What is BLDC Motor Controller and How It Works

Brushless DC motors provide several substantial advantages over brushed motors, owing primarily to electronic commutation. It enables the controller to switch the current quickly and so effectively regulate the motor’s characteristics. In this post, we will look at the characteristics of a brushless DC motor controller. You’ll learn about its operational principles, as well as the design aspects and problems you should be aware of before constructing your own device.

The first brushless DC (BLDC) motor was invented in 1962. The deployment of this new form of the electrical motor was made possible by the recent invention of a transistor switch. At the time, using electronics instead of a mechanical commutator using brushes was a milestone in electrical engineering.

BLDC motor controllers have found widespread use in a variety of industries, ranging from computer hard drives to electric transportation and industrial robots. Brushed DC (BDC) motors have practically been phased out in some industries. A Brushless DC motor has several advantages, including high performance and longevity. However, it will not entirely replace BDC motors because it is still a pricey solution with a sophisticated build and control system.

A brushed DC motor controller can perform the same functions and use the same methods as a BLDC motor controller. Their arrangement and implementation, however, have some conceptual variations. This article will explain the characteristics of a Brushless DC motor controller, including how it works, how it is constructed, and what it is best suited for.

What is a BLDC Motor Controller?

BL DC motor controllers, often known as electronically commutated motors, are available (ECMs, EC motors). Primary efficiency is a critical attribute of Brushless DC motors. Because the rotor is the lone magnet bearer and does not require any power, there are no connections, commutators, or brushes. Instead, the motor makes use of control electronics. Brushless DC motor controllers use rotary encoders, or a Hall sensor to detect where the rotor is at any given time.

Construction of Brushless DC motor

Permanent magnets are attached to the rotor of this motor. The stator houses the current-carrying conductors or armature windings. Electrical commutation is used to transform electrical energy into mechanical energy.

The fundamental design difference between brushed and brushless motors is the substitution of an electric switch circuit for a mechanical commutator. A BLDC motor is a form of synchronous motor because the magnetic fields created by the stator and rotor revolve at the same frequency.

A brushless motor has no current-carrying commutators. A brushless motor’s field is switched via an amplifier that is activated by a commutating device such as an optical encoder.

The layout of BLDC motor controllers might differ depending on whether it is “Outrunner” or “Inrunner.”

• Outrunner – The field magnet is a rotating drum rotor that revolves around the stator. This type is suited for applications that require strong torque but do not require high rpm.
• Inrunner- The stator is a stationary drum in which the field magnet revolves. This motor is noted for providing less torque than outrunner motors, but it can spin at extremely high rpm.

Advantages of Brushless DC motor

• Less overall upkeep owing to the lack of brushes
• Smaller size with considerably superior thermal properties
• Increased speed range and reduced electric noise generation
• It lacks a mechanical commutator, which causes issues.
• Because of the usage of a permanent magnet rotor, it has a high efficiency and output power-to-size ratio.
• Fast operation in both loaded and unloaded conditions due to the lack of brushes that limit the speed
• Smaller motor geometry and lower weight than BLDC motor controller and induction AC motors.
• Long life since the commutator system does not require inspection or maintenance.
• Improved dynamic response due to stator inertia and carrying windings
• Reduced electromagnetic interference
• Low noise owing to the lack of brushes

Limitations of Brushless DC motor

• These motors are expensive.
• The electronic controller required to control this motor is costly.
• necessitates complicated drive circuitry
• The requirement for additional sensors

BDC Motor Controller Circuit 

The so-called H-bridge configuration is used in the majority of current BDC motor controller circuits. When turned on diagonally, an H-bridge circuit consists of four switches that supply electricity and rotate the motor. Gate drivers take signals from a microcontroller (MCU) and then close or open the switches that supply the correct voltage level. For the switches, you can utilize a variety of transistors, including:

• MOSFET for power
• GaN
• IGBT

Depending on your needs, you can use discrete components or an H-bridge integrated circuit (IC). The same is true for gate drivers, which can be discrete or have built-in transistors. The gate driver IC is a developer-friendly solution, but it has one significant disadvantage: it is not adjustable. So, if you’re going to develop a custom controller for a high-power application, it’s best to use discrete components.

The complexity of a BLDC motor controller circuit might vary. A non-feedback or open-loop controller, for example, is simpler to design because it does not require any feedback mechanisms. A feedback or closed-loop control system must be included inside a controller if it is to monitor the motor’s condition and react to any changes in its behavior.

To control the speed, for example, a Hall-effect sensor or a rotary encoder mounted on the motor can be used. These sensors turn the revolutions of the motor into digital signals that the closed-loop controller can read.

Depending on the controller’s use, the BLDC motor controller design might have a variety of options and nuances. We’d like to focus on braking as one of the main duties provided by current DC motor controllers in this post.

