Traditional photovoltaic (PV) systems are stationary PV systems mounted in one location and, generally, receive consistent and even illumination across the PV panel. However PV cells can also be utilized in wearable applications, in which the PV cells are likely to experience uneven illumination. Under uneven illumination, traditional series-connected PV systems experience severely decreased output power and overall efficiency. The system output power can be increased by improving the power converter connection architecture and control method. To achieve optimal system efficiency, differential power processing (DPP) converters are adapted so that each PV cell can operate at its own maximum power point (MPP) even under uneven illumination. This paper introduces a PV power system with four DPP converters for a wearable application that allows the system to effectively utilize PV energy under even and uneven illumination conditions. The DPP converter design and control method are validated through simulation results, including dynamic illumination changes, and experimental results using a hardware prototype. Results show that each PV cell is controlled independently such that each PV cell operates at its own MPP under uneven illuminations.

Solar photovoltaic (PV) power is a widely used to supply power to the electric grid but can also be used in lower-power emerging applications, like in wearables or the internet of things. One fundamental challenge of using PV power in flexible wearable applications is that individual PV modules point at various angles, thus receiving different light intensities. Using a series configuration for the PV modules greatly decreases power utilization under uneven irradiance conditions. Parallel differential power processing (DPP) converters are employed to address this power reduction problem, while maintaining individual PV control and maximizing output power. Two parallel DPP configurations, with and without a front-end converter, are analyzed and compared for a target battery-charging application. The DPP system without a front-end converter shows consistently high performance and operates properly over a wider range of lighting conditions. Maximum power point tracking (MPPT) algorithms are also examined for parallel DPP systems. When the MPPT parameters are properly calibrated, simulation results indicate that voltage-offset resistive control is the most effective at maximizing PV power under unbalanced lighting conditions.