The control of an islanded AC microgrid with high penetration level of renewable generations is complicated and challenging due to its low inertia and fast changing operating conditions. To address ...the drawbacks of traditional droop control with low-voltage AC microgrid, an adaptive virtual impedance control is proposed to improve the active/reactive power sharing accuracy. To deal with the frequency and voltage deviation caused by the primary control while satisfying the fast response requirements and various users' preferences, a flexible distributed control strategy is proposed as the secondary control. The proposed control strategy can restore the frequency and voltage magnitude to the desired values in a finite-time manner, using only local and neighboring information. The finite-time convergence of the proposed distributed control algorithm is guaranteed through rigorous analysis. Simulation studies validate the effectiveness and scalability of the proposed distributed control strategy.
This review (with 335 references cited) is devoted to pentacyclic triterpenes. The total synthesis, semi-synthesis, structural modification, and metabolic behavior of naturally occurring pentacyclic ...triterpenes are described. We also cover the in vivo evidence, mechanistic studies, and clinical significance of pentacyclic triterpenes as multi-target therapeutic agents for the prevention and treatment of metabolic and vascular diseases.
In this note, we show that if a pseudo-Anosov map \phi :S\to S admits a finite cover whose action on the first homology has spectral radius greater than 1, then the monodromy of any fibered structure ...of any finite cover of the mapping torus M_{\phi } has the same property.
This paper presents a fully distributed reactive power optimization algorithm that can obtain the global optimum solution of nonconvex problems for distribution networks (DNs) without requiring a ...central coordinator. Second-order conic relaxation is used to achieve exact convexification. A fully distributed second-order cone programming solver (D-SOCP) is formulated corresponding to the given division of areas based on the alternating direction method of multipliers (ADMM) algorithm, which is greatly simplified by exploiting the structure of active DNs. The problem is solved for each area with very little interchange of boundary information between neighboring areas. D-SOCP is extended by using a varying penalty parameter to improve convergence. A proof of its convergence is also given. The effectiveness of the method is demonstrated via numerical simulations using the IEEE 69-bus, 123-bus DNs, and a real 1066-bus distribution system.
Because distributed generations are extensively integrated into active distribution grids (ADGs), the transmission and distribution coordinated economic dispatch (TDCED) should be investigated to ...optimally dispatch the generation resources and evaluate the locational marginal prices (LMPs) of the entire system. In this paper, the TDCED problem is formulated, and a new heterogeneous decomposition (HGD) algorithm is proposed. In the HGD algorithm, the transmission LMP at the boundary bus and ADGs' power are exchanged among transmission and ADGs. The optimality and convergency of HGD are proven and numerically verified. In addition, several related issues are further discussed: a) methods to improve the convergency of HGD, b) considerations regarding security issues and voltage constraints in TDCED and corresponding modified HGD algorithms, and c) the practicality of HGD in either separate or transparent interaction modes of transmission and distribution in future grids. Numerical simulations indicate that the generation resources are optimally utilized and that LMPs are reasonably evaluated in TDCED. Congestion in the traditional isolated dispatch mode can also be prevented. Moreover, simulations on several systems from T6D2 to T300D60 verify that the HGD algorithm is an efficient and robust algorithm with limited communication burdens to solve TDCED.
With the rapid development of smart grid, to solve the power enterprises’ requirement in short-term load forecasting, this paper proposes a short-term electrical load forecasting method based on ...stacked auto-encoding and GRU (Gated recurrent unit) neural network. Firstly, the method input historical data which contains power load, weather information, and holiday information, and use auto-encoding to compress the historical data; and then, the multi-layer GRU is used to construct the model to predict the power load. The experiment results show, compared with traditional models, the proposed method can effectively predict the daily variation of power load and have lower prediction error and higher precision.
