import time
import warnings
def _clamp(value, limits):
lower, upper = limits
if value is None:
return None
elif upper is not None and value > upper:
return upper
elif lower is not None and value < lower:
return lower
return value
try:
# get monotonic time to ensure that time deltas are always positive
_current_time = time.monotonic
except AttributeError:
# time.monotonic() not available (using python < 3.3), fallback to time.time()
_current_time = time.time
warnings.warn('time.monotonic() not available in python < 3.3, using time.time() as fallback')
[文档]class PID(object):
"""
PID controller of Mixlinker
"""
[文档] def __init__(self, kp=1.0, ki=0.0, kd=0.0,
set_pressure=0.5,
thresholds=(-10, 10),
throttle_limits=((30, 60), (40, 65), (50, 70)),
output_limits=(None, None),
auto_mode=True):
"""
:param kp: The value for the proportional gain kp
:param ki: The value for the integral gain ki
:param kd: The value for the derivative gain kd
:param set_pressure: The initial set_pressure that the PID will try to achieve
:param thresholds: the output threshold to decide whether to change
:param throttle_limits: the limits of throttle on every gear of burner
:param output_limits: The initial output limits to use, given as an iterable with 2 elements, for example:
(lower, upper). The output will never go below the lower limit or above the upper limit.
Either of the limits can also be set to None to have no limit in that direction. Setting
output limits also avoids integral windup, since the integral term will never be allowed
to grow outside of the limits.
:param auto_mode: Whether the controller should be enabled (in auto mode) or not (in manual mode)
"""
self.kp, self.ki, self.kd = kp, ki, kd
self.set_pressure = set_pressure
self.lower_threshold, self.upper_threshold = thresholds
self.throttle_limits = throttle_limits
self._min_output, self._max_output = output_limits
self._auto_mode = auto_mode
self._proportional = 0
self._integral = 0
self._derivative = 0
self._last_time = _current_time()
self._last_pressure = None
[文档] def __call__(self, input_pressure, input_gear, input_angle):
"""
Call the PID controller with *input_gear*, *input_pressure*, *input_angle*
and calculate and return a control output.
"""
if not self.auto_mode:
return input_gear, input_angle
now = _current_time()
dt = now - self._last_time if now - self._last_time else 1e-3
# compute error terms
error = self.set_pressure - input_pressure
d_input = input_pressure - (self._last_pressure if self._last_pressure is not None else input_pressure)
# compute the proportional term
self._proportional = self.kp * error
# compute integral and derivative terms
self._integral += self.ki * error * dt
self._integral = _clamp(self._integral, self.output_limits) # avoid integral windup
self._derivative = -self.kd * d_input / dt
# compute final output
output = self._proportional + self._integral + self._derivative
output = _clamp(output, self.output_limits)
# keep track of state
self._last_pressure = input_pressure
self._last_time = now
# decision conditions
if output > self.upper_threshold:
if input_angle - 5 < self.throttle_limits[input_gear - 1][0]:
output_gear = input_gear + 1
output_angle = input_angle
else:
output_angle = input_angle - 5
output_gear = input_gear
elif output < self.lower_threshold:
if input_angle + 5 > self.throttle_limits[input_gear - 1][1]:
output_gear = input_gear - 1
output_angle = input_angle
else:
output_angle = input_angle + 5
output_gear = input_gear
else:
output_gear = input_gear
output_angle = input_angle
return output_gear, output_angle
@property
def components(self):
"""
The P-, I- and D-terms from the last computation as separate components as a tuple. Useful for visualizing
what the controller is doing or when tuning hard-to-tune systems.
"""
return self._proportional, self._integral, self._derivative
@property
def tunings(self):
"""The tunings used by the controller as a tuple: (kp, ki, kd)"""
return self.kp, self.ki, self.kd
@tunings.setter
def tunings(self, tunings):
"""Setter for the PID tunings"""
self.kp, self.ki, self.kd = tunings
@property
def auto_mode(self):
"""Whether the controller is currently enabled (in auto mode) or not"""
return self._auto_mode
@auto_mode.setter
def auto_mode(self, enabled):
"""Enable or disable the PID controller"""
self.set_auto_mode(enabled)
[文档] def set_auto_mode(self, enabled, input_pressure=None):
"""
Enable or disable the PID controller, optionally setting the last output value.
This is useful if some system has been manually controlled and if the PID should take over.
In that case, pass the last output variable (the control variable) and it will be set as the starting
I-term when the PID is set to auto mode.
:param enabled: Whether auto mode should be enabled, True or False
:param input_pressure: The last output, or the control variable, that the PID should start from
when going from manual mode to auto mode
"""
if enabled and not self._auto_mode:
# switching from manual mode to auto, reset
self._last_pressure = input_pressure
self._last_time = _current_time()
self._proportional = 0
self._integral = (input_pressure if input_pressure is not None else 0)
self._integral = _clamp(self._integral, self.output_limits)
self._auto_mode = enabled
@property
def output_limits(self):
"""
The current output limits as a 2-tuple: (lower, upper). See also the *output_limts* parameter in
:meth:`PID.__init__`.
"""
return self._min_output, self._max_output
@output_limits.setter
def output_limits(self, limits):
"""Setter for the output limits"""
if limits is None:
self._min_output, self._max_output = None, None
return
min_output, max_output = limits
if None not in limits and max_output < min_output:
raise ValueError('lower limit must be less than upper limit')
self._min_output = min_output
self._max_output = max_output
self._integral = _clamp(self._integral, self.output_limits)
self._last_pressure = _clamp(self._last_pressure, self.output_limits)