8502ee3c5c
For now only the proportional (Kp) and derivative (Kd) components are used, the integral term is 0.
65 lines
1.2 KiB
C
65 lines
1.2 KiB
C
/* Copyright (c) 2025 Rodrigo Arias Mallo <rodarima@gmail.com>
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* SPDX-License-Identifier: GPL-3.0-or-later */
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#include "thermostat.h"
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#define TEMP_MIN 35.0 /* °C */
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#define DELTA_LOW 1.0
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#define DELTA_HIGH 1.0
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#define T_ERR_MIN 35.0 /* °C */
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void
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thermostat_set(struct thermostat *th, float temp_target)
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{
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if (th->st == THERMOSTAT_ON && th->temp_target == temp_target)
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return;
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th->st = THERMOSTAT_ON;
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th->temp_target = temp_target;
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th->temp_min = temp_target - DELTA_LOW;
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th->temp_max = temp_target + DELTA_HIGH;
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th->on = 1;
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}
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void
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thermostat_off(struct thermostat *th)
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{
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th->st = THERMOSTAT_OFF;
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th->on = 0;
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}
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static float
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pid(float T0, float T, float dT_dt)
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{
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float err_min = 2.0;
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/* The rate of change of error is the same as the temperature, as they
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* are only offset by a mostly constant value */
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float derr_dt = dT_dt;
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if ((T0 - T) < err_min)
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return 0.0;
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float Kp = 1.0 / 20.0;
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float Kd = - 1.0 / 3.0;
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float u = Kp * (T0 - T) + Kd * dT_dt;
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if (u < 0.0)
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u = 0.0;
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else if (u > 1.0)
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u = 1.0;
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return u;
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}
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/* Return a value in [0, 1] to set the heater duty cycle */
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float
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thermostat_state(struct thermostat *th, float T, float dT_dt)
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{
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if (th->st == THERMOSTAT_OFF)
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return 0.0;
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return pid(th->temp_target, T, dT_dt);
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}
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