Direct current offset controller for transformerless single-phase photovoltaic grid-connected inverters

Bowtell, L. and Ahfock, A. (2010) Direct current offset controller for transformerless single-phase photovoltaic grid-connected inverters. IET Renewable Power Generation, 4 (5). pp. 428-437. ISSN 1752-1416

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Limitation of direct current (DC) injection into the alternating current (AC) network is an important
operational requirement for grid-connected photovoltaic (PV) systems. One way to ensure that this requirement
is met is to use a power transformer as interface to the AC network. But this adds costs, mass, volume and power losses. In a transformerless system, the inverter forming part of the PV system has to be operated so that the DC content in its output current is below the specified limits. Ideally, there should be no DC at the output of
the inverter, but in practice, in the absence of special measures, a small amount of DC current is present. A
technique for elimination of the DC-offset is proposed. It is based on the sensing of the DC-offset voltage at the
output of the inverter. A sensor output is used to drive a feedback system designed to control the operation of the inverter so that the DC-offset is forced to stay within the acceptable limits. A mathematical model for the DC-offset controller is derived. A design procedure, based on the model, is proposed for the controller. The results of tests performed on a system of 1 kW nominal rating provide validation for the mathematical model.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: This paper is a postprint of a paper submitted to and accepted for publication in IET Renewable Power Generation and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at IET Digital Library.
Faculty/School / Institute/Centre: Historic - Faculty of Engineering and Surveying - Department of Electrical, Electronic and Computer Engineering
Date Deposited: 14 Mar 2011 01:33
Last Modified: 25 Jun 2014 06:02
Uncontrolled Keywords: DC-offset; power quality; DC-injection; AC networks; acceptable limit; alternating current; AS interfaces; DC current; DC offsets; design procedure; direct current; direct-current offsets; feedback systems; grid connected inverters; grid-connected photovoltaic system; operational requirements; output current; power-losses; PV system; sensor output; transformerless
Fields of Research : 09 Engineering > 0906 Electrical and Electronic Engineering > 090608 Renewable Power and Energy Systems Engineering (excl. Solar Cells)
01 Mathematical Sciences > 0102 Applied Mathematics > 010204 Dynamical Systems in Applications
09 Engineering > 0913 Mechanical Engineering > 091307 Numerical Modelling and Mechanical Characterisation
Socio-Economic Objective: D Environment > 96 Environment > 9603 Climate and Climate Change > 960302 Climate Change Mitigation Strategies
Identification Number or DOI: 10.1049/iet-rpg.2009.0043

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