PID anti-windup: conditional integration (back-calculation lite)

Src/heat.c

@@ -91,21 +91,24 @@ static void pid_compute(void) {
         return;
     }
 
-    /* 位置式 PID */
+    /* 位置式 PID（带抗积分饱和）：输出饱和时积分仅沿退饱和方向更新，
+       防止升温段积分顶满后长时间维持 100% 输出（此前实测目标 50℃ 冲到 59℃） */
     float err = s_target - t;
-    s_integral += err;
+    float u_noi = HEATER_PID_KP * err
-    {
+                + HEATER_PID_KD * (err - s_prev_err);   /* 比例 + 微分 */
-        /* 积分限幅（抗饱和）：积分项贡献不超过满量程 */
+    float integ_new = s_integral + err;
-        float imax = 100.0f / HEATER_PID_KI;
+    float u = u_noi + HEATER_PID_KI * integ_new;
-        if (s_integral > imax) s_integral = imax;
-        if (s_integral < -imax) s_integral = -imax;
-    }
-    float deriv = err - s_prev_err;
-    s_prev_err = err;
 
-    float u = HEATER_PID_KP * err + HEATER_PID_KI * s_integral + HEATER_PID_KD * deriv;
+    if (u > 100.0f) {
-    if (u < 0.0f) u = 0.0f;          /* 降温靠自然散热，输出不为负 */
+        u = 100.0f;
-    if (u > 100.0f) u = 100.0f;
+        if (err < 0.0f) s_integral = integ_new;   /* 超上限：仅误差为负（降温方向）才吸收 */
+    } else if (u < 0.0f) {
+        u = 0.0f;
+        if (err > 0.0f) s_integral = integ_new;   /* 超下限：仅误差为正（升温方向）才吸收 */
+    } else {
+        s_integral = integ_new;                   /* 未饱和：正常积分 */
+    }
+    s_prev_err = err;
 
     /* 输出量化到 10% 档位（四舍五入） */
     s_duty10 = (uint8_t)((u + (float)HEATER_PWM_STEP_PCT / 2.0f) / (float)HEATER_PWM_STEP_PCT);

temp_test_com.py

@@ -0,0 +1,76 @@
+# -*- coding: utf-8 -*-
+"""FilmForge PID anti-windup verification: target 50C, track steady-state."""
+import serial
+import time
+import threading
+
+def sum8(seq):
+    return sum(seq) & 0xFF
+
+def frame(cmd):
+    p = cmd.encode()
+    body = bytes([0xD5, 0x01, len(p)]) + p
+    return body + bytes([sum8(body[1:])])
+
+rx = bytearray()
+stop = threading.Event()
+
+def reader(buf, handle):
+    while not stop.is_set():
+        data = handle.read(256)
+        if data:
+            buf.extend(data)
+    handle.close()
+
+def frames(buf):
+    out, i, b = [], 0, bytes(buf)
+    while i < len(b):
+        if b[i] == 0xB5 and i + 3 < len(b):
+            total = 3 + b[i + 2] + 1
+            if i + total <= len(b):
+                out.append(b[i:i + total]); i += total; continue
+        i += 1
+    return out
+
+s5 = serial.Serial('COM5', 115200, timeout=0.5)
+t = threading.Thread(target=reader, args=(rx, s5))
+t.start()
+time.sleep(0.5)
+
+def cmd(c, wait=0.8):
+    rx.clear()
+    s5.write(frame(c))
+    time.sleep(wait)
+    fs = frames(rx)
+    payload = [f[3:3+f[2]].decode('ascii','replace') for f in fs if len(f) >= 4 and f[1] == 0xF0]
+    print('[%s] resp: %s' % (c, payload if payload else '<none>'))
+
+cmd('M4S50')
+cmd('M3S1')
+cmd('M2S500')
+print('--- heating to 50C, 150s sampling ---')
+t0 = time.time()
+last_print = -10
+peak = 0
+while time.time() - t0 < 150:
+    time.sleep(2.0)
+    fs = frames(rx)
+    vals = []
+    for f in fs:
+        if len(f) >= 4 and f[1] == 0xF0 and f[2] >= 2:
+            try:
+                vals.append(float(f[3:3+f[2]]))
+            except ValueError:
+                pass
+    if vals:
+        peak = max(peak, max(vals))
+    dt = time.time() - t0
+    if dt >= last_print + 10 and vals:
+        print('  t+%03ds  %.1f C  (peak %.1f)' % (dt, vals[-1], peak))
+        last_print = dt - (dt % 10)
+cmd('M3S0', wait=1.0)
+cmd('M2S0')
+
+stop.set(); t.join()
+print('PEAK=%0.1f  (target 50, overshoot %+.1f)' % (peak, peak - 50))
+print('DONE')