Yijie Sun

Surface flashover in vacuum is a critical factor restricting the stable operation of the high-power pulsed generators. Cross-linked polystyrene (XLPS) is always used to manufacture typical insulators for power pulsed generators, so it is important to study the surface insulation performance of the XLPS in a vacuum to improve the normal operation performance of the device. Based on the vacuum surface flashover test platform consisting of a solid-state gigawatt-level pulse generator and a test cavity, XLPS samples with a thickness of 13 mm were used to investigate the influence of roughness on the surface flashover characteristics. Samples with roughness of 1.3, 1.7, 2.2, and $2.7~\mu $ m were tested under both single and 10 Hz modes. It is found that the surface insulation performance of samples increases first and then decreases with the increase of roughness under both modes. Scanning electron microscope (SEM) was used to observe the micromorphology of the sample surface before and after the surface flashover events, enabling analysis of the effect of micromorphology on electron motion. Comparative analysis of the experimental results reveals that the first vacuum surface flashover voltage under both modes primarily depends on the surface roughness. Meanwhile, under 10 Hz mode, the first 50% flashover voltage, the conditioned flashover voltage, and the hold-on voltage are higher than those obtained in single mode, which indicates that the loading condition of the repetition rate pulse has a good aging effect on the sample.

Thermal runaway and electrical instability in pulsed thyristors under repetitive pulses critically limit the reliability of solid-state and compact high-power pulse generators. However, the bidirectional electrothermal effects of pulsed thyristors under repetitive pulses have not been studied. In this paper, they were explored based on mixed semiconductor device and circuit simulations and scaling experiments. The results show that within a ten-microsecond pulse, the maximum temperature rise occurs in the P2 region between the amplifying gate and the cathode under diode protection, whereas that occurs in the J1 junction near the anode without diode protection. The global maximum temperature decreases, and the heating region gradually expands with increasing pulse width. As the repetition rate increases, the temperature of the thyristor case is higher within the same testing time. Affected by higher temperature, the voltage drop and peak power dissipation increase and the anode current decreases. The residual temperature in the previous pulse further increases the heat generation in the next pulse. The electrothermal bidirectional coupling relationship under repetitive pulses was established theoretically, which can guide the application of high-power pulse generators in repetition rate mode.

Stacked Blumlein pulse generators are crucial for compact and solid-state pulsed power systems, facing a challenge for high efficiency. The study established a theoretical calculation model including electromagnetic coupling mechanism and proposed an improved design for the structure of inner conductors connected in parallel. Theoretical wave propagation analysis compares the output characteristics of two structures: inner conductors connected in series (traditional) and in parallel (improved). Calculation results show that the parallel structure exhibits a higher output voltage efficiency under the same conditions. Furthermore, PSPICE simulations verify the effect of coupled transmission lines on output waveform quality and voltage efficiency. The coupled transmission lines degrade waveform quality, with the electrical length determining distortion degree and characteristic impedance affecting voltage amplitude. Experimental tests confirm the superior voltage stacking efficiency of the structure of inner conductors connected in parallel. A 96.1% voltage efficiency with a five-stage Blumlein at 489-V charging voltage and 500- $\Omega$ load impedance was achieved, generating an output pulse with a pulsewidth of 72 ns and a rise time of 17 ns.

This paper presents a magnetically isolated gate driver for the fast switching of IGBT (Insulated Gate Bipolar Transistor) in compact pulsed power sources with sharp rising edges and flat-top pulses for the application of electromagnetic launch and food processing. The proposed gate driver is implemented based on a planar transformer with a half-turn winding arrangement to increase the amplitude of the driving voltage pulse. With the half-turn winding arrangement, the leakage inductance of transformers decreases by 31.1% compared to the interleaving structure. This decrease enables a fast rise time of the driving voltage pulse. Furthermore, the gate drivers are used to drive the IGBT switching a Blumlein pulse forming network. The results show that the di/dt of the applied commercially available Si IGBT is about 10.10 A/ns with a gate voltage of 50 V and a gate capacitance charging time of about 88 ns, proving the effectiveness of the gate driver and providing a high-performance driving scheme for the fast switching of Si IGBT.

The trigger generator made with a spiral generator (SG) has the advantages of light weight, compact structure, and low cost and has promising applications in the pulsed power field. This paper introduces a compact solid-state high-voltage pulse trigger system based on an improved SG, which has improved repetition rate and lowered the demands for semiconductor switches’ maximum current and current rise rate when compared with previous studies. The improvement is achieved by winding outward an additional layer of the passive layer and low-voltage metal strip, which realizes a significant reduction of the peak current and current rise rate of the discharge switch. The final dimension of the trigger is 25 × 10 × 10 cm3, excluding the power supply. An experiment carried out in single shot mode shows that the peak value of the output pulse can reach 50 kV with a leading edge of 57 ns. Repetitive experiments were carried out up to 1 kHz, with the peak voltage of the output pulse being 30.5 kV, the leading edge being 48 ns, and the jitter being 0.84 ns. Finally, the generator is used to trigger a gas switch, and it works stably and reliably.

