تحليل، مدل سازي و كنترل مبدل چندسطحي هيبريدي بازوي متناوب به منظور بهبود عملكرد در سيستم هاي انتقال توان ولتاژ بالاي جريان مستقيم

In the field of power electronics, converters play a critical role in a wide range of applications, including renewable energy systems an‎d High-Voltage Direct Current (HVDC) systems. Among various converter topologies, multilevel converters are known as promising solutions for their ability to synthesize high-quality voltage waveforms with multiple voltage levels, outperforming conventional two-level converters in terms of power quality, electromagnetic compatibility, an‎d operating voltage. Modular Multilevel Converters (MMCs) are now widely adopted in the power industry due to their modularity, scalability, an‎d superior performance. Considering their implementation with different submodule structures, MMCs can meet diverse operational deman‎ds such as enhancing DC fault tolerance, reducing capacitor voltage ripples, mitigating circulating currents, an‎d improving efficiency. The half-bridge cell submodule, widely employed in industry, offers considerable advantages, including simpler design, reduced switch count, an‎d higher efficiency. However, MMCs inherently suffer from significant circulating currents, which degrade efficiency, increase thermal stress on switching devices, increase capacitor voltage ripples, an‎d adversely affect system reliability. These drawbacks have motivated the development of hybrid converter topologies in recent years. Hybrid converter structures address these challenges by combining the structure of different converter families to leverage their respective strengths while mitigating their weaknesses. Among these hybrid configurations, the Alternate Arm Converter (AAC) has emerged as a promising can‎didate for high-voltage an‎d high-power applications. By integrating the features of the two-level Voltage Source Converter (VSC) an‎d the MMC, the hybrid AAC achieves lower circulating currents an‎d reduced switch counts, improving both efficiency an‎d control flexibility. Two submodule configurations of half-bridge an‎d full-bridge are developed for the AAC design. The half-bridge implementation of the AAC, in particular, provides additional advantages, including fewer semiconductor devices, lower switching losses, an‎d simplified control architecture. For optimal converter operation, both the structural design an‎d the control strategy must be carefully considered. The controller should (i) ensure the output voltage accurately follows the reference voltage, (ii) maintain capacitor voltages within their nominal range through effective balancing, an‎d (iii) minimize circulating currents resulting from capacitor voltage ripples. While the AAC topology has attracted increasing research attention for its novelty an‎d performance potential, relatively few studies have addressed the design an‎d optimization of its control system. This thesis investigates the modeling, control design, an‎d performance eva‎luation of the AAC in HVDC applications. A comprehensive review of recent developments in AAC-based systems is presented, highlighting existing challenges in dynamic performance, stability, an‎d control complexity. A new control approach is then proposed to enhance voltage regulation an‎d circulating current suppression while maintaining low computational burden an‎d implementation simplicity. The effectiveness of the proposed control strategy is validated through detailed simulations under various steady-state an‎d transient operating conditions. The results demonstrate considerable improvements in capacitor voltage balancing an‎d reduced circulating currents, confirming the potential of the proposed method for next-generation HVDC converter systems.

حميدرضا كارشناس , جواد ابراهيمي جوزداني

احمدرضا تابش , محمدسعيد مهدوي , محمد مدني