Four-quadrant Operation Mechanism and Control Method of Flexible Grounding Device at Neutral Point in Distribution Network

Aiming at the problem that existing flexible grounding devices in distribution network are easy to cause direct current (DC) side voltage instability, even DC capacitor breakdown, due to grid side energy backflow, the variation of the phase angle difference between injection current and neutral point voltage with system parameters is analyzed, and the influence mechanism of system parameters on the output active power and energy flow direction of device is revealed. The internal causes of system energy backflow are clarified. A four-quadrant flexible grounding device topology is proposed. The rectifier side adopts the voltage type three-phase half-bridge controllable rectifier topology, and it is connected to the power grid through the distribution transformer. This structure can keep two-way energy flow, improve DC side voltage stability, and realize DC-side power self-supply. Furthermore, a multi-objective compound control method is proposed. The network side unit power factor operation and DC side voltage stability are realized with the rectifier double-loop control, and the neutral point voltage is rapidly and accurately regulated with the inverter side control. Various operating and fault conditions are simulated in power simulation (PSIM) and 10 kV true distribution network test field. Simulation results show that the proposed device can deal with ground fault quickly, safely and reliably. © 2024 Chinese Society for Electrical Engineering. All rights reserved.