Second-order filter-based inertia emulation (SOFIE)for low inertia power systems—Part 2: Analysis and Comparative Evaluation

This article makes a comparative analysis between the classic first-order filter-based inertia emulation method and the more recent second-order filter-based approach, which manages to emulate the electrodynamic behaviour of the synchronous machine. The dynamics of the interactions between the control techniques, the filter capacitance and the parasitic grid inductance are analysed assuming ideal and real phase-locked loops (PLL) and current control loops. The results reveal how electromagnetic oscillatory modes between the controllers and the LL elements of the grid are exited, which in the case of the first-order filter-based inertia emulation methods impose severe restrictions on the maximum inertia that can be emulated and in the bandwidth of the converter current controllers and the PLL. These restrictions are released in the case of using the second-order filter-based inertia emulation approach. The results of the analysis are validated through simulations on the IEEE 9-bus low inertia power system. Hardware in the loop experimental results are presented to support the investigation.