What are the advantages of permanent magnet synchronous motors compared with AC asynchronous motors?
Release time:
2021-03-04 16:26
In the power system, you often hear the terms permanent magnet synchronous motor and AC asynchronous motor, and in terms of frequency, permanent magnet synchronous motor occupies the vast majority. 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 range | Large speed range |
| Low cost per unit power | High cost per unit power |
| No demagnetization | Large changes in temperature can cause demagnetization |
Compared with AC asynchronous motors, permanent magnet synchronous motors have the following advantages:
1. High efficiency, which can be explained from the following aspects
1. Since the magnetic field of the permanent magnet synchronous motor is generated by permanent magnets, the excitation loss caused by the magnetic field generated by the excitation current is avoided.
2. Compared with asynchronous motors, the external characteristic efficiency curve of permanent magnet synchronous motors has a higher efficiency value at light load. Compared with asynchronous motors, this is the characteristic of permanent magnet synchronous motors. The biggest advantage in energy saving.
Usually, when a motor drives a load, it rarely runs at full power because:
On the one hand, the user Usually when selecting a motor, the motor power is determined based on the extreme working conditions of the load, 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;3. The power factor of the permanent magnet synchronous motor is not affected by the number of motor poles. If the motor support system allows , then the number of poles of the motor can be designed to be more, the corresponding motor volume will be smaller, and the direct material cost of the motor will be lower. 2. High power factor, high power capacity of the motor Can be reduced, switches, cables and other auxiliary facilities can be smaller, the corresponding cost is lower1. High power factor, low motor current, reduced motor stator copper consumption, more energy-savingThe power factor of the permanent magnet synchronous motor can be adjusted during design, and can even be designed to be 1, regardless of the number of poles of the motor. , however, due to its own excitation characteristics, the asynchronous motor will increase as the number of poles increases, which will inevitably lead to a decrease in power factor. For example, an 8-pole motor has a power factor of usually around 0.85. A motor with a high power factor It has the following advantages:2. High power factor: 4. The system is highly efficient. The parameters of permanent magnet motors, especially the power factor, are not affected by the number of motor poles, so it is easy to design multi-pole motors, making it possible to manufacture traditional load motors that need to be driven by a gearbox into permanent magnet synchronous motors and motor-driven direct drive systems. The gearbox is omitted and the transmission efficiency is improved. 3. Since the power factor of the permanent magnet synchronous motor is high, its current is smaller than that of the asynchronous motor. Therefore, the stator copper loss of the motor is small and the efficiency is high. For induction motors, their efficiency is very low under light loads, while permanent magnet synchronous motors can still maintain high efficiency under light loads. When designers design motors, in order to ensure the reliability of the motor, users usually require a certain amount of power. Margin, so more than 90% of the actual operating motors operate at less than 70% of the rated power, especially for motors that drive fans or pumps. This results in the motor usually operating in a light load area.
On the other hand,
3. Simple and flexible structure: Since the parameters of the permanent magnet synchronous motor are not affected by the number of poles of the motor, it is easy to realize the motor directly driving the load, eliminating the need for high noise and high failure rate. of gearbox.
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