Search Results (312)

This article presents a low-cost, high-voltage excitation circuit (EC) for capacitive ultra-sonic transducers (CUTs) based on a dual-path architecture. The proposed design comprises two independent AC excitation channels (AC-branch) that share a regulated DC-bias voltage (DC-branch). The circuit was developed to satisfy a fundamental operational requirement of CUTs: simultaneous application of a static bias voltage and a time-varying drive voltage. Because the electrostatic force depends nonlinearly on the applied voltage, efficient first-harmonic actuation requires the superposition of DC and AC voltage components. To reach this objective, the circuit and the transducer must be treated as a coupled electrical, electrostatic, mechanical, and acoustic system. In the proposed implementation, the DC-branch uses a TL494-PWM controller, a TIP50 switching transistor, a step-up transformer, and a rectifier-filter stage to generate the high-voltage bias of up to 200 V_DC. Each AC-channel employs an LM3886TF amplifier followed by a 1:15 step-up transformer, enabling the generation of excitation signals of up 180 V_peak. A key feature of the proposed architecture is the electrical independence of the two AC-channels, which allows for distinct excitation frequencies with minimal mutual interference. Experimental validation, performed with and without ultrasonic loads, demonstrates the relation between excitation conditions and the acoustic performance of the CUTs. Full article

This paper addresses the trade-off between electromagnetic interference (EMI) and common-mode transient immunity (CMTI) performance in capacitively isolated gate drivers for high-frequency silicon carbide (SiC) applications. Starting from the fundamental architecture of on-off keying (OOK) modulation, a novel transmitter (TX) modulator architecture is proposed. The proposed architecture employs a dynamic high-frequency carrier regulation circuit to suppress electromagnetic interference caused by the fixed carrier at the spectral source, while simultaneously utilizing a dynamic substrate regulation circuit to mitigate the impact of common-mode transient interference on the TX side, thereby enhancing the overall CMTI performance. The chip is fabricated in a 0.18-μm BCD process. Simulated carrier spectrum peak attenuation across different process-temperature corners demonstrates that the attenuation ranges from 4.43 dB to 19.621 dB across the fundamental through the third harmonic components. Under the same typical process-temperature corner, the simulated CMTI reaches 220 V/ns, which fully validates the effectiveness of the proposed architecture in both spectral peak reduction for EMI suppression and CMTI enhancement. Post-fabrication chip testing primarily focuses on output performance, with both the simulated carrier spectrum results for EMI and the CMTI being simulation-verified indicators. The measured output voltage range is 15–24 V; at a supply voltage of 15 V, the charging and discharging currents are 5 A and 4.5 A, respectively, and at 24 V, they are 5.7 A and 5.3 A, respectively. Full article

In this study, n-channel 4H-SiC MOSFETs with a high-k/SiO₂ stacked gate dielectric and a p⁺-polysilicon gate are proposed and investigated via numerical simulations. The high-k dielectric increases the gate capacitance, thereby reducing the specific on-state resistance of the devices. The p⁺-polysilicon increases the work-function difference between the gate and the surface p-SiC, which compensates for the threshold voltage reduction caused by the high-k dielectric. Simulation results demonstrate that replacing the SiO₂ and n⁺-polysilicon with an Al₂O₃/SiO₂ stack and p⁺-polysilicon, respectively, reduces the specific on-resistance by 26.9% while lowering the threshold voltage by only 0.02 V at 25 °C. At 175 °C, the threshold voltage increases by 0.28 V. The temperature coefficient of the threshold voltage is reduced from −6.2 mV/°C to −4.1 mV/°C. In addition, the breakdown voltage, the high-frequency figure of merit, and the switching loss also improve, though the inter-electrode capacitances and the gate-to-drain charge increase. This work provides a practical solution for n-channel 4H-SiC MOSFETs adopting high-k gate dielectrics. Full article

