A Dynamic and Efficient Active Power Support Scheme Using VSC-HVDC System for Quick Frequency Restoration

For achieving carbon neutrality, increased renewable power generation is an emerging trend. Renewable power, often transmitted via VSC-HVDC, is variable, intermittent and could not contribute to grid inertia directly. Thus, quick restoration of system frequency should be prioritized, for which encapsulation of frequency regulators inside converter controllers is often suggested. Most of the reported frequency regulation schemes are only suited for converters carrying power below rated limits. The novelty of present work lies in its ability to regulate frequency by delivering power support above rated limits. In fact, by exploiting primary frequency reserves available at the other end and by efficiently utilizing converter’s entire permissible operating region, frequency can be restored quickly within acceptable range. This can have significant implication for extracting frequency support from offshore wind farms coupled via VSC-HVDC. The proposed technique, based on dynamic converter current modulation, renders significant active power support depending upon severity of encountered frequency excursion. Its performance is justified by testing it by introducing disturbances of different magnitudes in an IEEE 14-bus system. Interestingly, the simulation results obtained using MATLAB/Simulink have confirmed that by employing proposed scheme, for a 22% load/generation unbalance, VSC can arrest frequency nadir within one second by delivering nearly 30% above rated converter power. In fact, fast frequency regulation is achieved without compromising AC voltage stability of the disturbed grid.