A Systematic Approach for the Design of the Digital Low-Pass Filters for Energy Storage Systems in EV Applications

Low-pass filters have been used widely in the supervisory energy management controllers (EMC) for electric vehicle applications. However, there has not been a comprehensive methodology for the selection of their key design characteristics, such as the passband, stopband, and attenuation capabilities. In this article, a novel, step-by-step procedure, for the design of the digital low-pass filters (DLPF) is presented for the EMC. Mathematical models for a generalized battery/supercapacitor (SC) structure are derived for the impedance functions of the system. These impedance functions are used to investigate the behavior of the sources and the converter in the frequency domain. Moreover, using the extracted information from the frequency response curves, the guidelines for design of the DLPF are presented. In addition to the DLPF, a fuzzy logic controller is developed to monitor the state-of-charge (SoC) of the SC bank to ensure its operation in a safe region. The controller is designed and tested for the Urban Dynamometer Driving Schedule, using MATLAB/Simulink. Finally, the theory and simulations are validated using a Typhoon hardware-in-loop real-time emulator.