10-04-2017, 09:05 PM
A new high-efficiency single-phase transformerless PV inverter topology
Tam s Kerekes, Member, IEE, Remus Teodorescu, Senior Member, IEE, Pedro Rodr guez, Member, IEE,
Gerardo V zquez, Student Member, IEE, Emiliano Aldabas, Member, IEE
ABSTRACT:
There is a strong trend in the photovoltaic (PV) inverter technology to use transformer less topologies in order to acquire higher efficiencies combining with very low ground leakage current. In this paper a new topology, based on the H Bridge with a new AC bypass circuit consisting in a diode rectifier and a switch with clamping to the DC midpoint is proposed. The topology is simulated and experimentally validated and a comparison with other existing topologies is performed. High conversion efficiency and low leakage current is demonstrated.
I INTRODUCTION
Photovoltaic inverters become more and more widespread within both private and commercial circles. These grid connected inverters convert the available direct current supplied by the photovoltaic (PV) panels and feed it into the utility grid. According to the latest report on installed PV power, during 2007 there has been a total of 2.25GW of installed PV systems, out of which the majority (90%) has been installed in Germany, Spain, USA and Japan. At the end of 2007 the total installed PV capacity has reached 7.9 GW of which around 92% is grid connected [1]. There are two main topology groups used in case of grid connected PV systems and they are: with and without galvanic isolation [2]. Galvanic isolation can be on the DC side, in the form of a high frequency DC-DC transformer or on the grid side in the form of a big-bulky AC transformer. Both of these solutions offer the safety and advantage of galvanic isolation, but the efficiency of the whole system is decreased, due to power losses in these extra components. In case the transformer is omitted the efficiency of the whole PV system can be increased with an extra 1-2%. The most important advantages of transformer less PV systems can be observed in Fig. 1, like: higher efficiency, smaller size and weight compared to the PV systems that have galvanic isolation (either on the DC or AC side). 1 Fig. 1 has been made from the database of more than 400 commercially available PV inverters, presented in a commercial magazine about PV systems [3]. Transformer less inverters are represented by the dots (Transformer less), while the triangles represent the inverters that have a low-frequency transformer on the grid side (LF-transformer) and last the stars represent the topologies including a high-frequency DC-DC transformer (HF-transformer), adding a galvanic isolation between the PV and grid. The conclusion drawn from these graphs is that transformer less inverters have higher efficiency,
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