Brushless DC Motor (BLDC)

Hindi

Marathi

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🎓 Lesson: Brushless DC Motor (BLDC)

1. Introduction

A Brushless DC Motor (BLDC) is a type of DC motor that does not use brushes for commutation. Instead, it uses electronic control to achieve commutation through a controller. These motors are widely used in applications where high reliability, high efficiency, and compact size are critical — such as in drones, electric vehicles, robotics, and home appliances.

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2. Principle of Working

✅ Construction:

• Stator: Contains the windings (like a 3-phase stator in an AC motor).

• Rotor: Contains permanent magnets.

• Position Sensor: Usually Hall-effect sensors to detect rotor position.

⚙️ Operating Principle:

BLDC motors operate using the interaction between the magnetic field of the rotor and the rotating magnetic field of the stator. The key steps:

1. Electronic controller energizes stator windings in a specific sequence based on rotor position.

2. This creates a rotating magnetic field in the stator.

3. The rotor (with permanent magnets) follows this rotating magnetic field.

4. The controller switches the stator currents in sync with the rotor position — a process called electronic commutation.

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3. Features of BLDC Motors

Feature	Description
No Brushes	Reduced mechanical wear and noise
High Efficiency	Typically 85–95% due to no friction losses from brushes
Compact & Lightweight	Suitable for portable and embedded applications
High Torque-to-Weight	Useful in drones, EVs, and robots
Low Maintenance	No brush wear = less frequent servicing
Precise Control	Good for speed and torque control using feedback

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4. Speed Control System of BLDC Motor

BLDC motors are controlled using closed-loop or open-loop electronic controllers. The controller regulates speed by adjusting the duty cycle of a PWM (Pulse Width Modulated) signal.

Speed Control Techniques:

A. PWM Control (Open-loop or closed-loop):

• Controls average voltage supplied to motor.

• Speed ∝ Applied voltage.

B. Closed-Loop Control:

• Feedback from Hall sensors or encoders provides rotor position and speed.

• Controller adjusts voltage/current to maintain desired speed.

C. Vector Control / FOC (Field Oriented Control):

• Advanced method.

• Controls torque and flux independently for precise operation.

• Common in high-performance applications like EVs.

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5. Efficiency of BLDC Motor

BLDC motors are highly efficient because of:

• Absence of brush contact friction.

• Optimized commutation using sensors.

• Reduced power loss due to precise electronic control.

Typical Efficiency Range:

• 85% to 95% depending on load, speed, and design.

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6. Basic Calculations

A. Back EMF (Electromotive Force):

$$E = k_e \cdot \omega$$

Where:

• $E$: Back EMF (V)

• $k_e$: Back EMF constant (V/rad/s)

• $\omega$: Angular velocity (rad/s)

B. Torque Equation:

$$T = k_t \cdot I$$

Where:

• $T$: Torque (Nm)

• $k_t$: Torque constant (Nm/A)

• $I$: Current (A)

C. Speed Calculation (for a trapezoidal BLDC motor):

$$N = \frac{60 \cdot (V - I \cdot R)}{k_e \cdot p}$$

Where:

• $N$: Speed (rpm)

• $V$: Supply voltage (V)

• $R$: Winding resistance (Ω)

• $p$: Number of pole pairs

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7. Application Examples

• Electric vehicles (e-bikes, scooters, cars)

• Drones and UAVs

• CNC machines

• Air conditioners and washing machines

• Hard disk drives

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8. Summary

Aspect	BLDC Motor Summary
Commutation	Electronic (via controller)
Efficiency	High (85–95%)
Control	PWM, Closed-loop, FOC
Maintenance	Low, due to absence of brushes
Torque control	Linear with current
Applications	Widely used across industries

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