Quasi-vertical (QV) GaN Schottky barrier diodes (SBDs) have emerged as a promising device architecture that overcomes the limitations of conventional lateral and vertical SBDs while offering high electrical performance. However, the influence of the lateral and vertical current-transport dimensions on the electrical characteristics of QV GaN SBDs has not been systematically evaluated. In this study, the effects of the anode-to-drift length (L_AD), drift-to-cathode length (L_DC), and drift-layer thickness (DLT) on the DC and RF characteristics were systematically investigated. Variations in L_AD and L_DC produced relatively modest changes in the forward conduction characteristics, with the current density decreasing by up to 15% and the specific on-resistance (R_ON,SP) increasing by up to 29%, while the breakdown voltage (BV) varied by less than 4%. Increasing the DLT from 0.5 to 4 μm produced substantially larger variations, reducing the current density by 62% from 11.38 to 4.28 kA/cm² and increasing R_ON,SP by 171% from 0.17 to 0.46 mΩ·cm², while BV increased from 55 to 199 V. The stronger dependence on DLT, particularly in reverse blocking capability, identifies DLT as the dominant geometrical parameter governing the DC characteristics. RF characterization as a function of DLT showed that the series resistance (R_s) strongly depended on DLT, whereas the junction capacitance (C_j) exhibited comparatively moderate variation. The DLT = 0.5 μm device exhibited the highest estimated RC cutoff frequency (f_c) of 18.2 GHz, whereas the DLT = 1 μm device maintained a relatively high f_c of 15.3 GHz while providing a more balanced DC and RF performance. The device with L_AD/L_DC = 7/5 μm and DLT = 1 μm exhibited R_ON,SP = 0.21 mΩ·cm², turn-on voltage (V_ON) = 0.54 V, and BV = 128 V. These findings provide practical guidelines for the dimensional design of QV GaN SBDs for microwave rectifier applications. Full article

Taking a typical high-power microwave power supply system as the research object, this paper quantitatively simulates and compares electromagnetic disturbance characteristics under multiple operating conditions, systematically investigates the influence mechanism of the system on EMI, and verifies the proposed simulation model via prototype experiments. Firstly, the typical equipment composition and three operating modes of the system are elaborated. Standardized high-frequency equivalent circuits of thyristors, capacitors, and inductors are established, and parasitic parameters are extracted to construct a system-level high-frequency coupling model. Different from traditional static parasitic extraction and separated field-circuit simulation methods, the proposed global collaborative optimization co-simulation method with voltage-dependent thyristor parasitic model significantly improves EMI prediction accuracy under full-cycle multi-mode operation. Secondly, based on the dynamic device characteristics under resonant charging, energy recovery and energy supplement modes, the generation mechanisms of EMI are clarified with quantitative data. During modeling, the electrical characteristics of thyristor body diodes and inter-electrode capacitances are fully incorporated with reference to actual component parameters. The EMC co-simulation based on CST field-circuit coupling is adopted to collaboratively optimize all parameters, which reduces the approximation error introduced by local modeling and greatly improves simulation accuracy. Combined with simulation and prototype experimental verification, this paper reveals the multi-path EMI coupling mechanism of pulsed power systems. The proposed parasitic parameter-based SPICE modeling and field-circuit co-simulation method can provide quantitative analysis tools and theoretical support for the EMC suppression design of high-power microwave power supplies. Full article

The rapid growth of battery energy storage systems, renewable energy integration, electric vehicles, and DC microgrids has significantly increased the demand for compact, efficient, and bidirectional isolated DC–DC converters. Conventional Dual Active Bridge (DAB) converters commonly employ high-frequency transformers to provide galvanic isolation and bidirectional power transfer. Although transformer-based DAB converters offer excellent performance, their magnetic components increase converter volume, weight, core losses, leakage inductance, manufacturing complexity, and overall cost. Consequently, recent research has explored alternative high-frequency energy transfer techniques based on capacitive coupling, aiming to reduce magnetic components while preserving efficient resonant power conversion.This paper proposes a Capacitively Coupled Dual Active Bridge (CC-DAB) converter employing high-power metallized polypropylene (MKPH) capacitors as the high-frequency energy transfer medium. The proposed converter operates at a relatively low switching frequency while investigating the safe operating conditions of the capacitive coupling network to ensure reliable and efficient power transfer. A microcontroller-based single-phase-shift (SPS) modulation strategy is implemented to generate the gate-driving signals of the full bridges, whereas the switching frequency is selected to achieve zero-voltage switching (ZVS) throughout the investigated operating range. The phase-shift angle ($\varphi$) regulates the transferred power by controlling the voltage difference between the primary and secondary bridges across the capacitive coupling network. The proposed converter is analyzed theoretically and validated through simulation and experimental testing. Experimental results demonstrate stable bidirectional power transfer, soft-switching operation, and a peak conversion efficiency of 91.3% at a relatively low switching frequency of 52 kHz. The experimental verification confirms the practical feasibility of capacitive coupling for resonant bidirectional power conversion and demonstrates its potential as an alternative architecture for low- and medium-power applications requiring compact size, high efficiency, reduced magnetic component requirements, and reversible energy transfer. Furthermore, the proposed topology contributes to the ongoing development of transformerless resonant converters by experimentally validating a high-frequency capacitive coupling network capable of supporting efficient bidirectional power flow under practical operating conditions. Full article

