A streamlined start-up procedure for grid-connected photovoltaic system with DC power optimizers

In traditional grid-tied photovoltaic (PV) systems, the power output drops significantly when partial shadowing occurs between different PV modules in a string, as the PV string current is limited to the value delivered by the weakest module. This issue is mitigated by coupling a dc-dc converters (micro-converter) to every PV module, each being operated at the maximum power point (MPP). In this scenario, without communication links between the distributed micro-converter and the grid-tied inverter, a system start-up procedure must be carefully designed to avoid over-voltages occurring at the micro-converters/inverter interface, eventually leading to system breakdown or failure. In this paper, the control algorithm of each converter is enhanced to provide a seamless start-up operation, so that PV units can safely start transferring power to the inverter and the grid. Improving from previous works, the proposed control technique is simple and removes the need for current sensors at the output of each micro-converter and at the inverter dc-link, providing an economical advantage. Simulation results demonstrate the successful system start-up behavior, whilst confirming the benefits of the proposed control technique.