Control P-I-D library for esp32

[2dof]

I published small P-I-D control library in micropython for esp32 ( for other platforms should work too):
https://github.com/2dof/esp_control

It is based typical on functional code (as base to OOP) and provide PID algorithms and signal processing based on industrial standard implementation ( but without alarms).
Also I added a curve generator for Setpoint generation in thermal proces control.

from my test and simulations library should be used for proces samplins Ts > 0.1 sec.
In the furture I will add other algorithms (auto tuning mechanism, pole placement etc) and 'user-end-implementations' examples.

I hope description is clear and someone will find it usefull.

[peterhinch]

Impressive. And properly documented 👍

[2dof]

I have added small lib for Thermocouple type K functions ( based on Polynomials and lookup tables ) for non-linearity correction:
thermocouple type K .

It is good base for:

• AD8495 / AD8497 linearity correction using NIST Thermoelectric Voltage Lookup Tables.
• [AD7793+ADT7320 Measurement Solution] (https://www.analog.com/en/analog-dialogue/articles/measuring-temp-using-thermocouples.html)

Other types will be added later.

[2dof]

@ctimmer ..I forgot update file , now:
file in [pid_aw] https://github.com/2dof/esp_control/tree/main/src

basic usage:

1. copy file to your device
2. copy below code to to your device or locally to your IDE (Thonny etc.) and run,

Step responce of PID:

from pid_aw import *

# pid structure creation
pid_buf=bytearray(101)   # size of PID_REGS is 101 bytes, 
PID1 = uctypes.struct(uctypes.addressof(pid_buf), PID_REGS, uctypes.LITTLE_ENDIAN)
pid_init0(PID1)

# lets change some params 
PID1.Kp = 2
PID1.Tt = PID1.Ts            # 0.1
pid_tune(PID1)            

# set P-I D:
PID1.CFG.Psel=  True ; PID1.CFG.Isel = True ;  PID1.CFG.Dsel = True   
# or pid.CFG_REG=0x03


    
    # and test settings
PID1.CFG.Modesel = False # True
     
# get step responce  of PID e =sp-pv = 10 
sp =10.
pv=0.
for i in range(0,25):
    #u = pid_aw_updateControl(PID1,sp,pv,ubias = 0.)
    u = pid_awm_updateControl(PID1,sp,pv,ubias=0.,mv =0.)
    
    print("u:",u,"uk:",PID1.uk)    # PID1.uk is non limited cv (before limitation)

In this example a pid_init0(pid) function is used to load basic setting. For control thermal process like oven there time constants are at leastcouple of seconds the sampling time (Ts) -> PID1.Ts can be larger than now (0.1) , por example 0.5 or 1 sec. ( at least 5 to 10 times less than
time constant of oven).

the basic settings to start up play with oven:

1. set pid control to a P-I controller : 'PID1.CFG.Psel.True = True ; PID1.CFG.Isel = True ; PID1.CFG.Dsel = False
2. then using pid_aw algorithms, remember adjust Tm (= Ts) if neded.
3. set your own parameters P-I-(D) parameters KP, Ti (Td, Tm) , in practice You need to know about your thermal process:
   Gain, and Time constant -> You can perform a "step response of process" and note temp value every couple of seconds, after that you can estimate parameters calculate The PID parameters from Ziegler-Nichols Rules as your first "shot".
   note: most ( for baking) , of the ovens uses "on-off" control, i.e full power to the heater other (more fancy/specialized, use continuos ( Proportional Control: power from 0 to 100%) based on triacs etc.
   depending on Your solution You need remember what a "step" value will be.

[ctimmer]

@2dof
Thanks so much, this is just what I was looking for. My project is a modified electric smoker with an SSR for proportional control power.

Curt

[2dof]

"SSR for proportional control power" so it is standard ON/OFF control mod (like thermostat) amd if it is not other "fancy" on-off ( cycle mode or phase mode) You do not even need a PID controller, just simple relay (on-off) for Your SSR.

[ctimmer]

Using an SSR (see Operation section) works much better than a mechanical relay for switching AC power. A PID controller is still needed to set the duty cycle. I have my own algorithm for what is sometimes called slow PWM which works well with AC.

[2dof]

@ctimmer Example 2: Class controller example - implementing OOP tutorial
maybe will be helpful for You.

[2dof]

added:

1. On-Off controller - simple on-off control based on relay
   2.) [ type J thermocouples] (https://github.com/2dof/esp_control/tree/main/src/thermocouples#2-thermocouple-type-j) library based on its-90, but lockup tables calculate only in range 0 - 760 Celsjus ( from practical reason).

3. Added Example 2: Class controller example - implementing OOP tutorial , as example using pid functions in OOP. Part 1: class creating and pure soft simulation (Part 2 (in preparation) , using interrupts for practical use / template for example Hardware solution)

• reloaded pid_aw.py -> follow the updates

[2dof]

Some update about On-Off control: I have added in Examples:
Example_python_FOPDT_on_off.py - simulation script in python (same code as micropython version), also moved
on_off_control_example.py - simulation in micropython, o examples.
Also, I have added some comments to example about using on-off controller in follow-up control (and some comment about using it in electric ceramic kiln (simple) temperature control).