Gain-Scheduled Control of Modular Battery for Thermal and SOC Balancing

Paper in proceeding, 2016

This paper proposes a simple constrained proportional controller with gain scheduling for simultaneous thermal and state-of-charge (SOC) balancing of a multilevel converter based modular battery. The proposed balancing controller is devised by investigating structural properties of constrained linear quadratic (LQ) model predictive controller (MPC) introduced in our earlier study. This investigation reveals a particular factorization of time-varying control gain matrices, which leads to approximation of matrix gains as scalar gains under the assumption of small parametric variations among battery cells. The gains are scheduled in load current for nominal cells. This special structure enables the identification of two dominant operational modes of the balancing controller: SOC balancing mode in low to medium load current range and thermal balancing mode in high current range. This study also proposes a simple algorithm for control projection on constraint polytope. The proposed balancing controller is tested in simulations for a modular battery with four significantly mismatched cells. The performance is comparable to MPC, which uses true battery parameters. The performance and the simplicity of the controller make it attractive for real-time implementation in large battery packs.