Growth of renewable penetration will increase the requirement for flexible resources. It may be a simple solution to build more flexible resources, but it is too expensive. Recently, the new construction of power plant or transmission line has faced opposition by the resistance of the local residents. Depending on the needs, new methodologies are required in order to gain the flexibility of the power grids. This paper proposes the flexible frequency operation strategy with significant renewable penetration to achieve the flexibility of the power grids. Flexible frequency operation provides customized frequency through BTB HVDC, and the overall system is operated with relaxed frequency regulation. By reducing the need and role of the frequency ancillary service reserve, an operator does not need to secure additional governor response reserve for renewable energy. In order to model frequency dynamic of high renewable penetrated power system, the swing equation is modified in this paper. The case studies using MATLAB show effectiveness of flexible frequency operation strategy.

To date, power system analysis has been performed separately for transmission and distribution systems. Due to the small influence of distribution systems on transmission systems, separate analyses have had no accuracy problems in existing power systems. However, as the amount of distributed generation (DG) in distribution systems increases, neighboring distribution systems and even transmission systems can be affected by the distributed generation. Therefore, a power system operator needs a new system to analyze the power system, one that considers the mutual interactions between the transmission and distribution systems. This paper presents with applications and case studies a transmission and distribution integrated monitoring and analysis system for high DG penetration. The integrated system analyzes the mutual interaction between the transmission and distribution systems due to DG. The preliminary evaluation of the DG connections is automated in this system, using real time online data. Case studies with practical data show the need and effectiveness of transmission and distribution integrated monitoring and analysis for real power systems with high DG penetration.

Advanced controllers have been widely introduced in power system-related research to alleviate the uncertainties of renewable sources. The performance of the controllers should be verified in a realistic environment before the controllers are used in practical applications. This study focuses on voltage regulation of wind farms in voltage drop cases where communication failures occur and discusses modifications done on the online wind farm management system. The modified management system is designed to respond to a voltage drop when the outer reference signal from the upper-level controller is absent due to technical problems, especially communication errors. Such a situation has not been considered in most of the management systems in the literature. The predictable situations in real fields have been further verified under the hardware-in-the-loop simulation environment RTDS ^TM . During communication failure, the proposed method can respond automatically to voltage recovery, along with a designed objective function. A comparative analysis of actual control modes was also conducted to prove the relevance and effectiveness of the proposed method.

Considering the controllability and high responsiveness of an energy storage system (ESS) to changes in frequency, the inertial response (IR) and primary frequency response (PFR) enable its application in frequency regulation (FR) when system contingency occurs. This paper presents a coordinated control of an ESS with a generator for analyzing and stabilizing a power plant by controlling the grid frequency deviation, ESS output power response, equipment active power, and state of charge (SoC) limitation of the ESS in a power plant. The conventional generator and FR-ESS controllers were investigated and compared. To obtain the optimal frequency and power response, an ESS-based adaptive droop control method was proposed. The proposed control strategy was developed and implemented considering the changes and limitations of the dynamic characteristics of the system, FR requirements, and an ESS using the PSCAD/EMTDC software. The simulation results showed that the proposed method was more effective than the conventional droop-control-based FR-ESS, and the effectiveness of this method was validated.

The Korean government is targeting the development of a renewable energy penetration of 30–35% by 2040 of the total generation. These conditions will decrease network stability due to a lack of inertia, especially in isolated systems, such as Jeju Island. HVDC systems with several balancing arrangements of reserve operation are used to maintain variability and uncontrollability of RES penetration. This paper presents the fast frequency reserves of HVDC control systems for frequency stability enhancement in the isolated power system by using a combined frequency containment process with grid stability standards. A new MIDC reserve operation control with angle and voltage deviation at the bus converter was developed to provide a faster and more appropriate balancing arrangement compared to the other concept. In addition, two layers of energy and transfer-capacity flexibility were considered to prevent the need to hunt for that balancing arrangement, as well as low nadir frequency, unavailability of the reserve and other constraints caused by each region having a different network size, HVDC interconnection capacity, and type. The proposed control schemes were verified by simulations on the Korean power system model implemented in PSS/E for different sizes of disturbance.