of power distribution networks against hurricanes and strong winds. [ABSTRACT FROM PUBLISHER]

This paper aims to develop a novel method to evaluate Conservation Voltage Reduction (CVR) effects. A multistage Support Vector Regression (MSVR)-based model is proposed to estimate the load without voltage reduction during the CVR period. The first stage is to select a set of load profiles that are close to the profile under estimation by a Euclidian distance-based index; the second stage is to train the SVR prediction model using the pre-selected profiles; the third stage is to re-select the estimated profiles to minimize the impacts of estimation errors on CVR factor calculation. Compared with previous efforts to analyze the CVR outcome, this MSVR-based technique does not depend on selections of control groups or assumptions of any linear relationship between the load and its impact factors. In order to deal with the variability of CVR performances, a stochastic framework is proposed to assist utilities in selecting target feeders. The proposed method has been applied to evaluate CVR effects of practical voltage reduction tests and shown to be accurate and effective. [ABSTRACT FROM PUBLISHER]

System-wide disturbances in power systems area challenging problem for the utility industry because of the large scale and the complexity of the power system. When a major power system disturbance occurs, protection and control actions are required to stop the power system degradation, restore the system to a normal state, and minimize the impact of the disturbance. In some cases, the present control actions are not designed for a fast-developing disturbance and may be too slow. The report explores special protection schemes and new technologies for advanced, wide-area protection. There seems to be a great potential for advanced wide-area protection and control systems, based on powerful, flexible and reliable system protection terminals, high speed, communication, and GPS synchronization in conjunction with careful and skilled engineering by power system analysts and protection engineers in cooperation. [ABSTRACT FROM AUTHOR]

This paper presents a concept for local monitoring of the onset of voltage collapse and protective and emergency control in the presence of voltage sensitive loads. The onset of voltage collapse point is calculated based on the load characteristics and simulated voltage and current phasors measurements, which are provided by a network of phasor measurement units. If the stability margin is small and the reactive power reserves nearly exhausted, then controls to steer the power system away from the critical point will be activated. [ABSTRACT FROM PUBLISHER]