Research On State-type Grounding Mode Based On Flexible Control In Medium Voltage Distribution Network

With the continuous expansion of the scale of distribution network, increase the proportion of cable network reform and gradual penetration of new energy, single-phase to ground fault current increase sharply, excessive ground current is a serious threat to the safe operation of power system. While the neutral grounding are closely linked to the single-phase ground fault occurs frequently in the power system. It is the technical basis that to ensure electricity customers “uninterruptible power supply” and to ensure the safe and reliable operation of distribution network, it has important theoretical significance. Now the neutral ungrounded system, neutral ungrounded via arc suppression coil and neutral ungrounded via low resistance are largely used in the medium voltage distribution network, this single neutral point operation mode can not adapt requirements of active distribution grid operation, thus the study of distribution network with flexible ground operation mode to improve the distribution network ground fault self recovery and the ability to quickly isolate the fault line.Firstly, the traditional grounding mode of medium voltage distribution network is analyzed, for ungrounded systems analysis of ferromagnetic resonance and disconnection fault analysis, arc ground fault modeling analysis; for resonance grounding analysis of virtual ground and grounding fault line selection problem; for neutral resistance grounding system introduced high resistance, the resistance and low resistance grounding characteristics, and comparing the three kinds of grounding modes advantages and disadvantages. Then based on the theory of flexible control technique by using active inverter to the distribution network with neutral point injected different inverter current realized the active state of the connected way, make the new neutral grounding mode combines the ungrounded, resonant grounded and resistance grounded mode. Next, the ferromagnetic resonance, wire break fault and single phase grounding fault which are closely related to the grounding mode of distribution network are studied, a comprehensive fault identification criterion based on the integrated three-phase voltage, three-phase current time domain characteristic variation and zero sequence voltage are adopted. Then the implementation strategy of the inverter current tracking control based on the single pole double frequency triangular wave modulation is adopted, and by constructing the related model in Matlab/Simulink, the simulation is carried out to verify the correctness of the theory. Finally, built a low voltage simulation experimental platform, through the analysis of experimental results, further verifies the feasibility of the new active grounding mode.