This paper proposes an optimal distributed control strategy for the coordination of multiple distributed generators in an islanded microgrid (MG). A finite-time secondary frequency control approach ...is developed to eliminate the frequency deviation and maintain accurate active power sharing in a finite-time manner. It is demonstrated that the traditional distributed control approach with asymptotical convergence is just a special case of the proposed finite-time control strategy under the specific control parameter settings. Then, a secondary voltage control approach is presented to regulate the average voltage magnitude of all distributed generators to the desired value and achieve accurate reactive power sharing. The implementation of the proposed distributed control strategy only requires information exchange among neighboring local controllers through a sparse communication network. Simulations with an islanded MG testbed built in MATLAB/Simulink are conducted to validate the effectiveness of the proposed distributed control strategy.
This paper proposes a new distance-based distributionally robust unit commitment (DB-DRUC) model via Kullback-Leibler (KL) divergence, considering volatile wind power generation. The objective ...function of the DB-DRUC model is to minimize the expected cost under the worst case wind distributions restricted in an ambiguity set. The ambiguity set is a family of distributions within a fixed distance from a nominal distribution. The distance between two distributions is measured by KL divergence. The DB-DRUC model is a "min-max-min" programming model; thus, it is intractable to solve. Applying reformulation methods and stochastic programming technologies, we reformulate this "min-max-min" DB-DRUC model into a one-level model, referred to as the reformulated DB-DRUC (RDB-DRUC) model. Using the generalized Benders decomposition, we then propose a two-level decomposition method and an iterative algorithm to address the RDB-DRUC model. The iterative algorithm for the RDB-DRUC model guarantees global convergence within finite iterations. Case studies are carried out to demonstrate the effectiveness, global optimality, and finite convergence of a proposed solution strategy.
Wind Power Providing Flexible Ramp Product Runze Chen; Jianhui Wang; Botterud, Audun ...
IEEE transactions on power systems,
05/2017, Letnik:
32, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The deepening penetration of renewables in power systems has contributed to the increasing need for generation flexibility. Specifically, for short-term operations, flexibility here indicates that ...sufficient ramp capacity is available to respond to the varying load and intermittent generation. To address the growing needs for ramp capacity, markets for ramp products have been launched in practice such as those in California ISO and Midcontinent ISO. Sometimes, expensive fast-start units must be committed in real time to guarantee sufficient ramp capacity. Occasionally even worse, inadequate ramp capacity from the given generation portfolio might lead to curtailment of renewable generation or load shedding. Therefore, more supplies of ramp capacity are required. In fact, wind power producers (WPPs) are physically capable of offering ramp services, which gives us a potential option. In this paper, we attempt to explore the mechanism and economic impacts of including WPPs as ramp capacity providers. To conduct the analyses, a two-stage stochastic real-time unit commitment model considering ramp capacity adequacy is formulated. Case studies indicate that both the system and the WPPs can benefit in the proposed framework.
In a deregulated market, wholesale energy costs and distribution investment costs contribute significantly to consumers' electricity bills. However, in a low carbon electrical power system, the two ...cost pressure points may not be synchronous in time and space with each other. This paper develops a novel methodology for home area energy management as a key vehicle for demand response, using electricity storage devices. The aim is to enable energy storage at consumer premises to not only take advantage of lower wholesale energy prices, but also to support low voltage (LV) distribution networks for reducing network investment. New operation strategies for domestic energy storage to facilitate demand response (DR) are developed in the paper. They have the capability to maximize the overall savings in energy costs and investment costs. In the proposed approach, the operation of home-area energy storage devices is jointly conducted by end customers and network operators. The purpose is to fight for an optimal balance between DRs to energy price and to network congestion, and thus to maximize benefits for both consumers and network operators. An intensive study is carried out to investigate the impacts of different dispatch strategies on wholesale energy costs and network investment costs. Benefit quantification methods are introduced as well to evaluate the total benefits in terms of savings in energy costs and investment costs that can be brought along by the proposed operation approach. The demonstration is carried out on two practical distribution networks with varying utilization levels for one typical calendar day and a whole year.
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