Scott Graham, Ivan Wong, Won-Zon Chen, Alex Lazarevic, Keith Cleek, Northrop Grumman Corporation ; E. A. Walters, C. E. Lucas, O. Wasynczuk PC Krause and Associates, Inc; Peter Lamm, U.S. Air Force Research Laboratory Future Air Force intelligence, surveillance, and reconnaissance (ISR) platforms, such as high-altitude Uninhabited Aerial Vehicles (UAV), may drastically change the requirements of aircraft power systems. For example, there are potential interactions between large pulsed-power payloads and the turbine engine that could compromise the operation of the power system within certain flight envelopes. Until now, the development of large-scale, multi-disciplinary (propulsion, electrical, mechanical, hydraulic, thermal, etc.) simulations to investigate such interactions has been prohibitive due to the size of the system and the computational power required. Moreover, the subsystem simulations that are developed separately often are written in different commercial-off-the-shelf simulation programs. In this paper, a new technique useful for the numerical simulation of large-scale systems to overcome these obstacles, known as Distributed Heterogeneous Simulation (DHS), is utilized to form a dynamic system-level simulation of a high-altitude, long-endurance UAV-type of power system. This system includes detailed dynamic models of a turbine engine, high- and low-spool generators, and payloads. Although not necessary, all of the component models for this system were developed within the same simulation environment, specifically with MATLAB/Simulink. This enabled a single-computer integrated system model and a distributed computer system simulation to be formed thereby allowing for a direct comparison of simulation accuracy and computational performance for the two simulation approaches. From this comparison, it was determined that by distributing the system simulation across three computers, a 21-fold increase in simulation speed could be realized while producing nearly identical results. 2004 SAE Power Systems Conference, November 2-4, 2004 Paper #2004-01-3193 and Aerospace Engineering, November 2004,...
Read MoreCross-Platform Distributed Heterogeneous Simulation of a More Electric Aircraft Power System
C. E. Lucas, E. A. Walters, O. Wasynczuk, PC Krause and Associates, Inc; Peter T. Lamm, U. S. Air Force Research Laboratory To support research and analysis requirements in the development of future power systems, a flexible and efficient means of predicting the dynamic performance of large-scale multi-disciplinary systems prior to hardware trials is crucial. With the development of Distributed Heterogeneous Simulation (DHS), the technology now exists to enable this type of investigation. Previously, DHS was shown to allow the interconnection of component simulations running on a single- or distributed-computer network and developed using any combination of a variety of commercial-off-the-shelf software packages for the Microsoft Windows operating system. However, for large-scale systems, all subsystem models may not be developed in software packages operating under Windows thereby requiring a translation of such models in order to incorporate them within a system simulation. In this paper, the DHS technique is expanded to support the UNIX operating system, thus, allowing subsystem models developed and executed on either UNIX- or Windows-based computers to be interconnected to form a dynamic system simulation. For the purpose of demonstration, a more-electric fighter (MEF) power system, such as that found on the Joint Strike Fighter (JSF), has been selected as a study system. This system is comprised of ten component models each developed using MATLAB/Simulink, EASY5, or ACSL. Utilizing the system simulation, studies have been performed to illustrate the dynamic interactions between the subsystems when simulated on a heterogeneous computer network containing both Windows- and Unix-based machines. SPIE Defense and Security Symposium Proceedings, March 2005. Contact information:...
Read MoreAutomated Average-Value Modeling of Power Electronic Sources and Loads
N. Wu, O. Wasynczuk, Purdue University; E. A. Walters, C. E. Lucas, PC Krause and Associates, Inc; Peter T. Lamm, U.S. Air Force Research Laboratory Power systems that include regulated power-electronic sources and/or loads are susceptible to potentially destabilizing interactions between these components. A variety of techniques and methodologies have been developed to characterize the small- and large displacement stability of such systems. Perhaps the most common approach is to establish the input/output impedance-versus-frequency characteristics of all sources and loads, whereby Nyquist- and/or Bode-inspired criteria may be used to characterize interconnected system stability. Essential to this methodology is a means of accurately and efficiently determining the input and/or output impedance-versus-frequency characteristics of the power electronic components that comprise the overall system. These frequency-domain characteristics can be established by (1) direct measurement, (2) exercising detailed simulations, or, more commonly, (3) using state-space average-value models. The primary disadvantage of using direct measurements is that the hardware must be available a-priori which makes it difficult and/or expensive to change or tailor the impedance characteristics if instabilities occur. Calculation of the impedance characteristics from detailed simulations is generally time consuming, especially if the low-frequency characteristics are needed, and little insight is gained as to how the impedance characteristics are affected by the various design parameters. Average-value models overcome the previous disadvantages; however, they introduce a new one. In particular, the derivation of an average value models is typically time consuming, especially if the circuit topology is complex and/or the power converter exhibits multiple load-dependent modes of operation. In this paper, an automated approach of establishing average-value models of power electronic converters of arbitrary complexity is set forth. The user-supplied inputs consist of a standard Spice-like circuit description (branch parameters and network graph) whereupon the input/output impedance-versus frequency characteristics are automatically and rapidly established. In addition to eliminating the need for the analytical derivation of average-value models, this technique readily permits the inclusion of secondary effects such as conduction losses, switching losses, and magnetic nonlinearities, to name a few. This technique has been successfully applied to characterize the output impedance of a one-quadrant dc/dc buck converter and a three-phase generator/rectifier source. Proceedings 3rd International Energy Conversion Engineering Conference, August 15-18, 2005, San Francisco,...
