Aging Management Using a Reconfigurable Switch Network for Arrays of Nonideal Power Cells

Abstract

Power cells, such as battery cells, solar cells, and fuel cells, are often connected in series and parallel to satisfy a desired amount of power and energy density as well as the terminal voltage. However, it is allowed to compose an array of power cells only when the individual cell has the identical characteristics among each other. However, even originally identical cells eventually have different characteristics due to uneven aging as well as manufacturing process variations. Mixture use of nonidentical cells in the same array results in: 1) significant inefficiency of the whole array; 2) accelerated aging of the weak cells; and 3) degrading healthy cells due to overloading. This paper is first to introduce a system-level solution for cell aging management. The proposed method is dynamic reconfiguration to modify cell grouping and array structures to enable independent control of aged cells from healthy cells. The reconfiguration switch network regroups cells into healthy, aged, and residual array groups, regardless of the physical locations of the aged cells. The proposed network is highly scalable in that the number of switches grows linearly as the number of cells increases. We show practicality of the proposed reconfiguration switch network with a case study of a solid oxide fuel cell (SOFC) system. However, the proposed reconfiguration switch network can be applied to any power cell arrays with an aging effect. We demonstrate significant improvement on the operating hours of an SOFC array. Such improvement is comparable with cell-level independent aging control where every SOFC stack has its own dc-ac inverter.