BLDC Motor Speed Control Using Variable Frequency Drive: Design, Implementation, and Performance Analysis

Abstract

This paper presents the design, hardware implementation, and performance evaluation of a Brushless DC (BLDC) motor speed control system based on a Variable Frequency Drive (VFD) technique. Conventional speed control approaches relying on constant DC-link voltage with high-frequency PWM suffer from limited dynamic response and poor efficiency under varying load conditions. The proposed system employs an Arduino UNO (ATMega328P) microcontroller to generate variable-frequency six-step commutation signals, which drive a three-phase MOSFET inverter bridge operating in 120° conduction mode. A potentiometer-based reference interface allows smooth, real-time speed adjustment, while an infrared optical speed sensor provides closed-loop feedback. The switching frequency and corresponding motor RPM are displayed on a 16×2 LCD in real time. Hardware test results demonstrate stable closed-loop speed regulation with a measured output frequency of 50.51 Hz and a motor speed of 77 RPM using a 24 V, 250 W, 500 RPM BLDC motor prototype. The system achieves fine-tuned speed regulation, dynamic response, and load-disturbance rejection, making it suitable for electric vehicles, agricultural machinery, and industrial automation.

Introduction

Brushless DC (BLDC) motors are widely used in modern applications due to their high efficiency, long lifespan, low noise, and high power density compared to brushed DC motors. However, precise speed control under varying load conditions remains a key challenge. While PI controllers are commonly used, they often struggle with stability, leading researchers to explore alternatives like disturbance observers and variable-frequency drive (VFD) methods.

This paper presents a low-cost VFD-based BLDC motor speed control system using hardware components such as an Arduino UNO, MOSFET inverter bridge, IR speed sensor, and LCD display. The system adjusts motor speed by varying the supply frequency and voltage, maintaining proper flux and reducing issues like torque ripple seen in PWM-only methods. It also demonstrates the standard BLDC speed–frequency relationship N=120fPN = \frac{120 f}{P}N=P120f?.

The system architecture includes:

• AC to DC power conversion using transformers and rectifiers
• A three-phase MOSFET inverter operating in 120° six-step commutation
• Gate driver isolation using PC817 optocouplers
• Arduino-based control logic for frequency generation and RPM calculation
• IR sensor feedback for closed-loop speed monitoring
• LCD display for real-time frequency and speed output

The hardware design ensures safe operation by selecting appropriately rated MOSFETs, transformers, and filtering components. The Arduino firmware maps user input (potentiometer) to switching frequency and computes RPM using pulse timing.

Experimental results show:

• Stable linear relationship between frequency and speed
• Accurate speed control with minimal error
• About 77 RPM at ~50 Hz in a 24 V, 250 W BLDC motor
• Reliable operation across different speed ranges without commutation failure

The system achieves real-time, smooth, and efficient speed control using low-cost components, validating the feasibility of a simple VFD-based approach. It is suitable for applications such as electric vehicles, robotics, industrial automation, and agricultural machinery.

Conclusion

A hardware-validated BLDC motor speed control system employing a Variable Frequency Drive technique has been presented. The system integrates an Arduino UNO microcontroller, a six-MOSFET three-phase bridge operating in 120° conduction mode, PC817 optocoupler gate drivers, and an IR optical speed sensor. Component ratings were derived analytically from first principles, ensuring proper safety margins for both current and voltage stresses. Experimental results confirm that motor speed increases linearly with commutation frequency, with a measured operating point of 50.51 Hz / 77 RPM on a 24 V, 250 W prototype. The system provides real-time frequency and speed display, and smooth acceleration/deceleration without mechanical shock. Future work will address: (i) implementation of a closed-loop PI speed regulator to reject load disturbances; (ii) Field-Oriented Control (FOC) for reduced torque ripple and improved efficiency; (iii) adaptive EMI mitigation through spread-spectrum PWM; (iv) regenerative braking using a bidirectional DC–DC converter; and (v) self-tuning algorithms that automatically identify motor pole count and adjust commutation accordingly.

References

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Copyright

Copyright © 2026 Supriya Suresh Bhangi, Rutuja Srishail Mithari, Shravani Ajit Pote, Prof. Dhanyakumar Adagonda Patil. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.