692 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 29, NO. 2, , DEC 2015 Fig. 8. Simulation results: (a) Grid voltages, (b) Grid Currents (c) Unbalanced load currents, (d) Inverter Currents. the transient response of the compensation scheme. Fig. 9(a) shows that the line current becomes sinusoidal when the active power filter starts compensation, and the dc-voltage behaves as expected. Experimental results shown in Fig. 9(b) indicate that the total harmonic distortion of the line current (THDi ) is reduced from 27.09% to 4.54%. This is a consequence of the good tracking characteristic of the current references, as shown in Fig. 9(d). In Fig. 10, the transient response of the active power filter under a step load change is shown. The line currents remain sinusoidal and the returns to its reference with a typ-ical transient response of an underdamped second-order system (maximum overshoot of 5% and two cycles of settling time). In this case, a step load change is applied from 0.6 to 1.0 p.u. Finally, the load connected to phase u was u Fig. 9. Experimental transient response after APF connection. (a) Load Cur-rent iL , active increased from 1.0 to 1.3 p.u. The corresponding waveforms are u c u power filter current io , dc-voltage converter vd , and system current is . Associated shown in Fig. 11. Fig. 11(a) shows that the active filter is able to u s u v w compensate the current in the neutral conductor with fast transient frequency spectrum. (c) Voltage and system waveforms, vs and i , is , is . (d) response. u u Current reference signals , and active power filter current io (tracking characteristic). n Moreover, Fig. 11(b) shows that the system neutral current io is effectively compensated and eliminated, and system currents remain balanced even if an 11% current imbalance is applied.
692 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 29, NO. 2, , DEC 2015 Fig. 8. Simulation results: (a) Grid voltages, (b) Grid Currents (c) Unbalanced load currents, (d) Inverter Currents. the transient response of the compensation scheme. Fig. 9(a) shows that the line current becomes sinusoidal when the active power filter starts compensation, and the dc-voltage behaves as expected. Experimental results shown in Fig. 9(b) indicate that the total harmonic distortion of the line current (THDi ) is reduced from 27.09% to 4.54%. This is a consequence of the good tracking characteristic of the current references, as shown in Fig. 9(d). In Fig. 10, the transient response of the active power filter under a step load change is shown. The line currents remain sinusoidal and the returns to its reference with a typ-ical transient response of an underdamped second-order system (maximum overshoot of 5% and two cycles of settling time). In this case, a step load change is applied from 0.6 to 1.0 p.u. Finally, the load connected to phase u was increased from 1.0 to 1.3 p.u. The corresponding waveforms are shown in Fig. 11. Fig. 11(a) shows that the active filter is able to compensate the current in the neutral conductor with fast transient response. Fig. 9. Experimental transient response after APF connection. (a) Load Cur-rent iL u , active power filter current io u , dc-voltage converter vd c , and system current is u . Associated frequency spectrum. (c) Voltage and system waveforms, vs u and i s u , is v , is w . (d) Current reference signals u , and active power filter current io u (tracking characteristic). Moreover, Fig. 11(b) shows that the system neutral current io n is effectively compensated and eliminated, and system currents remain balanced even if an 11% current imbalance is applied.