def test_common_timebase_errors(self, i1, i2):
"""Test that common_timbase raises errors on invalid combinations"""
with pytest.raises(ValueError):
common_timebase(i1, i2)
# Make sure behaviour is symmetric
with pytest.raises(ValueError):
common_timebase(i2, i1)
def test_common_timebase(self, dt1, dt2, expected, sys1, sys2):
"""Test that common_timbase adheres to :ref:`conventions-ref`"""
i1 = tf([1], [1, 2, 3], dt1) if sys1 else dt1
i2 = tf([1], [1, 4, 5], dt2) if sys2 else dt2
assert common_timebase(i1, i2) == expected
# Make sure behaviour is symmetric
assert common_timebase(i2, i1) == expected
def rootlocus_pid_designer(plant, gain='P', sign=+1, input_signal='r',
Kp0=0, Ki0=0, Kd0=0, tau=0.01,
C_ff=0, derivative_in_feedback_path=False,
plot=True):
"""Manual PID controller design based on root locus using Sisotool
Uses `Sisotool` to investigate the effect of adding or subtracting an
amount `deltaK` to the proportional, integral, or derivative (PID) gains of
a controller. One of the PID gains, `Kp`, `Ki`, or `Kd`, respectively, can
be modified at a time. `Sisotool` plots the step response, frequency
response, and root locus.
When first run, `deltaK` is set to 0; click on a branch of the root locus
plot to try a different value. Each click updates plots and prints
the corresponding `deltaK`. To tune all three PID gains, repeatedly call
`rootlocus_pid_designer`, and select a different `gain` each time (`'P'`,
`'I'`, or `'D'`). Make sure to add the resulting `deltaK` to your chosen
initial gain on the next iteration.
Example: to examine the effect of varying `Kp` starting from an intial
value of 10, use the arguments `gain='P', Kp0=10`. Suppose a `deltaK`
value of 5 gives satisfactory performance. Then on the next iteration,
to tune the derivative gain, use the arguments `gain='D', Kp0=15`.
By default, all three PID terms are in the forward path C_f in the diagram
shown below, that is,
C_f = Kp + Ki/s + Kd*s/(tau*s + 1).
If `plant` is a discrete-time system, then the proportional, integral, and
derivative terms are given instead by Kp, Ki*dt/2*(z+1)/(z-1), and
Kd/dt*(z-1)/z, respectively.
------> C_ff ------ d
| | |
r | e V V u y
------->O---> C_f --->O--->O---> plant --->
^- ^- |
| | |
| ----- C_b <-------|
---------------------------------
It is also possible to move the derivative term into the feedback path
`C_b` using `derivative_in_feedback_path=True`. This may be desired to
avoid that the plant is subject to an impulse function when the reference
`r` is a step input. `C_b` is otherwise set to zero.
If `plant` is a 2-input system, the disturbance `d` is fed directly into
its second input rather than being added to `u`.
Remark: It may be helpful to zoom in using the magnifying glass on the
plot. Just ake sure to deactivate magnification mode when you are done by
clicking the magnifying glass. Otherwise you will not be able to be able to choose
a gain on the root locus plot.
Parameters
----------
plant : :class:`LTI` (:class:`TransferFunction` or :class:`StateSpace` system)
The dynamical system to be controlled
gain : string (optional)
Which gain to vary by `deltaK`. Must be one of `'P'`, `'I'`, or `'D'`
(proportional, integral, or derative)
sign : int (optional)
The sign of deltaK gain perturbation
input : string (optional)
The input used for the step response; must be `'r'` (reference) or
`'d'` (disturbance) (see figure above)
Kp0, Ki0, Kd0 : float (optional)
Initial values for proportional, integral, and derivative gains,
respectively
tau : float (optional)
The time constant associated with the pole in the continuous-time
derivative term. This is required to make the derivative transfer
function proper.
C_ff : float or :class:`LTI` system (optional)
Feedforward controller. If :class:`LTI`, must have timebase that is
compatible with plant.
derivative_in_feedback_path : bool (optional)
Whether to place the derivative term in feedback transfer function
`C_b` instead of the forward transfer function `C_f`.
plot : bool (optional)
Whether to create Sisotool interactive plot.
Returns
----------
closedloop : class:`StateSpace` system
The closed-loop system using initial gains.
"""
plant = _convert_to_statespace(plant)
if plant.ninputs == 1:
plant = ss2io(plant, inputs='u', outputs='y')
elif plant.ninputs == 2:
plant = ss2io(plant, inputs=['u', 'd'], outputs='y')
else:
raise ValueError("plant must have one or two inputs")
C_ff = ss2io(_convert_to_statespace(C_ff), inputs='r', outputs='uff')
dt = common_timebase(plant, C_ff)
# create systems used for interconnections
e_summer = summing_junction(['r', '-y'], 'e')
if plant.ninputs == 2:
u_summer = summing_junction(['ufb', 'uff'], 'u')
else:
u_summer = summing_junction(['ufb', 'uff', 'd'], 'u')
if isctime(plant):
prop = tf(1, 1)
integ = tf(1, [1, 0])
deriv = tf([1, 0], [tau, 1])
else: # discrete-time
prop = tf(1, 1, dt)
integ = tf([dt/2, dt/2], [1, -1], dt)
deriv = tf([1, -1], [dt, 0], dt)
# add signal names by turning into iosystems
prop = tf2io(prop, inputs='e', outputs='prop_e')
integ = tf2io(integ, inputs='e', outputs='int_e')
if derivative_in_feedback_path:
deriv = tf2io(-deriv, inputs='y', outputs='deriv')
else:
deriv = tf2io(deriv, inputs='e', outputs='deriv')
# create gain blocks
Kpgain = tf2io(tf(Kp0, 1), inputs='prop_e', outputs='ufb')
Kigain = tf2io(tf(Ki0, 1), inputs='int_e', outputs='ufb')
Kdgain = tf2io(tf(Kd0, 1), inputs='deriv', outputs='ufb')
# for the gain that is varied, replace gain block with a special block
# that has an 'input' and an 'output' that creates loop transfer function
if gain in ('P', 'p'):
Kpgain = ss2io(ss([],[],[],[[0, 1], [-sign, Kp0]]),
inputs=['input', 'prop_e'], outputs=['output', 'ufb'])
elif gain in ('I', 'i'):
Kigain = ss2io(ss([],[],[],[[0, 1], [-sign, Ki0]]),
inputs=['input', 'int_e'], outputs=['output', 'ufb'])
elif gain in ('D', 'd'):
Kdgain = ss2io(ss([],[],[],[[0, 1], [-sign, Kd0]]),
inputs=['input', 'deriv'], outputs=['output', 'ufb'])
else:
raise ValueError(gain + ' gain not recognized.')
# the second input and output are used by sisotool to plot step response
loop = interconnect((plant, Kpgain, Kigain, Kdgain, prop, integ, deriv,
C_ff, e_summer, u_summer),
inplist=['input', input_signal],
outlist=['output', 'y'], check_unused=False)
if plot:
sisotool(loop, kvect=(0.,))
cl = loop[1, 1] # closed loop transfer function with initial gains
return StateSpace(cl.A, cl.B, cl.C, cl.D, cl.dt)