Research Of New Energy Feedback Traction Rectifier System For Urban Rail Transit

A sustainable development of urban transport systems is a city's comprehensive transportation system which combines the travel-friendly modes including land resources, energy, environment and housing together. Urban Rail Transit (referred to as URT), as a low energy consumption, low pollution, high efficiency mode of transport, has been widely used in large and medium cities around the world.There are two problems concerning the current power supply pattern of urban rail transit. The first problem is no effective use of braking energy. The second problem is that, as the current urban rail transit power supply system usually uses thyristor and diode for rectifier, this rectifier is equal to inject a large number of harmonics and reactive power into the power grid, which would lead to power gird current distortion, and would even affect the power quality of power system seriously.This paper presents a new energy feedback traction rectifier system for urban rail transit, by puting a small-capacity four-quadrant converter in parallel with the existing thyristor, diode rectifier. The converter includes two operation modes, energy feedback and active power filter (APF). When there exsits braking energy which needs feedback, the four-quadrant converter would operate in the inverter mode, in order to transfer the power back to the power grid, as well as maintain the power factor close to-1 in grid side. In other time, it would operate as APF to improve the power grid current harmonics and power factor characteristics.To research on the rectifier system, this paper details the four-quadrant converter mathematical model, parameter design principles, current control techniques and grid current optimization techniques. And parameters design, two current control techniques, two current optimization techniques were simulated with the results displaying in the paper. Also the converter simulation operation in four-quadrant has been done. Second, the paper also details the harmonic current extraction technique and current control principle of APF. The simulations including a single APF under a variety of different conditions, the APF's parallel operation with 12/24-pulses rectifier and multiple APF in series have been done in the paper, too.Based on the foregoing theoretical description and simulation, the paper constructs a new energy feedback traction rectifier system simulation model. Under this model, the simulations of the energy feedback, APF and modes transfer have been done. Simultaneously, four-quadrant converter capacity problem's simulation and analysis have been done, too.Based on the theoretical study and simulation before, the paper finished the hardware and software design, built the new energy feedback traction rectifier experiment system. In this platform, many experiments concerning different operation conditions based on the four-quadrant converter and APF theory have been done. Eventually, the paper displays the energy feedback, APF and the two modes operation transfer experiment results. These results demonstrate that the four-quadrant converter and APF's research and analysis are correct. These also show that the new energy feedback traction rectifier system is feasible in the future urban rail power supply system.