مقاله انگلیسی رایگان در مورد بهره ولتاژ بالای مبدل DC-DC شبه SEPIC – نشریه IEEE 2018

High conversion gain dc-dc power converters have recently seen an increased demand in variety of power electronics applications. In fact, the main reasons behind this increased attention have three folds. Firstly, fast deployment of Renewable Energy (RE) based power systems has intensified the need for high conversion gain power converters. This is due to the low voltage generation inherent in most RE sources such as Photovoltaic (PV) modules and fuelcells, where stepping up the low input voltage (e.g., 20 V – 40 V) to higher voltage levels (e.g., 200 V – 400 V) is required in order to have a properly function grid-forming or grid-feeding converter [1], [2]. Secondly, prevalence of applications demanding higher voltage levels for better performance, from few hundreds of Volts such as for Light Emitting Diode (LED) in lightning [3] up to few kilovolts in pulsed power applications [4]. Lastly, one of the most relevant is the possibility of distributing electrical energy more efficiently at higher dc voltage levels (e.g., 380 V400 V or even higher). This is the case in applications such as telecommunication and dc power systems where electrical energy can be transferred with higher efficiency, reliability and power quality [5], [6]. Conventionally, the boost and buck-boost topologies can be employed in order to step-up the output voltage. However, practically achieving conversion gains of beyond six due to presence of parasitic elements is not feasible [2]. Moreover, operating at high duty cycles compromise the boost converter efficiency as small turn-off times which may incline Electromagnetic Interference (EMI) and ripple current levels, indicating a requirement for larger magnetic components [2], [7]. Another derivation of a buck-boost topology suitable for high voltage applications is the flyback converter [4], [8], [9]. Although this topology is well employed for high voltage applications with low parts count, it is only suitable for very low power levels (i.e., < 300 W). This is due to the high dc magnetization current requirement of its flyback transformer, which increases the size of the transformer and consequently the losses for higher power levels under continuous conduction mode operation [8]. From this standpoint, many research efforts have been devoted towards developing high voltage gain power converters without imposing extreme duty ratio. In general, the demanded performance can be obtained through utilizing coupled-inductor, switched inductors and switched capacitor cells [7], [10]-[16] and/or employing multi-cell configurations [4], [17]-[21]. All these attempts are made in order to overcome the existing technological limits (i.e., power switch breakdown voltage and limited power ratings) and to reach the required output voltage level with minimum duty ratio (i.e., obtaining better efficiency). However, in many practical situations, in order to obtain the required voltage gain and reduce voltage stress across the power switch many switched-cells are typically required. Furthermore, using an impedance network is also considered as another topological variant. The impedance network based power converters. known as Z-source, is initially proposed for dc-ac inverter operation [22], but it can be modified to operate as a high voltage gain dc-dc converter [23]. Recently, with the aim of reducing start-up inrush current and improving the voltage gain of conventional Z-source converter, a variety of modified impedance networks have been introduced. These modifications can be summarized as switched inductor, extended boost, switched inductor quasi Z-source and enhanced boost [24]-[29].While using the aforementioned topologies a high voltage gain with small duty cycle (D) is achievable, but the demerits of the aforementioned topologies are high parts counts (i.e., diodes, inductors and capacitors) and particularly the conduction of most diodes in (1-D) of the switching period, which lead to high power loss and low efficiency.