Investigation Of High Voltage Pulse Forming Based On Metal-Oxide Varistors

With the pulsed power systems being more widely used in the industry,the efforts to reduce the weight and volume of such systems have become crucial.However,the large volume of the pulse forming line limits the miniaturization of the pulse power system.A basic idea to minimize the pulsed power system is to reduce the steps of energy transferring,such as generating square pulses directly from a Marx generator rather than from a Marx with a pulse forming line.In this thesis,we proposed a new pulse power system based on Metal-Oxide Varistor(MOV).Due to the special volt-ampere characteristics,MOV can be used to replace the pulse forming line and to generator high voltage square pulses,which contributes to the miniaturization and solidification of the pulse power system.The main works of this paper are listed below.1.The analysis of the working principle and conduction mechanism of MOVBased on the microstructure of MOV,the nonlinear volt-ampere characteristics,conduction mechanism and pulse shaping principle of MOV were analyzed,and the equivalent circuit of MOV was established.2.Research of the pulse forming based on MOVThe volt-ampere characteristic parameters of MOV were determined,and the PSpice model of MOV was established.The working conditions of MOV were obtained by PSpice simulation.The pulse forming experiments based on single-chip MOV and multi-chip MOVs were carried out.The result of the first experiment was with voltage of 7.5 kV,current of 250 A,pulse width of 325 ns and rising edge of 30 ns.And the result of the second was with voltageof 35 kV,pulse width of 700 ns and rising edge of 50 ns.3.Research of high voltage pulse generator based on PFN-MOV circuitTo improve the waveform and reduce the energy loss,a pulse shaping scheme with the combination of PFN and MOV was proposed.The design principle of PFN-MOV circuit was studied,and the related circuit parameters were calculated.An eight-stage Marx generator was constructed to study the pulse forming of 100 kV level.A square pulse with voltage of 95 kV,pulse width of 500 ns and rising edge of 40 ns was obtained on a 50 ? load.Then,a high-voltage pulse of 300 k V was researched and a MOV component was designed and constructed.Electromagnetic field simulation researches were carried out by CST to test the low inductance and insulation design.4.Research of the falling edge sharping and pulse width adjustment based on the magnetic switchA falling edge sharping scheme based on the magnetic switch was proposed to get shorter falling edge,which contributes to the improvement of the repetition rate.The theoretical analysis and simulation study were carried out,and the circuit parameters were calculated.Based on the special working mechanism of the magnetic switch,the pulse width adjustment was realized by changing the reset current.And a negative pulse consuming circuit was proposed to obtaining the unipolar output.Finally,the test experiments of the falling edge sharping and the pulse width adjustment were carried out.The falling edge was sharpened to less than 50 ns and the pulse width is adjustable whithin 200 – 900 ns.