4.2. Balancing Module
4.2.1. Module Files
4.2.1.1. Driver
4.2.1.3. Unit Test
4.2.2. Detailed Description
4.2.2.1. Voltage-based Balancing
In voltage-based balancing, the balancing module takes the minimum battery cell voltage of the complete battery pack
and activates balancing for all the cells whose voltage is above the minimum + BAL_GetBalancingThreshold_mV(). Once all cells
have been balanced, the threshold is set to BAL_GetBalancingThreshold_mV() + BAL_HYSTERESIS_mV to avoid an oscillating
behavior between balancing and not balancing.
4.2.2.2. History-based Balancing
The SOC history-based balancing works as follows: at one point in time, when no current is flowing and the cell voltages have fully relaxed (e.g., after 3 hours rest time), the voltages of all cells are measured. With a suitable SOC versus voltage look-up table, the voltages are converted to their respective SOC. These SOC are then translated to Depth-of-Discharge (DOD) using the nominal capacity, with:
The cell with the highest DOD is taken as a reference, since it is the most discharged cell in the battery pack. Its charge difference is set to 0. For all other cells, the charge difference is computed via:
where \(C_{\mathrm{c}}\) is the considered cell and \(C_{\mathrm{r}}\) is the reference cell.
Balancing is then switched on for all cells. Every second, for each cell, the voltage is taken and the balancing current \(I_{\mathrm{balancing}}\) computed by
where \(U_{\mathrm{C}}\) is the cell voltage and \(R_{\mathrm{balancing}}\) is the balancing resistance.
The balancing quantity \(I_{\mathrm{balancing}} \times 1s\) is subtracted from the charge difference. Balancing is stays turned on until the charge difference reaches 0.
In SOC history-based balancing, BS_BALANCING_RESISTANCE_ohm must be defined identically to the balancing
resistances soldered on the Slave Board. When the imbalances are computed, they are set to a non-zero value to balance
each specific cell only if its cell voltage is above the minimum cell voltage of the battery pack plus a threshold. The
threshold is set in this case to BAL_GetBalancingThreshold_mV() + BAL_HYSTERESIS_mV.
The correspondence between cell voltage and SOC must be defined by the user depending on the specific battery cells
used.
Currently, it is done in the function SE_GetStateOfChargeFromVoltage() in
soc_counting.c, soc_debug.c, soc_none.c, or state_estimation.h.
This function gets a voltage in V and return an SOC between 0.0 and 1.0.
4.2.2.3. No Balancing
No balancing is performed on any cell.
