How to Control the Speed of a BLDC Motor?

In the world of modern motion control, Brushless DC (BLDC) motors have become a key technology driving innovation across industries. From electric vehicles and drones to industrial robots and HVAC systems, these motors are favored for their efficiency, compact size, and long service life. However, while BLDC motors are inherently efficient and reliable, their real potential is unlocked only when their speed is precisely controlled.

Speed control is not merely about making a motor spin faster or slower; it is about achieving performance, stability, and energy optimization in every application. For engineers and manufacturers, understanding how to control the speed of a BLDC motor is fundamental to designing products that meet both operational and cost objectives.

This blog by United Motion Inc. provides a comprehensive look into BLDC motor speed control methods, discussing everything from why speed control matters to advanced control strategies. Whether you are a design engineer or a business professional seeking a deeper understanding of motor control, this guide aims to clarify the technical concepts while highlighting real-world implications.

Why Speed Control Matters in Modern Applications?

The importance of BLDC motor speed control extends far beyond simple motion management. In modern applications, it directly affects energy consumption, noise level, system reliability, and even product quality.

For example:

• Electric Vehicles (EVs) need precise speed control for smooth acceleration and regenerative braking.
• Drones and UAVs require dynamic speed control for stable flight and maneuvering.
• Industrial Robots depend on accurate motor control for coordinated, repeatable motion.
• HVAC Systems use variable-speed BLDC fans for energy-efficient air circulation.

Without proper speed control, even the best BLDC motor can underperform or fail to meet application-specific demands. This is why choosing the right control method—and implementing it properly—is vital to achieving consistent, high-quality results.

Common Speed Control Methods

There are several methods to control the speed of a BLDC motor, each with its own advantages, limitations, and ideal use cases. The chart below summarizes the main techniques used in the industry.

Visual Chart: Comparison of BLDC Motor Speed Control Methods

This chart provides a quick overview of the main approaches engineers use to manage speed in BLDC systems. In the following sections, we’ll explore each method in greater detail to understand its function, benefits, and ideal application scenarios.

PWM Control Explained

Pulse Width Modulation (PWM) is one of the most widely used techniques to control the speed of a BLDC motor. The principle is simple yet effective: instead of changing the voltage continuously, the controller switches the power on and off at a very high frequency. The average voltage delivered to the motor is determined by the ratio of ON to OFF time (known as the duty cycle).

A higher duty cycle means a higher average voltage, resulting in higher speed. A lower duty cycle reduces the average voltage, thus reducing speed.

Key benefits of PWM control include:

• High energy efficiency
• Excellent linearity between speed and duty cycle
• Compatibility with both open-loop and closed-loop systems

In most industrial controllers, PWM frequency typically ranges from 8 kHz to 20 kHz to ensure smooth operation without audible noise. The method is particularly favored in applications like electric vehicles, drones, and fans, where precision and response speed are critical.

However, PWM control requires careful design to avoid switching losses, electromagnetic interference (EMI), and thermal buildup in the transistors or MOSFETs. United Motion Inc. recommends using well-designed driver circuits and shielded cabling for optimal performance and long-term reliability.

Voltage Regulation Method

The simplest way to control the speed of a BLDC motor is by adjusting its supply voltage. When voltage increases, the motor’s back EMF and speed rise proportionally; when it decreases, the speed drops.

While this method is intuitive and cost-effective, it’s primarily suitable for low-cost, non-critical applications such as small pumps, blowers, and simple household appliances.

Advantages:

• Simple circuitry
• Low cost
• Easy to implement

Disadvantages:

• Limited precision and response time
• Torque capability decreases with voltage
• Not suitable for dynamic load changes

Because BLDC motors are highly efficient, even small voltage fluctuations can significantly affect speed and torque. For this reason, voltage control is often paired with feedback sensors or microcontrollers to stabilize output and improve performance.

Closed-Loop Control Using Feedback

In more advanced applications, BLDC motor speed is controlled using closed-loop feedback systems. Unlike open-loop methods, closed-loop systems continuously monitor the motor’s actual speed or position and compare it to the desired setpoint.

