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Discretization

Discretization concerns the process of transferring continuous models and equations into discrete counterparts, suitable for numerical evaluation and implementation on computers.

  • Euler discretization
  • Zero order hold

Discretization is also somewhat connected to discrete mathematics.


Discretization of Linear State Space Models

The following continuous state space model

\dot{\mathbf{x}}(t) = A \mathbf{x}(t) + B \mathbf{u}(t)
\mathbf{y}(t) = C \mathbf{x}(t) + D \mathbf{u}(t)

may be discretized, assuming zero-order hold, to

\mathbf{x}(k+1) = A_d \mathbf{x}(k) + B_d \mathbf{u}(k)
\mathbf{y}(k) = C_d \mathbf{x}(k) + D_d \mathbf{u}(k)

where

A_d = \mathcal{L}^{-1}\{(sI - A)^{-1}\}_{t=T_s} = e^{A T_s}
B_d = \int_{\tau=0}^{T_s}e^{A \tau}d\tau B = A^{-1}(A_d - I)B, if A is nonsingular
Cd = C
Dd = D

and Ts is the sample time.

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