Aaron M. Cramer

Evolutionary Algorithms for Minimax Problems in Robust Design

Many robust design problems can be described by minimax optimization problems. Classical techniques for solving these problems have typically been limited to a discrete form of the problem. More recently, evolutionary algorithms, particularly coevolutionary optimization techniques, have been applied to minimax problems. A new method of solving minimax optimization problems using evolutionary algorithms is proposed. The performance of this algorithm is shown to compare favorably with the existing methods on test problems. The performance of the algorithm is demonstrated on a robust pole placement problem and a ship engineering plant design problem.

Performance Metrics for Electric Warship Integrated Engineering Plant Battle Damage Response

In military applications, it is important for a platform (warship, aircraft, etc.) or an installation (airbase, etc.) to maintain war-fighting ability after being damaged. In particular if the unit requires electric power, cooling, or other resources to perform its mission, then these resources must be available following a weapon detonation event. The integrated engineering plant (IEP) is responsible for providing these services to the mission-critical loads in a unit. Novel continuity-of-service metrics for IEPs are set forth herein. These metrics provide a means of predicting the average and worst-case level of service the plant can provide as well as the worst-case scenario over a class of disruptions. This provides a method of making meaningful comparisons between different designs. The computation and meaning of the proposed metrics are explored using a notional warship IEP.

Evolutionary Design of Electromagnetic and Electromechanical Devices

Evolutionary design refers to the use of evolutionary computing methods in the design process. Normally, this entails the formulization of the design problem as an optimization problem, which is solved using evolutionary techniques such as a genetic algorithm or particle swarm optimization. This paper provides three examples in the use of this highly effective method to the design of electromagnetic and electromechanical devices.

Synchronous Machine Model With Voltage-Behind-Reactance Formulation of Stator and Field Windings

A synchronous machine model with saturation and cross saturation and an arbitrary rotor network representation that uses a voltage-behind-reactance representation for both the stator windings and the field winding of the machine is proposed. This allows the stator windings and the field winding to be represented as branches in a circuit solver, permitting straightforward simulation with connected circuitry. In particular, the model can be simulated with rectifier loads or with rectifier sources applied to the field winding. The model is validated against experimental data, and its utility is demonstrated in an excitation failure case study.

Reactive-power control of photovoltaic inverters for mitigation of short-term distribution-system voltage variability

The output power variability of intermittent renewable sources can cause significant fluctuations in distribution system voltages. A local linear controller that exploits the capability of a photovoltaic inverter to provide both real and reactive power is described. This controller substitutes reactive power for real power when fluctuations in the output of the photovoltaic source are experienced. In this way, the inverter can help mitigate distribution system voltage fluctuations. The local linear controller has a control parameter called the substitution rate, and several methods of calculating this control parameter are described, including sensitivity minimization and violation optimization methods, which can be applied on a local or global basis and on a per-phase or phase-average basis. This controller is examined using an example distribution system, and it is found that the controller is effective at mitigating voltage violations. Furthermore, comparisons between the alternative methods of selecting the substitution rate are performed.

Metric Optimization-Based Design of Systems Subject to Hostile Disruptions

In many applications, engineering systems are required to operate acceptably well in hostile environments. In the past, survivability engineering has addressed this requirement using heuristic rule-based design approaches followed by analysis to determine if survivability constraints have been satisfied. The treatment of survivability as a constraint rather than an independent design objective hinders the ability of system engineers to trade off survivability with other design objectives, such as cost and performance. Herein, the survivability problem is posed in terms of maximizing expected performance and minimizing the risk of unacceptable performance. Design metrics that allow optimal selection of systems on the basis of these survivability dimensions are presented. The metrics are part of a systematic approach to system engineering in which survivability concerns are quantified and individual systems and entire classes of systems can be compared objectively. These metrics are a necessary step toward an integrated design process wherein tradeoffs between all design objectives can be identified. This methodology is demonstrated on the design of a notional electric warship integrated engineering plant (IEP) that is subject to hostile disruptions posed by antiship missiles. By use of this method, the performance of the IEP is shown to be improved.

Early-stage shipboard power system simulation of operational vignettes for dependability assessment

A principle motivation for the development of early-stage shipboard power system simulation techniques is the need to perform time-domain simulation during the early design stage. In particular, there is a need to understand the performance of a candidate system during challenging situations involving dynamic load profiles and disruptive conditions in order to assess the system dependability. An early-stage simulation technique is applied to simulate the performance of a candidate system for given operational vignettes. Using this early-stage approach allows simulations to be performed very quickly, allowing many vignettes to be considered and the overall system dependability to be assessed.

Modeling and Simulation of an Electric Warship Integrated Engineering Plant

A layered approach to the simulation of dynamically interdependent systems is presented. In particular, the approach is applied to the integrated engineering plant of a notional all-electric warship. The models and parameters of the notional ship are presented herein. This approach is used to study disruptions to the integrated engineering plant caused by anti-ship missiles. Example simulation results establish the effectiveness of this approach in examining the propagation of faults and cascading failures throughout a dynamically interdependent system of systems.

A New Procedure for Calculating Immittance Characteristics Using Detailed Computer Simulations

Immittance based methods are often used in the stability analysis of power electronics based systems. Because it is difficult and/or time consuming to develop average value models of some components, it is often desirable to extract immittance data from detailed simulations (simulations in which the switching of the power semiconductors is represented). Traditionally, this is accomplished by introducing a perturbation, extracting the fundamental component of the voltage and current waveforms at the perturbation frequency, from which the impedance at that frequency may be extracted using transform techniques. In this work, an alternate approach is suggested, which offers both reduced computational effort as well as increased accuracy.

Voltage and var control to enable high penetration of distributed photovoltaic systems

Increasing utilization of renewable energy will reduce reliance on fossil-fuel-based generation and reduce greenhouse gas and pollutant emissions, benefiting the environment and economic growth. However, the intermittent nature of renewable energy sources such as photovoltaic (PV) and wind energy systems imposes great challenges on power system voltage and reactive power control. This paper presents a novel solution based on Cyber-Physical System (CPS) design principles that removes this technical barrier so that more renewable energy sources can be deployed and integrated into the power grid. This paper focuses on solar power integration and control, but the proposed solution is expected to be also applicable to integrating other intermittent renewable energy sources such as wind energy. Camera and weather stations will be installed to capture weather data. The solar generation in a future time horizon will be estimated. An intelligent algorithm is then applied to maintain the required voltage levels. Proper communication schemes will also be designed to ensure interoperability and security of the CPS. This paper presents the overall framework of the proposed solution, designs of the major components of the system, and preliminary results.