Compensation characteristics of parallel active filters

This paper presents different compensation characteristics that can be applied in the control of parallel active filters or combined systems for parallel active and passive filters, in both cases considering the active part working as a current source in parallel with the power system. These control strategies, with their base in p-q theory and its extension, allow the compensation of harmonic currents, harmonic currents plus reactive power at fundamental frequency, and the last two and plus zero sequence components. In the case of combined filter systems, the reactive power at fundamental frequency and the very high harmonics are operated for passive filters; therefore the parallel active part presents low nominal rate. The aim is to combine passive filter robustness with active filter performance, improving system reliability. The analyses shown in the paper are practical alternatives to improve power quality.