Elias Kyriakides

Optimal Placement of Phasor Measurement Units for Power System Observability

This paper proposes a method for optimal placement of phasor measurement units (PMUs) for complete observability of a power system for normal operating conditions, as well as for single branch outages. A binary search algorithm is used to determine the minimum number of PMUs needed to make the system observable. In case of more than one solution, a strategy is proposed to select the solution resulting in the most preferred pattern of measurement redundancy. The proposed method is used to benchmark the optimal PMU placement solutions for the IEEE 14-bus, IEEE 24-bus, IEEE 30-bus and New England 39-bus test systems. The proposed method is applied on a 298-bus system to determine the optimal placement of PMUs when conventional measurements are available.

Measurements get together

This article deals with the synchronized measurement technology that has the potential of becoming the backbone for real-time monitoring system. The secure and reliable operation of modern power systems is an increasingly challenging task due to the ever-increasing demand for electricity, the growing number of interconnections, penetration of variable renewable energy sources, and deregulated energy market conditions. Power companies in different parts of the world are therefore feeling the need for a real-time wide area monitoring, protection, and control (WAMPAC) system. Synchronized measurement technology (SMT) has the potential of becoming the backbone of this system. The major advantages of using SMT are that 1) the measurements from widely dispersed locations can be synchronized with respect to a Global Positioning System (GPS) clock, 2) voltage phase angles can be measured directly, which was so far technically infeasible, and 3) the accuracy and speed of energy management system (EMS) applications increases manifold.

A GA-API Solution for the Economic Dispatch of Generation in Power System Operation

This work proposes a novel heuristic-hybrid optimization method designed to solve the nonconvex economic dispatch problem in power systems. Due to the fast computational capabilities of the proposed algorithm, it is envisioned that it becomes an operations tool for both the generation companies and the TSO/ISO. The methodology proposed improves the overall search capability of two powerful heuristic optimization algorithms: a special class of ant colony optimization called API and a real coded genetic algorithm (RCGA). The proposed algorithm, entitled GAAPI, is a relatively simple but robust algorithm, which combines the downhill behavior of API (a key characteristic of optimization algorithms) and a good spreading in the solution space of the GA search strategy (a guarantee to avoid being trapped in local optima). The feasibility of the proposed method is first tested on a number of well-known complex test functions, as well as on four different power test systems having different sizes and complexities. The results are analyzed in terms of both quality of the solution and the computational efficiency; it is shown that the proposed GAAPI algorithm is capable of obtaining highly robust, quality solutions in a reasonable computational time, compared to a number of similar algorithms proposed in the literature.

A Comparison of Smart Grid Technologies and Progresses in Europe and the U.S.

This paper discusses historical and technical events in the U.S. and Europe over the last few years that are aimed at modernizing the electric power grid. The U.S. federal government has ratified the “smart grid initiative” as the official policy for modernizing the electricity grid including unprecedented provisions for timely information and control options to consumers and deployment of “smart” technologies. European countries are unified in researching and developing related technologies through various structures supported by the European Union. This paper presents the development of smart grids and an analysis of the methodologies, milestones, and expected evolutions of grid technologies that will transform society in the near future.

PMU Measurement Uncertainty Considerations in WLS State Estimation

A method to assign weights to the measurements obtained through phasor measurement units (PMUs) in a weighted least squares (WLS) state estimation is presented in this paper. The uncertainties for direct measurements are obtained from the manufacturers specifications. For pseudo-measurements, the uncertainties are evaluated by using the classical uncertainty propagation theory. The propagation of measurement uncertainty as a function of line length and conductor type is also investigated. The lower and upper bounds of the estimated states considering the measurement uncertainties are found by using linear programming. The proposed method is applied on the IEEE 14-, 30-, 57-, and 118-bus test systems, and the state estimation results including the lower and upper bounds of the estimated states are presented.

