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The Advantages and Application Prospects of Permanent Magnet Synchronous Motors

Feb. 25, 2021
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A Permanent Magnet Synchronous Motor is composed of a stator and a rotor. The stator is the same as an asynchronous motor, consisting of a three-phase winding and a stator core. A pre-magnetized permanent magnet is installed on the rotor, and a magnetic field can be established in the surrounding space without additional energy, which simplifies the motor structure and saves energy. This article starts from the characteristics of permanent magnet synchronous motors and uses practical applications to illustrate the comprehensive benefits of promoting permanent magnet synchronous motors.


Outstanding advantages of permanent magnet synchronous motors


(1) Since the rotor is made of permanent magnets, the magnetic flux density is high, no excitation current is needed, and excitation loss is eliminated. Compared with the asynchronous motor, it reduces the excitation current of the stator side winding and the copper and iron losses of the rotor side, and greatly reduces the reactive current. Because the stator and rotor magnetic potentials are synchronized, the rotor core has no fundamental wave iron loss, so the efficiency and The power factor is higher than that of asynchronous motors. Permanent magnet synchronous motors are generally designed with high power factor and efficiency even when running at light loads.


(2) Permanent magnet synchronous motors have harder mechanical characteristics, and can withstand motor torque disturbances caused by load changes. The rotor core of the permanent magnet synchronous motor can be made into a hollow structure to reduce the rotor inertia, and the starting and braking time are much faster than the asynchronous motor. The high torque/inertia ratio makes the permanent magnet synchronous motor more suitable for the fast response condition than the asynchronous motor Run down.


(3) Compared with asynchronous motors, the size of permanent magnet synchronous motors is greatly reduced, and the weight is relatively lighter. The power density of a permanent magnet synchronous motor with the same heat dissipation conditions and insulating materials is more than twice that of a three-phase asynchronous motor.


(4) The structure of the rotor is greatly simplified, which is convenient for maintenance and improves the stability of operation.


Permanent Magnet Synchronous Motor

Permanent Magnet Synchronous Motor


Permanent magnet synchronous motor rotor assembly structure


Because the Three-Phase Asynchronous Motor needs to be designed with higher power factor, it is necessary to make the air gap between the stator and rotor small. At the same time, the uniformity of the air gap is also very important to the safe operation and vibration and noise of the motor. The requirements for the shape and position tolerances and assembly concentricity of the components are relatively strict, and the freedom to choose the bearing clearance is relatively small. The asynchronous motor with a larger frame usually uses the bearing of the oil bath lubrication method, and must work in the specified way. Adding lubricating oil within time, oil leakage in the oil cavity or untimely filling will accelerate bearing failure. In the maintenance of three-phase asynchronous motors, bearing maintenance accounts for a large proportion. In addition, due to the existence of induced current in the rotor of the three-phase asynchronous motor, the problem of electric corrosion of the bearing has also been concerned by many researchers in recent years.


Permanent magnet synchronous motors do not have such problems. Due to the large air gap of the permanent magnet synchronous motor, the related problems caused by the small air gap of the above asynchronous motor are not obvious in the synchronous motor. At the same time, the bearing of the permanent magnet synchronous motor adopts grease lubricated bearing with dust cover. The right amount of high-quality grease has been packed in the factory, which can be maintenance-free for life.


Typical applications of permanent magnet synchronous motors


1 Electro-hydraulic servo injection molding machine application program


The traditional injection molding machine uses a three-phase asynchronous motor with a quantitative pump. During the operation of the injection molding machine, the motor needs to run for a long time. Through the energy-saving transformation of the servo oil pump drive system, the rapid response and large starting torque of the permanent magnet synchronous motor, the permanent magnet synchronous motor can be started to drive the oil pump to generate pressure when the injection molding machine needs to complete the injection molding process. During the process of blanking and clamping , The main motor of the oil pump is in a shutdown state, achieving intermittent zero power consumption, and the energy saving rate can reach up to 85% through comparison.


Under the control of excellent servo motor algorithm, the noise is much lower than ordinary injection molding machine. In an ideal state with a low-noise screw pump, the overall noise of the injection molding machine is less than 70 decibels, achieving quiet operation and improving the working environment.


2 Energy-saving application on iron ore dry separator


The site of use is a mining farm in the northwest with a dusty environment. The equipment uses a total of 125 motors. When the hoisting equipment starts, a larger starting torque is required. During normal operation, the motor runs at a light load state of 30% to 50% of the rated power for a long time. The efficiency of the original three-phase asynchronous motor is It is only about 65%, and the power factor is about 0.4 to 0.6, causing serious energy waste. The use of permanent magnet synchronous motors has obvious energy-saving effects.


User concerns


1.Motor life


The life of the entire motor depends on the life of the bearing. The motor housing adopts the IP54 protection level, which can be increased to IP65 under special circumstances to meet the requirements of most dust and humid environments. Under the condition that the motor shaft extension is installed with good coaxiality and the radial load of the rotating shaft is appropriate, the minimum service life of the motor bearing is more than 20,000 hours. The second is the life of the cooling fan. The fan uses a single-phase 220V shaded pole motor, which has a longer service life than a capacitor running motor. During long-term operation in a dusty and humid environment, the viscous substances attached to the fan should be removed regularly to prevent the fan from burning due to overload.


2.Failure and protection of permanent magnet materials


The importance of permanent magnet materials to permanent magnet motors is self-evident, and its cost accounts for more than 1/4 of the entire motor material cost. The Quartet has formulated corporate standards for permanent magnet materials, which include corrosion resistance, consistency, high temperature demagnetization test, linear demagnetization curve test, etc. Current permanent magnet materials have been able to run for a long time under the allowable temperature rise of the motor windings, and the demagnetization rate is within 2%. Conventional permanent magnet materials require the surface coating to withstand a salt spray test for more than 24 hours. For environments with severe oxidation and corrosion, users should contact the manufacturer to select permanent magnet materials with higher protection technology.


3.The coil is burned out


The failure rate of traditional Asynchronous Motor coils is as high as 8%, which is mainly related to the thermal protection of the motor and the quality of electrical materials. The company's CM500 series permanent magnet synchronous motor coils are embedded with thermal elements. When the temperature rise of the coil reaches the F-class insulation limit temperature rise of 105K, the driver uses the temperature signal collected by the thermal element to protect the motor from overheating to ensure the safe operation of the motor. At the same time, the motor stator adopts twice vacuum dipping process, which greatly improves the qualification rate of the stator.


From the analysis of economic benefits: permanent magnet synchronous motors are particularly suitable for occasions of heavy start and light operation. The promotion of permanent magnet synchronous motors has positive economic and social benefits and is of great significance to energy saving and emission reduction. In terms of reliability and stability, permanent magnet synchronous motors also have valuable advantages. Choosing a high-efficiency permanent magnet synchronous motor is a long-term benefit from a one-time investment.


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