Research On SOC Measurement Method Considering Safety

With the world’s energy poverty and environmental disruption,energy conservation and environmental protection has become the theme of today’s world.Electric vehicle is as the representative of the new energy transport,because it has no fossil fuel and no pollution of gas emissions with electric energy as the driving force.The battery management system(BMS)as the link between power batteries and electric cars,controlling of the power batteries reasonably according to the output characteristics of electric vehicle requirements.The battery state of charge(SOC)is the core technology of BMS.Battery’s SOC real-time and accurate estimation directly influence the power batteries’ safety and energy utilization.Battery SOC plays a vital role in exploring the optimal performance of the electric vehicle.Therefore,the precise prediction of battery SOC is of great importance for the battery management system.The lithium iron phosphate(LFP)battery has the advantages of high specific energy,good thermal stability and long cycle life,etc.which becomes the most important power source for electric vehicles in China.However,there are a lot of issues to be resolved.Especially the power battery’s safety hazard and low battery energy utilization,directly affecting the reliability of electric vehicles and the driving range.The existence of these problems scares away drivers,seriously restricting the development and popularization of electric vehicles.In this paper,the experiment was carried out using single lithium iron phosphate battery.First of all,the terminal voltage as the working cut-off condition of lithium iron phosphate battery was in terms of the safety,the cycle life and the energy utilization.The limitation and harmfulness of the terminal voltage control method was proposed;Secondly,a new type of control strategy of the working threshold for the lithium iron phosphate battery was proposed,modeled and validated.The results proved that the new control method not only improves the battery’s safety,and reduces the chance of the explosion of batteries caused by over charged and over discharged,but also resolve the issues of the low energy utilization by the terminal voltage cut-off method while low temperature and high charging rate;Finally,based on the new type of critical condition for a battery,various influencing factors for Ah counting method using a mean field theory(RMF)were proposed.The improved Ah counting method could timely and accurately estimate the battery SOC in the case of real-time change of the working state of the power battery,ensuring the security and the efficiency of power battery.