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Brushless DC motors (BLDC) have become the preferred choice for modern electrical drive systems due to their high efficiency, reliability, and longevity. The application of Field Oriented Control (FOC) technology has significantly enhanced BLDC motor performance, particularly Hall sensor-based FOC implementation which enables BLDC motors to achieve performance levels approaching those of Permanent Magnet Synchronous Motors (PMSM).

Hall Sensor Application Principles in BLDC Motor FOC

Hall Sensor Operating Principles

Hall sensors operate based on the Hall effect, where a magnetic field exerts a transverse force on moving charges in a current-carrying conductor, producing a measurable voltage across the conductor. In BLDC motors, Hall sensors are embedded in the stator to detect rotor magnet positions.

Grofu (2021) notes that Hall sensors are typically arranged at 120° electrical degree intervals at the non-driving end of the motor. When rotor magnets pass the Hall sensors, they output high or low signals indicating the passing of N or S poles. The combination of these three Hall sensor signals determines the precise commutation sequence.

Key Technologies in Hall Sensor-Based FOC Implementation

Traditional BLDC control employs six-step (trapezoidal) commutation, which despite its simplicity, suffers from significant torque ripple issues. FOC technology, however, achieves smooth torque output and high efficiency through coordinate transformation, enabling independent control of torque-producing current component (iq) and flux-producing current component (id).

Hall sensor-based FOC implementation involves several key steps, as detailed in the research by Prayogo et al. (2023): position detection—Hall sensors provide discrete rotor position information, which can be refined using interpolation algorithms; Clarke transformation—converting three-phase currents (ia, ib, ic) into two orthogonal currents (iα, iβ); Park transformation—converting stationary reference frame currents to rotating reference frame (id, iq) based on position information from Hall sensors; current control—using PI controllers for independent control of id and iq, typically setting id reference to zero for maximum torque; inverse Park and inverse Clarke transformations—converting control outputs back to the three-phase system; and finally, SVPWM modulation—generating drive signals using Space Vector Pulse Width Modulation techniques.

Prayogo et al. (2023) confirm that compared to traditional six-step control, Hall sensor-based FOC control can reduce BLDC motor torque ripple by approximately 80% and lower the minimum stable operating speed by about 90%. This enables BLDC motors to achieve PMSM-like smooth torque output and precise speed control.

Outrunner BLDC Motor Structure and Advantages

While Hall sensor-based FOC can be implemented in various BLDC motor configurations, it delivers particularly impressive results when applied to outrunner BLDC motors—a design that has become increasingly popular for high-performance applications. Outrunner BLDC motors feature an external rotor with the stator at the center and permanent magnets fixed to the inner wall of the rotor. This design offers several key advantages. First, the outrunner design provides a larger torque arm, enabling the motor to generate higher torque and achieve greater torque density. Second, the heat-generating stator windings are in direct contact with the motor housing, providing a larger heat dissipation surface area and excellent cooling performance. Additionally, outrunner motors typically have lower speed characteristics, making them suitable for direct-drive applications without requiring additional reduction mechanisms.

These characteristics make outrunner BLDC motors particularly suitable for applications requiring high torque and precise low-speed control. With Hall sensor-based FOC control, outrunner BLDC motors (like our products SA13030 in product line of Planet Series brushless DC motors) excel in numerous fields due to their high torque, efficiency, and precise control capabilities. In electric transportation, such as e-bikes and e-scooters, these motors are favored for their high torque and efficiency; drone propulsion systems benefit from the high torque density and direct-drive capabilities of outrunner designs; home appliances like washing machines and air conditioners utilize these motors for their efficiency and low noise characteristics; industrial automation applications requiring precise position control and smooth torque output also employ these motors; while medical equipment chooses this motor technology for its low noise, high reliability, and precise control.

Quasi-PMSM Level BLDC Motors vs. Traditional PMSM

Structural Differences

The main structural differences between traditional BLDC motors and PMSM lie in back-EMF waveform and magnetic field distribution:

1.Back-EMF Waveform: BLDC motors typically have trapezoidal back-EMF, while PMSM have sinusoidal back-EMF (see an example in our SA13030 BLDC Motor)

2.Magnetic Field Distribution: The magnetic field distribution in BLDC motors is closer to a square wave, while in PMSM it approximates a sine wave

3.Control Methods: BLDC motors traditionally use six-step commutation control, while PMSM typically employ sinusoidal control or FOC

However, through special design and FOC technology application, our outrunner BLDC motors have achieved quasi-PMSM performance levels. Khajueezadeh et al. (2023) demonstrate that by optimizing motor structure and control algorithms, BLDC motor performance can approach or even reach PMSM levels.

Advantages Over PMSM

Hall sensor-based FOC-controlled BLDC motors offer multiple advantages. BLDC motors have relatively simpler structures, facilitating manufacturing and maintenance; they don't require the strict magnetic circuit structure specifications that PMSM demand, thus reducing manufacturing costs; particularly with outrunner designs, they provide higher power density; outrunner structures facilitate heat dissipation, reducing temperature rise issues; and they exhibit stronger robustness against parameter variations and control imprecisions. These features allow Hall sensor-based FOC-controlled BLDC motors to achieve control performance approaching that of PMSM while maintaining structural simplicity and cost advantages, making them the most cost-effective choice.

Hall sensor-based FOC-controlled outrunner BLDC motors represent a significant direction in motor technology development. By combining the high-torque characteristics of outrunner structures with the precise control capabilities of FOC, this motor technology achieves performance levels approaching PMSM while maintaining the cost and structural advantages of BLDC motors. As power electronics technology and control algorithms continue to advance, our company believes this motor technology applied in our product lines will play an increasingly important role across a wider range of applications.

References

Grofu, F., 2021. Field Oriented Control (FOC) for BLDC Motor. Fiabilitate si Durabilitate - Fiability & Durability, (1).

Khajueezadeh, M.S., Emadaleslami, M., Tootoonchian, F., Daniar, A., Gardner, M.C. and Akin, B., 2023. Comprehensive Investigation of the Resolver's Eccentricity Effect on the Field-Oriented Control of PMSM. IEEE Sensors Journal, 23(17).

Prayogo, R.C., Triwiyatno, A. and Riyadi, M.A., 2023. Field Oriented Control Implementation on BLDC Motor Controller with PI and SVPWM using STM32F103C8T6. Journal of Physics: Conference Series, 2622.