Static Voltage Stability Zoning Analysis Based on a Sensitivity Index Reflecting the Influence Degree of Photovoltaic Power Output on Voltage Stability

Abstract

The large-scale integration of photovoltaic (PV) power can bring a greatly negative influence on the grid-connected system’s voltage stability. To study the static voltage stability (SVS) of PV grid-connected systems, the traditional SVS index, L-index, was re-examined. It was firstly derived and proved that the PV active output Ppv is proportional to the voltage phase angle of the PV station’s POI (Point of Interconnection), based on a simplified two-node system integrated with a PV station operating in PV (active power—voltage) mode or PQ (active power—reactive power) mode with unit power factor. Then a novel voltage stability sensitivity index LPAS-index was proposed that takes the derivative of the L-index with respect to the POI’s voltage phase angle, so as to reflect the influence degree of Ppv on the SVS of each load node. A SVS zoning analysis method for the PV grid-connected system was designed according to the classification results of load nodes based on the proposed LPAS-index, the power grid can be zoned into three kinds of areas that reflect different correlations between the SVS and Ppv: strong correlation, moderate correlation and weak correlation. Since the LPAS-index is less impacted by Ppv, the SVS zoning results are relatively unchanged. On the basis of a classic 14-node system with PV, the practicability of the zoning analysis method was verified. The simulation results show that the PV access point in general falls within the strongly or moderately associated area with Ppv. When most of the load nodes fall within the weakly associated area with Ppv, it is not necessary to consider the impact of Ppv and load power is still the main influencing factor on the SVS. In the multi-PV case, owing to the expansion of areas more affected by Ppv, an excessive Ppv can cause adverse influence on the SVS of the whole power grid; and an effective PV power-shedding measure is proposed to solve this problem. The proposed SVS zoning analysis method can be used for reference by power grid dispatchers.