Research On Flexible Arc Suppression Control Strategy For Single-Phase Grounding Fault In Distribution Network Based On Cascade H Bridge

As a large number of cables and power electronic nonlinear loads are connected to the power grid,when single-phase grounding fault occurs in the power grid,there is not only capacitive fundamental component,but also a large proportion of active and harmonic components in the fault current.However,the traditional anti-arc cabinet has some disadvantages such as long response time and PT ferroresonance.The traditional arc suppression coil can only compensate the reactive fundamental wave component in the ground fault current,and the residual current at the fault point is large.Although the traditional main and auxiliary arc suppression coil has better arc suppression effect,it needs to be connected to Z-type transformer and the control process is complicated.Based on the principle of static synchronous compensator STATCOM,a flexible compensation device based on converter is developed.By controlling the output of the converter,the full compensation of ground current is realized.There are many kinds of converter devices,based on cascade H bridge multilevel converter,because of its high output voltage level,low voltage stress,good waveform quality,simple control and many other advantages.Based on the analysis of the neutral ungrounded system and the neutral grounding system through the arc suppression coil,the flexible arc suppression theory based on the cascade H bridge converter is established in this paper.It includes the modulation strategy of cascade H bridge,measurement of ground parameters,calculation of compensation current,DC side voltage stability control,DC side voltage balance control,AC side current tracking control and so on.Firstly,the traditional modulation strategy is improved.The traditional amplitude-shift modulation strategy has better output voltage waveform quality,but the output power is unbalanced among each unit.Although the output power of each unit is balanced,the output line voltage harmonics cannot reach the optimal level.The new modulation strategy proposed in this paper has the advantages of both.Secondly,a voltage stability control strategy based on mode switching is proposed for the capacitor+ power cascade H bridge.By collecting capacitor voltage and output current to switch modulation mode,capacitor charge and discharge control is realized,and the voltage utilization rate of the unit is effectively improved.Then,the quasi-proportional resonance controller is introduced into the current loop control to improve the actual tracking effect of the inner loop current.Finally,the subunit micro control method is introduced in the DC side voltage equalization control.Compared with other control methods,the subunit micro control method is more concise and has better equalization effect.In order to verify the effectiveness of the flexible arc suppression strategy proposed in this paper,a simulation model of flexible arc suppression based on cascaded H-bridge multilevel converter is built in PSCAD simulation software.The simulation results verify the feasibility of DC voltage stability control,DC balance control and AC current tracking control.The effect of arc elimination under different ground resistance and arc,and the effect of the converter on the elimination of the fifth and seventh harmonics are verified.In order to verify the effectiveness of the new modulation strategy and combined control method,a cascade H-bridge experimental platform was built.The effectiveness of the proposed power balancing modulation strategy and the proposed mode switching based capacitor voltage stability control are verified by experiments.Figure[81] Table[7] Reference[74]...