Distributed Control of Active Cell Balancing and Low-Voltage Bus Regulation in Electric Vehicles Using Hierarchical Model-Predictive Control
Zhe Gong, Bjorn A.C. van de Ven, Kshitij Gupta, Carlos B. da Silva, Cristina H. Amon, Henk Jan Bergveld, M.C.F. Donkers, Olivier Trescases
Abstract
Electric vehicle (EV) battery performance near end of life is limited by mismatched cell degradation, leading to an estimated 5-10% cell capacity variation across the pack. Active cell balancing hardware architectures incorporating a low-voltage (LV) bus supply have been introduced to unlock lost capacity due to cell imbalance at reduced cost, through elimination of the vehicle's 400-to-12 V dc-dc converter. In this article, a hierarchical model-predictive control scheme is applied to a time-shared isolated converter active balancing architecture that incorporates LV bus supply. The proposed controller efficiently divides computation among the battery management system (BMS) hardware components. The energy-buffering capability of the lead-acid battery, which is connected to the LV bus, is used to tradeoff balancing and bus regulation objectives, reducing peak power and improving the system cost-effectiveness. Simultaneous state-of-charge balancing and LV bus regulation is verified in simulation and experiment using real-world drive and LV load data collected from a GM Bolt EV. Similar controller performance compared to a central scheme is achieved in simulation. The experimental setup includes a custom 12S2P, 3.9 kWh, liquid-cooled Lithium Nickel Manganese Cobalt battery module with an embedded BMS. The controller performance is evaluated with an initial maximum state-of-charge imbalance of 6.8%.