MPPT for grid-connected photovoltaic systems using ripple-based Extremum Seeking Control: Analysis and control design issues

• Grid-connected PV systems without intermediary DC–DC converter stage are considered.
• An Extremum Seeking Control MPPT algorithm is proposed for such PV systems.
• The method uses the naturally occurring DC-link voltage ripple as dithering signal.
• Based on thorough analysis relevant control design guidelines are provided.
• Numerical simulation results under fast-changing irradiance scenarii are discussed.

This paper deals with an Extremum Seeking Control MPPT algorithm for grid-connected PV systems without intermediary DC–DC converter stage. The method uses the DC-link voltage ripple as dithering signal, which “naturally” results from the grid inverter operation. A thorough analysis emphasizes the significant variation of system behaviour with the irradiance. Relevant control design guidelines and necessity of an adaptive control approach for fast-changing irradiance tracking emerge from this analysis. MATLAB®/Simulink® numerical simulations are presented in order to illustrate the closed-loop dynamic performance under various scenarios, which also allows for assessing advantages and limitations of the proposed method.