Research On The Vehicle Controller Unit For Wheel Drive Motor Electric Vehicle

With the development of the automotive industry,the consumption of non-renewable energy,the development of electric vehicles has gradually become the main direction,and the wide platform of lithium-ion batteries due to their external characteristics has gradually become the best choice for electric vehicle power sources.The inconsistency between the single cells restricts the development of electric vehicles.And the impact on the series battery pack is particularly obvious.This inconsistency will increase the life of the single cell quickly until it fails,which is far from the service life indicated in the production.To achieve reliable application of large-capacity ion battery packs,an effective battery equalization system is a key technology to improve battery pack performance and extend battery pack life,and is also a research hotspot in battery management systems.The main research contents of this paper are as follows:1)Introduce the research background and significance of electric vehicles,research status and development trends at home and abroad,and analyze the existing problems of the equalization systems in BMS and their advantages and disadvantages.Considering that voltage equalization is easy to cause excessive equalization,and capacity balancing is not suitable for online implementation,the direction of adopting SOC equalization is proposed.2)High-accuracy lithium-ion battery online identification through HPPC experimental test of lithium ion battery.The characterization test was performed to obtain the OCV-SOC curve,and the battery capacity parameters,and the existing model was analyzed,and the improved Thevenin lithium-ion battery model was established in matlab/Simulink.The main performance parameters of the tested lithium ion battery were identified by model,and the accuracy of the improved Thevenin model was verified by experiments.The weighted EKF filtering algorithm is used to estimate the SOC of the battery,and the higher estimation accuracy is obtained,which provides effective data support for the equalization control.3)Through the analysis of the connection mode of the power battery pack,it is determined that the designed battery pack is connected in series.Based on the research and comparison of the existing equalization circuit,an active equalization circuit for energy bidirectional transmission of PWM control switch is designed.The equilibrium principle of the designed circuit is analyzed and the corresponding equalization control strategy is improved.It has been experimentally verified that the equalization rate of the four-cell lithium-ion battery is 60% longer than that of the conventional active-balance circuit.4)Select STM32Fl10ZET6 controller produced by ST company as the main control chip of this paper to build battery platform.Balanced battery is SONY lithium iron phosphate,the capacity is measured to be 1050 mAH.According to the requirements of the equalization circuit,the acquisition circuit,equalization circuit,communication circuit and safety protection circuit are designed.In the software design aspect,in the Keil uVision5 development environment,the code of each program is written and verified on the experimental platform.The experimental results verify the effect of the balanced expectation.