A high performance control strategy for three-level NPC EMU converters

A high performance control strategy for a three-level neutral-point-clamped (NPC) converter employed in electric multiple units traction drive system is proposed in this paper. The strategy is based on a multiple frequency tuned quasi-proportional resonant (PR) controller for the AC current loop. A notch filter is used in the DC bus voltage loop to filter out the ripple affecting the controller. A feed-forward loop is included in the inner current control loop to deal with AC power supply disturbances. The impact of the quasi-PR controller parameters on its performance is investigated through frequency-domain analysis. The generation of the low-order harmonics of the line current caused by the DC-link voltage fluctuations is analyzed from the control point of view. Simulation results presented in the paper validate that the proposed control strategy provides a better current tracking performance and a lower current harmonic content when compared with other more conventional control strategies.