Norton's current theorem based online voltage stability analysis for wind connected power grid

The impact of wind power integration on power system voltage stability has received extensive attention recently. A new voltage stability H-index based on the Norton's current distribution law is established, which could be quickly calculated by phasor measurement unit (PMU) data. For steady-state analysis, the voltage stability margin could be directly assessed by computing the difference between H-index and 1. Applicability of the proposed H-index is validated in the case of reverse power flow, i.e. the active power is transmitted from wind farms to the point of common coupling (PCC). Then, the characteristics of H-index with increased wind power are analyzed. Based on the relationship between H-index and wind farm current injection, an online voltage stability monitoring method is presented. In this monitoring process, three important currents are proposed to be mainly monitored along with the H-index, namely the ‘worry current’, ‘transition current’ and ‘limit current’. Therefore, the voltage stability analysis and control strategies can be implemented according to the monitored currents and H-index. Effectiveness of the proposed online voltage stability analysis method is further verified by simulation results performed in an improved 39-bus system.