From: Nicholas Oleksinski <

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To:

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Sent: Monday, February 20, 2017 7:00 PM

Subject: c2d output Interpretation

Hi:

I am trying to design a digital phase lead compensator using the c2d function in the Octave 4.0.0 control package.

The output of the b & a coefficients I fed in looks like this:

7.474 z^2 - 14.29 z + 6.829

y1: ---------------------------

z^2 - 1.52 z + 0.5772

I noticed a couple things about this output:

1) The powers of the 'a' coefficients start positive. Does that not make this system non-causal?

2) Why is this discrete time LTI model represented as "y1" and not "H(z)"? I fed in the coefficients of H(s) by running c2d this way:

comp_tf = tf(gain*numc,denc); %create the s domain LTI transfer function

comp_tf_d = c2d(comp_tf,0.001); % sample at 1kHz

Thanks

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By dividing both the numerator and denominator by z^2 you'll get an equivalent expression with non-positive powers of z.

--Sergei.

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