Research On Energy Efficiency Optimization In Fuel Cell Hybrid Power System

Proton Exchange Membrane Fuel Cell (PEMFC) takes hydrogen, this renewable power source, to face the challenge of the present global energy crisis, so it is significant to develop this technology for future environment protection. The combination of both fuel cell and battery as power sources to construct a hybrid power system is a great opinion of expanding the advantage of each other. In such a hybrid power system, fuel cell can be the main power source to meet the average power requirements of the load while the battery and its management system can supply the peak power of the load and absorb the surplus energy of the system.The thesis takes the coordination of both fuel cell and battery output power in order to improve the energy efficiency in hybrid power system under different load power requirements as the main research object, which includes the following aspects:1.in steady state, the relation between the system maximum output power and system maximum energy efficiency is revealed in system power-efficiency plot; 2.in transient state, the structure of the closed loop control system had been constructed to realize system fast dynamic response and stability in parameter change environment.To realize the research objective, each part of the fuel cell battery hybrid power system is presented with the analysis on system topology structure. The branch current formulas of fuel cell and battery are further derived under a given load profile. With the basis of the above analysis, different operation modes in steady state and how to optimize energy efficiency in each operation mode are studied. The construction of system power-efficiency plot reveals that system maximum output power doesn't coincide with system maximum energy efficiency. In order to obtain system fast dynamic response and stability in parameter change environment, one current regulator is designed to construct a closed loop control system with the basis of the small signal model of the hybrid power system.The simulation is executed in MATLAB/SIMULINK and its results coincide with the theoretical analysis of the system in steady and transient state.In the experiments, firstly, a boost converter based on UC3843 is designed to construct a pure fuel cell power system in order to make a fuel cell electrical bicycle. The road tests statistic proves that when the load power requirement is relatively constant, a pure fuel cell powertrain is able to meet such power requirements and when the load power requirements increase dramatically, a pure fuel cell powertrain has weak dynamic response because fuel cell output voltage is inclined to be unstable. Then a fuel cell battery hybrid power system is tested in Nexa Training System in order to improve system fast dynamic characteristic. The test result of the hybrid power system proves that the above theoretical analysis with simulation calculation of the system in steady state is correct and by comparison with the pure fuel cell power system, it also presents the advantage of the hybrid power system in system dynamic response to realize the objective of the energy efficiency optimization.