Abstract
The rise in renewable energy has increased the use of DC/AC converters, which transform the direct current to alternating current. These devices, generally called inverters, are mainly used as an interface between clean energy and the grid. It is estimated that 21% of the global electricity generation capacity from renewable sources is supplied by photovoltaic systems. In these systems, a transformer to ensure grid isolation is used. Nevertheless, the transformer makes the system expensive, heavy, bulky and reduces its efficiency. Therefore, transformerless schemes are used to eliminate the mentioned disadvantages. One of the main drawbacks of transformerless topologies is the presence of a leakage current between the physical earth of the grid and the parasitic capacitances of the photovoltaic module terminals. The leakage current depends on the value of the parasitic capacitances of the panel and the common-mode voltage. At the same time, the common-mode voltage depends on the modulation strategy used. Therefore, by the manipulation of the modulation technique, is accomplished a decrease in the leakage current. However, the connection standards for photovoltaic inverters establish a maximum total harmonic distortion of 5%. In this paper an analysis of the common-mode voltage and its influence on the value of the leakage current is described. The main topologies and strategies used to reduce the leakage current in transformerless schemes are summarized, highlighting advantages and disadvantages and establishing points of comparison with similar topologies. A comparative table with the most important aspects of each converter is shown based on number of components, modes of operation, type of modulation strategy used, and the leakage current value obtained. It is important to mention that analyzed topologies present a variation of the leakage current between 0 to 180 mA. Finally, the trends, problems, and researches on transformerless grid-connected PV systems are discussed.
Highlights
Nowadays, the increase in the world population, environmental pollution resulting from the burning of fossil fuels, and the need to deliver electricity to remote areas are factors that drive the use of renewable energy (RE)
PV modules must meet a range of regulations and standards before they are considered suitable for sale and for renewable energy funding programs
The rise in renewable energy has caused an increase in the use of inverters
Summary
The increase in the world population, environmental pollution resulting from the burning of fossil fuels, and the need to deliver electricity to remote areas are factors that drive the use of renewable energy (RE). It is possible to remove the transformer to reduce the weight, size, cost, and losses of the system In this way, the efficiency of the inverter is increased by 1 or 2%. The main problems are—an increase in losses, current harmonics, safety issues, and interference problems of electromagnetic effect [23] These problems have been reported in different papers [24,25,26,27]. We show a general comparison of the different converters and their main features; in this way, the reader can differentiate each topology based on the most important elements of each scheme. The authors provides useful information, serves as a reference for researchers and utility engineers on issues to be considered with regards to PV penetration
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