The active DC filter in HVDC resolved by the multiple PWM inverters

Because the environmental demand is becoming stricter and stricter, more and more attention should be paid to the harmonic problem in high-voltage direct current (HVDC) transmission systems. This paper details the principle of active DC filter applied in the HVDC system. It is clearly stated that the contradiction between the switching frequency of power switch and the high frequencies of harmonics in the DC side of HVDC is the main bottle-neck for the application of ADF. Multiple pulse width modulation (PWM) can increase the equivalent switching frequency, decrease the stress on switch and improve the performance of ADF in high frequency. Both results of simulations and experiments validate the proposed multiple PWM.