Islanding Operation of Distributed Generators in Active Distribution Networks

This paper presents a simulation study of islanding operation of distributed generators (DGs) in active distribution networks. It validates the technical feasibility of islanding operation of DGs to exploit their major advantages in providing ancillary services and in enhancing overall quality and reliability of energy supply. The grid-connected DGs are operated at PQ mode. On disconnection from grid, they are switched to V-f mode to operate as independent power islands with full controllability of bus frequency and voltage. Suitable controllers are employed separately for individual control of voltage and frequency at the DG bus. Stand-alone and interconnected 28.1 MVA, 11 kV gas turbines are used as DG in this study. The simulation results are validated through several case studies using DIgSILENT software package for both intentional and unintentional loss of grid (LOG) situations. It has been observed interconnected DG islands can better sham the system active and reactive power demand thereby leading to quick restoration of the system voltage and frequency within permissible bandwidth. However, further scope of this work is to study the operation of hybrid power islands with different types of DGs and storage facilities and to investigate economic options for re-synchronising the islanded DGs with the main grid as and when required.