提升对称故障下LVRT期间暂态同步稳定性的电流内环协同控制策略OA

[Objective]Grid-following converters(GFL)are widely employed in renewable energy grid integration systems.When grid faults cause voltage sags,the system enters a low voltage ride-through(LVRT)process.The conventional second-order model of the phase-locked loop(PLL)fails to accurately capture the dynamic characteristics of the system during LVRT due to its neglect of the transient current response,thereby limiting the improvement of transient synchronization stability.To address this issue,a current inner-loop collaborative control strategy suitable for the LVRT process is proposed to enhance the transient synchronization stability of the system in the event of symmetrical faults.[Methods]Based on the fourth-order dynamic model of the PLL and combined with the transient energy function method,this paper analyzes the impact of abrupt frequency variations at the PLL output and the coupling effect between the current inner loop and the PLL on the transient synchronization stability of the system.A corresponding control strategy is designed:the current reference value is dynamically adjusted according to the optimal impedance ratio to suppress the accumulation of transient energy during faults;meanwhile,a frequency deviation compensation mechanism is introduced into the feedforward decoupling term of the current inner loop to accelerate the dissipation of transient energy.The synergistic action of these two measures enhances the transient synchronization stability of the system during LVRT.[Results]PSCAD/EMTDC time-domain simulation results in the event of symmetrical faults demonstrate that the abrupt change in PLL output frequency at the instant of fault is proportional to the magnitude of the grid voltage sag,leading to increased risk of system instability.The proposed control strategy effectively suppresses the PLL output frequency deviation during the fault,significantly reduces the first-swing amplitude of the virtual power angle,and shortens the system recovery time after fault clearance.It demonstrates satisfactory adaptability under various grid parameters.[Conclusions]The collaborative current inner-loop control strategy proposed in this paper effectively suppresses transient energy accumulation during grid faults and accelerates transient energy dissipation after fault clearance,thereby significantly enhancing the transient synchronization stability of GFL grid integration systems during LVRT under symmetrical faults.