Analysis of the series-connected distributed maximum power point tracking PV system

The output power of a string of photovoltaic (PV) panels reduce significantly under mismatching and shading effect. Therefore, in order to optimal the output power of the PV panels, the distributed maximum power point tracking (DMPPT) PV systems with the feature to perform maximum power point tracking (MPPT) function on each PV panel have been proposed. Among various circuit topologies, the scheme with series-connected converter output terminals has found a lot of attention due to its low rating devices and low voltage conversion ratio. It is well known that the cross-coupling effect introduced by the series-connected structure can be suppressed under closed-loop control. However, the small-signal ac model and compensator design of a PV module in a string have never been developed and analyzed in detail. Therefore, in this paper the small-signal ac model with the remaining PV modules in the string considered is derived to analyze the stability of the system. The derived mathematical equations are verified with computer simulations and a prototype system consists of two series-connected four-switch buck-boost (FSBB) converters and a single phase grid-tied inverter.