Impedance-based Stability Analysis of a Power Hardware-in-the-Loop for Grid-Following Inverter Testing

Power Hardware-in-the-Loop (P-HIL) provides a reliable evaluation of real hardware interactions under realistic grid conditions in the Laboratory environment. A P-HIL setup comprises three main sectors: real-time simulator, Hardware-under-test (HuT), and interfaces. The limitations of interfaces and the delays between the sectors can result in stability issues. Therefore, a precise stability analysis is necessary before conducting laboratory experiments. This paper proposes the impedance-based approach to asses the stability constraints for a P-HIL using a grid-following inverter as HuT. The stability criterion is determined based on the impedances seen by the grid and the inverter at the PCC. The impact of interface dynamics, delays, and controller bandwidth is carefully regarded. All P-HIL components are implemented in Simulink first, then the actual setup with RTDS and linear amplifier has been configured to provide a more realistic reference for impedance verifications. The calculated impedances are verified with both simulations and experiments through frequency response. The comparison between the time domain response and the Nyquist criterion confirms the validity of the given stability criterion.