Field voltage testing after the maintenance of large converter transformers requires high-voltage response verification while preserving the restored equipment boundary. However, conventional direct voltage application on the grid side usually requires the disconnection of high-voltage leads and auxiliary devices, which may alter the original electrical boundary and increase field disturbance. To address this issue, this study develops an integrated framework with three core contributions: a minimal-lead-disconnection induced-voltage testing topology, a boundary-specific engineering-equivalent parasitic-capacitance model, and a terminal-referred phasor-based power-supply capacity-calibration method. Under the proposed testing topology, single-phase power-frequency excitation is applied on the valve side, and the induced-voltage response is established at the grid-side bushings while some of the restored auxiliary-equipment connections are retained. Considering the parasitic capacitance introduced by valve towers, tubular busbars, grading fittings, and grid-side auxiliary devices under the minimal-lead-disconnection boundary, an engineering equivalent model for extracting the valve-side stray capacitance is developed based on quasi-static electric field theory, geometric-envelope dimensional reduction, and conformal-mapping-based edge correction. The grid-side equivalent capacitance is further obtained using equipment parameters. On this basis, the induced-voltage distribution under the interconnection of multiple converter transformers is analyzed, and a power-supply capacity-calibration method considering the phasor relationship between inductive excitation current and capacitive current is established. Pre-test calculations yield a valve-side stray capacitance of 0.96 nF and a grid-side equivalent capacitance of 1.27 nF. When the grid-side induced voltage of phase C reaches 9.90 kV, the induced voltages of phases A and B are 4.56 kV and 5.14 kV, respectively, while the apparent power calculated from the field-measured RMS voltage and current is 1.34 kVA. The results verify the effectiveness of the proposed method for low-disturbance field testing and portable test-power-supply configuration. Full article

In aerospace applications, structural vibration can cause fatigue accumulation and shorten the service life of aircraft. This makes vibration suppression based on Macro Fiber Composite (MFC) piezoelectric composites an important research topic. Considering the asymmetric high-voltage operating range of the M-8557-P1 MFC from −500 V to 1500 V and its capacitive impedance characteristics within the 1000 Hz operating frequency band, this paper designs a laboratory prototype of a high-voltage driver. The prototype adopts a voltage–current dual closed-loop structure and a current-tracking PWM control strategy. Under the tested laboratory conditions, the prototype exhibited a relatively fast transient response and a certain dynamic driving capability for capacitive loads. Based on the laboratory prototype, an auxiliary signal-conditioning module and a digital control module equipped with an active control algorithm were further developed. These modules were integrated with the laboratory prototype to form a high-voltage closed-loop control system for MFC piezoelectric sensing and actuation. Ground laboratory tests were conducted on a high-aspect-ratio unmanned aerial vehicle wing. The experimental results show that, when the dominant vibration frequency is approximately 3.6 Hz, the response converges to a steady state within 4.77 s after control is applied. In the steady state, the root-mean-square displacement decreases from 15.57 mm to 4.28 mm, corresponding to a reduction of 72.52%. This result demonstrates the effectiveness of the active vibration control system under this representative application scenario. Full article

