The movement to more-electric architectures during the past decade in military and commercial airborne systems continues to increase the complexity of designing and specifying the electric power system. In particular, the electrical power system (EPS) faces challenges in meeting the highly dynamic power demands of advanced power electronics based loads.This paper explores one approach to addressing these demands by proposing an electrical equivalent of the widely utilized hydraulic accumulator which has successfully been employed in hydraulic power system on aircraft for more than 50 years.

An Intermittent Megawatt Generator (IMG) has been designed by Innovative Power Solutions (IPS) to meet the needs of future directed energy loads on high-performance aircraft. These loads significantly impact the electrical, mechanical, and thermal performance of the generator, load, and aircraft. If representative simulation models of the generator and other important subsystems can be obtained, the impact on system performance can be analyzed and optimized before the generator is deployed. The objective of this work was to utilize various modeling techniques to obtain accurate electrical, thermal, and mechanical performance models of the IMG, and to apply these models to analyze dynamic response transients to sudden load changes as seen for directed energy loads. Additionally, the models have been used to optimize the IMG control to mitigate voltage transients during these load changes.

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 in system analyses. The performance of the whole aircraft must also be considered with the combined interactions between the power and propulsion systems. The larger loading demands placed on the power and propulsion subsystems result in thrust, speed, and altitude transients that affect the whole aircraft. This results in different operating parameters for the engine. 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 of the aircraft/propulsion system. Using this method, a significant reduction in computational runtime is observed, and the airframe/turbine engine model is usable in a HIL environment. This also allows for a more complete analysis of the interactions between engine loading and aircraft performance by including some real hardware components. The dynamic interactions between aircraft subsystems highlight the need for system-level modeling using a combination of high-fidelity computer models and hardware in a real-time environment.

: Hybrid-electric military vehicles provide many advantages over conventional military vehicles powered solely by diesel or turbine engines. These advantages include improved acceleration and fuel economy, stealth capability for silent mobility and silent watch, and ability to carry future energy weapons and advanced armor protection. The U.S. Army Research, Development and Engineering Command (RDECOM) and Tank Automotive Research, Development and Engineering Center (TARDEC) have sponsored the modeling and distributed simulation of a hybrid-electric vehicle as a design and validation tool for the development of future military vehicles. This paper describes the structure of the electrical/propulsion system of the vehicle, and the modeling of the components within this system. In particular, modeling of the prime mover (a diesel engine), the generator/motor the vehicle control system, and other major components are discussed. Distributed simulation was accomplished using the Distributed Heterogeneous Simulation (DHS) tool. Specifically, the model of the system was divided into multiple subsystems, whereupon DHS was used to connect the subsystem models to form a synchronized simulation, which can be executed on one computer or multiple networked computers. In addition to increasing simulation speed, DHS also allows the interconnection between component models developed in different simulation languages, without requiring them to be translated into a common language. This advantage is particularly important if component models developed in other languages, likely from component manufacturers, are to be added to the vehicle model in the future. The performance of the vehicle system was evaluated under various operating conditions, and simulation results demonstrating the behavior of the system are presented.

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 (COTS) 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 (TM), EASY5 (TM), or ACSL (TM). 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.

A novel multirate 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 multirate 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.

A new paradigm for simulating large-scale dynamical systems is described and applied to an integrated naval power system. This approach enables the overall system simulation to be formed as an interconnection of interdependent dynamic simulations, each representing a specific electrical, mechanical, hydraulic, and/or thermal component/subsystem. Each simulation may be developed independently using possibly different commercial off-the-shelf simulation programs thereby allowing the most suitable language or tool to be used based on the design/analysis needs. The proposed simulation paradigm is applied to an advanced naval electric power system that includes a zonal dc electric distribution system and an integrated electric generation and propulsion system. The composite system simulation is implemented on a three-computer network of personal computers by interconnecting simulati ons of the constituent subsystems. It is shown that significant improvements in computational speed are achieved using this approach.

