With the steady expansion of renewable energy sources (RES), the provision of ancillary services is becoming an increasingly challenging task within system operation. In order to add regulation capacity, battery energy storage systems (BESS) have been recognized as an efficient tool in recent literature. In this context, this paper proposes a novel BESS control strategy to improve dynamic performance of automatic generation control (AGC). Such control strategy is applicable to power systems which evaluate AGC performance utilizing regulation response accuracy margins, which typically define the slowest and fastest permitted power response to a regulation signal. The primary goal consists in enhancing the regulation service by minimizing the rate of non-compliance with respect to the corresponding dynamic performance criteria and its defined accuracy margins. Additionally a comprehensive State-of-Charge-control (SoC-control) is included in the strategy. By utilizing the BESS only during designated regulation assistance periods, preventing extreme levels of charge and furthermore identifying and avoiding futile regulation efforts, BESS degradation is kept to a minimum. To verify effectiveness a case study is conducted with 400 hours of real AGC operation of various BESS sizes. The obtained results show that a BESS is able to minimize the rate of non-compliance considerably, whilst preserving low BESS usage and degradation.

This paper presents a systematic method for the design of robust and efficient underfrequency load-shedding (UFLS) schemes. UFLS schemes play an important role in protecting the system integrity. The systematic method consists first in selecting representative operating and contingency (OC) scenarios by means of a clustering algorithm and subsequently, in tuning UFLS scheme parameters by dint of a simulated annealing optimization algorithm. The approach is applied to a small isolated Spanish power system. The systematic method leads to a robust and efficient UFLS scheme. The resulting design is also compared to a design based on OC scenarios determined by the common practice of OC scenario selection. The possibility of rearranging UFLS stages and the influence of minimum allowable frequency constraints is analyzed as well. Finally, an analysis of the impact of increasing converter-connected generation (CCG) is presented.

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.

This letter presents a centralized underfrequency load-shedding (UFLS) scheme using the initial rate-of-change of frequency (ROCOF) to decide whether and how much load needs to be shed. The applicability of the centralized UFLS scheme is shown for a Spanish small isolated power system.