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AC Filterless Flexible LCC HVDC With Reduced Voltage Rating of Controllable Capacitors

This paper presents a further significant development to the developed flexible LCC HVDC system with controllable capacitors [1], which can provide ac voltage/reactive power control [2]. The development involves the installations of fixed parallel capacitors at the valve side of converter transformer, which brings the following significant benefits: First, ac filter banks at the ac side of converter transformer are not needed as a better harmonic filtering performance can be achieved; second, significant reduction of the HVDC station land requirement (compared with traditional LCC HVDC), as the ac filters together with the switchgear can occupy over 50% of the HVDC station footprint; third, up to 50% reduction of the required voltage rating and more than 60% reduction of the capacitance of controllable capacitors for commutation failure elimination can be achieved while similar power system dynamic performance (ac voltage/reactive power control) compared with that in [1] can be demonstrated. Detailed analyses are presented to illustrate the effective commutation process and superb harmonic filtering performance with the fixed parallel capacitors. Selections of the component values are presented. Simulation results in real-time digital simulator are presented to verify the effectiveness of commutation failure elimination, power system dynamic performance, harmonic filtering performance, and show voltage/current stress of the fixed parallel capacitors.