Characterization Research And Management System Design Of The Lithium-ion Ultracapacitor For HEV

Under the presure of energy crisis and environmental pollution, the development of new energy vehicles has draw a lot attention of goverments and OEMs. Hybrid electric vehicle(HEV), which combines the advantage of both combustion engine vehicle and pure electric vehicle, is one of the most attractive solutions under current technical conditions. As one of the key component in HEV,The performance of the vehicle energy storage system has significant influence on the dynamical performance, economy and safety of vehicle.Most common used power batteries at present,such as MH-Ni batteries and Li-ion batteries, all have drawbacks such as inability of bearing high current and short cycle life. In contrast,Li-ion ultracapacitor,a novel hybird ultracapacitor which has both high power density and long cycle life, is a better choice for HEV power source. Effective management an control is needed in order to take advantage of the Li-ion ultracapacitor. The only shortcoming of Li-ion ultracapacitor is its energy density is relatively low than batteries,so it’s crucial to improve the accuracy of SOC estimation to enlarge its available energy.Firstly, a series of test has carried out on the power battery test bench to study the charge/discharge characteristics of the Li-ion ultracapacitor.Its capacitance, inner resistance, performance under different currents and unbalance among the cells are analyzed. Base on the test data and the structure of the li-ion ultracapacitor, a practical equivalent circuit model is proposed and pulse current discharge test is used to obtain the parameters of the model.Using the simulate model established in Matlab, the effectiveness of the model is verified with high accuracy by comparison with test results under different load conditionsUltracapacitor pack used in HEV is comprised of a number of single cells connected in series, so the SOC of the pack is estimated by modeling the pack as a whole to get the average SOC and then amended according to the unbalance condition among the cells. Taking into consideration the fact that the SOC-OCV curve of li-ion ultracapacitor is approximately linear with a steep slope and Ah integral’s error is small in a short period.SOC is estimated using current based algorithm and voltage based algorithm respectively, then the final SOC is obtained by combining the two algorithm using a a factor.voltage based SOC estimation include the extended OCV algorithm under small current and set membership filtering method in dynamic working conditions. The SOC algorithm is verified by comparing the simulation results with testing results.It is proved that the algorithm have very good accuracyBase on the demand of the HEV,the hardware and software of the ultracapacitor management system is designed.the freescale’s16bit MCU,MC9S12DP512, is used as main control unit.The system has a master-slave structure,the cell sampling and balance module is separated for cell data acquisition and cell balance management. Based the hardware circuit,the software design of the key part including data acquisition and processing,SOC estimation and thermal management are discussed.The management system is tested on the testbed and the result shows that the system can sampling the data such as voltage and current precisely and the SOC estimation algorithm has high accuracy under actual vehicle operation conditions.