| Abstract: | Under frequency load shedding is an effective approach to maintain or restore the steady-state operation of the
power system when frequency accidents occur. An improved under frequency load shedding strategy based on
dynamic power flow tracking is proposed. The expression of the kinetic energy theorem in power system is derived
and combined with the power flow tracing method to analyze the relation between system energy distribution
and its frequency. The power system frequency influencing factors are then constructed and applied to find the
reasons of frequency decline and to quantify the contributions of the mechanical power of the generators, the load
power and the transmission losses for the frequency deviation. Finally, considering a variety of unbalanced power
scenarios in the system, the modified load shedding strategy is designed. Based on the results of dynamic power
flow tracing, the strategy can choose the suitable load node to control, and the defined load frequency contribution
indicator is utilized to determine the load shedding amount which each control object undertakes. The proposed
methodology is verified by the fault scenarios when the generator sets mistakenly cut off and the trip of important
tie-lines in the IEEE 39-bus system. Compared with the conventional strategies, the proposed strategy is more selective,
can reduce the blackout range, and improve the effect of stable frequency recovery |
