Application of the hottest frequency converter in

2022-08-15
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The application of frequency converter in maglev train

1 introduction

maglev train uses the magnetic force of electromagnet to support bogie and car body, so that the parts supporting the vehicle do not directly contact with the track, reducing the friction resistance and vibration noise of operation, which is suitable for high-speed intercity transportation and low-speed passenger transportation in cities. Because there is no mechanical contact, it cannot adopt the driving mode of transmitting traction power by the friction between wheel and rail in the traditional wheel rail system. It can only use linear motor to directly drive the bogie with magnetic force. Therefore, as long as the driving force of the linear motor is large enough, the vehicle can run on any ramp in theory, and the climbing capacity of the current maglev train can reach 80 ~ 100 ‰

because the high-speed maglev train has two types of Maglev: the constant conduction suction type and the superconducting repulsion type, they both choose the linear synchronous motor, which is expected to take 10-20 years for the popularization of Changding. The power supply is placed on the ground, and there is no need for current rail power supply, so the operation is more reliable. The stator armature of this kind of motor is installed on the track, and the three-phase winding of the long stator of the motor is powered by the switch cabinet on the ground, and the vehicle is driven by relay. This linear transmission structure is called the long primary and short secondary motor drive mode, and the traction converter can be installed on the ground. The normally conductive or superconducting magnetic poles in the suspension electromagnet supporting the vehicle constitute the secondary synchronous magnetic poles of the motor

the maglev train also has a medium and low speed constant conduction suction type maglev type suitable for urban rail transit. Because it can use the current rail for power supply, it uses a linear induction motor drive. Since the armature of the motor is installed on the bogie of the vehicle, and the secondary reaction plate is installed on the track, this direct fault elimination line transmission structure is called the short primary and long secondary motor drive mode, and the traction frequency converter can be installed in the vehicle

the driving characteristics of various maglev trains will be introduced below

2 normally guided high-speed maglev train

normally guided high-speed maglev train has a research history of more than 30 years. Three generations of vehicle tests with different structures have been carried out on Emsland test line in Germany, and has also passed the operation acceptance of the German Ministry of transport. Although the vehicle and bogie have been improved to varying degrees, the structure of the long stator linear motor has not changed

the levitation electromagnet of the normally conductive high-speed maglev train selects the convex structure, and the winding connection mode makes the magnetic poles form the distribution of N and S poles, that is, it becomes the secondary magnetic pole of the linear synchronous motor. Because the vehicle needs to turn and climb when running, the suspension electromagnet is divided into 3M long modules, which are evenly arranged under the long stator track. On the Shanghai high-speed maglev vehicle, seven suspension modules are installed on each side to make rubber raw materials from sugar, and one is also overlapped between the two carriages, making the suspension electromagnet an electromagnetic sliding plate type. In order to ensure that the vehicle has lateral guiding force, the bogie is also equipped with a guiding electromagnet with double U-shaped iron cores. The schematic diagram of the bogie with suspension, guiding and driving functions is shown in Figure 1

it can be seen from Figure 2 that the long stator core of the motor is the same as that of the conventional linear motor, except that only one wire is placed in each stator slot, which is distributed according to the single wave winding. The long stator is composed of a 1.032m long laminated iron core spliced in series and fixed on the road beam respectively. The electric pole distance of the long stator is 0.258m, that is, the power current changes by one cycle, and the moving distance of the air gap traveling wave is 0.516m. Since the motor is a linear synchronous motor, if the motor operates at a speed of 400km/h, the frequency of the three-phase power supply voltage should reach 215hz. It can also be seen from the figure that the secondary magnetic pole of the motor is the suspension electromagnet supporting the vehicle body, and the pole distance between the two convex magnetic poles is approximately equal to the stator traveling wave pole distance, one by one. The synchronous conditions during operation shall be considered for the suspension electromagnet. Six pairs of poles form a suspension module, which is installed on the bogie respectively. The spacing of each suspension module shall also meet the corresponding relationship of synchronous poles, as shown in Figure 3

during vehicle operation, the magnetic pole in the suspension module maintains an air gap of about 8mm with the stator core, which is controlled by the suspension control system. Because the motor operates in a synchronous state, the power factor and efficiency of the motor body are very high. Like the speed regulation mode of rotating synchronous motor, linear synchronous motor also uses the control mode of frequency conversion

voltage transformation, and the control strategy is traction (equivalent to torque control) closed-loop control. The position and speed during vehicle operation are calculated by the measuring elements on the bogie by measuring the slots of the long stator and the time of running a slot, and finally transmitted to the variable frequency power station through the wireless communication system on the vehicle to realize the closed-loop control of motor operation

the magnetic pole in the suspension module is also wound with a linear generator winding, and its pole distance is the same as the cogging width of the long stator. It uses the magnetic density change caused by the cogging effect when the vehicle is running to generate power, and after rectification and DC DC conversion, it charges the on-board equipment and battery. Of course, when the vehicle is stationary and running at low speed, the on-board equipment is still powered by the battery. The linear motor can only supply power after the speed reaches 70km/h. therefore, the high-speed maglev train does not need to use the current rail to provide the power supply of the whole vehicle

GTO is still used as the power element of the frequency converter on Shanghai high-speed maglev line, and the single machine power is 7.5mva. In the current localization research project, IGCT power components are being tested and used. The three-phase power module adopts a three-point topology, as shown in Figure 4. The maximum output voltage of each phase is 4310v. In order to ensure the motor voltage under high-speed conditions and balance the impedance voltage drop of the transmission cable, the frequency converter directly supplies power to the cable during low-speed operation. When the frequency rises to about 70Hz, the frequency converter switches from directly supplying power to the three-phase cable to the step-up transformer, and changes to using the transformer to supply power, so as to meet the requirements of variable frequency and voltage supply

high speed magnet is a device easy to block and leak. The long stator motor of floating train adopts the mode of section power supply, as shown in Figure 5. Each section depends on vehicles

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