Issues on Solar-Generator Interfacing With Current-Fed MPP-Tracking Converters

The large-scale harvesting of solar energy is an important action to decelerate the observed climate changes. Reliably operating solar-energy systems composing of solar arrays and their interfacing converters are of prime importance to maximize solar-energy harvesting. The paper investigates the solar-generator interfacing in terms of current-fed (CF) maximum-power-point (MPP) tracking converter. The investigations show that the CF converter under input-voltage control can usually operate from the short-circuit to open-circuit conditions of the solar generator without stability problems. When the output voltage or current has to be controlled constant, the converter may become unstable at the MPP due to the negative incremental resistance appearing at its input terminals. In practice, this means that the operating range of the CF converter has to be limited to the voltages less than the MPP voltage, when the output-voltage or current control is active. Practical evidence is provided based on a CF superbuck converter derived from the corresponding voltage-fed converter applying duality-transformation methods and supplied by an actual solar panel.