Abstract
The share of voltage source converter (VSC) technology is increasing in conventional power systems, and it is penetrating into specific transportation systems such as electric vehicles, railways, and ships. Researchers are identifying feasible methods to improve the performance of railway electrification systems (RESs) by utilizing VSC-based medium-voltage direct current (MVDC) railways. The continuous motion of electric trains makes the catenary resistance a variable quantity, as compared to the traction substation (TSS), and affects the current-sharing behavior of the system. A modified droop control technique is proposed in this paper for VSC-based MVDC RES to provide more effective current-sharing while maintaining catenary voltages above the minimum allowable limit. The droop coefficient is selected through an exponential function based on the ratio between the concerned TSS current and the system average current. This enables small adjustments of droop values in less concerning marginal current deviations, and provides higher droop adjustments for large current deviations. Meanwhile, the catenary voltages are regulated by considering the voltage data at the midpoint between two TSSs, which experiences the lowest voltages owing to the larger distance from the TSSs. The proposed techniques are validated via simulations and experiments.
Highlights
In recent years, the railway transportation system has become a rapid and reliable means of traveling
The results reveal a better current-sharing under the proposed droop control method when the trains are unequally spaced, in conjunction with an increased efficiency owing to the higher catenary voltages
This paper provides a modified droop control scheme for the voltage source converter (VSC)-based medium-voltage direct current (MVDC) railway electrification systems (RESs), with an objective of obtaining better current-sharing among the traction substation (TSS) in conjunction with acceptable catenary voltages
Summary
The railway transportation system has become a rapid and reliable means of traveling. Certain fundamental concepts and the framework of the VSC-based medium-voltage direct current (MVDC) RES for high-speed railways are available in [2, 11,12,13] Such MVDC systems consist of several VSC-based traction substations (TSSs) along the catenary line, providing energy to the system according to the requirement of the train loads. The major contributions of the paper can be summarized as follows: 1) Analysis of the effects of the dynamic traction line resistances caused by moving train loads, on the current-sharing behavior of VSC TSSs; analysis of the catenary voltage deviation caused by the conventional droop. This is achieved without compromising on the maximum permitted deviation in the voltage at critical points along the catenary
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