| The electric unmanned aerial vehicles(UAV)is more environmentally friendly compared with the traditional fuel UAV,but due to small body size,the low energy density of lithium battery and other reasons,the short endurance becomes a fatal disadvantage limiting the electric UAV’s performs.In this thesis,a UAV’s hybrid power system with fuel cell and lithium battery as the power source is proposed.The main components of the system include proton exchange fuel cell,lithium battery,DC-DC converter,system controller.Fuel cell is the main energy source for UAV power supply.Lithium battery provides instantaneous high power demand during flight.DC-DC is responsible for controlling fuel cell power output and stabilizing bus voltage.System controller is responsible for power distribution.Firstly,this thesis proposes a configuration design method to meet the performance requirements of UAV.The required power of the whole UAV is calculated according to the fuselage parameters of UAV.Setting the power system economy,system weight and flight endurance as the objectives,the maximum power demand of UAV and the variation range of lithium battery state of charge as constraints,a multi-objective and multi constraint optimization model is constructed.The optimization is solved by using the multi-objective optimization genetic algorithm NSGAII,and an improved dynamic programming algorithm is used to calculate the flight endurance.The multi-objective Pareto front is obtained,and the hybrid degree configuration of the power system is determined.Secondly,an energy management strategy based on deep reinforcement learning(DDPG)is proposed to improve the fuel economy and maintain the SOC of lithium battery in a stable range,then compared with the rule-based power following strategy and fuzzy logic control strategy in simulation.The simulated results show that the energy management strategy based on DDPG can effectively balance fuel economy and lithium battery protection.Finally,based on the built testing platform of fuel cell hybrid power system,a system controller based on s32k144 microchip is designed for the platform realizing the stable operation control of fuel cell stack and completing the energy management control test. |
