New Procedure for Measuring Dynamic MPP-Tracking Efficiency at Grid-Connected PV Inverters

At locations, where there are often variable cloudy conditions, besides the static also the dynamic MPPT-behaviour has to be considered. In the long-term monitoring projects performed by the PV laboratory of BFH- TI, it could be shown that dynamic MPP-tracking problems actually occur. In a paper presented at the 21 st EU PV conference in 2006, first results of dynamic MPP-tracking tests carried out with quasi rectangular variations between two different power levels were presented (3). Such tests can easily be realised with high measurement accuracy and give a good insight in the control behaviour of the inverter. More realistic are tests with ramps with rising and falling slopes of current (proportional to irradiance G) or MPP- power. It is more difficult to realise such tests with a high measuring accuracy. Like for static tests, before the start of a dynamic MPP-tracking test an initial set-up time is needed for stabilisation of the MPP-tracker in order to have a defined starting position. This stabilisation period is followed by a few test cycles during the actual measuring period TM. Inverters are always a little behind the effective MPP, therefore the offered MPP-power is not absorbed completely after a change. In this paper, these test patterns (according to the proposed new standard for inverter per- formance FprEN50530), results of many tests with them at different inverters and possible problems are discussed.