Abstract
In this paper, a modified DC/DC high step up converter is proposed. Maximum power point tracking, that is very important in photovoltaic (PV) applications, is depended on input current ripple of the PVs. In some other converters that the input current ripple is high, maximum power point cannot track properly. Therefore proposed converter is designed based on reducing input current ripple compatible with the photovoltaic energy sources. The proposed converter has six different modes that are described precisely in the paper. According to the proposed converter’s operation, all inductor currents are illustrated. The proposed converter is designed based on reducing input current ripple compatible with the photovoltaic energy sources. The output voltage gain and input current ripple of the proposed converter is investigated in this paper. The proposed converter is compared to the other recent high step up converter from viewpoint of input current ripple. Also, the sizing of the inductors used in the proposed structure is calculated. Finally, simulations are done in the PSCAD/EMTDC software package to verify the operations of the proposed converter.
Keywords: High step-up converter, DC/DC converter, input current ripple, inductor sizing.
1. Introduction
Recently applications of different kinds of fossil fuels like oil, gas and coal results in air pollution and many other environmental problems. Also, these kinds of energies are running out in the near future. Mentioned issues are reasons for the appearance of new energy sources. Micro grid systems that included several types of renewable energy sources and storage systems are proposed recently \cite{nema2009current}\cite{gandomi2014concentrated}\cite{guggenberger2012performance}\cite{gandomi2016water}\cite{gandomi2016situ}\cite{gandomi2016coupled}. Photovoltaic sources are one of these renewable energy sources that take an important part in this field and play a crucial role in grid-connected or standalone systems \cite{li2008review}\cite{strunz2013dc}\cite{benda2015photovoltaics}\cite{chen2016modeling}\cite{tofighi2013performance}\cite{el2014pv}. Due to this fact that generated output voltage of PV sources is low, some useful methods are used to solve this problem such as using different kinds of high gain converters. Different kinds of high step up converters are used in PV applications for increasing output voltage of them such as isolated converters with transformers. By changing turn ratio of transformer, obtaining high output voltage gain are accessible in these converters, while transformer with high turn ratio needs bulky inductors that cause to decrease efficiency of converter [\cite{nguyen2016isolated}\cite{chub2015review}\cite{gandomi2015transformer}. Also, non-isolated converters are used in PV applications such as coupled inductor-based converters. Beside high output voltage gain in these converters, energy stored in leakage inductors is the main problem of these converters \cite{liu2016overview}\cite{chen2016topology}\cite{saadat2016single}\cite{he2015advanced}. Switch capacitor (SC) converters are other kinds of non-isolated converters. Due to high number of semiconductor devices used in these converters in addition to high voltage spikes on capacitors, they are not practical in high power applications \cite{wu2014nonisolated}\cite{axelrod2008switched}. Another converter used in PV applications is coupled inductor-based switch capacitor converters \cite{hu2013high}\cite{alcazar2012dc}\cite{li2010review}. All of these converters have high ripple of input current, when used in high power applications, that this is the main problem of them \cite{el2014dc}\cite{schuck2015ripple}\cite{feyzi2017incorporating}. High current ripple can be reduced by enlarging the size of inductors, but this leads to increase cost, weight and size of converter \cite{el2014dc}.
In this paper, the switch capacitor DC/DC converter with interleaved inductors is proposed. The proposed converter is capable of reducing input current ripple by using parallel same cells. The topology proposed in this paper combines an interleaved structure in the input part of converter and a SC structure in the output part. This combination has outstanding advantages such as: high voltage gain without high duty cycle of switches, and reduced or cancelled input current ripple.
2. The proposed converter and its operation
2.1. Proposed topology
The proposed high step up DC/DC converter is shown in Fig. 1. As it can be seen in this figure, the proposed converter is comprised as one DC input, couple of interleaved inductors, 4 unidirectional switches, 6 diodes, 2 inductors and 4 capacitors.