User manual MATLAB MODEL PREDICTIVE CONTROL TOOLBOX 3

[. . . ] Model Predictive Control ToolboxTM 3 User's Guide Alberto Bemporad Manfred Morari N. Lawrence Ricker How to Contact The MathWorks Web Newsgroup www. mathworks. com/contact_TS. html Technical Support www. mathworks. com comp. soft-sys. matlab suggest@mathworks. com bugs@mathworks. com doc@mathworks. com service@mathworks. com info@mathworks. com Product enhancement suggestions Bug reports Documentation error reports Order status, license renewals, passcodes Sales, pricing, and general information 508-647-7000 (Phone) 508-647-7001 (Fax) The MathWorks, Inc. 3 Apple Hill Drive Natick, MA 01760-2098 For contact information about worldwide offices, see the MathWorks Web site. Model Predictive Control ToolboxTM User's Guide © COPYRIGHT 2005­2010 by The MathWorks, Inc. The software described in this document is furnished under a license agreement. [. . . ] Simulink® Test, Manipulated Variables on page 4-38 shows the corresponding manipulated variable moves (from the "MVs" scope in Paper Machine Headbox Control Using MPC Tools in Simulink® on page 4-36) which are smooth yet reasonably fast. For a disturbance size of 4, the results are still essentially the same as shown 4-37 4 Case-Study Examples in Test, Output Variables on page 4-38 and Simulink® Test, Manipulated Variables on page 4-38 (scaled by a factor of 4), but for a disturbance size of 6, the setpoint deviations are relatively larger, and the curve shapes differ (not shown). There are marked qualitative and quantitative differences when the disturbance size is 8. If such disturbances were likely, the controller would have to be retuned to accommodate them. Test, Output Variables Simulink® Test, Manipulated Variables 4-38 Bumpless Transfer in MPC Bumpless Transfer in MPC During startup of a continuous plant, the operators often adjust key actuators manually until the plant is near the desired operating point, and then switch to automatic control. If not done correctly, the transfer can cause a bump, i. e. , large actuator movements. A Model Predictive Controller must monitor all known plant signals even when it is not in control of the actuators. This improves its state estimates and allows a bumpless transfer to automatic operation. The following figure shows the block diagram. Simulink® Block Diagram for the MPC Bumpless Transfer Demo The plant is a stable single-input single-output system. Open-Loop Unit Step Response on page 4-40 shows its open-loop unit step response. 4-39 4 Case-Study Examples Open-Loop Unit Step Response MPC Block Configuration Settings on page 4-41 shows the MPC block configuration settings for this case. As shown in MPC Block Configuration Settings on page 4-41, the block's optional input port for externally supplied manipulated variables is selected. This adds the inport labeled ext. mv to the block (Simulink® Block Diagram for the MPC Bumpless Transfer Demo on page 4-39 shows how this is connnected). The optional input port for switching off the optimization is also selected, which adds the inport labeled QP switch to the block (see Simulink® Block Diagram for the MPC Bumpless Transfer Demo on page 4-39). 4-40 Bumpless Transfer in MPC MPC Block Configuration Settings The demo tests the effect of switching the controller from automatic to manual and back. To simulate this, a Pulse Generator block labeled switching signal sends either one or zero to a switch. When it sends zero, the system is in automatic mode, and the MPC block's output goes to the plant. Otherwise, the system is in manual mode, and the signal from the Operator Commands block goes to the plant. In both cases the actual plant input feeds back to the controller, as shown in Simulink® Block Diagram for the MPC Bumpless Transfer Demo on page 4-39 (unless the plant input saturates at -1 or 1). Thus, the controller can update its estimate of the plant state even when in manual. When the system switches to manual, a nonzero signal enters the controller's QP Switch inport, turning off the optimization calculations, thereby reducing computational 4-41 4 Case-Study Examples effort. The benefit is small in this trivial example but it could be significant in a demanding real-time application. As shown in Output, Reference and Switching Signal on page 4-42, the system is in automatic mode for the first 90 time units (switching signal is zero). During this time the controller smoothly drives the controlled plant output from its initial value, 0, to the desired reference value, -0. 5. Output, Reference and Switching Signal At time 90, manual operation begins (switching signal goes from zero to one). This causes the Switch element to send the operator commands to the plant instead of the controller output. [. . . ] The following graph shows a marker added to each output response and its corresponding setpoint. Data Marker Contents Each data marker provides information about the selected point, as follows: · Response ­ The scenario that generated the curve. · Amplitude ­ The signal value at the data marker location. · Input ­ Variable name for plant inputs and setpoints. 5-77 5 Reference for the Design Tool GUI Changing a Data Marker's Alignment To relocate the data marker's label (without moving the marker), right-click the marker, and select one of the four Alignment menu options. The above example shows three of the possible four alignment options. Relocating a Data Marker To move a marker, left-click it (holding down the mouse key) and drag it along its curve to the desired location. Deleting Data Markers To delete all data markers in a plot, click in the plot's white space. [. . . ]