An Improved Dual Second-Order Generalized Integrator Phased-Locked Loop Strategy for an Inverter of Flexible High-Voltage Direct Current Transmission Systems under Nonideal Grid Conditions

High-voltage flexible power systems, with their intrinsic characteristics, play an increasingly important role in electronic systems. Synchronization between the inverter and grid needs to be achieved by a phase-locked loop (PLL), performance of which determines quality transmission. This paper proposes PLL adapted extremely harsh conditions. Firstly, traditional synchronous reference frame dual second-order generalized integrator (DSOGI-PLL) are analyzed, errors phase-locking shortcomings these two methods presence DC components pointed out. Secondly, based on harmonic voltage, repetitive control internal model is introduced DSOGI realize real-time tracking regulation signals order suppress voltage disturbance. In addition, bias elimination frequency adaptive method proposed solve problems fluctuation achieve phase. Finally, superiority strategy verified through simulations experiments.