Extremal control of DC/DC Converters in photovoltaic configurations

The paper proposes an extremal control method through the design of a RST controller for a step-down DC-DC Buck Converter fed by a BGSP - P225 PV array. The input voltage for the converter is kept at the photovoltaic panel's maximum value by means of search algorithms for determining the Maximum Power Point. The algorithms used are Coggin's algorithm for the single variable dependent model P(U) and the gradient algorithm is used for the P(I,U) model. The voltage value can after that be identified again for different iradiance and temperature conditions. This gives the converter an extremal input voltage. Next, a dynamic model has been determined for the closed loop control system, starting from the converter's electrical components equations. A numerical RST controller used to achieve the performances of the system, was designed. A robustness analyses and correction has been performed for the RST polynomial control. The achieved performances of the DC-DC converter are validated through simulation by using the MATLAB / SIMULINK environment and the WinReg dedicated software. The novelty of the paper resides in the design of the RST controller for a photovoltaic panel and the robustness analysis.