Fixes and improvements to PID.

Marlin/Configuration.h

@@ -899,7 +899,7 @@
 #if ANY(PIDTEMP, PIDTEMPBED, PIDTEMPCHAMBER)
   //#define PID_OPENLOOP          // Puts PID in open loop. M104/M140 sets the output power from 0 to PID_MAX
   //#define SLOW_PWM_HEATERS      // PWM with very low frequency (roughly 0.125Hz=8s) and minimum state time of approximately 1s useful for heaters driven by a relay
-  #define PID_FUNCTIONAL_RANGE 10 // If the temperature difference between the target temperature and the actual temperature
+  #define PID_FUNCTIONAL_RANGE 20 // If the temperature difference between the target temperature and the actual temperature
                                   // is more than PID_FUNCTIONAL_RANGE then the PID will be shut off and the heater will be set to min/max.
 
   //#define PID_EDIT_MENU         // Add PID editing to the "Advanced Settings" menu. (~700 bytes of flash)

Marlin/src/lcd/sovol_rts/sovol_rts.cpp

@@ -1312,9 +1312,9 @@ void RTS::handleData() {
     #endif
 
     #if ENABLED(PIDTEMPBED)
-      case Hot_Bed_P: thermalManager.temp_bed.pid.Kp = float(recdat.data[0]) / 100.0f; break;
-      case Hot_Bed_I: thermalManager.temp_bed.pid.Ki = float(recdat.data[0]) * 8.0f / 10000.0f; break;
-      case Hot_Bed_D: thermalManager.temp_bed.pid.Kd = float(recdat.data[0]) / 0.8f; break;
+      case Hot_Bed_P: thermalManager.temp_bed.pid.set_Kp(float(recdat.data[0]) / 100.0f); break;
+      case Hot_Bed_I: thermalManager.temp_bed.pid.set_Ki(float(recdat.data[0]) * 8.0f / 10000.0f); break;
+      case Hot_Bed_D: thermalManager.temp_bed.pid.set_Kd(float(recdat.data[0]) / 0.8f); break;
     #endif
 
     #if HAS_X_AXIS

Marlin/src/module/temperature.h

@@ -173,7 +173,7 @@ typedef struct { float p, i, d, c, f; } raw_pidcf_t;
   struct PID_t {
     protected:
       bool pid_reset = true;
-      float temp_iState = 0.0f, temp_dState = 0.0f;
+      float temp_dState = 0;
       float work_p = 0, work_i = 0, work_d = 0;
 
     public:
@@ -217,17 +217,14 @@ typedef struct { float p, i, d, c, f; } raw_pidcf_t;
         }
         else {
           if (pid_reset) {
+            work_i = 0;
+            work_d = 0;
             pid_reset = false;
-            temp_iState = 0.0;
-            work_d = 0.0;
           }
 
-          const float max_power_over_i_gain = float(MAX_POW) / Ki - float(MIN_POW);
-          temp_iState = constrain(temp_iState + pid_error, 0, max_power_over_i_gain);
-
           work_p = Kp * pid_error;
-          work_i = Ki * temp_iState;
-          work_d = work_d + PID_K2 * (Kd * (temp_dState - current) - work_d);
+          work_i = constrain(work_i + Ki * pid_error, 0, float(MAX_POW - MIN_POW));
+          work_d += (Kd * (temp_dState - current) - work_d) * PID_K2;
 
           output_pow = constrain(work_p + work_i + work_d + float(MIN_POW), 0, MAX_POW);
         }