Permanent magnet synchronous motor and AC asynchronous motor are often heard in the power system, and permanent magnet synchronous motor accounts for the vast majority in frequency. What are the differences between them, and what are their advantages and disadvantages?
Permanent magnet synchronous motor vs AC asynchronous motor
Motor characteristics
AC asynchronous motor | Permanent magnet synchronous motor |
Low power density | High power density |
Small speed regulation range | Large speed regulation range |
Low cost per unit power | High cost per unit power |
No demagnetization | Large temperature changes can cause demagnetization |
Compared with AC asynchronous motor, permanent magnet synchronous motor has the following advantages:
First， High efficiency can be explained from the following aspects
1. Because the magnetic field of permanent magnet synchronous motor is generated by permanent magnet, the excitation loss caused by the magnetic field generated by excitation current is avoided.
2. Compared with asynchronous motor, the external characteristic efficiency curve of permanent magnet synchronous motor has higher efficiency value under light load. Compared with asynchronous motor, this is the biggest advantage of permanent magnet synchronous motor in energy saving.
Generally, when a motor drives a load, it rarely operates at full power because:
On the one hand, the user usually determines the motor power according to the extreme working conditions of the load when selecting the motor, and the chance of extreme working conditions is very small. At the same time, in order to prevent the motor from burning out under asynchronous conditions, the user will also leave a certain motor power margin;
On the other hand, when the designer designs the motor, in order to ensure the reliability of the motor, the power usually required by the user is to leave a certain power margin on this basis. Therefore, the working power of more than 90% of the actually running motor is lower than 70% of the rated power, especially for the motor driving the fan or pump. As a result, the motor usually works in the light load area.
For induction motor, its efficiency is very low under light load, while permanent magnet synchronous motor can still maintain high efficiency under light load.
3. Because the power factor of permanent magnet synchronous motor is high, its current is less than that of asynchronous motor. Therefore, the stator copper loss of motor is small and the efficiency is high.
4. High system efficiency. The parameters of permanent magnet motor, especially the power factor, are not affected by the number of motor poles, so it is easy to design multipole motor, so that the traditional load motor driven by gearbox can be manufactured into permanent magnet synchronous motor. The direct drive system driven by motor eliminates the gearbox and improves the transmission efficiency.
Second, high power factor: the power factor of permanent magnet synchronous motor can be adjusted during design, or even designed as 1, which is independent of the number of poles of the motor. However, due to its own excitation characteristics, asynchronous motor will increase with the increase of the number of poles, which will inevitably lead to the reduction of power factor. For example, the power factor of 8-pole motor is usually about 0.85, High power factor motors have the following advantages:
1. High power factor, low motor current, reduce motor stator copper consumption and save energy.
2. The power factor is high, the power capacity of the motor can be reduced, the switches, cables and other auxiliary facilities can be small, and the corresponding cost is low.
3. The power factor of permanent magnet synchronous motor is not affected by the number of motor poles. If the motor support system allows, the number of poles of the motor can be designed to be more, the corresponding motor volume is small, and the direct material cost of the motor is low.
Third, the structure is simple and flexible: because the parameters of the permanent magnet synchronous motor are not affected by the number of motor poles, it is convenient to realize the direct drive load of the motor and save the gearbox with high noise and high failure rate.
Hengda motor has a professional expert team to provide technical support and guidance in the whole process from customer demand understanding, design scheme provision, process quality control in motor production and manufacturing to after-sales service, so as to ensure that the highest quality standard has laid a good foundation for customers to use the motor safely and reliably.
