Detailed explanation of the role of Hall sensors in brushless motors

During the operation of the brushless DC motor, the controller must accurately know the real-time position of the rotor in order to decide how to switch the current direction and drive the motor to continue rotating. This perception of the rotor position is the premise of the entire commutation control. The Hall sensor is the key component to achieve this function.

 

Compared with brushed motors that rely on mechanical contacts to complete phase change, brushless motors rely entirely on electronic control. Therefore, the accuracy of position detection directly affects the motor's startup, operating stability, and response efficiency. Without reliable position feedback, the controller cannot correctly energize the stator winding, the motor will not start properly, or vibration, low efficiency, and other problems will occur during operation.

 

The job of the Hall sensor is to "observe" the changes in the rotor's magnetic field in real time, convert it into digital signals, and feed it back to the control system. These signals provide the driver with a "clock" for phase switching, ensuring that each phase current acts on the correct winding at the right time to achieve smooth and efficient operation.

 

It can be said that although the Hall effect sensor is only an auxiliary component, its position in the brushless motor is like "eyes to the brain": it does not drive any components, but determines whether the entire control system can "see the direction clearly". Next, we will take a deeper look at the working principle of the Hall effect and see how this small sensor supports the operation foundation of the entire control system.

 

To better understand how Hall sensors work, we have to start with a basic physical phenomenon - the Hall Effect.

 

The Hall effect refers to the fact that when current passes through a conductor or semiconductor material and the material is in a vertical magnetic field, a voltage perpendicular to the current and magnetic field will appear inside the material. This transverse voltage is called the "Hall voltage".

 

We can imagine it as a process like this:

1. Imagine there is water flowing in a pipe (representing electric current);

2. If you put a magnet next to this water pipe, the water flow will be "deflected" to one side under the influence of the magnetic force;

3. This deviation will cause a pressure difference on one side of the water pipe;

4. In electronic systems, this "pressure difference" manifests itself as voltage.

 

The Hall sensor uses this principle. It contains a small Hall element. When it is close to a magnetic field (such as the magnet on the motor rotor), the Hall element will sense the change in the magnetic field and output a corresponding voltage signal. This signal is then transmitted to the drive controller to determine the current position of the rotor.

 

According to the different output signals, Hall sensors can be divided into two categories:

• Analog Hall sensor: It outputs a continuously changing voltage value, which can accurately reflect the magnetic field strength and is suitable for high-resolution requirements such as position measurement and magnetic field analysis.
• Digital Hall sensor: The output has only two states: high level and low level. When the magnetic field reaches a certain threshold, it triggers switching. It is suitable for judging the change of magnetic poles and controlling phase change in brushless motors.

In brushless motors, the most commonly used is the digital Hall sensor, which has a simple structure, fast response, and strong adaptability. It is very suitable for real-time detection of rotor pole changes, thereby achieving precise electronic commutation control.

 

Now that we understand the principle of the Hall effect, we can look at how the Hall sensor is used in brushless motors.

 

1. Coordination between Hall sensor and rotor

Inside a brushless DC motor, the rotor is usually a cylinder with a magnet that has alternating N and S poles. As the motor turns, the magnetic poles on the rotor move toward and away from the Hall sensors on the stator.

 

Whenever a magnetic pole passes through the Hall element, it senses the change in the magnetic field and generates a high or low digital signal. This signal tells the driver: "Now it is the N pole" or "Now it is the S pole." In this way, the driver can determine which position the rotor has rotated to, and decide whether to switch the current direction to allow the motor to continue to run smoothly.

 

2. 120° arrangement of three Hall elements

In order to accurately sense the rotor position, three Hall sensors are usually used, evenly installed on the stator, with an electrical angle of 120°. Why three? Because the three-phase winding requires six different conduction combinations to achieve continuous commutation (that is, six-step commutation control).

 

Each Hall sensor outputs a high or low level. When the three sensors are combined together, six different states are formed.

A: 1 1 0 0 0 1

B: 0 1 1 1 0 0

C: 0 0 0 1 1 1

These six sets of signals change cyclically, instructing the driver to switch the current direction in sequence, driving the motor to rotate continuously.

 

Although the Hall sensor is small in size, it has a crucial impact on the performance of the brushless motor. Incorrect installation methods or accuracy deviations can lead to commutation errors, poor starting, and even accelerated motor aging. In this section, we will introduce key considerations in practical applications from the perspectives of installation angle, alignment accuracy, anti-interference and temperature drift.

