Root-Mean Square Model of Three-Phase Photovoltaic Inverter for Unbalanced Fault

The feed-in tariff, introduced in 2012, led to a significant increase in Photovoltaics (PVs) throughout Japan. About half of PVs are three-phase PVs that are connected to low voltage or medium voltage networks. Central Research Institute of Electric Power Industry (CRIEPI) has developed root-mean square-based time-domain power system analysis tools used by all the Japanese utilities for dynamic studies following balanced and unbalanced faults for over the last thirty years. Two 10 kW three-phase PV inverter were tested in the CRIEPI's test lab reproducing various levels of the voltage dips that come from three-phase balanced and unbalanced faults with various fault duration. The PV model was developed and validated, comparing measured responses obtained in the test lab with simulated responses obtained by the time-domain simulation tool. Sensitivities of identified parameters to the model error are carefully examined, which proves that the same model parameters may be used for balanced and unbalanced faults. Derived model parameters are further verified, comparing the simulated response of the combined two PV outputs with the measured response. The excellent match of those responses demonstrates that individually identified parameters for the two single PV inverters are also adequate for representing the combined PV dynamics.