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RAJSHAHI UNIVERSITY OF ENGINEERING & TECHNOLOGY
Department of Mechatronics Engineering
Lab Report
Experiment No: 01
Experiment Title: Simulation of Separately Excited DC Motor Characteristics using MATLAB
Simulink.
Course No. : EEE 2288
Course Title : Electro-Mechanical Systems and Drives Sessional
Submitted By:
Mohammad Rokibul Hasan Rakib
ID: 2208017
2nd Year, Even Semester
Department of Mechatronics Engineering
Rajshahi University of Engineering & Technology, Rajshahi.
Submitted To:
Sarafat Hussain Abhi Md Zunaid Hossen
Assistant Professor Lecturer
Department of Mechatronics Department of Mechatronics
Engineering Engineering
Rajshahi University of Engineering & Rajshahi University of Engineering &
Technology, Rajshahi-6204. Technology, Rajshahi-6204.
Date Of Submission: 26 July 2025
Experiment No: 01
Experiment Name
Simulation of Separately Excited DC Motor Characteristics using MATLAB Simulink.
Objectives
To simulate a separately excited DC motor using MATLAB Simulink.
To analyze Speed vs Armature Current characteristics.
To analyze Torque vs Armature Current characteristics.
To compare theoretical and simulated characteristics.
To develop Simulink modeling skills for electrical machines.
Theory
A Separately Excited DC Motor (SEDCM) is a type of direct current motor where the field
winding is powered by an independent external source, separate from the armature circuit. This
configuration offers precise control over the magnetic field and thus provides improved torque
and speed regulation compared to self-excited motors. In a separately excited configuration,
the field current remains constant (or is adjustable independently), making it easier to study
motor behavior under varying armature voltage and load conditions.
Figure 1: Equivalent Circuit of SEDCM
Basic Operation of SEDCM
The working principle of a DC motor is based on the interaction between the magnetic field
produced by the stator (field winding) and the current flowing in the rotor (armature winding).
When a voltage is applied across the armature terminals, a current flows through the winding.
This current, in the presence of the magnetic field generated by the separately excited field
winding, experiences a force according to Lorentz's law, which causes the armature to rotate.
The torque T and speed ω of a separately excited DC motor can be expressed as:
𝑉𝑎 − 𝐼𝑎𝑅𝑎
𝑁∝
Φ
T ∝ ΦIa
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Where:
Va = Armature voltage
Ia = Armature current
Ra = Armature resistance
The back EMF is:
Eb = V−IaRa
Eb = KΦN
Where:
Eb = back EMF
K = machine constant
Required Apparatus:
MATLAB with SIMULINK
Procedure
To simulate the characteristics of a separately excited DC motor, a systematic model is
developed using MATLAB Simulink. The following steps outline the process in an academic
format:
1. Initialize the Simulation Environment: Begin by launching MATLAB Simulink and
creating a new blank model. To configure the simulation environment appropriately,
insert the Powergui block, located under Simscape > Electrical > Specialized Power
Systems > Fundamental Blocks. This block is essential for simulations involving power
systems and electrical machines.
2. Incorporate the DC Machine Block: Add the DC Machine block, which can be found
under Simscape > Electrical > Specialized Power Systems > Machines. This block
represents the separately excited DC motor to be analyzed.
3. Configure Power Supply Inputs:
Utilize two DC Voltage Source blocks:
Connect the first voltage source to the field winding terminals (F+ and F−) of
the DC Machine. This serves as the independent field excitation.
Connect the second voltage source to the armature terminals (A+ and A−) to
power the armature circuit.
4. Apply Mechanical Load Torque: Insert a Constant block to simulate a fixed mechanical
load. Connect this block to the TL (Torque Load) input port of the DC Machine to apply
a constant load torque during the simulation.
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5. Monitor Output Parameters: To extract key performance variables from the DC
Machine, use a Bus Selector block. From the machine’s output bus, select and output
the following parameters:
Rotor speed (rad/s)
Armature current (A)
Electromagnetic torque (Nm)
6. Convert Speed to RPM: Introduce a Gain block to convert the speed from radians per
second (rad/s) to revolutions per minute (RPM). The gain value should be set to 9.56,
corresponding to the formula:
60
𝑅𝑃𝑀 = 𝜔 ×
2𝜋
7. Visualize Outputs: Place Display blocks in the model to observe numerical values for
the following outputs:
Motor speed (RPM)
Armature current (A)
Electromagnetic torque (Nm)
8. Plot Characteristic Curves: To analyze the relationships between motor variables, insert
XY Graph (Scope) blocks. Connect the relevant signals to plot the following
characteristic curves:
Speed vs Torque
Torque vs Armature Current
Speed vs Armature Current
9. Configure Simulation Settings: Set an appropriate simulation time under Simulation >
Model Settings. Ensure that the solver type and step size are chosen based on the desired
accuracy and performance.
10. Execute the Simulation: Run the simulation and monitor the waveforms using the
scopes. Analyze the outputs to observe the dynamic behavior and performance
characteristics of the separately excited DC motor under load.
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Circuit Diagram
Figure 2: Circuit Diagram
Output
N vs T Graph
Figure 3: N vs T Graph
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T vs I Graph
Figure 4:T vs I Graph
N vs I Graph
Figure 5:N vs I Graph
Result
The simulation of the separately excited DC motor was successfully completed using
MATLAB Simulink. The following observations were noted:
The motor achieved a steady-state speed of approximately 1758 RPM under the applied
load torque and armature voltage conditions.
The armature current stabilized around 20.82 A during steady-state operation.
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The electrical torque developed by the motor was approximately 21.06 Nm.
The simulation also provided clear graphical outputs:
Speed vs Torque (N vs T): Showed that as torque increases, the speed decreases slightly
due to increased armature current and voltage drop.
Torque vs Armature Current (T vs I): Showed a linear relationship, verifying that torque
is directly proportional to armature current under constant field excitation.
Speed vs Armature Current (N vs I): Showed that as armature current increases, the
speed slightly decreases, consistent with theoretical analysis.
Conclusion
In this simulation study, the operational characteristics of a separately excited DC motor were
analyzed using MATLAB Simulink. Constant voltage sources were applied to both the field
and armature circuits, and a fixed mechanical load torque was introduced to evaluate the
motor’s dynamic response. Key performance variables—including rotor speed,
electromagnetic torque, and armature current—were monitored throughout the simulation.
The results demonstrated that the motor attained a steady-state speed while drawing a
corresponding armature current and producing the required torque to counteract the applied
load. The plotted characteristic curves—Speed vs Torque, Torque vs Armature Current, and
Speed vs Armature Current—closely matched theoretical expectations. Notably, the simulation
verified the linear relationship between torque and armature current, a defining characteristic
of DC motors. Additionally, a slight reduction in speed with increased load torque was
observed, consistent with practical motor behavior under load.
Overall, the simulation provided valuable insights into the steady-state and dynamic
performance of a separately excited DC motor, reinforcing theoretical concepts through visual
and quantitative analysis.
References
1. https://www.researchgate.net/figure/Equivalent-circuit-of-separately-excited-DC-
motor-22-The-separately-excited-DC-motor_fig2_339007349
2. https://doi.org/10.1109/DeSE60595.2023.10469592
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