Cell Balancing
In Battery Management System, cell balancing can done in two ways Passive Balancing and Active Balancing.
The active balancing and driver circuit configuration comprises three capacitors in parallel for each cell. Specifically designed switches enable bidirectional DC current flow through the use of two MOSFETs with an interposed diode in the source-to-drain direction. When the MOSFET is in an ON state, current flows from drain to source; in the OFF state, current passes from source to drain via the diode. Initially, the three capacitors of 2200uF are connected in series, enabling voltage copying from each cell. Upon rearranging the capacitors in parallel, they either charge or discharge the cell based on its voltage. This active balancing process ensures equitable cell voltages by transferring charge from overcharged cells to less charged ones, minimizing energy wastage. The driver circuit, incorporating a timer circuit with controlled frequency and a Darlington transistor, plays a pivotal role. The timer generates a controlled frequency square wave for one Darlington transistor and its inverse for the other, orchestrating the series and parallel connections of capacitors.
In a Battery Management System (BMS), passive balancing is achieved by dissipating excess energy from higher-charged cells as heat through resistors. The BMS monitors the voltage of each cell and, when a cell’s voltage exceeds a predefined threshold, it activates a resistor across that cell. This resistor draws current, reducing the cell’s voltage by converting the excess energy into heat. This process continues until all cells reach a similar voltage level, ensuring balanced charge distribution across the battery pack, which enhances performance and extends the battery’s lifespan. Passive balancing is simple and cost-effective but less efficient than active balancing.
Active balancing uses capacitors and MOSFETs to transfer charge between cells, ensuring equitable voltages and minimizing energy loss. Passive balancing dissipates excess energy as heat through resistors, offering a simpler but less efficient method. Both techniques enhance battery performance and lifespan by maintaining balanced charge distribution across the battery pack.