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Journal Article

Impact of Transient Operating Conditions on Electrical Power System and Component Reliability

2014-09-16
2014-01-2144
Transient operating conditions in electrical systems not only have significant impact on the operating behavior of individual components but indirectly affect system and component reliability and life. Specifically, transient loads can cause additional loss in the electrical conduction path consisting of windings, power electronic devices, distribution wires, etc., particularly when loads introduce high peak vs. average power ratios. The additional loss increases the operating temperatures and thermal cycling in the components, which is known to reduce their life and reliability. Further, mechanical stress caused by dynamic loading, which includes load torque cycling and high peak torque loading, increases material fatigue and thus reduces expected service life, particularly on rotating components (shaft, bearings).
Journal Article

Software Tools for Efficient Model-Based Design of Energy Optimized Aircraft

2012-10-22
2012-01-2176
The diverse and complex requirements of next-generation energy optimized aircraft (EOA) demand detailed transient and dynamic model-based design (MBD) to ensure the proper operation of numerous interconnected and interacting subsystems. In support of the U.S. Air Force's Integrated Vehicle Energy Technology (INVENT) program, several software tools have been developed and are in use that aid in the efficient MBD of next-generation EOA. Among these are subsystem model libraries, automated subsystem model verification test scripts, a distributed co-simulation application, and tools for system configuration, EOA mission building, data logging, plotting, post-processing, and visualization, and energy flow analysis. Herein, each of these tools is described. A detailed discussion of each tool's functionality and its benefits with respect to the goal of achieving successful integrated system simulations in support of MBD of EOA is given.
Technical Paper

Large Displacement Stability by Design for Robust Aircraft Electric Power Systems

2012-10-22
2012-01-2197
More electric aircraft (MEA) architectures have increased in complexity leading to a demand for evaluating the dynamic stability of their advanced electrical power systems (EPS). The system interactions found therein are amplified due to the increasingly integrated subsystems and on-demand power requirements of the EPS. Specifically, dynamic electrical loads with high peak-to-average power ratings as well as regenerative power capabilities have created a major challenge in design, control, and integration of the EPS and its components. Therefore, there exists a need to develop a theoretical framework that is feasible and useful for the specification and analysis of the stability of complex, multi-source, multi-load, reconfigurable EPS applicable to modern architectures. This paper will review linear and nonlinear system stability analysis approaches applicable to a scalable representative EPS architecture with a focus on system stability evaluation during large-displacement events.
Technical Paper

A Modular Power System Architecture for Military and Commercial Electric Vehicles

2010-11-02
2010-01-1756
Numerous modern military and commercial vehicles rely on portable, battery-powered sources for electric energy. Due to their highly specialized functions these vehicles are typically custom-designed, produced in limited numbers, and expensive. To mitigate the power system's contribution to these undesirable characteristics, this paper proposes a modular power system architecture consisting of “smart” power battery units (SPUs) that can be readily interconnected in numerous ways to provide distributed and coordinated system power management. The proposed SPUs contain a battery power source and a power electronics converter. They are compatible with multiple battery chemistries (or any energy storage device that can produce a terminal voltage), allowing them to be used with both existing and future energy storage technologies.
Journal Article

Standardized Electrical Power Quality Analysis in Accordance with MIL-STD-704

2010-11-02
2010-01-1755
MIL-STD-704 defines power quality in terms of transient, steady-state, and frequency-domain metrics that are applicable throughout a military aircraft electric power system. Maintaining power quality in more electric aircraft power systems has become more challenging in recent years due to the increase in load dynamics and power levels in addition to stricter requirements of power system characteristics during a variety of operating conditions. Further, power quality is often difficult to assess directly during experiments and aircraft operation or during data post-processing for the integrated electric power system (including sources, distribution, and loads). While MIL-STD-704 provides guidelines for compliance testing of electric load equipment, it does not provide any instruction on how to assess the power quality of power sources or the integrated power system itself, except the fact that power quality must be satisfied throughout all considered operating conditions.
Journal Article

A Direct Torque-Controlled Induction Machine Bidirectional Power Architecture for More Electric Aircraft

2009-11-10
2009-01-3219
The performance of a more-electric aircraft (MEA) power system electrical accumulator unit (EAU) architecture consisting of a 57000 rpm induction machine (IM) coupled to a controllable shaft load and controlled using direct torque control (DTC) is examined through transient modeling and simulation. The simplicity and extremely fast dynamic torque response of DTC make it an attractive choice for this application. Additionally, the key components required for this EAU system may already exist on certain MEA, therefore allowing the benefits of EAU technology in the power system without incurring a significant weight penalty. Simulation results indicate that this architecture is capable of quickly tracking system bus power steps from full regenerative events to peak load events while maintaining the IM's speed within 5% of its nominal value.
Technical Paper

Integrated Electrical System Model of a More Electric Aircraft Architecture

2008-11-11
2008-01-2898
A primary challenge in performing integrated system simulations is balancing system simulation speeds against the model fidelity of the individual components composing the system model. Traditionally, such integrated system models of the electrical systems on more electric aircraft (MEA) have required drastic simplifications, linearizations, and/or averaging of individual component models. Such reductions in fidelity can take significant effort from component engineers and often cause the integrated system simulation to neglect critical dynamic behaviors, making it difficult for system integrators to identify problems early in the design process. This paper utilizes recent advancements in co-simulation technology (DHS Links) to demonstrate how integrated system models can be created wherein individual component models do not require significant simplification to achieve reasonable integrated model simulation speeds.
Journal Article

Electrical Accumulator Unit for the Energy Optimized Aircraft

2008-11-11
2008-01-2927
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.
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