## 4 Simulation Results
### Results of Actual Test for Smart Inverter Control  
In this paper, the multifunction (circuit and control) simulation software PLECS system developed by Swiss Company Flexim GmbH combined with RT box as an actual  
Figure 16: The three-phase output voltage and current waveforms of the smart inverter when the per-unit value of mains voltage was between 0.97 p.u. and 1 p.u. Figure 15: The mains voltage \(V_{grid}\) before and after regulation, the output PF regulation, real power, reactive power, and apparent power of the smart inverter when the per-unit value of mains voltage was between 0.97 p.u. and 1 p.u. test simulation controller and analog breakout board for test simulation to finish the actual control test on the smart inverter. Usually, when no abnormal fluctuation occurs at the voltage of a PV grid-connected system, the photovoltaic inverter generally controls both the output voltage and current under sine wave and the same phase, so the output PF becomes 1.0. Therefore, all the output power of the photovoltaic system can be connected and sent to the grid by means of real power. In the case of a sudden increase or reduction in insolation, the power of the grid-connected system fed from the grid-connected photovoltaic system would also experience a sudden increase or reduction. The same would occur in the voltage at the grid-connected point if the load end could not consume or refill if the voltage suddenly increased or reduced, which would cause damage to equipment at the load end. To avoid such a situation, the real and reactive power were regulated via a smart inverter for stabilizing the voltage at the grid-connected point. The per-unit value of the voltage of the grid-connected point was between 1.0 p.u. and 1.03 p.u., which meant that the reactive power of the grid system was negative (Q < 0), which made the leading PF of the grid system. Therefore, the output current of the smart inverter should be controlled to be lagging behind the voltage, so the PF was lagging, where the reactive power of the grid system could be absorbed to stabilize the voltage at the grid-connected point. Figure 17a,b displayed the three-phase balanced output voltage and current waveforms under the actual test of the smart inverter, while Figure 18a,b displayed the output voltage and current waveforms under the actual test of the smart inverter under Phase a and the waveforms after partial enlargement, respectively. From Figure 18b, it could be observed that when the per-unit value of the voltage of the grid-connected point was between 1.0 p.u. and 1.03 p.u., the smart inverter started to control the output current, the phase was lagging behind the output voltage and the PF was adjusted to be lagging for absorbing reactive power of the grid system. From the output power regulation under the actual test of the smart inverter in Figure 19, it could be observed that through the PF regulation of the smart inverter, the real power in the grid fed from the inverter reduced from 1600 W to 1440 W and absorbed the reactive power of 774 Var (Q > 0) in grid system. However, the total output of apparent power is still maintained at the PVMA capacity of 1600 VA.  
Figure 17: The three waveforms under the actual test of the smart three-phase inverter: (**a**) output voltage waveforms; (**b**) output current waveforms. As the current waveform in Figure 18 is the waveform obtained by actual measurement, the current signal is converted into a voltage signal by the current detector and then measured. To avoid the high switching frequency of the power semiconductor switch, the switch will be overheated and burned due to high switching loss. Therefore, the actual current control adopts hysteresis current control. The measured current switched control within the current width set by the current command's upper limit and lower limit.