## 5 Verification
### Verification Process  
#### 5.2.1 Verification of PV Storage Virtual Synchronous Generator System  
For the PV storage virtual synchronous generator system, its active frequency regulation capability as well as inertia characteristic need to be verified, which are verified respectively in the following subsections. (1) Verification of Frequency Regulation with Initiatives  
1 Generator Mode  
Figures 18 and 19 present the system characteristics from the external and internal perspectives, respectively. Figure 18 shows the external frequency regulation characteristic of the proposed PV storage virtual synchronous generator system and the conventional PV storage system in a generator mode. Figure 19 displays the internal situation of the proposed PV storage virtual synchronous generator system and the traditional PV storage system in a generator mode. In the initial state, traditional PV storage and microgrid share the active power of 10 kW and 50 kW, respectively, to meet the needs of 60 kW load. As can be seen from Figure 18a, traditional PV storage does not participate in the frequency regulation. After the load is reduced at the 2 nd second, the power imbalance of 20 kW is entirely assumed by the microgrid. As a result, the power sent by the microgrid \(P_{\text{out2}}\) drops from 50 kW to 30 kW, which results in a 0.5 Hz increase in frequency. The situation with the PV storage virtual synchronous generator system is different, which can be seen from Figure 18b. When the load decreases, the PV storage virtual synchronous generator system can participate in the frequency regulation together with the microgrid, according to the droop coefficient. Due to the ratio of the active power droop coefficient between the PV storage virtual synchronous generator system and the microgrid is 4:1, the PV storage virtual synchronous generator system and the microgrid share the power imbalance of 20 Kw, according to the ratio of 1:4. The power delivered by the PV storage virtual synchronous generator system is reduced from 10 kW to 6 kW and \(P_{\text{out2}}\) is reduced from 50 kW to 34 kW, which resulted in a 0.4 Hz increase in frequency. Above results indicate that the PV storage virtual synchronous generator system can participate in the frequency regulation actively in the generator mode, which is beneficial to improving the frequency stability of the system and reflecting the advantages of the PV storage virtual synchronous generator system compared to the traditional PV storage system. What can be found out in Figure 19 directly is that the two systems can realize the maximum power point tracking and stability of DC bus voltage. Figure 19a shows that the power emitted by the energy storage system is always \(-\)2 kW no matter how the load changes when the traditional PV storage system is adopted. In addition, the state of charge SOC slowly rise with a constant rate of change. The above phenomenon means that the energy storage unit in the PV storage system absorbes 2 kW active power to ensure that the PV storage system always tracks the power dispatching value and outputs 10 kW active power. It can be seen from Figure 19b that the power delivered by the energy storage system and the state of charge SOC varies when PV storage virtual is synchronous to a generator system is adopted. After the 2 nd second, a system power imbalance occurs due to the 20 kW load reduction. PV storage virtual synchronous generator system regulates frequency through the energy storage system. At the 2 nd second, the power emitted by the energy storage unit \(P_{st}\) starts to decrease from \(-\)2 kW and after about one second, it becomes \(-\)6 kW. Meanwhile the rate of increase of SOC starts to become faster at the 2 nd second. In other words, the energy storage system in the PV storage virtual synchronous generator system participates in the frequency regulation with initiatives by absorbing an extra 4 kW active power.