[gravatar email=”walters@pcka.com” class=”alignleft” size=”96″ default=”https://pcka.com/wp-content/uploads/2010/08/gravatar.jpg”]E. A. Walters received the BSEE, MSEE, and PhD from Purdue University in 1994, 1995, and 1999, respectively. His interests include the modeling of power-electronics-based power systems and Distributed Heterogeneous Simulation (DHS). He is currently Vice President and Chief Operating Officer (COO) for PCKA. Please update PCKA work/leadership. He has served as principal investigator for an Air Force SBIR Phase III Contract involving the DHS of an Aircraft Power System. He has previously served as the principle investigator the Marine Corp STTR Phases I, II, and Enhancement entitled Multi-Level Heterogeneous Modeling of AAAV Electric Power System, and the Integrated Power and Propulsion Simulation/Modeling (IPPoSMo) Program in support of the future Global Hawk platform. He is a co-inventor of DHS and has authored or co-authored over 25 papers in the area of modeling and simulation. Selected Publications E. A. Walters, M. Hasan, C. E. Lucas, O. Wasynczuk, P. T. Lamm, “Variable Communication Rates in a Distributed Simulation,” Proceeding 3rd International Energy Conversion Engineering Conference, August 15-18, 2005, San Francisco, CA. S. Graham, I. Wong, W. Chen, A. Lazarevic, K. Cleek, E. A. Walters, C. E. Lucas, O. Wasynczuk, P. Lamm, “Distributed Simulation,” Aerospace Engineering, November 2004, pp. 24-27. C. E. Lucas, E. A. Walters, J. Jatskevich, O. Wasynczuk, P. T. Lamm, “A Distributed Heterogeneous Simulation of a Representative Aircraft Power System,” Proceedings 2002 SAE Power Systems Conference, October 29-31, 2002, Coral Spring, FL. S. D. Pekarek, E. A. Walters, “An Accurate Method of Neglecting Dynamic Saliency of Synchronous Machines in Power Electronic Based Systems,” IEEE Transactions on Energy Conversion, vol. 14, no. 4, December 1999, pp....
Read MoreIntegrated Hardware-in-the-Loop Simulation of a Complex Turbine Engine and Power System
Suraj Ramalingam, Aaron Green, Peter Lamm, U.S. Air Force Research Laboratory; Hank Barnard, Scientific Monitoring, Inc; E. A. Walters, J. R. Wells, PC Krause and Associates, Inc. The interdependency between propulsion, power, and thermal subsystems on military aircraft such as the F-35 Joint Strike Fighter (JSF) and F-22 Raptor continues to increase as advanced war-fighting capabilities including solid-state radars, electronic attack, electric actuation, and Directed Energy Weaponry (DEW) expand to meet Air Force needs. Novel analysis and testing methodologies are required to predict these interdependencies and address adverse interactions prior to costly hardware prototyping. As a result, the Air Force Research Laboratory (AFRL) has established a dynamic hardware-in-the-loop (HIL) test-bed wherein transient simulations can be integrated through advanced real-time simulation with prototype hardware for integrated system studies and analysis. This paper details a test-bed configuration where a dynamic simulation of an aircraft turbine engine is utilized to control a dual-head electric drive stand. The drive stand is connected to an electric generator and associated power system implemented in hardware. The electromagnetic torque produced by the generator is measured and fed back into the turbine engine simulation as a load to the shaft. The HIL capability of this test-bed configuration enables reduced cost altitude testing, supports the design and analysis of integrated starter / generators and alternative power / propulsion architectures, and sets the stage for advanced integrated turbine engine / generator control design. 2006 SAE Power Systems Conference, November 7–9, 2006, New Orleans, LA. Paper...
Read MoreCoupled-Circuit Modeling of 3, 6, and 9-Phase Induction Machine Drive Systems
Juri Jatskevich, University of British Columbia, Canada; E. A. Walters, C. E. Lucas, PC Krause and Associates, Inc. This paper describes a coupled-circuit physical-variable modeling of multiphase induction motors. The presented modeling interface makes it straightforward to implement an induction machine with arbitrary number of phases and/or phase groups on the stator and the rotor. The 3-, 6-, and 9-phase motors are simulated and compared. It is shown that machines with higher number of phases have less severe torque pulsation and the stator current increase following a loss of one phase. For the 9-phase machine, several studies involving loss of multiple phases are also presented, wherein the relative location of the faulted phases is shown to have a significant impact on redistribution of currents and resulting electromagnetic torque. The proposed models can be used to represent induction motors and generators for transient studies involving multiple faults, system-level reconfiguration, and survivability. 2006 SAE Power Systems Conference, November 7–9, 2006, New Orleans, LA. Paper...
