Cut-through type cophase power supply system for cascaded input-free and output-free transformers

Abstract

The invention discloses a cut-through type cophase power supply system for cascaded input-free and output-free transformers. The system is mainly composed of a power electronics conversion device with three phases connected in parallel after each being cascaded with one or more AC-DC-AC converters of single phase-single phase structures. The three phases of the cascaded power electronics conversion device are directly connected with a traction contact net after being connected in parallel. The single phase-single phase AC-DC-AC converters can bear high voltage levels through the multi-module cascaded structure; meanwhile, the voltage levels output by converters are improved; thus, input and output transformers can be omitted, power required for locomotive loads is borne by the three phases on average, and energy can flow in two directions. Due to the fact that amplitude values, phases and frequencies of the output voltage can be controlled, contact nets close to substations can be directly connected to form a cut-through traction power supply network. By means of the cut-through type cophase power supply system, the input and output transformers of the traction substations can be omitted, the defects that the transformers in the traction substations are large in size, heavy in weight, troublesome to overhaul and high in manufacturing cost are overcome, the capacity of the traction substations is easily improved, and the running cost of the substations is reduced.

Description

technical field [0001] The invention relates to a cascaded three-phase-single-phase converter device, especially its application in a through-type in-phase power supply system without excessive phase intervals. Background technique [0002] At present, electrified railways in many countries in the world basically adopt a three-phase-two-phase (out-of-phase) power supply mode, and its structure is as follows figure 1 shown. The substation takes power from the three-phase power grid through the traction transformer and then divides it into two power supply arms to output power for the traction network. Since the voltage phase, amplitude and frequency of the power supply arms are difficult to be completely consistent, electric phase splitting must be set between the power supply arms. With the development of high-speed and heavy-haul railways, the following problems will become more prominent: [0003] (1) Power quality problem: The single-phase load of the existing out-of-p...

AI Technical Summary

Problems solved by technology

[0003] (1) Power quality problem: The single-phase load of the existing out-of-phase traction power supply system will generate negative sequence current when it is reflected on the three-phase grid, resulting in unbalanced three-phase voltage, and the increase of traction power of high-speed and heavy-duty trains will cause negative sequence problems become more and more prominent, and at the same time, there are still problems such as reactive power and harmonics

(2) Over-current phase separation problem: the existing traction power supply system must have electric phase separation, and the electric phase separation device has a complex structure and low reliability, which is the weak link and accident-prone point of the traction power supply system

(3) Power supply capacity problem: In the different-phase power supply system, the traction network is equipped with an electric phase separation device, and it is difficult to achieve mutual support between traction substations. The configured capacity of the electricity is difficult to be fully utilized, and the power supply capacity is limited

However, the system interface voltage, capacity and performance are limited, and the input still needs to match the three-phase step-down transformer

The three-phase step-down transformer has a large volume and quality, and the cost is high, which limits the power supply capacity and construction capacity of the substation

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