Large-scale grid-connected photovoltaic(PV)generation has an important effect on synchronous generators with rotational inertia

which causes the problem of insufficient inertia and insufficient frequency modulation capability. Therefore

there is an urgent need for PV generation to take part in frequency regulation. Taking the two-stage PV power generation as the research object

the conventional virtual inertia control based on the dynamics of the phase locked loop(PLL)is studied. At the same time

the virtual inertia control based on the dynamics of the low-voltage DC capacitor and the virtual inertia control based on the dynamics of the high-voltage DC capacitor are proposed

and the influence of control parameters of virtual inertia control is analyzed. The results show that: (1) in the case of conventional virtual inertia control

the narrower PLL control bandwidth is

the more PV power can be provided during the process of frequency sag; (2) in the case of virtual inertia control based on low-voltage DC capacitor dynamics

owing to the introduction of f-UPV compensation in the voltage control loop

the change of low DC voltage affects not only the frequency dynamic process but also the steady-state frequency deviation; (3) in the case of virtual inertia control based on high-voltage DC capacitor dynamics

PV generation can provide more power in the case of frequency sag

when the integral coefficient of the Boost converter voltage control loop rises to slow down the dynamic response of the DC voltage.