This paper addresses the optimal decision problem of a distributed energy resources (DER) aggregator who manages wind turbines, solar PV systems and battery energy storage (BES) units while ...implementing real-time pricing (RTP) demand response program. The DER aggregator can procure electricity by bidding in the electricity market and scheduling its DER to meet the load demand of its customers. In the bidding and scheduling processes, the intrinsic uncertainties of distributed renewable generations and customer’s responsiveness to RTP program have brought economical risks to the DER aggregator, which will lower the DER aggregator’s profit. However, most of the current researches only consider the uncertainty of renewable generations while neglecting the uncertainty of customer’s responsiveness. To this end, a robust optimization-based day-ahead optimal bidding and scheduling model is proposed for DER aggregator by jointly considering these two uncertainties. The objective of the proposed model is to maximize the aggregator’s profit via optimally determining the hourly bidding quantities in the day-ahead market and the scheduled output power of distributed renewable generations and BES units. Case studies demonstrate that the proposed robust optimization model can help DER aggregator reduce the bidding and scheduling costs to obtain a higher expected profit.
•The impact mechanism of price responsive load uncertainty is revealed.•Optimal bidding and scheduling strategies of a DER aggregator are proposed.•The necessity of considering price responsive load uncertainty is verified.•The proposed method is more effective for more price-sensitive customers.
Modern energy systems are experiencing the transition towards renewable-powered ones. Some conventional thermal units based on synchronous machines are gradually decommissioned and replaced by power ...electronics interfaced renewables. Thus, the lack of natural inertia and governor damping, which are the features of synchronous machines, raises significant concern about system frequency stability, including the faster rate of change and lower nadir point of frequency. Meanwhile, with the rapid development of communication and Internet of Things technologies, distributed energy resources can be aggregated as a virtual power plant to help balance real-time electricity demand and supply. However, the capability of utilizing the whole virtual power plant to provide adjustable inertia support has not been explored yet. In this paper, we propose a framework of the synchronous virtual power plant based on grid-forming inverter interfaced distributed energy resources. By coordinating the parameter settings of grid-forming inverters, the virtual power plant provides inertia support. Also, we design an online learning-based parameter settings method that makes the inertia of the virtual power plant adjustable. A case study in IEEE 34 nodes system illustrates the effectiveness of the proposed method.
With a large-scale integration of distributed energy resources (DERs), distribution systems are expected to be capable of providing capacity support for the transmission grid. To effectively harness ...the collective flexibility from massive DER devices, this paper studies distribution-level power aggregation strategies for transmission-distribution interaction. In particular, this paper proposes a method to model and quantify the aggregate power flexibility, i.e., the net power injection achievable at the substation, in unbalanced distribution systems over time. Incorporating the network constraints and multi-phase unbalanced modeling, the proposed method obtains an effective approximate feasible region of the net power injection. For any aggregate power trajectory within this region, it is proved that there exists a feasible disaggregation solution. In addition, a distributed model predictive control (MPC) framework is developed for practical implementation of the transmission-distribution interaction. At last, we demonstrate the performances of the proposed method via numerical tests on a real-world distribution feeder with 126 multi-phase nodes.
An auxiliary voltage controller is proposed for the fault ride-through (FRT) control of voltage-controlled inverters used in distributed energy resources. The proposed auxiliary controller can be ...added to different existing voltage control strategies with minimum or no need to alter the original structure of the voltage controller. The proposed controller prevents the transient overcurrent during grid faults and controls the exchange of real and reactive powers according to the governing grid standard. A fault detection algorithm is also implemented to detect the fault instant and determine the interval of fault during which the real and reactive power references are adjusted accordingly. Complete stability analysis of the proposed controller is performed through a new model. Successful performance of the proposed controller in achieving FRT requirements of German and Danish codes are illustrated by simulations. Extensive real-time and experimental results are also presented and discussed.
Handling energy resource management (ERM) in today's energy systems is complex and challenging due to uncertainties arising from the high penetration of distributed energy resources. Such penetration ...introduces various uncertain factors, such as renewable energy, energy storage, and electric vehicles, making it difficult for traditional mathematical methods to find effective solutions. However, Evolutionary Algorithms (EAs) have shown good performance in solving this problem. Therefore, in this paper, a self-adaptive collaborative differential evolution algorithm (SADEA) is proposed to solve the ERM problem under uncertainty. In SADEA, a three-stage adaptive collaboration strategy, includes boundary randomization stage, knowledge-assisted collaboration stage, and range restructuration stage, is used to generate collaborative solutions. The collaborative solutions generated in the above stages will jointly participate in the perturbation of DE strategies to explore promising solutions. In addition, different DE strategies are selected according to count values and random factors. At the end of the algorithm, boundary control, elite selection and retention are used to ensure the legitimacy and robustness of solutions. The proposed SADEA is compared to several state-of-the-art algorithms on a real-world distribution network located in Salamanca, Spain. The results show that SADEA is superior to its competitors in terms of the objective function, ranking index, and convergence. In summary, the proposed algorithm is effective to handle the ERM problem under uncertainty.
