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Technical Paper

Source Management of Aircraft Electrical Power Systems with Hardware in the Loop Verification

Future aircraft will demand a significant amount of electrical power to drive primary flight control surfaces. The electrical system architecture needed to source these flight critical loads will have to be resilient, autonomous, and fast. Designing and ensuring that a power system architecture can meet the load requirements and provide power to the flight critical buses at all times is fundamental. In this paper, formal methods and linear temporal logic are used to develop a contactor control strategy to meet the given specifications. The resulting strategy is able to manage multiple contactors during different types of generator failures. In order to verify the feasibility of the control strategy, a real-time simulation platform is developed to simulate the electrical power system. The platform has the capability to test an external controller through Hardware in the Loop (HIL).
Technical Paper

A Predictive Reference Governor for Synchronous Generator Regulation with a Pulsed Constant Power Load

In this paper, first an analytical model of a synchronous generator with a pulsed constant power load (CPL) is developed and numerically compared with a detailed simulation model. The analytical model is shown to possess good predictive abilities, thus enabling its use for control purposes. Second, the generator has a proportionalintegral (PI) control inner-loop, whose task is to regulate the generator’s output voltage to a desired reference. A novel outer-loop predictive reference governor (PRG) is designed and tested via simulation. The PRG uses the analytical model to predict the output behavior of the generator over a short time window, and continuously modifies the reference given to the inner-loop in order to maintain stringent steady-state requirements, in spite of demanding power requirements at the CPL. Simulation results illustrate the significant performance advantages of using the PRG versus using the inner-loop PI controller alone.
Technical Paper

A Multi-Domain Component Based Modeling Toolset for Dynamic Integrated Power and Thermal System Modeling

Design of modern aircraft relies heavily on modeling and simulation for reducing cost and improving performance. However, the complexity of aircraft architectures requires accurate modeling of dynamic components across many subsystems. Integrated power and thermal modeling necessitates dynamic simulations of liquid, air, and two-phase fluids within vapor cycle system components, air cycle machine and propulsion components, hydraulic components, and more while heat generation of many on-board electrical components must also be precisely calculated as well. Integration of these highly complex subsystems may result in simulations which are too computationally expensive for quickly modeling extensive variations of aircraft architecture, or will require simulations with reduced accuracy in order to provide computationally inexpensive models.
Technical Paper

Two Phase Thermal Energy Management System

The Air Force Research Laboratory (AFRL), in cooperation with the University of Dayton Research Institute (UDRI) and Fairchild Controls Corporation, is building a test facility to study the use of advanced vapor cycle systems (VCS) in an expanded role in aircraft thermal management systems (TMS). It is dedicated to the study and development of VCS control and operation in support of the Integrated Vehicle ENergy Technology (INVENT) initiative. The Two Phase Thermal Energy Management System (ToTEMS1) architecture has been shown through studies to offer potential weight, cost, volume and performance advantages over traditional thermal management approaches based on Air Cycle Systems (ACS). The ToTEMS rig will be used to develop and demonstrate a control system that manages the system capacity over both large amplitude and fast transient changes in the system loads.
Technical Paper

Integrated Engine/Thermal Architecture Model Interface Development

Integrated system-level analysis capability is critical to the design and optimization of aircraft thermal, power, propulsion, and vehicle systems. Thermal management challenges of modern aircraft include increased heat loads from components such as avionics and more-electric accessories. In addition, on-going turbine engine development efforts are leading to more fuel efficient engines which impact the traditionally-preferred heat sink - engine fuel flow. These conditions drive the need to develop new and innovative ways to manage thermal loads. Simulation provides researchers the ability to investigate alternative thermal architectures and perform system-level trade studies. Modeling the feedback between thermal and engine models ensures more accurate thermal boundary conditions for engine air and fuel heat sinks, as well as consideration of thermal architecture impacts on engine performance.
Technical Paper

Refrigerant Charge Management and Control for Next-Generation Aircraft Vapor Compression Systems

Vapor compression systems (VCS) offer significant benefits as the backbone for next generation aircraft thermal management systems (TMS). For a comparable lift, VCS offer higher system efficiencies, improved load temperature control, and lower transport losses than conventional air cycle systems. However, broad proliferation of VCS for many aircraft applications has been limited primarily due to maintenance and reliability concerns. In an attempt to address these and other VCS system control issues, the Air Force Research Laboratory has established a Vapor Cycle System Research Facility (VCSRF) to explore the practical application of dynamic VCS control methods for next-generation, military aircraft TMS. The total refrigerant mass contained within the closed refrigeration system (refrigerant charge) is a critical parameter to VCS operational readiness. Too much or too little refrigerant can be detrimental to system performance.
Technical Paper

