Impact on interarea modes of fast HVDC primary frequency control

Primary frequency control is often added to the control system of a high-voltage DC (HVDC) transmission that interconnects two nonsynchronous ac grids. As the active-power actuation lag is typically in the range of hundreds of milliseconds, the HVDC primary frequency control can be made fast enough to permit inertia sharing among the interconnected ac grids. This reduces the maximum frequency fall after a loss-of-generation contingency (the nadir). A fast HVDC primary frequency control may affect the interarea modes of the interconnected grids. To this end, it is shown that, at least for the cases studied, the modal damping never decreases through the introduction of the mentioned control.