If a difference (error) is detected, the controller automatically adjusts the drive signal to correct it. This allows for precise and stable operation even under varying loads or voltage fluctuations.

There are two common types of feedback sensors used:

Hall Effect Sensors – Provide rotor position data at fixed intervals.

Optical Encoders / Resolvers – Offer high-resolution feedback for precision motion control.

Applications include:

• Robotics
• CNC machinery
• Servo-driven systems
• High-end automation

Closed-loop control is essential for industries where accuracy and repeatability are mission-critical. Although it adds cost and complexity, it ensures reliability and consistency in demanding environments.

Advanced Control Techniques: FOC and PID

As applications demand greater performance, advanced control algorithms such as Field-Oriented Control (FOC) and Proportional-Integral-Derivative (PID) become vital.

Field-Oriented Control (FOC)

FOC—also known as Vector Control—is a sophisticated algorithm that independently controls the magnetic field and torque-producing currents in a motor. By aligning the stator current with the rotor’s magnetic field, FOC achieves maximum torque per ampere and smooth speed regulation across the full range.

Advantages of FOC:

• High torque efficiency
• Fast response to dynamic load changes
• Quiet, vibration-free operation

Applications: Electric vehicles, industrial robots, and servo drives.

PID Control

The PID controller is one of the most widely used feedback mechanisms in automation. It continuously calculates an error value (difference between desired and actual speed) and adjusts the control input proportionally, integrally, and derivatively.

Benefits:

• Stable, smooth speed control
• Minimal overshoot and oscillation
• Easy integration with microcontrollers

Proper tuning of PID parameters is essential to ensure optimal performance. Many of United Motion Inc.’s integrated motor driver solutions include pre-tuned PID loops designed for specific motor parameters, minimizing the setup effort for OEMs.

Challenges in BLDC Speed Control

Despite their advantages, BLDC motor control systems face several challenges in real-world applications:

• Temperature Sensitivity – High temperatures affect winding resistance and magnet strength, altering performance.
• Electromagnetic Noise – PWM and switching circuits can create EMI, impacting nearby electronics.
• Parameter Variation – Motor constants vary with aging or environmental conditions.
• Load Disturbances – Sudden load changes can cause overshoot or instability if control loops aren’t well-tuned.
• Hardware Costs – Advanced control systems require microcontrollers, sensors, and robust driver electronics.

Addressing these challenges requires not only good control algorithms but also high-quality motor design and manufacturing—areas where United Motion Inc. continuously invests through advanced CNC machining, automated assembly, and precision testing.

Choosing the Right Control Method

Selecting the ideal speed control method depends on the application’s complexity, required precision, and budget.

When designing or sourcing a BLDC system, consider both the motor characteristics and the control electronics. A well-matched system ensures not only optimal speed control but also longer life, lower heat, and reduced maintenance costs.

How United Motion Inc. Supports Precision Speed Control

At United Motion Inc., we understand that successful motor performance depends on both the motor and the control strategy. Our engineering teams design and produce BLDC motors with optimized magnetic circuits, precision-balanced rotors, and tightly controlled winding parameters to ensure consistent response across control methods.

We also provide custom motor-driver integration services, supporting clients with:

• Application-specific control algorithm tuning
• PWM and FOC optimization
• Embedded sensor solutions for speed feedback
• EMI reduction and thermal management

By combining advanced design capabilities with practical industry experience, United Motion Inc. helps clients across automation, robotics, and EV industries achieve precise, efficient, and reliable motor control tailored to their needs.

References

Krishnan, R. Permanent Magnet Synchronous and Brushless DC Motor Drives. CRC Press, 2010.

Boldea, I., & Nasar, S.A. Electric Drives: Modeling, Analysis, and Control. Prentice Hall, 2006.

IEEE Transactions on Industrial Electronics – Vol. 70, Issue 3 (2023).

Texas Instruments. BLDC Motor Control Fundamentals – Application Note AN885.

Microchip Technology. PID Control of Brushless DC Motors Using dsPIC Microcontrollers.