 

1. Introduction to installation angle

In brushless motors, the installation angle of the Hall sensor determines the timing of its induction of the rotor magnetic poles, which directly affects the commutation rhythm and motor operating efficiency. The following are several common arrangement angles:

 

• 120° electrical angle arrangement

This is the most common arrangement, with three Hall elements evenly distributed at an electrical angle of 120°. It is suitable for most three-phase brushless DC motors and is a natural match for the six-step commutation control logic. It has a symmetrical structure and simple control, and is the standard configuration for industrial and consumer motors.

 

• 60° electrical angle arrangement

The 60° arrangement is also used in some specific motor structures. This arrangement has denser signals and is suitable for use in situations that require high response frequency or fine control, but it has higher requirements on driver design and poor compatibility. When using it, you need to confirm that the driver supports the 60° commutation logic.

 

• Mechanical (physical) layout

In actual installation, the Hall sensor is installed according to the physical angle, such as 120° mechanical angle. However, since there is a conversion relationship between electrical angle and mechanical angle (depending on the number of pole pairs), the number of pole pairs of the motor must be considered during installation to correctly convert the mechanical angle into electrical angle. For example: in a 4-pole motor, 360° mechanical angle is equivalent to 720° electrical angle.

 

• Multi-Hall array (360° sensing)

Advanced applications may use multiple Hall elements in an array to achieve denser magnetic field sampling for brushless servo systems or precision positioning systems. This type of arrangement can improve angular resolution, but the structure is complex and the cost is high.

 

Regardless of which arrangement is chosen, it is necessary to ensure that the Hall signal can completely cover a full circle of the rotor's motion cycle and match the power-on sequence of the windings to ensure efficient operation of the motor.

2. Importance of Hall Effect Alignment Accuracy

The installation angle of the Hall element must be strictly synchronized with the commutation logic of the winding. If the installation angle deviation is too large, it will cause the commutation to be advanced or delayed, causing the following problems:

• The motor torque decreases and the efficiency becomes lower;
• The current fluctuates violently, and the heat increases;
• Stuttering or instability occurs during startup.

Therefore, in actual installation, it is usually necessary to observe the signal waveform through a special alignment fixture or oscilloscope and perform angle fine-tuning to ensure that the three Hall signals present a standard 120° electrical angle phase difference.

 

3. Anti-interference and temperature drift issues

The Hall sensor outputs a low-level signal, which is easily affected by the surrounding environment. In the motor system, the following points should also be noted to improve reliability:

• EMI shielding: The power line and Hall line should be wired separately, using shielded cables and grounded;
• Filtering and buffering: filter circuits or anti-interference chips can be added to the signal line to reduce false triggering;
• Temperature compensation design: Select Hall elements with low temperature drift coefficient, or compensate for temperature changes through software to improve stability under high and low temperatures.

 

Through the previous introduction to Hall sensors, we can see that Hall sensors play an extremely critical role in brushless DC motors. Its accuracy and stability directly affect the motor's commutation efficiency, running stability and overall control performance. Therefore, it is particularly important to choose a brushless motor manufacturer with mature technology and reliable quality.

 

VSD is a factory focusing on the research and development and manufacturing of high-precision DC motors, and has long been committed to the optimization of Hall control and electronic commutation technology. The brushless DC motor products we provide are widely used in automation equipment, robots, smart door locks, power tools, medical equipment and other fields.

 

Why choose VSD brushless motor

1. Support deep customization to meet diverse needs

Whether it is the location layout of the Hall sensor, motor size, voltage range, or special installation method, VSD supports customized development services. We can tailor a unique brushless motor solution based on the customer's specific application scenario to ensure performance fit, easy installation, and system compatibility.

 

2. Millions of dollars of annual R&D investment drives continuous technological evolution

VSD continues to invest millions of dollars in research and development every year. We have an experienced team of dozens of engineers, and the most senior R&D personnel have at least ten years of experience in our company. We actively promote intelligent manufacturing and digital design to ensure that our products always maintain the leading level in the industry.

 

3. Strict factory testing to ensure product stability and reliability

Every VSD brushless motor that leaves the factory will go through a comprehensive testing process, including Hall signal calibration, commutation waveform detection, operation stability evaluation, and high and low temperature aging tests. We firmly believe that good products are the basis for continued cooperation between the two parties.

 

If you are looking for a brushless motor product with reliable performance, flexible customization, and complete technical support, please choose VSD. We look forward to providing a powerful drive solution for your project.