High Voltage Power Conversion Research Articles

Emitted current self-balancing for spacecraft charging mitigation in a high-voltage power converter for electrospray thrusters

Electrospray thrusters offer remarkable efficiency at low power levels and compact form factor, positioning them as promising propulsion systems for small satellite platforms. The ability of electrospray thrusters to emit both positive and negative ion beams has significant implications for charge neutralization. In theory, electrosprays could function without the need for an external cathode. If two separate thrusters are operated simultaneously with one emitting a positive ion beam and the other an identical negative ion beam, the spacecraft would theoretically remain charge-neutral, allowing the thrusters to operate continuously without inducing spacecraft charging. This article explores the self-balancing of emitted currents, and consequently the ion beams, by incorporating a capacitor as a control element. This approach achieves current balancing without altering the operation of the power converter. The thruster’s behavior as an electrical load is simulated using a novel electrical model derived from experimental thruster data. This model, integrated within the converter, demonstrates that the inclusion of a capacitor effectively balances the emitted currents. Experimental validation aligns with the simulation results, confirming current balance with a relative error between polarities of only 1% in the final test cases.

Cosmic Radiation Reliability Analysis for Aircraft Power Electronics

Cosmic Ray induced failures are a major concern for the electronic system reliability of airborne and space systems. Power system voltages on aerospace platforms are on a steady upward trend. High voltage power converters suffer from Single Event Burnout failures caused by cosmic rays. The established standards propose a scaling factor based on measured background galactic cosmic rays intensity at operating altitude to apply de-rating factors. The radiation environment in the atmosphere can be increased due to the cascading of primary solar energetic particles during solar eruptions. In this work, the altitude profile of the radiation environment is simulated using a GEANT4 Monte-Carlo code. The failure rates due to both background Galactic Cosmic Rays and Solar Energetic Particles are quantitatively evaluated. Further to the known influence of geomagnetic shielding of cosmic rays, the geographical distribution of cosmic rays at flight altitudes of 10 km are also presented. The estimated cosmic ray intensity can then be combined with experimentally measured failure rate data to predict the impact on the reliability of power converters, giving a new level of accuracy in the modeling of such failure mode in more electric aircraft applications. It is shown for the first time in the scientific literature by using experimental data and state-of-the-art models, that the solar energetic particles storms fluxes vastly exceed the recommended standard and constitute a risk for the power electronics reliability.

Design and Flight Qualification of a Flying Capacitor Multilevel Converter for Electric Aircraft Applications

Multilevel switched-capacitor converters, such as the flying capacitor multilevel (FCML) converter, offer high energy density and efficiency, over a wide voltage range, making them suitable for applications in electrified aircraft. However, concerns of reliability due to the increased number of active and passive components have limited the use of high-level count converters in aircraft applications. This work addresses the challenges of designing a high-level count converter with the goal of extremely high efficiency and power density, with maintained reliability and flight readiness. We present detailed component selection and design techniques to achieve this goal, along with a high-performance 28.2 kW/kg, 99.52% efficient high-voltage dc-dc step-up power converter for experimental validation. Finally, we demonstrate successful completion of critical flight qualification testing of the hardware prototype, including thermal, shock and vibration.

A Design Methodology for High-Voltage, Highly-Integrated Switched-Capacitor Power Converters, and Implementation At 48 V-12 V, 23 W/cm$^{3}$ and 93.5% Peak Efficiency

In this work a design methodology and key considerations for high-voltage and highly-integrated switched-capacitor power converters is presented. The design methodology describes the power losses in high-voltage applications, where switching losses and gate-driver losses start becoming dominant compared to fully integrated, low voltage and low power applications. The design methodology is applicable for any highly-integrated switched-capacitor topology. To verify the design methodology a 48 V-12 V ladder switched-capacitor power converter in a 180 nm SOI BCD process, with external capacitors is implemented. The floating gate-drivers and a clock controller responsible for the power switch control are also presented. The peak efficiency of the proposed power converter is measured to be 93.5 %, and 24.5 W maximum output power, resulting in a power density of 23 W/cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> .