Working Principles of BLDC Motors and Controllers

A BLDC motor controller controls the motor’s speed and torque, as well as starting, stopping, and reversing its revolution. Let us begin with the fabrication of a brushless motor to better comprehend the controller’s operation. Its main components are as follows:

• An armature or rotor made of permanent and, in many cases, neodymium magnets;
• A stator has windings that, when powered, create a magnetic field.

The rotation of the motor is provided by the magnets on the rotor and the windings on the stator. They attract each other by having opposite poles and repel each other by having the same poles. A brushed DC motor goes through a similar process. The primary distinction is in the mechanism used to switch the current provided to the wire windings.

This is a mechanical operation in a BDC motor that is initiated by a commutator with brushes. It occurs electronically in a BLDC motor through transistor switches.

A BLDC motor controller senses the position of the rotor using sensors (such as a Hall-effect sensor) or without sensors. The sensors measure and transmit the rotor’s position. The controller receives the data and instructs the transistors to switch the current and energize the relevant stator winding at the appropriate time.

Types of BLDC Motors and Controllers

BLDC motors are classified into two categories based on the positioning of the rotor:

1. Inrunner engine (the rotor is internal, and the stator is on the outside of the motor)
2. Outrunner motor (since the rotor is external, the permanent magnets revolve around the stator together with the motor housing)

Because of their smaller spinning diameter, runners have a lighter construction and a faster rotational speed. Outrunner motors, on the other hand, have a larger torque due to the long arm and greater electromotive force supplied to the rotor.

Three-phase brushless DC motors can have one of two winding connections:

• Wye (Y) connection or star connection (windings meet at the center, forming a wye)
• The delta () connection (windings are connected in series, forming a triangle)

A neutral wire is connected to the ground in the wye design. It can safeguard the motor against overvoltage and overload. Because the delta connection lacks neutrals, it is better suited to motors with balanced loads. However, depending on your needs, each of these categories can provide efficient performance.

BLDC motor classifications

The technology used to detect the position of the rotor differs among BLDC motor controllers. Position sensors or a sensorless technique can be used to make the measurements.

There are numerous sensors to choose from, including:

• Hall-effect detectors
• Encoders that rotate
• Sensors with variable reluctance
• Resolvers
• Optical sensors

The sensorless BLDC motor controller operates in the absence of a sensor; it determines rotor position by estimating back electromotive force (back EMF). The revolving armature generates this voltage in the stator windings. The back EMF can be used to detect the position of the rotor: the stronger the back EMF, the closer the rotor’s magnet.

Application Area of BLDC Motors and Controllers

The primary advantages of a brushless DC motor stem from its design attributes. Electronic commutation allows for faster current switching. It results in higher torque, effective speed control over a wide range, and hence improved motor performance.

It is a low-maintenance and long-lasting solution since it uses electronics rather than mechanical parts that wear. Furthermore, the lack of brushes results in minimal power loss as well as low levels of electromagnetic interference (EMI) and noise.

As a result, BLDC motors are widely used in devices and systems with long operational lifetimes, such as:

• Applications in industry
• Electric automobiles
• Unmanned aerial vehicles
• Computer hardware
• Electronic consumer goods
• Robotics

Because of the configuration, BLDC motors may power small-sized but high-performance devices, which broadens their application area.

BLDC motor applications

There are, of course, low-power solutions that do not require a programmable brushless DC motor controller with feedback. In this case, a BDC motor with a basic controller may make more sense. However, if increased efficiency and longevity are more important to you than simplicity and cost-effectiveness, a brushless DC motor may be a suitable option for your project.

Building a BLDC motor controller necessitates extensive knowledge of both circuit design and embedded software development. A control unit, when properly applied, may ensure the smooth running of your motor and extend its lifespan. More information on how to develop a brushless DC motor controller will be provided in the following section of this article.

BLDC Motor Controller Circuit Design

A half-bridge or half-H bridge circuit is common in BLDC motor controllers. This circuit arrangement, unlike an H bridge, has only two switches: one high-side and one low-side transistor.

Most brushless motors are powered by two or three-phase systems. In a BLDC motor controller circuit design, this will look like two or three half-bridges with a pair of switches each (depending on the number of phases).

Let’s take a deeper look at a three-phase brushless DC motor controller with Hall-effect sensors to see how its circuit is designed.

The stator features three-phase windings that are 90° apart. Each winding represents the voltage and is currently applied to the stator as a vector.

The Hall sensors on the BLDC motor controller determine the position of the rotor. When the sensor data is received, the power MOSFETs switch the current, injecting it into the correct winding. IGBTs and GaN switches can be used to replace MOSFETs in a high-power brushless DC motor controller.

The transistors can be controlled by either integrated or discrete gate drivers. A brushless motor controller schematic’s drivers serve as go-betweens for switches and a microcontroller (MCU).

Six steps are required to complete a full switching cycle in the three-phase BLDC motor controller circuit (that is, to energize all three windings of the stator). Current passes through the stator windings in sequence by turning the high-side and low-side transistors on and off.

