thermostat/src/pid.rs

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use serde::{Serialize, Deserialize};
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#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
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pub struct Parameters {
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/// Gain coefficient for proportional term
pub kp: f32,
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/// Gain coefficient for integral term
pub ki: f32,
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/// Gain coefficient for derivative term
pub kd: f32,
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/// Output limit minimum
pub output_min: f32,
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/// Output limit maximum
pub output_max: f32,
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}
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impl Default for Parameters {
fn default() -> Self {
Parameters {
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kp: 0.0,
ki: 0.0,
kd: 0.0,
output_min: -2.0,
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output_max: 2.0,
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}
}
}
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#[derive(Clone)]
pub struct Controller {
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pub parameters: Parameters,
pub target : f64,
u1 : f64,
x1 : f64,
x2 : f64,
pub y1 : f64,
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}
impl Controller {
pub const fn new(parameters: Parameters) -> Controller {
Controller {
parameters: parameters,
target : 0.0,
u1 : 0.0,
x1 : 0.0,
x2 : 0.0,
y1 : 0.0,
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}
}
// Based on https://hackmd.io/IACbwcOTSt6Adj3_F9bKuw PID implementation
// Input x(t), target u(t), output y(t)
// y0' = y1 - ki * u0
// + x0 * (kp + ki + kd)
// - x1 * (kp + 2kd)
// + x2 * kd
// + kp * (u0 - u1)
// y0 = clip(y0', ymin, ymax)
pub fn update(&mut self, input: f64) -> f64 {
let mut output: f64 = self.y1 - self.target * f64::from(self.parameters.ki)
+ input * f64::from(self.parameters.kp + self.parameters.ki + self.parameters.kd)
- self.x1 * f64::from(self.parameters.kp + 2.0 * self.parameters.kd)
+ self.x2 * f64::from(self.parameters.kd)
+ f64::from(self.parameters.kp) * (self.target - self.u1);
if output < self.parameters.output_min.into() {
output = self.parameters.output_min.into();
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}
if output > self.parameters.output_max.into() {
output = self.parameters.output_max.into();
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}
self.x2 = self.x1;
self.x1 = input;
self.u1 = self.target;
self.y1 = output;
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output
}
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pub fn summary(&self, channel: usize) -> Summary {
Summary {
channel,
parameters: self.parameters.clone(),
target: self.target,
}
}
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pub fn update_ki(&mut self, new_ki: f32) {
self.parameters.ki = new_ki;
}
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}
#[derive(Clone, Serialize, Deserialize)]
pub struct Summary {
channel: usize,
parameters: Parameters,
target: f64,
}
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#[cfg(test)]
mod test {
use super::*;
const PARAMETERS: Parameters = Parameters {
kp: 0.03,
ki: 0.002,
kd: 0.15,
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output_min: -10.0,
output_max: 10.0,
};
#[test]
fn test_controller() {
// Initial and ambient temperature
const DEFAULT: f64 = 20.0;
// Target temperature
const TARGET: f64 = 40.0;
// Control tolerance
const ERROR: f64 = 0.01;
// System response delay
const DELAY: usize = 10;
// Heat lost
const LOSS: f64 = 0.05;
// Limit simulation cycle, reaching this limit before settling fails test
const CYCLE_LIMIT: u32 = 1000;
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let mut pid = Controller::new(PARAMETERS.clone());
pid.target = TARGET;
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let mut values = [DEFAULT; DELAY];
let mut t = 0;
let mut total_t = 0;
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let mut output: f64 = 0.0;
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let target = (TARGET - ERROR)..=(TARGET + ERROR);
while !values.iter().all(|value| target.contains(value)) && total_t < CYCLE_LIMIT {
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let next_t = (t + 1) % DELAY;
// Feed the oldest temperature
output = pid.update(values[next_t]);
// Overwrite oldest with previous temperature - output
values[next_t] = values[t] - output - (values[t] - DEFAULT) * LOSS;
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t = next_t;
total_t += 1;
println!("{}", values[t].to_string());
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}
assert_ne!(CYCLE_LIMIT, total_t);
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}
}