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 MoreAverage-Value Model of a High-Frequency Six-Phase Generation System
Juri Jatskevich University of British Columbia; E. A. Walters, C. E. Lucas, PC Krause and Associates, Inc; Peter T. Lamm U.S. Air Force Research Laboratory In this paper, a parametric average-value modeling approach is applied to a high-frequency six-phase aircraft generation subsystem. This approach utilizes a detailed switch-level model of the system to numerically establish the averaged dynamic relationships between the ac inputs of the rectifier and the dc-link outputs. A comparison between the average-value and detailed models is presented, wherein, the average-value model is shown to accurately portray both the large-signal time-domain transients and the small-signal frequency-domain characteristics. Since the discontinuous switching events are not present in the average-value model, significant gains can be realized in the computational performance. For the study system, the developed average-value simulation executed more than two orders of magnitude faster than the detailed simulation. SAE Transactions Journal of Aerospace, July 2005, pp. xxx, and 2004 SAE Power Systems Conference, November 2-4, 2004, Reno, NV, Paper...
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,...
Read MoreMulti-Fidelity Models for Design and Analysis of Directed Energy Weapon Power Systems
E. Walters, PC Krause and Associates, Inc; S. Pekarek, O. Wasynczuk, Purdue University; A. Koenig, J. Wells, B. P. Loop, PC Krause and Associates, Inc; P. Lamm, U. S. Air Force Research Laboratory Historically, the design of aircraft electrical systems has been divided into separate mechanical (turbine engine) and electrical subsystems, wherein the coupled dynamics have been ignored until hardware integration. However, future loads such as Directed Energy Weapons (DEW), a coupled multi-physics design and analysis capability is required to evaluate system feasibility and establish optimal components in the context of a system-level architecture. In this paper, modeling and simulation techniques that provide a backbone for such design and analysis is set forth. Simulation techniques include a distributed heterogeneous simulation toolbox for interconnecting dynamic component models created using different simulation packages and/or operating systems. Modeling tools include a partitioned finite element technique and a field reconstruction technique that dramatically reduces the computational effort required to perform fields-based simulation of electric machines. Herein, the multi-physics tools are demonstrated for a multi-MW DEW system. The impact of the DEW 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. 9th Annual Directed Energy Symposium, October 30-November 2, 2006, Albuquerque, NM. Contact Information:...
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