Introduction to the advantages and disadvantages of
permanent magnet synchronous motors
The rotor speed of permanent magnet synchronous motors is synchronized with the speed of the stator magnetic field. Its working process is that the stator winding is connected to the alternating current to generate a stator rotating magnetic field, and the permanent magnet rotor magnetic field is induced by the stator rotating magnetic field and rotates with it, and the motor rotates and outputs power.
The main advantages of permanent magnet synchronous motors are high power density, high operating efficiency, simple and compact structure, large and smooth torque, and good speed regulation performance.
1) High power density: The neodymium iron boron magnetic material of the permanent magnet synchronous motor has excellent magnetic properties. After magnetization, no external energy needs to be added, and a strong magnetic field can be constructed. At the same time, the magnetic field has permanent characteristics and does not require additional circuits for excitation (that is, energizing the conductor to generate a magnetic field), so that a small volume and light weight can be maintained. At rated power, the power density of a permanent magnet synchronous motor with the same heat dissipation conditions and insulation materials is usually more than twice that of an induction asynchronous motor.
2) High operating efficiency: Benefiting from the permanent magnets in the rotor, the rotor of the permanent magnet synchronous motor usually does not need to be energized (except for some self-starting conditions or eddy current losses), which can reduce related energy losses and have high efficiency.
3) Simple and compact structure: The permanent magnet synchronous drive motor does not have an excitation power supply structure and an excitation winding structure, which reduces the complexity of the related structure and is relatively compact, ensuring that the permanent magnet synchronous drive motor operates more reliably. Compared with the third generation, the stator diameter of the fourth-generation permanent magnet synchronous motor equipped in Toyota Prius has decreased by 20%, and the overall structure is more compact and smaller in size.
4) Large and smooth torque: Within the rated current range, increasing the current can quickly increase the torque of the permanent magnet synchronous motor. In addition, the rotating magnetic field formed by the three-phase alternating current in the stator is also relatively stable, and the torque pulsation is small. Especially under low-speed and high-torque conditions (corresponding to the starting and acceleration stage of new energy vehicles), permanent magnet synchronous motors have outstanding advantages over asynchronous induction motors.
5) Good speed regulation performance: The relationship between electricity, magnetism and force of permanent magnet synchronous motors is simpler than that of induction asynchronous motors, making them easier to regulate and control. The state equation of the asynchronous motor is fourth-order, and the equations of the rotor and stator are coupled (the current in the rotor is generated by the rotation of the stator magnetic field); the state equation of the permanent magnet synchronous motor is second-order, and the magnetic field of the permanent magnet exists independently. The control difficulty is significantly lower than that of the induction asynchronous motor under low-speed and high-speed (higher than the rated speed) conditions.
