0 Introduction

Synchronous motor relative to the asynchronous motor, with high power factor, high efficiency, rotor parameters can be measured, between the stator and rotor air gap, good control performance, small size, light weight, simple structure, high torque / inertia ratio, etc. Petroleum, chemical, textile, mining, vehicles, CNC machine tools, robots, and aerospace fields have been increasingly widely used, facing the high-power (high speed, high torque), high functionality and miniaturization The

Permanent magnet synchronous motor consists of stator and rotor, stator and asynchronous motor the same, composed of three-phase winding and stator core. The rotor is equipped with a pre-magnetized (magnetized) permanent magnet that eliminates the need for external energy to create a magnetic field in its surrounding space, which simplifies the motor structure and saves energy. In this paper, from the characteristics of permanent magnet synchronous motor, the actual application of convergence to explain the comprehensive benefits of permanent magnet synchronous motor.

1 permanent magnet synchronous motor outstanding advantages

(1) Since the rotor is made of permanent magnets, the magnetic flux density is high, and the excitation current is not required to eliminate the excitation loss. Compared with the asynchronous motor, the excitation current of the stator side winding and the copper and iron loss at the rotor side are reduced, and the reactive current is greatly reduced. Since the rotor magnetic field is synchronized and the rotor core has no base wave iron consumption, the efficiency Relationship active energy) and power factor (relational reactive energy) are higher than asynchronous motors. The permanent magnet synchronous motor is generally designed to have a higher power factor and efficiency even at light load. Figure 1 shows the comparison of the efficiency and power factor of a permanent magnet synchronous motor with the same type of asynchronous motor. From the motor load changes, rare earth permanent magnet synchronous motor can be 25% to 120% rated power range to maintain high power factor and high efficiency state of operation, and the general three-phase asynchronous motor is usually only 60% to 100% Rated power to maintain a higher performance work.

(2) permanent magnet synchronous motor speed and frequency to maintain a constant fixed relationship with the asynchronous motor load operation when there is a large difference in the difference between the permanent magnet synchronous motor has a hard mechanical properties, due to load changes caused by Of the motor torque disturbance has a strong bearing capacity. The permanent magnet synchronous motor rotor core can be made into a hollow structure to reduce the rotor inertia, and the permanent magnet synchronous motor starts, the braking time is much faster than the asynchronous motor, the high torque / inertia ratio makes the permanent magnet synchronous motor more responsive than the asynchronous motor fast.

Figure 1 Comparison of two motor efficiency and power factors

(3) permanent magnet synchronous motor size than the asynchronous motor greatly reduced, the weight is greatly reduced. The same thermal conditions and insulation materials, permanent magnet synchronous motor than three-phase asynchronous motor power density more than 2 times. Equipment covers an area of small, effective cost reduction.

(4) the rotor structure is greatly simplified, easy to maintain, improve the stability of the operation.

AC permanent magnet servo motor, the rotor on the magnet and the core is usually high-temperature adhesive together, glue curing time is generally longer, increasing the production cycle and cost, and the motor during the operation, the magnet in the temperature changes, Impact and so on under the repeated role of deformation and even the risk of falling off. In order to solve this technical problem, some manufacturers will be magnetic tile adhesive process by stainless steel sets of mechanical fastening, as shown in Figure 2, completely eliminate the risk of loose steel.

a) positive

b) measuring surface

Figure 2 Permanent magnet synchronous motor rotor assembly structure

Three-phase asynchronous motor due to the design of a higher power factor, it is necessary to make the air gap between the stator and rotor to do a very small, while the air gap uniformity of the safe operation of the motor and vibration noise is also essential, the asynchronous motor The position of the parts and tolerances and assembly requirements of the concentricity of the relatively strict, the freedom of choice of bearing clearance is also relatively small, the larger base of the asynchronous motor is usually used oil bath lubrication way bearings, must be in the provisions of the work Time filling lubricants, oil spills or filling is not timely will accelerate the bearing failure, in the three-phase asynchronous motor maintenance, bearing maintenance accounted for a large proportion. In addition, due to the presence of induced current in the three-phase asynchronous motor rotor, the corrosion problem of the bearing is also concerned by many researchers in recent years. The permanent magnet synchronous motor does not have such problems. Permanent magnet synchronous motor due to the larger air gap, the above-mentioned asynchronous motor air gap caused by the relevant problems in the synchronous motor performance is not obvious, while the permanent magnet synchronous motor bearings with dust cover grease lubricated bearings, bearings in The factory has been sealed into the right amount of high-quality grease, life-free maintenance.

