Distributed generation, or DG, involves utilization of small generators that are distributed in a power network, to supply the electric power demands of utility customers. This paper presents the analysis of droop based generation control schemes for DG inverters comprising of active power-frequency and reactive power-voltage controllers. This enables decentralized operation with load sharing in a microgrid containing several interconnected DGs. Small-signal models are developed for microgrids consisting of several DGs connected in a chain topology. Mathematical propositions for stability are developed and guidelines are provided for design of controllers to meet the IEEE P1547 performance specifications.

The use of back-to-back (BTB) voltage source converters (VSCs) to interface large scale asynchronous ac power systems is well established. BTB VSCs also provide a convenient means to interface small scale microgrids and the utility power grid. The relatively small size of such interfaces and broad scale of their application would mandate autonomous fast operation based on the health of the microgrids, although their preferred operating points (set-points) may be dispatched from relatively slow supervisory systems. This paper presents a method to control such interfaces so as to preserve microgrid-like operation of each ac system and to autonomously transfer power across the interfaces. The paper describes the control architecture, analytical model, and design method that ensure robust operation. We demonstrate the design of a 2-microgrid interface using a dynamic phasor model, which we show to be more accurate than the reduced order VSC model commonly used in microgrid analyses. The interface can also alter the steady state power flow between microgrids to suit energy management strategies in a smart grid. Finally, we present simulation and experimental test results of the interface operation.

The application of high voltage dc (HVDC) transmission for integrating large scale and/or off-shore wind generation systems with the electric grid is attractive in comparison to extra high voltage (EHV) ac transmission due to a variety of reasons. While the technology of classical current sourced converters (CSC) using thyristors is well established for realization of large HVDC systems, the technology of voltage sourced converters (VSC) is emerging to be an alternative approach, particularly suitable for multi-terminal interconnections. More recently, a more modular scheme that may be termed ‘bridge of bridge’ converters (BoBC) has been introduced to realize HVDC systems. While all these three approaches are functionally capable of realizing HVDC systems, the converter power circuit design trade-offs between these alternatives are not readily apparent. This paper presents an examination of these topologies from the point of view of power semiconductor requirements, reactive component requirements, operating losses, fault tolerance, multi-terminal operation, modularity, complexity, etc. Detailed analytical models will be used along with a benchmark application to develop a comparative evaluation of the alternatives that maybe used by wind energy/bulk transmission developers for performing engineering trade-off studies.

The deployment of small (<1-2 MW) clusters of generators, heat and electrical storage, efficiency investments, and combined heat and power (CHP) applications (particularly involving heat activated cooling) in commercial buildings promises significant benefits but poses many technical and financial challenges, both in system choice and its operation; if successful, such systems may be precursors to widespread microgrid deployment. The presented optimization approach to choosing such systems and their operating schedules uses Berkeley Lab's Distributed Energy Resources Customer Adoption Model [DER-CAM], extended to incorporate electrical storage options. DER-CAM chooses annual energy bill minimizing systems in a fully technology-neutral manner. An illustrative example for a San Francisco hotel is reported. The chosen system includes two engines and an absorption chiller, providing an estimated 11% cost savings and 10% carbon emission reductions, under idealized circumstances.