Summary
The demand of electric energy is increasing globally, and the fact remains that the major share of this energy is still being produced from the traditional generation technologies. However, ...the recent trends, for obvious reasons of environmental concerns, are indicating a paradigm shift towards distributed generation (DG) incorporating renewable energy resources (RERs). But there are associated challenges with high penetration of RERs as these resources are unpredictable and stochastic in nature, and as a result, it becomes difficult to provide immediate response to demand variations. This is where energy storage systems (ESSs) come to the rescue, and they not only can compensate the stochastic nature and sudden deficiencies of RERs but can also enhance the grid stability, reliability, and efficiency by providing services in power quality, bridging power, and energy management. This paper provides an extensive review of different ESSs, which have been in use and also the ones that are currently in developing stage, describing their working principles and giving a comparative analysis of important features and technical as well as economic characteristics. The wide range of storage technologies, with each ESS being different in terms of the scale of power, response time, energy/power density, discharge duration, and cost coupled with the complex characteristics matrices, makes it difficult to select a particular ESS for a specific application. The comparative analysis presented in this paper helps in this regard and provides a clear picture of the suitability of ESSs for different power system applications, categorized appropriately. The paper also brings out the associated challenges and suggests the future research directions.
In this manuscript, a comprehensive review is presented on different energy storage systems, their working principles, characteristics along with their applications in distributed generation power system. The novelty of the paper lies in the categorization of energy storage systems according to the power chain.
Microgrid technology has found applications in various areas including institutional campuses, military bases, and remote islands. Many research efforts focus on the development of the microgrid ...steady-state energy management system (EMS) that can provide the day-ahead schedule or the multi-interval economic dispatch (ED) for distributed energy resources (DERs). This study advances the state-of-the-art microgrid EMS technique by developing a novel EMS approach to achieve a flexible time frame (FTF) DER schedule combined with a single time interval optimal power flow (OPF)-based ED. The FTF DER schedule enables the microgrid to fully utilize the latest updated renewable and load forecasts, and the OPF-based ED integrates realistic microgrid operating constraints in the real-time control. In addition, a mode switching control function is included to re-dispatch DERs in the microgrid for the planned microgrid switching from grid-connected mode to island mode. The feasibility and effectiveness of the proposed microgrid EMS technology are tested and demonstrated using modified IEEE 34-node and 123-node systems.
Demand response has proven to be a distributed energy resource of great potential over the last decades for electrical systems operation. However, small or medium size facilities generally have a ...very limited ability to participate in demand response programs. When a facility includes several generation resources, energy storage systems, or even demand flexibility, the decision-making becomes considerably harder because of the amount of variables to be considered. This paper presents a method to facilitate end users' decision-making in demand response participation. The method consists of an algorithm that uses demand and generation forecasts and costs of the available resources. Depending on the energy to be reduced in a program, the algorithm obtains the optimal schedule and facilitates decision making, helping end users to decide when and how to participate. With this method, end users' capability to participate in these programs is clearly increased. In addition, the method is contrasted by simulations based on real programs developed at the Campus de Vera of the Universitat Politècnica de València. The simulations carried out show that the developed method allows end users to take advantage of the potential of their facilities to provide demand response services and obtain the maximum possible benefit.
•A method to facilitate decision-making in demand response is proposed.•The proposed algorithm enables facilities to participate in demand response programs.•The proposed method maximises the benefits that can be obtained with demand response.•A method to optimise demand response participation is tested.•Participation in demand response with distributed energy resources is facilitated.
Summary
Energy crisis and the global impetus to “go green” have encouraged the integration of renewable energy resources, plug‐in electric vehicles, and energy storage systems to the grid. The ...presence of more than one energy source in the grid necessitates the need for an efficient energy management system to guide the flow of energy. Moreover, the variability and volatile nature of renewable energy sources, uncertainties associated with plug‐in electric vehicles, the electricity price, and the time‐varying load bring new challenges to the power engineers to achieve demand‐supply balance for stable operation of the power system. The energy management system can effectively coordinate the energy sharing/trading among all available energy resources, and supply loads economically in all the conditions for the reliable, secure, and efficient operation of the power system. This paper reviews the framework, objectives, architecture, benefits, and challenges of the energy management system with a comprehensive analysis of different stakeholders and participants involved in it. The review paper gives a critical analysis of the distributed energy resources behavior and different programs such as demand response, demand‐side management, and power quality management implemented in the energy management system. Different uncertainty quantification methods are also summarized. This review paper also presents a comparative and critical analysis of the main optimization techniques used to achieve different energy management system objectives while satisfying multiple constraints. Thus, the review offers numerous recommendations for research and development of the cutting‐edge optimized energy management system applicable for homes, buildings, industries, electric vehicles, and the whole community.
In this paper, an adaptive directional overcurrent relaying technique based on the positive-sequence (PSQ) and negative-sequence (NSQ) superimposed currents is proposed for microgrid protection. Due ...to the change in mode of operation of microgrid, the level and direction of prefault current are altered. On occurrence of a fault in any line section of the microgrid, coordination between the primary and backup overcurrent relays is lost due to variations in level and direction of fault current. With inception of faults, the current contributed by the inverter-based distributed energy resource is in the range of 2 p.u. To solve protection coordination issue, this paper presents an adaptive overcurrent relay settings using PSQ and NSQ superimposed currents those are contributed during fault conditions. Further, the direction of the fault is obtained using the new phase change between prefault and superimposed sequence fault currents. The proposed technique is implemented on a dSPACE processor board, which is connected to a real-time digital simulator to carry out the hardware-in-the-loop test. Extensive simulation and hardware results obtained for several microgrid operating modes indicate the effectiveness of the proposed technique. This proposed approach is independent of the voltage information.
PDF
