Solve a Discrete Set MPC Problem in Simulink
This example shows how to solve, using Simulink®, an MPC problem in which some manipulated variables belong to a discrete set.
Create a Plant Model
Fix the random generator seed for reproducibility.
Create a discrete-time strictly proper plant with 4 states, two inputs and one output.
plant = drss(4,1,2); plant.D = 0;
Increase the control authority of the first input, to better illustrate its control contribution.
Design the MPC Controller
Create an MPC controller with one second sampling time,
20 steps prediction horizon and
5 steps control horizon.
mpcobj = mpc(plant,0.1,20,5);
-->The "Weights.ManipulatedVariables" property is empty. Assuming default 0.00000. -->The "Weights.ManipulatedVariablesRate" property is empty. Assuming default 0.10000. -->The "Weights.OutputVariables" property is empty. Assuming default 1.00000.
Specify the first manipulated variable as belonging to a discrete set of seven possible values. Note that you Could also specify it as an integer using the instruction
mpcobj.MV(1).Type = 'integer'; in which case the first manipulated variable will be constrained to be an integer.
mpcobj.MV(1).Type = [-1 -0.7 -0.3 0 0.2 0.5 1];
Use rate limits to enforce maximum increment and decrement values for the first manipulated variable.
mpcobj.MV(1).RateMin = -0.5; mpcobj.MV(1).RateMax = 0.5;
Set limits on the second manipulated variable, whose default type (continuous) has not been changed.
mpcobj.MV(2).Min = -2; mpcobj.MV(2).Max = 2;
Control the Plant Model in Simulink
Create an output reference signal equal to zero from steps
35 and equal to
0.6 before and after.
r = ones(1,50)*0.6; r(20:35) = 0;
Create a Simulink closed loop simulation using the MPC Controller block, with the
mpcobj object passed as a parameter, to control the double integrator plant. For this example, open the pre-existing Simulink model
You can now run the model by clicking Run or by using the MATLAB® command
-->No sample time provided for plant model. Assuming sample time = controller's sample time = 0.1. -->Assuming output disturbance added to measured output channel #1 is integrated white noise. -->The "Model.Noise" property is empty. Assuming white noise on each measured output.
ans = Simulink.SimulationOutput: tout: [51x1 double] SimulationMetadata: [1x1 Simulink.SimulationMetadata] ErrorMessage: [0x0 char]
After the simulation, the plots of the two scopes show that the manipulated variable does not exceed the limit and the plant output tracks the reference signal after approximately half a second.