Frontier Technology of Electromagnetics—Maglev Train
Abstract: With the development of science and technology, people's lives have undergone earth-shaking changes. Taking behavior as an example in basic necessities of life, from ancient times to the present, we have experienced changes such as walking-riding-horse-drawn carriage-train-car-airplane and so on. In recent years, maglev trains have attracted people's attention due to their advantages of high speed, environmental protection and energy saving.
Key points:
1. What is a maglev train?
2. The principle of the maglev train: a. Constant conduction type.b. The principle of electromagnetic pole repulsion with the same sex c. Permanent magnet type
3. Technical foundation of maglev train
4. China's domestic maglev train
5. Advantages of maglev trains
What is a maglev train?
High-speed maglev train is a technological invention of the 20th century, and its principle is not profound. It uses the property of magnets that "the same sex repels each other, and opposite sexes attract each other", so that the magnet has the ability to resist gravity, that is, "magnetic levitation". Scientists apply the principle of "magnetic levitation" to the railway transportation system, which makes the train completely detached from the track and floats, becoming a "wheelless" train with a speed of hundreds of kilometers per hour. This is the so-called "maglev train".
The principle of maglev train:
Maglev train is the product of modern high-tech development. The principle is to use the electromagnetic force to offset the gravity of the earth, and the traction is carried out by the linear motor, so that the train is suspended on the track (the suspension gap is about 1 cm). Its research and manufacturing involve many disciplines such as automatic control, power electronics technology, linear propulsion technology, mechanical design and manufacturing, fault monitoring and diagnosis, etc. The technology is very complicated, and it is an important symbol of a country's scientific and technological strength and industrial level. Compared with ordinary wheel-rail trains, it has low noise and the world's first maglev train demonstration operation line - Shanghai Maglev Train. After completion, from Pudong Longyang Road Station to Pudong International Airport, it will only take 6-6 kilometers for more than 30 kilometers. 7 minutes. With the characteristics of no pollution, safety, comfort, high speed and high efficiency, it has the reputation of "zero altitude aircraft". It is a new type of transportation with broad prospects, especially suitable for urban rail transit. Maglev trains are generally divided into repelling type and suction type according to different levitation methods, and can be divided into high speed and medium and low speed according to operating speed.
"Staying away" is the basic working state of the maglev train. Maglev trains use electromagnetic force to counteract Earth's gravitational pull, allowing the train to levitate on the track. During the operation, the car body and the track are in a state of "closeness", and the magnetic levitation gap is about 1 cm, so it has the reputation of "zero-height aircraft". Compared with ordinary wheel-rail trains, it has the characteristics of low noise, low energy consumption, no pollution, safety and comfort, high speed and high efficiency, and is considered to be a new type of transportation with broad prospects. especially in this
Low-speed maglev trains are especially suitable for urban rail transit due to their small turning radius and strong climbing ability.
The maglev high-speed trains being tested in the world have the following models:
1. Normally conductive (electromagnetic) type
Using the principle of electromagnetic opposites attracting each other, the vehicle is suspended on the track by about 1 cm. As early as 1976, Germany has developed a constant magnetic levitation experimental vehicle, currently represented by the German TR08 model (this model was imported from Germany in Shanghai), with a maximum speed of 500 kilometers per hour. When Premier Zhu visited Germany in June 2000, he tried to ride this high-speed train on the 31.5-kilometer spectacle-type slewing test line in Emslant ( ). As early as 1992, Germany had announced that the technology was ready for commercial application.
2. Using the principle of electromagnetic polar repulsion at ultra-low temperature, the vehicle is suspended about 10 cm above the track. In 1962, Japan began to study superconducting maglev high-speed train technology, and in 1989, an 18.4-kilometer test line was built in Yamanashi Prefecture. A manned record of 552 kilometers per hour was created with the MLX01 vehicle. Premier Zhu tried to ride this type of train when he visited Japan in September 2000, and is still continuing to test and improve it.
3. Permanent magnet type
Also known as maglev aircraft, it is actually a permanent magnet maglev high-speed train. It is a creation that the United States is researching and testing. The suspension height is 8-15 cm, and the speed can reach 550 kilometers per hour. Because there are "tooth wings" on both sides of the train (similar to the wings of an airplane), and a "tail" at the tail for balance, it is called a maglev aircraft. Four companies in Chengdu, Sichuan Province have established a joint venture with American Commercial Bank, Feimei Magnetic Levitation High-speed Aircraft Co., Ltd., and have reached an intentional cooperation agreement to introduce American technology. The two parties jointly funded the establishment of a production base and planned to build a test line about 2 kilometers long.
