Normal Conducting Low-speed Maglev Train, Suspension Chopper

Maglev chopper is the key component of maglev, and the concentrative embodiment of modern power electronics. This paper mainly studies on three different-type maglev choppers : traditional two-quadrant H-bridge maglev chopper, tri-level maglev chopper and zero transition soft-switching maglev chopper, that is basic on the study object of low and middle speed EMS maglev.Firstly, this paper introduces the characters of basic components of maglev chopper which including the character of freewheeling diode, the character of IGBT, the drive and protection of IGBT and the character of load.The traditional tow-quadrant H-bridge maglev chopper which has been long used in practice is provided with the merit of simple structure and the reliable quality. But its switching losses are serious , efficiency is low, hot is serious and the efficiency is less than 60% when suspend normally; as the voltage and current spike is large when engage the switching action, that you need to add RCD snubber, and the EMI is serious; it also makes countercurrent spike to power supply which is tend to cause the losses of power supply and filtering capacitance. With the development of power electronics, it is necessary to make use of new technology to reform traditional maglev chopper.Contrapose to the disadvantage of traditional maglev chopper whose output current ripple becomes larger with the increase of power supply voltage, we have worked out tri-level maglev chopper whose current ripple is basically has nothing to do with the power supply voltage. The tri-level maglev chopper is the same with the traditional one, except to stagger drive signal of the 2 IGBTs for 180° .Thus, every time switching action, the concerned switch elements will be reduced from 4 to 2, and the switching losses are reduced to half of the traditional one, the efficiency of normal suspension improve to 70%. Furthermore, there will be no reverse spikes toward power supply when the invariable current being output.There are obvious advantages to apply soft-switching technology to maglev chopper. This paper theoretically introduces how to apply quasi-resonant converter, multi-resonant converter, zero switching converter and zero transition converter to the maglev chopper, and realizes a zero transition soft-switching maglev chopper based on the traditional maglev chopper by colligating factors in all aspect. On levitation control the zero transition soft-switching chopper is entirely the same with the traditional chopper , without any reduce in control capability. Furthermore, it realizes the zero-voltage transform of main switch, the working conditions of switch improve greatly, the efficiency of normal suspension improves to 90%, and the EMI is improved obviously too. In a word, zero transition soft-switching chopper is a perfect maglev chopper.With the development of modern power electronics, maglev chopper should be perfect incessantly. In the future, we should step forward to study the integration method of maglev chopper, the high input voltage maglev chopper and the issue of complete soft-switching in large range and the new control way so as to improve the adjust speed of current.