No. 14-E-PQA-1599 A High Step-up Double-Input DC-DC Converter for Photovoltaic Power Conditioning Systems in Micro- Grids Mohammad Mohammadi, Jafar Milimonfared Faculty of Electrical Engineering Amirkabir University of Technology Iran, Tehran mohammadi9044@gmail.com Abstract—Hybrid power supply systems are widely used in many applications. Due to low reliability of Photovoltaics(PVs) in generating regulated electric power, requirement of energy storage devices with PVs is undeniable. In low voltage PVs, high gain DC-DC converters are used to connect them to 400V DC- link. In this paper a high step-up soft switching double input DC- DC converter is proposed to increase the performance of hybrid power supply systems. The proposed converter is analyzed and discussed. Operation intervals of the converter is presented in section II, Voltage gain of the converter is derived in section III and soft switching condition is presented in section IV. A Design example is carried out in section V and simulation results are presented in section VI to validate the characteristics of the proposed converter. Finally, a comparison is performed with other type of converters to show the advantages of the proposed hybrid supply system. Keywords—Current-fed DC-DC converter, high step-up converter, multi-input converter, photovoltaic, soft switching. I. INTRODUCTION Fossil fuels are the main energy resources in the world. But nowadays due to incrementing the pollution of the earth, decrementing these kind of fuels and also with the advent of Distributed Generation(DG) application which needs to use power resources in the vicinity of urban places, green power resources were more interested in. DGs are a kind of power generation method which generate power near the consumers to solve many problems in the power network. One popular green energy to be used in DGs are PVs. PVs converts solar energy to electricity, but PVs are unreliable power resources that their generated power is completely depends on sunlight. Due to this problem a well-known structure to use PVs is combining them whit Energy Storage devices(ES) and making hybrid power supplies. In this structure, when PV generates power more than what is required, the rest of power is stored in ES and when PV generates power less than the required energy, the rest is supplied by ES. Another important problem of PV is low voltage DC generated power which cannot be connected to overall power network and should connect to an inverter. high step-up DC-DC converters are a good idea for power conditioning system of PV to connect it to DC-link of inverter. In this structure which is shown in fig.1 ES is also connected to the DC-link with another DC-DC converter. In this structure due to large number of elements, in two converters, size and weight of the converter is increased, also the efficiency is decreased because of high losses of power elements which are used in the system. Many high step-up DC-DC converters were proposed in recent year which can be used in fig.1. [1], [2] presented new high step up converters based on boost cells in input side of the converter. [3] proposed a method to integrate transformers in a half bridge converter. In [4] a high step up converter with ripple free input current and in [5] a special switching method was used to achieve soft switching operation in light load situation. [6] used Z-source structures to achieve high gain characteristic. All the mentioned converters in the literature used large number of elements to achieve high voltage gain and if two of them is used in fig.1 total efficiency of the system is decreased because of large number of elements in power direction. Due to sensitivity of PVs to ripple current and requirement of high gain characteristic many converters in the literature use a conventional boost converter in the input of their converters [4], [7]–[10]. In these converters the topology contained a boosting cell and a voltage amplifier as show in fig.2. In this paper a new structure is used to connect PV and ES together. In this structure which is shown in fig.3 PV/ES power conditioning system is based on replacing conventional boost cell with a multi-port cell in the high step-up converter, Using this structure results in lower power elements which can increase reliability and efficiency and also decreases size and cost of the converter. The topology which is proposed in this paper is shown in fig.4. In this topology a special switching strategy is used to achieve soft switching operation in double input mode. The converter contains a tree switch leg which builds the multi-port cell. A boosting transformer and a voltage multiplier are used to increase the output voltage and achieve the required voltage for inverter. Magnetizing inductance of the primary side of transformer is used to achieve soft switching operation; also due to quasi-resonant operation of the converter the capacitors of voltage multiplier become small in size which reduced the size of the converter. Another advantage of operating in quasi-resonant operation is decreasing the sensitivity of the voltage gain to the output