Voltage Stability Preserving Invariants for Smart Grids

Voltage stability analysis is essential in any power system. This paper addresses the voltage stability in a typical smart grid type system with multiple independent entities. A typical smart grid operation involves various loading excursions (changes in power, both generated and consumed) undertaken by all these independent entities. For a smooth functioning of any generic smart grid type system, correct behavior of all these independent entities must be preserved when one or more of these entities are subjected to various loading levels. Correct behavior of all the entities (sub-systems) will ensure correct behavior of the overall system (smart grid). Invariants, if forced to be true, ensure correct behavior on a subsystem level and thus preserve the overall system correctness. An invariant is a logical predicate on a system state that should not change its truth value if satisfied by system execution [1]. This paper derives an invariant that preserves voltage stability. This invariant is based on an online indicator which is derived from fundamental Kirchhoff s laws and will predict the proximity of voltage collapse at one or more entities in a smart grid. The efficiency of the invariant in predicting voltage collapse has been verified with simulations performed on a typical seven node smart grid system. Thus an online monitoring of the system parameters gives an indication of the system voltage stability. The voltage stability invariant works for both static and dynamic states. This method is also a fast and powerful tool to predict the voltage stability margin of a generic smart grid system by a simple monitoring of the system parameters

Guidelines for the specification of models to be used in design-oriented simulations

Simulation-based design requires models at many levels of detail. In the early stages, models must approximate the coarse behavior of the system across many domains - power, efficiency, cost, size, and weight. In later stages, the models must represent the system with increasing accuracy - including dynamic performance, controllability, and other more-subtle manifestations. In this work, we focus on specification of the models for a simulation-based design of ship power systems. We address the issues of levels of detail in models, definition of model ports to support substitution of models at increasing levels of detail, and the application of multiple analyses to one set of simulation models. Eventually, we tackle very detailed issues such as insulation coordination and grounding scheme that are not at all important in the conceptual stages of design