The Shanghai maglev train is a "constant conduction magnetic attraction" (referred to as "constant conduction") maglev train. It is designed based on the principle of "opposites attract each other". It is a suction suspension system. It uses the suspension electromagnets installed on the bogies on both sides of the train and the magnets laid on the track. The suction force generated by the magnetic field makes the vehicle float. . Electromagnets are installed on the bottom of the train and on the top of the bogies on both sides. Reaction plates and induction steel plates are respectively installed above the "I" rail and below the upper arm part to control the current of the electromagnet so that a gap of 1 cm is maintained between the electromagnet and the track. , let the attraction between the bogie and the train and the gravity of the train balance each other, and use the magnetic attraction to float the train by about 1 cm, so that the train is suspended on the track. This must precisely control the current to the electromagnet.
The driving principle of the suspension train is exactly the same as that of the synchronous linear motor. In layman's terms, the alternating current flowing in the coil located on both sides of the track can turn the coil into an electromagnet, and the train will start due to its interaction with the electromagnet on the train.
The N pole of the electromagnet at the head of the train is attracted by the S pole of the electromagnet installed on the track a little ahead, and is repelled by the N pole of the electromagnet installed on the track a little later. When the train moves forward, the direction of the current flowing in the coil is reversed, that is, the original S pole becomes N pole, and the N pole becomes S pole. The cycle alternates, and the train runs forward.
Stability is controlled by a guidance system. The "normal conduction magnetic suction" guiding system is to install a group of electromagnets specially used for guiding on the side of the train. When the train deviates left and right, the guide electromagnet on the train
Interacts with the side of the guide rail to create a repulsive force that returns the vehicle to its normal position. When the train is running on a curve or a ramp, the control system controls the current in the guide magnet to achieve the purpose of controlling the operation.
The idea of the "normal conduction" maglev train was proposed by German engineer Hermann Kemper in 1922. The working principle of the "normal conduction" maglev train and the track and the motor are exactly the same. Just arrange the "rotor" of the motor on the train, and lay the "stator" of the motor on the track. Through the interaction between the "rotor" and "stator", the electric energy is converted into forward kinetic energy. We know that when the "stator" of the motor is energized, the "rotor" can be driven to rotate through electromagnetic induction. When power is transmitted to the "stator" of the track, the train is pushed to move in a straight line just like the "rotor" of the motor through electromagnetic induction. The technical basis of the maglev train:
The maglev train is mainly composed of three parts: the suspension system, the propulsion system and the guidance system, as shown in the figure
3. In the vast majority of current designs, all three functions are performed by magnets, although a propulsion system independent of magnetism could be used. The technologies used in these three parts are introduced respectively below.
Suspension system: At present, the design of the suspension system can be divided into two directions, namely the normal conduction type adopted by Germany and the superconducting type adopted by Japan. In terms of levitation technology, it is the electromagnetic levitation system (EMS) and the electric levitation system (EDS). Figure 4 shows the structural differences of the two systems. Electromagnetic levitation system (EMS) is a suction levitation system, in which the electromagnet on the locomotive and the ferromagnetic track on the guide rail attract each other to produce levitation. When the conventional magnetic levitation train is working, firstly adjust the suspension of the lower part of the vehicle and the electromagnetic attraction of the guide electromagnet, and react with the windings on both sides of the ground track to float the train. Under the reaction of the guide electromagnet at the lower part of the vehicle and the track magnet, the wheel and the track are kept at a certain lateral distance, and the non-contact support and non-contact guidance of the wheel-rail in the horizontal and vertical directions are realized. The suspension gap between the vehicle and the driving track is 10 mm, which is guaranteed by a high-precision electronic adjustment system. In addition, since the suspension and guidance are actually irrelevant to the speed of the train, the train can still enter the suspension state even in the parking state.
Electric Suspension Systems (EDS) use magnets on a moving locomotive to generate an electric current on the rails. As the gap between the locomotive and the guide rail decreases, the electromagnetic repulsion will increase, and the resulting electromagnetic repulsion provides stable support and guidance for the locomotive. However, the locomotive must be fitted with something like wheels to effectively support the locomotive during "takeoff" and "landing" because the EDS cannot maintain the locomotive's suspension at speeds below about 25 mph. EDS systems have been further developed under low-temperature superconducting technology.
The main feature of the superconducting maglev train is the complete conductivity and complete diamagnetism of its superconducting components at a relatively low temperature. Superconducting magnets are composed of superconducting coils made of superconducting materials. Not only does it have zero current resistance, but it can also conduct a powerful current that cannot be compared with ordinary wires. This feature makes it possible to make small-sized and powerful electromagnets. .
