Gekko PRED_HOR and CTRL_HOR vs m.time

user_4315940 0
Viewed 225

I'm trying to implement an online MPC controller and I'm a bit confused about what exactly the m.time does.

With m.options.IMODE = 6 #MPC and m.options.REQCTRLMODE=3, I try to define the prediction and control horizons:

m.options.CTRL_HOR=10
m.options.CTRL_TIME=0.05
m.options.PRED_HOR=10
m.options.PRED_TIME=0.05

If I understand it right the ctrl_hor and pred_hor sets how many future timesteps we calculate and the pred_time and ctrl_time defines how long is one timestep. But the problem is that the controller throws an error if I don't define m.time, but what exactly does it do and why isn't it enough to set ctrl and pred horizons with respective timesteps?

gekko
1 Answers

Gekko uses m.time by default instead of CTRL_HOR and PRED_HOR. You can define an equivalent control / prediction horizon in Gekko with:

import numpy as np
from gekko import GEKKO

m = GEKKO()
m.time = np.linspace(0,0.05,11)

The CTRL_HOR and PRED_HOR properties are optionally used when CSV_READ=0. However, Gekko uses the CSV file to insert information about default values for parameters and variables so I don't recommend that you turn it off. Using m.time is also more flexible because you can have a non-uniform control / prediction horizon such as:

m.time = [0,0.05,0.1,0.2,0.5,1.0]

This helps to have the fine resolution at the beginning and then larger steps to determine steady-state move plans. Here is a practical TCLab MPC application with real-time data.

MPC Application

user_23669410
Related