[Abstract]: Australian Standard AS 4777.2-2005, section 4.9udimposes limits on DC injection into the AC network byudgrid connected inverters. One way to ensure that thisudrequirement is met is to use a power transformer asudinterface between the output of the inverter and the ACudnetwork. But this adds costs, mass, volume and powerudlosses. It is, therefore, an advantage to design theudinverter system so that zero DC offset is guaranteed atudits output. Ideally no DC would be expected at the outputudof the inverter. In practice, however, in the absence ofudspecial measures, a small amount of DC is presentudbecause of circuit component imperfections. Techniquesudthat have been proposed so far for the elimination of theudDC offset current are based on the sensing of the DCudoffset voltage at the output of the inverter. The output ofudthe sensor is used to drive a feedback system designed toudcontrol operation of the inverter so that the DC offset isudeliminated. The focus of this paper is on theudmathematical modeling of a recently proposed dc offsetudsensor and dc offset control system. Experimentaludvalidation of the model is presented. It is demonstratedudthat while satisfactory performance is achievable theudtechnique has some serious disadvantages.
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