Fig. 1. Bode diagram of equivalent disturbance link

Fig. 2. Improved DOB disturbance suppression model

Fig. 3. Schematic diagram of DDOB disturbance suppression system model

Fig. 4. Suppression curve of inner loop disturbance observation link

Fig. 5. Desired disturbance suppression curves introduced by outer loop disturbance observation link. (a) Mode one; (b) mode two

Fig. 6. Disturbance suppression characteristic curve of inner loop disturbance observation link

Fig. 7. Disturbance suppression characteristic curve of outer loop disturbance observation link

Fig. 8. Disturbance suppression characteristic curve of DDOB system

Fig. 9. Comparison of system disturbance suppression characteristics before and after adding DDOB

Fig. 10. Step response curves of virtual prototype system before and after adding DDOB

Fig. 11. Comparison of theoretical output of control system under different frequency disturbances. (a) 15 Hz; (b) 40 Hz; (c) 60 Hz; (d) 120 Hz

Fig. 12. Comparison between virtual prototype and theoretical outputs of DDOB system under different frequency disturbances. (a) 15 Hz; (b) 60 Hz