Robust Stability Analysis of P-HIL in Power Converters Testing Under Asymmetrical Grid Faults

Power-hardware-in-the-loop (P-HIL) allows testing power converters and their non-linear behavior in various realistic operating scenarios, such as during the occurrence of faults. To ensure robust and stable operation of the P-HIL system, proper tuning of the bandwidth of the LPF, needed for the interface algorithm, is necessary. In fact, different device under test solutions as well as power amplifier (PA) latency values (TPA) have potential impacts on the P-HIL system stability. Furthermore, the multi-input-multi-output (MIMO) nature of the system makes the situation even more challenging. Indeed, for MIMO systems, the generalized Nyquist criterion (GNC) does not provide a precise and valuable information about the P-HIL stability margins. As such, in this paper, a µ-analysis-based technique for stability studies of multi-variable feedback systems is used to provide robust stability characterization of MIMO based P-HIL tests in faulty grids. A set of perturbed plants is identified through the definition of an uncertainty function, covering various power converter design configurations and parametric perturbations. Finally, a design procedure for a stable and robust interface algorithm based on an ideal transformer method with a low-pass filter is carried out. The analytical findings, obtained from the Matlab/Simulink environment analysis, are subsequently validated by experimental examinations.