Fuzzy Controller-Aided Input Series Output Series (ISOS) Modular Converters for Photovoltaic Applications Linss T. Alex 1 • S. S. Dash 2 • R. Sridhar 1 Received: 9 February 2018 / Revised: 28 April 2018 / Accepted: 14 June 2018 Ó Taiwan Fuzzy Systems Association and Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Researches on power extraction from renewable energy sources are increasing day by day. Solar energy source is one of the most available and cheap renewable resources. Power intermittency and power quality issues are the major concerns when extracting power from photo- voltaic system. Power conditioning devices and controllers play a vital role to avoid the concerned issues. This paper proposes a low distortion intelligent fuzzy-aided modular input series output series system. The performance of con- trollers is evaluated using MATLAB/Simulink environment, and the output is verified using hardware implementation. Keywords Photovoltaic Á Input series output series Á Renewable energy source Á Fuzzy logic controller 1 Introduction DC–DC converters can be connected in different combina- tions to reduce the demands for different levels of voltage, current and power in the input and output. Input series output series (ISOS) system connection of DC–DC converters is suitable for high-input and high-output voltage applications. Fuzzy logic controller (FLC) can accomplish equal sharing of voltage or current among the converter modules, which is a major concern, even in the presence of considerable mis- matches among the converter module parameters. Multiple DC–DC converters can be connected in par- allel or series at the input or output side in order to achieve desired voltage or current at both sides. The four possible structures in these types include input series and output series (ISOS), input parallel and output parallel (IPOP), input series and output parallel (ISOP), input parallel and output series (IPOS) [1]. These modular converters are used in telecommunication, computer, traction, industrial, X-ray and renewable energy system [2–7]. In the series connection of multiple modules, the power device rating of each module is relatively lower. Moreover, maintainability and reliability of the power conversion system can be improved due to the redundancy provided by multiple modules [8]. In order to ensure proper distribution of voltage and current at both input and output sides, dif- ferent control schemes have been proposed. DC–DC modular converter in ISOS configuration using parallel MOSFETs [9] increases the number of semiconductor switches and in turn the switching losses and having an overshoot of 2 V in an adjusting time of 100 ls. Decen- tralize voltage-sharing control strategy for fully modular ISOS structure [8] and an active voltage-sharing control scheme [10] required distributed controllers for each module. A general control strategy discussed in [11] nee- ded individual voltage-sharing loop and input current loops. Modular output capacitor and two phase-shifted full- bridge DC–DC converter are used in ISOS configuration [12, 13]. When compared to flyback or forward isolated converters, full-bridge converter required more switches and hence switching losses will be high. Modular single- switch and two-switch flyback converters operating in discontinuous and continuous conduction mode are explained [14, 15], respectively. Intrinsic voltage balancing mechanism can be used only for low power applications. The maximum power point tracking (MPPT), an & R. Sridhar sridharmanly@gmail.com 1 Department of EEE, SRM Institute of Science & Technology, SRM Nagar, Chennai, India 2 Department of Electrical Engineering, Government College of Engineering, Keonjhar, India 123 Int. J. Fuzzy Syst. https://doi.org/10.1007/s40815-018-0516-1