A Novel Adaptive Inertia Strategy in Large-Scale Electric Power Grids

The increasing penetration of new renewable sources of energy in today's power grids is accompanied by a decrease in available electromechanical inertia. This leads to a reduced dynamical stability. To counterbalance this effect, virtual synchronous generators have been proposed to emulate conventional generators and provide inertia to power systems. The high flexibility of these devices makes it possible to control the synthetic inertia they provide and to have them operate even more efficiently than the electromechanical inertia they replace. Here, we propose a novel control scheme for virtual synchronous generators, where the amount of inertia provided is large at short times - thereby absorbing local faults and disturbances as efficiently as conventional generators - but decreases over a tunable time interval to prevent long-time coherent oscillations from setting in. This new model is used to investigate the effect of adaptive inertia on large-scale power grids. Our model outperforms conventional constant inertia in all scenarios and for all performance measures considered. We show how an optimized geographical distribution of adaptive inertia devices not only effectively absorbs local faults, but also significantly improves the damping of inter-area oscillations.Comment: 6 pages, 5 figure

Transmission grid stability with large scale power flows due to renewables

We propose a general methodology for identifying critical lines in the long-distance transmission of power across large electrical networks. When the system is pushed to its limits of operation due to large power imbalances or contingencies, the network may lose synchrony. We analyze the Continental Europe grid as a case study and find that instabilities emerge due to topological constraints by which the system loses its stable fixed point (synchronized state), causing the grid to split into two asynchronous zones. We discuss also how the modes of the system provide information on which areas are more susceptible to lose synchrony.Comment: 10 pages, 9 figure

Vanishing Minors in the Neutrino Mass Matrix from Abelian Gauge Symmetries

Augmenting the Standard Model by three right-handed neutrinos allows for an anomaly-free gauge group extension G_max = U(1)_(B-L) x U(1)_(L_e-L_mu) x U(1)_(L_mu-L_tau). While simple U(1) subgroups of G_max have already been discussed in the context of approximate flavor symmetries, we show how two-zero textures in the right-handed neutrino Majorana mass matrix can be enforced by the flavor symmetry, which is spontaneously broken very economically by singlet scalars. These zeros lead to two vanishing minors in the low-energy neutrino mass matrix after the seesaw mechanism. This study may provide a new testing ground for a zero-texture approach: the different classes of two-zero textures with almost identical neutrino oscillation phenomenology can in principle be distinguished by their different Z' interactions at colliders.Comment: 12 pages; Extended and clarified discussion; comments on finetuning in the textures; matches published versio

Long wavelength coherency in well connected electric power networks

We investigate coherent oscillations in large scale transmission power grids, where large groups of generators respond in unison to a distant disturbance. Such long wavelength coherent phenomena are known as inter-area oscillations. Their existence in networks of weakly connected areas is well captured by singular perturbation theory. However, they are also observed in strongly connected networks without time-scale separation, where applying singular perturbation theory is not justified. We show that the occurrence of these oscillations is actually generic. Applying matrix perturbation theory, we show that, because these modes lie at the edge of the system's spectrum of eigenvalues, they are only moderately sensitive to increased network connectivity between well chosen, initially weakly connected areas, and that their general structure remains the same, regardless of the strength of the inter-area coupling. This is qualitatively understood by bringing together the standard singular perturbation theory and Courant's nodal domain theorem

Matrix perturbation theory of inter-area oscillations

Interconnecting power systems has a number of advantages such as better electric power quality, increased reliability of power supply, economies of scales through production and reserve pooling and so forth. Simultaneously, it may jeopardize the overall system stability with the emergence of so-called inter-area oscillations, which are coherent oscillations involving groups of rotating machines separated by large distances up to thousands of kilometers. These often weakly damped modes may have harmful consequences for grid operation, yet despite decades of investigations, the mechanisms that generate them are still poorly understood, and the existing theories are based on assumptions that are not satisfied in real power grids where such modes are observed. Here we construct a matrix perturbation theory of large interconnected power systems that clarifies the origin and the conditions for the emergence of inter-area oscillations. We show that coherent inter-area oscillations emerge from the zero-modes of a multi-area network Laplacian matrix, which hybridize only weakly with other modes, even under significant capacity of the inter-area tie-lines, i.e. even when the standard assumption of area partitioning is not satisfied. The general theory is illustrated on a two-area system, and numerically applied to the well-connected PanTaGruEl model of the synchronous grid of continental Europe

Energy-Information Trade-Offs between Movement and Sensing

While there is accumulating evidence for the importance of the metabolic cost of information in sensory systems, how these costs are traded-off with movement when sensing is closely linked to movement is poorly understood. For example, if an animal needs to search a given amount of space beyond the range of its vision system, is it better to evolve a higher acuity visual system, or evolve a body movement system that can more rapidly move the body over that space? How is this trade-off dependent upon the three-dimensional shape of the field of sensory sensitivity (hereafter, sensorium)? How is it dependent upon sensorium mobility, either through rotation of the sensorium via muscles at the base of the sense organ (e.g., eye or pinna muscles) or neck rotation, or by whole body movement through space? Here we show that in an aquatic model system, the electric fish, a choice to swim in a more inefficient manner during prey search results in a higher prey encounter rate due to better sensory performance. The increase in prey encounter rate more than counterbalances the additional energy expended in swimming inefficiently. The reduction of swimming efficiency for improved sensing arises because positioning the sensory receptor surface to scan more space per unit time results in an increase in the area of the body pushing through the fluid, increasing wasteful body drag forces. We show that the improvement in sensory performance that occurs with the costly repositioning of the body depends upon having an elongated sensorium shape. Finally, we show that if the fish was able to reorient their sensorium independent of body movement, as fish with movable eyes can, there would be significant energy savings. This provides insight into the ubiquity of sensory organ mobility in animal design. This study exposes important links between the morphology of the sensorium, sensorium mobility, and behavioral strategy for maximally extracting energy from the environment. An “infomechanical” approach to complex behavior helps to elucidate how animals distribute functions across sensory systems and movement systems with their diverse energy loads.National Science Foundation (U.S.) (grant IOS-0846032)Canadian Broadcasting Corporation (CBET-0828749)National Science Foundation (U.S.) (TeraGrid Project grant CTS-070056T)Argonne National Laborator