State of charge estimation and equalization’s board development for automotive battery management system

The automotive World is experiencing the biggest change of its history passing frominternal combustion engine to a total electric mobility due to the request for a more greenand sustainable economy.This transition requires new skills and new devices that up to now are not so common in avehicle, the representative one is the huge battery pack, that provides the necessary amountof energy to supply the new generation electric motors. The battery pack its made by a bignumber of cells placed in series and in parallel each other in order to satisfy the requiredhigh voltage and high current specifications, so its necessary something that monitors theseparameters at which it is to add also the temperature’s monitoring, a very critical parameterfor the lithium-ion battery cells. The Battery Management System (BMS) is in chargeof controlling the behaviours of the battery, but it also needs to accomplish other tasks:evaluating the State Of Charge (SOC) and the State Of Health (SOH), managing overchargeand overdischarge protections, controlling the precharge’s contactors, and many others.In particular in this thesis it will be studied the SOC estimations and different equalizationtechniques. So a control board, integrating this functions, is designed. The SOC estimationand equalization are two of the most important features of the BMS, because even if the cellsof the battery pack are declared equal, small differences exist and this leads to an unbalancecondition. The unbalance condition is dangerous for a battery pack, for example if one cellis empty while the others are not, all the pack is going to be turned off and the remainingenergy wasted. This leads to a fast aging of the cell, but also of the pack, that even if onlyone cell is not correctly working, it needs to be entirely substituted. To avoid this, the SOCneeds to be monitored periodically and to keep all the cell at the same level, when necessary,the equalization system have to be activated. So if the SOC is well managed, the life time ofthe battery pack and its reliability improve.