An Engineer’s Guide: The Essentials For Brushless DC Motor Control

A brushless DC (BLDC) motor is a kind of electric motor that modulates an electromagnetic field using direct current (DC) electric power to create traction. Typically, a BLDC motor is an electronically controlled asynchronous motor, which means that the electric current in the stator windings is utilized to create a spinning magnetic field that interacts with the permanent magnets in the rotor to produce torque. It has various benefits over its brushed equivalents, including a longer lifespan, greater efficiency, and less electromagnetic interference (EMI).

A BLDC motor controller is an electronic device that modulates the electric current in the stator windings to regulate the motor’s speed and torque.

This article will discuss the fundamentals of BLDC motor control, including the numerous controller types and the difficulties associated with controlling BLDC motors. We will also provide advice on how to overcome these obstacles.

Therefore, if you are an engineer seeking to begin BLDC motor control, this article is for you!

 

Introduction to brushless DC motors

Today’s motor control topologies include brushed, brushless DC (BLDC), stepper, and induction. The two kinds of brushless motors that are most closely linked are BLDC and permanent magnet synchronous motors (PMSMs). The former is the most prevalent motor topology because it offers a constant power supply and needs less starting energy than traditional permanent magnet motors.

Since they remove the need for motor brushes, brushless motors have gained popularity in various modern applications. These BLDC topologies rotate the rotor using commutation logic, making them more efficient and dependable.

PMSM motors do not need a starting current, unlike BLDC motors. In its place, the motor rotor, stator windings, output transformer, and output port are employed to construct a bridge that enables a very high-speed synchronous rotation. The rotor, stator, and output port are utilized to build a resonance circuit to minimize harmonics.

The BLDC and PMSM topologies may be integrated into a single topology: brushless BLDC synchronous motors. Among all motor topologies, this combination gives the maximum power and the lowest power consumption.

 

Understanding BLDC and PMSM Motor Types

BLDC and PMSM motors are based on the synchronous motor design. The rotor continues to chase the stator at each commutation, causing the motor to move constantly. However, the stator winding design of these two DC-type motors differs; hence their back-electromotive force (BEMF) responses are distinct. The BEFM of the BLDC is trapezoidal. Since the BEMF of the PMSM motor is sinusoidal, the coil windings are also wound sinusoidally. To optimize performance, these motors often use sinewave commutation.

Operating BLDC and PMSM motors create BEMF via their windings. The EMF made in a motor due to motion is known as back-EMF (BEMF) because the EMF induced in the motor opposes the EMF produced by the generator.

 

Field-Oriented Control

To drive the PMSM motor with a sinusoidal waveform, a field-oriented control (FOC) algorithm is necessary. Typically, FOC is used to enhance the efficiency of the PMSM three-phase motor. The sinusoidal controller for the PMSM is more complex and expensive than the trapezoidal controller for the BLDC. However, this increase in cost provides benefits such as reduced noise and fewer harmonics in the current waveform. The primary benefit of the BLDC is that it is easy to manage. Ultimately, the optimal motor is determined by the application.

 

Sensored vs. Sensorless PMSM and BLDC motors

BLDC and PMSM motors may be equipped with or without sensors. In applications requiring the motor to start under a load situation, sensored motors are used. They use Hall sensors implanted into the motor stator. The sensor is just a switch with a digital output proportional to the polarity of the detected magnetic field. Each phase of the motor needs a unique Hall sensor. Therefore, three Hall sensors are required for a three-phase motor. Motors without sensors need algorithms that use the motor as the sensor. They depend on BEMF-related data. By sampling the BEMF, it is possible to derive the rotor’s location, removing the requirement for hardware-based sensors. Regardless of motor architecture, controlling these devices need knowledge of the rotor position for optimal commutation.

 

The advantages of brushless DC motors

We all would agree that unless we knew the realities of brushless DC motors, we would have never known that despite their reputation for being all too expensive, with super high torque and high reliability, several practical and economic benefits make them unique. To begin with, they have low maintenance requirements.

One thing that you must understand is that brushless motors are by far the most efficient motors. The motors can achieve the highest torque with the most negligible electricity cost.

The exciting part is that most of the brushed DC motors we come across in the market are only capable of 5,000 to 10,000 RPM, depending on the motor. The Brushless motor is capable of up to 25,000 RPM, and its vast torque makes it more efficient than any other DC motor and allows us to use less energy.

 

The disadvantages of brushless DC motors

Brushless DC motors have several advantages over their brushed counterparts but also a few disadvantages. One of the most significant disadvantages of brushless DC motors is their cost. Because they are more complex than brushed motors, they cost more to manufacture. Additionally, brushless DC motors typically require special controllers that can add to the overall cost of the system.

Another disadvantage of brushless DC motors is that they can be less efficient than brushed motors due to their control. When properly designed and implemented, however, brushless DC motors can be just as efficient as brushed motors.

 

Applications of BLDC motors

The market for BLDC motors is anticipated to expand significantly throughout the forecast period. Their capacity to transform any energy, including electricity, mechanical power, and rotational power, into mechanical work, such as motor rotation, has contributed to the market’s expansion. In addition, the lowering cost of solid-state motors is driving the growth of the demand for BLDC motors.

In several applications, such as equipment automation, material handling, assembly, and distribution, BLDC motors are used. There are several applications for BLDC motors, which are extensively employed in various industrial applications, providing development possibilities for the BLDC motors market.

The market for automotive BLDC motors is anticipated to expand significantly throughout the forecast period. High demand for BLDC motors in the transportation sector for vehicles such as electric and hybrid cars has contributed to the market’s expansion. In addition, the increasing use of automation and electrification in cars fuels the evolution of the BLDC motor market for automotive.

Due to their excellent efficiency and low power consumption, BLDC motors are also becoming an increasingly attractive option in industrial applications. In addition, the rising demand for these motors is a result of their capacity to transform many external and internal energy sources into mechanical work, eventually resulting in greater efficiency.

 

Design considerations for brushless DC motor control

Today, software algorithms are used to drive BLDC and PMSM motors, much like computer programs. These software algorithms enhance efficiency and save operating expenses by monitoring and managing motor activities. The motor startup, Hall sensor rotor position detection, and switch signal verification for raising the current reference are among the critical roles of algorithms.

A BLDC motor with three phases has six states. The diagram below shows that a three-bit code may represent an opcode number between 1 and 6. Six of the eight opcodes are used to position the sensors for three-bit data output (1 through 6). This data is significant because it allows the controller to detect whether an illegal opcode has been given and to act on valid opcodes (1 through 6). The method retrieves and decodes the Hall sensor operation code, as seen below. The controller modifies the energization strategy to accomplish commutation when the Hall sensor opcode value changes. The microcontroller extracts energization information from the lookup table using the operation code. After the three-phase inverter is powered with the new sector instruction, the magnetic field shifts to the new location, pulling the rotor. As the motor functions, this procedure is repeated repeatedly.

 

Summing Up

BLDC Motors are a suitable alternative to other electric motors. The development of sensorless technology is giving a significant boost to these motors in terms of their size, cost & reliability. Therefore, they are increasingly used in modern devices that require low noise & low heat operations.

Cionlabs Private Limited is a leader in designing & manufacturing BLDC motors driver circuits. You can reach out to the team for any queries or supply requirements.