Analysis of the Impact of System Impedance Ratio on the Strength of Renewable Energy Generation Integrated Weak Grids

More renewable energy generations (REGs) will be integrated into the power system with longer transmission lines, known as the weak grid. Unlike high-voltage systems, the active and reactive power are deeply coupled with the resistance and reactance of the weak grid. It may reduce the accuracy of strength assessment if we only use a common index such as the short-circuit ratio (SCR). This paper proposed a comprehensive analysis of the relationship between the system impedance ratio (SIR), the power factor (PF), and the SCR when used to evaluate the system strength. First, the relationship between the strength assessment index and the impedance is introduced. The SCR represents the influence of impedance amplitude, and the SIR describes the impedance angle. Then, the effect of SIR on voltage stability is analyzed by sensitivity analysis. Increasing transmission power can improve the voltage stability when the SIR is smaller than the PF. Furthermore, the main influencing factors of the system impedance are discussed by establishing an analytical model, including the load level and the component impedance. A high load level can result in a low SIR. Finally, simulations prove the accuracy of the analysis. The strength of a weak system is related to the SIR, the SCR, and the PF. The heavy load area can accept more REGs if reactive power allocation is reasonable.