Systematic control strategy for inverter-based microgrids

Abstract

Small-scale power systems, microgrids (MGs), are becoming economically and technically feasible due to cost-effective battery storage with high-bandwidth inverter interfaces, thus facilitating efficient energy utilization from renewable sources to maintain autonomous operation without a grid connection. Therefore, control of inverter-based or inverter-dominant systems is gaining a lot of attention while posing different challenges compared to traditional power systems. Conventional droop-based control architectures can provide power-sharing capability, and are considered to be a cost-effective and reliable solution for microgrids. However, experimental studies have revealed that for small-scale microgrids, stability is significantly compromised by the droop control due to low X/R ratios and short lines. Therefore, a proper modeling framework for obtaining concise and accurate models becomes important to understand the physical nature of the instability. Such a framework can further facilitate a systematic control design for stability enhancement, allowing the development of power-sharing strategies and plug-and-play functionality for efficient microgrid operation. In this thesis, high-fidelity reduced-order models for microgrids are first developed and investigated. Then, based on the proposed models, concise and simple stability certificates are derived along with virtual impedance methods for local and global stability enhancement. Detailed discussions are carried out on the control design that aims at achieving both droop stability and controller robustness. Finally, a power and energy management scheme based on secondary compensation is developed to enhance operational efficiency. The integrated solution provides a comprehensive reference for the development of stable, reliable, and flexible inverter-based microgrids. All results are validated through both simulation and experimental studies.