121 lines
3.8 KiB
Python
121 lines
3.8 KiB
Python
"""dtime.py
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Functions for manipulating discrete time systems.
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Routines in this module:
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sample_system()
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"""
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"""Copyright (c) 2012 by California Institute of Technology
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All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions
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are met:
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1. Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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2. Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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3. Neither the name of the California Institute of Technology nor
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the names of its contributors may be used to endorse or promote
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products derived from this software without specific prior
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written permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL CALTECH
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OR THE CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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SUCH DAMAGE.
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Author: Richard M. Murray
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Date: 6 October 2012
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$Id: dtime.py 185 2012-08-30 05:44:32Z murrayrm $
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"""
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from .lti import isctime
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from .statesp import StateSpace, _convertToStateSpace
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__all__ = ['sample_system', 'c2d']
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# Sample a continuous time system
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def sample_system(sysc, Ts, method='zoh', alpha=None):
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"""Convert a continuous time system to discrete time
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Creates a discrete time system from a continuous time system by
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sampling. Multiple methods of conversion are supported.
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Parameters
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----------
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sysc : linsys
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Continuous time system to be converted
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Ts : real
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Sampling period
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method : string
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Method to use for conversion: 'matched', 'tustin', 'zoh' (default)
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Returns
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-------
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sysd : linsys
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Discrete time system, with sampling rate Ts
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Notes
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-----
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See `TransferFunction.sample` and `StateSpace.sample` for
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further details.
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Examples
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--------
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>>> sysc = TransferFunction([1], [1, 2, 1])
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>>> sysd = sample_system(sysc, 1, method='matched')
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"""
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# Make sure we have a continuous time system
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if not isctime(sysc):
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raise ValueError("First argument must be continuous time system")
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return sysc.sample(Ts, method, alpha)
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def c2d(sysc, Ts, method='zoh'):
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'''
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Return a discrete-time system
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Parameters
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----------
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sysc: LTI (StateSpace or TransferFunction), continuous
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System to be converted
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Ts: number
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Sample time for the conversion
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method: string, optional
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Method to be applied,
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'zoh' Zero-order hold on the inputs (default)
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'foh' First-order hold, currently not implemented
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'impulse' Impulse-invariant discretization, currently not implemented
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'tustin' Bilinear (Tustin) approximation, only SISO
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'matched' Matched pole-zero method, only SISO
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'''
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# Call the sample_system() function to do the work
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sysd = sample_system(sysc, Ts, method)
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# TODO: is this check needed? If sysc is StateSpace, sysd is too?
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if isinstance(sysc, StateSpace) and not isinstance(sysd, StateSpace):
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return _convertToStateSpace(sysd) # pragma: no cover
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return sysd
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