RESULTS OF THE OPTINOS PROJECT - DEFICITS AND UNCERTAINTIES IN PHOTOVOLTAIC INVERTER TEST PROCEDURES

Abstract

Every PV inverter and electricity meter available on the market is tested according to the standards which are valid for the individual product. Nevertheless, malfunctions of some electronic electricity meters have been detected, when used in conjunction with special PV inverters. In one case, the meter displayed only 85% of the real energy fed into the public grid by the PV inverter (1). The meter was checked in a calibration laboratory without negative results. Investigations by ISET have shown that the RF ripple current of the inverter influenced the meter. In most inverters, the frequency of the ripple current lies between 3 kHz and 150 kHz. Unfortunately, no emission and immunity requirements exist for inverters and meters within this frequency range (2) (3) (4). ISET/IWES has developed a special test setup, which can simulate electric ripple currents, similar to those generated by inverters. Investigations on inverter EMC test setups with low differential mode impedance AC artificial mains networks (AMN) are in progress. 1. INVERTER INFLUENCES POWER METER On some PV plants, conflicting measurement results of the energy meter reading and the PV monitoring data records have occurred. This happened on PV plants which were supplied with electronic energy meters. The affected meters were calibrated and approved by the PTB (national metrology institute of Germany). IWES carried out in-situ energy measurements over one week in one of the affected PV-plants. A comparison between meter reading and IWES measurement has shown that the energy meter displayed only about 80% of the correct energy amount. Additional EMC measurements have shown a high RF disturbance on the AC-lines of the inverter with a large current magnitude at the switch frequency of the inverter (Figure 1).