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In this study, a new non-linear dynamic controller is proposed for regulating the output voltage of a DC/DC boost power converter in a stand-alone photovoltaic (PV) system. The controller provides directly the duty-ratio input of the converter, bounded in the permitted range, and as it is proven it achieves the desired voltage regulation independently from the PV source voltage, the converter parameters and the kind of the load. An appropriate mathematical analysis is used to indicate that the proposed control scheme guarantees closed-loop system stability with the state trajectories converging to the desired equilibrium. Particularly, using as generic concept the fundamental property of passivity of the original system, the proposed controller scheme results in a closed-loop system wherein (i) the passivity and damping properties are maintained and (ii) the conditions which exploit these properties in a manner that guarantees stability are met. Extended simulation and experimental results verify effectiveness of the controller for the case of a DC/DC boost converter with resistance-inductance load. The system performance, operating with the proposed non-linear (voltage) controller is compared with that obtained by implementing conventional cascaded (voltage-current) controllers under input voltage step disturbances or load variations. Finally, some experimental resuts for the case of a non-linear load consisted of a three-phase voltage source inverter and a three-phase resistance-inductance load are illustrated.

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A systematic and general method that proves state boundedness and convergence to nonzero equilibrium for a class of nonlinear passive systems with constant external inputs is developed. First, making use of the method of linear-timevarying approximations, the boundedness of the nonlinear system states is proven. Next, taking advantage of the passivity property, it is proven that a suitable switching storage function can be always obtained to show convergence to the nonzero equilibrium by using LaSalle's Invariance Principle. Numerical and simulation results illustrate the proposed theoretical analysis.

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