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

The energy systems are evolving towards a comprehensive and massive integration of power electronic based technologies such as photovoltaics, wind turbines and electric vehicles. All of these emerging and promising power conversion technologies need to be tested for grid codes compliance, especially during severe grid fault events, before their commercialisation. Low-voltage ride-through (LVRT) field tests are conducted to prove the ability of the converter to ride through faults. These field tests are expensive and require bulky equipment, whereas 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 provide 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 (MIMO) systems, to study the P-HIL accuracy and stability in grid-connected converter testing under asymmetrical line-to-line fault conditions. The accuracy and stability analysis was performed analytically and validated by Matlab/Simulink simulations and by experimental P-HIL tests. This article demonstrates that correct fault modeling leads to correct assessment of the reactive power injected under faults and resonances avoidance.