| dc.description.abstract | This dissertation presents an analytical study on virtual synchronous machine-based power control in active rectifiers for micro grids supported by prototype modelling, simulation results and discussions.Popularity and demand of the distributed energy resources and renewable energy sources are increasing due to their economic and environmental friendliness. Concept of micro grid with an active rectifier (AR) interface has been found to be promising for smart integration of such distributed generation units. Having the presence of a synchronous generator (SG) in a micro grid introduces several advantages in terms of stability and reliability in the power system. This is mainly owed to the inertia, damping and load sharing properties of SG. This in return, gives rise to the question if an AR of a micro grid can imitate the behaviour of a synchronous generator, can the stability and reliability introduced by SG be replicated in a micro grid. A research on the state-of-the-art for uninterruptible power supplies (UPS) has been carried out to identify the implementation and the control strategies of redundancy and parallel operation as UPS has been an established technology over the last decades. The theoretical study on virtual synchronous machine (VSM) concept in the fall, 2011, has been extended in developing a model with classical inner current control and outer voltage control loops based on the synchronous reference frame.The complete active rectifier model has been able to emulate the inertia, damping and load sharing properties of a SG and redundancy and expandability of parallel UPS systems. It must be emphasized that due to the flexibility of the virtual machine parameters and the absence of magnetic saturation and eddy current losses, a much improved performance have been achieved with a VSM compared to a synchronous generator.Simulations have been carried out for single and parallel operation of active rectifiers in island and grid-tied modes with satisfactory stability, damping and power sharing features.Key words Active rectifier, virtual synchronous machine, micro grid, uninterruptible power supply, load sharing, redundancy, island mode, grid-tied mode, synchronous reference frame | nb_NO |
