توصيفگر ها :
مبدلهاي بسيار افزاينده , مبدلهاي فوق افزاينده , منابع شبكه امپدانسي , كليدزني نرم , مبدل كوادراتيك , تنش ولتاژ كم
چكيده انگليسي :
Today, the need for high voltage gain in many applications such as electric power generation from renewable sources and energy harvesters, electric vehicles, and high-voltage pulse generators has led to increased attention on step-up and high step-up converters. Employing the basic boost converter, consisting of only a power switch, an output diode and an inductor at the input, is a simple method for increasing the voltage level of the input source. Although the basic boost converter is popular due to its simple structure and easy implementation, but it has certain limitations. In this converter, the only way to increase the voltage gain is by increasing the main switch duty cycle, which increases the converter loss and control complexity at extreme duty cycles. Furthermore, to transfer a specific power to the output, reducing the power transfer time to the output increases the current stress on the output diode, which intensifies the negative effects of the diode reverse recovery and reduces the converter efficiency. The need for high voltage gain and simultaneously maintaining the system high efficiency in some applications has led to the development of new methods to increase the voltage gain of the boost converter without the increasing the duty cycle. In this research, the existing methods for increasing the voltage gain in step-up converters, such as using the switched capacitors, voltage multiplier cells, switched inductors and voltage lift circuits, magnetic coupling and multi-level converters, are investigated, and the performance, advantages and disadvantages of each method is explained. Then, four high step-up and ultra step-up topologies are proposed using the Y-source impedance network. In the first converter, by combining the quadratic topology with the Y-source converter structure, while creating an ultra step-up converter with only one switch, the voltage stress of the output diode, quadratic diode and the switch are greatly reduced, also by using a switch with low conduction resistance and diodes with lower forward voltages, the converter efficiency is improved. Finally, the simulation results are presented to verify the theoretical results. The second proposed topology is the combination of the boost converter with the Y-source structure, which creates a high quadratic voltage gain, and by replacing the quadratic diode with the boost switch, the gate driver circuits are simplified and the high conduction loss caused by the quadratic diode is eliminated. Also, the RMS amount and current stress of the Y-source structure switch is reduced by removing the quadratic diode, which improves the converter efficiency at high powers. In this converter, the clamp circuit prevents the voltage spike on the Y-source topology switch by absorbing the leakage inductance energy. At the end of this chapter, the simulation results are presented to verify the converter theoretical results. Since one of the power loss sources, especially at high frequencies, is the switching losses, two additional converters are proposed to reduce the number of elements and create soft-switching conditions for the second proposed converter. In both structures, the converter switches are turned on and off under ZVS condition, which reduces the switching losses. Moreover, by increasing the switching frequency, it is possible to increase the converter power density by reducing the magnetic elements sizes, Also both converters operate at high voltage gains wit low voltage stresses on their semiconductor devices. Finally, to validate the theoretical results, the converters simulation and implementations results are presented.
