Kevin Tomsovic

Development of models for analyzing the load-following performance of microturbines and fuel cells

Abstract Utility restructuring, technology evolution, public environmental policy, and expanding power demand are providing the opportunity for microturbines and fuel cells to become important energy resources. Deregulation has begun to allow for the provision of various ancillary services, such as load-following. In order to investigate the ancillary services ability of these units in distribution systems, new simulation tools are needed. This paper presents simplified slow dynamic models for microturbines and fuel cells. Their stand-alone dynamic performances are analyzed and evaluated. A distribution system embedded with a microturbine plant and an integrated fuel cell power plant is used as an example. The control strategy and load-following service in this distribution system are simulated. It is illustrated that microturbines and fuel cells are capable of providing load-following service, significantly enhancing their economic value.

Placement of dispersed generation systems for reduced losses

Recent improvements in fuel cell technology along with an increasing demand for small generator units have led to renewed interest in dispersed generation units. This work demonstrates a methodology for deploying dispersed fuel cell generators throughout a power system to allow for more efficient operation. A detailed study of the system losses and sensitivities on Eastern Washington system as part of the larger WSCC system has been completed. This work presents an algorithm to determine the near optimal, with respect to system losses, placement of these units on the power grid. Further, the impacts of dispersed generation at the distribution level are performed with an emphasis on resistive losses, and capacity savings. The results show the importance of placement for minimizing losses and maximizing capacity savings.

Designing the Next Generation of Real-Time Control, Communication, and Computations for Large Power Systems

The power grid is not only a network interconnecting generators and loads through a transmission and distribution system, but is overlaid with a communication and control system that enables economic and secure operation. This multilayered infrastructure has evolved over many decades utilizing new technologies as they have appeared. This evolution has been slow and incremental, as the operation of the power system consisting of vertically integrated utilities has, until recently, changed very little. The monitoring of the grid is still done by a hierarchical design with polling for data at scanning rates in seconds that reflects the conceptual design of the 1960s. This design was adequate for vertically integrated utilities with limited feedback and wide-area controls; however, the thesis of this paper is that the changing environment, in both policy and technology, requires a new look at the operation of the power grid and a complete redesign of the control, communication and computation infrastructure. We provide several example novel control and communication regimes for such a new infrastructure.

Application of linear matrix inequalities for load frequency control with communication delays

Load frequency control has been used for decades in power systems. Traditionally, this has been a centralized control by area with communication over a dedicated and closed network. New regulatory guidelines allow for competitive markets to supply this load frequency control. In order to allow an effective market operation, an open communication infrastructure is needed to support an increasing complex system of controls. While such a system has great advantage in terms of cost and reliability, the possibility of communication signal delays and other problems must be carefully analyzed. This paper presents a load frequency control method based on linear matrix inequalities. The primary aim is to find a robust controller that can ensure good performance despite indeterminate delays and other problems in the communication network.

Overview and literature survey of fuzzy set theory in power systems

Increasing interest has been seen in applying fuzzy set theory to power systems problems from the number of publications on this topic. As a relatively new research topic a need is felt to pay more attention to the understanding of the basic principles of the theory and the identification of problems suitable for solving by this method. This paper presents a survey of publications on applications of fuzzy set theory to power systems and the basic procedures for fuzzy set based methods to solve specific power systems problems. Simple numerical examples are used to show the practical procedures of problem formulation and solution. Theses examples are: generator maintenance scheduling, dynamic programming, and power system stabiliser. >

An Expert System Assisting Decision-Making of Reactive Power/Voltage Control

An expert system is developed to assist in the decision-making of the reactive power/voltage control problem. The knowledge required to perform the task is identified. To alleviate a voltage problem, empirical rules are used to generate appropriate control actions when slight voltage violations occur. Controls such as shunt capacitors, transformer tap changers and generator voltages are utilized. Theoretical justification of the empirical rules is presented. When it is judged that the voltage problem is so severe that empirical judgements may not be reliable, the developed expert system can help in formulating the problem so that an available application software package can be effectively utilized. In this paper, production rules are proposed to perform the above functions. Numerical examples are also presented.

A fuzzy linear programming approach to the reactive power/voltage control problem

The integration of traditional and heuristic techniques is considered for the reactive power/voltage control program. The steady-state reactive power problem is addressed. Fuzzy sets are used to modify the linear programming (LP) approach to voltage control and to incorporate some heuristic concepts of the expert system approach. Multiple objectives and soft constraints are modeled using fuzzy sets. Piecewise linear convex membership functions for the fuzzy sets are defined. Under this definition, the fuzzy optimization problem is reformulated as a standard linear programming problem. The objective function represents the compromise among the original competing objectives and the soft constraints. In addition, discrete constraints are considered. Numerical examples demonstrate the approach. >

Adaptive power flow method for distribution systems with dispersed generation

Recently, there has been great interest in the integration of dispersed generation units at the distribution level. This requires new analysis tools for understanding system performance. This paper presents an adaptive distributed power flow solution method based on the compensation-based method. The comprehensive distributed system model includes three-phase nonlinear loads, lines, capacitors, transformers, and dispersed generation units. The numerical properties of the compensation-based power flow method are compared and analyzed under different situations, such as load unbalance, sudden increase of one-phase loads, degree of meshed loops, number of generator nodes and so on. Based on these analyses, an adaptive compensation-based power flow method is proposed that is fast and reliable while maintaining necessary accuracy. It is illustrated that this adaptive method is especially appropriate for simulation of slow dynamics.

Communication models for third party load frequency control

With deregulation of the power generation sector, the necessity for an enhanced and open communication infrastructure to support an increasing variety of ancillary services is apparent. A duplex and distributed communication system seems to be the most suitable solution to meet and ensure good quality of these services. Parameters needed and additional limits introduced by this new communication topology must be investigated and defined. This paper focuses on the communication network requirements for a third party load frequency control service. Data communication models are proposed based on queuing theory. Simulation is performed to model the effects of certain types of signal delays on this ancillary service.

A fuzzy information approach to integrating different transformer diagnostic methods

Methods for identifying transformer fault conditions include dissolved gas analysis, liquid chromatography, acoustic analysis, and transfer function techniques. Researchers have applied artificial intelligence concepts in order to encode these diagnostic techniques. These attempts have failed to fully manage the inherent uncertainty in the various methods. A theoretical fuzzy information model is introduced. An inference scheme which yields the most consistent conclusion is proposed. A framework is established that allows various diagnostic methods to be combined in a systematic way. Numerical examples demonstrate the developed system. >