[Ushiba, Hirose]

Because the SRM was highly unstable in the 0.1–1 Hz band, we switched off the integrator in the OLDAMP of the IM stage and switched on a “DC” filter acting as an integrator into the TM stage.

After that, the integrator was further adjusted to include a gain of 10 dB or more in the 0.1–1 Hz range. 
Furthermore, regarding the Damp filter, since the phase does not rotate in the high-frequency band, the high-frequency section of the current filter was replaced with a Chebyshev filter. 
We also adjusted the gain to ensure phase margin stability in the UGF. 
(FIG1, FIG2: PIT and YAW filter with sus model. Blue shows before adjustment, and red shows after adjustment.)
Currently, I have added modified filters to FM3 and FM5 of the PITYAW control filters for the SRM and TM OLDAMPs. After PLL work is completed, I will run tests, and if stability appears to be sufficient, I will replace the current filters in FM1 and FM9 with these modified ones.

Note：
・The suspension model was already included in OLDAMP's FM10. We have confirmed that this is a filter, just like the following files that will be updated in the latest health check.
/users/VISsvn/HealthCheck/PLANT_SRM_PAY_FLOAT_TM_TEST_{P,Y}.xml

・The Chebyshev filter is normalized such that the peak gain in the passband is 0 dB. In the 1 dB ripple Chebyshev filter used here, the DC gain is −1 dB. Therefore, a gain of +1 dB was applied to the entire filter to set the DC gain to 0 dB.