An Estimator of Solar Irradiance in Photovoltaic Arrays With Guaranteed Stability Properties

Photovoltaic cells are characterized via a static relationship that describes their current-voltage relationship. This relationship is a complicated implicit algebraic equation that depends, in a nonlinear way, on two critical uncertain parameters: temperature and solar irradiance. The efficient operation of the panel relies on the knowledge of these key parameters. While it is technologically feasible to measure the former, a sensor for the latter is usually expensive and difficult to calibrate. In this paper, we propose a globally convergent estimator for solar irradiance which is developed using the principles of immersion and invariance recently reported in the control literature. To design the estimator, a suitable reparameterization of the current-voltage characteristic, which effectively exhibits a monotonic behavior, is introduced. The approach is validated through detailed computer simulations and experimental prototyping using real outdoor measurements.