.Modelica_LinearSystems2.WorkInProgress.DiscreteZerosAndPoles

Information

This record defines a transfer function by its zeros, poles and a gain:

         product(p - z[i])
  y = k*------------------- * u
         product(p - n[i])

where z[:] is a Complex vector of zeros, n[:] is a Complex vector of poles and k is an additional multiplicative factor. The elements of the two Complex vectors must either be real numbers or conjugate complex pairs (in order that their product results in a polynomial with Real coefficients).

In the record, the zeros and poles are transformed into a product of first and second order polynomials. The data structure is especially useful in applications where first and second order polynomials are naturally occurring, e.g., as for filters. In fact, via function ZerosAndPoles.Design.filter, a ZeroAndPole transfer function is generated from low and high pass analog filters (CriticalDamping, Bessel, Butterworth, Chebyshev). The filters are available in normalized (default) and non-normalized form. In the normalized form, the amplitude of the filter transfer function at the cutoff frequency is 3 dB.

A ZeroAndPole transfer function is internally stored by the coefficients of first and second order polynomials, and by an additional multiplicative factor k:

         product(s + n1[i]) * product(p^2 + n2[i,1]*p + n2[i,2])
  y = k*---------------------------------------------------------
         product(p + d1[i]) * product(p^2 + d2[i,1]*p + d2[i,2])

Note, the degrees of the numerator and denominator polynomials are given as:

   degree of numerator   = size(n1,1) + 2*size(n2,1);
   degree of denominator = size(d1,1) + 2*size(d2,1);

Example:

                          (p+1)
  zp = 4* -------------------------------------
           (p - 1)*(p - (2+j*3))*(p - (2-j*3))

with j=sqrt(-1), is defined as

   import Modelica_LinearSystems2.Math.Complex;
   import Modelica_LinearSystems2.ZerosAndPoles;

   zp = ZerosAndPoles(z = {Complex(-1,0)},
                      p = {Complex(1,0),
                           Complex(2,3),
                           Complex(2,-3)},
                           k=4);

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