A Novel Co-Phase Power-Supply System Based on Modular Multilevel Converter for High-Speed Railway AT Traction Power-Supply System

The existing problems of the traction power-supply system (i.e., the existence of the neutral section and the power quality problems) limit the development of railways, especially high-speed railways, which are developing rapidly worldwide. The existence of the neutral section leads to the speed loss and traction loss as well as mechanical failures, all of which threaten the fast and safe operation of the train and the system. Meanwhile, the power quality problems (e.g., the negative sequence current, the reactive power, and the harmonic) can bring a series of problems that cannot be ignored on the three-phase grid side. In response, many researchers have proposed co-phase power-supply schemes to solve these two problems simultaneously. Given that the auto-transformer (AT) power-supply mode has become the main power-supply mode for the high-speed railway traction power-supply system, it has a bright future following the rapid development of the high-speed railway. In addition, there is no co-phase power-supply scheme designed for AT power-supply mode in the existing schemes. Therefore, the main contribution of this paper is to propose a specifically designed power-supply mode more suitable for the AT, as well as to establish the control systems for the rectifier side and the inverter side. In addition, for the proposed scheme, the operation principle is analyzed, the mathematical model is built, and the control system is created, and its functionality is verified by simulation, and its advantages are compared and summarized finally. The result proves that it can meet functional requirements. At the same time, compared with the existing co-phase power-supply scheme, it saves an auto-transformer in terms of topology, reduces the current stress by 10.9% in terms of the current stress of the switching device, and reduces the power loss by 0.25% in terms of the entire system power loss, which will result in a larger amount of electricity being saved. All of this makes it a more suitable co-phase power-supply scheme for the AT power-supply mode.

Effects of the Power Supply Mode and Loading Parameters on the Characteristics of Micro-Arc Oxidation Coatings on Magnesium Alloy

Micro-arc Oxidation (MAO) is a technology for non-ferrous metal surface treatment through growth ceramic coating in situ. To determine the influence of the power supply mode and the loading parameters on the film forming of magnesium alloy micro-arc oxidation processing, the different power supply modes of pulsed direct current DC, pulsed bipolar current (BC) and the pulsed with a discharge loop current (DLC) was used with MAO technology on the AZ91D magnesium alloy. The power load parameters were optimized. The average energy consumption was calculated. Results showed that the role of the negative voltage in the bipolar pulse power supply is to restrain the large arc tendency. Under the pulse power supply with a discharge loop, the current and energy consumption decreases with the increase of the discharge resistance at the same pulse parameters. The big arc phenomenon can be effectively avoided and the impact of load capacitance could be effectively avoided by using the pulse power supply with a discharge loop. Moreover, the processing of the micro-arc oxidation is stable, the arc point is uniform, the surface of the film is smooth, the hole is uniform and the coating is dense, and the film efficiency is improved effectively.