Antonis G. Tsikalakis

Centralized Control for Optimizing Microgrids Operation

Microgrids are low-voltage (LV) distribution networks comprising various distributed generators (DGs), storage devices, and controllable loads that can operate either interconnected or isolated from the main distribution grid as a controlled entity. This paper describes the operation of a central controller for microgrids. The controller aims to optimize the operation of the microgrid during interconnected operation, i.e., maximize its value by optimizing the production of the local DGs and power exchanges with the main distribution grid. Two market policies are assumed including demand-side bidding options for controllable loads. The developed optimization algorithms are applied on a typical LV study case network operating under various market policies and assuming realistic spot market prices and DG bids reflecting realistic operational costs. The effects on the microgrid and the distribution network operation are presented and discussed.

Centralized control for optimizing microgrids operation

Microgrids are low-voltage (LV) distribution networks comprising various distributed generators (DGs), storage devices, and controllable loads that can operate either interconnected or isolated from the main distribution grid as a controlled entity. This paper describes the operation of a central controller for microgrids. The controller aims to optimize the operation of the microgrid during interconnected operation, i.e., maximize its value by optimizing the production of the local DGs and power exchanges with the main distribution grid. Two market policies are assumed including demand-side bidding options for controllable loads. The developed optimization algorithms are applied on a typical LV study case network operating under various market policies and assuming realistic spot market prices and DG bids reflecting realistic operational costs. The effects on the microgrid and the distribution network operation are presented and discussed.

Improved wind power forecasting using a combined neuro-fuzzy and artificial neural network model

The intermittent nature of the wind creates significant uncertainty in the operation of power systems with increased wind power penetration. Con- siderable efforts have been made for the accurate prediction of the wind power using either statistical or physical models. In this paper, a method based on Artificial Neural Network (ANN) is proposed in order to improve the predictions of an existing neuro-fuzzy wind power forecasting model taking into account the evaluation results from the use of this wind power forecasting tool. Thus, an improved wind power forecasting is achieved and a better estimation of the confidence interval of the proposed model is provided.

Determining and exploiting the distribution function of wind power forecasting error for the economic operation of autonomous power systems

Many efforts have been presented in the bibliography for wind power forecasting in power systems and few of them have been used for autonomous power systems. The impact of knowing the distribution function of wind power forecasting error in the economic operation of a power system is studied in this paper. The papers proposes that the distribution of the wind power forecasting error of a specific tool can be easily derived if, for that model, an evaluation of its performance is made off-line comparing the forecasted values of the tool with the actual wind power values in the same horizon. The proposed methodology is applied to the autonomous power system of Crete. It is shown that the improvement of the performance of wind power forecasting tool has significant economic impact on the operation of autonomous power systems with increased wind power penetration. The obtained results for various levels of wind power production and load show that using only mean absolute percentage error (MAPE) leads to significant change in the estimation of the wind power to be shed to avoid technical limits violation, especially if the wind power forecasting tool presents underestimation of the actual production

Wireless Monitoring and Remote Control of PV Systems Based on the ZigBee Protocol

Systems that convert the sunlight into electrical energy like photovoltaics (PV) have been becoming widespread worldwide. The prospect of using the promising technology of wireless sensor networks (WSN) in the field of PV plant supervising and monitoring is studied here. The knowledge of the status and good working condition of each PV module separately as well as of any PV system component will lead in a more efficient way for power management. The nature of the wireless sensor networks (WSN) offers several advantages on monitoring and controlling applications over other traditional technologies including self-healing, self-organization and flexibility. The versatility, ease of use and reliability of a mesh network topology offered by the ZigBee technology that is based on the IEEE 802.15.4 standard, is used here to offer its maximum advantages on a system that is capable for real time measurements and event alerts.

The effect of island interconnections on the increase of Wind Power penetration in the Greek System

Greece is a country with many dispersed islands where favorable conditions for exploiting RES exist. Cyclades is a group of islands that some of them are not so far away to be interconnected with the mainland and among them. This interconnection will reduce the need for operating the local oil- fired stations and extending the area they occupy to meet future needs. This paper presents an additional benefit from the Interconnection of Cyclades to the mainland, the exploitation of the very favorable wind conditions of the area. With the use of geographical information systems (GIS) the most promising locations for installing wind power have been identified with the restriction of the thermal limits of the interconnection lines. The results from investment analysis of wind power after interconnection of Cyclades show clear financial benefits for the potential investors even without subsidy.

Techno-Economic and Environmental Evaluation of Large Scale PV Integration in Greece

This paper evaluates the current status of renewable energy sources integration and future trends, especially of the photovoltaics, in the interconnected power system of Greece and the power system of Crete Island, which is the largest isolated power system in Greece. Focusing on the ongoing developments and prospects, the paper investigates the impacts of the expected sufficient photovoltaic installations on the energy market and the greenhouse gas emissions, as well as the reduction in CO2 emissions costs due to the installation of photovoltaics and other renewable energy technologies.

Impact of Increased RES Generation on Power Systems Dynamic Performance

In this paper, the impact of high wind power and photovoltaics penetration on the dynamic behavior of an island power system like one operates in Crete is investigated. Several simulations were performed leading to the fact that it is possible to achieve higher level of renewable energy sources penetration without significant dynamic security problems, if power units spinning reserve exists and the corresponding control systems have a sufficiently fast response.

Analytical Assessment of DC Components Generated by Renewable Energy Resources with Inverter-Based Interconnection System due to Even Harmonics

This paper deals with the assessment of DC components generated by renewable energy resources with inverter-based interconnection system to the electric grid. DC injection is a critical issue related to power quality of distribution network systems with high penetration of inverter-based interconnection systems. This type of interface systems may improve the performance of the electric generation unit and affect positively or negatively the power quality of the distribution network depending on the proper or improper designation. The investigation of the various causes of DC components and the analytical assessment of their maximum levels are crucial for the proper operation of inverter-based interface systems and the limitation of DC injection. A method based on analytical calculations using a computer software has been implemented for the assessment of DC components contained on an inverters output voltage when even harmonics are present on the network voltage. Moreover, a simulation package was used to demonstrate the existence of DC components under various conditions. It was proved by the current analysis that the amounts of DC components generated when even harmonics are present on the network voltage can be high under abnormalities on the power grid but they are not considerable under normal operating conditions.

Current status and future prospects of Crete's power system

Cretes power system faces already a significant contribution up to 25% in its energy balance by renewable energy sources. Although, there is even higher capacity of RES that could be utilized, the current power system operation and control, special restrictions, emerge limitations, which hold back their further expansion. More precisely, this study analyses current system operation and demonstrates benefits and obstacles of future prospects for of ultra-high share of RES.