A Reformatory Model Incorporating PNGV Battery and Three-Terminal-Switch Models to Design and Implement Feedback Compensations of LiFePO4 Battery Chargers

Abstract

This study developed and implemented a LiFePO4 battery pack (LBP) rapid charger. Using the three-terminal switch and partnership for a new generation of vehicles (PNGV) battery models, this study could obtain a small-signal system matrix to derive transfer functions and further analyze frequency responses for the charge voltage and current loops; therefore, both voltage and current feedback controllers could be designed to fulfill the constant-voltage (CV) and constant-current (CC) charges. To address practical applications, the proposed equivalent model also considered the wire resistance-inductance of the power cable. According to the derived high-order transfer function, the pole-zero break frequency in the Bode plot was observed that approximated the practical measurement; therefore, the pole-zero compensation could be accomplished for both charge loop requirements. Moreover, the design features for implementing the CV and CC charges are presented in detail herein, and the current overshoot during the start-up phase could be mitigated using the method of zero break frequency shifting and a novel proportional shifting proportional-integral control. The LBP parameter estimations, model construction processes, and frequency response analyses are also presented. The feedback compensation design based on the proposed model was validated through simulations and experiments. The results were determined to be in excellent agreement with theoretical derivations.