DC motor modeling in Simulink - Step-by-Step Execution

Concept Flow - DC motor modeling in Simulink

Start: Define motor parameters

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Build electrical circuit model

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Build mechanical system model

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Connect electrical and mechanical parts

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Add input voltage and load torque

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Run simulation

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Observe motor speed and current outputs

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End

The flow shows building the DC motor model step-by-step in Simulink, from parameters to simulation and output observation.

Execution Sample

Simulink

1. Define motor constants (R, L, Kt, Ke, J, B)
2. Create electrical subsystem (Voltage, Resistor, Inductor)
3. Create mechanical subsystem (Inertia, Friction, Torque)
4. Connect subsystems with feedback
5. Run simulation to get speed and current

This code outlines the main steps to model a DC motor in Simulink and simulate its behavior.

Execution Table

Step	Action	Parameter/Variable	Value/State	Output/Result
1	Define resistance R	R	2 Ohms	R set
2	Define inductance L	L	0.5 H	L set
3	Define torque constant Kt	Kt	0.1 Nm/A	Kt set
4	Define back EMF constant Ke	Ke	0.1 V/(rad/s)	Ke set
5	Define inertia J	J	0.01 kg.m^2	J set
6	Define friction B	B	0.001 Nms	B set
7	Build electrical circuit	Voltage input	24 V step	Electrical subsystem ready
8	Build mechanical system	Load torque	0.05 Nm	Mechanical subsystem ready
9	Connect electrical and mechanical	Feedback loop	Connected	Complete motor model
10	Run simulation	Time	0 to 5 seconds	Simulation running
11	Observe speed output	Speed	Ramps to ~200 rad/s	Speed output plotted
12	Observe current output	Current	Peaks then stabilizes	Current output plotted
13	Simulation ends	Time	5 seconds	Simulation complete

💡 Simulation ends after 5 seconds, motor speed and current outputs are stable.

Variable Tracker

Variable	Start	After Step 6	After Step 9	After Step 12	Final
R (Resistance)	undefined	2 Ohms	2 Ohms	2 Ohms	2 Ohms
L (Inductance)	undefined	0.5 H	0.5 H	0.5 H	0.5 H
Kt (Torque Const.)	undefined	0.1 Nm/A	0.1 Nm/A	0.1 Nm/A	0.1 Nm/A
Ke (Back EMF Const.)	undefined	0.1 V/(rad/s)	0.1 V/(rad/s)	0.1 V/(rad/s)	0.1 V/(rad/s)
J (Inertia)	undefined	0.01 kg.m^2	0.01 kg.m^2	0.01 kg.m^2	0.01 kg.m^2
B (Friction)	undefined	0.001 Nms	0.001 Nms	0.001 Nms	0.001 Nms
Speed (rad/s)	0	0	starts rising	approx 200	approx 200
Current (A)	0	0	peaks ~12	stabilizes ~2.5	stabilizes ~2.5

Key Moments - 3 Insights

Why does the motor speed start at zero and then increase during simulation?

At step 11 in the execution table, the speed output ramps up because the motor starts from rest and accelerates due to the applied voltage and torque.

Why does the current peak early and then stabilize?

As shown in step 12, current peaks initially to overcome inertia and friction, then stabilizes as the motor reaches steady speed.

How are electrical and mechanical parts connected in the model?

Step 9 shows the feedback loop connection where electrical torque affects mechanical speed and back EMF affects electrical voltage.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of resistance R after step 6?

A 0.1 Nm/A

B 0.5 H

C 2 Ohms

D Undefined

💡 Hint

Check the 'Parameter/Variable' and 'Value/State' columns at step 1 and step 6.

At which step does the simulation start running?

A Step 9

B Step 10

C Step 7

D Step 12

💡 Hint

Look for the row where 'Action' is 'Run simulation' in the execution table.

If the load torque is increased, how would the speed output change in the simulation?

A Speed would decrease or stabilize at a lower value

B Speed would increase faster

C Speed would remain the same

D Speed would become zero immediately

💡 Hint

Consider the mechanical load effect on speed from the 'Mechanical subsystem' step in the execution table.

Concept Snapshot

DC Motor Modeling in Simulink:
- Define motor parameters (R, L, Kt, Ke, J, B)
- Build electrical and mechanical subsystems
- Connect subsystems with feedback
- Apply input voltage and load torque
- Run simulation to observe speed and current outputs

Full Transcript

This visual execution trace shows how to model a DC motor in Simulink step-by-step. First, motor parameters like resistance, inductance, torque constant, back EMF constant, inertia, and friction are defined. Then, the electrical circuit and mechanical system are built separately. These subsystems are connected with feedback loops to represent the motor's behavior. Input voltage and load torque are applied. The simulation runs from 0 to 5 seconds, during which motor speed starts at zero and ramps up to about 200 radians per second, while current peaks initially and then stabilizes. Key moments include understanding why speed ramps up, why current peaks, and how electrical and mechanical parts interact. The quiz questions check understanding of parameter values, simulation steps, and effects of load torque on speed.

