This example shows how to inspect the optimized sequence of manipulated variables computed by a model predictive controller at each sample time.
The plant is a double integrator subject to input saturation.
The basic setup of the MPC controller includes:
A double integrator as the prediction model
Prediction horizon of 20
Control horizon of 10
-1 <= u(t) <= 1
Configure the MPC controller.
Ts = 0.1; % Sample time p = 20; % Prediction horizon m = 10; % Control horizon mpcobj = mpc(tf(1,[1 0 0]),Ts,p,m); % MPC object mpcobj.MV = struct('Min',-1,'Max',1); % Input saturation constraints nu=1; % Number of manipulated variables
-->The "Weights.ManipulatedVariables" property of "mpc" object is empty. Assuming default 0.00000. -->The "Weights.ManipulatedVariablesRate" property of "mpc" object is empty. Assuming default 0.10000. -->The "Weights.OutputVariables" property of "mpc" object is empty. Assuming default 1.00000.
To run this example, Simulink® is required.
if ~mpcchecktoolboxinstalled('simulink') disp('Simulink(R) is required to run this example.') return end
Open the Simulink® model, and run the simulation.
mdl = 'mpc_sequence'; open_system(mdl) sim(mdl)
-->Converting the "Model.Plant" property of "mpc" object to state-space. -->Converting model to discrete time. Assuming no disturbance added to measured output channel #1. -->The "Model.Noise" property of the "mpc" object is empty. Assuming white noise on each measured output channel.
The MPC Controller block has an
mv.seq output port, which is enabled by selecting the Optimal control sequence block parameter. This port outputs the optimal control sequence computed by the controller at each sample time. The output signal is a (p+1)-by-Nmv array, where p is prediction horizon and Nmv is the number of manipulated variables.
In a simlar manner, the controller can output the optimal state sequence (
x.seq) and the optimal output sequence (
The model exports this control sequence to the MATLAB® workspace at each simulation step, logging the data as
Plot the optimal control sequence at specific time instants.
times = [0 0.2 1 2 2.1 2.2 3 3.5 5]; figure('Name','Optimal sequence history'); for t = 1:9 ct = times(t)*10+1; subplot(3,3,t) h = stairs(0:p,useq.signals.values(ct,:)); h.LineWidth = 1.5; hold on plot((0:p)+.5,useq.signals.values(ct,:),'*r') xlabel('prediction step') ylabel('u') title(sprintf('Sequence (t=%3.1f)',useq.time(ct))) grid axis([0 p -1.1 1.1]) hold off end
The MPC controller uses the first two seconds to bring the output very close to the new set point. The controller output is at the high limit (+1) for one second and switches to the low limit (-1) for the next second, which is the best control strategy under the input constraint limits.