Grid-forming Control of the Grid-connected Voltage Source Converter System

For the grid-connected converter system with intermittent and fluctuating input power, a grid-forming control strategy is proposed in this paper. The control strategy takes the dc-link voltage as the control target, and the autonomous synchronization is realized according to the dynamics of dc-link capacitor. The cascaded control structure with the outer power loop, middle voltage loop and inner current loop is adopted for the grid-connected converter. Under this control structure, the dc-link voltage of the grid-connected converter can track the grid frequency and play the role of a frequency-locked loop. Moreover, a startup control loop and flexible startup control method for this grid-forming voltage source converter system are proposed, which can improve the engineering application value of this grid-forming control strategy. Finally, by building the simulation model of grid-connected voltage source converter system in Matlab/Simulink, the effectiveness of the proposed control strategy is verified.