Brushless DC Motors – Part I: Construction and Operating Principles
This switching of the stator to build up the rotation is known as commutation. For 3-phase windings, there are 6 steps in the commutation; i.e., 6 unique combinations in which motor windings will be energized.
Driving circuitry and waveforms for the implementation of a BLDC motor will be discussed in the second part of this article.
Torque and EfficiencyFor the study of electric motors, torque is a very important term. By definition, torque is the tendency of force to rotate an object about its axis.
Thus, to increase the torque, either force has to be increased – which requires stronger magnets or more current – or distance must be increased – for which bigger magnets will be required. Efficiency is critical for motor design because it determines the amount of power consumed. A higher efficiency motor will also require less material to generate the required torque.
Having understood the above provided equations, it becomes important to understand the speed vs. torque curve.
- With an increase in speed, the torque reduces (considering the input power is constant).
- Maximum power can be delivered when the speed is half of the “no load” speed and torque is half of the stall torque.
ApplicationsSingle-speed – For single-speed applications, induction motors are more suitable, but if the speed has to be maintained with the variation in load, then because of the flat speed-torque curve of BLDC motor, BLDC motors are a good fit for such applications.
Adjustable speed – BLDC motors become a more suitable fit for such applications because variable speed induction motors will also need an additional controller, thus adding to system cost. Brushed DC motors will also be a more expensive solution because of regular maintenance.
Position control – Precise control is not required applications like an induction cooker and because of low maintenance; BLDC motors are a winner here too. However, for such applications, BLDC motors use optical encoders, and complex controllers are required to monitor torque, speed, and position.
Low-noise applications – Brushed DC motors are known for generating more EMI noise, so BLDC is a better fit but controlling requirements for BLDC motors also generate EMI and audible noise. This can, however, be addressed using Field-Oriented Control (FOC) sinusoidal BLDC motor control.
- Implement efficient control of multiple Brushless DC motors
- Field-oriented control by the numbers
- BLDC motor control for respirators
- Modular Approaches to Brushless DC Motor Drives
- Implementing Embedded Speed Control for Brushless DC Motors
- Designing a MCU-driven permanent magnet BLDC motor controller
About the Author
In the next part of this article, we will address controlling the speed, position, and torque of BLDC motors. Click here to read part 2.
Pushek Madaan is currently working with Cypress Semiconductor India Pvt. Ltd. as a Senior Application Engineer. His interests lie in designing Embedded system applications in C and assembly languages, working with analog and digital circuits, developing GUIs in C# and, above all, enjoying adventure sports. Pushek can be reached at email@example.com.