An electric motor is an electromagnetic device that converts or transmits electrical energy based on the law of electromagnetic induction. Motors can be classified into many subtypes according to different standards such as application and operating principle. To enhance your understanding of motors, this article will introduce induction motors, brushless motors, and the differences between the two. If you are interested in motors, please continue reading.
I. Induction Motor
An induction motor is a type of motor that uses electromagnetic induction between the stator and rotor to induce current in the rotor, thereby achieving electromechanical energy conversion. The stator of an induction motor consists of three parts: the stator core, the stator windings, and the frame.
The rotor consists of a rotor core, rotor windings, and a shaft. The rotor core is also part of the main magnetic circuit and is generally made of stacked silicon steel sheets with a thickness of 0.5 mm. The core is fixed to the shaft or rotor support. The entire rotor has a cylindrical shape. Rotor windings are divided into two types: squirrel-cage type and wound type.
Under normal circumstances, the rotor speed of an induction motor is always slightly lower or slightly higher than the speed of the rotating magnetic field (synchronous speed), hence the induction motor is also called an "asynchronous motor".
When the load on an induction motor changes, the rotor speed and slip will change accordingly, causing corresponding changes in the electromotive force, current, and electromagnetic torque in the rotor conductors to adapt to the load requirements. Based on the sign and magnitude of the slip, induction motors have three operating states: motor, generator, and electromagnetic brake.
An induction motor utilizes the principle of electromagnetic induction. The three-phase current in the stator generates a rotating magnetic field, which interacts with the induced current in the rotor windings to produce electromagnetic torque, thus converting energy. Under normal circumstances, the rotor speed of an induction motor is always slightly lower or slightly higher than the speed of the rotating magnetic field (synchronous speed); therefore, induction motors are also called "asynchronous motors."
When the load on an induction motor changes, the rotor speed and slip will change accordingly, causing corresponding changes in the electromotive force, current, and electromagnetic torque in the rotor conductors to adapt to the load requirements. Based on the sign and magnitude of the slip, induction motors have three operating states: motor, generator, and electromagnetic brake.
II. Brushless Motor
A brushless DC motor consists of a motor body and a driver, and is a typical mechatronic product. Because brushless DC motors operate under self-control, they do not require an additional starting winding on the rotor like synchronous motors that start under heavy loads with frequency conversion speed regulation, nor do they experience oscillations or loss of synchronism during sudden load changes. The permanent magnets in small and medium-capacity brushless DC motors now mostly use high-energy-level rare-earth neodymium iron boron (Nd-Fe-B) materials. Therefore, the size of a rare-earth permanent magnet brushless motor is one frame size smaller than that of a three-phase asynchronous motor of the same capacity.
Although brushless motors have a relatively short history of development in my country, they have experienced rapid growth due to increasingly mature and sophisticated technology. They are now widely used in various fields such as model aircraft, medical devices, home appliances, and electric vehicles, and have formed a nascent industrial chain in cities like Shenzhen, Changsha, and Shanghai. Professional manufacturers such as Shenzhen Weiye Motor and Changsha Keda are continuously driving industry development through technological advancements. In recent years, brushless motors have become a driving force for rapid development in the model industry. Due to production volume and price constraints, brushless motors were primarily used in mid-to-high-end model aircraft in the past. However, thanks to rapid advancements in machining technology, the production cost of brushless motors has decreased significantly, and they are now penetrating all levels of the model industry, from electric remote-controlled cars to electric remote-controlled boats and electric model airplanes—they are ubiquitous.
III. Which is better, an induction motor or a brushless motor?
Both induction motors and brushless motors have their own advantages and applicable scenarios.
An induction motor is a traditional AC motor with advantages such as simplicity, reliability, and low cost. It is suitable for low-speed, high-torque applications, such as electric motors, power tools, and household appliances. The output power of an induction motor is related to the power supply voltage, speed, and load, and its output needs to be controlled by adjusting the power supply voltage and frequency.
A brushless motor is a type of DC motor that offers advantages such as high efficiency, high power density, and programmable control. It is suitable for high-speed, low-torque applications, such as drones, robots, and electric vehicles. Brushless motors achieve highly efficient speed and torque control by electronically controlling current and voltage.
Therefore, the choice between an induction motor and a brushless motor depends on the specific application and requirements. For applications requiring high speed and low torque, a brushless motor is a better choice; for applications requiring low speed and high torque, an induction motor may be more suitable.
Induction motors and brushless motors are both common types of electric motors, and they have the following differences:
The underlying principles differ: Induction motors operate based on electromagnetic induction, requiring a rotating magnetic field to induce a current in the rotor, thereby generating torque. Brushless motors, on the other hand, use an electronic controller to control current and voltage to excite the magnetic field on the rotor, thus producing torque.
The power supply is different: induction motors require AC power to operate, while brushless motors require DC power.
Maintenance costs differ: Induction motors are relatively simple, highly reliable, and have relatively low maintenance costs; while brushless motors are more complex, requiring electronic controllers and other supporting equipment, resulting in higher maintenance costs.
The control methods differ: Induction motors are relatively simple to control, generally by changing the frequency and voltage of the power supply to control the speed; while brushless motors require an electronic controller to precisely control the current and voltage to achieve more accurate control.
The applicable scenarios are different: induction motors are suitable for some low-speed, high-torque applications, such as electric motors, power tools, and household appliances; while brushless motors are suitable for some high-speed, low-torque applications, such as drones, robots, and electric vehicles.
