Exploring the Permanent Magnet Motor

In recent years, compared with the original DC traction motor system, permanent magnet motor has obvious advantages, its outstanding advantages are small size, light weight (its mass is 0.5-1.0kg / Kw), high efficiency, basic maintenance-free, Wide range of speed. 

First, the permanent magnet motor overview

In this DC motor, with the DC current to produce the main pole of the magnetic field excitation, known as the current excitation; if the permanent magnet to replace the current excitation to produce the main pole magnetic field, this motor is called permanent magnet motor. 

In many cases can be achieved brushless, so it is mostly used for small and micro-motor.  When using variable frequency power supply, permanent magnet motor can also be used for speed drive system.  With the continuous improvement of permanent magnet material performance and improve the permanent magnet motor has been in household appliances, medical equipment, automotive, aviation and defense and other fields have been widely used. 

The shortcomings of the permanent magnet motor are that, if used improperly, at an excessively high temperature or at a low temperature, under the action of the armature reaction caused by the inrush current, or under severe mechanical vibration, there may be irreversible Demagnetization, so that the performance of the motor down, or even can not be used.  Therefore, the use of permanent magnet motor should be given special attention. 

In the case of the same power level, the permanent magnet generator is twice as high as the output power of the excitation generator, that is, the actual type of excitation generator of the permanent magnet generator. 

The main reason is that the permanent magnet generator is a switch-type rectifier regulator, high precision regulator, charging effect is good.  To avoid over-current charging caused by shortened battery life.  Permanent magnet generator with the beginning of the rectifier output of the battery using a small current pulse charge, the same charge current charge better, thus extending the battery life. 

4.  Small size, light weight, higher than the power

The use of permanent magnet rotor structure, making the internal structure of the generator design is very compact, volume, weight greatly reduced.  The simplification of the permanent magnet rotor structure also reduces the rotor inertia, the practical speed increases, and the ratio of the power (ie, the ratio of power to volume) reaches a high value. 

5.  Use self-starting regulator

No external excitation power supply.  The generator can generate electricity as long as it rotates.  When the battery is damaged, as long as the engine is running, the car charging system can still work often.  If the car does not have the battery, just shake the handle or slip car, but also to achieve ignition operation. 

6.  High efficiency

Permanent magnet generator is an energy-saving product.  The permanent magnet rotor structure eliminates the mechanical power required to produce the rotor magnetic field and the mechanical loss of the friction between the carbon brush and the slip ring, which greatly improves the efficiency of the permanent magnet generator.  Ordinary excitation generators have an average efficiency of only 45% to 55% of the speed range between 1500 rpm and 6000 rpm and up to 75% to 80% for permanent magnet generators. 

7.  No radio interference

Permanent magnet generator without carbon brush, no slip ring structure, eliminating the carbon brush and slip ring friction generated by radio interference; eliminate the spark, especially suitable for explosive environments with greater risk of work, but also reduce the generator Requirements for ambient temperature. 

8.  Particularly suitable for damp or dusty harsh environments. 

Third, the principle of permanent magnet motor

1.  Magnetic circuit structure and design calculation

Permanent magnet in the motor is both a magnetic source, but also a part of the magnetic circuit.  The magnetic properties of the permanent magnet are not only related to the manufacturing process of the manufacturing plant, but also to the shape and size of the permanent magnet, the capacity of the magnetizing machine and the method of magnetizing, and the specificity of the performance data is very large.  And the magnetic flux and the magnetomotive force that the permanent magnet can provide in the motor also change with the material performance, the size and the motor running state of the rest of the magnetic circuit.  These have increased the complexity of the permanent magnet generator electromagnetic calculation, so that the accuracy of the calculation results are lower than the electric excitation generator.  Therefore, it is necessary to establish a new design concept, to reanalyze and improve the magnetic circuit structure and control system; must use modern design methods to study the new analytical methods to improve the accuracy of design calculations; must study the use of advanced testing methods and manufacturing Process. 

