Conceptual Design For Solar/Hydrogen Hybrid Powered Small-scale UAV

As current domestic and international environmental issues are increasingly seriousand global energy supply is increasingly tight， countries are struggling to find clean energysources to replace traditional fossil fuels; meanwhile, varieties of vehicles, which arepowered by clean energy sources, is becoming a hot topic. Electric aircrafts, that poweredby non-polluting green energy like solar cells, fuel cells and so on, have come into being.Solar-powered or fuel-cell-powered aircrafts, being limited by the characteristics of powersources, often cost highly in design process to meet the design requirements, such as the useof unconventional aerodynamic layout, high aspect ratio flexible wing and so on.Following the global trend of UAV developments, aiming at the over night endurancedemand from small UAVs that using non-polluting green energy, asolar/hydrogen-hybrid-powered UAV concept is proposed in this article, meanwhile, the keytechnologies of conceptual design of the hybrid powered small UAVs have been studied,and accomplished works include:(1) For the application environment and the main task demand of small UAVs,considering the characteristics of the hybrid power system, the research on the missionprofile and environmental models is carried out. By analyzing the main task demands ofsmall UAVs and a plenty of recording data of missions, a UAV typical mission profile isestablished according to the type of tasks, providing a basis for the conceptual design ofUAVs. According to the requirements of environmental parameters from subsystems ofhybrid powered UAV, the environmental models of UAV flights are established.(2) Aiming at the main subjects that the conceptual design of hybrid UAV concerns,subsystem modeling has been studied. The models of major subsystems of the hybrid UAVare established, including weight subject, solar cell system, fuel cell system and lithiumbattery system models. Weight subject model includes the weight estimation models ofairframe structure, power system and propulsion system. Theoretical and engineeringmodels of solar cell and solar array are established and verified through experiments. Theexperiments on output characteristics of fuel cell system are carried out and a approximatemodel of fuel cell output power is built based on the measured data. Estimation models oflithium battery output characteristic and state of charge (SOC) are established and thesimulation data are verified by the experimental measured data.(3) To satisfy the requirements for the entrie hybrid UAV power management, the power management strategies of finite state machine and power tracing are studied,followed by the corresponding accomplishments of hybrid UAV power managementstrategy models. The modeling of UAV mission profile, flight environment, power systemand power control strategies are completed and the integrated simulation is also conducted.In given conditions and flight profile, the outputs and working parameters of each powersources and controllers of the hybrid power system in the entrie fight process are simulated.The simulation results give a quantitative analysis of the impacts of UAV flight manners onthe performance of the solar cell, a validation of the feasibility of power managementstrategy, and the advantages of hybrid power system over the traditional electric powerpropulsion system.(4) A hybrid UAV energy/weight coupled analysis method is proposed according to therequirements of hybrid UAV design. The estimation of hybrid UAV takeoff weight can beachieved by using this method with sufficient considerations of the coupling relationshipsbetween energy, aerodynamic, and weight subjects. A multidisciplinary design optimizationplatform for hybrid UAV is built, basing on the integration of weight and performancecoupled analysis models in Matlab/Simulink environment. A physical programming basedoptimization strategy and the genetic algorithm are employed to optimize the design plan,resulting a fairly good optimal design.(5) A ground test platform for the hybrid power system of the UAV is constructed toaccomplish the ground tests of the main systems. The test platform mainly consists of solarcell system, fuel cell system, lithium battery system, electric propulsion system and powermanagement system. A large number of ground tests on Solar cell, fuel cell and lithiumbatteries are executed, providing reliable experimental data for the establishment andverification of engineering models. The hardware development of UAV power controlsystem based on finite state machine management strategy is completed. The combinedhybrid power system ground tests confirm the practicality of finite state machinemanagement strategy and the power controller, and thus show the strong realizability of thehybrid UAV concept.