Doctor of Philosophy
Electrical and Computer Engineering
This thesis is focused on the modular multilevel converter (MMC) for Photovoltaic (PV) applications. It is an attempt to address the issues associated with the modeling, control, and power mismatch elimination of the MMC-based PV systems. Firstly, a new real power reference generation scheme is proposed that creates a linear relationship between the real power reference of the system and the dc link voltage of the submodules. Further, a new power mismatch elimination strategy is proposed for the MMC-based PV system which ensures balanced currents are delivered to the host grid regardless of leg and arm power mismatches. The thesis also proposes a new configuration for embedding battery energy storage(BES) systems into the arms of the converter. Then, an enabling control scheme is proposed for the MMC-based PV-BES system which employs the embedded BES systems to eliminate power mismatches and smoothen the output power of the PV generators. To mitigate large power mismatches which are outside the power rating of the BES systems, the proposed strategy uses a combination of power exchange with BES systems and power transfer between the legs of the converter. Finally, a modified power mismatch elimination strategy is proposed to ensure balanced grid currents even if the grid voltage is unbalanced. To achieve this goal, unequal powers are delivered to the grid from the phases of the system according to the voltage magnitude of each phase.
Bayat, Hasan, "Transformerless High-Power Medium-Voltage Multi-Module PV Converters" (2018). Electronic Thesis and Dissertation Repository. 5630.