Control strategies in an islanded microgrid with high penetration of renewables

This thesis presents the control and performance of a hybrid Microgrid (MG) which integrates photovoltaic (PV), battery and conventional sources. A hybrid MG offers advantages in improving system reliability, economic efficiency and renewable penetration level. For a MG with a high penetration level of PV, system requirements and constraints are different to traditional electric grid. In particular, traditional grid-following PV sources are expected to provide ancillary services, e.g. frequency regulation and voltage support. However, the intermittent, varying and uncertain nature of PV generation imposes challenges on its realization. The coordination strategy for multiple parallel connected MG sources are presented, with the aim of improving renewable penetration level, system reliability while considering power characteristics of individual sources. In detail, an innovative real power sharing scheme is first proposed which prioritizes renewable power sources in power supply. Meanwhile, a decentralized implementation strategy is also investigated which enables “peer to peer' and “plug and play” functionalities. The issues in reactive power sharing are then reviewed and two new approaches for reactive power sharing are proposed to improve system reliability and applicability. The reactive power sharing accuracy is also improved by a new method and its performance relative to the established virtual impedance method is evaluated. Small-signal models for the proposed control strategies are established to evaluate the stability. Simulation and experimental results are both presented that evaluate and validate the performance of the proposed control strategies. The results show that the proposed control techniques offer desired performance.