چكيده انگليسي :
With the rapid development of clean energy applications such as solar panels, the use of bidirectional DC-DC converters has expanded significantly. In addition, bidirectional converters are used for charging and discharging energy storage sources in applications such as fuel cells, uninterruptible power supplies, and motor drives for hybrid power systems. Bidirectional DC-DC converters are classified into two main categories: isolated and non-isolated. In isolated converters, by changing the turns ratio of the transformer, it is possible to achieve high step-up/down voltage gain. However, these converters have disadvantages such as high conduction losses, low efficiency, large number of switches, high voltage stress across the switches, high cost and weight, as well as complicated control compared to non-isolated converters. Therefore, in applications where isolation is not required, non-isolated bidirectional converters have become the focus of attention for designers and engineers. Most non-isolated bidirectional converters are developed based on Buck/Boost, Spike/Zeta and Cuk/Cuk converters. To increase the voltage gain of these converters, coupled inductor and switching capacitor are used. Given that bidirectional converters are used for charging and discharging energy storage sources such as batteries, and the energy of these sources is limited, it is highly valuable to minimize losses and provide an efficient and economical structure for these converters. On the other hand, to reduce the size and weight of the converters, their operating frequency must be increased, which leads to higher switching losses and reduced converter efficiency. Therefore, soft switching methods are used to reduce switching losses. As a result, one of the challenges in designing bidirectional converters is to provide soft switching conditions for semiconductor components.
At the beginning of this thesis, some applications of bidirectional DC-DC converters, as well as the design challenges of these converters, are presented. In chapter two, the structures of non-isolated bidirectional DC-DC converters and the methods used to increase voltage gain, as well as to create soft switching conditions based on ideas proposed in recent years, are examined. Subsequently, in chapter three, the first proposed converter, which features soft switching conditions, a simple structure, and relatively high voltage gain, is introduced. In chapter four, the second proposed converter is introduced to reduce the current ripple in battery packs of bidirectional converters and to increase the voltage gain. Following that, in chapter Five, the third bidirectional converter is introduced, designed to increase voltage gain, reduce voltage stress on semiconductor components, and improve efficiency. In this thesis, a comprehensive evaluation of the performance of the proposed converters is conducted, along with theoretical analyses and simulation results provided to validate the effectiveness of the proposed converters. Additionally, the practical implementation results of the first and third proposed converters are displayed to assess their performance. In chapter six, a conclusion of the discussed topics and suggestions for future work are presented.
