132 lines
3.9 KiB
C
132 lines
3.9 KiB
C
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#include "fan_controller.h"
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/*
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* The control loop is based on a temperature corridor concept. While the
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* temperature is inside the corridor, the PWM duty cycle will not be changed.
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*
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* If it is above the corridor’s maximum temperature, the duty cycle increases
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* as defined by a PI controller, i.e. there is a dynamic/temporary part (P)
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* that depends on how far outside the corridor the temperature is, and there
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* is a persistent part (I) that is continuously increased while the
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* temperature is outside the corridor.
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*
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* If the temperature is below the corridor’s minimum temperature, similar
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* rules are applied to decrease the fan speed. However, the P part makes
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* little sense here so its gain is usually set to 0.
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*
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* The fan starts in a stopped state and stays there until the temperature
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* rises above the startup temperature. Once that happens, the PWM is set
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* to a specific duty cycle (high enough to reliably start the fan) and
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* regulation begins.
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*/
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/* Note:
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* - all temperatures are in °C represented in fxp_t.
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* - all duty cycles are in percent represented in fxp_t.
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*/
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// corridor definition
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#define CORRIDOR_MIN_TEMPERATURE (40 << POINTPOS)
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#define CORRIDOR_MAX_TEMPERATURE (45 << POINTPOS)
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// The fan is started when temperature rises above this temperature.
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#define FAN_START_TEMPERATURE (42 << POINTPOS)
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// The fan is stopped when the temperature falls below this point.
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#define FAN_OFF_TEMPERATURE (30 << POINTPOS)
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// Emergency temperature level. If this is reached, the duty cycle is directly
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// set to the maximum to skip a long ramp-up phase.
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#define EMERGENCY_TEMPERATURE (60 << POINTPOS)
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// The fan PWM duty cycle cannot fall below this limit. It is held until
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// temperature falls below the off-temperature.
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#define DUTY_CYCLE_MIN (5 << POINTPOS)
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// The fan PWM duty cycle cannot go above this limit. Should be set to 100.
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#define DUTY_CYCLE_MAX (100 << POINTPOS)
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// The fan is always started with this duty cycle. Do not set too low.
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#define DUTY_CYCLE_START (20 << POINTPOS)
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// gain unit: percent duty cycle change per °C deviation per update cycle
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#define GAIN_T_HIGH_P 0x00020000 // 2.000
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#define GAIN_T_HIGH_I 0x00002000 // 0.125
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#define GAIN_T_LOW_P 0x00000000 // 0.000
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#define GAIN_T_LOW_I 0x00002000 // 0.125
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// integer unit ^
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static fxp_t m_duty;
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void fan_controller_init(void)
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{
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m_duty = 0; // fan off by default
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}
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uint8_t fan_controller_update(fxp_t temperature)
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{
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fxp_t duty_out = m_duty;
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// check emergency case. Directly starts the fan, if necessary.
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if(temperature > EMERGENCY_TEMPERATURE) {
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m_duty = duty_out = DUTY_CYCLE_MAX;
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}
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if(m_duty == 0) {
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// we are currently in off state. Check whether we need to start.
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if(temperature > FAN_START_TEMPERATURE) {
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m_duty = duty_out = DUTY_CYCLE_START;
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}
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} else {
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// fan is currently on
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// corridor handling: too warm
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if(temperature > CORRIDOR_MAX_TEMPERATURE) {
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fxp_t delta_above = fxp_sub(temperature, CORRIDOR_MAX_TEMPERATURE);
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fxp_t duty_p = fxp_mult(delta_above, GAIN_T_HIGH_P);
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fxp_t duty_i = fxp_mult(delta_above, GAIN_T_HIGH_I);
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m_duty = fxp_add(m_duty, duty_i);
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if(m_duty > DUTY_CYCLE_MAX) {
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m_duty = DUTY_CYCLE_MAX;
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}
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duty_out = fxp_add(m_duty, duty_p);
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if(duty_out > DUTY_CYCLE_MAX) {
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duty_out = DUTY_CYCLE_MAX;
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}
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}
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// corridor handling: too cold
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if(temperature < CORRIDOR_MIN_TEMPERATURE) {
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fxp_t delta_below = fxp_sub(temperature, CORRIDOR_MIN_TEMPERATURE);
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fxp_t duty_p = fxp_mult(delta_below, GAIN_T_LOW_P);
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fxp_t duty_i = fxp_mult(delta_below, GAIN_T_LOW_I);
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m_duty = fxp_add(m_duty, duty_i);
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if(m_duty < DUTY_CYCLE_MIN) {
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m_duty = DUTY_CYCLE_MIN;
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}
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duty_out = fxp_add(m_duty, duty_p);
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if(duty_out < DUTY_CYCLE_MIN) {
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duty_out = DUTY_CYCLE_MIN;
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}
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}
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// fan stop handling
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if(temperature < FAN_OFF_TEMPERATURE) {
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m_duty = duty_out = 0;
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}
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}
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return FXP_TO_INT(duty_out);
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}
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