A Current-Source Modular Converter for Large-Scale Photovoltaic Systems

The world is shifting toward renewable energy sources (RESs) to generate clean energy and mitigate the stress of global warming caused by CO2 emissions in recent decades. Among several RES types, large-scale photovoltaic (LSPV) plants are a promising source for meeting ambitious clean energy targets and being part of power generation. With the progress of high-power modular inverters, new opportunities have arisen to integrate them into LSPV systems connected to medium-voltage (MV) grids to obtain high efficiency and reliability, better system flexibility, and improved electrical safety compared with string or central inverters. This thesis presents and implements a new current source three-phase modular inverter (TPMI) based on a novel dual-isolated SEPIC/CUK (DISC) converter. The TPMI is designed with a single power processing stage comprised of seriesconnected DISC submodules (SMs) to deliver MV into the utility grid. It outperforms conventional high-power inverters in terms of modularity, scalability, galvanic isolation compliance, and distributed maximum power point tracking (MPPT) capabilities. The DISC converter employed as an SM in the proposed TPMI generates bipolar output (i.e., both positive and negative voltages). In addition to having step-up and step-down capabilities with a continuous input current, this converter shares an input side inductor, thereby reducing the number of components. The DISC structure, modulation method, operation, novel state-space model, and parameter design procedure are analysed in details. Then, simulation results are presented to validate the theoretical and analytical analyses of the DISC converter. The proposed TPMI inverter is subsequently integrated into the LSPV grid connection to prove its suitability for such applications. In the theoretical analysis, the advantages of TPMI structure over conventional topologies are discussed. Then, the modulation technique, and operational concept are presented, followed by a dedicat