Mitigation of Deane and Hamill phenomenon in gallium nitride high-voltage power supply for electric propulsion system application

The step-up resonant converters are widely adopted to provide high voltage in kV-level for electric propulsion system due to their high efficiency,low mass,modularisation,and high-power density.The bipolar Cockcroft-Walton voltage multiplier(BiCWVM)is a major circuit that steps up the voltage in the resonant converter.However,the diode nonlinearity in BiCWVM can introduce self-sustained quasi-periodic oscillations in the voltage and current waveforms,which is commonly known as the Deane and Hamill(DH)phenomenon.The oscillation can lead to higher magnetic loss and control failure,and it is more likely to present in the gallium nitride-based converter due to the highfrequency operation.The authors aim to investigate and mitigate the DH phenomenon systematically so that proper mitigation can be implemented.To facilitate the investigation,the circuit before the BiCWVM in the converter is derived and modelled as a voltage source v_(m)and a series inductor L_(sy).Also,the reverse recovery process of the diode in the BiCWVM can be represented by a piecewise-linear(PWL)model,with the simplified circuit and PWL model,the relationship between voltage and current under different operating conditions can be determined with ease.The relationship allows to understand the mechanism of diode reverse recovery in BiCWVM that leads to DH phenomenon.Finally,a hybrid-/full-silicon carbide(SiC)design is proposed to mitigate the DH phenomenon,which is verified experimentally for a 300-kHz,5-W,20-V/1.5-kV GaN-based step-up resonant converter.

Significant strain-rate dependence of sensing behavior in Ti0_(2)@carbon fibre/PDMS composites for flexible strain sensors

Carbon fibre(CF)embedded into elastomeric media has been attracting incredible interest as flexible strain sensors in the application of skin electronics owing to their high sensitivity in a very small strain gauge.To further improve the sensitivity of CF/PDMS composite strain sensor,the relatively low temperature prepared TiO_(2) nanowire via hydrothermal route was employed herein to functionalize CF.The results showed a significant increase in the sensitivity of the TiO_(2)@CF/PDMS composite strain sensors which was reflected by the calculated gauge factor.As the prepared TiO_(2) nanowire vertically embraced the surroundings of the CF,the introduced TiO_(2) nanowire contributed to a highly porous structure which played a predominant role in improving the sensitivity of strain sensors.Moreover,the significant strain rate dependent behavior of TiO_(2)@CF/PDMS strain sensor was revealed when performing monotonic tests at varied strain rate.Therefore,introducing TiO_(2) nanowire on CF offers a new technique for fabricating flexible strain sensors with improved sensitivity for the application of flexible electronics.