Autonomous Operation of Grid Synchronizing Breakers with Low Voltage Ride Through (LVRT) Capabilities

Abstract

With rapidly increasing penetration level of renewable energy sources (RES) in electric grids, it is noteworthy that stable and reliable operation of electric power systems is urgently needed, given the inverter interfaced RES has less inertia compared to conventional rotational generation units. Meanwhile, it should be also noted that grid operation can be categorized as normal and abnormal conditions. For each type of grid operation condition, the inverter interfaces should produce reliable power generation into the grid. Especially during fault operation, low-voltage ride through (LVRT) is a critical operation condition that needs to be achieved in each interface inverter. Furthermore, when the system is operated in severe conditions, the faulty areas should be effectively isolated from the rest of the system. Considering the operation requirements in electric grids, in this paper, an autonomous operation of grid synchronizing breakers is designed and implemented. Particularly, the developed grid synchronizing breakers can autonomously detect grid operation condition by measuring the grid-connected current and grid side voltage. An extended LVRT curve is designed to support the original LVRT curve so that enhanced fault mitigation and isolation can be achieved. In the meantime, the designed circuit breaker can automatically synchronize with the external grid voltage. Therefore, transient process when breaker is turned on or off can be successfully controlled without violating the existing standards. A simulation model is implemented in MATLAB/Simulink to verify the effectiveness of the proposed method.