This article shows how to implement a PID controller in LUA.

Basics

A PID controller is a versatile control loop mechanism that compares an input reading with a setpoint and writes a control value based on the controller parameters and state.

Implementation

The required items and parameters are specified when creating the PID controller using the AddPidController() function. After that, the controller loop is automatically called every ta seconds.

Therefore it is sufficient to add the PID controller in the OnStartEvent() function. In this example we use the following parameters:

function OnStartEvent()
	AddPidController("NETx\\VIRTUAL\\BuildingA\\Floor1\\RoomA\\Current", "NETx\\VIRTUAL\\BuildingA\\Floor1\\RoomA\\Setpoint", "NETx\\VIRTUAL\\BuildingA\\Floor1\\RoomA\\Control", 10, 0.2, 0.00002222222, 0, 0, 255, -2, 65536, true)
end

Background information

Kp is the proportional factor which 1/P where P is the gain of the controller in K (Kelvin). Notable hardware vendors suggest for warm water heating a P of 5 K. Therefore, Kp for heating is 0.2.

Ki is calculated as Kp/Tr where Tr is the reset time in seconds of the controller. A typical value for warm water heating is 150 minutes . Thus, Ki = 0.2/150*60 = 0. 00002222222 for heating.