Brushless DC motors (BLDC) and permanent magnet synchronous motors (PMSM) are two types of motors widely used in the field of modern electric motors.
Although they share many similarities, there are still some important differences between them. This article provides an exhaustive, factual and detailed comparison of these two types of engines from various aspects.
1. Principle and structure of brushless DC motor
Brushless DC Motor:
The brushless DC motor operates in a rotating magnetic field formed by the magnetic potential at the end of the shaft, synchronizing phase switching through the sensing pole to drive rotor movement.
Its structure is composed of a rotor made up of permanent magnets, a stator wrapped in coils and a position sensor. By changing the direction and magnitude of the current, the movement of the rotor can be controlled.
Permanent magnet synchronous motor:
The permanent magnet synchronous motor acts on the interaction of magnetic potentials between the stator and the rotor, generating torque to drive the rotor movement.
The rotor generates a rotating magnetic field through permanent magnets, while the stator coils create an exciting magnetic field. The interaction of these two magnetic fields drives the rotor.
The structure of a permanent magnet synchronous motor is similar to that of a brushless DC motor, but the difference lies in the function of the stator coils: in brushless DC motors, they assist the magnetic field, while in permanent magnet synchronous motors, they generate the excitation magnetic field.
2. Brushless DC Motor Control Methods:
Brushless DC Motor:
The control of brushless DC motors mainly involves two methods: Hall sensor feedback and back electromotive force control. The Hall sensor feedback method determines the switching time by detecting the position of the rotor, controlling the direction and magnitude of the current.
The back electromotive force control method estimates the position of the rotor and measures the back electromotive force of the armature coils for control. This method allows for high efficiency and high torque.
Permanent magnet synchronous motor:
Control methods for permanent magnet synchronous motors mainly include current control and field-oriented control. The current control method controls the torque and speed of the motor by measuring the current.
Field-oriented control estimates rotor position and measures rotor back electromotive force to control current, achieving more precise control and response.
3. Power Density and Efficiency Brushless DC Motor:
Brushless DC Motor:
Brushless DC motors have high power density and efficiency. Due to their simple structure, free of brushes and brush wear problems, they can achieve high power.
Additionally, the use of reverse electromotive force control reduces copper and iron losses, allowing for efficient operation.
Permanent magnet synchronous motor:
Permanent magnet synchronous motors have high power density but relatively lower efficiency. Due to their complex structure and the need to maintain an excitation magnetic field in the stator coils, losses of copper and iron occur.
Furthermore, the presence of a rotating magnetic field leads to extra eddy current losses. However, efficiency can be improved through optimized control strategies and advanced material technologies.
4. Response Characteristics and Control Range Brushless DC Motor
Brushless DC Motor:
Brushless DC motors feature good response characteristics and a wide control range. As their rotors are made of permanent magnets, they have low rotor inertia and fast response speed. Additionally, brushless DC motors can achieve precise control by adjusting the magnitude and direction of current to meet various operational requirements.
Permanent magnet synchronous motor:
Permanent magnet synchronous motors have relatively poorer response characteristics and a narrower control range. Due to the greater inertia of the rotor, the response speed of the rotor is slower. Furthermore, control of permanent magnet synchronous motors is more complex, requiring accurate estimation of rotor position and reverse electromotive force for accurate control.
5. Finish
In summary, brushless DC motors and permanent magnet synchronous motors have noticeable differences in aspects such as principle and structure, control methods, power density and efficiency, as well as response characteristics and control range. Depending on the application requirements, the appropriate type of motor can be chosen.
Brushless DC motors are suitable for applications that require high power and precise control, while permanent magnet synchronous motors are suitable for applications that require high power density and a wider control range.
