Comparative analysis of DC to AC conversion cells for application in PV-linked grid-connected modular multi-level cascaded converters

This study provides a detailed analysis of a dc to ac conversion unit as a building block of a modular multilevel converter for grid integration of photovoltaic (PV) systems. Each conversion unit contains a PV-linked multi-active-bridge (MAB) dc-dc converter followed by a grid-connected single-phase cascaded inverter. Using MAB topology can reduce the size and cost of the entire system as more conversion cells are connected to the same transformer. To integrate the PV outputs and maintain the maximum power point tracking (MPPT), different conversion cell topologies are feasible for the MAB converter. This study provides a comparison between the feasible topologies of the conversion cells in terms of the conversion efficiency, reliability, power transfer ability, cost, size, control complexity and generated ripple. The steady-state operation and the control technique of the selected topology are presented in detail. Some control techniques are introduced to improve the system's efficiency and MPPT performance of the conversion cell. A prototype of the conversion cell is developed to validate the proposed topology and the control techniques.