Optimal controllers design in indirect current control system of active DC-Traction substation

Abstract

This paper is focused on the optimal design of the controllers in an active filtering and regeneration system for DC railway traction substation. The control algorithm of the system is based on the indirect current control method and uses two closed loops with PI controllers: an outer one for the DC voltage control and the other for the grid current control. In order to perform the energy regeneration function during the braking process, the filtering and regeneration system is connected to the power grid by a regeneration transformer. Thus, comparative with the direct coupling and direct current control technique, the transfer functions of the system are different. The DC voltage controller is tuned in accordance with the Modulus Optimum criterion and the grid current controller is tuned by the Symmetrical Optimum criterion. In order to verify the operation of the system and assess its performance, detailed computer simulation studies were conducted using the Matlab/Simulink package. The practical case of the 12-pulse parallel rectifier in the traction substation is taken into consideration. The simulation results are presented to prove the validity of the proposed procedure of the controllers' design.