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Entry  Fri Sep 23 17:57:34 2011, Paul, Update, SUS, Oplev filter optimization for 2 poles and 2 zeros optimised2p2z_v1.pngoptimised2p2z_v1_TFs.png
    Reply  Sat Sep 24 01:51:02 2011, rana, Update, SUS, Oplev filter optimization for 2 poles and 2 zeros 
       Reply  Tue Sep 27 08:51:29 2011, Paul, Update, SUS, Oplev filter optimization for 2 poles and 2 zeros 
    Reply  Sat Sep 24 02:09:43 2011, kiwamu, Update, SUS, Re:Oplev filter optimization for 2 poles and 2 zeros 
       Reply  Sat Sep 24 17:45:56 2011, Paul, Update, SUS, Re:Oplev filter optimization for 2 poles and 2 zeros 
Message ID: 5532     Entry time: Fri Sep 23 17:57:34 2011     Reply to this: 5536   5537
Author: Paul 
Type: Update 
Category: SUS 
Subject: Oplev filter optimization for 2 poles and 2 zeros 

I have made a function to optimise the overall gain, pole frequencies and zero frequencies for the oplev filter. The script will optimize any user defined number of poles and zeros in order to minimise the RMS motion below a certain cut off frequency (in this case 20Hz). The overall gain is adjusted so that each trial filter shape always has a UGF of 10 Hz.

I have a attached a plot showing the power spectrum and RMS curves for the optimization result for 2 zeros and 2 poles, optimized to give a minimal RMS below 20Hz.

I have also attached a plot showing the loop gain and the filter transfer function.

The noise spectrum shows that the optimised filter gives a better noise performance below 10Hz, but a servo oscillation at the UGF of 10 Hz means it injects a lot of motion around this frequency. Should I consider some more aggressive way to force the script to keep a decent phase margin?

The fminsearch results show that the 'optimized' solution is two resonant peaks:

 

 -- Optimisation completed after 571 iterations--

 Started with: 

 Pole 1 frequency = 1 Hz 

 Pole 2 frequency = 2 Hz 

 Zero 1 frequency = 0.1 Hz 

 Zero 2 frequency = 5 Hz 

Overall gain = 1 

 Finished with: 

 Pole 1 frequency = 0.0497181 Hz 

 Pole 2 frequency = 2.01809 Hz 

 Zero 1 frequency = 0.0497181 Hz 

 Zero 2 frequency = 2.01809 Hz 

Overall gain = 71970.1 

 Initial RMS below 10 Hz = 5.90134e-06

 Remaining RMS below 10 Hz = 8.42898e-07

 

 

 

Attachment 1: optimised2p2z_v1.png  12 kB  | Hide | Hide all
optimised2p2z_v1.png
Attachment 2: optimised2p2z_v1_TFs.png  12 kB  | Hide | Hide all
optimised2p2z_v1_TFs.png
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