Research On Four-Quadrant-Soft-Switch Of Maglev Chopper

Maglev train is a new type of vehicle on railway track. It levitated over the rails by electromagnetism suction or repulsion, the body of the train does not touch the ground, As a perfect vehicle on land, maglev train is characterized by high velocity, less energy consuming, lower noise, safety and comfort. Therefore, it is potential modern transportation vehicle in the future. The current maglev train suspension systems include two basal structures, EMS and EDS. The suspending power of EMS is complete provided by electromagnet, therefore, energy loss cannot be ignored, and the enlargement of gap is limited and a higher rail precision is required. Aiming at the problems, this dissertation designs hybrid electromagnetic suspension(EMS) systems, it is a combination of permanent magnet and electromagnet, static counterbalance is provided by permanent magnet and dynamic counterbalance is provided by electromagnet when it suspend steadily. The electromagnet not only provided magnetism, but also suspension, maglev chopper not only provided positive current, but also provided negative current, so use four-quadrant maglev chopper. There are obvious advantages to apply soft-switching technology to maglev, it has little switching losses and the efficiency of the chopper can be improved.Firstly, this paper introduces the characters of basic components of four-quadrant maglev chopper which including the character of freewheeling diode, the character of IGBT, the drive and protection of IGBT. Secondly, ordinary introduces the sort of soft-switching, design four-quadrant maglev chopper of zero-voltage-switching PWM converter and zero-voltage-transition PWM converter based on soft-switching and maglev chopper, analyzes the characteristics of soft-switching chopper and design its parameters detailedly. Secondly, modeled and simulated the converter structures by PSpice and compared their advantages and disadvantages. The result proves that the soft-switching converter can improve the switch characteristic of main circuit. It also can decrease the switch stress and current stress of switch equipment. Lastly, modeled and simulated the transient response of load, the result isconsistent with expectation, and has a good speciality of transient response.The main-switches of the zero-voltage-switching PWM soft-switching chopper have zero-voltage turn-on and turn-off totally, so it has little switching losses. The realization of the ZVS has no concerned with the attribute of load. But, as the chopper provides the ZVS condition with an assistant switch, which work in hard switching, it has some losses in switching even using a snubber network. There is another more, the snubber can be resonant with the inductor, that brings on a huge spike on the source voltage. The zero-voltage-transition soft-switching PWM soft-switching chopper realizes the zero-voltage transform of main switch, the working conditions of switch improve greatly.