The mutual influence of the key parameters for the power loop of virtual synchronous storage converter is analyzed in small signal model

which provides a reference for the design and selection of the power loop parameters. According to the deficiency of power deviation and limit under grid-connected operation for virtual synchronous storage converter

a PQ mode control strategy of virtual synchronous machine which is suitable for grid-connected operation is presented

and the switching between PQ mode and the virtual synchronous generator(VSG)mode which is operated when it is necessary. The PQ mode control can not only realize constant power operation in steady state

but also have certain inertia and damping in transient process. It can realize self-synchronization in grid-connected state

and the phase-locked loop is not needed. Finally

the simulation and experimental results show that the proposed control strategy is stable

and smooth switch is also reliable.