2 Typical applications of permanent magnet synchronous motors

2.1 electro-hydraulic servo injection molding machine application program

Traditional injection molding machine using three-phase asynchronous motor with quantitative pump, injection molding machine work process, the motor needs long-term continuous operation. Through the servo pump drive system energy-saving transformation, permanent magnet synchronous motor fast response and large starting torque, you can need to complete the injection molding machine to start the permanent magnet synchronous motor drive pump pressure, in the process of cutting and mold, The main pump is in a shutdown state, to achieve a batch of zero power consumption, through the comparison of energy efficiency up to 85%.

In the excellent servo motor algorithm control, the noise is much lower than the ordinary injection molding machine. In the ideal state of low noise screw pump, the noise of the whole injection molding machine is less than 70 decibels. To achieve quiet operation, improve the working environment.

2.2 iron ore dryers on the energy-saving applications

Use the site for a mining field in the northwest, more dust environment. The equipment used a total of 125 motors, Yang volume equipment need to start a larger starting torque, and the normal operation of the motor long-term operation in the 30% to 50% rated power light load state, the original use of three-phase asynchronous motor efficiency Only about 65%, the power factor of 0.4 to 0.6 or so, resulting in a serious waste of energy, the choice of permanent magnet synchronous motor, energy-saving effect is very obvious. Power saving test statistics in Table 1. Figure 3 is the replacement of the scene before and after the photo.

Table 1 125 permanent magnet synchronous motor and high efficiency three-phase asynchronous motor energy-saving parameters comparison

a) frequency conversion three-phase asynchronous motor

b) Permanent magnet synchronous motor

Figure 3 permanent magnet synchronous electric replacement of asynchronous motor on the use of iron ore dryers

3 users are more concerned about several issues

3.1 motor life

Synchronous motor with durable encoder as the angle measurement device, to meet the motor high-precision control requirements. In the control accuracy is slightly lower, no overload requirements under the conditions of use, you can use sensorless vector control, saving the cost of the angle measurement device. The life of the entire motor depends on the bearing life, the motor housing IP54 generally used in the protection level, the special environment can be increased to IP65, to meet most of the dust and humid environment requirements. In ensuring the motor shaft extension installation coaxial degree is better, the shaft radial load of the case, the motor bearing the minimum life of more than 20,000 hours. Followed by the life of the cooling fan, the fan is a single-phase 220V pole pole motor, the service life than the capacitor running motor long. In the dusty environment, long-term operation, the need to regularly remove the viscous material attached to the fan to prevent the fan due to heavy load and burned.

3.2 failure and protection of permanent magnetic materials

The development of permanent magnet motor is closely related to the development of permanent magnetic materials. Since entering the 21st century, with the continuous improvement and improvement of the performance of permanent magnetic materials, high magnetic flux density, high coercivity, high magnetic energy product and linear demagnetization curve Of the excellent magnetic materials are particularly suitable for the manufacture of motors, in particular the NdFeB permanent magnet thermal stability and corrosion resistance improvement and the gradual reduction of prices, making the permanent magnet motor research and use has made rapid development.

Permanent magnet material on the importance of permanent magnet motor is self-evident, the cost of the total cost of electrical materials nearly 1/4 or more. This Division I also specifically for the permanent magnet materials to develop a corporate standard, which focuses on corrosion resistance, consistency, high temperature demagnetization test, linear demagnetization curve test and so on. The permanent magnet material has been able to run for a long time under the permissible temperature rise of the motor windings, with a demagnetization rate of less than 2%. Conventional permanent magnetic materials require surface coating to withstand more than 24 hours of salt spray test, the more serious oxidation of the environment, the user need to contact the manufacturers to choose more protective technology permanent magnet material.

3.3 coil burned

The traditional asynchronous motor coil burn failure rate of up to 8% or more, mainly with the motor thermal protection and electrical quality of the material. The traditional asynchronous motor almost no thermal protection components, the pursuit of production manufacturers in the motor insulation processing is also greatly reduced, after the maintenance of the motor, insulation treatment is more weak. Permanent magnet synchronous motor can be embedded in the coil with thermal components, when the coil temperature rise to F-class insulation temperature limit of 105K, the driver through the thermal sensor temperature signal on the motor overheating protection to ensure the safe operation of the motor, while the motor Stator with two vacuum impregnation process, greatly improving the stator pass rate.

4 Conclusion

From the economic analysis: permanent magnet synchronous motor is particularly suitable for restart the use of light to run the occasion to promote the use of permanent magnet synchronous motor has a positive economic and social benefits, significant significance of energy saving. In terms of reliability and stability, permanent magnet synchronous motors also have valuable advantages.