Modeling of Asymmetrical Grid Faults for P-HIL Accuracy and Stability Analysis in LVRT Tests

The energy systems are evolving toward the comprehensive and massive integration of power electronics-based technologies, such as photovoltaic, wind turbines, and electric vehicles. All these emerging and promising power converters technologies must be tested to comply with the grid codes, especially during severe grid fault events, before their commercialization. Low-Voltage Ride-Through (LVRT) field tests are usually conducted to prove the ability of the converter to ride through faults. These field tests are expensive and require bulky equipment, while Power-Hardware-in-the-Loop (P-HIL) offers a more cost-effective and flexible alternative. However, the P-HIL must be stable and accurate to get reliable results. The accuracy of a P-HIL test is directly influenced by its interface algorithm. This paper proposes a frequency domain approach, based on the concept of singular values in Multi-Input Multi-Output systems, to study the P-HIL accuracy and stability in grid connected converter testing under asymmetrical line-to-line fault conditions. Accuracy and stability analysis have been performed analytically and validated by Matlab/Simulink simulations and by experimental P-HIL tests. This paper demonstrates that correct fault modeling leads to correct assessment of the reactive power injected under faults and of avoiding resonances.