2.  Control problems

Permanent magnet generator made without external energy to maintain its magnetic field, but also caused by external regulation, control of its magnetic field is extremely difficult.  These have limited the scope of application of permanent magnet generators.  However, with the rapid development of control technology for power electronic devices such as MOSFETs and IGBTs, permanent magnet generators only require magnetic field control in the application and only the motor output control.  Designed to require NdFeB materials, power electronic devices and computer control of three new technologies together, so that permanent magnet generators in a new operating conditions. 

3.  Cost issues

As the current price of rare earth permanent magnet materials is still relatively expensive, the cost of rare earth permanent magnet generators are generally higher than the electric excitation generators, but this will be in the motor high performance and operation to get better compensation.  In the future design will be based on the specific use of the occasion and requirements, performance, price comparison, and structural innovation and design optimization to reduce manufacturing costs.  There is no denying that the cost of the product being developed is slightly higher than the current generators, but we believe that as the product becomes more perfect, the cost problem will be well resolved. " The customer's focus is on the cost per kilometer of watt."  His statement fully demonstrates that the market prospects for AC permanent magnet generators will not be plagued by cost problems, according to the head of the US DELPHI (Delphi) technology department. 

4.  irreversible demagnetization problem

If the design and use of improper, permanent magnet generator in the high temperature (NdFeB permanent magnet) or too low (ferrite permanent magnet), the impact of the current generated by the armature reaction, or in the severe mechanical vibration When it is possible to produce irreversible demagnetization, or called loss of magnetic, so that motor performance is reduced, or even can not be used.  Therefore, it is necessary to study and develop the methods and apparatus for inspecting the thermal stability of permanent magnetic materials for use in motor manufacturers, and to analyze the anti-demagnetization capability of various structural forms in order to ensure that the use of the corresponding measures in the design and manufacture The magnetic generator does not lose its magnetism. 

Fourth, the new development of permanent magnet motor

1993, the US Department of Energy, Ministry of Commerce, Ministry of Trade, Ministry of Defense, EPA, NASA, the National Science Foundation under the seven government departments under the United States three largest car manufacturing company, Chrysler, Ford and GM, established a new generation of vehicles Partnership, the goal is to develop a new generation of motor vehicle technology to enhance the strength of the US auto industry.  From 1998 to 2002, the National Natural Science Foundation of China (NSF) funded the US National Power Electronics Center (formed by the United States Virginia and the United States Wisconsin four universities) research and development vehicle electronic power drive system, electronic servo control system and a variety of vehicles IC module to improve the reliability of automotive electrical and electronic components, reduce the cost and seize the vehicle automation technology of the commanding heights, and enhance the competitiveness of the international market.  The X-by-wire system will be a very important technology in the future, and the technology can be integrated into a variety of independent systems (such as steering, braking, suspension, etc.)  by the computer control, so that The maneuverability of the car, the safety and the overall structure of the car are greatly improved, and the flexibility of the design is greatly increased.  At present, the electronic power steering wheel and wire brake has been used in some European models, in this system has been reduced a considerable number of mechanical components, such as hydraulic pumps.  Automotive electronic servo technology is a revolutionary technology, with the use of this technology, many of the traditional mechanical parts will disappear in the future of the car, and more and more car servo motor will appear in the future of the car. 

The world's largest auto parts company, a US Delphi Automotive Systems, predicts that in the next 3-5 years, the world's cars will gradually use electronic servo drive systems, such as electronic power steering wheel and wire brake servo drive system.  At present, the United States Delphi Automotive Systems is looking for an annual output of more than 3 million units of electronic power steering wheel AC servo motor partners. 

Five, concluding remarks

This paper mainly starts from the overview of permanent magnet motor, introduces the advantages of permanent magnet motor in detail, and elaborates its related starting principle, and looks forward to the new development of permanent magnet motor.