Inertia Emulation Control Strategy for VSC-HVDC Transmission Systems

There is concern that the levels of inertia in power systems may decrease in the future, due to increased levels of energy being provided from renewable sources, which typically have little or no inertia. Voltage source converters (VSC) used in high voltage direct current (HVDC) transmission applications are often deliberately controlled in order to de-couple transients to prevent propagation of instability between interconnected systems. However, this can deny much needed support during transients that would otherwise be available from system inertia provided by rotating plant. This paper proposes a novel VSC-HVDC control system termed INEC (INertia Emulation Control) which enables a VSC-HVDC system to provide support that emulates the inertia of a synchronous generator (SG). The energy to do so comes from the capacitance of the HVDC connection, which may be augmented by the installation of additional capacitance. This paper indicates that the proposed INEC system allows a VSC-HVDC system with a fixed capacitance to emulate a wide range of inertia constants (H) by specifying the amount of permissible DC voltage variation. The proposed INEC scheme has been demonstrated through simulations, and its performance is evaluated for transients that include faults and also changes in load.