Ian Dobson | Iowa State University (original) (raw)
Papers by Ian Dobson
IEEE Transactions on Power Systems, vol. 28, pp. 3410-3419, Aug 2013
Branching processes can be applied to simulated cascading data to describe the statistics of the ... more Branching processes can be applied to simulated cascading data to describe the statistics of the cascades and quickly predict the distribution of blackout sizes. We improve the procedures for discretizing load shed data so that a Galton-Watson branching process may be applied. The branching process parameters such as average propagation are estimated from simulated cascades and the branching process is then used to estimate the distribution of blackout size. We test the estimated distributions with line outage and load shed data generated by the improved OPA and AC OPA cascading simulations on the IEEE 118-bus system and the Northeast Power Grid of China.
PESC `92 Record. 23rd Annual IEEE Power Electronics Specialists Conference, 2000
The authors describe two bifurcation instabilities of a thyristor controlled reactor (TCR) circui... more The authors describe two bifurcation instabilities of a thyristor controlled reactor (TCR) circuit in which switching times suddenly change and system stability is lost. The instabilities are unexpected because they are quite different from what might be expected from conventional theory in that they occur without the usual indications such as eigenvalues of a Jacobian matrix crossing the unit circle.
2015 48th Hawaii International Conference on System Sciences, 2015
We compare and test statistical estimates of failure propagation in data from versions of a proba... more We compare and test statistical estimates of failure propagation in data from versions of a probabilistic model of loading-dependent cascading failure and a power systems blackout model of cascading transmission line overloads. The comparisons suggest mechanisms affecting failure propagation and are an initial step towards monitoring failure propagation from practical system data. Approximations to the probabilistic model describe the forms of probability distributions of cascade sizes.
Ultra-Wide Band Traveling Wave Tube Amplifiers (TWTAs) (multioctave bandwidth) provide for the po... more Ultra-Wide Band Traveling Wave Tube Amplifiers (TWTAs) (multioctave bandwidth) provide for the possibility of several independent communication channels through multitone drive signals. However, due to nonlinearities in the beam-wave interaction the output spectrum typically contains much more than amplified drive tones. This is exacerbated by the wide bandwidth in which harmonics and intermodulation products can interact with each other as well as the drive tones. It is highly desirable to develop linearization strategies so that the drive tones may be run near saturation input levels without excessive distortion of the output signal. As a first step to developing these strategies we consider a model of a multitone TWTA akin to those originally formulated in the 1960's 1 and still in use today. 3 Numerical solutions to this model strongly resemble the output of a linear system up to a point just before saturation. We attempt to model the linear system by approximating our model with a Taylor series expansion. Results of these attempts are presented.
IEEE Conference Record - Abstracts. 2002 IEEE International Conference on Plasma Science (Cat. No.02CH37340), 2002
ABSTRACT
ICOPS 2000. IEEE Conference Record - Abstracts. 27th IEEE International Conference on Plasma Science (Cat. No.00CH37087), 2000
Summary form only given. Due to the increasing bandwidth of Traveling Wave Tube Amplifiers (TWTAs... more Summary form only given. Due to the increasing bandwidth of Traveling Wave Tube Amplifiers (TWTAs), broadband klystrons, and the possibility of electron-beam modulation using Field Emitter Arrays (FEAs), there has been a resurgence of interest in understanding the electron beam-wave interaction when the beam and wave initially have multifrequency content. In the case of the klystron, this corresponds to understanding how the electron beam propagates a multitonal velocity or density disturbance. In a distributed interaction device like the TWTA the beam dynamics, and hence radiation dynamics, are further complicated since a beam electron interacts with a forcing field on the circuit for its entire trip through the device. We choose the simpler device, an idealized broadband klystron model, to study harmonic and intermodulation distortions in the multifrequency beam-wave system. The beam dynamics are modeled by nonlinear fluid equations, and the question of how the beam propagates general (multitonal) input conditions is addressed. Although the question has been considered before in some generality, we simplify the beam model and consider specifically multitonal excitation as would be used in a communications application
Design techniques for sigma-delta modulators from communications are applied and adapted to impro... more Design techniques for sigma-delta modulators from communications are applied and adapted to improve the spectral characteristics of high frequency power electronic applications. A high frequency power electronic circuit can be regarded as a quantizer in an interpolative Σ∆ modulator. We review one dimensional sigma-delta modulators and then generalize to the hexagonal sigma-delta modulators that are appropriate to three-phase converters. A
IEEE Transactions on Power Systems, 2015
If an interarea oscillatory mode has insufficient damping, generator redispatch can be used to im... more If an interarea oscillatory mode has insufficient damping, generator redispatch can be used to improve its damping. We explain and apply a new analytic formula for the modal sensitivity to rank the best pairs of generators to redispatch. The formula requires some dynamic power system data and we show how to obtain that data from synchrophasor measurements. The application of the formula to damp interarea modes is explained and illustrated with interarea modes of the New England 10-machine power system.
a See Friday morning mini-course poster session for more detail and discussion.
