Design and simulation of a fuel cell hybrid emergency power system for a more electric aircraft : evaluation of energy management schemes

As the aircraft industries are moving toward more electric aircraft (MEA), the electrical peak load seen by the main and emergency generators becomes higher than in conventional aircraft. Consequently, there is a major concern regarding the aircraft emergency system, which consists of a ram air turbine (RAT) or air driven generator (ADG), to fulfill the load demand during critical situations; particularly at low aircraft speed where the output power is very low. A potential solution under study by most aircraft manufacturers is to replace the air turbine by a fuel cell hybrid system, consisting of fuel cell combined with other high power density sources such as supercapacitors or lithium-ion batteries. To ensure the fuel cell hybrid system will be able to meet the load demand, it must be properly designed and an effective energy management strategy must be tested with real situations load profile. This work aims at designing a fuel cell emergency power system of a more electric aircraft and comparing different energy management schemes (EMS); with the goal to ensure the load demand is fully satisfied within the constraints of each energy source. The fuel cell hybrid system considered in this study consists of fuel cell, lithium-ion batteries and supercapacitors, along with associated DC-DC and DC-AC converters. The energy management schemes addressed are state-of-the-art, most commonly used energy management techniques in fuel cell vehicle applications and include: the state machine control strategy, the rule based fuzzy logic strategy, the classical PI control strategy, the frequency decoupling/fuzzy logic control strategy and the equivalent consumption minimization strategy (ECMS). Moreover, a new optimal scheme based on maximizing the instantaneous energy of batteries/supercapacitors, to improve the fuel economy is proposed. An off-line optimization based scheme is also developed to ascertain the validity of the proposed strategy in terms of fuel consumption. The energy management schemes are compared based on the following criteria: the hydrogen consumption, the state of charges of the batteries and supercapacitors and the overall system efficiency. Moreover the stress on each energy source, which impacts their life cycle, are measured using a new approach based on the wavelet transform of their instantaneous power. A simulation model and an experimental test bench are developed to validate all analysis and performances. The main results obtained are as follows: the state machine control scheme provided a slightly better efficiency and stresses on the batteries and supercapacitors. The classical PI control and the proposed scheme had the lowest fuel consumption and more use of the battery energy. As expected, the lowest fuel cell stress and lowest use of the battery energy was achieved with the frequency decoupling and fuzzy logic scheme, but at the expense of more fuel consumption and lower overall efficiency. The DC bus or supercapacitor voltage was maintained nearly constant for all the schemes. Also, the proposed strategy performed slightly better than the ECMS in terms of efficiency and fuel consumption, with an increase in fuel economy by 3 %. The energy management scheme suitable for a MEA emergency system should be a multischeme EMS such that each scheme is chosen based on a specific criterion to prioritize. As an example, depending on the operating life of each energy source, the energy management strategy can be chosen to either minimise the stress on the fuel cell system, the battery system or supercapacitor system, hence maximizing the life cycle of the hybrid power system. Also if the target is to reduce the fuel consumption, the proposed or the classical PI strategies are better alternatives

Descriptive analysis of viability of fuel saving in commercial aircraft through the application of photovoltaic cells

This paper presents the analysis of the technical feasibility to use a photovoltaic system to supply the electrical demand on two referential commercial aircraft, Airbus A340–300 and Cessna Conquest 441. The methodology approach comprises a process given by the selection of the photovoltaic technology, the calculation of the available solar radiation, the determination of the electrical demand, the layout definition of solar cells, the photovoltaic system capacity calculation, the estimation of the photovoltaic system weight, the estimation of fuel savings for photovoltaic system equipped aircrafts, and finally, the extrapolation of results to other aircrafts. The study concludes that the use of photovoltaic technology to supply power to the aircraft electrical system can result viable from the point of view of operational profitability, generating savings in fuel consumption. These fuel savings depend on the type of aircraft, the flying route and schedules of operation.El documento sera publicado en la versión impresa de la revista Volume 51, November 2015, Pages 138–15

