Feasibility Study of AC- and DC-side Active Filters for HVDC Converter Terminals

The active filter concepts are compared with the passive filters, both on the dc-side and the ac-side of the HVDC terminal. The Dickinson terminal of the CU HVDC transmission line is used as the basis for this study. Based on this study, the following conclusions are reached for the dc-side and the ac-side active filters: DC-Side Active Filters 1. The active filter is designed for filtering of the three dominant harmonics at the 12th, the 24th and the 36th harmonic frequencies. Computer simulations indicate that these three dominant harmonics can be attenuated to less than 1 % at the transmission line terminal, compared to the harmonic voltages produced by the converter. It should be noted that any other harmonic frequencies which may be troublesome can be included in the injection current to filter these harmonics. Higher order harmonics have small amplitudes; hence, the required total injection current and the total kVAs of the components in the active filter are not changed significantly by adding higher order harmonics. 2. The effective cost of the dc-side active filter is estimated to be 186 k$, which also includes the present worth of the additional 17.3 kW losses in the active filter, as compared to the passive filter. The active filter costs is lower by only 27 k$, as compared to the passivefilter cost of 213 k$. Given the uncertainty in the cost estimates, both filters are comparable in terms of cost.