Review on Capacity Optimization of Traction Transformer for High-Speed Railway

In electrified railways,traction load not only fluctuates between peaks and valleys,but also has a situation of low utilization rate of average load throughout the day and short overload.The traction transformer selects the capacity with the peak load as the demand boundary,which will cause the capacity utilization rate to be low and even lead to the economic decline of the traction power supply system.This article summarizes the existing configuration methods for capacity optimization of traction transformer.Then under the conditions of energy storage and new energy access to traction power supply system,the three aspects are described as follows.Firstly,the energy storage device is connected to the system,which can pull the capacity of traction transformer to achieve peak shifting and valley filling.Then,the possibility of integrated configuration of new energy and traction power supply system to optimize the capacity of traction transformer and the methods of optimal configuration of traction transformer capacity by using new energy such as wind and light are summarized.Finally,this paper discusses the current structure of new energy access to traction power supply system,and it looks forward to the feasibility of new energy access to traction power supply system cooperating with energy storage devices to optimize the capacity of traction transformer.

Difficulties in Parameters Identification of Traction Transformer Multi-port Equivalent Scheme with Hidden Construction Defect

While modeling a power supply system for an electric railway traction, knowing equivalent circuits of locomotives supplied this way is an essential issue. In alternating current traction, it is important to diagnose inter alia processes taking place in transformers installed on electric vehicles. This article presents specific phenomena occurring during the work of mono-phase, multi-winding, multisystem （systems AC： 50 Hz, 16.7 Hz） laboratory traction transformer. It also shows difficulties encountered during the process of identifying multi-port equivalent scheme＇s elements of the described device, in which a construction defect occurs.

Low-Frequency Stability Analysis of Power Electronic Traction Transformer Based Train-Network System

Power electronic traction transformers(PETTs)will be increasingly applied to locomotives in the future for their small volume and light weight.However,similar to conventional trains,PETTs behave as constant power loads and may cause low-frequency oscillation(LFO)to the train-network system.To solve this issue,a mathematical model of the PETT is firstly proposed and verified based on the extended describing function(EDF)method in this paper.In the proposed model,the LLC converter is simplified to an equivalent circuit consisting of a capacitor and a resistor in parallel.It is further demonstrated that the model can apply to various LLC converters with different topologies and controls.Particularly,when the parameter differences between cells are not obvious,the PETT can be simplified to a single-phase rectifier(i.e.,conventional train)by equivalent transformation.Based on the model of PETT,the system low-frequency stability and influential factors are analyzed by using the generalized Nyquist criterion.Lastly,the correctness and accuracy of theoretical analyses are validated by off-line and hardware-in-the-loop simulation results.

Development of HTS Transformers and a 10 kVA HTS Transformer Prototype Design

With the improvement of high temperature superconductor （HTS） practical performance, research and development concerning the applications of HTS transformers have been progressed actively worldwide. This paper provides a comprehensive summary on various HTS transformers, and studies the design of a single-phase 10 kVA （220V/24V） HTS transformer prototype to verify HTS for practical transformer applications.

Solid-state transformer-based new traction drive system and control

A new type of traction drive system consisting of solid-state traction transformer （SSTT）, inverter unit, auxiliary inverter, traction motor and other key components is built in order to suit the demand of developing the next-generation electric traction system which will be efficient and lightweight, with high power density. For the purpose of reducing system volume and weight and improving efficiency and grid-side power quality, an efficient SSTT optimized topology combining highvoltage cascaded rectifiers with high-power high-frequency LLC resonant converter is proposed. On this basis, an integrated control strategy built upon synchronous rotating reference frame is presented to achieve unified control over fundamental active, reactive and harmonic components. The cartier-interleaving phase shift modulation strategy is proposed to improve the harmonic performance of cascaded rectifiers. In view of the secondary pulsating existing in a single-phase system, the mathematical model of secondary power transfer is built, and the mechanism of pulsating voltage resulting in beat frequency of LLC resonant converter is revealed, so as to design optimum matching of system parameters. Simulation and experimental results have verified that the traction system and control scheme mentioned in this paper are reasonable and superior and that they meet the future application requirements for rail transit.