Documentation

Parametric Sweep for a Simscape Thermal Model

Test and optimize a physical system using a test sequence, test harness, and the test manager. Copyright 2015 The MathWorks, Inc.

Objective

This example demonstrates how to test a physical system, and how to optimize a parameter using a test harness, test sequence, and the test manager. The example uses a system-level thermal model of a projector which includes Simscape® thermal blocks. Run the following to set paths and names for the example.

Model = 'sltestProjectorFanSpeedExample';
Harness = 'FanSpeedTestHarness';
Path = fullfile(matlabroot,'toolbox','simulinktest','simulinktestdemos');
TestSuite = 'sltestProjectorFanSpeedTestSuite.mldatx';
open_system(Model);

Test Plan and System Requirements

This test demonstrates sweeping through several fan speeds to determine the optimal value. In short, the optimal fan speed results in the fastest response without damaging the system. In detail, the optimal fan speed:

  • Prevents the system from exceeding the specified maximum temperature.

  • Minimizes the time for the system to reach the temperature at which the lamp emits visible light.

The document sltestProjectorFanSpeedExampleRequirements.txt captures these detailed requirements and the test procedure. You can find the document in the folder specified by Path above.

Test-specific model items reside in the test harness, keeping the main model free of unnecessary blocks, suitable for code generation, and suitable for integration with other models.

Open the Test File

Open the Test Manager to view the test suite controlling the parameter sweep. From the menu click Analysis > Test Manager. In the toolbar, select Open and open the test suite located on the example path.

You can also enter

open(fullfile(Path,TestSuite))

Description of the Test

The test investigates the transient and steady-state thermal characteristics of the system. The test sequence initializes the system to ambient temperature, then powers the projector lamp. When the system reaches a steady-state condition, the lamp switches off. This test is modeled in a test harness using a Test Sequence block. Run the following to open the test harness:

sltest.harness.open(Model,Harness);

Requirements Linking

The test suite contains links to the requirements document. You can view the requirements link by opening the test suite in the Test Browser, and clicking the links in the Requirements section.

The Test Sequence

Double-click the Test Sequence block to open the test sequence editor.

The T0out and T0in signals store the initial projector temperature at each test step.

PowerOnTime stores simulation time when the lamp signal activates. This facilitates subsequent data analysis.

The transition condition detects the steady-state condition. At steady-state, the system temperature change is a small fraction (Threshold) of the difference between the current projector temperature and the initial projector temperature at each step. This condition must hold for a minimum time DurationLimit, in this case 10 seconds.

Description of the Parameter Sweep

The pre-load callbacks contain the command to set the fan speed for each test case under the Fan Speed Parametric Study test suite. The parameter overrides contain the command to recalculate fan airflow from fan speed, and then override the test harness parameter. You can view these commands in the Callbacks and Parameter Overrides section of each test case.

Run the Test

In the Test Browser, highlight Fan Speed Parametric Study and click Run. When the test suite simulation completes, open the results for each test case and select ProjectorTemp. View the results in the Test Manager.

Export the Data

With the Test Manager you can export data for post-processing. In the Results and Artifacts pane of the Test Manager, right-click Sim Output for each test case and select Export.

This example includes the exported data in four MAT files, located in the folder specified by Path:

ProjectorTempFanSpeed800.mat
ProjectorTempFanSpeed1300.mat
ProjectorTempFanSpeed1800.mat
ProjectorTempFanSpeed2300.mat

Investigate Response Time and Maximum Projector Temperature

Since the test sequence transitions execute when the system reaches steady-state, and the fan speed changes the system response, the lamp activates at different simulation times for each of the four test cases. Simplify the graphical results analysis by plotting each response with the lamp activation at the same time.

Extract the lamp activation response data, and plot the system response for the four fan speeds. Evaluate the results against these criteria:

  • The temperature shall not exceed 65 deg C.

  • The lamp emits visible light above 45 deg C. Minimize the time to reach this temperature.

Load the results. At the command line, enter

DataAt800 = load('ProjectorTempFanSpeed800.mat');
DataAt1300 = load('ProjectorTempFanSpeed1300.mat');
DataAt1800 = load('ProjectorTempFanSpeed1800.mat');
DataAt2300 = load('ProjectorTempFanSpeed2300.mat');

The script ArrangeProjectorData.m arranges the temperature and power on data from the output for each run. You can open the file at the location specified by Path to see the details of the script.

ArrangeProjectorData

The script PlotProjectorThermalResponse.m plots the thermal response of the projector after the lamp activates, for each of the fan speeds. You can open the file at the location specified by Path to see the details of the script.

PlotProjectorThermalResponse

Results Interpretation

The results show that while the highest fan speed results in the lowest maximum temperature, it also takes the longest time to reach the lamp activation temperature. The lowest fan speed results in the fastest lamp activation, but the system exceeds the maximum specified temperature by a significant margin.

Fan speed = 1300 keeps the system under the maximum temperature spec, and the system also reaches lamp activation temperature approximately 3 seconds faster than with the highest fan speed.

close_system(Model,0);
clear Model;
clear Harness;
close(figure(1));
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