Refine, Test, and Debug a Subsystem

Test harnesses provide a development and testing environment that leaves the main model design intact. You can test a functional unit of your model in isolation without altering the main model. This example demonstrates refining and testing a controller subsystem using a test harness. The main model is a controller-plant model of an air conditioning/heat pump unit. The controller must operate according to several simple requirements.

Model and Requirements

Access the model. Enter

cd(fullfile(docroot,'toolbox','sltest','examples'))

Copy this model file and supporting files to a writable location on the MATLAB^® path:
```
sltestHeatpumpExample.slx
sltestHeatpumpBusPostLoadFcn.mat
PumpDirection.m
```
Open the model.
```
open_system('sltestHeatpumpExample')
```

In the example model:

The controller accepts the room temperature and the set temperature inputs.
The controller output is a bus with signals controlling the fan, heat pump, and the direction of the heat pump (heat or cool).
The plant accepts the control bus. The heat pump and the fan signals are Boolean, and the heat pump direction is specified by +1 for cooling and -1 for heating.

The test covers four temperature conditions. Each condition corresponds to one operating state with fan, pump, and pump direction signal outputs.

Temperature condition	System state	Fan command	Pump command	Pump direction
`\|Troom - Tset\| < DeltaT_fan`	idle	`0`	`0`	`0`
`DeltaT_fan <= \|Troom - Tset\| < DeltaT_pump`	fan only	`1`	`0`	`0`
`\|Troom - Tset\| >= DeltaT_pump and Tset < Troom`	cooling	`1`	`1`	`-1`
`\|Troom - Tset\| >= DeltaT_pump and Tset > Troom`	heating	`1`	`1`	`1`

Create a Harness for the Controller

Right-click the Controller subsystem and select Test Harness > Create for ‘Controller’.
Set the harness properties:
In the Basic Properties tab:
- Name: devel_harness1
- Clear Save test harness externally
- Sources and Sinks: None and Scope
- Clear Add separate assessment block
- Select Open harness after creation
Click OK to create the test harness.

Inspect and Refine the Controller

In the test harness, double-click Controller to open the subsystem.
Connect the chart to the Inport blocks.
In the test harness, click the Save button to save the test harness and model.

Add Test Inputs and Test the Controller

Navigate to the top level of devel_harness1.
Create a test input for the harness with a constant Tset and a time-varying Troom. Connect a Constant block to the Tset input and set the value to 75.
Add a Sine Wave block to the harness model to simulate a temperature signal. Connect the Sine Wave block to the conversion subsystem input Troom_in.
Double-click the Sine Wave block and set the parameters:
- Amplitude: 15
- Bias: 75
- Frequency: 2*pi/3600
- Phase (rad): 0
- Sample time: 1
- Select Interpret vector parameters as 1–D.
Connect Inport blocks to the Data Store Write inputs.
In the Configuration Parameters dialog box, in the Data Import/Export pane, select Input and enter u. u is an existing structure in the MATLAB base workspace.
In the Solver pane, set Stop time to 3600.
Open the scope in the test harness and change the layout to show three plots.
Click Run to simulate.

Debug the Controller

Observe the controller output. fan_cmd is 1 during the IDLE condition where |Troom - Tset| < DeltaT_fan.
This is a bug. fan_cmd should equal 0 at IDLE. The fan_cmd control output must be changed for IDLE.
In the harness model, open the Controller subsystem.
Open controller_chart.
In the IDLE state, fan_cmd is set to return 1. Change fan_cmd to return 0. IDLE is now:
```
IDLE
entry:
fan_cmd = 0;
 pump_cmd = 0;
 pump_dir = 0;
```
Simulate the harness model again and observe the outputs.
fan_cmd now meets the requirement to equal 0 at IDLE.

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