In contrast with conventional microgrids (MGs) with fixed boundaries, a smart and flexible MG with dynamic boundary is introduced in this paper. Such a MG can dynamically change its boundary by picking up or shedding load sections of a distribution feeder depending on its available power, leading to more flexible operation, better utilization of renewables, smaller size of energy storage system, higher reliability, and lower cost. To achieve a flexible MG, the main challenges in MG design are addressed, including recloser placement, MG asset sizing considering resilience, system grounding design, and protection system design. Meanwhile, a hierarchical structure is employed to design and implement the MG controller. On top of the functions defined in IEEE 2030.7-2018, a few new functions, e.g., online topology identification and PQ balance, are added, while the planned/unplanned islanding and reconnection functions are enhanced. The controller is implemented on a CompactRIO, a general-purpose hardware platform provided by National Instruments (NI), and tested on a controller hardware-in-the-loop setup based on an OPAL-RT real-time simulator and a reconfigurable power electronic converter-based hardware testbed. The test results have validated the performance of the developed controllers. Such a flexible MG and its controller have been deployed at a municipal utility, and part of the controller's functions have been tested on-site.
The purpose of this study was to identify factors that would explain the observed longitudinal correlations between educational measures commonly secured at the primary and middle grades. Data obtained on two samples of over 300 pupils each were subjected to canonical variate analysis. The canonical correlations and canonical loadings indicated the existence of a single dominant factor between the primary and middle grade data. This factor was interpreted as general scholastic ability, and the results were discussed along with educational implications.Requests for reprints should be sent to Bruce G. Rogers, Dept. of Educational Psychology, University of Northern Iowa, Cedar Falls, IA 50613.
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