Control of an IMMC-based multilevel converter using an MPPT–SPWM strategy for voltage balancing of submodules in large-scale photovoltaic systems

Abstract

The Isolated Modular Multilevel Converter (IMMC) has emerged as a promising topology for medium-voltage photovoltaic (PV) systems due to its modular architecture and inherent electrical isolation capability. However, in large-scale PV installations, non-uniform solar irradiance across distributed arrays often results in unequal power generation among modules. This condition can lead to voltage imbalance among the converter modules, thereby deteriorating the overall system performance. To overcome this limitation, this paper proposes a unified control strategy for a three-phase IMMC, where each phase consists of two arms, with four modules per arm. The proposed method integrates a DC/DC converter with an enhanced Maximum Power Point Tracking (MPPT) scheme to simultaneously achieve maximum power extraction from each PV source and coordinated power distribution among modules. Through this coordinated control mechanism, voltage balancing among the modules can be inherently achieved without introducing additional balancing control loops. On the inverter side, Sinusoidal Pulse Width Modulation (SPWM) is employed to synthesize the converter output voltage. Simulation results verify that the proposed control strategy effectively improves voltage balance among the modules, ensures stable converter operation, and enhances dynamic performance under varying irradiance conditions, demonstrating its suitability for large-scale PV applications.