Stability Analysis of PHIL Systems in Open-Loop and Closed-Loop Modes: Impacts of Source Impedance and Signal Processing

The instability problem of Power-Hardware-in-the-Loop (PHIL) simulation systems is inherent in their closed-loop power interface. In certain scenarios, the open-loop power interface is preferred in merit of minimizing the number of transfer function poles. Their stability boundaries require systematic analysis. This paper presents a comparative study of the PHIL stability in open-loop and closed-loop modes. The Nyquist stability analysis model demonstrates that the stability boundaries of the two modes are different, and the source impedance and the signal processing blocks have a nonlinear and nonmonotonic impact. The stability boundaries and the impact of time delay are validated through PHIL experiments. Specifically, the closed-loop mode without low-pass filter exhibited the narrowest stable region. The low-pass filter implementation expands the stability boundaries by two to four times. The open-loop mode showed intermediate stability with superior source inductance tolerance. The time delays have nonlinear and nonmonotonic degradation impacts. All modes suffered 40–60% stable region reduction under 150μ s injected time delay. The results provide systematic guidelines for PHIL system design, emphasizing the trade-offs between control modes, delay control, and source impedance compatibility. ... mehrThe proposed methodology establishes a framework giving systematic assessment of PHIL systems with inductive load where system stability is critical.