Dimitrios I. Doukas

Impact of penetration schemes to optimal DG placement for loss minimisation

This paper examines the impact of different penetration schemes to the optimal distributed generation placement problem for loss minimisation. The four variables of the problem are presented and a concept based on degrees of freedom (DoF), representing the number of the variables that undergo any kind of limitation during the solution process, is introduced. Four commonly utilised penetration schemes subject to various limitations are examined and compared with a fifth penetration scheme, which is unconstrained and is proposed as the optimal one. All schemes are implemented under a local-particle swarm optimisation-variant algorithm and applied on the IEEE 33 and IEEE 118 bus systems. The results indicate that the proposed penetration scheme with four DoF provides the optimal solution both in terms of loss minimisation and voltage profile improvement.

Energy storage sizing for large scale PV power plants base-load operation - comparative study & results

With greenhouse gas emissions increasing and global environmental policies changing, renewable energy sources have gained significant attention over the last 15 years. However, the intermittent nature of renewable generation makes its integration to the grid a challenging task. Thus, energy storage systems are usually proposed as a way to overcome this problem. This paper deals with energy storage for very large PV power plants (larger than 100MW). Different operating strategies have been defined for the PV power plant and the required energy storage capacity was estimated for each of them via a sizing methodology that will be briefly described. In addition, six areas of favorable solar radiation characteristics have been chosen as case studies to evaluate the presented methodology. Finally, a time series analysis was conducted in order to estimate the confidence interval for which both PV generated energy and energy storage are sufficient to fulfill the specific operating strategy. This analysis was performed for each operating strategy and location and thus, a comparative study will be presented.

Energy storage integration into grid connected utility-scale photovoltaic (PV) systems

This paper takes into account energy storage sizing results from previous research activities regarding base-load implementation of an energy storage system integrated into a PV power plant, for six locations of favorable meteorological characteristics [1]. The main target is to evaluate scenarios of integrating energy storage in different positions of a grid connected PV power plant in terms of transmission cost and transmission losses. The analysis deals with different transmission voltage levels and proposes where and how energy storage should be included within a very large scale utility PV power plant for base-load operation and after taking into account the drivers for using Energy Storage. Furthermore, this paper analyses different power electronics (PE) interface techniques for integration of energy storage into grid connected utility-scale applications. Various alternatives are identified and presented in this paper, while advantages and disadvantages for all scenarios are highlighted.

Application and evaluation of UPSO to ODGP in radial Distribution Networks

In this paper, a new effort regarding the Optimal Distributed Generation Placement (ODGP) problem is presented. Loss minimization is considered as the objective while considering the networks technical characteristics as constraints, i.e. node voltage and line thermal limits. The proposed method, called Unified Particle Swarm Optimization technique (UPSO), combines the advantages while at the same time extinguishes the disadvantages of the two basic PSO variants, the Global and Local PSO. The implemented analysis demonstrates that an enhanced performance is achieved, both in terms of a better optimal solution as well as faster convergence. The method is evaluated upon IEEE-16 and IEEE-33 bus systems and compared with other techniques.

Volume Element Method for Thermal Analysis of Superconducting DC Transmission Cable

The ever increasing need for cost-efficient, high-density power transmission brought to the fore applied superconductivity as an alternative worth investigating. Especially, high-temperature superconducting (HTS) dc cables emerge as a promising solution for bulk power transmission and their use in the near future is expected to be increased. HTS cables have the special characteristic of varying performance under different critical conditions, especially under different operating temperatures. Therefore, detailed thermal analysis of HTS cables representing thermodynamics and heat transfer for varying length and time is of significant importance. The analytical mathematical formulation presented in this paper solves heat transfer equations for a two-dimensional axisymmetric cable model and identifies temperature distribution over length and time. The analysis is conducted on a bipolar cable suggested by the Electric Power Research Institute for long-distance HTS dc transmission, while both steady-state and transient scenarios are examined.

Energy loss reduction in Distribution Networks via ODGP

In this paper the Optimal Distributed Generation Problem (ODGP) towards energy minimization is solved for a large number of scenarios regarding power loss minimization. Load variations are taken into account by the formulation of different snapshots concerning the networks operational status. These snapshots refer to various load compositions and for each one the ODGP problem is applied. Load variations are formed stochastically under a uniform distribution while the initial loading conditions are considered as the mean load profile of the network. The solution algorithm relies on a Local PSO Variant and the results indicate that for not extreme load variations some specific nodes tend to participate in the majority of the different solutions. Thus, the analysis proposes a fixed solution that could yield the highest energy reduction despite the fact that it is not the optimal for each individual operating state with different load composition.

Comparative analysis of heuristic techniques applied to ODGP

In this paper, a comparative analysis and evaluation of several heuristic techniques, when applied to the Optimal Distributed Generation Placement (ODGP) problem, is presented. Loss minimization is considered as the objective, while the networks technical characteristics as the constraints. Three versions of Particle Swarm Optimization (PSO), Global, Local and Unified (GPSO, LPSO and UPSO, respectively), Genetic Algorithm (GA), Artificial Bee Colony (ABC), Cuckoo Search (CS) and Harmony Search (HS) are compared. The implemented analysis demonstrates that all Heuristic Techniques examined can solve the ODGP problem efficiently, although UPSO emerge as the most promising, in terms of solution and convergence performance, whereas regarding execution time, HS is the most prominent. The study is evaluated upon typical 33 and 30 bus systems.

Techno-economic analysis for optimal energy storage systems placement considering stacked grid services

The increasing penetration of Renewable Energy Sources (RES) and generation uncertainties, brought to the fore new challenges and problems regarding efficient Distribution Networks (DNs) operation. Energy Storage Systems (ESS) can play a significant role in more reliable, secure and flexible DN operation since they can deal with difficult-to-predict changes. This study provides a detailed methodology among the corresponding mathematical formulation for the optimal sizing and allocation of ESS considering optimum operation schedule.

Grid integration scenarios for superconducting DC transmission systems

Superconducting dc systems present a promising alternative for power transmission. Advantages of dc transmission, such as enhanced controllability combined with the lossless characteristic of superconductivity result in an advantageous mixture, especially for bulk power transmission. This paper presents alternative concepts for integration of superconducting dc links within conventional ac or dc grids. Focus is given on how a superconducting dc link could coexist with conventional transmission systems in order its advantages to be exploited, while its operation is secured. Appropriate system configurations, cable models, advantages of superconducting transmission, such as reduction of transmission losses as well as modeling feasibility are analytically discussed. A selection of the grid integration scenarios is tested under both steady-state as well as fault conditions.

Battery energy storage systems modeling for online applications

Over the last decade the use of battery energy storage systems (BESS) on different applications, such as smart grid and electric vehicles, has been increasing rapidly. Therefore, the development of an electrical model of a battery, capable to estimate the states and the parameters of a battery during lifetime is of critical importance. To increase the lifetime, safety and energy usage, appropriate algorithms are used to estimate, with the lowest estimation error, the state of charge of the battery, the battery impedance, as well as its remaining capacity. This paper focuses on the development of model-based online condition monitoring algorithms for Li-ion battery cells, which can be extended to battery modules and systems. The condition monitoring algorithms were implemented after considering an optimal trade-off between their accuracy and overall complexity.