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Transformerless DC/AC inverter for 30 kW power

: Schätzle, R.; Laukamp, H.; Schmid, J.

European Commission, Directorate-General for Science, Research and Development:
Photovoltaic power generation. European Research and Development
Brussels, 1989
Book Article
Fraunhofer ISE ()
four-quadrant operation; high efficiency; inverter

At the Fraunhofer-Institute for Solar Energy Systems a 1 ph-3 kW-Inverter had been constructed, specifically for photovoltaic power generation (PV) systems. In the current project the power handling capability of this design shall be increased to 10 kW for a 1 ph-version, i.e. 30 kW for a 3 ph-version. Furthermore the future inverter shall be able to allow for any power factor, even negativ ones. This means that it not only could deliver energy from the DC-side to the AC-side but also act as a rectifier accepting energy from the AC-side and delivering it to the DC-side, e.g. to charge batteries. This capability shall be achieved while maintaining the properties of the existing 3 kW-inverter especially the very good efficiency over a wide power range and the low harmonic distortion. The improved inverter will allow simply structure hybrid-systems with the inverter coupled to an induction generator driven by another power source e.g. wind turbine or diesel engine. The two goals extended power capability and negativ power factor capability are pursued separately. Currently a laboratory 1 ph prototype has been tested succesfully up to a power output of about 6 kW ohmic and inductive loads. For experiments for negative power factor capability a test set-up has been constructed consisting of a battery, the inverter, under test and a single phase induction generator driven by a 3 ph-induction motor as additional power source. So far succesful experiments have been limited to small negativ power factors. Backflow power has until now reached 10% of nominal inverter rating.