Research on Negative Harmonics Suppression Results of Parallel Active Filter in the State of Under-compensation

Parallel active filters may exhibit negative harmonics suppression results in the state of under-compensation, which will cause harmonics amplification in the surrounding power grid. In this paper, the reason for negative harmonics suppression is analyzed based on the principle of active filtering technology. The electrical scenarios that are prone to negative harmonics suppression are summarized and classified. The concept of harmonic short-circuit ratio is proposed. When the harmonic short-circuit ratio falls on a specific position in the complex plane, there may be negative harmonics suppression, presented as harmonic voltage amplification, harmonic current amplification, or both amplification. Finally the rationality of the theoretical analysis is verified by simulation.