Suppression of Neutral Point Potential Drift on DC Bus for Fault-Tolerant APF

The control performance of the APF is affected by neutral point potential drift of the DC bus when the APF runs in the fault-tolerant mode; thus, in this paper, a compensation method of neutral point voltage difference feed-forward control is proposed. After detecting fault in the APF via the current vector trajectory slope method and switching the APF to the fault-tolerant state, the method regards the difference between the two split capacitor voltages of the DC bus as the feed-forward value, then combines it with the feed-forward coefficient that originates from the mathematical modeling of the fault-tolerant APF, and the resulting value is added to the fundamental active component of the current reference value to suppress the potential drift. The feasibility of this method is verified via both simulation and experimentation. The results demonstrate that the fault-tolerant APF can effectively compensate the harmonics of the power grid; the THD was found to be reduced from 27.24% to less than 5%, which satisfies the national standard under fault-tolerant circumstances, and the results conform to the theoretical analysis. This illustrates that the proposed method can guarantee the stable operation of the APF during fault-tolerant operation, and that the APF can effectively compensate harmonics with high reliability.