AN INNOVATIVE ALGORITHM FOR A HYBRID FC/BATTERY SYSTEM ENERGY MANAGEMENT

Purpose. This paper targets to manage the energy of a hybrid fuel-cell (FC)/battery power system using an innovative algorithm. The hybrid FC/Battery power system is based on four stacks PEM FCs and a NiMH battery, boost and buck DC choppers for controlling the FC and the battery input currents respectively and a developed algorithm both for managing the power system energies and for delivering the FC and the battery reference output voltages compulsory for the DC/DC converters control circuits. The study is verified by means of computer simulations using MATLAB/Simulink where several cases of the battery SOC and the power demand levels were taken into account. The results demonstrate a good functioning of the proposed hybrid FC/Battery power system managing algorithm.Мета. Стаття спрямована на управління енергією гібридної системи живлення від паливного елемента/акумулятора за допомогою інноваційного алгоритму. Гібридна система живлення паливний елемент/акумулятор заснована на чотирьох батареях паливних елементів з протонообмінними мембранами та NiMH акумуляторі, підсилювачах і послаблювачах постійного струму для управління паливним елементом та вхідними струмами батареї відповідно та розробленому алгоритмі як для управління енергією енергосистеми, так і для подачі на паливний елемент і акумулятор вихідної напруги, обов'язкової для схем управління перетворювачами постійного струму. Дослідження перевірено за допомогою комп’ютерного моделювання з використанням MATLAB/Simulink, де було враховано кілька випадків рівня заряду акумулятора та рівнів споживання енергії. Результати демонструють добре функціонування запропонованого гібридного алгоритму управління системою живлення від паливного елемента/акумулятора

Examining the Conceptual Design Process for Future Hybrid-Electric Rotorcraft

Hybrid-electric propulsion systems introduce immense complexity and numerous design challenges not previously encountered in aircraft design. Traditional conceptual-level rotorcraft design approaches may not adequately capture the level of propulsion system detail desired for hybrid-electric vehicle conceptual design. As part of a NASA Small Business Innovative Research (SBIR) Phase II contract, Empirical Systems Aerospace (ESAero) investigated the implementation of several hybrid-electric propulsion architectures onto three rotorcraft configurations. Unique hybrid-electric variants of these configurations were compared against their conventionally-powered counterparts using typical metrics such as payload, range, and energy efficiency. The feasibility and performance of these vehicles was also investigated in the +15 and +30-year timeframes based on third-party estimations for future component performance. Using the lessons learned during this trade study, ESAero then conducted a conceptual design effort for a hybrid-electric tiltrotor demonstrator based on the XV-15. A detailed integration of the hybrid-electric propulsion system into the vehicle airframe was also performed. The hybrid-electric XV-15 concept vehicle was estimated to achieve a 10% reduction in cruise fuel consumption compared to the original NASA XV-15 at the cost of increasing the vehicle empty weight by almost 25%. The success of this design effort suggests that the design of a manned, hybrid-electric tiltrotor is technically feasible at current technology levels

Control and Optimization of Fuel Cell Based Powertrain for Automotive Applications

