Contributions to distributed generation:

grid-supporting control of multi-source grid-tied power converters

Abstract

The increasing demand for clean and reliable electrical energy has intensified research into distributed generation systems that can efficiently integrate renewable sources. As the use of nonrenewable energy becomes progressively constrained by environmental and policy factors, renewable technologies such as solar, wind, biofuel, hydropower, and green hydrogen are emerging as sustainable alternatives for modern power systems. However, the extensive penetration of converter-based generation introduces challenges in maintaining voltage and frequency stability, particularly in low-inertia and islanded microgrids. Among the converter topologies, DC–DC boost converters followed by DC-AC inverters are often found to interface renewable energy sources with the grid. Despite numerous advancements in multi-input converter topologies, achieving both flexible power integration and robust grid support remains a significant challenge. In particular, converters must provide dynamic services such as frequency and voltage regulation while ensuring high efficiency and reliability. This thesis proposes a family of
impedance-source converters based on the split-source inverter, along with associated control strategies for the coordinated integration of multiple low-power renewable sources, aimed at applications in microgrids and nanogrids. The work emphasizes converter designs that enhance reliability, power quality, and resilience, while also contributing to grid-support functions. A detailed continuous- and discrete-time state-space analysis forms the basis for developing a Model Predictive Control approach for switching control. Furthermore, a space vector analysis at fixed switching frequency is employed to establish the operational limits of the converter and to guide its design and performance evaluation. Building upon the grid-supporting control concept, this thesis proposes a novel strategy that utilizes the energy stored in the DC bus capacitors to deliver a fast frequency response, enabling coordination with larger storage systems. The proposed control framework and converter topologies are validated through a combination of software-in-the-loop simulations, hardware-in-the-loop experiments, and laboratory prototypes. The results demonstrate effective collective power injection from multiple independent sources and confirm the grid-supporting potential of inverter-based distributed resources, even when connected to larger power systems.