A maglev train is a train that is driven by magnetic levitation (i.e., the attraction and repulsion of magnets). Because the magnetic force of its track makes it float in the air, it does not need to touch the ground when walking, so its resistance is only the resistance of the air. The maximum speed of the maglev train can reach more than 500 kilometers per hour, which is faster than the more than 300 kilometers of the wheel-rail high-speed train. Research on magnetic levitation technology originated in Germany. As early as 1922, German engineer Hermann Kemper proposed the principle of electromagnetic levitation and applied for a patent for a maglev train in 1934. After the 1970s, as the economic strength of the world's industrialized countries continued to strengthen, in order to improve transportation capabilities to meet the needs of their economic development, developed countries such as Germany and Japan began to plan the development of maglev transportation systems.
Magnetic levitation trains are mainly composed of three parts: levitation system, propulsion system and guidance system. Although propulsion systems that have nothing to do with magnetism can be used, in most current designs, the functions of these three parts are the same. Done by magnetism. The technologies used in these three parts are introduced below.
Suspension system
: The current design of suspension systems can be divided into two directions, namely the normally conducting type used in Germany and the superconducting type used in Japan. In terms of suspension technology, it is electromagnetic suspension system (EMS) and electric suspension system (EDS). Figure 4 shows the structural differences between the two systems. Magnetic levitation train
Electromagnetic levitation system
(EMS) is an suction levitation system. The electromagnets on the locomotive and the ferromagnetic tracks on the guide rails repel each other to create levitation. When a normally guided maglev train works, the electromagnetic repulsive force of the suspension and guide electromagnets at the lower part of the vehicle is adjusted first, and the magnets react with the windings on both sides of the ground track to levitate the train. Under the reaction of the guide electromagnets at the bottom of the vehicle and the track magnets, the wheels and the tracks are kept at a certain lateral distance, achieving contactless support and contactless guidance of the wheel rails in the horizontal and vertical directions. The floating gap between the vehicle and the track is 10 mm, which is ensured by a high-precision electronic adjustment system. In addition, since levitation and guidance are actually independent of the train's running speed, the train can still enter the levitation state even when it is stopped.
Electric Suspension System
(EDS) uses magnets on a moving locomotive to generate electric current on the guide rails. Since the electromagnetic repulsion force will increase when the gap between the locomotive and the guide rail is reduced, the resulting electromagnetic repulsion force provides stable support and guidance for the locomotive. However, the locomotive must be equipped with a wheel-like device to effectively support the locomotive during "takeoff" and "landing" because EDS cannot maintain levitation when the locomotive speed is below approximately 25 mph. EDS systems have achieved greater development under low-temperature superconducting technology. The most important feature of the superconducting maglev train is the complete conductivity and complete diamagnetism of its superconducting elements at very low temperatures. Superconducting magnets are composed of superconducting coils made of superconducting materials. They not only have zero current resistance, but can also conduct powerful currents that are simply unmatched by ordinary wires. This characteristic allows them to be made into small-sized and powerful electromagnets. . Linear Motor Principle Illustration
The vehicle of the superconducting maglev train is equipped with on-board superconducting magnets and constitutes induction power integrated equipment, and the drive windings and suspension guide windings of the train are installed on both sides of the ground guide rails. Induction power integrated equipment consists of three parts: power integrated winding, induction power integrated superconducting magnet and suspended guided superconducting magnet. When a three-phase alternating current with a frequency consistent with the speed of the vehicle is provided 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. At this time, the on-board superconducting magnet on the train will be affected by a The thrust that is synchronized with the moving magnetic field is what propels the train forward. The principle is like surfing, where the surfer stands on the top of the wave and is propelled 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 motion of moving electromagnetic waves.
To this end, high-precision instruments for detecting the position of vehicles are installed on the ground guide rails. The three-phase alternating current supply mode is adjusted based on the information from the detectors, and the electromagnetic waveform is accurately controlled so that the train can run well.
Propulsion system
: The drive of the maglev train uses the principle of synchronous linear motor. The support electromagnet coil in the lower part of the vehicle acts like the excitation coil of the synchronous linear motor. The three-phase moving magnetic field drive winding on the inside of the ground track acts as the armature, which is like the long stator winding of the synchronous linear motor. From the working principle of the motor, we can know that when the armature coil as the stator is powered, the rotor of the motor is pushed to rotate due to electromagnetic induction. Similarly, when the substations arranged along the line provide three-phase frequency modulation and amplitude modulation power to the drive windings on the inside of the track, the load-bearing system together with the train is pushed into linear motion like the "rotor" of a motor due to electromagnetic induction. Therefore, in the suspended state, the train can completely realize non-contact traction and braking.