Battery Temperature Assessment for FOPI and PI Based Electric Vehicle Traction System

Abstract

Fractional Order Proportional-Integral (FOPI) controllers are attractive due to their robustness, disturbance rejection properties, and at the same time the low control effort imposed. This work investigates the use of FOPI controllers on a prototype electric vehicle (EV) traction system consisting of an Indirect Field Oriented Control (IFOC) based induction motor (IM) system. The overall setup is driven by an inverter, powered by an SOOV Li-ion battery bank. The main focus of this paper is comparison of the battery bank temperature and overall speed regulation performance when speed regulation is done via FOPI or integer order Proportional Integral (PI) control. Two major classes of tests are considered, first the performance of a Ziegler Nichols (ZN)-PI controller is compared against an FOPI controller tuned via existing rules in the literature. Then, the FOPI controller is made to use the same gains as the ZN-PI controller, but only the order of the integral is varied to non-integer values lesser than unity. Comparison based on simulation results show that simply using the ZN-PI gains but changing the order of the integral to values lower than unity, has definite effects on battery temperature, and SOC, and without sacrificing speed regulation performance compared to a tuned FOPI controller or a using a tuned PI controller. This has the potential to help in comparison of controller behavior from the point of view of protecting and extending the life of an EV battery bank. Because small temperature increases if sustained over a long time, may significantly harm an EV’s battery bank.