During the entire service cycle, the Electro-Hydrostatic Actuators (EHAs) are subjected to multi-physical stresses, including coupling effects, including high temperatures, severe temperature variation, and high-frequency pulses. These stresses not only act on the mechanical structures but also continuously degrade the dielectric properties and mechanical strength of the insulation materials, with long-term accumulation potentially leading to deterioration in insulation performance. Consequently, whether the insulation system can remain stable under such harsh conditions becomes a core factor constraining EHA reliability, and its insulation reliability directly determines the operational safety of aircraft actuation systems. Targeting the aerospace EHA motor insulation system, this paper aims to construct a systematic condition assessment method and a life degradation feature based on the dynamic evolution characteristics of multi-dimensional dielectric parameters. This study conducts accelerated thermal aging and thermal cycling tests on a 270 V Type I aerospace EHA motor insulation system, with multi-parameter tracking of equivalent capacitance (Ceq), partial discharge inception voltage (PDIV), and leakage current (I). The results indicate that Ceq exhibits high sensitivity to early-stage insulation damage. PDIV presents non-monotonic fluctuations during aging, and combined with Paschen’s law, the reduction in air-gap dimensions due to thermal expansion in the mid-stage is the physical origin of its phased recovery—verifying the rationale in using PDIV as the electrical safety boundary. In contrast, leakage current shows significant hysteresis, remaining robust at 0.35–0.55 mA until a sharp jump signals the formation of through-going conductive channels, which serve as the ultimate failure criterion. On this basis, a hierarchical assessment framework is constructed: Ceq captures degradation precursors, PDIV defines the safety boundary, and leakage current acts as the final failure indicator. This study refines the multi-stress evaluation method for aerospace motor insulation and provides experimental support for reliability assessment and life prediction of actuation systems in next-generation more-electric aircraft. Full article

The increasing penetration of inverter-based renewable energy sources and the growing share of underground cable lines significantly modify the frequency-dependent characteristics of medium-voltage distribution networks, increasing the risk of harmonic resonance. Existing resonance studies are often based on detailed electromagnetic models that are difficult to apply during routine distribution network planning and operation. This paper proposes an engineering-oriented methodology for the preliminary assessment of harmonic resonance risk using an equivalent lumped-parameter model that incorporates overhead and cable lines, transformer inductance, photovoltaic generation, and the short-circuit strength of the supplying system. The methodology is applied to a representative 20 kV distribution network to investigate the influence of cable penetration, photovoltaic capacity, transformer loading, and grid strength on resonance conditions. The results show that increasing network capacitance and reducing short-circuit power shift the resonance frequency toward lower-order harmonics, increasing the probability of harmonic amplification. The highest resonance risk is observed under the combined conditions of high photovoltaic generation, low transformer loading, and weak-grid conditions. Unlike detailed electromagnetic simulation models, the proposed methodology enables rapid engineering assessment using parameters readily available to distribution system operators, thereby supporting network planning and operational decision-making in medium-voltage distribution systems with high photovoltaic penetration. Full article

This paper presents the comprehensive design, analytical modeling, and simulation validation of a dual active bridge (DAB) converter for bidirectional power interfaces in microgrid applications. The proposed analysis is developed under single phase shift (SPS) modulation and is based on the voltage applied across the leakage inductance of the high-frequency transformer (HFT), from which the interval-by-interval evolution of the current is derived. This formulation allows the main electric variables of the HFT to be obtained analytically, including the transferred power, average output current, output power, and RMS current stress. The proposed sizing procedure also considers different operating cases according to the power flow direction and the voltage relation between the high- and low-voltage (HV and LV) DC buses. Particular attention is given to the sizing of the DC bus capacitors, whose capacitance and RMS current requirements are determined based on charge variation and the allowable voltage ripple. The analytical results are validated using a PSIM simulation model under both HV-to-LV and LV-to-HV power flow, including operation under a significant voltage mismatch condition. In addition, calculated and simulated results are reported for all four operating cases, demonstrating good agreement between the analytical formulation and the converter’s simulated behavior. Full article