Practice

1. What is the main purpose of using Simulink for DC motor modeling?

easy

A. To write code for motor control algorithms

B. To manufacture DC motors automatically

C. To simulate motor behavior before building physical hardware

D. To measure motor speed with physical sensors

Solution

1. Step 1: Understand Simulink's role

   Simulink is a tool for creating visual models and running simulations, not for manufacturing or direct measurement.

2. Step 2: Identify the correct purpose

   Simulink helps simulate motor behavior to predict performance before hardware is built.

3. Final Answer:

   To simulate motor behavior before building physical hardware -> Option C

4. Quick Check:

   Simulate motor behavior = To simulate motor behavior before building physical hardware [OK]

Hint: Simulink simulates, it does not build or measure [OK]

Common Mistakes:

• Confusing simulation with physical measurement
• Thinking Simulink writes hardware code
• Assuming Simulink manufactures motors

2. Which Simulink block is typically used to represent the electrical input voltage to a DC motor?

easy

A. Step block

B. Integrator block

C. Constant block

D. Gain block

Solution

1. Step 1: Identify input voltage representation

   Step block is commonly used to simulate a voltage that changes at a specific time, like turning the motor on.

2. Step 2: Compare other blocks

   Gain scales signals, Constant holds fixed value, Integrator accumulates signals, so Step fits best for input voltage changes.

3. Final Answer:

   Step block -> Option A

4. Quick Check:

   Voltage input changes = Step block [OK]

Hint: Use Step block for voltage changes over time [OK]

Common Mistakes:

• Using Constant block for changing voltage
• Confusing Gain with input source
• Thinking Integrator models voltage input

3. Given this Simulink model snippet for a DC motor, what will the scope display if the input voltage is a step from 0 to 12V at 1 second?

Electrical input: Step block (0 to 12V at t=1s)
Motor speed output connected to Scope

medium

A. Motor speed decreases after 1s

B. Motor speed jumps instantly to max at 1s

C. Motor speed remains zero throughout

D. Motor speed gradually increases after 1s

Solution

1. Step 1: Understand motor response to voltage step

   When voltage steps up, motor speed does not jump instantly due to inertia; it rises gradually.

2. Step 2: Analyze scope output

   Scope shows motor speed increasing smoothly after 1 second, reflecting physical motor acceleration.

3. Final Answer:

   Motor speed gradually increases after 1s -> Option D

4. Quick Check:

   Motor inertia causes gradual speed rise [OK]

Hint: Motor speed changes smoothly, not instantly [OK]

Common Mistakes:

• Expecting instant speed jump
• Thinking speed stays zero
• Assuming speed decreases after voltage step

4. You built a DC motor model in Simulink but the motor speed output stays zero even after applying voltage. What is the most likely error?

medium

A. Step block voltage set to zero

B. Integrator block missing in the mechanical subsystem

C. Scope block not connected to output

D. Gain block value set to negative

Solution

1. Step 1: Check mechanical subsystem setup

   Integrator block models motor speed from acceleration; missing it means speed never changes.

2. Step 2: Evaluate other options

   Voltage zero means no input but question says voltage applied; scope connection affects display but not speed; negative gain affects direction but not zero speed.

3. Final Answer:

   Integrator block missing in the mechanical subsystem -> Option B

4. Quick Check:

   Missing integrator means no speed change [OK]

Hint: Mechanical integrator needed to get speed from acceleration [OK]

Common Mistakes:

• Ignoring missing integrator effect
• Assuming scope connection causes zero speed
• Confusing gain sign with zero output

5. You want to model a DC motor in Simulink that includes both electrical and mechanical dynamics with load torque changing over time. Which approach is best?

hard

A. Use separate electrical and mechanical subsystems connected by torque and speed signals, with a time-varying load torque input

B. Model only electrical subsystem and ignore mechanical load

C. Use a single Gain block to represent entire motor behavior

D. Apply a Constant block for load torque and ignore time variation

Solution

1. Step 1: Understand modeling requirements

   Electrical and mechanical parts affect motor behavior; load torque changes over time must be included.

2. Step 2: Choose modeling approach

   Separate subsystems allow clear representation and connection via torque and speed signals; time-varying load torque input models real conditions.

3. Step 3: Evaluate other options

   Ignoring mechanical or load dynamics oversimplifies; Gain or Constant blocks cannot capture dynamics properly.

4. Final Answer:

   Use separate electrical and mechanical subsystems connected by torque and speed signals, with a time-varying load torque input -> Option A

5. Quick Check:

   Separate subsystems + time-varying load = Use separate electrical and mechanical subsystems connected by torque and speed signals, with a time-varying load torque input [OK]

Hint: Model electrical + mechanical parts separately with load input [OK]

Common Mistakes:

• Ignoring mechanical subsystem
• Using constant load torque only
• Oversimplifying motor as single Gain block