At present, China has a large amount of electric motor, consumes a large amount of electric energy, aging equipment, and has low efficiency. It has completely entered the period of renewal, and the permanent magnet synchronous motor (PMSM) has small volume, high efficiency, high power factor, large starting torque, and force. It has the characteristics of good index and low temperature rise.
Basic principle of permanent magnet synchronous motor
* The motor is an electromagnetic device that converts mechanical energy and electrical energy into each other by using a magnetic field as a medium.
* There are two methods for establishing the air gap magnetic field necessary for electromechanical energy conversion in the motor: one is to generate a magnetic field by using a current in the motor winding, such as a common DC motor, a synchronous motor and an asynchronous motor; The other is to generate a magnetic field from a permanent magnet, that is, a permanent magnet synchronous motor.
* From the basic principle: permanent magnet synchronous motor is the same as traditional electric excitation synchronous motor. The only difference is that the traditional electric excitation synchronous motor generates magnetic field by inputting current into the excitation winding, and the permanent magnet synchronous motor It is through the permanent magnet to establish the magnetic field, and thus the difference between the two analysis methods.
Advantages of permanent magnet synchronous motor compared to AC asynchronous motor
1. High efficiency and more energy saving:
a, since the magnetic field of the permanent magnet synchronous motor is generated by the permanent magnet, thereby avoiding the excitation loss (copper consumption) caused by the excitation current to generate the magnetic field;
b. The external characteristic efficiency curve of the permanent magnet synchronous motor is much higher than that of the asynchronous motor at light load. This is the biggest advantage of the permanent magnet synchronous motor in terms of energy saving compared with the asynchronous motor. Because usually when the motor is driving the load, it is rarely operated at full power. This is because: on the one hand, when the motor is selected, the motor power is generally determined according to the limit working condition of the load, and the opportunity of the limit condition occurs. It is rare. At the same time, in order to prevent the motor from being burnt in abnormal conditions, the user will further reserve the power of the motor. On the other hand, when designing the motor, the designer usually guarantees the reliability of the motor. On the basis of the power required by the user, further reserve a certain power margin, which results in more than 90% of the actual operating motor is working below 70% of the rated power, especially in driving the fan or pump load, thus causing the motor Usually work in light load areas. For asynchronous motors, the efficiency is very low at light loads, while permanent magnet synchronous motors can still maintain high efficiency in light load areas, and their efficiency is higher than that of asynchronous motors by more than 20%.
c. Since the permanent magnet synchronous motor has a high power factor, the motor current is smaller than that of the asynchronous motor, and accordingly, the stator copper consumption of the motor is smaller and the efficiency is higher.
d, high system efficiency: permanent magnet motor parameters, especially power factor, are not affected by the number of motor poles, so it is easy to design into a multi-pole motor (such as more than 100 poles), so for the traditional need to drive the load motor through the reduction box It can be made into a direct drive system driven directly by a permanent magnet synchronous motor, thereby eliminating the reduction gear box and improving the transmission efficiency.
2. High power factor:
Since the permanent magnet synchronous motor is designed, its power factor can be adjusted, and even a power factor equal to 1 can be designed, regardless of the number of motor poles. As the number of poles increases, the excitation factor of the asynchronous motor itself will inevitably lead to lower and lower power factor. For example, the number of poles is 8-pole motor, and its power factor is usually about 0.85. The more poles, the corresponding power. The lower the factor. Even the 2-pole motor with the highest power factor has a power factor of 0.95. The high power factor of the motor has several advantages:
a, high power factor, small motor current, reduced copper loss of the stator of the motor, more energy efficient;
b. The power factor is high. The power supply of the motor, such as inverter and transformer, can have lower capacity. At the same time, other auxiliary facilities such as switches and cables can be smaller, and the corresponding system cost is lower.
c. Since the power factor of the permanent magnet synchronous motor is not limited by the number of motor poles, the number of poles of the motor can be designed to be higher in the case of the motor supporting system, and the volume of the corresponding motor can be made smaller. Direct material costs are lower.
3. The motor structure is simple and flexible:
a. Because the stator, end ring or rotor winding needs to be installed on the rotor of the asynchronous motor, the flexibility of the structure of the asynchronous motor is greatly limited, and the rotor structure design of the permanent magnet synchronous motor is more flexible. For example, for the traction motor of the railway, the rotor of the motor can be used. The magnetic steel can be directly mounted on the rotating shaft of the wheel pair of the machine, thereby eliminating the reduction gear box and greatly simplifying the structure; and, like the permanent magnet wind power generator, the motor is made of the outer rotor direct drive structure, and the rotor and the impeller of the motor are made. In one piece, it rotates with the impeller, and the stator is fixed on the support tower.
b. Since the parameters of the permanent magnet synchronous variable frequency speed regulating motor are not limited by the number of motor poles, it is easy to realize the direct driving load of the motor, eliminating the noise box with high noise and high failure rate, and increasing the flexibility of mechanical transmission system design.
4. High reliability:
From the comparison of the motor body, the reliability of the permanent magnet synchronous variable frequency speed regulating motor and the asynchronous motor is equivalent, but due to the flexibility of the structure of the permanent magnet synchronous motor, it is easy to realize the direct driving load, and the gear box with low reliability is omitted; Under some load conditions, the motor can even be designed inside the driving device, such as the wind power direct drive device and the winch drive device of the oil drilling rig, so that the bearing with high failure rate of the conventional motor can be omitted: the reliability of the transmission system is greatly improved. .
5, small size, high power density:
The advantages of small size and high power density of the permanent magnet synchronous variable frequency speed control motor are concentrated in the load of driving low speed and high torque. One is the increase of the number of poles of the motor, and the volume of the motor can be reduced. There is also: the increase of motor efficiency, corresponding loss reduction, motor temperature rise is reduced, the size of the motor can be designed smaller with the same insulation level; the flexibility of the motor structure can save the motor Many invalid parts, such as winding ends, rotor end rings, etc., can be smaller in size.
6. Large starting torque, low noise and low temperature rise:
a. The permanent magnet synchronous motor can still maintain a good working state at low frequency, and the output torque at low frequency is larger than that of the asynchronous motor, and the noise during operation is small;
b, the rotor has no resistance loss, the stator winding has almost no reactive current, so the motor temperature rise is low, the same volume, the same weight of the permanent magnet motor power can be increased by about 30%; the same power capacity of the permanent magnet motor volume, weight, used The material can be reduced by 30%.
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