A Novel VSG Control Strategy for Automatic Current Sharing of Parallel DC/DC Converters

In the two-stage power conversion system (PCS) with parallel DC/DC converters of storage battery, existing Virtual Synchronous Generator (VSG) strategy leaves all the DC-link voltage control task to the former DC/DC converter, thus PI controllers have to be adopted in parallel DC/DC converters to maintain DC-link voltage constant. However, it cannot realize automatic current sharing due to the accumulation of different sampling errors in parallel DC/DC converters. Aimed at automatic current sharing between parallel DC/DC converters when PCS provides inertia and damping to the grid, a novel VSG strategy is proposed in this paper. It makes the DC/DC converter provide damping to the grid by droop control between currents and DC-link voltage, and realize automatic current sharing between DC/DC converters by design the droop coefficient proportional to the DC/DC converter's rated capacity. Besides, it makes the DC-link capacitor provide inertia to the grid by proportional control of output frequency and DC-link voltage. The simulation results verify that the proposed VSG can provide equivalent inertia and damping with the exiting VSG under the designed parameters in this paper. Meanwhile, the proposed VSG achieves much better performance of automatic current sharing and reduction in the impact on the storage battery current than existing VSG.