Comparative Analysis of Unipolar and Bipolar Control of Modular Battery for Thermal and State-of-Charge Balancing
Journal article, 2017

Thermal and state-of-charge imbalance is a well known issue to cause nonuniform ageing in batteries. The modular battery based on cascaded converters is a potential solution to this problem. This paper presents bipolar control (BPC) of a modular battery and compares it with previously proposed unipolar control (UPC) mode in terms of thermal/SOC balancing performance and energy efficiency. The BPC needs four-quadrant operation of full-bridge converter using bipolar pulse-width modulation (PWM) inside each module, whereas UPC only needs half-bridge converter with unipolar PWM. The BPC, unlike UPC, enables charging of some cells while discharging others. An averaged state-space electro-thermal battery model is derived for a convex formulation of the balancing control problem. The control problem is formulated on a constrained LQ form and solved in a model predictive control framework using one-step ahead prediction. The simulation results show that BPC, without even requiring load current variations, gives better balancing performance than UPC, but at the cost of reduced efficiency. The UPC requires at least current direction reversal for acceptable balancing performance. In short, the UPC is a more cost and energy efficient solution for EV and PHEV applications whereas the BPC can be beneficial in applications involving load cycles with high current pulses of long duration.

averaging

model predictive control

Modular battery

thermal balancing

SOC balancing

multilevel converters

Author

Faisal Altaf

Chalmers, Signals and Systems, Systems and control

Bo Egardt

Chalmers, Signals and Systems, Systems and control

IEEE Transactions on Vehicular Technology

0018-9545 (ISSN) 1939-9359 (eISSN)

Vol. 66 4 2927-2941 7505945

Driving Forces

Sustainable development

Areas of Advance

Transport

Energy

Subject Categories

Control Engineering

Other Electrical Engineering, Electronic Engineering, Information Engineering

DOI

10.1109/TVT.2016.2587720

More information

Created

10/7/2017