A Power Mismatch Elimination Strategy for an MMC-Based Photovoltaic System

This paper proposes a power mismatch elimination strategy for a medium-voltage modular multilevel converter (MMC)-based photovoltaic (PV) system. In the MMC-based PV system, each submodule of the MMC is energized by multiple PV generators, each interfaced with the dc port of the submodule by a corresponding isolated dual active bridge dc-dc converter. This configuration allows for a transformerless connection to the host grid and independent maximum power point tracking for the PV generators. The paper then proposes a power mismatch elimination strategy that ensures that the current delivered to the host grid is balanced in spite of unbalanced PV generator outputs. The proposed power mismatch elimination strategy employs a dc differential current to equalize the leg powers, and an ac differential current to stabilize the dc voltages of the submodules. The effectiveness of the proposed power mismatch elimination strategy is demonstrated by time-domain simulations conducted on a model of the PV system in PSCAD/EMTDC software environment.