Autotune leading to ZeroDivisionError exception

[ScratMan]

Hello, I configured the smart_thermostat on my Home Assistant core (docker contained) instance.

I set the climate entity with the following configuration :

- platform: smart_thermostat
name: salle_de_bain
heater: switch.seche_serviette
target_sensor: sensor.popp_mold_salle_de_bain_temperature
min_temp: 7
max_temp: 30
ac_mode: False
target_temp: 24
keep_alive:
seconds: 5
# initial_operation_mode: "off"
kp : 5
ki : 3
kd : 2
pwm : 1
autotune : ziegler-nichols
difference : 100
noiseband : 0.5

I set the target temperature so that the thermostat could activate the heater at reboot, as the temperature in the room was 23°C at that moment. Otherwise the autotune left the thermostat completely off.

The smart thermostat kept the heater ON for 2h30' and then stopped it when temperature sensor indicated 24.7°C. The temperature then continued to raise up to 25.9 during 1h30'. The temperature then slowly decreased for 4h down to 24.8°C and then the autotune tried to compute the parameters and failed with the following error:

2021-10-01 20:37:32 ERROR (MainThread) [homeassistant] Error doing job: Task exception was never retrieved
Traceback (most recent call last):
File "/config/custom_components/smart_thermostat/climate.py", line 433, in _async_control_heating
await self.calc_output()
File "/config/custom_components/smart_thermostat/climate.py", line 476, in calc_output
params = self.pidAutotune.get_pid_parameters(self.autotune)
File "/config/custom_components/smart_thermostat/pid_controller/init.py", line 188, in get_pid_parameters
ki = kp / (self._Pu / divisors[1])
ZeroDivisionError: float division by zero

It seems the self._Pu remained at 0 during the full process, but no information why.