Increasing penetration of distributed renewable energy sources (DRESs) has resulted in the emergence of distributed energy resource aggregators (DERAs). A DERA participates in the transmissionlevel market operated by a transmission system operator (TSO), and the DERA's resources are connected to a jurisdiction of the distribution system operator (DSO). Inspired by the structure of the Korean power industry, this study assumes a minimal DSO that cannot directly dispatch the resources in its system. In this study, we develop a detailed procedure for prequalification wherein the DSO checks the DERA's bids that are submitted to the TSO markets. The proposed prequalification enables the DSO to secure the reliability of its system by providing limited network information to the DERA. The DERA modifies its bid until potential overvoltage and overflow problems are resolved, even in the worst case, including uncertainties. The proposed prequalification process is verified using the IEEE 33-bus distribution network. Compared to previous studies, the results demonstrate that the proposed prequalification can deal with distribution system constraints, even though uncertainties are included. The proposed prequalification process can be applied to power industries where the DSO does not have the full dispatch authority on DRESs.
Although the Korean government plans to increase its share of variable renewable energies (VREs), the Korean power market is not sufficiently mature to accommodate a large increase in VRE generation. Thus, the Korean system operator plans to introduce a two-settlement, and an imbalance settlement is also under consideration, among several options. Therefore, this study analyzes how many incentives are given for prediction accuracy under several imbalance settlement schemes adopted from European and US power markets. Results show that the imbalance settlement consisting of threshold and penalty terms is useful for rule-makers, who can control revenue differences between the groups with different prediction accuracies by adjusting the two terms. The suggestion given in the paper will be useful for not only the Korean power market but also for the countries that plan to establish the imbalance settlement rules while increasing renewable energy.
A distributed energy resource aggregator (DERA) participates in the wholesale energy market (WEM) on behalf of aggregated distributed renewable energy sources (DRESs). The DERA manages DRESs according to the dispatch signal from the system operator (SO). However, a conventional independent SO that operates the WEM and transmission system does not monitor the distribution system. Therefore, overvoltage or overflow problems can occur during the generation of DRESs in a distribution system in which bids are accepted in the WEM. To address these problems, previous studies proposed the prequalification process. In the process, a distribution SO (DSO), which is responsible for the reliability of the distribution system, reviews DERA's bids before it is submitted to the WEM. However, these studies do not consider the outages of the system components. Therefore, we propose an N‐1 contingency prequalification process (N‐1 PP). The DSO manages the DERA's bid considering both the uncertainties and system states after the reconfiguration in contingency situations. In the proposed scheme, the DERA's bid is reviewed for severe faults and post‐reconfiguration systems. The results indicate that the N‐1 PP is more stable and durable than the prequalification process of previous studies.
Imbalance band market is an alternative to traditional market structures which is proposed to ensure that system frequency remains within acceptable bounds. In an imbalance band market environment, the load‐serving entities (LSEs) can purchase bands or reduce the load deviation by operating a battery energy storage system (BESS) to avoid the penalty for causing imbalance. The market concept would be effective in sharing balancing responsibility between a system operator (SO) and load‐serving entities. In this study, the authors proposed a planning framework for a load serving entity (LSE) considering cloud energy storage (CES) business as a useful resource in the imbalance band market environment. The term of cloud energy storage is used as a platform that the operator owns and operates the storage, while subscribed clients pay a service fee for requesting charging and discharging operations. The simulation results show that operating cloud energy storage business is economically rational strategy for the LSE. The authors verified that a LSE operating the cloud energy storage business under an imbalance band market environment to pursue its own benefit better performs a part of the balance‐maintaining obligation of the SO compared with a LSE not operating the cloud energy storage business.
The concept of a virtual power plant (VPP) was introduced for supporting market participation of small-scale renewable energy-based generators (REGs). In a VPP, energy storage systems (ESSs) and micro-turbine-based generators (MTGs) are used together to mitigate the variability of the output of REGs. To keep the output of a VPP at the contracted value in a market, centralized feeder flow control (FFC) methods can be adopted for the VPP. However, conventional centralized FFC methods lack careful consideration of different characteristics of various resources and require high-speed communications and several central control units. Therefore, this paper proposes a new FFC method considering various characteristics of resources and enabling operation with less communication dependency. The effectiveness of the proposed method is verified by comparing the results of the proposed method with those of the conventional method with performance analysis, stability analysis, and simulations with Simulink/MATLAB.
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