This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE JOURNAL OF PHOTOVOLTAICS 1 Analysis and Control of a Novel Transformer-Less Microinverter for PV-Grid Interface Mini Rajeev , Student Member, IEEE, and Vivek Agarwal, Fellow, IEEE Abstract—In this paper, a novel single-phase, transformer-less microinverter conﬁguration derived from the basic ¨ Cuk topology is proposed for photovoltaic (PV)-grid interface applications. The topology has a direct connection between the grid neutral and the negative terminal of the PV array, which completely eliminates the ground leakage current. Further, the proposed topology has several appealing features such as high reliability due to the ab- sence of shoot-through problems, symmetrical operation, low grid current distortion, capability of processing reactive power, low volt- age ride through capability, and simple control for tracking the output current reference. Small-signal analysis has been employed to derive the topology’s dynamic model using which a proportional resonant (PR) controller is designed and implemented. A step by step design procedure for obtaining the optimized proportional and integral gains of the PR controller, considering the effects of pulsewidth modulation transport and digital sampling delays, is presented. Theoretical claims and simulation results are corrobo- rated by experimental studies carried out on a 200 W laboratory prototype controlled by using DSP TMS320F28335 controller. Index Terms— ¨ Cuk converter, grid connected, leakage current, microinverter, proportional resonant (PR) controller, solar PV, transformer-less. I. INTRODUCTION T HE growth of high-speed semiconductor devices with higher power handling capability, the advent of powerful controllers (such as DSP), and the drop in the prices of photo- voltaic (PV) modules have led to the development of efﬁcient, compact, and cost-effective grid-connected solar PV systems. Usually, either a line frequency or a high-frequency transformer is used in such systems to step-up the voltage and/or isolate the PV source from the grid. Use of a transformer, though safer, de- creases the overall efﬁciency of the PV-grid interface, increases the cost, and makes the system bulky [1]. In view of this, in re- cent years, the elimination of transformer in the grid-connected solar PV systems has gained considerable popularity. The main challenges associated with transformer-less inverters include minimization of the ground leakage current and preventing the injection of direct current into the grid [2]. A major issue with Manuscript received January 20, 2018; revised March 12, 2018; accepted April 6, 2018. This paper was presented in part at the IEEE Power and Energy Conference at Illinois, Urbana, IL, USA, February 19–20, 2016. (Corresponding author: Mini Rajeev.) The authors are with the Department of Electrical Engineering, Indian In- stitute of Technology Bombay, Mumbai 400 076, India (e-mail:, minirajeev1 @yahoo.co.in; agarwal@ee.iitb.ac.in). Color versions of one or more of the ﬁgures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identiﬁer 10.1109/JPHOTOV.2018.2825298 Fig. 1. Block diagram of single power stage PV-grid interface. solar PV systems is their inability to extract optimal power from the PV source during partial shading and/or mismatched condi- tions. Microinverters can extract optimal power from the source as they deal with only one PV module [3]. Ground leakage current is due to the variation of potential across the parasitic capacitance, which is formed by the PV cells and the grounded metallic frame of the PV panel. The leak- age current is prohibitive as it deteriorates grid current quality, causes electromagnetic interference, increases the losses, causes degradation of the PV panel, and creates issues related to safety and protection coordination. As speciﬁed in the German stan- dard VDE 0126-1-1, the leakage ground current needs to be limited below 300 mA (rms value). Another challenge is the dc injection into the grid. According to IEEE 1547 and IEC 61727 standards, dc injection should be less than 0.5% of the rated output current. All these problems need to be mitigated when the transformer is eliminated in grid-tied PV applications [4]. Fig. 1 shows the block diagram of a single power stage, single- phase transformer-less grid-connected PV system (GCPVS). Compactness, lower component count, higher efﬁciency, lower cost, and ease of implementation are the beneﬁts of the single- stage power conversion [5]. However, the inverter control strat- egy should incorporate: 1) extraction of peak power from the PV panel; 2) grid synchronization; 3) active power transfer by controlling grid injected current; 4) reactive power support, which enhances the grid voltage proﬁle and provides low voltage ride through (LVRT) capability to the PV inverters during grid faults [6], [7]. Most of the transformer-less inverter topologies reported in the literature to overcome the challenges due to the elimination of transformer are buck derived [2], [8], [9]. But for renewable energy sources like solar PV, where there is a wide range of input voltage variation, Buck–Boost (B–B) derived topologies could be a better option for GCPVS. Therefore, the proposed 2156-3381 © 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information.