## 5 Introduction and Analysis of Experimental Results of the Demonstration System
### Analysis of Running Effect and Experimental Waveform  
Figures 27-30 display the history curves of the monitoring system. In each figure, the abscissa is time and the ordinate is power. The red curve is the photovoltaic power curve, referred to as PV; the  
Figure 26: Interface of the monitoring system. Figure 25: Photos of key equipment of the microgrid. green curve is the ESS power curve, referred to as ESS; positive values represent ESS charging and negative values represent ESS discharge; purple curves are load power curves, referred to as LOAD; and the blue curve is the PCC power curve, referred to as PCC. A positive signifies that the microgrid system uses power from the grid, and a negative sign represents that the microgrid system sends power to the grid. The right side is a graphic illustration that shows the maximum and minimum values of the corresponding data. Figure 28: Experimental waveform of a cloudy day in the heating season. Figure 27: Experimental waveform of a sunny day in the heating season. From the experimental waveforms, it can be seen that when the photovoltaic power generation is greater than the load power after 8 am, photovoltaic power generation charges the ESS. After 12:00, the ESS is full, and excess electricity from photovoltaic power generation is sold to the grid. At night when the electricity price is very high, the ESS releases electricity to make up for the shortage of load. In order to prevent the battery from stagnating at a low level for a long period of time, resulting in excessive life loss, the battery is charged until the power level reaches the SOCpro value during the night when the electricity price is low. It can be seen from the actual running waveform that because of the program for pre-charging the battery, the ESS is charged from the grid when the midnight electricity price is low. When the electricity price is high at 8 a.m., photovoltaic power generation cannot meet the load demand, the ESS is discharged, and the power shortage is replenished. After the early peak electricity price, the electricity price in the afternoon is in the parity period, and the electricity price of the grid is lower than the cost of the ESS. During the period when the peak electricity price is high at night, the power in the ESS is discharged. Then, electricity is replenished at low electricity prices during the night. This scenario does not include pre-charging of the ESS because, during the day, photovoltaic power generation is greater than the load, and there is therefore a lot of electricity. Basically, the battery can be fully charged during the day, and will not be in a low SOC level for a long time, which will damage the battery life. From the waveforms of the demonstration system operation, it can be seen that at night, there is no operation of charging the ESS. At around 8 a.m. when the peak electricity price is high, photovoltaic power generation cannot yet meet the load power consumption, and the ESS discharge makes up for the margin. After 9 a.m., the photovoltaic power generation exceeds the load  
Figure 30: Experimental waveform of a cloudy day in the non-heating season. Figure 29: Experimental waveform of a sunny day in the non-heating season. power consumption, and the ESS begins to charge. Because the ESS is not charged at night, the ESS is fully charged until 4 p.m., and the remaining portion of photovoltaic power generation is sold to the grid. During the night when the electricity price is high, the ESS discharges to supplement the power margin. In this scenario, photovoltaic power generation is relatively small and, at the same time, the power of the load will be less than the heating season. Because photovoltaic power experiences greater power changes due to weather, it can basically be used by the load. In order to prevent the ESS from being in a low-power state for a long period of time, a control strategy that preferentially charges ESS is implemented.