Integrating battery energy storage with a BMS for reliability, efficiency, and safety in vehicles

The choice of energy storage chemistry and battery management for transportation applications is at best challenging. The use of regenerative braking puts strain on some chemistries and the BMS (Battery Management System) needs to manage disparate criteria (temperature, altitude, maximum C rate, state of charge, cycle life, etc) to obtain maximum energy storage, round trip efficiency and safety. The different requirements of POWER needs compared with ENERGY needs are yet another set of constraints. The advent of PHEV (Plug in Hybrid Electric Vehicles) adds more complication and the vision of V to G (Vehicle to Grid) complicates the matter significantly more. This paper reviews safety criteria for lithium ion battery chemistries system and then introduces criteria for matching the battery type to the BMS system. The question of why a computer notebook type BMS isn´t the best choice for a vehicle is discussed. Since most vehicles can stop faster than they start, there is more kinetic power available with regenerative braking than the power necessary for accelerating the vehicle. This gives rise to either choosing symmetric charge-discharge chemistries or over designing for a non-symmetric case. The marriage of the battery energy storage system to the BMS/power electronics provides the system with efficiency, reliability, and safety. This marriage must be completely understood for optimized system design.