Andrej F. Gubina

Prediction of Power System Security Levels

In the paper, Markov chains in conjunction with Monte Carlo simulation are used to predict the power system security level. The new approach uses a Markov chain for each identified security range to track the development of security level through time. Based on the forecasted and recorded data, the proposed procedure offers a useful tool to the system operator to predict a future power system security level. The method has been tested on the Bosnian power system using the recorded data on security levels during a one-year period. The forecasted results show a striking coincidence with the real security levels. By means of a simple and computationally fast method, the system operator can estimate the probability of a power system blackout. The presented method could be incorporated in the wide-area monitoring system in control centers.

Agent-based modeling of the demand-side flexibility

The paper presents an agent-based approach to model the flexibility of the demand-side. It uses Q-learning algorithm to model a behavior of a demand-side agent, so to investigate the elasticity of the demand to the change in price. Often, market simulation models assume that the demand elasticity is known, however due the lack of data this elasticity is not easy to determine. The objective of this paper is to evaluate the flexibility of the total system demand, and the shift in the consumption with the price, i.e. increase in the demand when the price is low, and a decrease in the demand when the price is high. The here presented model of a demand-side agent is incorporated into the market simulator with double-sided auctions, and is tested on the Slovenian market. However, this approach can be used to estimate flexibility in any system for which the forecasted demand data and generation offers are know.

Unified Approach to Reliability Assessment in an Isolated RES System

Due to their unique characteristics, renewable energy sources (RES) are an ideal energy source for small isolated power systems (SIPS). At the same time, the reliability impacts of RES electricity supply should be carefully studied, especially in SIPS with significant RES installed capacity. One of the most potent methods for this purpose is system well-being analysis, accounting for deterministic and stochastic reliability factors. In the paper, we present a novel method for calculation of system well-being indices based on contingency enumeration (CE) method. We also investigate the energy-oriented energy not served (ENS) index and propose an improved method for its calculation. The indices are then used to analyze the impacts of different hybrid generation structures and RES penetration levels on supply reliability of the system. We investigate the suitability of different reliability assessment schemes and pertaining indices for reliability of hybrid energy sources in SIPS. The results show-that due to the ability of the ENS index to measure the severity of the risky state, both types of indices are needed to satisfactorily observe the supply reliability, especially in hybrid-supplied SIPS

Intelligent coordinative voltage and reactive power control

A novel local voltage control is proposed where each voltage controller of a generating unit is equipped with additional coordinative voltage controller (CVC), which incorporates intelligent control into the power system. The controllers use artificial neural networks (ANN), trained on a large set of power system states. Optimal power flow (OPF) results serve as the optimal target in the ANN training process. All data the controller needs for operation are acquired locally. The proposed ANN voltage control maintains a sub-optimal power system voltage profile and reduces the power system losses. When equipped with ANN controllers, the system responds satisfactorily to changes in the power system topology, thus improving the power system security.

The flexible demand influence on the joint energy and reserve markets

Advances in control and information technology in electric grids of the future offer new possibilities in the markets for the consumers. Using their flexible demand, not only can they influence the prices in the energy market but can also participate in the system reserve market. In the paper we present a new approach to the stochastic modeling of the demand-side reserve provision in co-optimized day-ahead electricity and reserve markets, where the consumers has the opportunity to participate as a reserve provider. The consumer participates in both markets for the cost reduction and the benefits obtained in them. The approach features a new method for the price determination of the demand-side reserve provision. The approach has been tested on IEEE RTS. The results illustrate the influence of demand flexibility on the ability of the consumers to provide reserve and on their subsequent benefits, including the reduced security cost.

The composite fuzzy reliability index of power systems

Abstract This paper describes a method for fuzzy calculation of power system reliability. It introduces a composite fuzzy security and fuzzy adequacy indices encompassing the power system segments of generation, transmission, and the segment of load nodes. The fuzzy security index is determined by the security membership grades of the power system components which are found to be the worst in their segments. The fuzzy adequacy index is based on the adequacy indices of generation, transmission, and transmission integration segments. The composite fuzzy reliability index enables the system operator to have a continuous insight into the distance between the power systems actual state and the closest unreliable state by tracking the systems components with the lowest security and adequacy membership grades of the respective segments. The algorithm has been tested on the models of the IEEE Three Area RTS-96 and Bosnia–Herzegovina power systems.

