Power-flow study

About: Power-flow study is a research topic. Over the lifetime, 8091 publications have been published within this topic receiving 155053 citations. The topic is also known as: load-flow study.

Nonactive Power Loss Minimization in a Bidirectional Isolated DC–DC Converter for Distributed Power Systems

Abstract: Originated from analyzing nonactive power loss, a novel optimization method and modulation solution for bidirectional isolated dual-active-bridge (DAB) dc-dc converters are proposed in order to achieve high efficiency in a wide operating range. A comprehensive nonactive power loss model is developed, including both the nonactive components delivered back to the source and from the load. This paper points out that when the minimum nonactive power loss is achieved, zero-voltage soft switching can be naturally fulfilled. The optimal phase-shift pair obtained by the proposed method can keep low values of both root mean square (RMS) current and circulating power. Rather than using ideal power flow analysis, the nonactive power loss model directly embodies practical nonideal factors, including device voltage drops. Based on the analysis, an extended dual phase shift is proposed, and different operation cases are analyzed with comparison of performance indices. Experimental tests verify the theoretical analysis and show effectiveness of the proposed approach to achieve nonactive power loss minimization and efficiency improvement.

Distributed Energy Resources Topology Identification via Graphical Modeling

Abstract: Distributed energy resources (DERs), such as photovoltaic, wind, and gas generators, are connected to the grid more than ever before, which introduces tremendous changes in the distribution grid. Due to these changes, it is important to understand where these DERs are connected in order to sustainably operate the distribution grid. But the exact distribution system topology is difficult to obtain due to frequent distribution grid reconfigurations and insufficient knowledge about new components. In this paper, we propose a methodology that utilizes new data from sensor-equipped DER devices to obtain the distribution grid topology. Specifically, a graphical model is presented to describe the probabilistic relationship among different voltage measurements. With power flow analysis, a mutual information-based identification algorithm is proposed to deal with tree and partially meshed networks. Simulation results show highly accurate connectivity identification in the IEEE standard distribution test systems and Electric Power Research Institute test systems.

Power Flow Analysis for Low-Voltage AC and DC Microgrids Considering Droop Control and Virtual Impedance

Abstract: In the low-voltage (LV) ac microgrids (MGs), with a relatively high R/X ratio, virtual impedance is usually adopted to improve the performance of droop control applied to distributed generators (DGs). At the same time, LV dc MG using virtual impedance as droop control is emerging without adequate power flow studies. In this paper, power flow analyses for both ac and dc MGs are formulated and implemented. The mathematical models for both types of MGs considering the concept of virtual impedance are used to be in conformity with the practical control of the DGs. As a result, calculation accuracy is improved for both ac and dc MG power flow analyses, comparing with previous methods without considering virtual impedance. Case studies are conducted to verify the proposed power flow analyses in terms of convergence and accuracy. Investigation of the impact to the system of internal control parameters adopted by DGs is also conducted by using proposed method.

A comparison of voltage stability indices

Abstract: Voltage stability has become a very important issue of power systems analysis. This paper discusses some important aspects related to voltage stability indices in electric power systems. Some techniques previously studied in the literature are analyzed and a comparison of the performance of several indices is presented. The effectiveness of the analyzed methods are demonstrated through numerical studies in IEEE 14 busbar test system, using several different scenarios of load increase.

Conceptual Study for Open Energy Systems: Distributed Energy Network Using Interconnected DC Nanogrids

Abstract: We describe the general concept and practical feasibility of a dc-based open energy system (OES) that proposes an alternative way of exchanging intermittent energy between houses in a local community. Each house is equipped with a dc nanogrid, including photovoltaic panels and batteries. We extend these nanogrids with a bidirectional dc–dc converter and a network controller so that power can be exchanged between houses over an external dc power bus. In this way, demand-response fluctuations are absorbed not only by the local battery, but can be spread over all batteries in the system. By using a combination of voltage and current controlled units, we implemented a higher-level control software independent from the physical process. A further software layer for autonomous control handles power exchange based on a distributed multiagent system, using a peer-to-peer like architecture. In parallel to the software, we made a physical model of a four-node OES on which different power exchange strategies can be simulated and compared. First results show an improved solar replacement ratio, and thus a reduction of ac grid consumption thanks to power interchange. The concept’s feasibility has been demonstrated on the first three houses of a full-scale OES platform in Okinawa.