Research On The Key Technologies Of BMS In Electric Vehicles And The Construction Of Hardware-in-the-loop Testing System

With the emergence of energy depletion and environmental pollution problems,the development of new energy vehicles has become an important measure to promote the strategic transformation of transportation energy in the world.In recent years,many countries have focused on the investment in electric vehicles and have provided preferential support policies.Power battery management technology is one of the key technologies used in electric vehicles.Many research institutions and companies have introduced their power battery management technology and related products.Several problems are still observed in the power battery management system based on the research and analysis of the technical route and market performance of these products.The main researches of the article are as follow.Firstly,a series battery pack model based on first-order RC equivalent circuit model is constructed,and a low voltage low frequency insulation detection model is built based on the battery model to increase the accuracy of insulation detection between the power battery system and vehicle chassis under complex working conditions.To suppress the influence of measured noises,an extended Kalman filter is designed for the nonlinear system,and the measured noises are filtered.Experimental and simulation results show that the proposed monitoring model and extended Kalman filtering algorithm for insulation resistance monitoring present satisfactory estimation accuracy and robustness.The measuring error is less than 1.5% when the system is stable.Secondly,inconsistencies that are associated with parallel-connected cells used in electric vehicles induce a state of charge(SOC)in each cell that varies with open-loop voltage.Thus,the loop current in the battery pack is inevitable and reduces the overall capacity,energy utilisation rate,and pack lifetime.However,no method is reported to address the loop current.To reduce the loop current and the influence of battery inconsistency,a novel simscape model that is based on a parallel-connected cell pack and considers the influence of thermal effect is successfully constructed.Furthermore,the strategy of parallel-connected cell energy management(PCCEM)is proposed to utilise the fuzzy logic control strategy that automatically adjusts the cell number in a circuit in accordance with load demand and induces the first N switches in the corresponding SOC order.The New European Driving Cycle driving cycle simulation shows that the PCCEM strategy considerably reduces the loop current,improves the consistency of battery performance and utilization rate of battery power and decreases energy consumption by 45.5%.Thirdly,the capacity or voltage inconsistency between the cells in a series battery is inappropriately handled.A high efficiency bidirectional active equalization scheme,where its balance current is tunable,is developed in this study.On the basis of the performance matrix,a fast model predictive control(MPC)algorithm is applied to balance the SOC of battery pack.This scheme relies on bidirectional DC/DC converter to transfer energy between the cell and its adjacent battery pack and achieves multiple simultaneous equalization.This scheme overcomes the shortcomings of traditional balance strategies,such as,low energy transfer efficiency,long equilibrium time and unsuitable large battery pack capacity.The bench test shows that the MPC scheme can effectively reduce the SOC difference between the battery monomers and can also reduce the equilibrium time.Fourthly,a set of hardware-in-the-loop(HiL)testing platforms based on NI PXIe real-time system is designed for the newly developed battery management system.Firstly,the battery pack and automobile power system models are built by Simulink software,and the input and output interfaces are configured.Secondly,the C language model is generated through the MATLAB automatic code generation tool.Furthermore,the C language model is translated into a DLL file by the VC compiler.Then,the model is operated in the NI Veristand simulation environment.Finally,the HiL simulates the change of battery voltage,temperature and current,monitors real-time tasks online and interacts with them through the user interface by changing the operation mode of the vehicle power model.By using this method,a comprehensive and accurate test on BMS products is conducted,the defects and improvements are established and the safety,stability,and reliability of BMS products are ensured.In this paper,the key technologies of BMS in electric vehicles are studied,and a HiL testing system is constructed to conduct a comprehensive inspection for BMS products;The research has certain theoretical significance and engineering application value.