Power quality enhancement for nonlinear unbalanced loads through improved active power filter control

This paper presents a modified synchronous reference frame for Active Power Filter control (APF) to compensate for harmonics and reactive power for both balanced and unbalanced non-linear loads. The proposed controller autonomously detects different power quality problems, filters out load created harmonics and compensates for unbalances and/or DC offsets resulting from non-linear loads connected at the point of common coupling (PCC). The main objective of the controller is to force the AC grid currents at the PCC to be balanced three-phase currents with minor harmonics regardless of the characteristics of the local AC load. In addition, the developed controller uses only current measurements which reduces the cost and complexity of system implementation. The performance of the developed controller was examined under several extreme cases, including: non-linear loads, distorted load currents, unbalanced loads, loss of one supply phase and existence of DC current component conditions. The results show that the developed controller succeeds to improve power quality at the PCC under various loading conditions.