A Tranformerless Grid-Connected Photovoltaic(3)

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Fig. 4. Simulation results of the conventional system in sunny mode.

Fig. 6. Simulation results of the proposed system in sunny mode.

Fig. 5. FFT results of the conventional system in sunny mode.

Fig. 7. FFT results of the proposed system in sunny mode

Figure 8 shows the simulation results of the proposed system in the night mode. As shown Fig. 8(a), the grid current is sinusoidal waveform, which is in phase with the grid voltage. The grid supplies the active power which is needed to loads and the inverter compensates all the reactive power. Fig. 9 illustrates the FFT results of the grid current, the inverter current and the load current. The THD of the grid current is 2.95%. The power factor of the proposed system is 0.99.

From fig. 4(f), the PV system supplies 100% active power to the grid before the load change at 0.5 sec. However, in case that the load change occurs at 0.5sec, the PV system supplies the active power which is needed to loads and others are supplied to the grid. As shown Fig. 4(b), the grid current (Ig) is bitterly distorted. Fig. 5 illustrates the FFT result of the grid voltage and current, the inverter current and the load current. The total harmonic distortion (THD) of the grid current is 57.2%. The power factor of the conventional system is 0.86.

Figure 6 shows the simulation results of the proposed system in sunny mode where the load changes from no load to 1kVA nonlinear load at 0.5sec. From fig. 6(f), the PV system supplies 100% active power to the grid before the load change at 0.5 sec. However, in case that the load change occurs at 0.5sec, the PV system supplies the active power which is needed to loads and others are supplied to the grid. The load current (ILoad) is bitterly distorted. The grid current (Ig), on the other hand, can be observed to keep a nearly sinusoidal waveform through the compensating operation of the inverter. Fig. 6(a) show the grid voltage and current, showing that the grid current is inverse phase with the grid voltage. As shown Fig. 6(e), the DC-link voltage control maintains the desired level of 380V. Fig. 7 illustrates the FFT results of the grid voltage and current, the inverter current and the load current. The THD of the grid current is 2.54%. The power factor of the proposed system is

0.98.

Fig. 8. Simulation results of the proposed system in night mode.

The improvement in power quality can be observed through the THD analysis displayed in Fig. 7 and Fig. 9 and the THD of