Investigations on the Effects of DC Voltage Control on Inertia Provision in HVDC Converter Stations

To mitigate the low-inertia challenges in future power-electronics-dominated grid, grid-forming control with virtual inertia has been proposed to grid-connected power converters, including the converter stations in high-voltage-direct-current (HVDC) transmissions, where DC voltage also needs to be tightly controlled. This paper first demonstrates that if there is only one station in charge of DC voltage control, this station cannot provide any real inertia power during frequency events but instead adversely produces a small equivalent negative inertia. Then, an improved grid-forming control with enhanced DC voltage droop control that has been recently proposed is examined in same perspective. It is found that with this novel control real inertia power can be delivered while poses negligible disturbances on the DC voltage, rendering it an excellent control strategy to sharing inertia reserves from different AC areas without commnunications. All findings are validated in electromagnetic simulations with MMC models of 400 sub-modules.