Overvoltage Suppression Based On Double-loop PI Control Of Flexible Grounding Device For Distribution Network

With the rapid development of smart grid,the safety,reliability and economy of distribution network become the research focus nowadays.In traditional non-effectively earthed networks,the unbalance of three-phase parameters,heavy single-phase load and ferromagnetic resonance may all contribute greatly to the overvoltage of neutral point,which damage the reliability of power system seriously.Thereby,it is of great meanings to study the suppression method of neutral voltage in distribution systems.First of all,the traditionalsuppression methodsof neutral voltage is studied in the paper,such as the static varcompensator(known as the SVC)and the shunt reactor compensation method.Also,the differences between these methods are analyzed.Whereas most suppression concepts have disadvantages,this work presents a flexible grounding device which is able to inject a certain amplitude and phase current to the neutral point to suppress neutral voltage.Secondly,various control strategies such as PI control,dead-beat control,repetitive control and proportional resonant control are compared to choose a best control strategy.By the means of modeling and simulation,adual closed-loop PI control strategy was chosen and the parameters of controller were designed.At last,an experimental prototype and 10 kV distribution network laboratory were built and verified the feasibility and benefits of dual closed-loop control strategy as well as the voltage suppression method.Simulation and experimental results show thatthe neutral overvoltageis fast and real-time suppressed without the measurement of grounding parameters,and the optimization of controller parameters is of great use to fast the response speed,improve the precision and enhance systemic robust.