Battery Management Systems for Electric Vehicles.ppt
Battery Management Systems for Electric Vehicles Comparison:Lead vs. Lithium in EVs Charging Lead-acid batteries charges well in a long string Over voltage in a cell is not good, but generally passes the current to the next cell in an equalization cycle with little damage. Cell balancing can be done with a sophisticated charger (IUIa cycle) Lithium batteries OK in a string, but over voltage on a individual cell can do serious cell damage. Individual cell charging is solution, or Balancing cells and charge in a string. Discharging Lead can tolerate discharging to 0% State of charge (SOC) with some cycle life damage. Lithium will have serious damage when discharging below , can pletely ruined. Lead-Acid Discharge Curve teryMaintenance/ 6V Lead Acid Battery Discharge Curve Battery Voltage State of Charge Lithium Discharge Curves Lithium Batteries have a fairly flat discharge curve with sharp shoulders /content/view/105/88/ Lithium BMS Challenges Must not Over-Charge an individual cell Must not Over-Discharge an individual cell Must not let cells get too hot during charge or discharge ENTER THE LITHIUM BMS Many thoughts and discussions on what constitutes a Battery Management System (BMS): Monitor and Detect Cell Over-Charge, and cut off charger Monitor and Detect Cell Over-discharge and alert operator, or cut off system power. Cell Balance for string charging Temperature Monitoring Remaining State of Charge determination This is done in your cell phone & laptop, why not in your car? High voltages and high currents make it difficult Sparse BMS technology availability has held up Lithium conversion projects. BMS Topology: Distributed Put voltage monitor and discharge balancer on each cell, with munications for charger cutoff and status. Advantages: Simpler design and construction and its potential for higher reliability in an automotive environment.
Disadvantages: Large number of mini-slave printed circuit boards which are needed a
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