Research On Marx Generator Based On Photoconductive Switches

With the development of science and technology and today’s needs in the fields of scientific research,aerospace,industry and national defense,the industry is concerned about the output power,output energy,pulse frontier,pulse frontier rise rate,repetition frequency,pulse width and volume of pulsed power systems.There are more stringent requirements,among which the switching technology has a significant impact on the performance of the system.As a new type of switch with the advantages of fast response,strong flow capacity,high voltage resistance,high repetition frequency,low jitter and small size,the photoconductive switch has a significant improvement in the performance of the pulse power system.This article takes the Marx generator as the research object,and the main work is as follows:(1)The structure and charging and discharging methods of the classic Marx generator with spark gap switch as the main switch are theoretically analyzed,and then several solid-state Marx generator structures are analyzed.Among them,the inductively isolated Marx generator has fast speed and high charging efficiency.Diode-isolated Marx generators and switch-isolated Marx generators have a small charging equivalent loop time constant,and the charging time is relatively short,which can achieve a high repetition rate.In addition,when the discharge loop switch is not turned on synchronously,the diode can quickly clamp the switch voltage to prevent the switch from being damaged by overvoltage.Taking into account the convenience of reflecting the switching performance and frequency requirements,resistance-isolated Marx generators and switch-isolated Marx generators are selected for simulation and circuit design.(2)Using a dual-channel independent control input and output drive chip,and internal electrical isolation,together with the peripheral circuit to form an IGBT drive circuit unit.There are multiple units on the drive circuit,which can control multiple IGBTs with good synchronization.It can output 15 V signals with adjustable frequency and pulse width.The frequency and pulse width are the same as the input PWM signal.Two-stage and four-stage resistance-isolated Marx generators and switch-isolated Marx generators are tested.Under the test conditions of charging voltage 500 V and 50 Ω load,the Marx generators of the two structures work in the saturation zone because of the IGBT.The on-resistance is so large that the theoretical pulse amplitude cannot be output.After increasing the load resistance,the IGBT working area is close to the linear area,and the output amplitude is close to the theoretical value.(3)An experimental platform was built,and a pulse-generating test circuit was designed to test the conduction performance of high-purity Si C photoconductive switches and vanadium-doped Si C photoconductive switches.The on-resistance of the high-purity switch is 891.6 Ω,and there is an obvious step phenomenon at the rising edge of the switch.The on-resistances of the two vanadium-doped photoconductive switches are 124.8 Ω and72.5 Ω,respectively,and the rise times are 2.7 ns and 3.75 ns,respectively.Two vanadium-doped photoconductive switches are used in the two-stage resistance-isolated Marx generator.Under the test conditions of 500 V and a laser repetition frequency of 10 Hz,the pulse output amplitude on the load is-87 V,the rise time is 4.38 ns,the pulse width is 4.25 ns,and the rise time rate of change is-15.9 V/ns.(4)Based on theoretical analysis and experimental results,research directions that can improve system performance are proposed.The use of pulse steepening technology to achieve a faster cutting-edge method can make up for the lack of switching performance.Reducing the on-resistance of the photoconductive switch can increase the pulse amplitude obtained on the load.The switch is made of materials that can make the photoconductive switch work in a non-linear mode.When the switch works in the non-linear mode,the demand for laser energy can be greatly reduced,and weak light triggering can be realized.In this case,a small laser can be used to achieve a compact system.At the same time,small lasers can usually perform pulse width modulation,control the output energy,etc.,to achieve precise control of the photoconductive switches.