Research On Design And Power Allocation Strategy Of Composite Power System For Electric Vehicles

Last few years,electric vehicles have been rapidly developed because they do not produce any pollution.However,there are many problems in its development.For example,the low power density of the battery leads to poorer power performance of the entire vehicle,frequent high-current charging/discharging results in short cycle life,etc.Therefore,in this paper,the supercapacitor with high specific power and long cycle life is combined with the battery to form a composite power source as the energy system of the electric vehicle,and its power distribution strategy is compared and studied.First of all,Based on the charge and discharge test of battery and super capacitor,their working characteristics were analyzed in detail.It has been proposed that the super capacitor connect with bidirectional DC/DC converter firstly and then connected in parallel with batteries by comparing and analyzing the advantages and disadvantages of different composite power supply systems,and described the different operating modes in detail.Completed the parameter matching of battery and super capacitor according to prototype parameters,and determined the performance requirements of bidirectional DC/DC converter and finished its design,mainly inductive and capacitive design.According to the circuit principle of the bidirectional DC/DC converter,a simulation model is established and simulated.The result show that the designed bidirectional DC/DC converter has good buck-boost capability and dynamic response capability.Secondly,build a simulation model in MATLAB/Simulink based on the working principle of battery and super capacitor and efficiency model based on efficiency test data of bidirectional DC/DC converters.This paper has proposed a simple logic threshold control strategy and a fuzzy control strategy base on the analysis already existing control strategies,then built a simulation model successfully.At present,ADVISOR software is widely used in the simulation of electric vehicles and hybrid vehicles because of its fast analysis of various performance of automobiles.However,the energy storage system in ADVISOR is a single power system,so secondary development of ADVISOR is needed.Import the built composite power system model into ADVISOR to replace the single power system Modify the top model,and modify the corresponding M file and GUI connection to complete the secondary development.Based on the UDDS operating conditions to simulate and compare single power system and composite power system,the results show that the super capacitor in the composite power system can play a role of “clipping”,reduce the output power of the battery and also reduce the energy consumption rate of the 100 kilometers of the battery by 8.6%.Comparing different control strategy simulation results show that the fuzzy control strategy has stronger robust and better control effect.Compared with the simple logic threshold control strategy,the fuzzy control strategy reduces the energy consumption rate of battery a hundred kilometers by 3.56%.Finally,tested the composite power system designed on the test bench.First,the high and low voltage sides of the bi-directional DC/DC converter are connected to the analog battery and the super-capacitor module respectively,and the performance of the bi-directional DC/DC converter is verified through the charging and discharging test of the super-capacitor module.The results show that the designed bidirectional DC/DC converter has good buck-boost pressure and dynamic response performance,which can meet the actual work requirements.Then,using the resistor as the load,perform power supply experiments for a single power system and a composite power system separately.The results show that the super capacitor can share the high power output of the battery to protect the battery.