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Entry  Wed Nov 22 17:52:25 2017, gautam, Update, Optimal Control, Visualizing cost functions globalCosts.pdf
    Reply  Tue Jan 2 16:37:26 2018, gautam, Update, Optimal Control, Oplev loop tuning loopOpt_180102_1706.pdfglobalCosts.pdf
       Reply  Wed Jan 3 12:33:16 2018, rana, Update, Optimal Control, Oplev loop tuning 
          Reply  Wed Jan 3 16:25:32 2018, awade, Update, Optimal Control, Oplev loop tuning 
       Reply  Tue Jan 9 21:57:29 2018, gautam, Update, Optimal Control, Oplev loop tuning loopOpt_180108_2232.pdf
Message ID: 13520     Entry time: Tue Jan 9 21:57:29 2018     In reply to: 13497
Author: gautam 
Type: Update 
Category: Optimal Control 
Subject: Oplev loop tuning 

After some more tweaking, I feel like I may be getting closer to a cost-function definition that works.

  • The main change I made was to effectively separate the BR-bandstop filter poles/zeros and the rest of the poles and zeros.
  • So now the input vector is still a list of highest pole frequency followed by frequency separations, but I can specify much tighter frequency bounds for the roots of the part of the transfer function corresponding to the Bounce/Roll bandstops.
  • This in turn considerably reduces the swarming area - at the moment, half of the roots are for the notches, and in the (f0,Q) basis, I see no reason for the bounds on f0 to be wider than [10,30]Hz.

Some things to figure out:

  1. How the "force" the loop to be AC coupled without explicitly requiring it to be so? What should the AC coupling frequency be? From the (admittedly cursory) sensing noise measurement, it would seem that the Oplev error signal is above sensing noise even at frequencies as low as 10mHz.
  2. In general, the loops seem to do well in reducing sensing noise injection - but they seem to do this at the expense of the loop gain at ~1Hz, which is not what we want.
    • I am going to try and run the optimizer with an excess of poles relative to zeros
    • Currently, n(Poles) = n(Zeros), and this is the condition required for elliptic low pass filters, which achieve fast transition between the passband and stopband - but we could just as well use a less rapid, but more monotonic roll-off. So the gain at 50Hz might be higher, but at 200Hz, we could perhaps do better with this approach.
  3. The loop shape between 10 and 30Hz that the optimizer outputs seems a but weird to me - it doesn't really quite converge to a bandstop. Need to figure that out.
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