This paper studies the impact of the size and controller settings of an ultracapacitor (UC) on frequency stability. Underfrequency load-shedding (UFLS) schemes play an important role in protecting the system against frequency instability and their performance is used as a measure for the enhancement of frequency stability thanks to the UC. To this end, a simplified but still accurate model of the UC is developed. In addition, a meaningful procedure is proposed to size the UC's power and energy storage capacities in function of the system parameters and operation constraints in order to improve frequency stability. Finally, the impact of the UC on the UFLS scheme is studied for many generation dispatch scenarios and for all possible single generating unit outages of a Spanish isolated power system. An analysis with respect to the UC's control parameters and its size in terms of power and energy storage capacities is carried out, too. Appropriate control parameter settings improve the UC's impact on frequency stability.

The aim of this paper is to analyze the profitability of wind technology as a potential participant in the frequency regulation, specifically in the secondary regulation market. The study is conducted for the Spanish system using existing market rules. However, although this system has some peculiarities the main methodology could be applied in other systems. Firstly, a bibliographical review of the relevant technical possibilities of this technology is carried out. Then, a simulation study based on real data is conducted in order to evaluate the maximum possible incomes. Later, a specific offer strategy is proposed and the income is estimated based on statistical modeling and checked by simulating its performance using the actual and forecasted productions of a wind portfolio. It is concluded that under the current generation structure and regulatory framework in the Spanish system, the incomes obtained from the participation of wind technology would be modest. However, secondary regulation by wind generators might facilitate higher penetration levels of this technology. In the long term, with expected wind generation subsidies much reduced, a greater need for regulation reserves and a possible increase in regulation prices, regulation-related incomes might become a sizeable fraction of the total income of wind generators.