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This paper presents a novel approach to the modeling and control of AC microgrids that contain spinning machines, power electronic inverters and energy storage devices. The inverters in the system can adjust their frequencies and power angles very quickly, so the modeling focuses on establishing a common reference frequency and angle in the microgrid based on the spinning machines. From this dynamic model, nonlinear Hamiltonian surface shaping and power flow control method is applied and shown to stabilize. From this approach the energy flow in the system is used to show the energy storage device requirements and limitations for the system. This paper first describes the model for a single bus AC microgrid with a Hamiltonian control, then extends this model and control to a more general class of multiple bus AC microgrids. Simulation results demonstrate the efficacy of the approach in stabilizing and optimization of the microgrid. [ABSTRACT FROM AUTHOR]

Penetration of the power grid by renewable energy sources, distributed storage, and distributed generators is becoming increasingly common. Increased utilization of these distributed energy resources (DERs) has given rise to additional protection coordination concerns, particularly where they are utilized in an unbalanced manner or where loading among phases is unbalanced. Digital relays such as the SEL-751 (produced by Schweitzer Engineering Laboratories, Pullman, WA, USA) series have the capability of being set on a per-phase basis. This capability is underutilized in common practice. Additionally, in optimization algorithms for determining relay settings, the time-overcurrent characteristics (TOCs) of relays are generally not treated as variables and are assigned before running the optimization algorithm. In this paper, TOC options themselves are treated as discrete variables to be considered in the optimization algorithm. A mixed integer nonlinear programming problem (MINLP) is set up where the goal is to minimize relay operating times. A genetic algorithm (GA) approach is implemented in MATLAB where two cases are considered. In the first case, the TOC and Time dial setting (TDS) of each relay is set on a three-phase basis. In the second case, per-phase settings are considered. Relay TDSs and TOCs are both considered as simultaneous discrete control variables. Despite the stochastic nature of using per-phase settings for unbalanced systems is found to generally allow for shorter operating times. However, for relatively balanced systems, it is best to use three-phase settings if computation time is of importance. [ABSTRACT FROM AUTHOR]

Pulse loads on an electric ship are becoming more prevalent as ship component technologies move to more electric power. However, these pulse loads, such as electromagnetic aircraft launch systems, rail guns, lasers, and radar all can have a destabilizing effect on the ships power distribution network. Typically these types of loads are modeled as constant power and are analyzed for stability with small-signal models and techniques. However, small-signal methods are insufficient for pulse power load stability. This paper will present a brief overview of small-signal methods. Then a large signal metastable analysis method based on a Hamiltonian surface shaping and power flow control methodology based on the average-mode model of dc–dc converters will be presented. The results show that the nonlinear time-variant load pulses create nonlinear limit cycles and dynamics. The stability of the limit cycles can be assessed through a comparison of the power generated versus power dissipated in the system. Simulation, hardware-in-the-loop, and hardware experimental results will be presented. [ABSTRACT FROM PUBLISHER]