Research On Variable Bus Voltage Control Method Of Electric Propulsion System

As the power system of electric aircraft,electric propulsion system has become a research hotspot because its efficiency determines the flight time of aircraft under limited batteries.However,the actual working condition of electric propulsion system is relatively complex,which will lead to wide range of system speed,torque and so on,and then cause wide range of efficiency fluctuation under the electric propulsion system with fixed bus voltage.At the same time,the electric propulsion system is powered by electric energy such as lithium batteries and hydrogen fuel cells.Compared with lithium batteries,hydrogen fuel cells have higher energy density and can make the aircraft travel longer.Therefore,the hydrogen electric propulsion system with hydrogen fuel cell as the energy supply mode is more in line with the requirements of high efficiency and high power density of electric aircraft,and has a greater application prospect.However,hydrogen fuel cells have the problem of low output voltage,which cannot meet the voltage requirements of electric propulsion system.Boost circuit is usually used to raise the battery output voltage to the required voltage of the system.In this paper,a variable bus voltage control method is proposed to solve the above problems.This method can calculate the bus voltage reference value with less system loss according to the different current operating conditions of the system,and change the bus voltage of the system through the boost circuit,so as to improve the efficiency of the electric propulsion system under wide operating conditions.Its main research contents are as follows:Firstly,according to the requirements of hydrogen electric propulsion system and variable bus voltage control,Boost circuit is added to the circuit structure,so as to solve the problem that the low output voltage of hydrogen fuel cell cannot meet the system voltage,and provide the realization means for variable bus voltage control.Secondly,under the above circuit topology,system loss is taken as the research entry point,and the system loss model is established by analyzing the mechanism of system loss.The relationship between bus voltage and operating condition and system loss is studied,and the mathematical model of the relationship between bus voltage and operating condition and system loss is established.A simulation model is built to verify the effect of bus voltage and working condition on system loss.Then,according to the mathematical model of the relationship between system loss and bus voltage and working condition,a variable bus voltage control method of electric propulsion system is proposed considering the parameter variation and space harmonic effect.On this basis,the variable bus voltage control simulation model of electric propulsion system is built and simulation research is carried out.Several operating points are selected as system Settings in a wide range,and under these operating points,the variable bus voltage control method and the fixed bus voltage method are compared and simulated.Finally,the experimental platform of variable bus voltage control method of electric propulsion system is designed and built,and the experimental verification is carried out on this experimental platform.According to the rated parameters of the experimental platform,several operating points are selected as system Settings in a wide range for comparative experimental analysis.The simulation and experimental results verify the effectiveness and feasibility of the proposed method.Compared with the traditional fixed bus voltage control method,the variable bus voltage control method has the advantages of high efficiency,low current ripple and harmonics.