  This paper presents a centralized recursive optimal scheduling method for a
battery system that consists of parallel connected battery modules with
different open circuit voltages and battery impedance characteristics. Examples
of such a battery system can be found in second-life, exchangeable or
repurposed battery systems in which batteries with different charge or age
characteristics are combined to create a larger storage capacity. The proposed
method in this paper takes advantage of the availability of buck regulators in
the battery management system (BMS) to compute the optimal voltage adjustment
of the individual modules to minimize the effect of stray currents between the
parallel connected battery modules. Our proposed method recursively computes
the optimal current scheduling that balances (equals) each module current and
maximize total bus current without violating any of the battery modules
operating constraints. Recursive implementation guarantees robust operation as
the battery modules operating parameters change as the battery pack
(dis)charges or ages. In order to demonstrate the capability of this method in
real battery system, an experimental setup of 3 parallel placed battery modules
is built. The experimental results validate the feasibility and show the
advantages of this current scheduling method in a real battery application,
despite the fact that each module may have different impedance, open circuit
voltage and charge parameters.