Heterocyclic Functionalized Donor-Acceptor Hole-Transporting Materials for Inverted Perovskite Solar Cells.

Hole transport materials (HTMs) with appropriate energy levels and comprehensive passivation effects help to obtain highly efficient and stable perovskite solar cells (PSCs). Electron-deficient character-induced HTMs can generate varying energy level alignments near the HTM/perovskite interface. Herein, we report the synthesis and investigation of two new dipolar HTMs, WWC103 and WWC105, based on 2-(1,1-dicyanomethylene)rhodamine and 4-cynophenylacetonitrile acceptors, enabling high-efficiency mixed-cation mixed-halide perovskite solar cells. Apart from having different acceptors, these HTMs are built on a heterocyclic frame, which can provide passivation effects and improve the morphology of the perovskite layer. As a result, these dopant-free HTM-based solar cells show a high open-circuit voltage and good power conversion efficiency. Among both, the solar cell based on the HTM with 2-(1,1-dicyanomethylene)rhodamine exhibits a high open-circuit voltage of 1.09 V with a champion power conversion efficiency of over 20.51%. The improved performance of WWC103 over WWC105 (19.74%) is attributed to the new acceptor, which, in addition to providing good energy-level alignments and hole mobility, also holds the ability to passivate the defects. The findings suggest a new acceptor unit for constructing dopant-free HTMs for efficient PSCs.

10kV+ Rated SiC n-IGBTs: Novel Collector-Side Design Approach Breaking the Trade-Off between dV/dt and Device Efficiency

10kV+ rated 4H- Silicon Carbide (SiC) Insulated Gate Bipolar Transistors (IGBTs) have the potential to become the devices of choice in future Medium Voltage (MV) and High Voltage (HV) power converters. However, one significant performance concern of SiC IGBTs is the extremely fast collector voltage rise (dV/dt) observed during inductive turn-off. Studies on the physical mechanisms of high dV/dt in 4H-SiC IGBTs revealed the importance of collector-side design in controlling the phenomenon. In this paper we propose a novel collector-side design approach, which consists of four n-type layers with optimized doping densities and allows the control of dV/dt independently from the device performance. Further, we demonstrate a reduction of dV/dt by 87% without degrading the high switching frequency capability of the device, or the on-state performance, through the addition of two n-type epitaxial layers in the collector side, between the buffer and the drift regions.

An Analysis of Multilevel Converter for Faster Current Control in a DC Micro grid with Extremely Low- Impedance Interconnections

Improved power converter configurations and semiconductors innovation capable of driving the required power have emerged in response to the rising global need for energy. It is still a constant endeavour to create semiconductors with greater current or voltage power to propel high power systems. In this way, modern gadgets can handle high voltage or current with ease. Traditional high-voltage semiconductor-based power converter schemes face stiff opposition from innovative medium-voltage device-based alternatives. DC microgrids, with their very limited line impedance, are developing as the upcoming type of small-scale power transmission connections. Due to this phenomenon, even a little change in voltage can create significant currents in microgrids, making quick rapid reaction and accurate power flow regulation essential. In order to provide fast and precise power flow regulation in a dc microgrid, this research employs multi-level converters as the controllers. A multilevel converter allows for a compact output filter. In addition, the final LC filter of a MLC that satisfies a current ripple demand has been designed and is presented in this work. In comparison to traditional two-level converters, we were able to demonstrate that a multi-level converter with a more compact filter may provide high-speed &amp; high-precision power flow regulation under low line impedance situations. Using the simulation results from MATLAB/Simulink, the overall performance of every output current is assessed in the system response, taking into account the transient variations in the power flow.

