electrical,

Our Battery Management System

Sep 01, 2019 · 2 mins read
Our Battery Management System
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Unlike IC engine vehicles that powers the motor through a piston-cylinder system and uses fuels for its combustion procedure, an electric vehicle draws its power from a battery pack for this operation.

The cells in battery pack are connected in series and when you draw current continuosly from the batterey pack then there is disbalancing between cell voltages. In brief terms that means thet all the cell voltages aren’t equal when you draw current from a battery pack beacause we consider all the cells are identical but they aren’t. So because of that all the internal parameters of the cell aren’t same so disbalancing occurs.

Though minor difference in between cell voltages may seem insignificant but they aren’t. In long run they can have major impact on the battery pack life. Thus we need a control system in order to balance the cells wherever disbalancing occurs without affecting the current output from the accumulator pack. If there is a huge cell voltage difference then to stop the current output from the battery pack, first balance the battery pack and after that allow the current output from the accumulator pack. We call this system as the Battery Management System(BMS) or Accumulator Managemet System(AMS).

There are two ways for us balance the cells: actively and passively.

Active Battery Management System: In active balancing there is no power loss while balancing the cells. To achive this kind of system we charge a capacitor with the first cell. Then we check all the individual cell voltages and compare it with the capacitor voltage. If there is a siginificant difference between the two that requires the need for balancing then we connect that cell with the capacitor in parallel. In this type of balancing the cells will come to a mean voltage of the two disbalanced cells. (If the cell voltages between which balancing occurs is 3.306 and 3.308, then both the cells will attain 3.307.) Thus the two will attain equal voltage. Then we will disconnect the capacitor from that cell and repeat the above procedure once again. If the difference between a particular cell and the capacitor is significant then we’ll just stop the current ouput from the battery pack. Since there is no active element present in the balancing circuit, hence there is no power loss.

Passive Battery Management System: In Passive balancing there is power loss in the balancing circuit. In this system we monitor every cell voltage simultaneously. If there is disbalancing between adjacent cells of the accumulator pack then we simply connect the two cells in parallel with a resistor between them. Since resistor is an active element, hence their is power loss in the balancing circuit. In this type of balancing the cells will come to the voltage level that is lower between the two cells. (If the cell voltages between which balancing occurs is 3.306 and 3.308, then both the cells will attain 3.306.) Thus the two will attain equal voltage. Monitoring of the cells occur synchronously and if disbalancing occurs then the cells will in parallel for the respective clock cycle. If the difference between two adjacent cells is significant then we’ll just stop the current ouput from the battery pack.