A Constrained Formulation for Hybrid State Estimation

This paper presents a new hybrid constrained power system state estimator. The conventional and synchrophasor measurements are simultaneously incorporated in the estimation problem without using any transformation of measurements. This constrained formulation makes it possible to take advantage of information from phasor measurement unit (PMU) branch current and voltage measurements, improving the accuracy of the existing estimators. The methodology is applied on the IEEE 14-, 57-, and 118-bus test systems, and its performance is compared with other hybrid estimators.

Short Term Electric Load Forecasting: A Tutorial

Short term load forecasting is an important tool for every electric utility. A significant number of operating decisions are based on short term load forecasts. The accuracy of these forecasts leads to significant savings in operating costs and to an enhanced system reliability. The technical literature is abundant with techniques and approaches for performing or improving short term load forecasting. A number of approaches work well with certain power systems or certain geographical areas, while they fail for some other systems due to the nature of the electric load demand: it is complex, highly nonlinear, and dependent on weather, seasonal and social factors. This chapter provides a tutorial introduction to the short term load forecasting problem and a brief summary of the various approaches that have been proposed, from conventional to computational intelligence methods.

A New Hybrid PLL for Interconnecting Renewable Energy Systems to the Grid

There is a need to develop new control strategies for interconnecting Renewable Energy Sources (RES) to the power system due to the ever increasing penetration of RES and in particular for wind power systems (WPS). The control strategies are typically based on a fast and accurate detection of the phase angle of the grid voltage which may be estimated by using a Phase-Locked Loop (PLL) control circuit. The performance of the PLL under normal and abnormal operational conditions is a crucial aspect, since the RES is desired to operate to support the power system under grid fault conditions. This paper investigates the performance of three different PLLs: a synchronous reference frame PLL (dqPLL), a stationary reference frame PLL (αβPLL), and a decoupled double synchronous reference frame PLL (ddsrfPLL). The results of this investigation motivate to the development of a new hybrid PLL which is a combination of the abovementioned PLLs and uses the advantages of each PLL. The proposed decoupled stationary reference frame PLL (dαβPLL) may be an appropriate solution to use in an interconnected RES with Ride Through Fault (RTF) capability, since it prevails the other PLLs with regards to its accuracy under unbalanced faults. Further, it has a lower deviation of the estimated phase after the fault occurs. The performance of the new hybrid dαβPLL is verified through simulations and experiments. Further the new PLL is used in an interconnected RES through experiments under normal and RTF operation.

Hybrid Ant Colony-Genetic Algorithm (GAAPI) for Global Continuous Optimization

Many real-life optimization problems often face an increased rank of nonsmoothness (many local minima) which could prevent a search algorithm from moving toward the global solution. Evolution-based algorithms try to deal with this issue. The algorithm proposed in this paper is called GAAPI and is a hybridization between two optimization techniques: a special class of ant colony optimization for continuous domains entitled API and a genetic algorithm (GA). The algorithm adopts the downhill behavior of API (a key characteristic of optimization algorithms) and the good spreading in the solution space of the GA. A probabilistic approach and an empirical comparison study are presented to prove the convergence of the proposed method in solving different classes of complex global continuous optimization problems. Numerical results are reported and compared to the existing results in the literature to validate the feasibility and the effectiveness of the proposed method. The proposed algorithm is shown to be effective and efficient for most of the test functions.

A Robust Synchronization to Enhance the Power Quality of Renewable Energy Systems

The increasing penetration of renewable energy sources (RESs) in the power grid requires high-quality power injection under various grid conditions. The synchronization method, usually a phase-locked loop (PLL) algorithm, is directly affecting the response of the grid-side converter of the RES. This paper proposes a new PLL algorithm that uses an advanced decoupling network implemented in the stationary reference frame with limited requirements for processing time to enable a fast and accurate synchronization even under harmonic distorted voltage and low-voltage grid faults. The robust response of the proposed PLL is validated, and the effect of the proposed synchronization on the performance of the grid-connected renewable energy system is investigated. This investigation proves that the robust, accurate, and dynamic response of the new PLL can enhance the quality of the injected power from the RES and can also enable an appropriate fault-ride-through operation under harmonic distorted voltage and grid faults.