After the recent Free Space implementation, today we tested new control filters for CARM and DARM while locked on the beating signals. The idea was to make more robust the lock on the green by increasing the bandwidth of the loops.
In fig.1 is reported the comparison of the OLTF of DARM (for reference) with the older controllers (blue), the extracted model (red) and the new open loop TF with the new controller. We were able to increase the accuracy pushing up the badwidth to ~25 Hz (G.M. of a factor 2), by adjusting the roll-off in order to not renintroduce too much correction noise. To be noted that there's still margin to increase the bandwidth without occurring towards corr saturations, in case it is needed (see fig.3).
In fig.2 is reported the plant measurements. Both in DARM and CARM a notch strutcture at around 70 Hz was present. After some digging in Acl we found that in CEB_ALS process, filters for CARM and DARM (double structure at 68 and 72 Hz) are implemented in order to compensate some INJ structure (?). During the controller design we compensated this structure with a resonant gain at the same frequencies and Qs, so to gain more phase at that region.
In fig.3 are reported the first comparison of DARM and CARM signals and corrections spectra before and after the implementation of the new control filters. In order to reduce the bump visible at ~50 Hz and to reach the declared factor 2 of gain margin, we slightly adjusted the loop gains accordingly.
N.B.
modification performed (automation side) are the following:
- DARM/CARM control filter: ALS_Arm_control4 -> ALS_Arm_control5;
- carm_gain_boost_final: 0.006 -> 0.0138;
- darm_gain_boost_final: 0.018 -> 0.0138;
- darm_line_ampl: 0.07 -> 0.03;