Geoelectric field observations play a vital role in geophysical exploration, geological disaster early warning, and underground resource detection. Traditional contact non-polarisable electrodes, which require burial and electrolyte coupling, are hindered by several issues, such as limited adaptability to challenging terrain, significant electrode potential drift, and high susceptibility to environmental interference. Existing non-contact electric field sensors often exhibit insufficient coupling capacitance, poor impedance matching for ultra-weak high-impedance signals, and inadequate low-frequency noise suppression, rendering them unsuitable for the precise acquisition of natural microvolt-level geoelectric field signals. To address these challenges, this study introduces an innovative non-contact geoelectric field sensor with a three-layer composite structure. The sensor operates based on the principle of a parallel-plate capacitor, with a conductive silver paste layer at the top acting as the signal acquisition electrode plate, which forms an equivalent parallel-plate capacitance model with the ground to achieve non-contact capacitive coupling for geoelectric field detection. The intermediate layer uses lead zirconate titanate (PZT) piezoelectric ceramics as a support medium with a high dielectric constant. At the bottom is a silicon-based, flexible, sensitive ground-contacting layer with high elasticity, which allows it to adapt to micro-level surface irregularities, eliminating air gaps between the electrode plate and the ground, increasing plate-to-ground coupling capacitance, and ensuring the stability of the capacitance. The three-layer structure was created using a dry-press sintering integration approach, which eliminates interlayer bonding materials while ensuring consistent dielectric performance and efficient charge transfer. Additionally, a specialised signal-conditioning circuit was designed to match the ultra-high-impedance sensitive unit, utilising the ADA4528-2 ultra-low-noise precision operational amplifier, which achieved low-loss conversion and strong noise suppression for ultra-weak high-impedance charge signals. The circuit simulation results demonstrate that the designed circuit achieves an input impedance of no less than 10 TΩ, an effective operating bandwidth from 0.02 Hz to 20 kHz, and a voltage noise density lower than 1.5 μV/√Hz at 10 Hz, fully covering the ultra-low-frequency effective band of natural geoelectric fields. Field experiments comparing artificial and natural field signals revealed that the proposed sensor could be quickly deployed by simply attaching it to the ground without burial. Its time-domain waveform consistency and frequency-domain component matching were nearly identical to those of commercial standard solid non-polarisable electrodes, with a cross-correlation coefficient greater than 0.98, indicating no significant potential drift or power-frequency interference. By structurally eliminating the inherent electrode potential difference, the sensor offers advantages such as ease of deployment, strong environmental adaptability, high precision for weak signal acquisition, and excellent engineering substitutability. It is well suited for long-term geoelectric field observations in complex field scenarios, including deserts, Gobi areas, and frozen soil regions, and provides a high-performance, novel sensing solution for geoelectric field detection in extreme environments. Full article

We examine the bias- and temperature-dependent direct current, radio frequency, and equivalent-circuit characteristics of a 150 nm AlGaN/GaN/SiC high-electron-mobility transistor (HEMT) for high-frequency applications. DC and S-parameter measurements on the wafer were conducted under various gate-bias settings within a varying thermal condition (−40 °C to 150 °C). The findings suggest a distinct decrease in drain current and transconductance with rising temperature, mostly attributed to heightened carrier dispersion and self-heating effects. At V_ds = 15 V, the I_ds decreases from 247.63 mA at −40 °C to 142.94 mA at 150 °C. The maximum transconductance decreases from approximately 56.5 mS to 31.5 mS. The assessed thermal resistance varies from 6.3 °C·mm/W to 11 °C·mm/W, signifying an increasing thermal limitation at elevated temperatures. The device has a point at which the temperature coefficient is zero at V_gs = −7.0 V, where the threshold-voltage shift and mobility degradation counterbalance one another. Small signal investigation indicates that f_t decreases from approximately 53 GHz to 39 GHz, whereas f_max declines from 107 GHz to 74 GHz within this temperature range. The derived equivalent-circuit characteristics demonstrate the temperature sensitivity of intrinsic capacitances, resistances, transconductance, and delay components, but extrinsic capacitances and inductances exhibit comparatively lower temperature sensitivity. The measured and modeled S-parameters are in strong agreement, hence validating the extraction methodology. The findings may serve as valuable guidance for bias optimization and thermally conscious RF circuit design with GaN HEMT technology. Full article

