Transformerless Inverter Topologies for Single-Phase Photovoltaic Systems:A Comparative Review

In photovoltaic (PV) applications, a transformer is often used to provide galvanic isolation and voltage ratio transformations between input and output. However, these conventional iron-and copper-based transformers increase the weight/size and cost of the inverter while reducing the efficiency and power density. It is therefore desirable to avoid using transformers in the inverter. However, additional care must be taken to avoid safety hazards such as ground fault currents and leakage currents, e.g., via the parasitic capacitor between the PV panel and ground. Consequently, the grid connected transformerless PV inverters must comply with strict safety standards such as IEEE 1547.1, VDE0126-1-1, EN 50106, IEC61727, and AS/N ZS 5033. Various transformerless inverters have been proposed recently to eliminate the leakage current using different techniques such as decoupling the dc from the ac side and/or clamping the common mode (CM) voltage (CMV) during the freewheeling period, or using common ground configurations. The permutations and combinations of various decoupling techniques with integrated voltage buck-boost for maximum power point tracking (MPPT) allow numerous new topologies and configurations which are often confusing and difficult to follow when seeking to select the right topology. Therefore, to present a clear picture on the development of transformerless inverters for the next-generation grid-connected PV systems, this paper aims to comprehensively review and classify various transformerless inverters with detailed analytical comparisons. To reinforce the findings and comparisons as well as to give more insight on the CM characteristics and leakage current, computer simulations of major transformerless inverter topologies have been performed in PLECS software. Moreover, the cost and size are analyzed properly and summarized in a table. Finally, efficiency and thermal analysis are provided with a general summary as well as a technology roadmap.</p

A Classification of Single-Phase Transformerless Inverter Topologies for Photovoltaic Applications

© 2018 IEEE. In Photovoltaic (PV) applications, a transformer is often used to provide galvanic isolation and voltage ratio transformations. However, a transformer based inverter is bulky and has high conduction losses, therefore lead to a reduction in the inverter efficiency. To overcome this issue, the transformerless inverter topologies are addressed widely, but the main challenge of a transformerless inverter is common mode issue. Numerous topological modifications with their control and modulation techniques makes them difficult to follow, generalize and highlight the advantages and disadvantages. To address the issue, this paper gives an overview on transformerless inverter and classify them into subsection to discuss the merit and demerit of some of the major topologies. Five subsections based on common mode behavior, voltage clamping and decoupling techniques have been demonstrated (i.e., common ground, mid-point clamping, AC-decoupling, DC-decoupling and AC+DC decoupling). To verify the finding and for general consensus, major transformerless topologies are simulated using PLECS. A general summary is presented at the end to stimulate readers to acknowledge the problems and identify solutions

Hybrid bypass technique to mitigate leakage current in the grid-tied inverter

The extensive use of fossil fuel is destroying the balance of nature that could lead to many problems in the forthcoming era. Renewable energy resources are a ray of hope to avoid possible destruction. Smart grid and distributed power generation systems are now mainly built with the help of renewable energy resources. The integration of renewable energy production system with the smart grid and distributed power generation is facing many challenges that include addressing the issue of isolation and power quality. This paper presents a new approach to address the aforementioned issues by proposing a hybrid bypass technique concept to improve the overall performance of the grid-tied inverter in solar power generation. The topology with the proposed technique is presented using traditional H5, oH5 and H6 inverter. Comparison of topologies with literature is carried out to check the feasibility of the method proposed. It is found that the leakage current of all the proposed inverters is 9 mA and total harmonic distortion is almost about 2%. The proposed topology has good efficiency, common mode and differential mode characteristics

Comparison of single-phase transformerless photovoltaic grid-connected inverter topologies with high efficiency and low ground leakage current

When a transformer is taken out of a photovoltaic (PV) inverter system, the efficiency of the whole system can be improved. Unfortunately, the additional ground leakage current appears and needs to be considered. The problem of ground leakage current is that it poses an electrical hazard to anyone touching the photovoltaic (PV) array's surface. For safety issues, the ground leakage current should be less than 300 mA, which follows the VDE-0126-1-1 German standard. To minimize the ground leakage current in the transformerless PV grid connected inverter system, the proposed inverter topologies (SC-HB inverter, bipolar H-Bridge inverter with CD-Boost converter, modified unipolar HBridge inverter with CD-Boost converter and modified unipolar H-Bridge inverter with modified boost converter) are analyzed, verified and compared in this thesis. In order to analyze the effect of unbalanced filter inductance on the transformerless bipolar H-Bridge inverter topology, the matching ratio of inductance :Lr = Lfl/Lfln and L12IL12n ) is investigated. In addition, the effect of parasitic capacitance value on the transformerless bipolar H-Bridge inverter topology is studied. The effect of modulation techniques using bipolar SPWM and unipolar SPWM on the transformerlcss H-Bridge inverter topology is compared and analyzed in terms of common-mode voltage and ground leakage current. TMS320F28 I 2 is used as a controller to generate the PWM control signal, maximum power point tracking (MPPT) based on power balance and Proportional-Integral (PI) controller. PSIM 9.0 simulation software is used to design the proposed transformerless inverter topologies. Simulation and experimental results verified the proposed inverter's feasibility in addressing issues of transformerless DC/ AC converters in grid-connected PV systems

Hybrid Transformerless PV Converters with Low Leakage Currents:Analysis and Configuration

Abstract This paper proposes a hybrid transformerless photovoltaic (PV) converter with simultaneous AC and DC outputs. It is specifically suitable for residential PV systems due to its high efficiency, versatility and flexibility, while maintaining lower leakage currents. The proposed converter is configured by replacing the control switch of the boost converter with a transformerless voltage‐source inverter (VSI), enabling multiple outputs. In addition, a symmetrical boost inductor is adopted to clamp the common‐mode voltage as a constant, resulting in low leakage currents. To illustrate the configuration principle, a hybrid converter with a highly efficient and reliable inverter concept (HERIC) as the VSI is exemplified. Besides, the dedicated modulation scheme for the proposed converter is detailed to achieve low leakage currents, reactive power injection and high efficiency. Furthermore, as the shoot‐through state of inverter legs is allowable for the proposed converter, i.e. no need to add dead time, the reliability and power quality of the proposed converter can be improved. Simulations and experimental tests are performed on an example hybrid converter (with an HERIC as the VSI) to validate the analysis