A system-level harmonic mitigation method for HVDC systems – A practical case study

• The system-level harmonic mitigation method proposed in this paper can significantly reduce the number and the cost of harmonic mitigation. • Compared with passive filters, using active filters for distributed harmonic mitigation can reduce the number of filters, which is attractive in practical implementation. • The selection of passive filter used for resonance suppression directly affects the optimization results of distributed harmonic mitigation and it is challenging to infer either the ST filter or the C-Type filter leads to better results. • Taking into account both capital and installation costs, a C-Type filter for resonance suppression combined with active filters for harmonic mitigation could be the optimal choice. In recent years, non-characteristic harmonic resonance was observed in several high-voltage direct current (HVDC) systems in China. Intuitively, additional filters can be installed to mitigate the resonance. However, such a solution does not prevent the harmonic penetration from nearby substations. As a result, the harmonic issue in HVDC systems cannot be well addressed. In view of the above, this paper presents a system-level harmonic mitigation method. The basic idea is to address the harmonic pollution by mitigating harmonic sources and harmonic resonance simultaneously. To achieve this goal, candidates of filters to suppress the resonance at the HVDC station are investigated first. Then, an optimal filter design problem is established to determine the location, type and capacity of multiple filters that can achieve the system-level harmonic mitigation with the minimum cost. Particularly, an improved particle swarm algorithm with adaptive mutation operators is tailor-designed to solve the proposed optimization problem. Finally, the proposed method is applied to address the harmonic problem faced by a real-life HVDC system in eastern China. The result demonstrates that compared with the solutions solely mitigating harmonic sources or resonance, the method presented in this paper is more cost-effectiveness.