A Control Algorithm for Thyristor-Type Railway Substations System

Abstract

Recently thyristors are employed in railway substations instead of silicon rectifiers. The thyristors as rectifiers of substations would make it possible to control service voltage of power feeding line. Such a system would improve the quality of service power for trains and would reduce installed rating of substations.
This paper evaluates limits to reduce fluctuation of pantograph point voltage by controlling the feeding voltage every moment in an ideal power feeding system in which all substations are thyristor-type and have invertors to accept regenerated power. The control algorithm consists of
(1) distributed feeding voltage control, which compensates for the drop of feeding voltage by estimating related pantograph point voltages of the objective substation, by making use of voltage and current values of the substation and its adjacent substations, and (2) cross current control which prevents cross current generated by service voltage control. This control algorithm was evaluated by computer simulation using an electric circuit model which consists of branches and nodes for the feeding system. The simulation showed that the proposed control algorithm reduces 11-23V of deviation in minimum pantograph point voltage and 10-20V in average pantograph point voltage with the comparison of conventional system. The installed rating of substations reduces 5-20%, on condition that the control of pantograph point voltage is combined the demand control and the current of root mean square control.