What is it about?
When Distributed Energy Resources (DERs) are connected to the main electricity grid, DC current of DERs is injected into the grid via a power processing unit. The function of this unit, called an inverter, is to convert the input DC current to an output AC current with acceptable specifications based on the grid requirement. In this paper, in the output LCL filter of the grid connected inverter, a nonlinear inductor is designed and utilized. Furthermore, a new control scheme based on the combinational feedback of inverter-side and grid-side currents with online adaptive estimation of inductor value is proposed to harness the nonlinear behavior of the output filter. The proposed strategy improves quality of the injected current to grid, while the system performance is enhanced, and filter cost is reduced.
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Why is it important?
Using nonlinear inductor in the output LCL filter of grid connected inverter reduces the volume and cost of the inverter-filter unit. Moreover, with the new control scheme, the quality of the injected power is improved.
Perspectives
In distributed generation systems, the cost of a grid-connected inverter is becoming more significant in the total system price. In other words, high performance and low cost inverter systems are becoming more and more important in spreading out green energy. At the inverter output, using a LCL-type output filter, instead of conventional L-type or LC-type filters, aims to reduce the size of the reactive elements comprising the output filter of the inverter. However, further size and cost reductions are also achievable by designing the inductors to operate in their nonlinear region of the B-H curve. This is what we practiced in this paper. In order to harness the adverse effects of nonlinear inductance, a combinational feedback control technique with proportional resonant controllers is proposed.
Dr Farzad Rajaei Salmasi
University of Tehran
Read the Original
This page is a summary of: Enhanced control of grid-connected inverters with non-linear inductor in LCL filter, IET Power Electronics, August 2016, the Institution of Engineering and Technology (the IET),
DOI: 10.1049/iet-pel.2015.0312.
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