This study proposes a cost-based adaptive (CBA) droop control strategy for use in a voltage source converter (VSC)-based multi-terminal high voltage direct current (MTDC) system. Rather than using a fixed droop gain, we suggest the CBA droop control scheme, which reduces the total incremental generation cost of ac systems, while sharing the burden based on the available capacity of VSCs at the postcontingency- steady-state operating point. Following a certain VSC outage in the MTDC system, unbalanced power is allocated based on the equal incremental cost principle to reduce the total active power generation cost. The results were verified through a transient simulation on an MTDC system with four monopole VSCs, and outage contingency scenarios were presented with three groups of generation cost curves. The results indicate that the CBA droop control strategy can provide greater contributions to the economic operation of the MTDC system, while achieving robust control.

As the penetration rate of renewable enery resources (RES) in the power system increases, uncertainty and variability in system operation increase. The application of energy storage systems (ESS) in the power system has been increased to compensate for the characteristics of renewable energy resources. Since ESS is a controllable and highly responsive power resource, primary frequency response and inertia response are possible in case of system contingency, so it can be utilized for frequency regulation (FR) purposes. In frequency regulation, reduction of the Rate of Change of Frequency (RoCoF) and increase the frequency nadir by improving the response characteristics are important factors to secure frequency stability. Therefore, it is important to control ESS with proper parameters according to changing system situation. In this paper, we propose a method to calculate and apply a frequency droop, which is basically required according to the power system condition based on swing equation and effective inertia assessment. In addition, a method to estimate RoCoF droop according to the correlation with frequency by estimating the systematic inertia in the current situation is proposed. The case study for verification of the proposed method was performed through dynamic simulation using actual Korean power system data. The results show that the proposed method is more effective than the governor-free of the conventional thermal generator and conventional droop control-based FR-ESS.

This study proposes an adaptive droop control strategy to be used in hybrid static synchronous compensator (STATCOM) systems. The proposed voltage-sensitivity-based adaptive droop control scheme using a hybrid STATCOM system is introduced to eliminate the possibility of interference with the other voltage regulation devices while achieving better voltage regulation without having to implement a full observation of the corresponding network. The sensitivity-analysis is performed by the voltage control of STATCOM system and the sliding-mode-control is included for control system robustness. A comparison between fixed and adaptive control methods is made through case studies of the IEEE 39-bus test system. The results were further verified through a transient simulation of the hybrid STATCOM system that considers both low and high penetration levels of inverter-based reactive power resources.

The increasing penetration of photovoltaic (PV) generators has led to a shift of the operational policy of the distribution system operator (DSO) from passive to active intervention in distribution networks (DNs), where a centralized controller governs the operation of voltage regulation devices. However, the PV output uncertainty hinders the verification of the impact of PVs on DNs. Therefore, the hosting capacity (HC) analysis framework for PV penetration should reflect both the operational benefit of the DSO and the PV output uncertainty. Thus, in this study, a two-stage optimization-based framework is proposed to analyze the probabilistic HC for PV under active network management (ANM) of DNs. In the first stage, the optimal PV base capacity (PVBC) to maximize the sum of the HC for PVs is determined based on a heuristic optimization method; in the second stage, using the predefined load and PV output profile, the maximum available power generation curve for PVBC is calculated, and the maximum HC for PV is derived by the calibration of PVBC through a comparison with the actual PV generation profile curve. The proposed method considers the time-series-based load flow results, reflecting the time-scheduling strategy by the DSO. Moreover, the uncertain characteristics of PV output are stochastically considered using a Monte Carlo simulation-based repetitive calculation approach. Case studies were implemented using the modified IEEE-123 test system, and the simulation results provided a quantitative comparison of the effect of the probabilistic HC improvement on the utilization of controllable resources and the centralized ANM by the DSO.

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.