Relative-Degree-Based Discrete-Time Linear Active Disturbance Rejection Control of a Zeta Converter for Wide Input Voltage Range Photovoltaic Applications

Photovoltaic applications require stable output voltage regulation across a wide input voltage range and varying load conditions. The Zeta converter offers advantages for these applications; however, its fourth-order, switched, nonlinear dynamics create significant challenges for controller design. This study proposes a relative-degree-based discrete-time linear active disturbance rejection control (D-LADRC) strategy to address these complexities. This approach preserves the dynamics of the fourth-order Zeta converter and derives a second-order input–output model based on the relative degree. Dynamics not explicitly represented in the model are estimated by an observer and incorporated into the control action. The observer and controller are developed based on the second-order input–output model. A current-estimator-based linear extended state observer (CE-LESO), formulated in discrete time, uses the most recent output measurement at each sampling instant to estimate the total disturbance encompassing system dynamics, parametric uncertainties, and external disturbances. Comparative analysis with a PI controller indicates that D-LADRC provides faster reference tracking, reduced overshoot, and enhanced disturbance rejection in both simulations and experiments. D-LADRC also maintains consistent performance under inductance and capacitance uncertainties, as demonstrated by corner-case studies. The results support the effectiveness of the proposed approach for voltage regulation in Zeta converters used in photovoltaic applications.