Supervisor:
Professor Zhe Chen

Co-Supervisor:
Assistant Professor Yanbo Wang

Assessment Committee:
Associate Professor Sanjay Kumar Chaudhary, AAU Energy (Chair)
Professor Seddik Bacha, University of Grenoble
Mauro Cappelli, ENEA Frascati Research Center

Moderator:
Associate Professor Sanjay Kumar Chaudhary

Abstract:

With the increasing exploitation of renewable energies, distributed power generation and power-electronics developments leads to innovative concepts of microgrids. The emerging microgrid concept can promote integration of renewable energies into the utility grid. However, there are also challenges to execute microgrids. At converter control level, accurate power sharing performance is important for converter lifetime but can be affected seriously by increasingly used nonlinear components. At system optimization level, power sharing ratio can be optimized for system efficiency and operation cost, which are highly coupled and cannot be optimized by independent optimization of either of them. Therefore, it is necessary to develop analysis and control methods for desired power control performance in microgrids both at converter level and system level.

The aim of this project is to develop advanced control methods to improve power sharing performance of microgrids considering nonlinear components impacts and efficiency and cost optimization. The thesis is organized as follows. Chapter 1 introduces the background, challenges and objectives of this project. The thesis outline is also presented in this chapter. Chapter 2 analyzes the influence of filter inductor nonlinearity on system power control performance. And a robust droop controller is designed to ensure accurate reactive power sharing performance regardless of impacts of nonlinear filter inductors. Chapter 3 establishes an efficiency model to analyze the core relationship between power sharing ratio and system efficiency. An efficiency-prioritized droop controller is further developed to reduce system power loss by adjusting power control references dynamically. Chapter 4 presents a self-optimization droop controller to enhance system performance considering efficiency and cost together according to proposed multi-objective optimization model. Chapter 5 summarizes conclusions of this research and explains potential future research topics.

The main contributions of this project are drawn as follows. (1) The power control performance of microgrids is analyzed under impacts of nonlinear filter inductors. (2) The reactive power distribution deviation caused by nonlinear inductor is mitigated so that the system power control performance is ensured even with cost-effective nonlinear filter inductors. (3) The optimization conditions of maximum system efficiency are derived based on the core relationship between power sharing performance and system efficiency. (4) System efficiency is improved by decentralized controller without using communication devices. (5) The coupling behaviour of system efficiency and operation cost is analyzed and the overall system performance is improved with consideration of efficiency and cost at the same time.