Real-Time Implementation of an Extended Kalman Filter and a PI Observer for State Estimation of Rechargeable Li-Ion Batteries in Hybrid Electric Vehicle Applications—A Case Study

Abstract

Abstract:The Li-Ion battery state-of-charge estimation is an essential task in a continuous dynamic automotive industry for large-scale and successful marketing of hybrid electric vehicles. Also, the state-of-charge of any rechargeable battery, regardless of its chemistry, is an essential condition parameter for battery management systems of hybrid electric vehicles. In this study, we share from our accumulated experience in the control system applications field some preliminary results, especially in modeling, control and state estimation techniques. We investigate the design and effectiveness of two state-of-charge estimators, namely an extended Kalman filter and a proportional integral observer, implemented in a real-time MATLAB environment for a particular Li-Ion battery. Definitely, the aim of this work is to find the most suitable estimator in terms of estimation accuracy and robustness to changes in initial conditions (i.e., the initial guess value of battery state-of-charge) and changes in process and measurement noise levels. By a rigorous performance analysis of MATLAB simulation results, the potential estimator choice is revealed. The performance comparison can be done visually on similar graphs if the information gathered provides a good insight, otherwise, it can be done statistically based on the calculus of statistic errors, in terms of root mean square error, mean absolute error and mean square error.

On-Board State-of-Charge Estimation of Li-Ion Battery in Hybrid Electric Aircraft Vehicles Using State Estimators – Case Study

“…We are focused also on real time implementation simplicity in MATLAB R2017a simulation environment. The electrical circuit model is relatively accurate to capture the dynamic circuit characteristics of a battery cell, such as the opencircuit voltage, terminal voltage, transient response, and self-discharge, as is mentioned also in [10]. However, since in "real life" the battery dynamics is seriously affected by the temperature efects and changes in battery SOC on the model parameters remains for us an interesting open research field direction to be investigated in the future work.…”

“…In addition, it is worth to mention that this model is applied today for many other similar energy storage applications [9]. However, in this research paper we are more interested in the "proof concept" algorithmic considerations as motivated by the requirements imposed by the environment and the vehicle [10]. This battery model selection choice gives us more flexibility to prove the effectiveness of the proposed Li-Ion battery SOC estimators in terms of SOC estimation accuracy, speed convergence, robustness to different changes in battery model parameters (i.e.…”

“…This battery model selection choice gives us more flexibility to prove the effectiveness of the proposed Li-Ion battery SOC estimators in terms of SOC estimation accuracy, speed convergence, robustness to different changes in battery model parameters (i.e. internal resistance, battery capacity affected by aging degradation and repeated charging and discharging cycles) and to current sensor level noise, similar as is done in [10]. We are focused also on real time implementation simplicity in MATLAB R2017a simulation environment.…”

“…The discrete time state space model that describes the dynamics of the Li-Ion battery is similar introduced as in [6][7][10][11] as follows …”

“…Also, Table 5.4, p.100, based on the assumption that the parameters are time constant and independent on the battery SOC changes and temperature effects. In addition, the values of these parameters differ for charging and discharging cycles, as well as the coloumbic efficiency, thus the cell's voltage behavior will be described by two sets of parameters, one for charging and one for discharging, as is shown in [6][7]10]. In a realistic environment of operating conditions the battery's parameters are variable with respect to the temperature, the SOC and the current direction, making the overall Li-Ion battery one nonlinear model nonlinear.…”