A DC-link Oscillation Suppression Strategy in Metro Traction Drive System Based on Virtural Damping Resitor

The negative input impedance with the constant power load causes dc-link voltage and current oscillations in the metro traction drive system (MTDS) and weakens the stability of the system. In this digest, a small signal model of the simplified equivalent circuit of the MTDS is established, and the oscillation mechanism is analyzed. This digest proposes an active damping method based on the virtual damping and pseudolinear enhanced phase-locked loop (PL-EPLL). The stabilization scheme is realized by three parts: 1) the estimation of the dc-link voltage variation; 2) the generation of damping power; and 3) generation of stator current command. The dc-link voltage variation is firstly estimated by the PL-EPLL. And damping power is achieved by virtual damping resister in series with line inductor. Based on the inverter power control, q-axis current is obtained. Simulation results show that the active damping method effectively suppresses dc-link oscillation and improves the stability of MTDS.