## 5 Simulation and Experiment
### Experimental Verification
Next, a comparative analysis of the oscillation control effects of the adaptive quasi-resonant controller and the quasi-resonant controller was carried out to verify the effectiveness of the two resonant controllers in suppressing oscillation when the SSO frequency was abruptly changed. The experimental results are shown in Figure 20.  
Figure 16: The DFIG determining the rotor current at different speeds: (**a**) rotor speed of 900 r/min; (**b**) rotor speed of 1200 r/min. Figure 17: The oscillation suppression suppressed-contrast waveforms at SSO frequency of 30 Hz: (**a**) DFIG rotor speed; (**b**) grid voltage oscillation waveform; (**c**) before oscillation suppression; (**d**) after oscillation suppression. In Figure 20, the initial value of the simulated sub-synchronous voltage frequency was 30 Hz, and the oscillation amplitude was the same as the experiment described above. At time \(T_{1}\), the quasi-resonant controller and the adaptive quasi-resonant controller were respectively put into control. By observing the stator current, it could be seen that, after  
Figure 12:0 The oscillation suppression suppressed-contrast waveforms at SSO frequency of 10 Hz: (a) DFIG rotor speed; (b) grid voltage oscillation waveform; (c) before oscillation suppression; (d) after oscillation suppression. Figure 12:1 Comparison of the waveforms of the oscillation suppression effects of the two resonant controllers: (a) grid voltage oscillation waveform; (b) stator current waveform comparison. Figure 12:2 The oscillation suppression suppressed-contrast waveforms at SSO frequency of 20 Hz: (a) DFIG rotor speed; (b) grid voltage oscillation waveform; (c) before oscillation suppression; (d) after oscillation suppression. the two resonant controllers were put into use, the oscillation component in the DFIG stator current was significantly weakened, and both controllers could suppress the 30 Hz sub-synchronous current. However, at \(T_{2}\), the SSO frequency suddenly changed to 10 Hz, while the oscillation amplitude did not change. At this time, the control frequency of the quasi-resonant controller was 30 Hz, but the frequency of the sub-synchronous current suddenly exceeded its control range, and a corresponding 10 Hz oscillation component appeared in the stator current after time \(T_{2}\). The adaptive quasi-resonant controller could still control the sub-synchronous current after the oscillation frequency switched. After the changed sub-synchronous voltage frequency was maintained for about 100 ms, the oscillation component in the stator current was suppressed, and the DFIG stator current returned to the sinusoidal output. This experiment confirmed that the adaptive quasi-resonant controller could control the broadband DFIG stator sub-synchronous current, which proves that the SSO suppression strategy proposed in this paper is effective. Finally, the inhibition effect of the proposed SSO inhibition strategy was verified. The rotor speed was increased from 800 r/min to 1200 r/min, and the SSO inhibition link performed RSC control at 840 r/min and 1060 r/min, respectively. The oscillatory components in the stator current were observed, and the experimental results are shown in the following Figure 12:3  
It can be seen that, when the SSO inhibition of DFIG was run at sub-synchronous and super-synchronous speeds, both the sub-synchronous components in the stator current could be effectively suppressed, and the change in the rotor speed had no effect on the control exerted by the adaptive quasi-resonant control. This experiment demonstrated that the SSO inhibition strategy could satisfy the dynamic response requirements of the DFIG. Furthermore, FFT spectrum analysis was carried out on the stator current when the SSO frequency changed, and the harmonic content in the stator current was observed when the quasi-resonant controller and adaptive quasi-resonant controller were used to suppress the stator sub-synchronous current.