Enhanced grid forming control for MMC-HVDC with DC power and voltage regulation

An enhanced grid forming (GFM) control strategy is proposed for modular multilevel converter -based highvoltage direct current (MMC-HVDC) transmission. Compared with the traditional GFM control with only AC side control, the proposed method can achieve the decoupled AC and DC side control. The AC side control includes the hybrid synchronization unit and the cascaded voltage -current loop. The AC side control realizes the inertia emulation of the synchronous machine (SM) in a wide range of short circuit ratio. The DC side control realizes the DC power or DC voltage control by controlling the inserted submodule number with the inner DC current loop. The DC side control imitates the primary frequency control of the governor for SM. Based on the decoupled AC and DC side control, the inertia and primary frequency control are obtained from the AC and DC side control, respectively, instead of only the AC side from the traditional GFM control. It provides complete mapping from the AC side and governor side of the SM to the AC side and DC side of the MMC. The system model is built to guide the parameter design, and the simulations are provided to validate the proposed methods.