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Evaluation and Control Design of Virtual-Synchronous-Machine-Based STATCOM for Grids with High Penetration of Renewable Energy

Fig. 1. Single-line diagram of the test bed.
When a step change of the wind turbine input power is applied, the wind turbine frequency ωs will increase or decrease at first, then come to a new steady state that is synchronized with the grid. During the transients, the STATCOM will synchronize with vPCC, which will also suffer a change in frequency before returning to the nominal 50 Hz, where the VSM-based STATCOM will be less sensitive to the frequency change due to the virtual inertia applied, and stay closer to the nominal frequency than the D-Q frame controlled STATCOM. This is shown in Fig. 2. Thanks to the better synchronization performance plus virtual impedance, the PCC voltage regulation is also better, as shown in Fig. 3. Furthermore, the synchronization can be improved via virtual inertia, and the virtual impedance contributes voltage regulation and robustness to system disturbances.

Fig. 2. Comparison of synchronization performance under power fluctuation.

Fig. 3. Comparison of voltage regulation under power fluctuation.
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