MMC Submodule Topology for Integrated Photovoltaic and Energy Storage Converters and Its Double-Layer Balance Control Strategy
Abstract
: The rapid growth of distributed photovoltaic (PV) power generation has led to higher requirements for reliable and efficient photovoltaic-storage integrated converters. Traditional half bridge sub-module structures face significant challenges, including limited DC fault-blocking capability and uneven loss distribution among sub-modules due to variations in the conduction characteristics of power devices. To address these issues, this study proposes innovations in both topology and control strategy. A clamp double energy storage submodule (CDESSM) with inherent fault self-blocking capability is designed, improving system safety under fault conditions. Furthermore, a nearest level modulation (NLM) algorithm based on conduction time equalization is developed, combined with a dual-layer sub-module capacitor voltage balancing scheme to maintain uniform voltage distribution across sub-modules. The proposed design effectively reduces voltage deviation, balances losses, and enhances overall converter performance. Simulation demonstrates that the improved system maintains stable output under normal operating conditions and can isolate DC faults within milliseconds, validating its reliability. RT-LAB testing further confirms the engineering feasibility of the proposed topology and control strategy, indicating its potential for practical applications in PV-storage integrated systems. The combination of structural innovation and advanced control methods provides a promising approach for enhancing the performance, safety, and longevity of next generation PV-storage converters.