A DC side injected method for improving AC line condition applied in an 18-pulse converter system

In this paper, a new compensation strategy for receiving clean power is proposed with a conventional 18-pulse AC/DC rectifier scheme. In the proposed strategy, the compensation currents are injected at the dc side in front of the inter-phase transformer. The injected currents generated by a three-phase current-controlled inverter effectively improve the total harmonic distortion (THD) of the ac main currents. Compared to the conventional active filters set at the ac side, the three-phase inverter used in the proposed method operates with a rather low kVA rating. Moreover, the 18-pulse AC/DC rectifier draws nearly sinusoidal currents from the ac source under the operation of the proposed compensation strategy. A digital-signal-processor (DSP, TMS320F2812) based digital controller is employed to calculate the desired compensation currents and deals with the trigger signals needed for the three-phase inverter. Simulation of the proposed system is conducted for evaluation and a 1.5kW laboratory prototype is built for test as well. Both the simulated and the experimental results are presented to show the validity of the proposed compensation strategy.