One of the negative effects of the rapid increase in the number and capacity of photovoltaic power sources distributed in consumption areas by connecting to existing low-, medium-, and high-voltage distribution networks is the increased risk of amplifying the non-sinusoidal steady-state condition caused by high-power inverters. This amplification occurs if the peak values of harmonic impedance in the sections of the respective grid zone, which depend on the values of the equivalent shunt capacitances present in the grid, correspond to frequency values that coincide with or are close to the frequencies of the harmonic currents injected by the distributed sources. The risk is particularly high in cases of malfunction or failure of the filters within the installations associated with these sources. High shunt capacitance values are not only caused by the capacitive compensators used to increase the power factor of consumers or to improve the voltage level in the grid, but also by long power lines, particularly long underground lines. Risks increase as the proportion of underground power lines in the network area with sources of harmonic currents rises. This article refers to a real high-voltage grid area where the distribution operator plans to install high-power photovoltaic sources, the connection of which requires grid expansion through the construction of new substations and high-voltage power lines (110 kV). Based on the designer’s intention for the new high-voltage power lines to be underground and of relatively long lengths—which implies the presence of high natural capacitances—the authors conduct two case studies to predictively evaluate the harmonic impedance in the network sections resulting from the expansion, with the aim of identifying the frequencies at which parallel resonances may occur. The authors use two software tools for numerical analysis, Mathcad 14.0 and MATLAB–Simulink 2025A, and compare the results obtained for two design variants of the new high-voltage lines: overhead and underground, respectively. Using the mathematical model of long lines in steady state with uniformly distributed parameters, the analysis highlights that the highest values of harmonic impedance correspond to the overhead line design variant. The use of this design variant increases the risk of parallel resonances, not only by increasing the harmonic impedance values but also by widening the frequency ranges for which the impedance has high values. In both the overhead line and underground line variants, increasing the load leads to a reduction in the maximum values. Compared to the design variant using overhead lines, the variant with underground lines increases the risk of parallel resonances by increasing the number of frequency intervals for which the harmonic impedance has high values, but this increase is limited by narrowing these frequency intervals and reducing the harmonic impedance values. An important contribution of the article lies in arguing the need to extend the conventional node-based evaluation of harmonic impedance by treating harmonic impedance as a continuous spatial frequency characteristic of the transmission network. The impedances seen at nodes become the impedances seen in particular sections/sections of the network, identified by the value of the variable that specifies their position in space, more precisely the distance from the end of one of the feeders on which they are located. Full article

Generator-side transient overvoltage may occur in DC 600 V AC–DC–AC railway power supply systems because switching-induced common-mode voltage generated by the front-end rectifier can propagate in reverse through cable distributed parameters, grounding impedance, and generator parasitic capacitance. Although AZSVPWM has been widely studied as a common-mode voltage reduction technique, its application to the suppression of generator-side reverse transient overvoltage in railway DC 600 V power supply systems has not been sufficiently investigated. In this paper, AZSVPWM is applied to the front-end active rectifier as a source-side suppression strategy. A high-frequency electromagnetic transient model is developed by considering the generator equivalent impedance, cable distributed parameters, grounding path, and generator winding-to-ground parasitic capacitance. The model is validated by comparing simulated and measured generator terminal voltages under AZSVPWM operation. Based on this model, the common-mode voltage excitation mechanism, reverse propagation path, and overvoltage suppression effect of AZSVPWM are analyzed. The results show that, compared with conventional SVPWM under identical active-rectifier conditions, AZSVPWM reduces the representative peak transient voltage at the generator terminals from 751.37 V to 557.71 V under the 8 m cable condition, corresponding to a reduction of approximately 25.77%. In addition, AZSVPWM-based active rectification improves the low-frequency voltage quality compared with conventional thyristor rectification, and the THD is estimated to decrease from approximately 14.8% to 0.8% based on the FFT spectrum. Parametric analysis further shows that AZSVPWM maintains stable suppression performance for cable lengths of 2–15 m and generator parasitic capacitances of 5–20 nF, with the maximum peak-voltage deviation caused by parasitic capacitance variation being approximately 1.15%. These results indicate that AZSVPWM provides a practical and robust source-side suppression strategy for generator-side transient overvoltage in railway DC 600 V power supply systems. Full article