This paper presents a single-phase transformerless grid-connected photovoltaic converter based on two cascaded full bridges with different dc-link voltages. The converter can synthesize up to nine voltage levels with a single dc bus, since one of the full bridges is supplied by a flying capacitor. The multilevel output reduces harmonic distortion and electromagnetic interference. A suitable switching strategy is employed to regulate the flying-capacitor voltage, improve the efficiency (most devices switch at the grid frequency), and minimize the common-mode leakage current with the help of a novel dedicated circuit (transient circuit). Simulations and experiments confirm the feasibility and good performance of the proposed converter

Photovoltaic (PV) power systems have been in the spotlight of scientific research for years. However, this technology is still undergoing developments, and several new architectures are proposed each year. This study describes the main challenges facing grid-connected PV systems without galvanic isolation, then carries out a review of the state-of-the-art of single-phase systems. The converter topology review is focused on the match between the different types of converters and the different PV panel technologies, determined by the common-mode voltage between the PV string terminals and the ground. The ground leakage current, due to time variations of this voltage, is a source of electric safety and electromagnetic interference (EMI)-related problems, and its amplitude is constrained by international standards. The basic principles of operation of the different solutions are described, along with their strengths and drawbacks. Conversion efficiency is evaluated qualitatively comparing the semiconductor power losses. Finally, the future trends regarding semiconductor devices, PV panels and international regulations for single-phase grid-connected equipment are discussed, and indications on how these might steer future research efforts in PV converters are inferred

This paper presents a modified two-level three-phase inverter for the reduction of the leakage current. With respect to a traditional two-level inverter, the proposed solution reduces the common-mode voltage, both in amplitude and frequency. Between the DC source and the traditional three-phase bridge, two active DC-decoupling devices and a voltage-clamping network have been added. A dedicated control strategy was developed adopting a modified Space Vector PWM modulation, oriented to the reduction of the common-mode voltage. Simulations showing the good performance of the solution are presented. A preliminary prototype was developed and experimental results are presented.

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(2016) Performance evaluation of a 3-level ANPC photovoltaic grid-connected inverter with 650V SiC devices and optimized PWM. IEEE Transactions on Industry Applications, 52 (2). pp. 2475 -2485 . ISSN 1939 Access from the University of Nottingham repository: http://eprints.nottingham.ac.uk/33387/1/Performance%20Evaluation%20of%20a%203-Level %20ANPC%20Photovoltaic%20Grid-Connected%20Inverter%20with%20650V%20SiC %20Devices%20and%20Optimized%20PWM.pdf Copyright and reuse:The Nottingham ePrints service makes this work by researchers of the University of Nottingham available open access under the following conditions. This article is made available under the University of Nottingham End User licence and may be reused according to the conditions of the licence. For more details see: http://eprints.nottingham.ac.uk/end_user_agreement.pdf A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Abstract-Photovoltaic (PV) energy conversion has been on the spotlight of scientific research on renewable energy for several years. In recent years the bulk of the research on PV has focused on transformerless grid-connected inverters, more efficient than traditional line transformer-based ones, but more critical from a power quality point of view, especially in terms of ground leakage current. Neutral point clamped (NPC) inverters have recently gained interest due to their intrinsically low ground leakage current and high efficiency, especially for MOSFET-based topologies. This paper presents an active NPC (ANPC) topology equipped with 650 V SiC MOSFETs, with a new modulation strategy that allows to reap the benefits of the wide-bandgap devices. An efficiency improvement is obtained due to the parallel operation of two devices during the freewheeling intervals. Simulations and experimental results confirm the effectiveness of the proposed converter.

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This paper proposes a solution for reducing the\ud ground leakage current in transformerless single-phase gridconnected\ud photovoltaic converters. This is obtained with the\ud introduction of an active common-mode filter able to compensate\ud for variations of the output common-mode voltage of the\ud power converter. The active common-mode filter is applied to a\ud widespread and efficient full-bridge driven by a three-level pulse\ud width modulation, allowing the power converter to operate with\ud low ground leakage current and with an arbitrary power factor.\ud After showing the desired voltage waveform for common-mode\ud voltage compensation, this paper presents the design guidelines\ud for the needed additional magnetic component together with the\ud power loss considerations for all the devices added for the proposed\ud solution. Experimental results show the performance of the\ud proposed solution in terms of ground leakage current reduction,\ud effectiveness of dead-time compensation, total harmonic distortion\ud of the injected grid current, and power losses