Improved Inverters for Grid Connected PV Systems

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In this thesis work the performances of two inverters are compared. The inverters are connected to a grid-connected PV system located on the roof of the main building of Hogskolan Dalarna. The system totally consists of 72 photovoltaic modules of 45Wp each. One system has 40 modules and an inverter of type SOLWEX 2065, which was functioning starting from 1994. The other system consists of 32 modules and a new inverter of model NT1800. An overall performance evaluation of the inverters was done. The DC current, DC voltage, AC current and AC voltage of the two systems were measured using a data logger and the result was analyzed and compared. Further the output power of the two systems was calculated and the annual yield estimated. It is found out that the old SOLWEX inverter performs below the manufacturer’s specifications. Its efficiency is more than 10% less. It doesn’t always track the maximum power point of the PV array and its threshold power is more than three times higher than the value given by the manufacturer. The new NT 1800 inverter has a wider MPPT voltage range and tracks the maximum power effectively. The daily output of both systems is plotted as a function of daily global irradiation. The new inverter has a better performance for all irradiation levels. Especially for days with low irradiation levels the new inverter gives ...