Research On Power Distribution Strategy Of Electric Vehicle Hybrid Power System

In recent years,with the increasing serious of energy crisis and environmental pollution problems,electric vehicle have developed rapidly due to their advantages in energy conservation and environmental protection.Because of the low specific power,the existing power source lithium battery of electric vehicle can not meet the high-power load change demand when the vehicle accelerates rapidly.Therefore,high specific power of super-capacitor is introduced,and to combine with lithium battery to form a hybrid power system.At present,research on hybrid power system has become a hot issue in the field of automobile.In order to make full use of the advantages of the two power sources in the hybrid power system,the power performance and mileage of the electric vehicle can be improved by rationally distributing the power between the lithium battery and the super-capacitor.The hybrid power system is taken as the research object in this thesis,we found that the power distribution method of the low-pass filter can not effectively decompose the high-frequency or peak components in the load power by through the analysis of it,and the cut-off frequency of the filter is fixed,both of them make the charging and discharging current of the lithium battery not be well regulated,and the instantaneous charging and discharging current of lithium battery can easily change abruptly when the load changes with high power.Therefore,in view of the above problems,based on consulting a large number of related references in this thesis,power distribution method of wavelet transform based on fuzzy control be adopted.Firstly,by analyzing the characteristics and operating principle of lithium batteries,super-capacitors and DC/DC converters,the mathematical models are established.Secondly,based on the filtering control,the wavelet transform method is used to effectively decompose the low-frequency component and the high-frequency component of the load current.Thirdly,according to the change of load current and super-capacitor state of charge(SOC),fuzzy control is applied to dynamically adjust the decomposition factor of wavelet transform.And the lithium battery and super-capacitor adjust the low-frequency and high-frequency current components decomposed by wavelet transform in real time respectively.Compared with the filtering control method,this method can effectively decompose the load power and control the charging and discharging current of the lithium battery and the super-capacitor in real time.The peak value of the instantaneous charging and discharging current of lithium battery can be reduced to the greatest extent,and to prolong its working life under the premise of meeting the power demand of electric vehicles,and the economic performance of the EV can be improved.At the same time,the high specific power characteristics of super-capacitors can be fully utilized to improve the acceleration performance of electric vehicle.Finally,according to the control strategy adopted in this thesis,the simulation model of hybrid power system is built in MATLAB/Simulink environment.And by comparative analysis,this thesis verifies the feasibility and efficiency of wavelet transform distribution strategy based on fuzzy control.