Comparative study of a structured neural network and an extended Kalman filter for state of health determination of lithium-ion batteries in hybrid electricvehicles

Abstract

State of health (SOH) determination becomes an increasingly important issue for a safe and reliable operation of lithium-ion batteries in hybrid electric vehicles (HEVs). Characteristic performance parameters as capacity and resistance change over lifetime and have to be determined precisely.This work deduces two different parameter estimation methods to identify the SOH of battery resistance and investigates the feasibility of an application in HEVs. First, a knowledge-based algorithm of a developed structured neural network (SNN). Thereby, the structure of the network is adopted from the mathematical description of the electrical equivalent circuit model. Two main advantages expected from a SNN compared to a regular neural network are: first a reduced structure and complexity of the network through predefined functions and thus faster computation, second the possibility to get access to internal parameters of the model. In order to verify a proper operation and performance of the developed SNN, a model-based second parameter estimation method is used with the well established the extended Kalman filter (EKF) algorithm.Furthermore, the developed algorithms are applied on real-vehicle data of a HEV battery at begin of life and after 170,000km. A verification of the identified states against reference data based on electro-chemical impedance spectroscopy shows nearby identical results for SNN and EKF. Additionally, a comparison of implementation effort and computation time isgiven.