توصيفگر ها :
مبدل هاي بسيار افزاينده , تنش ولتاژ پايين , كليدزني نرم , جريان ورودي پيوسته , كلمپ فعال
چكيده انگليسي :
In power generation systems based on renewable energy sources such as photovoltaic cells (PVs) and fuel cells (FCs),
high step-up DC/DC converters are used as interfaces between these sources and the next part of the system such as inverters.
In addition, high step-up converters are wildly employed in hybrid vehicles and uninterruptible power supplies. Important
parameters related to high step-up converters include high voltage gain, continuous input current, soft switching condition
for semiconductor devices and low switches voltage stress. To improve the voltage gain, some well-known techniques such
as switched capacitors and coupled inductors along with voltage boosting methods such as conventional quadratic boost
structure can be adopted. In addition, in fuel cells and photovoltaic cells, the input current must be continuous and this
increases the lifespan of the batteries as well. It is also possible to use high quality switches if their voltage stress is low
which leads to reduced conduction losses. The purpose of this thesis is to present methods to improve the voltage gain in
high step-up DC/DC converters by reducing the voltage stress of the converter switches and also, establishing soft switching
conditions while maintaining the continuous input current. Thus, the first proposed converter is developed based on the
conventional quadratic boost converter due to the fact that its inherent voltage gain is higher than the basic boost structure.
Moreover, continuous input current and relatively soft switching conditions are also provided for semiconductor elements.
However, the relatively high voltage stress of the switch, the conduction losses due to the input diodes, the limitation in
determining the duty cycle and the high number of diodes used are its disadvantages. In the next step, in order to solve these
problems, the conventional boost structure is used to develop the second proposed converter. In this converter, in spite of
positive features such as the use of only one magnetic core that reduces the volume and weight of the converter, as well as
low voltage stress of the switches compared to the first converter and also the reduction of conduction losses along with
fully soft switching conditions by active clamp circuit, the input current is discontinuous. To overcome this problem, basic
converters can be used that inherently utilize two magnetic cores. By using these converters, the input inductor is selected
independently to maintain the input current continuous and the second inductor is replaced by coupled inductors to increase
the voltage gain. Accordingly, the third proposed converter is designed based on the conventional SEPIC converter, which
in addition to making continuous input current, uses the least number of semiconductor devices among the first and second
converters. In this converter, the voltage gain is improved by relocating the capacitor of the SEPIC converter which reduces
the output voltage, and using a pair of coupled inductors instead of the middle inductor. However, lower voltage gain than
previous converters is the main drawback of this converter. By changing this structure in order to improve the voltage
gain
