| At present,Chinese distribution network mainly uses the way of neutral point grounding through arc suppression coil.When a single-phase grounding fault occurs in the power grid,the arc suppression coil provides inductive current to compensate the power frequency capacitive current of the grounding point,so that the fault arc can eliminate acceleratedly and further avoid severe consequences of the escalation of arc reignition accidents.However,with the use of power cables in urban distribution networks and the increase of non-linear loads,coupled with the diversity of distribution network operation modes,the residual current of the single-phase grounding faults in distribution network with conventional arc suppression coil is more serious,which intensified the difficulty of single-phase grounding fault arc suppression.In order to achieve arc suppression effectively,it is necessary to thoroughly study the full-current compensation to achieve the key technology of ground fault current to zero,which helps to further improve the safety and reliability of the distribution network.Firstly,a single-phase grounding fault circuit model is constructed to deeply analyze the sources and characteristics of grounding residual currents.Based on the characteristics of residual currents and the shortcomings of current arc suppression systems,the new compensates topology of “Arc-suppression coil + cascaded H-bridge inverter” is proposed,that both the capacity of arc suppression devices can be reduced and the measurement accuracy of grounded parameters measurements can be improved.Then a circuit model for the grounding current compensation of the distribution network based on this topology is established,and a command compensation current that can promote the ground current to be zero is deduced;In order to realize the command compensation current,the key parameters of the active arc suppression system and cascaded H-bridge control method are designed.The control system model of the cascaded H-bridge inverter active compensation distribution network is established,and the mechanism of the effect of neutral point voltage on command current is deduced,for this problem,a voltage feed-forward suppression method is proposed.Then,the parameters of the current closed-loop regulator followed the power frequency and multiple harmonics are designed,the entire active full compensation system is designed finally.Secondly,on the basis of completing the design of active arc suppression system,for the problem of inaccurate command compensation current due to measuring grounded parameters inaccurately,the resonant measurement principle of the injected sweep signal is introduced firstly,and then deduced the characteristics of windowed DFT with linear phase and suppressed the spectral leakage,then proposed a windowing DFT phase difference detection and Newton interpolation method applied to the measurement of accurate resonance determination.Finally,a distribution network simulation model with harmonic sources is established in MATLAB.Under the given conditions of the grounded parameters,the effectiveness of the control system and the arc suppression strategy were verified,the simulation results show that the active arc suppression system can follow complicated instruction currents without deviation and the effect of arc suppression is remarkable;Using the arc suppression simulation model to inject the sweep frequency signal verifies the effectiveness of measuring grounded parameters scheme of the windowed DFT,the results show that the measurement method has high accuracy for the measurement of distribution network grounded parameters of different operation modes;The laboratory physical model of the distribution network is designed,the hardware and software design ideas of the active arc suppression system experiment platform are introduced in detail,the experimental results show that the system is operating normally and has good performance,and the test has obtained basic experimental data. |
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