Radio Interference of Photovoltaic Power Systems

One important part of a photovoltaic (PV) power system is the inverter, which transforms the DC current from the solar generator into AC current. Thus a connection to public mains becomes possible. The DC- AC transformation is performed by means of a fast switching, commonly with pulse width modulation of the semiconductor devices at some ten kilo Hertz. Therefore strong interference currents at radio frequencies on the AC and DC lines are expected. These interferences must be suppressed, in order to avoid disturbances in other electronic equipment. For a qualification of the interferences standardised test set-ups and limits are necessary. Conducted emissions on AC lines and radiated emissions from the inverter housing are sufficiently covered by existing standards. However the DC side of PV components is still undefined in standardisation. Because of the large spatial extension of PV generators and long lines (several 10 meters) the DC side of PV systems must be investigated in terms of EMC (Electromagnetic Compatibility). In our work we characterise the whole PV system from a radio frequency (RF) point of view by means of measurements and simulations. Test set-ups are defined in order to measure electromagnetic disturbance signals on DC Lines. In the frequency range below 30 MHz the disturbance voltage on DC lines is measured. A standardised stabilisation of the RF impedance of the DC line is necessary in order to make reproducible measurements. This is achieved by means of a special line impedance stabilisation network (LISN) which acts as a standardised replacement for the PV generator in terms of radio frequencies. Based on measurements and simulations of radiated electromagnetic fields at different PV plants, new limit lines for emissions on DC lines are defined. Measurements of PV inverters with regard to the new limit lines show that a compliance with the limits is easily possible with reasonable technical effort. Based on our research results we suggest to establish an EMC product standard for photovoltaic systems.