Contribution à la commande d’un système photovoltaïque connecté à un réseau électrique

Abstract

This thesis focuses on the design and control of a photovoltaic (PV) system connected to a single-phase grid. The conversion structure of the system includes two stages: a DC-DC boost converter and a Pulse-Width Modulated Voltage Source Converter (PWM-VSC), connected in cascade through a DC bus. This structure enables the extraction of the maximum power from the PV array as well as the conversion and the injection of excess or all of the produced PV power into the grid. This research work mainly focuses on the development of different control strategies to manage the operation of the PV system under various situations, including normal operation without any faults and operation under a specific grid fault, named islanding. Under normal operation, the DC-DC boost converter connected to the PV array is equipped with an MPPT control technique based either on the fixed-step size or on the variable-step size Perturb and Observe (P&O) algorithm. Its control strategy uses an outer loop based on a simple PI controller and an inner loop based on a hysteresis current controller (HCC). The PWM-VSC connected to the grid through a filter is controlled by a control strategy that employs an outer loop based on a PI controller and an inner loop based either on a HCC or on a predictive current controller (PCC). The system performances are verified through digital simulations carried out in the Matlab/Simulink environment and experimentally validated in real-time using a dSPACE 1104 card . For operating under grid islanding conditions, the PV system uses a control strategy that manages its operating in two modes : grid-connected mode under normal conditions and stand-alone mode in case of islanding, with a smooth transition between these two modes. In the absence of the grid, the DC-DC boost converter is controlled by a control technique that combines the variable-step size P&O MPPT technique with a Non-MPPT technique, while the PWM-VSC is controlled by a predictive voltage controller (PVC). The system performances are verified via digital simulations under different operating conditions .