Thermal Regulation Module

Author: Pranav Rayapureddi

Purpose

Maintain safe operating temperatures for the coolant pumps and radiator fan using closed-loop PID control, adjusting PWM duty cycles in response to live temperature data before hardware thresholds are reached.

How It Works

thermal_regulate() runs three independent PID controllers — one per actuator — against a shared temperature input. Each controller returns a normalized scalar in [0.0, 1.0] representing cooling effort, which maps to a PWM duty cycle.

computePID() Behavior

computePID() is a custom PID function designed specifically for thermal regulation.

• dt is computed from FreeRTOS tick counts via xTaskGetTickCount() / configTICK_RATE_HZ.
• If input < setPoint, the controller resets state and returns 0 — no cooling below threshold.
• Anti-windup: integral only accumulates when the actuator is unsaturated.

Output Inversion

Higher cooling effort requires a higher duty cycle, so the PID output is inverted before writing:

pwmDuty = DUTY_CYCLE_MAX × (1 − pidOutput)

Integration

float temp = max(DTI_GetDTIData()->controllerTemp, DTI_GetDTIData()->motorTemp);

float fanOutput   = computePID(&fan,   FAN_THRESHOLD, temp, FAN_KP,   FAN_KI,   FAN_KD);
float pump1Output = computePID(&pump1, FAN_THRESHOLD, temp, PUMP1_KP, PUMP1_KI, PUMP1_KD);
float pump2Output = computePID(&pump2, FAN_THRESHOLD, temp, PUMP2_KP, PUMP2_KI, PUMP2_KD);

analogWrite(FAN_PIN,   DUTY_CYCLE_MAX * (1 - fanOutput));
analogWrite(PUMP1_PIN, DUTY_CYCLE_MAX * (1 - pump1Output));
analogWrite(PUMP2_PIN, DUTY_CYCLE_MAX * (1 - pump2Output));

PID states are static locals in thermal_regulate() and persist across calls. PWM is initialized at 25 kHz (ANALOG_WRITE_FREQUENCY) in thermal_Init(). thermal_forceOn() and thermal_forceOff() bypass PID for fault states or bench testing.

Limitations

• All gain constants are placeholder values requiring physical tuning.