Issues on Solar-Generator Interfacing with Voltage-Fed MPP-Tracking Converters

The large-scale harvesting of solar energy is an important action to decelerate the observed climate changes and ensuring the availability of energy also in the future. Reliably operating solar-energy systems composing of solar arrays and their interfacing converters are of prime importance to maximize solar-energy harvesting. The main obstacle for the improvements in the reliability is turned out to be the lack of full understanding of the solar-generator interfacing. The paper investigates the interfacing in terms of voltage-fed maximum-power-point (MPP) tracking converters. The investigations confirm that there are two reasons for the observed problems of which the one is the violation of Kirchhoff’s current law governing the operation of a solar generator and the other is the phenomenon known as negative resistance oscillation (NRO) causing instability. In practice, this means that the voltage-fed converter can reliably operate only at the voltages higher than the maximum-power-point (MPP) voltage. Practical evidence is provided based on a coupled-inductor superbuck converter supplied by a real solar panel and loaded with a storage battery.