Investigations on modern control techniques for multi-source energy conversion systems connected to microgrids

Abstract

Microgrids are small-scale electrical networks integrating renewable energy sources, distributed generators, and local loads. They are designed to provide reliable and high-quality power supply in various operating modes, whether islanded or connected to the main grid, ensuring a seamless transition between these two modes. Thistype of system faces numerous technical challenges related to the nature of the loads, interruptions in energy sources, and the interconnection of components with different characteristics, which can impact the quality of the supplied power and the overall stability of the microgrid. With the emergence of modern power electronics converters and advanced control devices, a large part of these challenges can be solved. The work conducted as part of this thesis aligns with this context. Based on the robust performance of modern control systems, including fractional-order control, sliding mode control, and fuzzy logic control, we have developed new strategies and control tools for microgrids. Modern types of voltage source inverters, called Z-source and quasi-Z-source inverters, have been integrated. Through their design and adopted control strategies, an input voltage boosting function is enabled. Thanks to modifications in universal droop control, an improved hierarchical structure and a new decentralized structure were designed for managing multiple voltage-source inverters connected in parallel. The decentralized control strategy was proposed as a solution to manage the various operating modes of the microgrid without the need for communication lines. This approach avoids the drawbacks of centralized secondary control in hierarchical structures, such as delays or data loss, which could lead to a complete system failure. Furthermore, modern metaheuristic algorithms were employed to determine the optimal values for control parameters.