System adaptive AC filter for a line commutated converter high voltage DC transmission system

This paper proposes a novel AC filter system for a line commutated converter high voltage DC (LCC-HVDC) transmission system. Through the coordination of the hybrid active power filters (APF) and the existing reactive compensation devices, the proposed filter system can not only enhance the suppression performance for LCC-HVDC harmonics, but also optimize the AC yard layout with reduced reactive power subbanks, reducing the cost of HVDC projects. The novel filter system adopts a serial passive resonance topology obtained by careful comparison of different APFs. A proper control scheme is then designed integrating the control strategy of the APF and impedance characteristics of the HVDC system, which is able to realize harmonic suppression and dynamic reactive power support simultaneously. In addition, a novel self-adaption digital low-pass filter algorithm is presented, which is used in the APF harmonic detecting step, enhancing both high precision and fast dynamic response. On the basis of a real HVDC project, the advantages of proposed filter system in harmonic suppression, reactive power regulation, and sub-banks reduction are simulated and demonstrated.