Dynamic management of electrical and thermal power

03/02/2015
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Dynamic management of electrical and thermal power

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application/pdf Dynamic management of electrical and thermal power Kader Benmachou, Mael Guerin
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Dynamic management of electrical and thermal power

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Dynamic management of electrical and thermal power Kader Benmachou (1), Mael Guerin (2) 1 : Liebherr Aerospace Toulouse SAS, 408 Avenue des Etats-Unis, BP52010, 31016 Toulouse kader.benmachou@liebherr.com 2 : Thales Avionics Electrical Systems, 41 boulevard de la République, BP 53 78401 Chatou mael.guerin@fr.thalesgroup.com, Abstract In order to contribute to the global weight reduction of the systems for more electrical aircraft, Liebherr Aerospace Toulouse and Thales Avionics Electrical Systems decided to take an innovative system approach by going beyond the traditional ATA chapters. Their main focus is on developing an electrical and thermal power management approach on a large perimeter including the major electrical loads on the aircraft. Introduction The environmental objectives defined by the Advisory Council for Aeronautics Research in Europe (ACARE) and the French Civil Aviation Research Council (CORAC) are very ambitious: 50% reduction of CO2 emissions, 80% of NOx emissions and 50% of perceived noise in horizon 2020. Only technological breakthrough at system level, with the introduction of more electrical technologies, will enable to address these objectives. In this context, Liebherr Aerospace Toulouse and Thales Avionics Electrical Systems have joined their efforts to take an innovative system approach by going beyond the traditional ATA chapters. Their main focus is to optimize the electrical power consumption and the needs for cooling the system architecture by developing a global electrical and thermal power management approach. This will contribute to the weight reduction of the systems for more electrical aircraft. The system architecture analysis was conducted by considering the major electrical loads with a specific focus on: - engine starter/generator - electrical conversion - electrical driven air conditioning system - cooling systems These activities were carried out in the frame of GETI research project (“Gestion dynamique de la puissance Electrique et de la ThermIque” − dynamic management of electrical and thermal power) financially supported by the French Civil Aviation Authority (DGAC). System architecture definition by considering thermal and electrical aspects The design of an aircraft electrical system without a strong knowledge of the thermal aspects, in particular the operating time of the different electrical loads (compressors for air conditioning system, fans, wing ice protection system,…) leads to an architecture with converters dedicated to their electrical loads. The resulting number of converters drives to an overweighed architecture with high direct maintenance costs. Moreover, safety margins would be applied during the sizing of each system/components without considering the dispatch capabilities of other parts of the architecture system. This would lead to an unnecessary oversizing of equipments. The design of aircraft architectures in a global approach by considering electrical and thermal aspects enables to perform some optimizations, as described hereafter: - Possibility to work on the power balance of each power supply channel in order to release the constraints on the networks and by considering power consumptions required for the major loads according to their operating time - Rationalization of resources to decrease the converters number by sharing for example the inverter between loads with different operating time. This approach also enable reconfigurations capabilities on failure cases to increase the overall availability. The global analysis at thermal and electrical point of view of the system architectures in failure modes may also contribute to the weight reduction of the system. As an example, in case of the failure of one of the electrical resources, the performance of the air conditioning system may be reduced according to the limited electrical power supply available until an acceptable threshold. This will conduct to low cabin temperature rise with a limited need of dispatch capabilities from other electrical resources. Such an approach will contribute directly to the weight reduction of electrical resources. Methodology to simulate a global system architecture considering both thermal and electrical aspects A model enabling to simulate the performance of both electrical and thermal aspects was defined by Thales and Liebherr. It enables to define a global system architecture by considering the strong link between the thermal and electrical management. The model is used to simulate the operating points of the architecture using several parameters as inputs: the climatic conditions, the operating mode (nominal configuration, single or multiple failures, dispatch cases), altitude and aircraft speed (see Fig. 1). Fig. 1: Flight envelope (A/C altitude and speed) This simulation enables to highlight design cases among all the simulated operating points (highest power consumptions or temperature reached above limitations…). The electrical and thermal architectures are closely tied together, as illustrated in Fig. 2, since thermal losses from electrical converters are evacuated through the cooling system and the electrical power consumed by the thermal system is supplied through the electrical network. Fig. 2: illustration of the strong link between electrical and thermal architectures. An iterative process is performed between three entities for the computation of each operating case: Fig. 3: Electrical and thermal management simulation process The electrical entity embeds models which simulate the behavior of the electrical network. After execution, this entity computes the power flowing at every point of the electrical network and especially at the converters and power sources level. It’s also computing the global amount of electrical losses and addresses it to the thermal model. The thermal management takes into account these electrical losses. Depending on the computation case (altitude, mach, external temperature), it defines Environmental control system and cooling regulation modes (cooling, heating , failure cases…) and its objectives. It then launches thermodynamic simulation. Once the operating case has been computed, it returns the amount of electrical power necessary for each internal loads (compressors, fans, heaters…). It also sends the expected temperature in the cabin and at the electrical converters cooling’s outputs temperatures. The Power Management entity is specific to the electro-thermal optimized architectures. As the loads are not able to operate simultaneously because of the resource sharing between the two systems, the power management assigns the available resources (electrical & thermal power, inverters loads affectation) between the operating loads according to a priority order. In case of failure, the available power at an electrical source or converter’s output could be unsufficient to supply all the loads at the expected power. The Power Management analyzes the electrical loads involved in the deficient power supply path and order power limitations to the ones with the lowest priority. This management of the Electrical Power by power limitations or load shedding also enables to smooth the power peak consumptions. The overload sizing applied to generators and electrical converters could be lowered. A few iterations between these three entities allow the variables exchanges at the interfaces to converge to the final results. Models validation in a representative system platform One of the most outcomes of GETI project is a large test platform developed by Liebherr and Thales and installed at Liebherr-Aerospace’s test center in Toulouse (see Fig. 4). The platform integrates major electrical and thermal power consumptions of an aircraft, and is able to handle the dynamic behavior of both electrical and thermal loads during a flight mission thanks to smart power management. The platform features generic open architectures in order to represent a wide range of commercial aircraft. It is able… - to simulate the concept of centralized architecture using “power electronics module” and to compare it with architectures using dedicated power electronics per load. According to this concept, one module can be used for different electrical loads. For example, one module can be used either for the air conditioning pack or for the starter generator - to simulate global thermal management by considering all loads and their dynamic behavior - to optimize the system architecture by considering simultaneously both electrical and thermal management - to optimize and validate the dispatch capabilities of the system during the different flight operations Fig. 4: GETI demonstration platform This platform brings an experimental approach to validate system architectures for the overall flight envelop with a focus on transient modes. Thanks to the platform, the electrical and thermal management model can be validated. The models will be highly helpful to play other configuration and/or scenario and optimize the global management, even in transient modes. References 1 F. Delhasse, L. Fayolle, Optimisation des architectures électrique et thermique, Decielec conference, April 2013 2 C. Mevenkamp, G. Galzin, Electrical Environmental Control System, Paper – More Electrical Aircraft Forum, Barcelona, Sept 2009 3 Susan Liscouet-Hanke et al, A Model-Based Methodology for Integrated Preliminary Sizing and Analysis of Aircraft Power System Architectures, Doctoral Thesis, September 2008 4 Xiuxian Xia et al, Dynamic Power Distribution Management for All Electric Aircraft, Doctoral Thesis, Cranfield University, Feb.2009