Multilevel converters with cascaded h-bridges under power imbalance conditions for grid-connected photovoltaic and energy storage applications.

Abstract

This dissertation investigates the use of Cascaded H-Bridge (CHB) inverters in grid-connected photovoltaic (PV) systems, addressing power imbalance challenges and exploring the integration of energy storage systems. Control and modulation strategies are proposed and analyzed to mitigate DC-Link voltage oscillations and ensure stable operation under asymmetric generation conditions. Furthermore, the research explores the application of hybrid energy storage systems (HESS) combining batteries (BESS) and supercapacitors (SC) to optimize energy management and extend battery lifespan in zero-grid injection operation. A reduced-switch count CHBtopology is also presented and analyzed. Level-Shifted Pulse Width Modulation (LS-PWM) and Phase-Shifted Pulse Width Modulation (PS-PWM) techniques are detailed, along with their corresponding control strategies. The dissertation includes a comprehensive analysis of control diagrams, mathematical formulations for controller gains, and an analysis of individual CHB cell control. Simulation and experimental results are presented to validate the effectiveness of the proposed strategies in maintaining power balance, reducing voltage fluctuations, and improving system robustness and efficiency. A comparative analysis between LS-PWM and PS-PWM is conducted, highlighting their differences and suitability for the studied topologies. The conclusions of this research contribute to advancing the applicability of CHB converters in distributed PV generation systems under variable conditions and with integrated energy storage.