IEEE TRANSACTIONS ON POWER ELECTRONICS A Single-switch Single-magnetic Core High Conversion Ratio Converter with Low Input Current Ripple and Wide Soft-switching Range for Photovoltaic Applications Milad Heidari, Hosein Farzanehfard, Member, IEEE, and Morteza Esteki, Student Member, IEEE Abstract— In this paper, a novel high conversion ratio DC-DC converter suitable for photovoltaic applications is presented. Utilizing single-switch and single-magnetic core, low ripple input current and low voltage stress across the semiconductors are the major advantages of the proposed converter. In order to provide soft-switching condition for the converter switch at a wide range of output power, a passive lossless snubber is employed. The presented converter is adequate for photovoltaic applications due to mentioned properties. Operating principles are analyzed and design considerations are provided. In order to validate the theoretical analysis, a prototype of the proposed converter is implemented and the experimental results are exhibited. Index Terms— High conversion ratio; lossless passive snubber; photovoltaic applications; soft-switching; single-magnetic core; single-switch; I. INTRODUCTION ODAY, photovoltaic (PV) systems as popular renewable energy sources have gained numerous applications [1]-[5]. In these systems, usually at the first stage, a DC-DC converter is required to increase the low level DC voltage of the PV panel (less than 50V) to the desired high level voltage (200V~400V) suitable for connecting to the DC bus voltage. This DC-DC converter is known as high step-up converter and in addition to PV systems [2], is needed in fuel cell systems [3], uninterruptible power supplies [4] and hybrid electric vehicles [5]. Generally, high step-up converters can be classified into isolated and non-isolated topologies. Although in isolated topologies the high voltage gain can be obtained by adjusting the transformer turns ratio, these topologies suffer from complexity in design and structure, large volume and low efficiency [6]. Thus, non-isolated structures are preferred when galvanic isolation is not required. The conventional boost converter as the simplest non-isolated step-up converter, must operate at very high duty cycles to provide high conversion ratio which leads to low efficiency due to high conduction losses [1]. In addition, high voltage stress across the converter switch and the output diode and high switching losses due to hard switching operation are other disadvantages of the boost converter which makes it unsuitable for the mentioned applications. In order to improve the conventional boost Milad Heidari and Hosein Farzanehfard are with the Department of Electrical and Computer Engineering, Isfahan University of Technology, Isfahan 84156- 83111, Iran (e-mail: milad.heidari@ec.iut.ac.ir; hosein@cc.iut.ac.ir). Morteza Esteki is with the Department of Electrical and Computer Engineering, University of Alberta, Edmonton, AB, Canada (e-mail: mesteki@ualberta.ca). (corresponding author to provide e-mail: hosein@cc.iut.ac.ir). converter features and make it suitable for high step-up applications, many techniques are presented [7]-[19]. One of these techniques is cascading two boost converters to provide high voltage gain which degrades the overall efficiency and reduces the converter stability. In addition, high voltage stress is applied across the semiconductors at the output stage [7]. In order to reduce the voltage stress of semiconductors, three-level boost converter can be used at the output stage of the cascade boost converter, but the converter circuit and control complexity is increased [8]. Another technique is replacing the boost converter inductor by tapped-inductors [9]-[11]. This increases the voltage gain but causes many problems in the converter such as the voltage spike and ringing on the switch due to the energy stored in the leakage inductance of the tapped inductors, pulsating input current with high ripple which influences the longevity of the PV panel and complicates the maximum power point tracking process. In order to reduce the input current ripple as well as increasing the power density, interleaved technique is used [12]. Although the mentioned drawbacks are eliminated in the converter presented in [12], too many passive and active components are used which makes it unsuitable for low power applications. Alongside other mentioned techniques, basic converters such as boost, flyback and SEPIC converters are integrated together to create a converter with high voltage gain and low voltage stress on semiconductors [13]-[14]. However, switching losses, large input current ripple or pulsating input current are the major disadvantages of these converters. Pulsating input current problem can be removed by using more than one magnetic core, but, this would increase the converter cost and volume similar to the converter presented in [15]. This converter provides a high voltage gain by combining boost and SEPIC converters, along with switched capacitors. This structure reduces voltage stress across the switch, but, utilizes too many diodes and capacitors which causes high conduction losses. Hard switching operation and using two magnetic cores are other disadvantages of this converter. Likewise, the boost converter with input- parallel output-series structure in [16] reduces the input current ripple and increases the converter voltage gain. However, this converter suffers from switching losses in addition to employing two switches and two magnetic cores that leads to higher cost, volume and control complexity. Therefore, introducing a single-magnetic core converter with continuous or non-pulsating input current is very valuable. In addition to limited voltage gain, switching losses and the diodes reverse recovery problem are other problems associated with the conventional boost converter which limit the converter switching frequency and overall achievable efficiency. In T