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In a previous paper, we have introduced a simulation and optimization framework for the integration of renewable generators into an electrical distribution network. The framework searches for the optimal size and location of the distributed renewable generation units (DG). Uncertainties in renewable resources availability, components failure and repair events, loads and grid power supply are incorporated. A Monte Carlo simulation–optimal power flow (MCS–OPF) computational model is used to generate scenarios of the uncertain variables and evaluate the network electric performance with respect to the expected value of the global cost ( ECG ). The framework is quite general and complete, but at the expenses of large computational times for the analysis of real systems. In this respect, the work of the present paper addresses the issue and introduces a purposely tailored, original technique for reducing the computational efforts of the analysis. The originality of the proposed approach lies in the development of a new search engine for performing the minimization of the ECG , which embeds hierarchical clustering analysis (HCA) within a differential evolution (DE) search scheme to identify groups of similar individuals in the DE population and, then, ECG is calculated for selected representative individuals of the groups only, thus reducing the number of objective function evaluations. For exemplification, the framework is applied to a distribution network derived from the IEEE 13 nodes test feeder. The results show that the newly proposed hierarchical clustering differential evolution (HCDE) MCS–OPF framework is effective in finding optimal DG-integrated network configurations with reduced computational efforts. [ABSTRACT FROM AUTHOR]

Abstract: In this paper a novel frequency-independent control method suitable for distributed generation (DG) is presented. This strategy is derived based on the abc/αβ transformation and abc/dq transformation of the ac system variables. The active and reactive currents injected by the DG are controlled in the synchronously rotating orthogonal dq reference frame. The transformed variables are used in control of the voltage source inverter that connects DG to distribution network. Due to importance of distributed resources in modern power systems, development of new, practical, cost-effective and simple control strategies is obligatory. The new control method of this paper does not need a Phase Locked Loop (PLL) in control circuit and has fast dynamic response in providing active and reactive power to nonlinear load. From extensive simulation results, high performance of this control strategy in DG application is demonstrated with improved voltage profile, increased power factor and reduced total harmonic distortion. [Copyright &y& Elsevier]

In this paper, a multi-objective optimization model for the investment planning and operation management of distributed heat and electricity supply systems is presented. Different energy efficiency measures and supply options are taken into account, including various distributed heat and power generation units, storage systems and energy-saving renovation measures. Furthermore, district heating networks are considered as an alternative to conventional, individual heat supply for each building. The optimization problem is decomposed into three subproblems to reduce the computational complexity. This enables a high level of detail in the optimization and simultaneously the comprehensive investigation of districts with more than 100 buildings. These capabilities distinguish the model from previous approaches in this field of research. The developed model is applied to a district in a medium-sized town in Germany in order to analyze the effects of different efficiency measures regarding total costs and emissions of CO 2 equivalents. Based on the Pareto efficient solutions, technologies and efficiency measures that can contribute most efficiently to reduce greenhouse gas emissions are identified. [ABSTRACT FROM AUTHOR]

• Compact shifted-frequency analysis models transferred readily from the time-domain models. • Flexible simulation model switching method that accelerates the multi-timescale simulations. • Flexible discontinuity treatment that exploits inherent phase information of the shifted-frequency analysis provides high accuracy during the discontinuities. The growing proportion of distributed generators in active distribution networks highlights the importance of multi-timescale system dynamics. The electromagnetic transient simulators with detailed modeling have been widely used for high-fidelity simulations, which leads to a contradiction between the efficiency and accuracy in the studies of the multi-timescale property of the ADNs. The shifted-frequency analysis method integrated with state-space based exponential integration is introduced in this paper, which possesses both high accuracy of exponential integration and the advantage of system-level modeling. It accurately simulates the networks considering the nonlinearities with the advantage that allows large time-steps in the simulations wherein the signals have a small bandwidth around the fundamental frequency. A model-switching method based on the integral transformation of the shifted-frequency models is designed to address the inefficiency of multi-timescale simulations. In addition, a flexible discontinuity treatment in the shifted-frequency domain is introduced for the reduction of the errors brought by the detections and interpolations of discontinuities in the time-domain. Numerical studies are conducted considering the distributed generations, the shifted-frequency models are generated integrally from the original time-domain models. The results of the multi-timescale simulations with model-switching in different domains show the high efficiency of the proposed method, and the discontinuity treatment presents higher accuracy compared with the time-domain solution. Those combined advantages compose the flexible shifted-frequency analysis for the multi-timescale simulations of active distribution networks. [ABSTRACT FROM AUTHOR]

Abstract: In this paper is presented an analysis of energy efficiency for the Multiport Power Converters (MPCs) used in Plug-in Fuel Cell Vehicles (PFCVs). A generic MPC architecture for PFCVs is proposed, which is analyzed for different operating modes of MPC in relation with PFCV operating regimes and the plug-in feature. The basic MPC architecture is described in relation with the PFCV operating regimes. Two MPC architectures are derived from the basic MPC architecture: (1) the MPC1 architecture, which is the MPC architecture without reverse power flow during regenerative braking process, and (2) the MPC2 architecture – MPC architecture without charging mode of Energy Storage System (ESS) from the FC system. Taking in account the imposed window for the ESS state-of-charge, the MPC can be connected to Plug-in Charging Stations (PCS) to exchange power with the Electric Power (EP) system, which will include renewable Distributed Generation (DG) systems. The Energy Management Unit (EMU) of MPC can communicate with the EP system to determine the moments that match the energy demand of plug-in vehicle with the supply availability of the EP system, stabilizing the EP system. The MPC features regarding its energy efficiency were shown by analytical computing performed and appropriate simulations presented in relation with the ESS that can be charged (discharged) from (to) the home/DG/EP system. [Copyright &y& Elsevier]

Abstract: This paper presents the analysis and comparison of the main active techniques for islanding detection used in grid-connected microinverters for power processing of renewable energy sources. These techniques can be classified into two classes: techniques introducing positive feedback in the control of the inverter and techniques based on harmonics injection. Accurate PSIMTM simulations have been carried out in order to perform a comparative analysis of the techniques under study and to establish their advantages and disadvantages according to IEEE standards. [ABSTRACT FROM AUTHOR]