توصيفگر ها :
مبدلهاي افزاينده و بسيار افزاينده غيرايزوله , منابع شبكه امپدانسي , كليدزني نرم , تنش ولتاژ كم , جريان ورودي پيوسته
چكيده انگليسي :
Nowadays, the growing demand for reducing fossil fuel consumption has led to significant expansion in the use of renewable energy sources for power generation. Photovoltaic and fuel cells, as key renewable sources, produce low output voltages that require boosting before connection to inverters. For this purpose, step-up and high step-up DC-DC converters are widely used. Among them, the conventional boost converter is popular due to its simplicity, but its voltage gain relies solely on high duty cycles, which causes various limitations. To overcome these drawbacks, several techniques such as voltage multiplier cells, switched capacitors, coupled inductors, and impedance-source networks have been introduced. This research investigates different high-gain step-up topologies and analyzes their desired features, including high efficiency, reduced device stresses, continuous input current, common ground, high power density, low component count, and soft-switching operation. Accordingly, this thesis proposes non-isolated high step-up converters with improved gain and efficiency while maintaining simplicity and achieving full soft-switching. First, a boost-based topology integrating a coupled inductor and voltage multiplier cells is presented, using a single power switch, optimized magnetizing inductor, and a lossless snubber to realize complete soft-switching, reduced voltage stress, elimination of diode reverse recovery, continuous input current, and common ground. Additionally, a quasi-Y-source based high step-up converter with one power switch is proposed. By repositioning the switch, employing a lossless snubber, and combining a passive clamp with switched-capacitor cells, this design enhances voltage gain, reduces switch stress, eliminates diode reverse recovery, and maintains continuous input current with a common ground. Finally, by replacing the input diode with a switch in the quasi-Y-source structure, high conduction losses are avoided, and complete zero-voltage soft-switching is achieved for both switches. Turn-on occurs under ZVZCS through body diode conduction, eliminating switching and output capacitance losses, while turn-off ZVS is ensured with a snubber capacitor. The leakage energy is absorbed by a passive clamp, and the switched-capacitor further increases the voltage gain. It is noteworthy that this structure also retains the advantages of the previously proposed converters. In this thesis, the performance of the proposed converters has been fully analyzed, and to validate the theoretical results and equations, laboratory prototypes with an input voltage of 40 V and an output voltage of 400 V have been implemented. The efficiencies of the proposed converters at output powers of 150 W, 200 W, and 200 W were measured as 98.36%, 96.72%, and 97.77%, respectively. Furthermore, the superiority of the presented structures has been confirmed through comparison with other similar converters.
