Impact of shunt active harmonic filter on harmonic current distortion of voltage source inverter-fed drives

When applying an active harmonic filter (AHF) to mitigate the harmonic currents of voltage source inverter-fed drives (VSI), the required capacity of the AHF is generally determined by the measured harmonic current of the drives. Nevertheless, when the AHF is connected to the electrical power distribution system, the total harmonic current distortion of the load actually increases owing to the change in the commutation behavior of rectifier. Therefore, a higher AHF output capacity is demanded to meet the expected filtering requirement. This paper investigates the impact of the AHF on the changes of the harmonic current distortion of VSI. For this purpose, correlation analysis models are constructed, and case studies are presented to illustrate the effect with different system short circuit levels, load conditions, and ac chokes of the VSI. Furthermore, several actual field measurement results are presented for verification. On the basis of the measured and calculated results, a margin factor is recommended for use when determining the capacity of the AHF.