J. Jatskevich, O. Wasynczuk, S. D. Pekarek, Purdue University; C. E. Lucas, E. A. Walters, PC Krause and Associates, Inc. In the analysis of power-electronic-based energy conversion systems, it is important to identify the operational modes of the associated converters and inverters. However, as the number of switching elements increases, it becomes more difficult to analytically establish all possible modes of operation. In this paper, a modeling technique is described wherein a state-space representation of the overall system is generated automatically and updated dynamically as each new topology is encountered. Utilizing this approach, it becomes possible to identify the operational modes of converters and inverters based upon the cyclically repeated sequences of topologies that can be observed during steady-state operation. To demonstrate this technique, an example system comprised of a 6-phase synchronous machine, rectifier, and interphase transformer is considered. This system exhibits several distinct modes of operation that depend upon specific circuit connections. These operating modes are automatically identified using the proposed methodology and the results are compared with measured dynamic performance. SAE Transactions Journal of Aerospace, sec. 1, set 3, Month, 2000, pp....
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 MoreAutomated State Model Generator for Simulation and Analysis of Power Electronic Systems
J. Jatskevich, University of British Columbia; O. Wasynczuk, Purdue University; C. E. Lucas, E. A. Walters, PC Krause and Associates, Inc. An algorithmic method of developing the state equations of complex power circuits and systems has recently been developed. In this approach, referred to as he Automated State Model Generator (ASMG), the system is described by the pertinent branch parameters and the circuit topology; however, unlike existing circuit-based approaches, the difference equations are not implemented at the branch level. Instead, the composite system state equations are established automatically and updated dynamically for each new topology of the switching network. Since the state equations are available, linearization, eigensystem analysis, and model-order reduction can be performed quickly and conveniently at the system level. In addition, it becomes possible to identify the operational modes of converters and inverters based on the cyclically repeated sequence of topologies. The ASMG includes a built-in switching logic for common power-electronic switching devices. The proposed simulation approach is particularly effective when modeling advanced power electronic systems that include special-purpose multi-phase electrical machines, transformers, and other components that are not available in the libraries of commonly used circuit simulators. An ASMG toolbox that is compatible with MATLAB/SIMULINK has been developed and used to implement a detailed simulation of a 6-phase generator/rectifier system. Proceedings 6th International Conference of Computational Methods for the Solution of Electrical and Electromagnetic Engineering Problems, September 10-12, 2003, Split, Croatia, WIT Press, pp....
Read MoreAn Efficient Multi-Rate Simulation Technique for Power Electronic-Based Systems
S. D. Pekarek, O. Wasynczuk, Purdue University; E. A. Walters, J. V. Jatskevich, C. E. Lucas, N. Wu, PC Krause and Associate, Inc; P. T. Lamm, U.S. Air Force Research Laboratory A novel multi-rate method of simulating power-electronic-based systems containing a wide range of time scales is presented. In this method, any suitable integration algorithm, with fixed or variable time-step, can be applied to the fast and/or slow subsystems. The subsystems exchange coupling variables at a communication interval that can be fixed or varied dynamically depending upon the state of the system variables. The proposed multi-rate method is applied to two example power systems that include power-electronic subsystems. Increases in simulation speed of 183-281% over established single-rate integration algorithms are demonstrated. IEEE Transactions on Power Systems, vol. 19, no. 1, February 2004, pp....
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 MoreGCU for Megawatt Class Directed Energy Weapons Pulse Generators
Lev Sorkin, Innovative Power Solutions, LLC; E. A. Walters, PC Krause and Associates, Inc. Directed Energy weapon (DEW) systems are being developed for both ground and airborne applications. Typically, they consist of microwave or laser powered guns. Both the microwave application and the diode based laser applications require significant amount of power. This power ranges from several hundred kilowatts (kW) for microwave applications to Megawatts (MW) for laser applications. The laser application requires that the full power be available for short duration, typically 5 seconds, which could be repeated several times with short pauses in between. The control of a generator, which delivers Megawatt of the intermittent power greatly differs from the of normal steady state generator control. It poses significant challenges. Application of power (and for this matter its removal) is a transient phenomenon that takes time and its effects ripple through the whole system. In the case at hand, the large applied power, which is required for a short duration, can have a more significant effect on the system. Furthermore, it is imperative that the full power will be available for the required duration with no degradation in quality on both ends (application and removal). There are four entities that interact affecting the performance of the...
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