UC San Diego

Used batteries that are no longer fit for their original applications can be combined to form

usable battery packs. Cells can be connected in series to form modules with higher voltage, and

these modules can be connected in parallel to build up the capacity of the battery pack. Parallel

connections may cause stray currents within the battery pack due to heterogeneous operational

parameters of the modules, so the current output by each module must be controlled to eliminate

this problem. We present an approach to control such a configuration by buck regulating the

terminal voltage of each module. The novelty of the proposed control algorithm is to separate

the control into two components: an occasional update to estimates of slow-varying system

parameters, and a frequent update of control inputs to accommodate fluctuations in the load. The

estimated system parameters are communicated infrequently by a central processor, while the

modules individually calculate control inputs. The required communication between modules and

the central processor is greatly reduced by distributing the calculation of control inputs, allowing

the system to scale up efficiently even as the number of modules grows large.