| High power microwave(HPM)technology is becoming practical after many years of development.Long life,high efficiency and stable repetitive operation are of the important developing directions of HPM technology.It is high time to replace the gas switch with a solid state switch.Although a lot of research has been carried out on the application of semiconductor switching pulse power,the repetitive HPM driver based on semiconductor switching is not available yet.It is of great significance to study a new all-solid-state,highefficiency and modularized pulse power driver,which can meet the requirements of low jitter,long life and high repetition rate of HPM system.This paper presents a technical scheme of linear transformer driver(LTD)based on IGBT switch and pulse forming network(PFN).Theoretical analysis,circuit simulation and experimental study of solid state LTD were carried out.A solid-state pulse power driver with output voltage of 500 k V and output power of 3GW was designed and developed successfully,and it was applied to the experimental study of HPM generation.The main work of this paper includes:The principle circuit of FLTD(Fast-LTD)was analyzed.An independent primary and secondary current loop structure for solid state LTD was proposed.Based on this,a solid state LTD system structure with pulse generating module and linear transformer was proposed.The equivalent circuit of LTD system was established by using pulse transformer model,and the influence factors of two key parameters of system efficiency and pulse front were studied by using a single stage LTD equivalent circuit.It was found that the influence law of load matching impedance on the two parameters is opposite.A method to calculate the matching impedance corresponding to the highest transfer efficiency of LTD under the condition of given core and primary and secondary circuits was proposed.The optimal matching impedance reveals the low resistance characteristics of linear transformer.In the design of 500 k V system,the compromise between pulse front and system efficiency was considered,and the final matching impedance value of the system was determined to be 85Ω,and the total series was 50.Finally,the structure parameters of the output coaxial line using transformer oil as insulation medium were calculated,and then the size and system structure of the magnetic core were determined.The relationship between various parts of THE LTD system was given,and the weight and volume of the system were analyzed briefly.A pulse forming network based on multilayer ceramic capacitors(MLCC)was proposed and studied.Firstly,the pulse forming network was analyzed theoretically,and the characteristic impedance and pulse width of PFN were solved.The cutoff frequency of PFN was calculated and the minimum order of PFN was deduced.Combined with software simulation,the rising edge estimation formula of single wire plus switch was obtained.The edge slowing of pulse in single line transmission was studied,and the edge estimation method of pulse generation module based on Blumlein line was obtained.The characteristics of MLCC were analyzed and tested,and MLCC of C0 G ceramic material was selected.A compact interstage inductance was designed using multi-section copper-clad wire on PCB and combined with MLCC to form a compact PFN.Blumlein-PFN had been tested and its voltage resistance was more than 5k V,output pulse width was close to 120 ns,and discharge efficiency was more than 93%,which can meet the requirements of long time operation.A solid-state switch scheme of IGBT array with series magnetic switch was proposed.The main influencing factors of IGBT’s di/dt were analyzed.The comparison analysis and test of several compact IGBT were performed.The problems of voltage and current equalization among different IGBTs in IGBT switch array were solved.A high voltage trigger circuit of switch array with maximum delay time less than 2ns was developed,and a6×6 IGBT switch array was designed.In order to further reduce the rising time of the output pulse,magnetic switches were connected in series in the IGBT switch discharge circuit.The principle and key parameters of magnetic switch compression pulse front were studied,and the core material with high rectangular ratio was selected and the magnetic switch structure was designed.The experimental verification of series magnetic switch shortening pulse front was completed.The voltage of the solid-state combined switch was over 5k V,the current was close to 1k A,and the pulse front was less than 20 ns.A design of pulse generating module was proposed.Pulse generating module includes two pulse generation units in series,charging circuit,linear transformer reset circuit,output voltage clamp circuit,fault detection and protection circuit,etc.The structure and interface of pulse generating module were designed.Inverse voltage suppression circuit was invented.The technical scheme of fault detection and information transmission was studied.The pulse generating module of LTD had been successfully developed and tested for a long time.The output voltage was 10 k V,the efficiency was 93%,and the test pulse number was 108.The single-stage LTD was built using pulse generating modules and tested.The output high voltage pulse with peak voltage of 9.7k V,current of 4.6k A and front edge of 18 ns was obtained on the matched resistance load,and the calculated energy efficiency was 86.3%.Moreover,a 5-stage 50 k V LTD test platform was built,the output voltage was about 35 k V,the current was 4.6k A,the power reached 161 MW,the pulse front was 22.5ns,the pulse width was 138 ns,and the estimated energy efficiency was more than 80%.A LTD pulse power driver,which consists of 400 pulse generating modules and 50 stage units,had been successfully developed,including supporting control and protection system,high voltage charging power supply,magnetic core reset power supply and trigger system,etc.The total weight of the pulsed power driver was 2.2 tons and the length was2 m.The system was debugged with water resistance load.The output voltage,current and output power of 100Ω water resistance load are about 500 k V,5k A and 2.5GW,which can work under the rep-rate 50 Hz.Finally,the experiment of high power microwave generation was carried out on a foil-free diode load with the relativistic back-wave-oscillator.The output voltage was 500 k V,the pulse width was 125 ns,the pulse front was 28 ns,and the peak power reached 3GW. |
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