Sara Sulis

Efficient Branch-Current-Based Distribution System State Estimation Including Synchronized Measurements

Deregulation and privatization actions are creating new problems of control, management and reliability, because of new players and new technologies spreading in distribution systems. Such new scenarios require more comprehensive and accurate knowledge of the system to make control actions efficient and reliable. In particular, attention must be paid to phase angles estimation to avoid critical situations. In this context, the use of phasor measurement units (PMUs) looks promising. This paper presents an efficient branch-current-based distribution systems state estimation. The estimator allows synchronized phasor measurements provided by PMUs to be included. In addition, the branch current state model is extended so that the knowledge of the voltage profile is significantly improved. The estimator is expressed both in polar and rectangular coordinates and a comparison between the obtainable accuracy and computational efficiency is presented. Furthermore, the possibility to treat radial and weakly meshed topology, also in presence of dispersed generation, is analyzed. The results obtained on different distribution networks are presented and discussed.

A Flexible GPS-based System for Synchronized Phasor Measurement in Electric Distribution Networks

Large-scale distributed measurement systems are the object of several applications and research. The goal of this paper is to develop, by employing global positioning system (GPS) receivers, measurement techniques that are suited to the continuous monitoring of the electrical quantities in distribution networks in terms of synchronized phasors. The proposed measurement procedures, differently from commercially available phasor measurement units, are based on general-purpose acquisition hardware and processing software, thus guaranteeing the possibility of being easily reconfigured and reprogrammed according to the specific requirements of different possible fields of application and to their future developments.

DMS Cyber-Physical Simulation for Assessing the Impact of State Estimation and Communication Media in Smart Grid Operation

Energy management systems for the operation of distributed energy resources, distribution storage devices, and responsive loads will be embedded in distribution management systems (DMSs) as advanced functions that rely on accurate input data and fast communication signals. For a proper DMS design, the impact of the state estimation uncertainties and of the communication system delays should be evaluated. The paper presents an integrated software package for the cyber-physical simulation of DMS taking into account the accuracy of state estimation and measurements. The effectiveness of a wireless Wi-Max communication system has been tested on the rural Italian representative network produced by the research project ATLANTIDE. Results proved the need of cosimulation packages in modern distribution systems.

Optimal Allocation of Multichannel Measurement Devices for Distribution State Estimation

This paper proposes an optimization algorithm that is suitable for choosing the optimal number and position of the measurement devices in distribution state estimation (DSE) procedures used in modern electric distribution networks. The algorithm is based on the techniques of dynamic programming, and its goal is to guarantee both the minimum cost and the accuracy required for the measured data needed to operate management and control issues, such as energy dispatch and protection coordination. Both the uncertainty introduced by the measurement devices and the tolerance in the knowledge of the network parameters (line impedances) are taken into account in the proposed approach. The aggregation of the quantities to be measured in a few measurement points has been favored to reduce the overall cost of the measurement system. Random changes in the loads are considered to establish adequate reference conditions for the tests. Tests relevant to real distribution networks are presented to show the validity of the proposed approach. The results emphasize how both the influence of the tolerance on the network parameters and the cost of the measurement system can dramatically be minimized by suitably choosing the algorithm to be implemented to solve the DSE problem.

Optimal Meter Placement for Robust Measurement Systems in Active Distribution Grids

Future active distribution grids are characterized by rapid and significant changes of operation and behavior due to, for example, intermittent power injections from renewable sources and the load-generation characteristic of the so-called prosumers. The design of a robust measurement infrastructure is critical for safe and effective grid control and operation. We had earlier proposed a placement procedure that allows finding an optimal robust measurement location incorporating phasor measurement units and smart metering devices for distribution system state estimation. In this paper, the lack of detailed information on distributed generation is also considered in the optimal meter placement procedure, so that the distributed measurement system can provide accurate estimates even with limited knowledge of the profile of the injected power. Possible non-Gaussian distribution of the distributed power generation has been taken into account. With this aim, the Gaussian mixture model has been incorporated into the placement optimization by means of the so-called Gaussian component combination method. The occurrence of either loss of data or degradation of metrological performance of the measurement devices is also considered. Tests performed on a UKGDS 16-bus distribution network are presented and discussed.

