Research Of Flexible Arc-suppression Method And Control Strategy In Power Distribution Systems

With the development of power distribution network,power cables and nonlinear loads have been increasingly employed in the distribution network.When the instantaneous single-phase-to-ground fault occurs,the active and harmonic components in arc current are increased,which make failure arc be difficult to extinguish by itself.Since the active inverter technology could produce the active components and the harmonic components.To achieve the full-compensation of fault current,active inverter technology must been utilized in the hardware to overcome the drawback of single passive device which can only compensate the passive components.On the basis of the existing technique of active arc suppression and the multilevel converter technology,the flexible arc-suppression method(FASM)based on the three-phase cascaded H-bridge(CHB)converters has been proposed in this paper.The FASM adopts topological structure of CHB and accesses the system through each phase line.This method avoids z-type transformer and improves the reliability of FASM,because different CHB could alternate to each other.FASM controls CHB to inject compensation current when the single-phase-to-ground fault occurs,and limits the phase-voltage to zero to achieve arc-suppressionDifferent modulation methods will have affects on their output characteristics and design ideas for CHB.Traditional modulation methods adopt centralized control idea,which contain carrier phase-shifted(CPSPWM)and carrier disposition PWM(CDPWM).Cascaded numbers are limited since single centralized controller haven't enough I/O pins.Improved Distributed Commutations PWM(1DCPWM)greatly expands ability of controlling and calculation for each module of CHB.Moreover,it is easy to achieve modular design.Meanwhile,based on existing FASM the influence of line parameters and load current on arc-suppression of single-phase-to-ground fault are analyzed in this paper.Optimized arc-suppression method integrated with current arc-suppression method(CASM)and voltage arc-suppression method(VASM)is proposed.Switch condition is calculated through analyzing the residual currents of CASM and VASM.As a comparison of CASM,when the earth resistance is less than switch condition,VASM is more sensitive to load current.When the earth resistance is large than switch condition,VASM is an optimized choose due to the fact that it not only suppresses the fault current rapidly,but also is less affected by load current.Based on the different fault conditions,optimized method switches the CASM and VASM to realize the complementary advantages.In order to verify the feasibilities of FASM and IDCPWM,the contrastive experiments of software simulation verification and principle prototype verification have been carried out in this paper.On the basis of theoretical analysis,experimental platform which consists of five cascaded.units is constructed.Multiple single-phase-to-ground fault experiments have been carried out in the distribution network physical simulation system.The real experimental data of waveforms have been obtained via flexible arc suppression method to inject the corresponding compensation currents with CHB.The experimental results show that the proposed flexible arc suppression method can effectively suppress the fault current and curb arc.