Power limits specification

Overview

The purpose of the power limit function is to provide a maximum and a minimum power the battery can sustain at time t. Following the power limits should result in respecting the current limits and the cell voltage and temperature limits. It is common to control an inverter in power (active power setpoint) and in this case, the inverter must know what the battery is able to deliver in terms of power.

Power limit charge:

The power limit charge is derived as follows: P_lim_chg = I_lim_chg * V_cell(t+30s | I_lim_chg) Where V_cell(t+30s | I_lim_chg) is the estimation of the cell voltage in the next 30s if the cell is under I_lim_chg A. V_cell(t+30s) = Vocv + Rint*I_lim_chg

Note: this needs to be done for each cell. One simpler way of resolving this, is to estimate V_cell(t+30s | I_lim_chg) for all cells, and pick the maximum of all the V_cell(t+30s | I_lim_chg).

P_lim_chg for the whole pack then becomes: P_lim_chg = I_lim_chg * max(V_cell(t+30s | I_lim_chg)).

Power limit discharge:

The power limit discharge is derived as follows: P_lim_dch = - I_lim_dch * V_cell(t+epsilon | I_lim_dch) Where V_cell(t+epsilon | I_lim_dch) is the estimation of the cell voltage a few milliseconds after applying I_lim_dch A. V_cell(t+epsilon) = Vocv + R0int*I_lim_dch

Note: power limit discharge is a positive value. Note: this needs to be done for each cell. One simpler way of resolving this, is to estimate V_cell(t+epsilon | I_lim_dch) for all cells, and pick the maximum of all the V_cell(t+epsilon | I_lim_dch).

P_lim_dch for the whole pack then becomes: P_lim_dch = - I_lim_dch * max(V_cell(t+epsilon | I_lim_dch)).