R.R. Mohler

An EMTP study of SSR mitigation using the thyristor controlled series capacitor

This paper presents an EMTP (Electro-Magnetic Transient Program) simulation study of the subsynchronous resonance (SSR) mitigation effect of thyristor controlled series VAr compensation (TCSC) operated in the vernier mode, based on a simplified model of the North-Western American Power System (NWAPS). The study shows that TCSC vernier operation provides significant mitigation of SSR in some cases. An analysis of the equivalent TCSC impedance with respect to different frequencies is used to supplement these studies. >

Neural-network-based load modeling and its use in voltage stability analysis

Voltage stability analysis is very important for predicting potential voltage instability. Load modeling plays a key role in voltage stability assessment. In the literature, most available approaches to the voltage stability problem are either static or quasistatic, which do not take load dynamics into account. First, this paper presents a survey of those approaches, makes a comparison between them, and points out the possible consequences of not considering load dynamics, which at worst can be a complete voltage collapse. Based on this observation, modeling of load dynamics is considered in this paper, and neural networks including recurrent neural networks are applied for load modeling. Furthermore, this paper presents the strategies for the first time to incorporate the neural-network-based load model into static and dynamic voltage stability analysis. The computation of the relevant sensitivity is carried out for the neural-network-based load model, and the results are used in the popular modal analysis. The proposed methods are tested on both the IEEE 14-bus system and real data.

Biological modeling with variable compartmental structure

Many biological processes such as water balance and temperature regulation may be modeled by a variable-structure compartmental system of ordinary differential equations. In some cases the system is naturally bilinear, and in others the bilinear system may be a valid approximation of a complex nonlinear process. Tracer dynamics and associated methodology, which can be used to realize certain properties of the system, are analyzed. The theory is applied to tracer experiments for the development of a mammalian water-balance model.

Hopf bifurcations in a SMIB power system with SSR

This paper presents a Hopf bifurcation analysis for a single-machine infinite-bus (SMIB) power system experiencing subsynchronous resonance (SSR) by applying a Hopf bifurcation theorem combined with numerically solution of the Monodromy matrices. A Hopf bifurcation in the power system is predicted, together with stable periodic orbits.

Nonlinear control methods for power systems: a comparison

The design and performance of two nonlinear controllers for power systems is explored in this paper. The designs are based on nonlinear discrete-time predictive control and feedback linearizing control, considering a simplified nonlinear single-machine infinite bus (SMIB) power system model equipped with a series-capacitor controller. Simulations are presented for nonideal conditions such as bounded control, the uncertainties in the chosen model parameters, and the presence of inter-area-type persistent disturbances. The results indicate that superior performance can be obtained using the nonlinear predictive controller when compared with the feedback linearizing controller and a standard linear quadratic regulator. >

Stability analysis of bilinear systems

The stability of the differential bilinear systems is studied. The authors consider time-varying bilinear systems with output feedback. The input or control u(t) is not only a signal but also an input with output feedback, i.e., u(t)=f(Y(t)). It is assumed that the feedback function f is in a function space which contains the class of linear functions, functions satisfying the Lipschitz condition, and quadratic functions. >

Immunology and disease control: a systems approach

The application of system theory (or more precisely, differential equations) to immunology and disease, in general, is presented here. Particular results from U.S.-Russian research collaboration depict the potential role of such systematic analysis for more effective health care and disease control. In particular, some emphasis is given to control of influenza. After a brief systematic overview of immunology, a simple infectious disease model is developed to explain four basic forms of disease: subclinical, acute, lethal and chronic. Then, disease treatment is studied.<<ETX>>

An application study for sizing and rating controlled and conventional series compensation

A step by step method for determining controlled and conventional series compensation requirements is developed. The Montana 500 kV transmission system is taken as an example in this study. A base transfer rating of 2200 MW for the system already exists, and it is assumed that as its power loading increases, controlled series compensation is needed to reinforce the system. Combination of conventional and thyristor-controlled series compensators (TCSCs) is considered as a means of increasing the system transfer capability. Powerflow and transient stability studies are performed to rate and size the series compensators. The TCSC reactance control capabilities are established for steady-state and transient conditions. An installation sequence is developed relating facility requirements to system loading.

Distribution models of recirculating lymphocytes

Linear time-invariant, linear time-variant, and linear time-delay models are compared to a more accurate nonlinear model for the distribution of recirculating lymphocytes to various relevant organs of the immune process. The models are based on various degrees of approximation to the complex nonNewtonian tubule flow and tissue diffusion phenomena. From the measured data, it is apparent that the basic premise of cel-population conservation is not valid within the organs measured. In other words, counts are lost due to nonrecirculation and removal, natural death, and migration to organs not measured. The analysis does successfully decouple the recirculating (passive) lymphocyte dynamics from the dynamic response (and active migration) which is due to antigenic (alien substance) stimulation.<<ETX>>

Hierarchical intelligent control with flexible AC transmission systems application

Abstract A novel hierarchical intelligent controller configuration is proposed using an artificial neural network as a control-mode classifier in the supervisory level and a set of pre-designed controllers in the lower level. Controller outputs are modified nonlinearly by the classifying signals in a structure resembling one artificial neuron with adaptively changed weights. The lower-level local controllers are implemented using neural networks. An illustrative example of this approach is based on the transient stabilization of a single-machine infinite-bus system studied in Flexible AC Transmission Systems (FACTS) research.