Utilization of the Impedance-based Stability Criterion for Stability Assessment of PHiL Interface Algorithms

The expansion of renewable energy sources is resulting in steadily growing use of power electronic converters in distribution and transmission grids. However, before these converters are integrated into the existing grid infrastructure in large numbers, their impact on the overall system stability must be ensured by means of suitable test procedures. Given the risk, cost and complexity of field testing, an alternative promising approach to develop and test such power electronic components in a close-to-reality environment is Power-Hardware-in-the-Loop (PHiL). However, guaranteeing the stability and accuracy when coupling physical and virtual systems in a PHiL setup is still a major challenge. More specifically, a large part of that challenge lies in the interface between both system parts. To analyze the stability of the resulting PHiL system, this paper utilizes the Nyquist and the impedance-based stability criterion. In doing so, this paper shows that instabilities may result for higher frequency ranges where the AC network emulation has higher deviations to the respective theoretical model due to the implemented interface algorithms. These instabilities can be addressed by corresponding filter configurations. Furthermore, it shows that for three phase applications all impedance sequence components must be considered for stability analysis