Rapid Evaluation of Post-fault Steady-state Frequency Considering State Switching

With the large-scale integration of renewable energy generation (REG) and the rapid development of power electronic devices, frequency stability problem has become increasingly prominent. As one of the evaluation indicators for frequency security, the post-fault steady-state frequency is primarily governed by the steady-state characteristics of various dynamic components. However, current calculation methods suffer from either inadequate accuracy or prolonged computation periods. To address this, the paper proposes a post-fault equilibrium point calculation model that incorporates state switching of all components in power system by introducing the steady-state frequency variable. This approach transforms the steady-state frequency calculation problem into the traditional power flow analysis problem, both in the form of nonlinear equations. Then it is solved by alternating iteration method utilizing the frequency deviation of the synchronous machine on slack bus. The proposed method is validated on the modified IEEE 39-bus system, proving both the accuracy and computational efficiency of the frequency equilibrium point calculation approach.