Fuel cell powered electric vehicles, with fast-refueling time, high energy density, and zero CO2 emissions, are becoming a promising solution for future fossil-free transportation. However, the relatively slow dynamic response and the inability of recovering the regenerative energy make vehicles solely powered by fuel cells not an immediately attractive solution. Instead, hybrid vehicles powered by fuel cells combined with energy buffers such as batteries and supercapacitors could be of more interest. Due to the unique characteristics of each energy buffer, the vehicle performance may vary with the hybrid energy storage system configuration. This thesis performs a comprehensive study on various energy storage configurations for applications in fuel cell hybrid electric vehicles. This thesis first examines the fuel cell/supercapacitor passive hybrid configuration where the fuel cell and supercapacitor share the same DC-link voltage. The power distribution between them is inherently determined by their internal resistances. Therefore, the DC-link voltage varies and depends on the vehicle power demand. In this work, a fuel cell/supercapacitor passive hybrid powertrain is first modeled and evaluated. Simulation results show that the energy efficiency is 53%–71% during propulsion and 84%–94% during braking, respectively. Moreover, a 3 kW lab-scale fuel cell/supercapacitor passive hybrid system is designed and investigated. Experimental results show that the fuel cell takes time to respond to a load change, while the supercapacitor provides the transient power, which makes it possible to downsize the fuel cell.Since the passive configuration loses the active controllability, this thesis further considers a fully-active fuel cell/supercapacitor system to improve the controllability of the power distribution. This configuration requires a boost converter for the fuel cell and a buck-boost converter for the supercapacitor. In this work, an adaptive power split method is used to smooth the fuel cell current and prevent the supercapacitor from exceeding its lower and upper charge limits. The cut-off frequency of the low-pass filter is adaptively controlled by the spectrum area ratio. Experimental results show that the supercapacitor state-of-charge is effectively controlled within the desired range. Moreover, a load disturbance compensator is proposed and demonstrated to improve the control performance such that the DC-link voltage fluctuation caused by the load current variation is significantly reduced.This thesis also investigates the cost-effectiveness of different energy buffers hybridized with fuel cells in various trucking applications. First, a chance-constraint co-design optimization problem is formulated. Convex modeling steps are presented to show that the problem can be decomposed and solved using convex programming. Results show that the power rating of the electric machine can be dramatically reduced when the delivered power is satisfied in a probabilistic sense. Moreover, the hybridization of fuel cells with lithium-ion batteries results in the lowest cost while the vehicle using lithium-ion capacitors as the energy buffer can carry the heaviest payload. This work also develops a robust co-design optimization framework considering the uncertainties in parameters (e.g., vehicle movement) and design decision variables (e.g., scaling factors of fuel cells and batteries). Results show that these uncertainties might propagate to uncertainties in state variables (e.g., battery energy) and optimization variables (e.g., battery power), leading to a larger battery capacity and therefore a higher total cost in robust optimal solutions. In summary, this thesis performs a comprehensive study on control and optimization of fuel cell based powertrains for automotive applications. This will provide a guidance on component selection and sizing, as well as powertrain system configuration and optimization for design of fuel cell powered electric vehicles

An adaptive power split strategy with a load disturbance compensator for fuel cell/supercapacitor powertrains

Electric vehicles powered by fuel cell and supercapacitor hybrid power sources are of great interest. However, the power allocation between each power source is challenging and the DC bus voltage fluctuation is relatively significant in cascaded PI control schemes. This paper develops a power control strategy with an adjustable cut-off frequency, using an artificial potential field, to adaptively split the load current between the fuel cell and the supercapacitor under various load conditions. The adaptive cut-off frequency is calculated by cutting the load frequency spectrum with an allocation ratio that changes with the supercapacitor state of charge. Therefore, the relatively lower frequency portion of the load current is provided by the fuel cell and the supercapacitor handles the higher frequency portion. To enhance the control performance of the DC bus voltage regulation against the load disturbance, a load disturbance compensator is introduced to suppress the DC bus voltage fluctuation when the load variation occurs, which is implemented by a feed-forward controller that can compensate the load current variation in advance. The effectiveness of the proposed strategy is validated by extensive experiments

The Enabling Technologies for a Quasi-Zero Emissions Commuter Aircraft

The desire for greener aircraft pushes both academic and industrial research into developing technologies, manufacturing, and operational strategies providing emissions abatement. At time of writing, there are no certified electric aircraft for passengers’ transport. This is due to the requirements of lightness, reliability, safety, comfort, and operational capability of the fast air transport, which are not completely met by the state-of-the-art technology. Recent studies have shown that new aero-propulsive technologies do not provide significant fuel burn reduction, unless the operational ranges are limited to short regional routes or the electric storage capability is unrealistically high, and that this little advantage comes at increased gross weight and operational costs. Therefore, a significant impact into aviation emissions reduction can only be obtained with a revolutionary design, which integrates disruptive technologies starting from the preliminary design phase. This paper reviews the recent advances in propulsions, aerodynamics, and structures to present the enabling technologies for a low emissions aircraft, with a focus on the commuter category. In fact, it is the opinion of the European Community, which has financed several projects, that advances on the small air transport will be a fundamental step to assess the results and pave the way for large greener airplanes

Energy: A continuing bibliography with indexes, issue 12

This bibliography lists 584 reports, articles, and other documents introduced into the NASA scientific and technical information system from October 1, 1976 through December 31, 1976