High-frequency power converters enabled by wide bandgap (WBG) and silicon semiconductor devices offer distinct advantages in power density and dynamic performance. However, switching oscillations are commonly observed in these circuits with undesirable consequences. This paper reviews the impacts, root causes, and mitigation techniques of switching oscillations through literature survey, modeling analysis, and experimental investigation. We categorize the following root causes for oscillations during switching transients: 1) damped oscillation triggered by high di/dt and/or dv/dt coupled with parasitic elements; 2) undamped oscillation of WBG devices as part of a negative resistance oscillator; and 3) semiconductor device physical mechanisms such as the negative capacitance phenomenon due to conductivity modulation in insulated gate bipolar transistors or impact ionization in MOSFETs, the plasma extraction transit-time effect in bipolar power devices, and the reverse conduction property of GaN HEMTs. Furthermore, this paper discusses various circuit techniques to suppress switching oscillations, and techniques of extracting parasitic inductances of power devices.

The parasitic inductances of silicon carbide (SiC) power MOSFETs have a major influence on their operation and circuit performance. They incur negative effects such as switching oscillations, power losses and electromagnetic interference (EMI) noise. This paper introduces a new technique to accurately characterize the parasitic inductances of SiC power MOSFETs in both discrete packages and power modules based on two-port S-parameters measurement. By treating a power MOSFET as a two-port network, we obtain the scattering (S) and impedance (Z) parameters from network analyzer measurement. These parameters, through detailed network analysis, provide more accurate values of the internal parasitic inductances than the commonly used single-port impedance measurement technique. The new approach is first verified with high frequency circuit simulation and then applied in the case study of SiC power MOSFETs in a TO-247 discrete package and a half-bridge power module. In addition, a number of silicon power MOSFETs and IGBTs in TO-247, TO-220, D2PAK, DPAK, SO-8 packages are also characterized for comparison. A comparison between the characterization results from the new two-port and the prior art one-port methods reveals a significant difference ranging from 12.6% to 93.9%.

A new series-type hybrid circuit breaker (S-HCB) concept for dc fault protection is reported that is fundamentally different from other prior-art hybrid circuit breakers (HCB) or solid-state circuit breakers (SSCB) in the literature. The S-HCB conducts its load current through metal wires instead of power semiconductor switches and curtails its fault current to near zero throughout the entire opening process of a series mechanical switch. It offers the low on -resistance of the conventional mechanical contacts for normal operation and µs-scale fault response even faster than the fast-acting SSCBs. A proof-of-concept S-HCB prototype experimentally demonstrates the interruption of a fault current of 30 A within 10 μs at a dc voltage of 600 V. The operating principle, simulation, and experimental results are discussed in this letter.

Efficient first-principle simulation with self-consistence of the feedback-interferometric fiber laser sensor has been studied. The feedback-interferometric fiber laser sensor consists of a Distributed Bragg Reflectors/Distributed Feedback (DBR/DFB) fiber laser and an external feedback sensing element. The approach is self-consistent in that it effectively integrates the inter-dependence of the 980-nm pump/1550-nm laser powers and the rate equations of the Er/Yb co-doped fiber laser medium. The 1550-nm laser field is efficiently solved by Coupled Modes Theory (CMT) method while the solutions of the rate equations are obtained with the iterative Newton-Raphson method. Four types of external reflection schemes have been simulated: 1) without reflection at either side; 2) reflection at the pump side; 3) reflection at the remote side; and 4) reflections at both sides of the fiber laser. With the self-consistent simulation, the lasing wavelength and lasing signal power for various reflection schemes are obtained. In this investigation, the procedure to optimize the reflections to achieve optimal sensor sensitivity is demonstrated.

One disadvantage of conventional iris-loaded accelerating structures is the high ratio of the peak surface electric field to the peak axial electric field useful for accelerating a beam. Typically this ratio Es/Ea⩾2. The high surface electric field relative to the accelerating gradient may prove to be a limitation for realizing technologies for very high gradient accelerators. In this article, we present a scheme that uses a hybrid dielectric and iris-loaded periodic structure to reduce Es/Ea to near unity, while the shunt impedance per unit length r and the quality factor Q compare favorably with conventional metallic structures. The analysis based on MAFIA simulations of such structures shows that we can lower the peak surface electric field close to the accelerating gradient while maintaining high acceleration efficiency as measured by r/Q. Numerical examples of X-band hybrid accelerating structures are given.