The solid-state pulsed power generators (PPGs) are widely used in various modern industrial applications for their high repetition rate and long lifetime. The output characteristics of the generators are significantly affected by the dynamic characteristics of the semiconductor switches. Wide bandgap (WBG) semiconductor power devices, such as silicon carbide metal–oxide–semiconductor field-effect transistors (SiC MOSFETs), have the potential to structure solid-state PPGs due to many advantages, such as a high rated voltage, low on-resistance, high operational temperature, and fast switching speed. Typically, these devices are used in series/parallel connections to enhance the power level of the generators. However, this approach often leads to increased parasitic inductance of the switching modules, which results in flattened rising edges of the output pulse and reduced power transmission efficiency. The chip-on-board (COB) packaging method exhibits excellent high-frequency performance by allowing current paths to be more flexible, which is suitable for constructing the power module. This article proposes a solid-state PPG with Blumlein pulse forming network (BPFN) and COB packaging SiC-based switching module. The switching module is based on a four-layer printed circuit board (PCB). SiC MOSFET bare dies, gate drivers, and auxiliary elements are directly soldered on the top layer of the PCB. Separate conducting layers are connected to the terminals of the switching module by vias, which provides extra flexibility in designing and enables the stray inductance of the power loop to be minimized to 5.14 nH by optimizing the current communication loops. A 5-kV prototype of the solid-state PPG is fabricated based on the designed switching module. Under a resistive load of 2.8 $\Omega$ , a quasi-square pulse with a 62-ns pulsewidth and a 45-ns rise time can be obtained. Additionally, this generator has been tested at a 500-Hz repetition rate in the burst mode, and the di/dt of the switching module is about 80 A/ns, proving the effectiveness of the solid-state PPG.

Pulsed power generators utilizing magnetic switch technology within the 100 ns scale have become widespread for surface treatment, high power microwave generation, and food processing, in which the dynamic characteristics of the magnetic switch perform an important function. The saturation process, electric field between layers, and energy loss are closely associated with the applied time scale of the magnetic core, which affects the dynamic characteristics of the switch. However, compared with the study within the microsecond scale, the dynamic characteristics of magnetic switches within the 100 ns scale have not been studied in depth. In this paper, the dynamic characteristics of a coaxial magnetic switch modulating pulse forming networks (PFNs) are studied via both field-loop co-simulation and scaled experimental test. It is found that increasing PFN section number (Ns) leads to an acceleration in the saturation process of the core, which helps understand the switch performance of the magnetic core more clearly. With respect to a specific magnetic switch based on a ferromagnetic core, it is quantitatively analyzed that increasing Ns from 1 to 10 leads to a 16.1% reduction in core saturation time (tsat), a 13.4% increase in eddy loss (EET), and a 5.7% rise in maximum interlamination field strength (Emax) under the 100 ns scale; however, tsat is reduced by 19.3%, EET increases by 5.2%, and Emax rises by 2.3% under the microsecond scale. The results could provide a design reference for magnetic switches in pulsed power generators.

A pulse forming network (PFN) is a significant component, contributing a lot to the overall dimension of pulse generators. In order to both reduce the size of PFN and improve the output waveform quality, this paper proposes a compact low-impedance PFN with a rotational symmetry structure. The PFN consists of four groups of Blumlein pulse forming units (PFUs) connected in parallel along the angular direction, and the spline curve structure is applied in each PFU, which achieves a higher space utilization rate. The theoretical maximum energy density of PFN is 6.6 J/L as the dimensions of PFN are φ500 × 138 mm. Field-circuit co-simulation is carried out based on the spatial model of PFN and the double switch modulation circuit to analyze the effects of switch delay time (time between main switch and steep discharge switch), as well as the output port position affecting the output pulse waveform. The results show that the PFN is appropriate to achieve quasi-square wave pulse modulation as the switch delay time is 290 ns with the output port positioned at the periphery. The verification experiments are also carried out. The results show that the PFN can generate a quasi-square wave pulse with an output voltage of 49.6 kV, a pulse width of 83 ns, and a peak power of 1 GW on a matched load. The output pulse exhibits a distinct flat top, with the fluctuation of the plateau being less than 3%.

The non-uniform current distribution in high-power thyristors leads to a significant rise in local junction temperature (Tlj), potentially threatening the reliability of high-power thyristors. For online monitoring Tlj, a novel temperature-sensitive electrical parameter (TSEP) method was proposed based on peak stray gate current (ipsg). First, simplified turn-off models for high-power thyristors with an amplifying gate were set up to explore the variations of gate-cathode voltage and stray gate current in the turn-off transition. Subsequently, the theoretical relationship between ipsg and Tlj was established. Significantly, the physical meaning of Tlj was illustrated by the theoretical relationship and the temperature distribution simulation. Next, the feasibility of the proposed method was verified by the temperature calibration experiment. Considering self-heating, the temperature sensitivity is 89 mA/℃ at a thyristor voltage of 1.0 kV, which increases with increasing thyristor voltage. Finally, an online monitoring Tlj case was carried out based on a tunnel magnetoresistance current sensor. The proposed method is easy to implement and is capable of measuring local junction temperature concerning major heat generation regions, which is suitable for high-voltage applications.

Pulsed thyristors widely used in pulsed power generators are more easily confronted with damage problems in the turn-on process due to insufficient lateral current spreading under short pulses. This study aims to explore the spatial and temporal characteristics of the lateral current spreading under short pulses and reveal the relationship between the lateral current spreading and the external circuit with inductive load. Based on turn-on characteristics experiments of a thyristor with an amplifying gate and emitter shorts, mixed semiconductor device, and circuit simulations were carried out to compute the variation of current density in the thyristor under a ten-microsecond pulse. The results show that the current spreads incompletely under 17 $\mu $ s pulse due to the external circuit and the emitter short. For comparison, the current can continue spreading at the back of the first emitter short as the pulsewidth is 150 $\mu $ s. The relationship between the current lateral spreading and the external circuit with inductive load under short pulses is established, and a necessary condition for the current to spread at the back of the first emitter short is proposed.