Research on Transient Characteristics of an Improved Phase-locked Loop Topology Suitable for VSC Converters

To solve the problem of deteriorating performance and poor stability of traditional PLL connected to weak AC system, an improved PLL structure is proposed in this paper. By measuring the angular velocity and initial phase Angle of the system respectively, the angular velocity of the system is first stabilized to ensure the synchronization between VSC and AC power grid, and then the initial phase Angle of the system is tracked by PI link to achieve accurate estimation and fast tracking of AC power grid phase Angle value. Finally, taking a classic VSC grid-connected system as an example, the effectiveness and stability of the improved PLL are verified by simulation.