Study On The Operation Characteristics Of Solid-state Compact PFN-Marx Generators

PFN-Marx is one of the hot issues in HPMT?High power microwave technology? due to its capability of voltage boosting and pulse forming. The PFN-Marx generator utilizing high voltage capacitors with intensive energy storage density becomes an important means for the compactness, miniaturization and modularization of pulsed power platforms. In this thesis, the charging and discharging theories of a single PFN are elaborated and the analysis about a pulse transformer charging to the Marx is accomplished. Then, the PFN-Marx discharging process is analyzed and the influence of system stray parameters together with inter-stage electromagnetic coupling is simulated. Based on the built multistage PFN-Marx generator, the single stage test and 10-stage output experiment are carried out. Through comparison, the effect that different parasitic parameters have on the waveforms of output and measurement signal is studied. The influence of both isolating inductors placement and ultraviolet coupling on the system establishment time is investigated as well. The detailed contents are as follows.1. Based on LC ladder theory, the charging and discharging characteristics of a PFN are elaborated and simulated. The network latency of the PFN makes itself propagate waves like a PFL. The PFN characteristic impedance is derived as?L/C?^1/2. It can output a rectangular pulse with the amplitude of V/2 and pulse width of 2n?LC?^1/2 to the matched load. The capacitors in the network discharge one after another. And smaller section inductance and capacitance make signal rise faster. Falling time is lengthened as node number increases.2. Three types of isolating inductors placement are investigated and the process of a pulse transformer charging to the serial type Marx generator is focused on. It is possible to derive the voltage expressions on each PFN applying KVL?Kirchhoff Voltage Law? with the reduction method and Euler's method of differential equations. The consistency of charging voltages can be improved by increasing the primary capacitance Cp and the inductance Lp, or decreasing the value of isolating inductor Li, stage capacitance Ci and stage number n. It is irrelevant to all the parameters above in the parallel type generator because of the identical charging circuits. And in the serial-parallel type, good consistency can be achieved by optimizing the parameters. The derivation reveals when the isolating inductance is greater than 8C0RL²/n², the output waveform of the Marx can be nearly the same with that of a resistors isolated generator. The parallel and serial-parallel PFN-Marx generators have more outstanding switch over-voltages due to their circuit structures, while the transient over-voltages of serial type rely on the distributed capacitance.3. The influence of parasitic parameters on the output is adequately analyzed. The investigations claim that the inductance of leads and switches in the output circuit lengthens the pulse rising time and stray resistance drops the pulse amplitude. The pulse width will be affected if the load has self-coupled capacitance. The inter-stage coupled transmission lines not only overlay high frequency oscillation on the output but also narrow the pulse width. The wave propagation analysis and circuit simulation indicate that the higher its impedance is the less impact the inter-stage coupled transmission line would bring.4. The platform is carefully designed and built, on which the related experiments are carried out with PFN-Marx structure compact and energy storage solid-state. Through comparison, the cause of superimposed oscillation on the output is then studied. The ground capacitance of the load together with the system grounding inductance forms LC resonance which overlaps low frequency oscillation on the pulse. And the reverse voltage and high frequency oscillation can be found on the measurement signal because of the capacitance between the voltage divider and ground as well. The 10-stage PFN-Marx generator can output a good pulse waveform with a compact structure by minishing the value of the stray parameters mentioned ahead. The experiment results declare that not only the parallel placement of isolating inductors connected to the ground but also ultraviolet coupling phenomenon in the multistage switch can shorten the Marx establishment time. Moreover, as the air pressure goes up and the break-down voltage increases, the jitter of the spark gap switch is reduced.