An Integrated Chemical Reactor-heat Exchanger based on Ammonium Carbamate

In this work we present our recent effort in developing a novel heat exchanger based on endothermic chemical reaction (HEX reactor). The proposed HEX reactor is designed to provide additional heat sink capability for aircraft thermal management systems. Ammonium carbamate (AC) which has a decomposition enthalpy of 1.8 MJ/kg is suspended in propylene glycol and used as the heat exchanger working fluid. The decomposition temperature of AC is pressure dependent (60°C at 1 atmosphere; lower temperatures at lower pressures) and as the heat load on the HEX increases and the glycol temperature reaches AC decomposition temperature, AC decomposes and isothermally absorbs energy from the glycol. The reaction, and therefore the heat transfer rate, is controlled by regulating the pressure within the reactor side of the heat exchanger. The experiment is designed to demonstrate continuous replenishment of AC.
Technical Paper

In-situ Charge Determination for Vapor Cycle Systems in Aircraft

The Air Force Research Laboratory (AFRL), in cooperation with the University of Dayton Research Institute (UDRI) and Fairchild Controls Corporation, is operating an in-house advanced vapor compression refrigeration cycle system (VCS) test rig known as ToTEMS (Two-Phase Thermal Energy Management System). This test rig is dedicated to the study and development of VCS control and operation in support of the Energy Optimized Aircraft (EOA) initiative and the Integrated Vehicle ENergy Technology (INVENT) program. Previous papers on ToTEMS have discussed the hardware setup and some of the preliminary data collected from the system, as well as the first steps towards developing an optimum-seeking control scheme. A key goal of the ToTEMS program is to reduce the risk associated with operating VCS in the dynamic aircraft environment.
Technical Paper

Cycle-Based Vapor Cycle System Control and Active Charge Management for Dynamic Airborne Applications

Numerous previous studies have highlighted the potential efficiency improvements which can be provided to aircraft thermal management systems by the incorporation of vapor cycle systems (VCS), either in place of, or in conjunction with, standard air cycle systems, for providing the needed thermal management for aircraft equipment and crews. This paper summarizes the results of a cycle-based VCS control architecture as tested using the Vapor Cycle System Research Facility (VCSRF) in the Aerospace Systems Directorate of the Air Force Research Laboratory at Wright-Patterson Air Force Base. VCSRF is a flexible, dynamic, multi-evaporator VCS which incorporates electronic expansion valves and a variable speed compressor allowing the flexibility to test both components and control schemes. The goal of this facility is to reduce the risk of incorporating VCS into the thermal management systems (TMS) of future advanced aircraft.
Journal Article

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

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

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.
Technical Paper

GCU for Megawatt Class Directed Energy Weapons Pulse Generators

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.
Journal Article

Electrical Accumulator Unit for the Energy Optimized Aircraft

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.
Journal Article

A MATLAB Simulink Based Co-Simulation Approach for a Vehicle Systems Model Integration Architecture

In this paper, a MATLAB-Simulink based general co-simulation approach is presented which supports multi-resolution simulation of distributed models in an integrated architecture. This approach was applied to simulating aircraft thermal performance in our Vehicle Systems Model Integration (VSMI) framework. A representative advanced aircraft thermal management system consisting of an engine, engine fuel thermal management system, aircraft fuel thermal management system and a power and thermal management system was used to evaluate the advantages and tradeoffs in using a co-simulation approach to system integration modeling. For a system constituting of multiple interacting sub-systems, an integrated model architecture can rapidly, and cost effectively address technology insertions and system evaluations. Utilizing standalone sub-system models with table-based boundary conditions often fails to effectively capture dynamic subsystem interactions that occurs in an integrated system.
Technical Paper

Automated 6DOF Model Generation and Actuator Sizing within AFSIM

The Air Force Research Laboratory has interest in automatically generating the extensive aerodynamic databases essential for six degree of freedom (6DOF) models and the use of 6DOF models for design. To be most useful, automation must include all aspects of producing the database including meshing, control surface deflections, running the CFD solution, and storage of the results. This effort applies newly-developed software to produce the desired results. Firstly, AFRL software called Computational Aircraft Prototype Syntheses (CAPS) allows automated meshing using the Advancing Front Local Reconnection (AFLR) software from Mississippi State University1 and automated control surface deflection using Engineering Sketch Pad (ESP) software from MIT/Syracuse. CAPS includes the ability to run the NASA CFD code FUN3D and interpret the FUN3D results via an Application Interface Module (AIM). This may sound like a complicated process.
Journal Article

Integrated Power and Thermal Management System (IPTMS) Demonstration Including Preliminary Results of Rapid Dynamic Loading and Load Shedding at High Power

An IPTMS hardware facility has been established in the laboratories of the Aerospace Systems Directorate of the Air Force Research Laboratory (AFRL) at Wright-Paterson Air Force Base (WPAFB). This hardware capability was established to analyze the transient behavior of a high power Electrical Power System (EPS) coupled virtually to a Thermal Management System (TMS) under fast dynamic loading conditions. The system incorporates the use of dynamic electrical load, engine emulation, energy storage, and emulated thermal loads operated to investigate dynamics under step load conditions. Hardware architecture and control options for the IPTMS are discussed. This paper summarizes the IPTMS laboratory demonstration system, its capabilities, and preliminary test results.