When designing a BLDC motor controller, you might consider several current switching techniques, such as trapezoidal and sinusoidal commutation. The names of these methods are derived from signal waveforms.

Two windings out of three can be activated at the same time using trapezoidal commutation. The phase shift in the sinusoidal control method follows the law of sines. It allows for smoother current cycling between phases.

Trapezoidal commutation is easier, although it may produce motor vibration at low speeds. The use of sinusoidal current waveforms can ensure that your motor runs smoothly. However, at high speeds, this mode of transportation becomes difficult.

A sinusoidal brushless motor controller circuit often employs pulse-width modulation (PWM). It aids in the regulation of the current supplied into the rotor’s windings, allowing the commutation process to function more smoothly and efficiently. This is especially true for closed-loop controllers that use output signal feedback to regulate input power by adjusting the duty cycle.

A duty cycle is the ratio of the current pulse to the full cycle of the current signal. To generate sinusoidal impulses, a BLDC motor speed controller modifies PWM duty cycles.

The switching frequency of PWM might vary depending on the application. However, it should be sufficient to avoid power loss. The maximum frequency level is determined by the stator’s physical restrictions. There are, however, specifications for the control unit itself.

As a result, even if the stator permits you to increase the PWM frequency, you will be unable to do so due to the limitations of the DC brushless motor controller.

You can use hysteresis to control the operation of a BLDC motor as an option. This method is also related to sinusoidal commutation. It allows you to set the upper and lower limits of the motor’s current supply. When the current hits its upper or lower limit, the transistor switches turn off or on, changing the average current using the law of sines.

A BLDC motor controller half-bridge can be implemented as an integrated circuit (IC) or as discrete components. It is one of the most common problems you may encounter when you learn how to develop a BLDC motor controller.

Because the components must be built and soldered onto the board separately, a discrete circuit is less reliable. A brushless DC motor controller integrated circuit is smaller in size has lower production costs, and streamlines the design process. Integrated circuits, on the other hand, have power constraints. Above that, a component failure will necessitate the replacement of the complete BLDC motor controller IC, not just this component.

Challenges of Making a BLDC Motor Speed Controller

When designing a brushless DC motor controller circuit, you may encounter several difficulties. Depending on the functionality and application of the motor, you’ll need to select appropriate hardware and implement the necessary algorithms.

In power electronics, for example, BLDC motor controllers deal with high currents and voltages. They necessitate a fast switching frequency. Discrete components, including external high-power transistors such as IGBT and GaN, will make sense in this case.

One of the most difficult challenges for any brushless motor controller is rotor positioning accuracy. This can be accomplished by a sensor or sensorless measurements.

Position sensors provide a reasonably basic detection approach that can be implemented without the use of complex control algorithms. However, their use complicates the motor’s setup and maintenance.

The sensorless method (back EMF measurement) can lower your bill of materials (BOM) and simplify the design of your brushless DC motor controller. Because back EMF does not emerge when the rotor is at rest, the main problem here is to make the rotor move first. As a result, the controller will not obtain the necessary information.

Furthermore, back EMF is proportional to rotor speed. As a result, running the motor at low speeds reduces positioning precision.

To accurately measure the back EMF, consider your brushless DC motor controller schematic as well as its software. Installing current and voltage converters, adding noise filters, and developing digital signal processing (DSP) algorithms are all required.

However, much is dependent on how the measuring system is implemented. You can combine multiple strategies to improve accuracy.

You can, for example, combine an optical sensor and a rotary encoder with a Hall-effect sensor. You can also monitor the back EMF and receive data from a Hall-effect or laser position sensor installed on the motor to detect the rotor’s position.

The main programming issues in a BLDC motor controller design are in the firmware development of the microcontroller. It performs commutation, rotor position detection, PWM signal generating, and other operations.

Some microcontroller vendors provide embedded software tools to assist you in writing custom firmware for your motor controller’s MCU. For example, our STMicroelectronics partners developed the STM32 ecosystem for motor control, which includes hardware and software development kits, firmware libraries, and other toolsets for the construction of BLDC motor controllers.

A proportional-integral-derivative (PID) algorithm is typically used by the MCU of a closed-loop motor controller. It is required for adjusting the motor’s speed, torque, and other features. A PID algorithm, for example, can process the current speed, compare it to the setpoint, and determine the frequency of the output signals that should be applied to the motor to stabilize its speed.

We designed a BLDC motor controller circuit for a custom gear drive in one of our projects. Our main responsibilities were detecting the rotor’s position and accurately regulating the rotational speed.

The use of a rotary encoder aided in the locating process, but speed control proved difficult. The problem arose due to the low resolution of the MCU peripherals, specifically the timer that generated PWM signals. To compensate for the limited range of bits, we built a special PID algorithm.

Conclusion

Brushless direct current motors have been in operation for more than fifty years. Their spectrum of applications includes everything from simple consumer gadgets to complex industrial automation systems. The all-electronic control system increases torque, improves wide-range speed management, and improves the motor’s other features.

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