# Enhanced Control Strategy for Three-Level T-Type Converters in Hybrid Power-to-X Systems
###### Abstract  
This paper presents a dual-loop control system designed for three-level three-phase T-type converters, optimizing their performance in the hybrid operation of Power-to-X systems. Due to the increasing of distributed power generation based on renewable energy sources, Power-to-X systems convert surplus renewable energy into other forms of energy, such as hydrogen, synthetic fuels, or chemical storage, which can be stored and later converted back to electricity or used in other applications. Bidirectional converters play a crucial role in hybrid system operation, which requires an efficient and reliable power conversion to maintain stability and performance. The proposed dual-loop control system includes an inner current loop for fast current regulation and an outer voltage loop to maintain stable voltage levels, ensuring precise control of the output of the converter and enhancing its response to dynamic changes in load and generation. Additionally, the control system incorporates a technique to balance the split DC-link capacitors voltages, a major challenge in three-level converters. Comprehensive simulation and experimental results demonstrate the efficacy of the proposed control system in maintaining high power quality and supporting the hybrid operation of Power-to-X systems.  
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Footnote †: journal: Applied sciences  
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hybrid systems [12; 13; 14]. Among these, T-type converters have been chosen in this paper due to their lower conduction losses, reduced complexity, and improved efficiency compared to NPC and ANPC topologies. NPC converters, while effective at balancing capacitor voltages, suffer from higher conduction losses and increased component count. ANPC converters offer additional control flexibility but introduce higher switching losses and complexity in implementation. T-type converters provide an optimal balance between efficiency, implementation feasibility, and performance in P2X applications, making them the preferred choice for this paper [15; 16]. DC-to-AC converters (also known as inverters) are used in the integration of batteries and fuel cells in P2X systems, which enhances the flexibility and resilience of energy management [17]. Batteries offer rapid response capabilities and high efficiency for short-term energy storage, while fuel cells provide long-term storage solutions and high energy density. In addition, inverters are a key component in renewable energy integration to hybrid systems such as photovoltaic systems connected to the grid [11; 18; 19]. The need for this research arises from the growing challenge of maintaining power quality and system stability in hybrid P2X energy conversion systems. Current methods, as detailed in the Literature Survey section that follows, suffer from steady-state errors, limited adaptability to grid disturbances, and inefficient power flow management. To address these limitations, this study develops a novel dual-loop control strategy that improves system robustness, enhances power quality, and ensures precise tracking of reference signals. This approach is essential for enabling more efficient and reliable integration of renewable energy into the power grid.