Abstract：In a power distribution network, active power filters（APFs）and power factor correction（PFC）capacitors are frequently employed in a hybrid system to improve power quality. However, dynamic interactions may induce harmonic resonance in the weak grid, thereby compromising system stability. The placement of PFC capacitors significantly affects the associated oscillation mechanism, further undermining the effectiveness of existing damping methods. Moreover, the negative influence of existing methods has not been concluded. Therefore, this paper analyzed the main causes of harmonic resonance under different PFC capacitor placement configurations. Underlying mechanisms and resonance characteristics were thoroughly studied. Further, the negative influence of existing damping methods was evaluated. A novel load current feedforward（LCF）damping method was proposed to suppress resonance while preserving response speed. Firstly, a small-signal interaction model of the source-current-detected APF was established, accounting for the capacitor's dynamics. Then, the underlying mechanism of harmonic resonance was elucidated. The dynamic behavior of APF interacts with the system dynamics during harmonic compensation. Harmonic resonance is induced when these dynamics mutually excite each other on a similar time scale. The resonance-causing factors were identified in different cases of PFC capacitor placement. When capacitors are installed away from the load, an open-loop pole is introduced by the inductive line and PFC capacitors. As compensation frequencies are approached, the open-loop pole will be converted to a closed-loop right-half-plane pole, which induces resonance. In this scenario, the dominant devices include grid line, load, and PFC capacitors, and there is only a single resonance frequency. When capacitors are installed near the load, APF's compensation effect equivalently modifies the phase of the capacitor impedance. Therefore, line inductors resonate with PFC capacitors at all compensation frequencies. In comparison, the resonance is more severe, and the dominant devices are only the grid line and PFC capacitors. Moreover, the damping effect and negative influence of existing damping methods are evaluated. The results show that the selective harmonic compensation method achieves system damping across various cases. However, APF's filtering performance is substantially degraded. The harmonic virtual admittance method is applicable only to grid-side capacitor installations and exhibits limited damping effectiveness. Therefore, this paper proposes a novel load-current feedforward（LCF）damping method. Hybrid compensation prevents the generation of right-half-plane poles in a high-compensation-ratio system, thereby enabling damping control. Therefore, LCF suppresses resonance under different PFC capacitor placements. Besides, active damping is performed without deteriorating APF's dynamic/steady performance. An experimental platform was built to validate the resonance analysis and the proposed method. Experiments were conducted with different PFC capacitor values（50 μF to 250 μF）and installations. The results demonstrated the correctness of resonance mechanisms in various scenarios. Related waveform characteristics were also confirmed. The proposed LCF method was further validated. The method successfully suppressed oscillations in all scenarios, outperforming existing approaches. Furthermore, it maintained APF's performance, confirming the advantages.
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2026, Vol. 41 
