Calculations for Asymmetrical Fault Synthesis for Evaluating Ride-Through of Grid Connected Solar Inverters

Evaluating the efficacy of grid-tied solar inverters requires specific tests to be conducted. With the ability to provide a simulated grid environment, various voltage and frequency conditions can be applied to a device under test (DUT) to assess its performance. A characteristic such as ride-through capability requires the device to be exposed to specified voltage events to validate its conformity to industry standards. However, interconnections between the grid simulator environment, inverters, and grid-tie transformers provide challenges in determining the voltages to output in the grid simulator that are seen by the inverter. This paper details the voltage sag analysis used to obtain grid-side voltage references based on different transformer connections and type of sag condition. Formulas are presented based on the specific type of connection and voltage sag event. Simulation and experimental data are provided to confirm the calculations based on the equations given.