Maximum power tracking in solar cell arrays using time-based reconfiguration

Directly harnessed solar power is an attractive primary energy source for integration into fully wire-free, self-sufficient, portable electronic devices. Maximum power (MPP) tracking of photovoltaic (PV) cells is an essential part of PV energy harvesting and several methods are available to track MPP efficiently. With more than one cell, power-balancing is also a significant concern and global MPP tracking, parallel connection of PV cells, and active array reconfiguration are all techniques designed to address this issue. This work shrinks array reconfiguration from two-dimensional arrays of PV cells to a single string of PV cells, which are particularly relevant to portable systems. Each string element has individual MPP tracking and power balancing at low circuit complexity using a modular, time-domain array-reconfiguration (TDAR) approach. Both, a discrete control loop that demonstrates the concept and a 150 μW microchip that implements TDAR for three PV cells were developed. The energy harvesting efficiency of the TDAR approach is more than 80% improved compared to static (non-reconfigurable) strings of PV cells. While other array reconfiguration approaches can offer comparable improvements in efficiency, the reduced complexity of the TDAR approach makes it the only scalable approach that can be practically applied to array reconfiguration in portable systems.