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Inverters (dc/ac converters) are commonly used to connect distributed energy resources (DERs) to the grid. Hence, the penetration rate of inverters is growing in distribution systems along with DERs. Depending on their development and penetration level, grid requirement standards for DERs are revised. New grid codes allow DERs to control their output reactive power to provide reactive power ancillary service. In this paper, the main contribution is reactive power management of inverter-based DERs (IBDER) through a practical procedure, which controls the available volt-ampere (headroom) of inverters to improve voltage profile and distribution system operation when confronting with short-term voltage magnitude variations. In this regard, a two-level control strategy (namely, central and local control levels) is proposed. In the central controller, reactive power management of IBDERs is optimized in short time intervals for mitigating voltage variations. The optimized data is sent to the local controllers of IBDERs to increase the speed of reaction to voltage variations in each time interval. The improvement of distribution systems operation with a high penetration rate of IBDERs is illustrated by performing the simulation of the proposed control strategy on a smart distribution test system. [ABSTRACT FROM AUTHOR]

Abstract—This article proposes a method that enables ideal sharing of reactive power among converter-based micro-sources in a microgrid with a decentralized control strategy. Power sharing must be properly performed among micro-sources to avoid circulating currents or overloading. Using conventional droop characteristics to achieve power sharing is not satisfactory, as system asymmetry will greatly impact the quality of sharing. In the proposed method, droop characteristic parameters are modified upon a change in system operating point such that ideal sharing takes place after the modification process. Simulation results are presented to show the validity of analysis. [ABSTRACT FROM PUBLISHER]

The first part of this article reviews the concepts of apparent power and power factor in single-phase circuits with non-negligible line impedances. The study is based on the well-known definition that the apparent power is the maximum load power subject to constant line losses and constant load voltage. In reality, however, all transmission/distribution lines have some finite impedance, and thus, the constant voltage condition cannot be maintained at the load terminals. In this article, the constant load voltage condition is relaxed and allowed to change, as long as it remains within acceptable range of application. This is a scenario that better reflects the realistic situations. Modified expressions for the apparent power and power factor are derived and discussed. The second part of the article presents a new concept called the current factor as the ratio of the minimal current to the actual current while keeping the load power constant. The current factor coincides with the power factor when the line impedances are neglected. The article explains how the current factor can be superior to the power factor when the line impedances are not negligible. The current factor is then extended to non-sinusoidal current factor for a non-linear load and is examined. [ABSTRACT FROM AUTHOR]