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;
-    {
-        /* 积分限幅（抗饱和）：积分项贡献不超过满量程 */
-        float imax = 100.0f / HEATER_PID_KI;
-        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_noi = HEATER_PID_KP * err
+                + HEATER_PID_KD * (err - s_prev_err);   /* 比例 + 微分 */
+    float integ_new = s_integral + err;
+    float u = u_noi + HEATER_PID_KI * integ_new;
 
-    float u = HEATER_PID_KP * err + HEATER_PID_KI * s_integral + HEATER_PID_KD * deriv;
-    if (u < 0.0f) u = 0.0f;          /* 降温靠自然散热，输出不为负 */
-    if (u > 100.0f) 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);