Simulating a DC Motor-Driven Fan Load in Simscape

Welcome to the Physical Modeling in Simscape with Simulink & MATLAB blog series! In this edition, we’ll explore how to model and simulate a DC motor-driven fan load, a common example of an electromechanical system. This blog focuses on integrating electrical and mechanical components using MATLAB Simscape, providing a practical guide for beginners and advanced users alike. 

This tutorial is part of Skill-Lync Simscape Training, designed to help you understand physical modeling using MATLAB Simscape through real-world examples. 

Understanding the System: A DC Motor and Fan Load 

In this simulation, we model a fan driven by a DC motor. The fan’s torque (TLT_LTL ) is proportional to the square of its angular speed (ωM\omega_MωM ): 

TL=C⋅ωM2T_L = C \cdot \omega_M^2TL =C⋅ωM2  

Where CCC is the constant of proportionality. 

Key elements of the system include: 

• DC Motor: Converts electrical energy into mechanical rotation. 
• Fan Load: Consists of aerodynamic drag, inertia, and torque-speed characteristics. 
• Electrical Supply: Provides the necessary voltage and current to drive the motor. 

This system demonstrates how electrical inputs (voltage and current) influence mechanical outputs (speed and torque). Such models are invaluable for understanding Simscape physical systems. 

Building the Model in Simulink 

Defining the Subsystem: 

• The fan load subsystem includes the aerodynamic drag modeled using the equation TL=C⋅ωM2T_L = C \cdot \omega_M^2TL =C⋅ωM2 . 
• Add an ideal rotational motion sensor to measure angular speed (ωM\omega_MωM ) and a torque source to apply torque to the motor shaft. 

Connecting the DC Motor: 

• Use the Simscape electrical library to add a DC motor block. 
• Connect the motor’s mechanical ports (R for rotating and C for casing) to the fan load subsystem. 

Adding a DC Voltage Source: 

• Incorporate a DC voltage source to power the motor. 
• Use a current sensor to measure the current flowing through the motor. 

Signal Routing with From and Goto: 

• To simplify signal routing across subsystems, use Goto blocks to send speed and torque values and From blocks to receive them at the scope. 

Simulating the System 

With Fixed Voltage: 

• Apply a fixed voltage of 100V. 
• Observe constant current and a gradually increasing speed due to the fan’s inertia. 

With Variable Voltage: 

• Replace the fixed voltage source with a controlled voltage source. 
• Use a ramp block to simulate a voltage rising linearly from 0 to 100V over 20 seconds. 

Key Observations 

Inertia Effects: 

• Adding an inertia block to the motor shaft results in a gradual increase in speed. 
• Without inertia, the speed reaches its steady state immediately. 

Exponential Speed Behavior: 

• When voltage is increased gradually, the speed rises exponentially due to the aerodynamic drag characteristics of the fan. 

Torque-Speed Relationship: 

• The torque remains relatively constant while the speed increases, showcasing the square-law relationship between torque and speed. 

Conclusion 

This simulation demonstrates the dynamic interaction between electrical and mechanical systems, showcasing the power of Simscape physical modeling. By integrating DC motor characteristics, fan load dynamics, and variable voltage sources, you gain insights into real-world applications like exhaust fans and ceiling fans. 

To deepen your understanding, enroll in Skill-Lync’s Simscape Course Online, where you’ll learn to design and simulate complex systems. Stay tuned for the next blog, where we’ll explore advanced signal routing and parameter tuning. 

This blog is part of our ongoing Physical Modeling in Simscape with Simulink & MATLAB. If you missed the previous posts, check them out here.  

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