Analysis and Support Policy Recommendation of Renewable Energy Sources in Western China

Reduction of greenhouse gas emission levels in China is of great importance, because of their significant growth. Development of renewable energy sources is a key to the sustainable development of China while pursuing the low GHG emissions goals. In the paper, we present an overview of the development in the renewable energy sources (RES) in the Western Region of China (WRC). We analyze the abundant renewable energy resources in WRC with different energy specifications. We focus on Chinas WRC as the most important region for development of renewable energy in the future years. Due to its diversity in RES sources and different RES support initiatives, Western Region could serve as a testing ground for wider application of a uniform RES support policy in China. We analyze two cases of Chinese experience with RES support policy based on Tibet and Sichuan provinces located in West Region of China. We identify various barriers and success factors to promote RES development in WRC. We also review the current policy mechanisms, especially investment- or generation- based price-driven and capacity-driven mechanisms, ranging from investment incentives for the development of renewable energy projects, feed-in tariffs, production tax incentives, tendering systems, and quota obligations based on tradable green certificates. Based on European Union experience, we propose policy measures to stimulate RES development in WRC and present some instruments for its implementation.

Risk management in the retail electricity market: the retailer's perspective

The retail company on the liberalized electricity market faces an increasing price risk exposure, stemming from the uncertain demand and the wholesale market price volatility. In the paper the influence of the stochastic parameters on the retailers overall risk exposure is analyzed. After constructing the appropriate models for consumer demand, electricity spot price and forward price curve, the influence of the wholesale forward-price volatility in combination with the maturity of the sales-contract offer on the retailers risk exposure is investigated. The proposed model was used for risk-premium determination, and the results were compared with those of a traditional technique from option-pricing theory. The results of a Monte Carlo simulation illustrate how forward-price volatility influences the retailers total risk. The model is of immediate practical value to the electricity retailer since it enables the evaluation of risk arising from the different stochastic drivers.

The Security of Electricity Supply: The Economic Downturn's Influence in Slovenia

In every country, one of the most important performance criteria for the electricity sector is the security of the electricity supply. In this article, the influence of the economic downturn on the national security of the electricity supply is analyzed, using the proposed methodology for an integrated assessment of the security of the electricity supply. It is composed of an integrated model, featuring the security of the electricity supply performance indices of the distinct dimensions of a power system. These distinct dimensions are assessed using the best practices available. An aggregated index for measuring the security of the electricity supply is constructed on the basis of three distinct dimensions: the security of the primary energy supply, the environmental performance, and the power system reliability. Using the proposed index, the security of the electricity supply for Slovenia is calculated, before and after the economic downturn, highlighting the key drivers and their influence on the security of the electricity supply.

Long-Term Security of Supply Assessment under Open Electricity Market - Energy Policy Impacts in Slovenia

Following the steady demand growth and diminishing generation capacity margin due to lack of generation investment, Slovenia is already importing almost a quarter of electricity needed to cover its demand. Coupled with the deregulated electricity market and the European Union (EU) climate change mitigation measures implemented through EU Emissions Trading Scheme (EU ETS), the economic as well as environmental factors limit the necessary power system development and endanger future security of supply. A framework is needed to assess the generation expansion options taking into account all the limitations and associated risks, and to propose the optimal policy measures to insure long-term security of supply in Slovenia. In the paper, the current energy balance status is investigated, followed by several development scenarios for the period up to 2030. The paper briefly describes the Day-Ahead Market Simulator (ELMASplus), developed at the University of Ljubljana that is used to simulate the electricity price development on the market for the purpose of forecasting energy policy impacts in Slovenia. The simulation results are presented covering the future primary energy supply mix, power system adequacy indices, electricity import dependency, CO2 emissions, electricity market prices and other relevant indicators. The two most promising development generation development scenarios with different associated risks are introduced and evaluated. Based on the results, the appropriate policy measures are suggested.