From 5260af8bbd28e0f716cf10c4bf94af372acc234c Mon Sep 17 00:00:00 2001
From: jens <jens.ahrensfeld@gmx.de>
Date: Tue, 1 Dec 2020 21:59:03 +0100
Subject: [PATCH] - PID: Reset yi on error sign changes

---
 brewpi.py             |  2 +-
 components/pid/pid.py | 20 +++++++++++---------
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/brewpi.py b/brewpi.py
index f43a18a..86406a8 100644
--- a/brewpi.py
+++ b/brewpi.py
@@ -229,7 +229,7 @@ if __name__ == '__main__':
 					"kp": 0.8,
 					"ki": 0.00001,
 					"kd": 0.0,
-					"rho": 0.0
+					"rho": 1.0
 				}
 			},
 			"Heat": {
diff --git a/components/pid/pid.py b/components/pid/pid.py
index 2c96470..06441d6 100644
--- a/components/pid/pid.py
+++ b/components/pid/pid.py
@@ -1,3 +1,4 @@
+import numpy as np
 
 
 class Pid:
@@ -6,12 +7,11 @@ class Pid:
         self.yi = 0
 
         # Differentiator
-        self.xd = 0
+        self.err = 0
 
         # Auto windup
         self.y_min = -1.0
         self.y_max = 1.0
-        self.d = 0
 
         # Output
         self.y = 0
@@ -23,7 +23,7 @@ class Pid:
 
     def reset(self):
         self.yi = 0
-        self.xd = 0
+        self.err = 0
 
     def process(self, dt, params, err):
         kp = params['kp']
@@ -31,21 +31,23 @@ class Pid:
         kd = params['kd']
         rho = params['rho']
 
-        yi = self.yi + ki*dt * err - ki*dt - self.d * rho
-        yd = err - self.xd
+        yi = rho*self.yi + ki*dt * err
+        yd = err - self.err
 
         _yp = kp * err
         _yi = yi
         _yd = kd/dt * yd
 
+        # Reset yi on error sign changes
+        if np.sign(err) != np.sign(self.err):
+            _yi = 0
+
         y = _yp + _yi + _yd
 
         self.y = max(self.y_min, min(self.y_max, y))
-        self.d = max(0, self.y - y)
-        if self.d < 0:
-            print("d = {}".format(self.d))
+        print("y = {}".format(_yi))
         self.yi = yi
-        self.xd = err
+        self.err = err
 
     def get_y(self):
         return self.y