Read MoreVariable Communication Rates in a Distributed Simulation
E. A. Walters, M. Hasan, C. E. Lucas, PC Krause and Associates, Inc; O. Wasynczuk, Purdue University; P. T. Lamm, U.S. Air Force Research Laboratory As a result of the increased capabilities (surveillance, directed energy weapons, fuel efficiency, etc.) for both military and civilian aircraft, new architectures are being proposed for integrated power and propulsion systems. To analyze these new designs, large-scale multi-disciplinary (aerodynamic, electrical, mechanical, hydraulic, thermal, etc.) system simulations are required. To this end, distributed simulation has become a vital tool by enabling subsystem models developed using different commercial-off-the-shelf simulation programs to be interconnected to form an end-to-end system simulation that can execute orders of magnitude faster than comparatable single-model (non-distributed) implementations. Although distributed simulation has been successfully applied to numerous military aircraft systems, engineering expertise is required when selecting the fixed-rate communication intervals between subsystems to guarantee that the dynamics are adequately portrayed for all modes of operation. This engineering judgment has typically led to conservative selections wherein needless communications are performed, thereby hindering the overall simulation speed. In this paper, a new variable-communication-interval algorithm is established wherein the communication intervals are selected based upon user-specified error criteria. With this algorithm, the communication intervals for each model-to-model interface are selected independently and determined based upon the dynamics of the exchanged variables. The advantages of this technique include: reduced engineering time required to establish a distributed simulation by simply allowing error criteria to be specified, an increased assurance of system simulation accuracy, and increased simulation speeds by eliminating unnecessary communications. This technique is applied to an example system wherein it is shown that a five-fold increase in simulation speed can be achieved with the same accuracy when compared to the traditional fixed-rate approach, or a six-fold increase in accuracy can be achieved for the same simulation speed. 3rd International Energy Conversion Engineering Conference, August 15-18, 2005, San Francisco,...
Read MoreAn Algorithm for the Optimal Allocation of Subsystem Simulations within a Distributed Heterogeneous Simulation
C. E. Lucas, E. A. Walters, PC Krause and Associates, Inc; O. Wasynczuk, Purdue University; Peter T. Lamm, U. S. Air Force Research Laboratory An allocation algorithm for optimally assigning the various subsystem simulations, within a distributed heterogeneous simulation, to a specific set of computational resources has been developed. This algorithm uses a cost function that approximates the simulation execution time for each of the subsystems based upon the model complexity and the performance parameters of the available computer resources. The cost function is then evaluated to determine the optimal allocation that ensures the overall simulation execution time is minimized. In this paper, the allocation algorithm is applied to a large-scale power-electronic-based aircraft electrical power system. This study system is comprised of ten component simulations that together are modeled by 85 state variables and include 74 switching devices. Both optimal and sub-optimal allocations are considered and the predicted simulation run times are verified experimentally. SAE Transactions Journal of Aerospace, July 2005, pp. 1871-1878 and 2004 SAE Power Systems Conference, November 2-4, 2004, Reno, NV, Paper #...
Read MoreTools for Evaluation of Directed Energy Weapon Power Systems
E. A. Walters, PC Krause and Associates, Inc; S. D. Pekarek, O. Wasynczuk, Purdue University; A. C. Koenig, PC Krause and Associates, Inc; P. T. Lamm, U.S. Air Force Research Laboratory Historically, the simulations of aircraft power systems have been divided into separate mechanical (turbine engine) and electrical subsystems, wherein the coupled dynamics have been neglected. However, for future high power concepts such as Directed Energy Weapons, a coupled multi-physics design and analysis capability is required to evaluate system feasibility and establish an optimal architecture. In this paper, such a simulation environment is set forth. The environment contains tools for creating rapid component/system-level simulations. These include a distributed heterogeneous simulation toolbox for interconnecting dynamic component models created using different simulation packages and/or operating systems, as well as a partitioned finite element technique that dramatically reduces computational effort. Herein, the multi-physics tools are demonstrated for a multi-MW gyrotron system. The impact of the gyrotron load on the electrical, mechanical, and energy storage are evaluated under both transient and steady-state conditions and an attempt is made to search for architectures/ designs that minimize weight subject to maintaining stable system performance. 8th Annual Directed Energy Symposium, November 14-18, 2005, Lihue,...
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