IEEE Transactions on Power Systems, vol. 28, pp. 3410-3419, Aug 2013
Branching processes can be applied to simulated cascading data to describe the statistics of the ... more Branching processes can be applied to simulated cascading data to describe the statistics of the cascades and quickly predict the distribution of blackout sizes. We improve the procedures for discretizing load shed data so that a Galton-Watson branching process may be applied. The branching process parameters such as average propagation are estimated from simulated cascades and the branching process is then used to estimate the distribution of blackout size. We test the estimated distributions with line outage and load shed data generated by the improved OPA and AC OPA cascading simulations on the IEEE 118-bus system and the Northeast Power Grid of China.
PESC `92 Record. 23rd Annual IEEE Power Electronics Specialists Conference, 2000
The authors describe two bifurcation instabilities of a thyristor controlled reactor (TCR) circui... more The authors describe two bifurcation instabilities of a thyristor controlled reactor (TCR) circuit in which switching times suddenly change and system stability is lost. The instabilities are unexpected because they are quite different from what might be expected from conventional theory in that they occur without the usual indications such as eigenvalues of a Jacobian matrix crossing the unit circle.
2015 48th Hawaii International Conference on System Sciences, 2015
We compare and test statistical estimates of failure propagation in data from versions of a proba... more We compare and test statistical estimates of failure propagation in data from versions of a probabilistic model of loading-dependent cascading failure and a power systems blackout model of cascading transmission line overloads. The comparisons suggest mechanisms affecting failure propagation and are an initial step towards monitoring failure propagation from practical system data. Approximations to the probabilistic model describe the forms of probability distributions of cascade sizes.
Ultra-Wide Band Traveling Wave Tube Amplifiers (TWTAs) (multioctave bandwidth) provide for the po... more Ultra-Wide Band Traveling Wave Tube Amplifiers (TWTAs) (multioctave bandwidth) provide for the possibility of several independent communication channels through multitone drive signals. However, due to nonlinearities in the beam-wave interaction the output spectrum typically contains much more than amplified drive tones. This is exacerbated by the wide bandwidth in which harmonics and intermodulation products can interact with each other as well as the drive tones. It is highly desirable to develop linearization strategies so that the drive tones may be run near saturation input levels without excessive distortion of the output signal. As a first step to developing these strategies we consider a model of a multitone TWTA akin to those originally formulated in the 1960's 1 and still in use today. 3 Numerical solutions to this model strongly resemble the output of a linear system up to a point just before saturation. We attempt to model the linear system by approximating our model with a Taylor series expansion. Results of these attempts are presented.
IEEE Conference Record - Abstracts. 2002 IEEE International Conference on Plasma Science (Cat. No.02CH37340), 2002
ABSTRACT
ICOPS 2000. IEEE Conference Record - Abstracts. 27th IEEE International Conference on Plasma Science (Cat. No.00CH37087), 2000
Summary form only given. Due to the increasing bandwidth of Traveling Wave Tube Amplifiers (TWTAs... more Summary form only given. Due to the increasing bandwidth of Traveling Wave Tube Amplifiers (TWTAs), broadband klystrons, and the possibility of electron-beam modulation using Field Emitter Arrays (FEAs), there has been a resurgence of interest in understanding the electron beam-wave interaction when the beam and wave initially have multifrequency content. In the case of the klystron, this corresponds to understanding how the electron beam propagates a multitonal velocity or density disturbance. In a distributed interaction device like the TWTA the beam dynamics, and hence radiation dynamics, are further complicated since a beam electron interacts with a forcing field on the circuit for its entire trip through the device. We choose the simpler device, an idealized broadband klystron model, to study harmonic and intermodulation distortions in the multifrequency beam-wave system. The beam dynamics are modeled by nonlinear fluid equations, and the question of how the beam propagates general (multitonal) input conditions is addressed. Although the question has been considered before in some generality, we simplify the beam model and consider specifically multitonal excitation as would be used in a communications application
Design techniques for sigma-delta modulators from communications are applied and adapted to impro... more Design techniques for sigma-delta modulators from communications are applied and adapted to improve the spectral characteristics of high frequency power electronic applications. A high frequency power electronic circuit can be regarded as a quantizer in an interpolative Σ∆ modulator. We review one dimensional sigma-delta modulators and then generalize to the hexagonal sigma-delta modulators that are appropriate to three-phase converters. A
IEEE Transactions on Power Systems, 2015
If an interarea oscillatory mode has insufficient damping, generator redispatch can be used to im... more If an interarea oscillatory mode has insufficient damping, generator redispatch can be used to improve its damping. We explain and apply a new analytic formula for the modal sensitivity to rank the best pairs of generators to redispatch. The formula requires some dynamic power system data and we show how to obtain that data from synchrophasor measurements. The application of the formula to damp interarea modes is explained and illustrated with interarea modes of the New England 10-machine power system.
a See Friday morning mini-course poster session for more detail and discussion.