VSC-Based Active Synchronizer for Generators

Abstract

Fast synchronization of generators and microgrids will be a critical technology in future power systems with high penetration of nondispatchable power resources. Existing synchronization methods rely on generator controls and their performance is limited by the generator characteristics. Speed of microgrid synchronization is further limited by the communication link among generation units. These factors lead to a slow and sometimes faulty synchronization, predominantly because of the phase mismatch during interconnection. This paper frames the generator synchronization problem as a phase-locked loop (PLL) design problem and introduces a voltage-source converter (VSC) based synchronizer for implementing the PLL-based active synchronization method. The VSC-based synchronizer is connected at the point of common coupling and it relies only on local measurements for control. It ensures zero phase error during interconnection by taking the advantage of the fact that the phase is not regulated in the generator controls. Relation between the synchronizer rating, control design, and synchronization speed is developed using describing function analysis of frequency and phase control loop gains. The operation and performance of the VSC-based synchronizer is demonstrated using simulations of a 555 MVA, 24 kV synchronous generator.