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Discrete to continuous #888

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578b177
added discrete2cont()-funciton to convert discrete LTI-systems back t…
Apr 27, 2023
ee22b8a
Added function discrete2cont() to convert discrete LTI systems to con…
Apr 27, 2023
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38 changes: 38 additions & 0 deletions control/statesp.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1988,3 +1988,41 @@ def linfnorm(sys, tol=1e-10):
fpeak /= sys.dt

return gpeak, fpeak

def discrete2cont(sys, method='zoh'):
""" Transform a discrete state-space system to a continuous state-space system.
Parameters
------
sys : Discrete LTI (StateSpace or TransferFunction) system to transform
method: The method that was used for discretization

Returns
------
sysc : Continuous LIT (StateSpace or TransferFunction) system depending on the input form.
"""
# check if system is of type state space and convert if not
#if sys.

if not(isinstance(sys, StateSpace)):
sys = convert_to_statespace(sys)
was_tf = true
if method == 'zoh':
Ac = scipy.linalg.logm(sys.A)/sys.dt
Bc = np.linalg.inv(np.linalg.inv(Ac)@(sys.A-np.eye(np.shape(sys.A)[0])))@sys.B

# remove small numbers
Ac = np.around(Ac/1e-6)*1e-6
Bc = np.around(Bc/1e-6)*1e-6

# turn -0 to 0
Ac[np.abs(Ac)<1e-6] = 0
Bc[np.abs(Bc)<1e-6] = 0

sysc = StateSpace(Ac,Bc,sys.C,sys.D,0)
else:
raise NotImplementedError("Method: " + method + " is not implemented in this function!")

if was_tf:
sysc = ss2tf(sysc)

return sysc