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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.