mpcmove command for real time application

I am trying to use MATLAB's mpcmove function to calculate optimal control actions for a real time application (controlling level in a tank). My process variable values (ym) are being read from the plant using OPC. I then feed these values into the mpcmove command, calculate the new u(k) and then output this to my manipulated variable in the field. I have tested this and my mpcmove command only seems to output my lower constraint. I am not sure if there is an issue with my methodology as far as using OPC to try and achieve control or if there is maybe an issue using mpcstate for the mpcmove command.

If anyone had any ideas as to what I was doing wrong it would be greatly appreciated. I have attatched my MATLAB code to see exactly what I am doing. I use MATLAB's tic and toc function to run a while loop for a pre-determined amount of time.

% This MATLAB code will connect with the Experion Pilot plant server PPserver1

% via a OPC connection and control the level in CSTR3 using PP_681.

clear

clc

% ======================== Setup OPC Connection ===========================

% Client and server configuration

data_access = opcda('ppserver1', 'HWHsc.OPCServer');

% Connect to the above server data_access

connect(data_access);

% Set up group for CSTR3 Temp transmitter control module TT_663

temp_CSTR3 = addgroup(data_access, 'TT_663');

PV_temp_CSTR3 = additem(temp_CSTR3, 'TT_663.TT_663.PV', 'double');

% Set up group for CSTR3 Level transmitter control module LT_667

level_CSTR3 = addgroup(data_access, 'LT_667');

PV_level_CSTR3 = additem(level_CSTR3, 'LT_667.LT_667.PV', 'double');

% Set up group for CSTR1 Steam valve control module FCV_622

steam_CSTR3 = addgroup(data_access, 'FCV_662');

PV_steam_CSTR3 = additem(steam_CSTR3, 'FCV_662.FCV_662.PV', 'double');

% Set up group for Drain pump control module PP_REF_681

drain_CSTR3 = addgroup(data_access, 'PP_REF_681');

PV_drain_CSTR3 = additem(drain_CSTR3, 'PP_REF_681.PP_681.PV', 'double');

% Set up group for Drain pump control module PP_REF_681

drain_CSTR3_on = addgroup(data_access, 'PP_OFF_681');

PVFL_drain_CSTR3 = additem(drain_CSTR3_on, 'PP_OFF_681.PP_ON_OFF.PVFL', 'double');

% Set up group for Drain pump control module PP_REF_681

CSTR3_agitator_on = addgroup(data_access, 'AG_661');

PVFL_agitator_CSTR3 = additem(CSTR3_agitator_on, 'AG_661.AG_ON_OFF.PVFL', 'double');

%================== Model Predictive Control Setup ========================

% LTI model for CSTR3 Level and Product Pump

plant_model = ss(tf(-0.297, [1 0]));

% Design MPC Controller using mpc command

Ts = 0.1; % Controller sample time

P = 20; % Prediction horizon

M = 6; % Control horizon

Weights.MV = 0.5; % Input weighting factor

Weights.OV = 1; % Output weighting factor

% MV.RateMin = -10; % Minumum rate of change of manipulated variable

% MV.RateMax = 10; % Maximum rate of change of manipulated variable

MV.Min = 0; % Upper constraint on MV

MV.Max = 100; % Lower constraint on MV

mpccontroller = mpc(plant_model, Ts, P, M, [], MV);

% mpccontroller.plant.Nominal.U = 5; % Assigns initial/steady state value to input

% mpccontroller.plant.Nominal.Y = 1; % Assigns initial/steady state value to output

xstate = mpcstate(mpccontroller); % Initial state of the controller for use in mpcmove command

set_point = 80; %Setpoint/reference signal for mpcmove command

% Modify MPC upper bound for simulation

MPCopt = mpcmoveopt; % mpcmove options

MPCopt.MVMin = 2; % Lower constraint for input - mpcmove command

MPCopt.MVMax = 40; % Upper constraint for input - mpcmove command

% ======================= Define Variables ================================

sim_time = 30; % Loop time in seconds

turn_on = 1; % Turning on pump/agitator

turn_off = 0; % Turning off pump/agitator

iteration = 0;

PV_array = [];

write(PVFL_drain_CSTR3, turn_on) % Turns on pump for control

tic

% ====================== Implement Control via OPC ========================

while toc < sim_time % this while loop will run for sim_time

iteration = iteration + 1;

% Setpoint changes according to toc counter

if toc > 180

set_point = 85;

elseif toc > 360

setpoint = 75;

elseif toc > 540

setpoint = 80;

end

current_level = read(PV_level_CSTR3); %Reads current level via OPC

PV_array = [PV_array; [current_level.Value]];

ym = PV_array(iteration,:);

[MV, info] = mpcmove(mpccontroller, xstate, ym, set_point, [], MPCopt); % Calculate control action

xstate.LastMove = MV;

new_control_action_level = MV;

if new_control_action_level > 40 % if statement incase constraints did not work

new_control_action_level = 40;

elseif new_control_action_level < 1

new_control_action_level = 1;

end

write(PV_drain_CSTR3, new_control_action_level); % Writes control action to PP_681

display = [ym new_control_action_level set_point toc]; % Displays current process values

disp( ' Level Pump_OP Setpoint Time ' )

disp(display) % Displays current process values

pause(1);

end