The function of sag control inverter is limited, it can only adjust its own power output to a certain extent, and can not directly solve the problem of the lowest frequency of the grid. To solve the problem of the lowest frequency, it is usually necessary to take other measures, such as increasing the power supply capacity, improving the stability of the grid, optimizing the grid operation strategy, etc.
The synchronous generator restores the network frequency by reducing the power deficit through increasing the generated power. The increase in power comes due to an increase in drive power (hydraulic turbine, steam turbine). The inverter can increase output power within a limited range and for a short time. It is possible to provide a larger installed capacity of the inverter and batteries, but the cost will increase. If we are talking about distributed generation or a centralized network, then it is necessary to study it specifically in each case.