Universal Journal of Electrical and Electronic Engineering Vol. 2(4), pp. 170 - 177
DOI: 10.13189/ujeee.2014.020405
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Interfacing Renewable Energy Sources to the AC Grid by a CMLI with Voltage Regulation under Low THD

M. El-Bakry ^*
Electronics Research Institute, Egypt

ABSTRACT

This paper proposes a 27-level cascaded multilevel inverter (CMLI) as an interface between renewable energy sources and the grid, that can provide output voltage regulation against many fluctuations in these sources while keeping low value of the total harmonic distortion (THD) in its output voltage. Renewable energy sources of different types are treated as dc sources (e.g. dc voltage from PV panels, rectified ac voltage from wind turbines, etc.) that represent a part of, or all, the input dc sources of the individual H-bridges of the CMLI. The values of these sources are subject to natural fluctuations. An approach using a mixed integer linear programming (MILP) optimization model is applied to determine the switching angles of the power switches of this CMLI to minimize the values of the undesired low order harmonics equally till the 31st harmonic. . The model is applied for the single phase and three phase cases. For each case, an output voltage amplitude is selected first for normal operation at the nominal values of the dc sources , whose harmonics absolute values agree with the IEEE standards 519-1992 for voltage distortion limits. Then some disturbances are analyzed, including fluctuations of all the dc sources within ±20% of their nominal values, dropping some dc sources to 50% of their values and dropping of some dc sources to zero values, and the model is applied under the required value of the output voltage with an allowed deviation within ±5%. Solutions are obtained that give the switching angles of the inverter at these disturbances in the dc sources while keeping low values of the output voltage THD.

KEYWORDS
Cascaded Multilevel Inverters, Harmonic Values Minimization, Mixed Integer Linear Programming, Renewable Energy Utilization, Tied Grid Inverters, Total Harmonic Distortion

Cite This Paper in IEEE or APA Citation Styles
(a). IEEE Format:
[1] M. El-Bakry , "Interfacing Renewable Energy Sources to the AC Grid by a CMLI with Voltage Regulation under Low THD," Universal Journal of Electrical and Electronic Engineering, Vol. 2, No. 4, pp. 170 - 177, 2014. DOI: 10.13189/ujeee.2014.020405.

(b). APA Format:
M. El-Bakry (2014). Interfacing Renewable Energy Sources to the AC Grid by a CMLI with Voltage Regulation under Low THD. Universal Journal of Electrical and Electronic Engineering, 2(4), 170 - 177. DOI: 10.13189/ujeee.2014.020405.