Read MoreTransient Turbine Engine Modeling and Real-Time System Integration Prototyping
Michael Corbett, Jessica Williams, Mitch Wolff, E. A. Walters, J. R. Wells, PC Krause and Associates, Inc; Peter Lamm, U.S. Air Force Research Laboratory Aircraft power demands continue to increase with the increase in electrical subsystems. These subsystems directly affect the behavior of the power and propulsion systems and can no longer be neglected or assumed linear in system analyses. The complex models designed to integrate new capabilities have a high computational cost. This paper investigates the possibility of using a hardware-in-the-loop (HIL) analysis with real time integration. A representative electrical power system is removed from a turbine engine model simulation and replaced with the appropriate hardware attached to a 350 horsepower drive stand. In order to update the model to proper operating conditions, variables are passed between the hardware and the computer model. Using this method, a significant reduction in runtime is seen, and the turbine engine model is usable in a real time environment. Scaling is also investigated for simulations to be performed that exceed the operating parameters of the drive stand. Similar results are generated with and without the scale factor implemented. Excellent agreement is shown between the HIL and stand alone model results. These results validate the capability of HIL experimentation and provide the opportunity for significant future propulsion configuration studies with minimal cost. 2006 SAE Power Systems Conference, November 7–9, 2006, New Orleans, LA. Paper...
Read MoreAn Observer-Based Automated Averaging Technique for Power Electronic Circuits
E. A. Walters, O. Wasynczuk, J. V. Jatskevich, C. E. Lucas, PC Krause and Associates, Inc. Average-value models are commonly used in the design and analysis of power electronic-based systems as a method of portraying the overall system dynamics while neglecting discontinuities that arise from switching. Although numerous averaging methodologies have been developed to eliminate discontinuities, they are typically limited to specific circuits operating in specific modes. Therefore, substantial analytical effort is generally required to select an appropriate averaging technique and develop the corresponding average-value model that is valid for a given converter. To reduce this effort, an automated averaging technique is set forth in which an averaged model is established via coupling with a detailed simulation of the system. The structure of the averaged model is based upon state-space averaging with the detailed simulation used to calculate state models for each switching topology, the time spent per cycle in each topology, and the operating mode (continuous or discontinuous) of the circuit. However, since classical state-space averaging is not applicable to circuits with state-dependent switching logic and does not portray high- frequency dynamics associated with discontinuous states, a state feedback loop is introduced such that the high-frequency dynamics associated with state- dependent switching or discontinuous modes are accurately portrayed. To demonstrate the new technique, to example systems are examined, a PWM-controlled buck converter operating in both continuous and discontinuous modes and buck converter with a hysteresis current controller. The new averaging technique is verified by comparison with established analytical and numerical methods. SAE Transactions Journal of Aerospace, sec. 1, set 3, Month 2000, pp....
Read MoreImprovements in the Distributed Heterogeneous Simulation of Aircraft Electric Power Systems
B. P. Loop, C. E. Lucas, E. A. Walters, M. Hasan, PC Krause and Associates, Inc; S. Field , N. Kumbar, Naval Air Systems Command Two recent enhancements to Distributed Heterogeneous Simulation (DHS) are variable communication rates and higher-order predictors. Variable communication automatically controls the communication interval between any two subsystems in an attempt to achieve a desired accuracy during transient periods and maximize speed during steady-state periods. Higher-order predictors can better estimate the values of exchanged variables between data exchange instances, which can improve accuracy and possibly require fewer exchanges. A comparison between a single-computer simulation of an aircraft electric power system and an equivalent three-computer DHS show that the variable communication technique enables more accuracy and higher speed distributed simulations than fixed-step communication. In addition, higher-order predictors are shown to increase accuracy in some cases. 2006 SAE Power Systems Conference, November 7–9, 2006, New Orleans, LA. Paper...
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