## 5 Verification
### Verification Process
#### 5.2.1 Verification of PV Storage Virtual Synchronous Generator System
Figure 19: (**a**) Internal state quantities of traditional PV storage in the generator mode; (**b**) Internal state quantities of PV storage virtual synchronous generator system in the generator mode. Figure 20 indicates the external frequency regulation characteristic of the proposed PV storage virtual synchronous generator system and the conventional PV storage system in motor mode. Figure 21 illustrates the internal situation of the proposed PV storage virtual synchronous generator system and the traditional PV storage system in the motor mode. Figure 18: (**a**) Frequency regulation results of traditional PV storage system in generator mode; (**b**) Frequency regulation results of PV storage virtual synchronous generator system in the generator mode. In the initial state, the microgrid assumes 70 kW of active power to meet a 60 kW power demand because the PV storage virtual synchronous generator system absorbs 10 kW active power. Figure 20a shows that the traditional PV storage still does not participate in the frequency regulation as a generator mode. After the load is reduced at the 2 nd second, the power emitted by the microgrid drops from 70 kW to 50 kW and the frequency rise by 0.5 Hz. As can be seen from Figure 20b, when the PV storage virtual synchronous generator system is adopted, the output power of it \(P_{\text{out1}}\) reduces from \(-10\) kW to \(-14\) kW and \(P_{\text{out2}}\) reduces from 70 kW to 54 kW. The new PV storage can help microgrid to share the frequency regulation pressure with a final frequency of 50.4 Hz and 0.1 Hz lower than the result of traditional PV system. From the above results, it can be seen that the PV storage virtual synchronous generator system can still participate in the frequency regulation actively and improve the frequency stability, which shows the superiority of the new PV storage virtual synchronous generator system compared with the conventional one. As shown in Figure 21, both kinds of systems can ensure the maximum power output of PV array and maintain the stability of DC bus voltage. Figure 21a indicates that the power output by the energy storage system is always \(-22\) kW. Moreover, the \(SOC\) of the energy storage system rises rapidly and the rate of change remains unchanged. The above results illustrates that the energy storage unit in  
Figure 21: (**a**) Internal state quantities of traditional PV storage in the motor mode; (**b**) Internal state quantities of PV storage virtual synchronous generator system in the motor mode. Figure 20: (**a**) Frequency regulation results of traditional PV storage system in the motor mode; (**b**) Frequency regulation results of PV storage virtual synchronous generator system in the motor mode. the PV storage system absorbs 22 kW active power, which ensures that the PV storage system can absorb 10 kW power. It can be seen from Figure 21b that when the proposed new PV storage system is adopted, after the 2 nd second, the power output by the energy storage unit \(P_{st}\) decreases from \(-22\) kW to \(-26\) kW. Additionally, the rate of increase of SOC begins to be slightly faster at the 2 nd second. It is clear that PV storage virtual synchronous machine system can participate in the frequency regulation process together with microgrid in the motor mode. (2) Verification of the Inertia Characteristic  
As can be seen from Figure 18a, the frequency of the traditional PV storage system changes rapidly with little inertia, which is not conducive to the stable operation of the power grid. The new PV storage system in Figure 18b has a smoother transient process due to the introduction of VSG technology. The comparison between Figure 18a,b shows that the transient process of the PV storage virtual synchronous generator system is relatively smooth, which can support the stability of the system frequency maximally. It should be pointed out that the same conclusion can also be drawn from the comparison between Figure 20a,b.