Experimental verification for seamless mode transitions of multiple microgrids using fuzzy-based droop controller

Abstract

Continuous growth in electricity demand, increasing awareness for global warming and other en- vironmental issues have triggered attention to a new type of electricity generation-the so-called distributed generation consisting of various renewable energy sources. Despite the technological, economic and environmental benefits that the new generation system brings about, intermittent and uncontrollable nature of the renewable energy sources creates new type of challenges. The emergence of microgrids, prompted by such background, can offer a platform for effective integra- tion of distributed generation systems.
In this thesis, two microgrids network interconnected through a backbone bus is developed. The main feature of this system is the absence of ICT infrastructure. Instead, the so-called droop con- trol is used to regulate power outputs among the interconnected microgrids; frequency information obtained from local measurements, is the only signal used for communications.
Within this context, the thesis focuses on improvements of issues related to short-term dynamics of the droop control. To be more specific, it concerns the seamless transitions between islanded and backbone connected mode. The novel advanced controllers were developed in order to en- able these seamless transitions. They also aim to overcome the challenges found in the previous works within the same project. Three main functions exist in the controllers implemented for this thesis: synchronisation, seamless intentional(planned) and unintentional(unplanned) islanding. These developed controllers were verified and validated through both simulations and experimen- tal analysis. A significantly improved synchronisation performance was found, with the use of the newly introduced Synchronous Reference Frame-Phase Locked Loop (SRF-PLL) method. A fine tun- ing of the control parameters for voltage source inveters helped to shorten the preparation time for planned islandings. Last but not least, the introduction of the fuzzy droop controller reduced tran- sients in the microgrids during unexpected disconnections.
The software platform used for the development was LabVIEW, and GPIC FPGA was utilised as the hardware platform. The functionality of the controllers were tested under several base and extreme case studies and scenarios. The results were compared to that of the previous controllers and the agreement between simulation and experimental results were evaluated.