Source code for cpsim.controllers.PID_incremental

#!/usr/bin/python
#
# This file is part of IvPID.
# Copyright (C) 2015 Ivmech Mechatronics Ltd. <bilgi@ivmech.com>
#
# IvPID is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# IvPID is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

# title           :PID.py
# description     :python pid controller
# author          :Caner Durmusoglu
# date            :20151218
# version         :0.1
# notes           :
# python_version  :2.7
# ==============================================================================

# add utils limit - Lin
# update DTerm using delta_pv - Lin

"""Ivmech PID Controller is simple implementation of a Proportional-Integral-Derivative (PID) Controller in the Python Programming Language.
More information about PID Controller: http://en.wikipedia.org/wiki/PID_controller
"""
import time

from .controller_base import Controller


[docs] class PID(Controller): """PID Controller """ def __init__(self, u_0, P=0.2, I=0.0, D=0.0, current_time=None): self.Kp = P self.Ki = I self.Kd = D self.u_0 = u_0 self.sample_time = 0.00 self.current_time = current_time if current_time is not None else time.time() self.last_time = self.current_time self.clear(current_time) self.control_lo = None self.control_up = None
[docs] def clear(self, current_time=None): """Clears PID computations and coefficients""" self.current_time = current_time if current_time is not None else time.time() self.last_time = self.current_time self.SetPoint = 0.0 self.PTerm = 0.0 self.ITerm = 0.0 self.DTerm = 0.0 self.last_error = 0.0 self.last_pv = None # Windup Guard self.int_error = 0.0 # self.windup_guard = 20.0 self.output = 0.0
[docs] def update(self, feedback_value: float, current_time=None) -> float: """Calculates PID value for given reference feedback .. math:: u(t) = K_p e(t) + K_i \int_{0}^{t} e(t)dt + K_d {de}/{dt} .. figure:: images/pid_1.png :align: center Test PID with Kp=1.2, Ki=1, Kd=0.001 (test_pid.py) """ error = self.SetPoint - feedback_value self.current_time = current_time if current_time is not None else time.time() delta_time = self.current_time - self.last_time delta_error = error - self.last_error if (delta_time >= self.sample_time): self.PTerm = self.Kp * error self.ITerm += error * delta_time if (self.ITerm < -self.windup_guard): self.ITerm = -self.windup_guard elif (self.ITerm > self.windup_guard): self.ITerm = self.windup_guard delta_pv = 0 if self.last_pv: delta_pv = feedback_value - self.last_pv self.DTerm = 0.0 if delta_time > 0: self.DTerm = delta_pv / delta_time # Remember last time and last error for next calculation self.last_time = self.current_time self.last_error = error self.last_pv = feedback_value self.output = self.u_0 + self.PTerm + (self.Ki * self.ITerm) + (self.Kd * self.DTerm) if self.control_up is not None and self.control_up < self.output: self.output = self.control_up elif self.control_lo is not None and self.control_lo > self.output: self.output = self.control_lo return self.output
[docs] def set_reference(self, ref: float): self.SetPoint = ref
[docs] def setKp(self, proportional_gain): """Determines how aggressively the PID reacts to the current error with setting Proportional Gain""" self.Kp = proportional_gain
[docs] def setKi(self, integral_gain): """Determines how aggressively the PID reacts to the current error with setting Integral Gain""" self.Ki = integral_gain
[docs] def setKd(self, derivative_gain): """Determines how aggressively the PID reacts to the current error with setting Derivative Gain""" self.Kd = derivative_gain
[docs] def setWindup(self, windup): """Integral windup, also known as integrator windup or reset windup, refers to the situation in a PID feedback controller where a large change in setpoint occurs (say a positive change) and the integral terms accumulates a significant error during the rise (windup), thus overshooting and continuing to increase as this accumulated error is unwound (offset by errors in the other direction). The specific problem is the excess overshooting. """ self.windup_guard = windup
[docs] def setSampleTime(self, sample_time): """PID that should be updated at a regular interval. Based on a pre-determined sampe time, the PID decides if it should compute or return immediately. """ self.sample_time = sample_time
[docs] def set_control_limit(self, control_lo: float, control_up: float): self.control_lo = control_lo self.control_up = control_up