Improved LVRT Control Strategy for Wind Power and Photovoltaic Grid-connected Systems Based on Active Power Injection Control

To address the problem of weak voltage support capability at grid-connected points caused by random fluctuations in wind power and photovoltaic(PV) hybrid grid-connected systems, an improved low voltage ride through(LVRT) control strategy based on active power injection control is proposed. This strategy aims to enhance the system's voltage support capability following faults and improve its LVRT performance. Firstly, based on the topology of the wind-PV hybrid grid-connected system, mathematical models of the PV generation system and wind power generation system are established respectively, forming the state space model of the hybrid generation system. Secondly, a numerical model of the wind-PV system is developed in Matlab, and the corresponding electromagnetic transient simulation model is constructed on the PSCAD/EMTDC platform. By comparing the simulation results of both models, the accuracy of the numerical simulation model is verified. Furthermore, the impact of parameter variations on system stability is analyzed. Thirdly, the voltage dip drop at the point of common coupling(PCC), as well as the dynamic response characteristics of the converter's output power, are investigated when a three-phase short circuit occurs on the load side. Based on LVRT technical specifications, an improved LVRT control strategy is proposed, wherein smaller-capacity PV inverters prioritize LVRT control, while larger-capacity DFIG converters maintain active power output. Finally, the effectiveness of three different LVRT control strategies in supporting the voltage at the grid connection point is analyzed post-fault. Simulation results show that the proposed control strategy can raise the voltage at the grid connection point to 0.21 p.u. when a fault occurs in the wind-PV grid-connected system, meeting the standard requirements for voltage support at the grid connection point, while also ensuring the efficiency of active power output. The proposed method effectively enhances the voltage support capability and active power output of wind-PV grid-connected systems during low voltage ride-through, thereby improving the power supply continuity of renewable energy grid-connected systems.