Principle of brushless dc electric motor and use in two-wheeled vehicles

Principle of brushless dc electric motor and use in two-wheeled vehicles
The brushless dc electric motor uses a permanent magnet to make the rotor, and there is no coil in the rotor. So there is no need for commutators and brushes for energizing. Instead, there is a coil that acts as a stator.
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    Converting the electrical signal into a force is the transmission, or the motor. A wide variety of motors are active in many fields. Among them, what are the characteristics of the brushless motor that can be used so widely?

    This article mainly introduces the characteristics, principles, structures and applications of brushless dc electric motor, which is rapidly developing and widely used in motor types.


    Introduction to brushless dc electric motor

    A brushless dc electric motor is a type of DC motor that does not use mechanical commutation contacts (carbon brushes), and replaces the traditional carbon brushes by means of an electric motorcycle controller. Therefore, it is also called electronic adjustable speed DC motor or electronic commutation DC motor.

    The working principle of brushless dc electric motor

    The brushless dc electric motors work on a similar principle to brushed DC motors. Whenever a current-carrying conductor is placed in a magnetic field, it is subjected to a force.

    As a result of the reaction force, the magnet will experience an equal and opposite force. In a brushless dc electric motor, the current-carrying conductor is stationary, while the permanent magnet is in motion.

    When the stator coil gets power from the power supply, it becomes an electromagnet and starts creating a uniform magnetic field in the air gap. Although the power supply is DC, the switch creates a trapezoidal AC voltage waveform.

    The rotor continues to rotate due to the interaction force between the electromagnet stator and the permanent magnet rotor. As the winding switches in the direction of energizing, it induces a magnetic field that alternates between the north and south poles.

    The working principle of brushless dc electric motor

    The north and south poles of the permanent magnet rotor are pushed to align with the stator poles, thus rotating the electric motor for bicycle. Unlike conventional DC motor rotors, brushless dc electric motor rotors are fitted with permanent magnets.

    The control is achieved by an external converter to transfer the power supply to the corresponding stator coil. The on/off sequence of the stator coils is determined by feedback from a Hall sensor mounted on the motor, which displays the position of the rotor.

    The structure of a brushless dc electric motor

    A single brushless motor is not a complete power system, and the brushless motor must be controlled by the brushless controller, that is, the ESC, in order to achieve continuous operation.

    Ordinary carbon brush motors rotate the windings, while brushless motors rotate magnets regardless of the outer rotor structure or the inner rotor structure. Therefore, any motor is composed of a stator and a rotor.

    • Magnet

    It is installed on the rotor and is an important part of the brushless motor, and most of the performance parameters of the brushless motor are related to the magnet, including power, speed, torque, etc.

    • Silicon steel sheet

    It is an important part of the slotted brushless motor, of course, the slotless brushless motor does not have a silicon steel sheet, but the vast majority of brushless motors are slotted. Its role in the whole system is mainly to reduce the magnetic resistance and participate in the operation of the magnetic circuit.

    The structure of a brushless dc electric motor

    • Rotating shaft

    It is the direct stressed part of the motor rotor, and the hardness of the rotating shaft must be able to meet the requirements of high-speed rotation of the rotor.

    • Bearing

    It is the guarantee of smooth operation of the motor, the bearing can be divided into sliding bearings and rolling bearings, and the rolling bearings can be subdivided into ten categories, such as deep groove ball bearings, needle roller bearings and angular contact bearings, and most of the brushless motors are currently using deep groove ball bearings.

    Advantages and disadvantages of brushless dc electric motors

    ● Advantages

    • Since there are no brushes, there is less maintenance overall.
    • Smaller size and superior thermal characteristics.
    • A larger speed range results in less electrical noise.
    • There are no mechanical commutators and related problems.
    • Due to the use of permanent magnet rotors, the efficiency is high and the output power density is high.

    Advantages and disadvantages of brushless dc electric motors

    • Since there are no speed-limiting brushes, it can be operated at high speeds even under loaded and no-load conditions.
    • Compared to brushed DC motors and induction AC motors, the motor is smaller in size and lighter in weight.
    • The commutator system does not require inspection and maintenance, so it has a long service life.
    • Higher dynamic response due to low inertia in the motorcycle stator and loaded windings.
    • Low electromagnetic interference.
    • Since there are no brushes, the noise is low.


    ● Disadvantages

    • Motors are expensive.
    • The electronic controllers required are expensive.
    • Complex drive circuits are required.
    • Additional sensors are required.

    Typical applications for brushless dc electric motors

    The brushless dc electric motors are used in a wide range of applications. In general, it can be divided into the following three main uses:

    • Sustained load applications

    It is mainly used in fields that require a certain speed but do not require high speed accuracy, such as fans, pumps, hair dryers, etc. Typically, these applications are low-cost and mostly open-loop controlled.

    Typical applications for brushless dc electric motors

    • Variable load applications

    It mainly refers to the application that the motor speed needs to change within a certain range, and in this kind of application, there are higher requirements for the high speed characteristics and dynamic response characteristics of the electric motor brake. Electrical controllers, engine controls, and electronic tools, among others, are also good examples. It is well used by Benlg product.

    • Locate apps

    Most of the applications in industrial control and automation fall into this category. In these applications, energy is often conveyed, such as gears or conveyor belts, so the system has special requirements for the dynamic response and torque of the motor.


    Compared with traditional brushed motors and induction motors, brushless dc electric motors have excellent characteristics such as high speed and torque ratio, good dynamic characteristics, high efficiency, long life, low noise, wide speed range and easy manufacturing.

    In particular, the power output characteristics per unit volume allow it to be used in applications where size and weight are sensitive. These excellent characteristics make BLDC have a wide range of applications in the field of industrial control, automotive industry, aerospace and other fields.

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