DC Motor Model

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 model, open the PWM-Controlled DC Motor 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

1. Create a new model.

2. Add to the model the blocks listed in the following table. The Library column of the table specifies the hierarchical path to each block.

   Block	Library	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 ssc_new with domain type electrical to create a Simscape model that contains these blocks:

   • Simulink-PS Converter

   • PS-Simulink Converter

   • Scope

   • Solver Configuration

   • Electrical Reference

3. Rename and connect the blocks as shown in the diagram.

   

Now you are ready to specify block parameters.

Specify Model Parameters

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

Model Setup Parameters

The following 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.

1. Set the DC Voltage Source block parameters as follows:

   • Constant voltage to 2.5

2. Set the Controlled PWM Voltage block parameters as follows:

   • PWM frequency to 4000

   • Simulation mode 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.

3. Set the H-Bridge block parameters as follows:

   • Simulation mode 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 DC Motor block parameters as follows, leaving the unit settings at their default values where applicable:

• Electrical Torque tab:

  • Model parameterization to By rated power, rated speed & no-load speed

  • Armature inductance to 0.01

  • No-load speed to 4000

  • Rated speed (at rated load) to 2500

  • Rated load (mechanical power) to 10

  • Rated DC supply voltage to 12

• Mechanical tab:

  • Rotor inertia to 2000

  • Rotor damping to 1e-06

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 because Simscape Electrical models only run with a continuous-time solver. Increase the maximum step size the solver can take so the simulation runs faster.

1. In the model window, select Modeling > Model Settings to open the Configuration Parameters dialog box.

2. Select ode15s (Stiff/NDF) from the Solver list.

3. Expand Additional options and enter 1 for the Max step size parameter value.

4. 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

In this part of the example, you run the simulation and plot the results.

In the model window, select Simulation > Run to run the simulation.

To view the motor current and torque in the Scope windows, 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.

The following plot shows the motor current.

Motor Current

The next plot shows the motor rpm.

Motor RPM

As expected, the motor runs at about 2000 rpm when the applied DC voltage is 2.5 V.