The vehicle of the superconducting maglev train is equipped with on-board superconducting magnets and constitutes an induction power integration device.
The train's drive winding and suspension guiding winding are installed on both sides of the ground guide rail. The induction power integration equipment on the vehicle consists of power integration winding, induction power integration superconducting
The guide magnet consists of three parts. When the three-phase alternating current that is consistent with the vehicle speed frequency is supplied to the drive windings on both sides of the track, a moving electromagnetic field will be generated, thus generating magnetic waves on the train guide rail, and the on-board superconducting magnet on the train will be subjected to a The thrust, synchronized with the moving magnetic field, is what propels the train forward. Its principle is like surfing, the surfer stands on the crest of the wave and is pushed forward by the wave. Similar to the problems faced by surfers, superconducting maglev trains also have to deal with the problem of how to accurately control the peak movement of moving electromagnetic waves. To this end, a high-precision instrument for detecting the position of the vehicle is installed on the ground guide rail, and the three-phase alternating current supply mode is adjusted according to the information from the detector, and the electromagnetic waveform is precisely controlled so that the train can run well.
Propulsion system: The drive of the maglev train uses the principle of synchronous linear motor. The coil of the electromagnet supporting the lower part of the vehicle acts like the field coil of a synchronous linear motor, and the three-phase moving magnetic field drive winding inside the ground track acts as an armature, which acts like the long stator winding of a synchronous linear motor. From the working principle of the motor, it can be known that when the armature coil as the stator is powered, the rotor of the motor is driven to rotate due to electromagnetic induction. Similarly, when the substation arranged along the line provides three-phase FM and AM power to the drive winding inside the track, the bearing system together with the train is pushed to move in a straight line like the "rotor" of the motor due to electromagnetic induction. Therefore, in the suspended state, the train can completely realize non-contact traction and braking.
In layman's terms, the alternating current flowing in the coil located on both sides of the track can turn the coil into an electromagnet. Due to its interaction with the superconducting electromagnet on the train, it makes the train move. The train moves forward because the electromagnet (N pole) at the head of the train is attracted by the electromagnet (S pole) mounted on the track a little further ahead, and at the same time is attracted by the electromagnet (N pole) ) are rejected. As the train moves forward, the direction of current flowing in the coils is reversed. The result is that the original S-pole coil is now an N-pole coil, and vice versa. In this way, the train can continue to run forward due to the switching of the electromagnetic polarity. According to the vehicle speed, the frequency and voltage of the alternating current flowing in the coil are adjusted by the power converter.
China's domestic maglev train:
The world's first manned high-temperature superconducting maglev train developed by Southwest Jiaotong University in 2000
The "Century" and the "Future" manned normal temperature and normal magnetic levitation train developed later have received high attention and full affirmation from Hu Jintao, Jiang Zemin and other party and state leaders.
According to reports, as early as 1994, Southwest Jiaotong University successfully developed China's first low-speed maglev train capable of carrying people, but it was successfully operated under completely ideal laboratory conditions. In 2003, Southwest Jiaotong University completed the maglev train line in Qingshan, Chengdu, Sichuan. The maglev test track is 420 meters long. It is mainly aimed at tourists, and the ticket price is lower than the taxi fare. The world's first maglev train demonstration operation line - Shanghai Maglev Train, after completion, it will take only 6-7 minutes to travel more than 30 kilometers from Pudong Longyang Road Station to Pudong International Airport.
On the principle of magnetic levitation
Shanghai Maglev Train
Compared with today's high-speed trains, maglev trains have many incomparable advantages:
Because the maglev train runs on the track, there is no actual contact between the guide rail and the locomotive, and it becomes a "wheelless" state, so there is almost no friction between the wheel and the rail, and the speed is as high as several hundred kilometers per hour; the reliability of the maglev train It is large, easy to maintain, and low in cost. Its energy consumption is only half of that of a car and a quarter of that of an airplane. The noise is low. When the speed of the maglev train reaches more than 300 kilometers per hour, the noise is only 656 decibels, which is only equivalent to a person talking loudly. , which is smaller than the sound of cars passing by; because it is powered by electricity, it will not emit exhaust gas along the track, and has no pollution. It is a veritable green transportation tool.
References: Working Principles and Structural Features of High-speed EMUs/Dong Ximing/China Railway Press? 2007.12.1; Little Newton Science Museum--Electric and Magnetic Levitation Trains (Fourth Series) Guizhou Education Press, 2011.12.9
