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[en] Highlights: • A reliability assessment approach for Integrated Energy Systems (IES) is proposed. • A hierarchical decoupling optimization framework is developed for IES. • An impact-increment based state enumeration (IISE) method is accommodated. • A reduction technique of higher order contingencies is presented. - Abstract: A new reliability assessment approach to Integrated Energy Systems (IESs) is introduced in this paper. The optimal load curtailment (OLC) algorithm and reliability assessment algorithm are both improved in the proposed approach. For the OLC problem, this paper develops a hierarchical decoupling optimization framework for both the energy hub optimal dispatch and the optimal power flow problems. This feasible solution can make the OLC calculation more efficient and accurate. For the reliability assessment algorithm, an impact-increment based state enumeration (IISE) method is accommodated for IESs to accelerate the reliability assessment process. Also, a reduction technique of higher order contingencies is presented for the reliability evaluation of IESs to further enhance the computational efficiency. Case studies are performed on an IESs test case combined the IEEE-33 bus system with 14-node gas system and a practical case combined the IEEE 118-bus power system with Belgian natural gas network Numerical results demonstrate the efficient and robust performance of the proposed approach. Besides, the impacts of energy conversion process and energy hubs on IESs reliability are analyzed in detail.
[en] Highlights: • A new two-stage optimization method for optimal DGs planning is proposed. • The maximum output of energy storage is determined by chance-constrained programming. • Impacts of energy storage integration are analyzed via probabilistic power flow. • Test results show the proposal is superior to other state-of-the-art approaches. • Energy storage makes the DGs operate at the rated capacities with high probability. - Abstract: A two-stage optimization method is proposed for optimal distributed generation (DG) planning considering the integration of energy storage in this paper. The first stage determines the installation locations and the initial capacity of DGs using the well-known loss sensitivity factor (LSF) approach, and the second stage identifies the optimal installation capacities of DGs to maximize the investment benefits and system voltage stability and to minimize line losses. In the second stage, the multi-objective ant lion optimizer (MOALO) is first applied to obtain the Pareto-optimal solutions, and then the ‘best’ compromise solution is identified by calculating the priority memberships of each solution via grey relation projection (GRP) method, while finally, in order to address the uncertain outputs of DGs, energy storage devices are installed whose maximum outputs are determined with the use of chance-constrained programming. The test results on the PG&E 69-bus distribution system demonstrate that the proposed method is superior to other current state-of-the-art approaches, and that the integration of energy storage makes the DGs operate at their pre-designed rated capacities with the probability of at least 60%.
[en] Highlights: • Analysis of the impact of reduced system inertia on primary frequency control. • Quantification of the primary frequency response requirements in the future GB low-inertia systems. • Assessment of the cost and emission driven by primary frequency control. • Evaluation of the benefits of EVs in supporting primary frequency control. • Identification of the synergy between primary frequency control support and “smart charging” strategy. - Abstract: System inertia reduction, driven by the integration of renewables, imposes significant challenges on the primary frequency control. Electrification of road transport not only reduces carbon emission by shifting from fossil fuel consumption to cleaner electricity consumption, but also potentially provide flexibility to facilitate the integration of renewables, such as supporting primary frequency control. In this context, this paper develops a techno-economic evaluation framework to quantify the challenges on primary frequency control and assess the benefits of EVs in providing primary frequency response. A simplified GB power system dynamic model is used to analyze the impact of declining system inertia on the primary frequency control and the technical potential of primary frequency response provision from EVs. Furthermore, an advanced stochastic system scheduling tool with explicitly modeling of inertia reduction effect is applied to assess the cost and emission driven by primary frequency control as well as the benefits of EVs in providing primary frequency response under two representative GB 2030 system scenarios. This paper also identifies the synergy between PFR provision from EVs and “smart charging” strategy as well as the impact of synthetic inertia from wind turbines.
[en] Highlights: • A coordinated control strategy for EVs and power plants in frequency regulation is presented. • A robust stability criterion to determine delay margin of frequency control system is proposed. • The time-varying delays and uncertain inertia are considered in the stability criterion. • The control strategy can decrease frequency deviations and output variations of power plants. - Abstract: Nowadays, large scale intermittent renewable energy is being integrated to power systems as a solution for the low-carbon development worldwide. With the increasing penetration of renewable power generation, system frequency stability is becoming more and more serious. To increase the utilization of renewable energy, electric vehicles (EVs) are suggested to participate in load frequency control (LFC) through aggregators due to their vehicle-to-grid (V2G) capability and quick response characteristic, which is denoted as EV-LFC controller in this paper. In order to fully take the advantages of EVs in the LFC, this paper presents a coordinated control strategy between EV-LFC controller and traditional power plants based LFC (PP-LFC) controller for frequency regulation. In this strategy, the EV-LFC has a priority in response than the PP-LFC when the system deviation violates its acceptable range. However, the LFC integrating EVs is with inevitable time delays due to the data and control signal transmission. Meanwhile, the system inertia uncertainty caused by renewable energy in power system may also cause instability problem. For this reason, an improved robust stability criterion is proposed to estimate the asymptotically stable for LFC system considering the inertia uncertainty and time-varying delays simultaneously. Additionally, a PI controller for EV-LFC controller is used to enhance the system frequency stability. Finally, the effect of increasing EVs number on the frequency stability is investigated, which may guide system operator to utilize EVs to the LFC properly. Case studies are carried out based on a simplified Great Britain (GB) power system. Simulation results show that the proposed coordination strategy can not only provide effective frequency regulation, but also reduce the output of traditional power plants, in which the inertia uncertainty and time delays are properly considered.