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This paper presents a new droop-based control strategy for hybrid microgrids (HMG) with improved power sharing. When ac microgrids (AC-MG) and dc microgrids (DC-MG) are present in a distribution grid, there is an opportunity to interconnect them via an interlinking converter (IC) and form a HMG. Power sharing and adequate voltage/frequency control are the main functions of AC-MG and DC-MG control systems in standalone mode. When it comes to a HMG, active power sharing throughout the whole system must also be properly achieved by controlling the IC active power throughput. Furthermore, the possibility of participation of IC in AC-MG reactive power adds some complexity to a HMG control system. In this paper, a new decentralized control strategy is presented for a HMG which relies on regulating the voltage magnitude of a common bus in each microgrid. In this regard, new droop characteristics for sources across both microgrids as well as IC are proposed. The proposed droop characteristics result in better active/reactive power sharing across both microgrids and at the same time results in better voltage regulation. The derivation of new droop characteristics is thoroughly discussed in this paper. Simulation results are used to show the improvement achieved. [ABSTRACT FROM AUTHOR]

SUMMARY This paper is concerned with determining the compensation capability of an interline dynamic voltage restorer (IDVR) under various balanced and unbalanced voltage sag scenarios. An IDVR consists of two or more DVRs with a common dc link which enables active power exchange among DVRs. This feature increases the compensation range of an IDVR as compared with separate but otherwise similar DVRs with no energy storage. The steady-state modeling and analysis of an IDVR is briefly explained in this paper. The expressions governing power requirement for compensating various voltage sags are derived. Consequently, the constraints associated with an IDVR operation are obtained and an algorithm is developed to calculate the compensation range of an IDVR and two similar storage-less DVRs. Illustrative graphs demonstrate the operating characteristics of an IDVR and compare these characteristics with those of two similar storage-less DVRs. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

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]