DC-Side Impedance Modeling and Stability Assessment in Grid-Forming Modular Multilevel Converters

Incorporation of inverter-based resources is progressively increasing in modern power systems. The absence of inherent physical inertia in converter-based systems has resulted in a decrease in the total inertia of the grid. Grid-forming control of voltage source converters emulates the workings of a conventional synchronous generator through frequency droop control, allowing the converter to provide inertial support while contributing to the support of grid voltage. This paper presents a dc-side impedance model of a grid-forming modular multilevel converter. A control interaction between a grid-forming and a grid-following converter in a back-to-back structure is investigated and a stabilizing compensator is proposed.