Investigation on Multipoint Measurement Techniques for PQ Monitoring

The problem of locating the sources of harmonic distortion in power networks is still a critical task. Several methods based on multipoint measurement techniques have been recently proposed in the literature for harmonic-pollution monitoring. The main goal of this paper is to compare the two most powerful tools designed for this purpose. In this paper, the results of both computer simulations on an IEEE test network and experimental tests performed by means of simultaneous measurements on an ad hoc benchmark power system are presented along with a discussion on the practical usability of such monitoring techniques

Investigation on the accuracy of harmonic pollution metering techniques

The main goal of this paper is to investigate the robustness of some procedures recently proposed in the literature for harmonic pollution metering, in respect to the effects of the uncertainty sources present in the measurement chain. Both single point and multipoint methods are discussed. The research is based on computer simulations performed on an IEEE test system suitable for studies related to harmonics in power distribution networks. The estimate of the combined uncertainty affecting the measurement results is achieved by exploiting a Monte Carlo statistical approach. The results are discussed to highlight some important findings on the practical usability of these monitoring techniques.

Effects of Measurements and Pseudomeasurements Correlation in Distribution System State Estimation

Distribution system state estimation (DSSE) is one of the key elements of the monitoring activity of an active distribution network, and is the basis for every control and management application. The DSSE relies on real measurements collected by the distributed measurement system and on other available information, mainly obtained from historical data that help in obtaining observability. This prior information is necessary to derive the so called pseudomeasurements. Accurate input data are fundamental for an accurate estimation, as well as knowledge on possible correlation in the measured and pseudomeasured data. A degree of correlation can exist in the measured data, due to measurement devices, and among power consumptions or generations of some particular nodes. This paper presents an exhaustive analysis on the influence of correlations on the quality of the estimation. The importance of including correlation in the weighted least square estimation approach is discussed using both traditional and synchronized measurements. Results obtained on a 95-bus distribution network are presented and discussed.

State Estimation for the Localization of Harmonic Sources in Electric Distribution Systems

Throughout the last years, with the liberalization of the energy market, the localization of the sources of power quality disturbances has become a nodal point for operators and customers. In the liberalized market, knowledge of the system status, along with the uncertainty affecting the estimated data, is required to operate management and control issues such as energy dispatching and protection coordination. In distribution systems, too many measurement instruments would be needed to obtain a complete observation of the electric quantities. Thus, model-based state-estimation techniques can be implemented to exploit the few real-time measurements from the field and all the other available information to estimate the desired quantities. In this paper, a novel approach to the estimation of the harmonic sources by means of a Bayesian approach is proposed. The procedure also allows the ldquoqualityrdquo of the obtained estimates to be assessed. The theoretical fundamentals of the method are discussed, and results relevant to a simple distribution network are presented.

Robustness-Oriented Meter Placement for Distribution System State Estimation in Presence of Network Parameter Uncertainty

Distribution systems require ad hoc estimators, distribution system state estimation (DSSE) techniques, to acquire knowledge about the system status. An incorrect evaluation of the accuracy of the DSSE creates decision risks in network management. The possible variations in the network parameter values and the decays of the metrological characteristics of the measurement system elements are uncertainty sources very often not considered. Considering these possible lacks of accuracy, this paper focuses on the robustness of distributed measurement systems aimed to obtain accurate DSSE results. The problem of the proper assessment of the accuracy of the DSSE results obtained through a weighted least squares (WLS) approach is faced. A method capable of including different uncertainty sources in the uncertainty estimation of the WLS approach is presented. Furthermore, this paper proposes an optimal meter placement algorithm robust with respect to possible malfunctions in measurement system components. The results obtained on a portion of an Italian distribution network, along with their accuracy, are presented and discussed.