In this paper, a new technique useful for the numerical simulation of large-scale systems is presented. This approach enables the overall system simulation to be formed by the dynamic interconnection of the various interdependent simulations, each representing a specific component or subsystem such as control, electrical, mechanical, hydraulic, or thermal. Each simulation may be developed separately using possibly different commercial-off-the-shelf simulation programs thereby allowing the most suitable language or tool to be used based on the design/analysis needs. These subsystems communicate the required interface variables at specific time intervals. A discussion concerning the selection of appropriate communication intervals is presented herein. For the purpose of demonstration, this technique is applied to a detailed simulation of a representative aircraft power system, such as that found on the Joint Strike Fighter (JSF).This system is comprised of ten component models each developed using MATLAB/Simulink(TM), EASY5(TM), or ACSL(TM). When the ten component simulations were distributed across just four personal computers (PCs), a greater than 15-fold improvement in simulation speed (compared to the single-computer implementation) was achieved.

An algorithmic method of developing the state equations of complex power circuits and systems has recently been developed. In this approach, referred to as the 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.

A common approximation used in the analysis of power systems is the neglect of the dynamic saliency in synchronous machines. In this paper, it is shown that eliminating the error associated with neglecting dynamic saliency can be accomplished with the addition of a singular perturbation(s) into the machine model. By considering the elimination of error in such a way, singular-perturbation-based model-order-reduction techniques are used to derive detailed- and reduced-order models of synchronous machines where dynamic saliency is eliminated with zero error and no added numerical cost.

An automated state model generator (ASMG) is a tool for modeling and analysis of lumped-parameter power-electronic-based systems. In this modeling approach, the minimal state-space representation of the overall system is generated automatically and updated dynamically based upon the topological state of the system. However, due to the changing topology, simulation of a switched circuit using the ASMG requires the concatenation of solutions to the initial value problems (IVPs) corresponding to the time intervals between commutations. In this paper, a transformation of state variables is derived such that the states are continuous throughout the simulation process. This feature eliminates the need to re-initialize the ODE solver. The continuous state algorithm is verified on a high-pulse-count power supply and sets the stage for state-space averaging and system-level analysis of switched circuits

The state variable approach is a numerically efficient and analytically meaningful method of predicting and characterizing the transient responses of power-electronic-based systems. An automated method of establishing state-space models of switched electrical networks is considered. In this modeling approach, the minimal state-space representation of the overall system is generated dynamically as each topology is encountered. Due to the changing topology, the simulation of a switched circuit requires concatenation of the solutions of initial value problems (IVPs) corresponding to time intervals between switching events. In this paper, a transformation of state variables is derived such that the computer-generated equations have the same dimension and the new states are continuous throughout the study. This feature eliminates the need for re-initializing the ODE solver and sets the stage for automated state-space averaging and system-level analysis of switched circuits. The algorithm is verified using a practical example of a synchronous machine-rectifier system

When analyzing machine/converter systems it is convenient to represent the stator variables in physical (abc) form. It has been shown that a physical-variable voltage-behind-reactance form of the synchronous machine model can be derived which is numerically more efficient than existing physical-variable models. In this research, a new voltage-behind-reactance model is derived which incorporates the effects of magnetic saturation. This model is shown to have the same numerical efficiency of the unsaturated model and is readily implemented in either circuit-based or differential-equation based simulation languages. An example system is provided which demonstrates the accuracy and efficiency of this model for a wide-range in operating conditions.

In this paper, motivations for neglecting dynamic saliency in the detailed models of power electronic based systems are presented. A new method of neglecting dynamic saliency is then introduced in which approximate operational impedances are derived from original dynamic salient models. New machine parameters are obtained by fitting to the approximate impedance curves, yielding model parameters in which dynamic saliency is eliminated. An example synchronous machine/converter system is provided that demonstrates the accuracy and increased simulation efficiency resulting from this technique. Therein, errors resulting from neglecting dynamic saliency are reduced from greater than 25% using traditional approximations to less than 0.6%. In addition, simulations using the new approximate model are greater than 48% faster than simulations based upon the original dynamic salient model.