Compared with ordinary three-phase asynchronous motors, permanent magnet synchronous motors have the advantages of high starting torque, short starting time, and high overload capacity. They can reduce the installed capacity of equipment driving motors according to the actual shaft power, saving energy and reducing investment in fixed assets at the same time.
Comparatively speaking, permanent magnet synchronous motor control is convenient, the speed is only determined by the frequency, the operation is smooth and reliable, and does not change with the load and voltage fluctuations. In view of the characteristics of the permanent magnet synchronous motor speed strictly synchronous, determines the motor dynamic response performance is good, more suitable for frequency control.
The advantage of permanent magnet synchronous motor lies more in its two low and two high, that is, low loss and temperature rise, high power factor and efficiency, which is exactly what people are seeking for the performance of the motor, which also determines the market application status of permanent magnet motor.
Why do permanent magnet motors have low losses and low temperature rise?
Because the magnetic field of the permanent magnet synchronous motor is generated by the permanent magnet, it avoids excitation losses caused by generating a magnetic field through excitation current, which is what we call copper losses.
When the motor is running, there is no current in the rotor operation, significantly reducing the temperature rise of the motor. According to incomplete statistics, under the same load conditions, the temperature rise will be reduced by about 20K.
High power factor and high efficiency of permanent magnet synchronous motor.
Compared to asynchronous motors, permanent magnet synchronous motors have much higher efficiency at light loads. They have a wide range of efficient operation, with efficiency greater than 90% within a load range of 25% to 120%.
The rated efficiency of permanent magnet synchronous motors can meet the current national standard's level 1 energy efficiency requirements, which is their biggest advantage compared to asynchronous motors in terms of energy saving.
In actual operation, electric motors rarely run at full power when driving loads. The reasons are as follows: On one hand, during the selection of the motor, designers generally determine the motor power based on the load's extreme operating conditions.
However, the occurrence of these extreme conditions is rare. Additionally, to prevent motor burnout during abnormal operating conditions, designers also provide a power margin for the motor.
On the other hand, motor manufacturers usually leave a certain power margin on top of the power required by the user to ensure the motor's reliability.
As a result, most motors in actual operation work at less than 70% of their rated power, especially when driving fan or pump loads, where the motor typically operates in a light load range.
For asynchronous motors, their efficiency is low in light load conditions, while permanent magnet synchronous motors can maintain relatively high efficiency in the light load range.
Permanent magnet synchronous motors have a high power factor, which is independent of the motor rating. When operating at full load, the power factor of the motor is close to 1.
Compared to asynchronous motors, this results in lower motor current and reduced copper losses in the stator, leading to higher efficiency. On the other hand, the power factor of asynchronous motors decreases with increasing motor rating. Additionally, due to the high power factor of permanent magnet synchronous motors, the capacity of the power supply (transformer) theoretically can be reduced, along with the specifications of associated switchgear and cables.
Disadvantages of permanent magnet synchronous motors
Permanent magnet synchronous motors also have their disadvantages, such as: the starting current of permanent magnet synchronous motors is about 9 times that of asynchronous motors; permanent magnet synchronous motors cannot be started by voltage reduction.
Because under the condition of voltage reduction, the drop in starting torque of permanent magnet synchronous motors is greater than that of asynchronous motors, which can cause difficulties in starting. There are significant differences in the self-starting characteristics of permanent magnet synchronous motors and the feedback current during system short-circuit among different equipment manufacturers, and due to the difficulty in obtaining relevant data, the application of permanent magnet synchronous motors may introduce some uncertain factors to the short-circuit level and start-up calculation verification of the power system.
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