Build and Simulate a Simple DC Motor

In this example, you model a DC motor driven by a constant input signal that approximates a pulse-width modulated signal and look at the current and rotational motion at the motor output.

To see the completed version of the model you create in this example, open the Control DC Motor with PWM Voltage Source and H-Bridge Driver example.

Select Blocks to Represent System Components

Select the blocks to represent the input signal, the DC motor, and the motor output displays.

The following table describes the role of the blocks that represent the system components.

Block	Description
Solver Configuration	Defines solver settings that apply to all physical modeling blocks
PS-Simulink Converter	Converts the input physical signal to a Simulink^® signal
Controlled PWM Voltage	Generates the signal that approximates a pulse-width modulated motor input signal
H-Bridge	Drives the DC motor
DC Motor	Converts input electrical energy into mechanical motion
Current Sensor	Converts the electrical current that drives the motor into a measurable physical signal proportional to the current
DC Voltage Source	Generates a DC voltage
Electrical Reference	Provides the electrical ground
Mechanical Rotational Reference	Provides the mechanical ground
Ideal Rotational Motion Sensor	Converts the rotational motion of the motor into a measurable physical signal proportional to the motion
Scope	Displays motor current and rotational motion

Build the Model

Create a new model.

Add the blocks in this table. The Library Path column specifies the hierarchical path to each block.

Block	Library Path	Quantity
Solver Configuration	Simscape > Utilities	1
PS-Simulink Converter	Simscape > Utilities	2
Controlled PWM Voltage	Simscape > Electrical > Integrated Circuits	1
H-Bridge	Simscape > Electrical > Semiconductors & Converters > Converters	1
DC Motor	Simscape > Electrical > Electromechanical > Brushed Motors	1
Current Sensor	Simscape > Foundation Library > Electrical > Electrical Sensors	1
DC Voltage Source	Simscape > Foundation Library > Electrical > Electrical Sources	1
Electrical Reference	Simscape > Foundation Library > Electrical > Electrical Elements	1
Mechanical Rotational Reference	Simscape > Foundation Library > Mechanical > Rotational Elements	1
Ideal Rotational Motion Sensor	Simscape > Foundation Library > Mechanical > Mechanical Sensors	1
Scope	Simulink > Commonly Used Blocks	2

Note

You can use the Simscape™ function sscnew with domain type electrical to create a Simscape model that contains these blocks:

Simulink-PS Converter
PS-Simulink Converter
Scope
Solver Configuration
Electrical Reference

Rename and connect the blocks as shown in the diagram.

Now you are ready to specify block parameters.

Specify Model Parameters

Specify these parameters to represent the behavior of the system components:

Model Setup Parameters

These blocks specify model information that is not specific to a particular block:

Solver Configuration
Electrical Reference
Mechanical Rotational Reference

As with Simscape models, you must include a Solver Configuration block in each topologically distinct physical network. This example has a single physical network, so use one Solver Configuration block with the default parameter values.

You must include an Electrical Reference block in each Simscape Electrical™ network. You must include a Mechanical Rotational Reference block in each network that includes electromechanical blocks. These blocks do not have any parameters.

For more information about using reference blocks, see Grounding Rules.

Motor Input Signal Parameters

You generate the motor input signal using these blocks:

The DC Voltage Source block (PWM reference voltage) generates a constant signal.
The Controlled PWM Voltage block generates a pulse-width modulated signal.
The H-Bridge block drives the motor.

In this example, all input ports of the H-Bridge block except the PWM port are connected to ground. As a result, the H-Bridge block behaves as follows:

When the motor is on, the H-Bridge block connects the motor terminals to the power supply.
When the motor is off, the H-Bridge block acts as a freewheeling diode to maintain the motor current.

In this example, you simulate the motor with a constant current whose value is the average value of the PWM signal. By using this type of signal, you set up a fast simulation that estimates the motor behavior.

In the DC Voltage Source block, set the Constant voltage parameter to 2.5 V.
Set the parameters of the Controlled PWM Voltage block:
- PWM frequency — 4000 Hz
- Simulation mode — Averaged
  This value tells the block to generate an output signal whose value is the average value of the PWM signal. Simulating the motor with an averaged signal estimates the motor behavior in the presence of a PWM signal. To validate this approximation, use value of PWM for this parameter.
In the H-Bridge block, set the Simulation mode parameter to Averaged.
This value tells the block to generate an output signal whose value is the average value of the PWM signal. Simulating the motor with an averaged signal estimates the motor behavior in the presence of a PWM signal. To validate this approximation, use value of PWM for this parameter.

Note

The simulation mode for both the Controlled PWM Voltage and H-Bridge blocks must be the same.

Motor Parameters

Configure the block that models the motor.

Set the parameters of the DC Motor block, leaving the unit settings at their default values where applicable:

Electrical Torque section:
- Model parameterization — By rated load and speed
- Armature inductance — 0.01 H
- No-load speed — 4000 rpm
- Rated speed (at rated load) — 2500 rpm
- Rated load (mechanical power) — 10 W
- Rated DC supply voltage — 12 V
Mechanical section:
- Rotor inertia — 0.0002 kg*m^2
- Rotor damping — 0.5e-5 N*m/(rad/s)

Current Display Parameters

Specify the parameters of the blocks that create the motor current display:

Current Sensor block
PS-Simulink Converter1 block
Current scope

Of the three blocks, only the PS-Simulink Converter1 block has parameters. Set the PS-Simulink Converter1 block Output signal unit parameter to A to indicate that the block input signal has units of amperes.

Torque Display Parameters

Specify the parameters of the blocks that create the motor torque display:

Ideal Rotational Motion Sensor block
PS-Simulink Converter block
RPM scope

Of the three blocks, only the PS-Simulink Converter block has parameters you need to configure for this example. Set the PS-Simulink Converter block Output signal unit parameter to rpm to indicate that the block input signal has units of revolutions per minute.

Note

You must type this parameter value. It is not available in the drop-down list.

Configure the Solver Parameters

Configure the solver parameters to use a continuous-time solver. Simscape Electrical models only run with a continuous-time solver when you clear the Local Solver parameter of a Solver Configuration block. Use the Configuration Parameters dialog box to change the simulation end time, tighten the relative tolerance for a more accurate simulation, and remove the limit on the number of simulation data points Simulink saves.

In the model window, select Modeling > Model Settings to open the Configuration Parameters dialog box.
In the left pane, click Solver:
- Set Stop time to 10.
- Set Solver to ode15s (Stiff/NDF).
- Set Max step size to 1.
- Set Relative tolerance to 1e-3.
Click OK.

For more information about configuring solver parameters, see Simulating an Electronic, Mechatronic, or Electrical Power System.

Run the Simulation and Analyze the Results

Run the simulation and plot the results. In the model window, select Simulation > Run.

To view the motor current and torque, double-click the Scope blocks. You can do this before or after you run the simulation.

Note

By default, the scope displays appear stacked on top of each other on the screen, so you can only see one of them. Click and drag the windows to reposition them.

This figure shows the motor current.