This paper proposes the droop control algorithm for multiple distributed Battery Energy Storage Systems (ESS) with their state of charge (SOC) feedback, shown to be effective in providing grid services while managing the SOC of the ESS. By extending the mathematical links between the ESS SOC and power dynamics for frequency regulation, this paper elaborates on how the proposed scheme integrates multiple ESS into the load frequency control and the ESS effectively augments the functional roles of the incumbent generators. The control performance for a group of ESS in grid operations is evaluated and characterized by using metrics such as the cutoff frequency and settling time, and the initial and final value theorems. Theoretical insights and practical issues are discussed. Various numerical examples and case studies for a simplified Australian network with high penetration of renewables demonstrate the validity and efficacy of the proposed method. INDEX TERMS Energy storage system (ESS), frequency regulation, reserve, droop control, state of charge (SOC), energy feedback, SOC management. HEEJIN KIM (S'10-M'15) received the B.S. and Ph.D. degrees in electrical engineering from Yon

This paper proposes an effective control methodology for the Energy Storage System (ESS), compensating for renewable energy intermittency. By connecting generation variability and the preset service range of the State of Charge (SOC), this methodology successfully secures the desired SOC range while smoothing out power fluctuations. Adaptive to grid conditions, it can adjust response time (control bandwidth) of the ESS via energy feedback coefficients subject to the ESS capacity and its SOC range. This flexibility facilitates the process of developing ESS operation and planning strategies. Mathematical analysis proves that the proposed method controls the ESS to perform best for specific frequency bands associated with power fluctuation. Time-domain simulation studies along with power-spectrum analysis using PSCAD and MATLAB demonstrate the excellent power-smoothing performance to the power grid.

Increasing number of Flexible AC Transmission System (FACTS) devices have been be installed to reinforce the existing grid and build the envisioned "Smartness" into the grid through controls and optimization. However, it has been noticed that adverse interactions among multiple FACTS controllers may occur when they are not properly coordinated with each other and other slowly acting system equipment. These interactions can amplify oscillations and even destabilize the system by influencing the damping properties of individual FACTS controllers or increasing voltage deviations. This paper presents an extensive survey on the existing cases, system studies and assessment techniques to help system planners understand the underlying mechanism of diverse interactions among multiple FACTS controllers and develop coordinated control schemes for preventing or mitigating any harmful interactions. Control interactions are categorized and discussed in terms of their root causes and resulting frequency ranges. Unfriendly interactions involving shunt FACTS devices are detailed in which Korean Electric Power Corporation (KEPCO) is particularly interested.

No abstract

No abstract