RESEARCH ARTICLE A new structure of single‐phase two‐stage hybrid transformerless multilevel PV inverter Sateesh Kumar Kuncham | Kirubakaran Annamalai | Subrahmanyam Nallamothu Department of Electrical Engineering, National Institute of Technology Warangal, Warangal, India Correspondence Kirubakaran Annamalai, Department of Electrical Engineering, National Institute of Technology Warangal, Warangal 506 004 (T.S.), India. Email: kiruba81@nitw.ac.in Summary Transformerless inverters are becoming popular for grid‐connected photovol- taic applications due to their simplicity, reduced size, weight, cost, and higher efficiency. In this paper, a two‐stage hybrid transformerless multilevel inverter (MLI) for single‐phase grid‐connected photovoltaic power generation system (PVPGS) is presented. The proposed topology comprises a multilevel boost con- verter (MLBC) and a symmetrical hybrid MLI. MLBC combines the boosting and switched capacitor voltage functions to produce self‐balanced multiple voltage levels. The proposed MLI is derived from a combination of bidirec- tional switches, a half bridge, and a diode‐clamped branch, which can produce only two variations in the total common mode voltage and is capable of sup- pressing leakage current as per DIN VDE 0126‐1‐1 grid standards. It offers the advantages of scalability, reactive power capability, reduced total harmonic distortion, and filter size. The proposed hybrid transformerless seven‐level inverter is simulated in MATLAB, and experimental setup is built to validate the effectiveness of the proposed configuration. Finally, a comprehensive com- parison is made with other seven‐level inverter topologies. KEYWORDS bidirectional switch, leakage current, modular structure, multilevel inverter 1 | INTRODUCTION Photovoltaic‐based renewable energy sources (RES) have proved their potential, and so far, around 400‐GW capacities of photovoltaic (PV) plants have been installed across the globe till 2017. This also effectively alleviates greenhouse gas emission and global warming associated with conventional fossil fuels. 1,2 The increased penetration of PV‐based RES into the electric grid has drawn the attention of researchers, leading to the design of compact, highly reliable, low cost, and very efficient grid‐connected photovoltaic power generation systems (PVPGS). Two‐level single‐stage grid‐ connected PV inverters are well commercialized in industries and residential applications due to the simple structure and higher efficiency. 3 RES like PV/fuel cell are usually connected in series to meet the grid peak voltage in two‐level single‐stage inverter structures. However, these inverters have the following drawbacks: poor maximum power point tracking (MPPT), imbalance in power sharing due to partial shading that result in overheating of the nonshaded PV panel, and lower safety of operation. 4 In addition, it requires high voltage–rated power semiconductor switches, and it has low quality of output power. 5 Therefore, two‐stage power conversion has become more popular and is capable of overcoming the shortcomings of single‐stage inverters by employing a front‐end DC‐DC converter stage. It boosts the lower PV voltage to higher DC‐link Received: 26 June 2018 Revised: 24 September 2018 Accepted: 7 October 2018 DOI: 10.1002/cta.2580 Int J Circ Theor Appl. 2018;1–23. © 2018 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/cta 1