Multi-step model predictive iterative techniques for battery system peak power estimation

1. A method comprising:

receiving, at a controller of an electrified vehicle, measured current, voltage, and temperature of a battery system of the electrified vehicle;

determining, at the controller, operating parameters for the battery system based on the measured current, voltage, and temperature, wherein the operating parameters for the battery system include its state of charge (SOC);

determining, at the controller, an initial peak current at a start of a current prediction period for the battery system based on the operating parameters;

determining, at the controller, an instantaneous peak current of the battery system based on its initial peak current by performing voltage-limited extrapolation of resistances and open-circuit voltage (VLERO) of a battery model for the battery system; and

controlling, by the controller, the battery system and an electric motor of the electrified vehicle based on the determined instantaneous peak current,

wherein the battery model is an asymmetric equivalent circuit model having asymmetric parameters for charging and discharging of the battery system,

wherein the asymmetric equivalent circuit model includes an ohmic resistance, an open circuit voltage (OCV), and at least one resistor-capacitor (RC) pair, each RC pair corresponding to a resistance and a capacitance for either charging or discharging of the battery system,

and wherein performing VLERO further includes performing first-order extrapolation of all resistors of the asymmetric equivalent circuit model and extrapolation of the OCV using constant RC time constants.

2. The method of claim 1 , wherein the operating parameters of the battery system further include at least one of its state of charge (SOC) and its impedance.

3. The method of claim 1 , wherein the OCV is a sum of a one-state hysteresis voltage component and a voltage component dependent on the SOC of the battery system.

4. The method of claim 3 , further comprising determining, at the controller, the SOC based on a ratio between remaining usable capacity and full capacity of the battery system.

5. The method of claim 4 , further comprising determining, at the controller, a predicted voltage of the battery system after a period based on the initial peak current.

6. The method of claim 5 , wherein determining the predicted voltage further includes iteratively (i) incrementing the SOC and (ii) calculating voltage states for a plurality of time steps of the period.

7. The method of claim 6 , further comprising determining, at the controller, whether the predicted voltage is within a voltage threshold from a critical voltage of the battery system, wherein the critical voltage is a minimum or maximum allowable voltage of the battery system.

8. The method of claim 7 , further comprising determining, at the controller, the instantaneous peak current based on the predicted voltage when the predicted voltage is within the voltage threshold from the critical voltage of the battery system.

9. The method of claim 2 , further comprising determining, at the controller, the impedance of the battery system based on its temperature.

10. The method of claim 1 , further comprising controlling, by the controller, the battery system to provide the instantaneous peak current to the electric motor.

11. An electrified vehicle, comprising:

an electric motor;

a battery system configured to power the electric motor; and

a controller configured to:

receive measured current, voltage, and temperature of the battery system,

determine operating parameters for the battery system based on the measured current, voltage, and temperature, wherein the operating parameters for the battery system include its state of charge (SOC),

determine an initial peak current at a start of a current prediction period for the battery system based on the operating parameters,

determine an instantaneous peak current of the battery system based on its initial peak current by performing voltage-limited extrapolation of resistances and open-circuit voltage (VLERO) of a battery model for the battery system, and

control the battery system and the electric motor based on the determined instantaneous peak current,

wherein the battery model is an asymmetric equivalent circuit model having asymmetric parameters for charging and discharging of the battery system,

wherein the asymmetric equivalent circuit model includes an ohmic resistance, an open circuit voltage (OCV), and at least one resistor-capacitor (RC) pair, each RC pair corresponding to a resistance and a capacitance for either charging or discharging of the battery system,

and wherein the controller is configured to perform VLERO by performing first-order extrapolation of all resistors of the asymmetric equivalent circuit model and extrapolation of the OCV using constant RC time constants.

12. The electrified vehicle of claim 11 , wherein the operating parameters of the battery system further include its impedance.

13. The electrified vehicle of claim 11 , wherein the controller is further configured to determine the SOC based on a ratio between remaining usable capacity and full capacity of the battery system.

14. The electrified vehicle of claim 13 , wherein the controller is further configured to determine a predicted voltage of the battery system after a period based on the initial peak current.

15. The electrified vehicle of claim 11 , wherein the controller is configured to determine the instantaneous peak current of the battery system using a multi-step model predictive iterative (MMPI) method.