The DC power flow model is in widespread utilization in electricity-market applications and contingency analysis. The presented versions of this model can be classified into two categories: state-dependent, or Hot-Start, models and state-independent, or Cold-Start, models. A reasonable accuracy is reported in the literature regarding Hot-Start models as they take into account branch losses and bus voltages by using available base point. On the contrary, due to the absence of base point in Cold-Start models, branch losses must be either neglected or guessed (which is an uncertain precautionary measure), or evaluated by a cumbersome iteration process. In addition, the bus voltage profiles are inevitably considered to be flat. Hence, the accuracy of available Cold-Start models in different circumstances remains of great concern. This paper addresses this concern and unveils a new Cold-Start model that does not rely on a risky assumption. In other words, there will be no lossless or flat voltage profile assumption in the presented approach whereas the equations remain linear. Besides, the exact effect of the net reactive loads on phase angles is considered and, consequently, the reactive power balance equations are reflected in the model for the first time.Index Terms-Cold-start models, DC power flow, hot-start models, loss modeling, modified phase angle.

Purpose -The purpose of this paper is to pursue two following main goals: first, theorizing a new concept named as equivalent bus load in order to make a promising simplification over power system analysis. Second, proposing an outstanding fast and simple approach based on introduced concept for voltage estimation after multiple component outages while satisfying required accuracy. Design/methodology/approach -Equivalent load bus theory introduces three transfer matrices that describe power system topology. Mentioned matrices could be calculated simply after system reconfiguration without matrix inversion. Using transfer matrices a large-scale power system can be modeled by a simple two-bus power system from the viewpoint of any desired bus so that load flow calculation leads to same value. The analysis of simplified power system yields to extract a new incremental model based on equivalent bus load theory that will be distinguished as an outstanding fast method for voltage estimation aim. Findings -A deep study for fast voltage estimation aim is dedicated to evaluate proposed method from the accuracy and quickness point of view and the outcomes are compared to a well-known method as Distribution Factors (DF). Results and computational times unveil that presented approach is more accurate and much faster. Originality/value -A novel and new fast voltage estimation method for assessment of power system component outages is introduced. present, he has been with the Department of Electrical Engineering of the Amirkabir University of Technology, where he is now a Professor. His main fields of research are high voltage, electrical insulation, power system transient, lightning protection, and pulse power technology. He has authored and coauthored more than 300 papers and six books on high-voltage engineering and power system. Professor Behrooz Vahidi is the corresponding author and can be contacted at: vahidi@aut.ac.ir Sajjad Abedi received the BS Degree in Electrical engineering from the Isfahan University of Technology (IUT), Isfahan, Iran, in 2008, and the MS Degree (with honors) in Electrical Engineering, majoring in electrical energy management, from the Amirkabir University of Technology (AUT), Tehran, Iran, in 2011. Presently, he is a Graduate Research and Teaching Assistant in Electrical Engineering Department at AUT. He currently leads a number of research projects related to power system planning and economics, stochastic optimization, renewable energy integration, as well as smart grids development and deployment.Dr Hassan Rastegar received the BSc, MSc, and PhD Degrees in Electrical Engineering from the Amirkabir University of Technology, Tehran, Iran, in 1987, 1989, and 1998 Currently, he is an Associate Professor at the Amirkabir University of Technology. He has published many papers in journals and conferences. His research interests include power system control, application of computational intelligence in power systems, simulation and analysis of power systems, and renewable energy.

Penetration of Plug-in Electric Vehicles (PEVs) parking lots into distribution systems and microgrids offers useful decision tools for improving energy management and operations of power systems. In this paper, with an objective to minimize the operation cost while subject to the system, unit and security constraints, a microgrid energy management scheme is proposed, by taking into account PEVs throughout the grid as distributed storage responsive to the nodal prices. The presented method comprises the ex-ante optimal dispatch to minimize the anticipated operation cost, followed by a near real-time dispatch to manage the violation of security constraints regarding any congestion and voltage limit in the microgrid. The second dispatch, as recourse to the ex-ante dispatch, aims to minimize the operation cost and the deviation from the ex-ante dispatch decisions, while any possible binding constraint occurred in the ex-ante dispatch is mitigated. Simulation results on a test microgrid system demonstrate that the presented scheme can effectively ensure secure and economic operations of the microgrid as well as the risk reduction of the ex-ante decisions.Index Terms-Plug-in Electric Vehicle (PEV), microgrid, energy management, price-responsive demand, nodal pricing, power system security.

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