To obtain high voltage gain from conventional boost converter, higher duty cycle (D) values are selected that increase voltage stress on switching components and therefore low efficiency is obtained due to high losses [2 and 4]. Also diode would not have sufficient time for reverse recovery. Various topologies have been introduced to obtain high voltage gain with proper D values. Among them, coupled inductor is a suitable choice due to its high voltage gain that is obtained with proper D and by adjusting turn ratio (n) [4]. A suitable DC-DC converter for PV application must have acceptable efficiency besides its high gain. It should also be able to harvest maximum power from PV with low input current ripple. Reference [1] presents a high step up high efficiency DC-DC converter. This topology faces high input current variations, because it has no input inductor. Therefore, maximum power point tracking (MPPT) is difficult and somehow impossible. Also high turn ratio leads to big leakage inductor and high volume of the converter. A modified SEPIC converter is proposed in [16] that introduces higher voltage gain than the conventional SEPIC by implementation of coupled inductors. This topology has lower gain than our proposed converter. References [17 and 18] present single switch coupled inductor-based switched capacitor high step up converters that have used voltage doubler technique. These two converters have same voltage gain but both lower than the topology presented in this paper. DC-DC topologies presented in [19,20], are based on coupled inductor with asymmetrical voltage multiplier network and continuous input current, respectively for PV applications. Both converters provide lower voltage gains than proposed converter for the same n and D conditions. A new high step up converter based on coupled inductor and voltage doubler circuit is introduced in [21, 22] that has lower voltage gain and higher input current ripple in comparison with the proposed converter. In [23], a coupled inductor-based high step up converter based on voltage doubler circuit and clamp circuit is presented that has lower efficiency, higher input current ripple and lower voltage gain in comparison with topologies discussed above. A new topology of DC-DC converters with two coupled inductors and two switches is presented in [24]. Besides implementing two coupled inductors, its voltage gain is lower than our proposed converter. In [25], a coupled inductor high step up converter with three windings and a voltage doubler is presented for PV applications. Higher input current ripple and lower voltage gain are its disadvantages in comparison with the proposed topology. All abovementioned gain comparisons with proposed converter are conducted for similar n and D values.
In this paper, a low ripple input current non-isolated high gain high efficiency DC-DC converter is presented. Coupled inductor and switched capacitor technologies lead to high voltage gain of this converter. Characteristics of the quadratic boost circuit are used in the proposed structure. Passive clamp circuit causes high efficiency of the converter by recovery of the leakage inductor energy and reducing switch voltage stress. Operation principles of the proposed converter for CCM, DCM and boundary modes are discussed in section III. Simulation and experimental results are also provided in section IV. In this paper for simplicity a DC voltage source has been used instead of PV panel.
1.    Operation principle of the proposed topology
Due to the low voltage level and low efficiency of PV panels, converters with high voltage gain and acceptable efficiency are necessary to harvest maximum power from PV with low input current ripples. An exact design procedure that has led to the efficient topology derivation makes it a good candidate for PV application. Fig.2 shows the proposed converter.