Slew rate control of switching transient for SiC MOSFET in boost converter using digital active gate driver

This paper experimentally validates a fully digitalized active gate driver for suppressing the switching surge voltage of SiC MOSFETs in a boost converter. High-voltage power conversion systems are expected to adopt SiC unipolar power devices utilizing their high-speed switching capability. The high-speed switching operation causes the switching surge voltage in its switching transient. Active gate driving is a key technology for suppressing it. A fully digitalized active gate driver is particularly focused upon, which freely shaped the output gate-source voltage waveform by a multi-bit gate control signal. This driver achieves the dynamical control of the voltage/current behaviours of MOSFET in the switching transient by taking the Miller effect into account. It contributes to suppressing the switching surge voltage. This paper applies this digital active gate driver to a high voltage power conversion circuit. The switching surge voltage is experimentally suppressed by slew rate control with the digital active gate driver for various operating conditions. The results clarify the control strategy of the digital active gate driver for SiC MOSFET in a power conversion circuit.

(Invited) Optical Characterization of Bulk GaN Substrates and Homoepitaxial Films

Low ON-resistance and high breakdown voltage, made possible by improved critical electric field and mobility, has promoted GaN from a potential to the most promising semiconductor material for use in the next-generation of medium- and high voltage-power converters. The commercial availability of large area substrates, produced by HVPE (Hydride Vapor Phase Epitaxial, a quasi-bulk deposition technique) and ammonothermal bulk growth method, provides wafers with reduce concentrations of extended defect, allows the deposition of electronic grade epitaxial films and the realization of high performance electronic devices. Despite that, many steps of substrate preparation, such as miss-cut orientation and surface finishing, must be improved and standardized to yield reproducible epitaxial film growth. To verify the importance of substrate characteristics on the intrinsic properties of homoepitaxial MOCVD films, we initially evaluated substrate provided by various commercial supplies. The substrate effects on epi morphology, uniformity, and impurity incorporation were substantiated by growing simultaneously on wafers from different vendors. The goal of this work is to detect and identify defects in GaN substrates with a series of quick, non-destructive, inexpensive techniques with capabilities of mapping whole wafers.All evaluated substrates had nominally similar as-received specifications (resistivity, thickness, off-cut angle, bow, surface finish). The substrates were evaluated with a variety of techniques including Raman spectroscopy, photoluminescence, white light interferometry, and Nomarski imaging, enabling the detection of different concentrations of grain boundaries, impurities, point defects, v-shaped pits, polishing defects, crystal stress damage, and non-uniform insulating and conductive regions. The substrates can be grouped in two different categories: those with uniform characteristics, including carrier concentration, and those without. Comparing these results to those from homoepitaxial growth on the same wafers, the effects are both subtle and overt. Macroscopic surface morphology, which has shown a direct correlation to leakage current, copies and exaggerates that of the underlying substrate. Photoluminescence of the homoepitaxial surface along with Raman spectroscopy show that non-uniformities in the substrate carrier concentration can continue into the epitaxy.If time permits, results from vertical Schottky diodes, fabricated to quickly evaluate device performance, will presented. While most of the films showed the ability to withstand high electric fields, more uniform electrical properties were observed for those grown on substrates having more uniform properties. These results show that improving bulk substrates is the path to high voltage vertical devices, and that such substrates have a significant influence on device performance. Acknowledgments: Work at NRL is supported by the Office of Naval Research

What Is Next for Automotive Electronics? [Automotive Electronics

The automotive industry is experiencing a remarkable move from the internal combustion engine (ICE) to an all-electric power platform. This natural shift is essentially supported by electric drive development where wide-bandgap (WBG) materials are at the center of this transformation. The shift to gallium nitride (GaN)- or silicon carbide (SiC)-based power electronics is taking place due to the theoretical limits of Si MOSFETs that has been reached by the industry for many power systems. Battery charging is maybe the first high-volume market to demonstrate GaN adoption, and SiC devices are now increasingly used in high-voltage power converters with stringent size, weight, and power requirements <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> . Definitively, EVs are considered the heart of the global push toward a more sustainable future.

Advanced insulating materials contributing to “carbon neutrality”: Opportunities, issues and challenges

Advanced insulating materials contributing to “carbon neutrality”: Opportunities, issues and challenges

Improved Coordinated Control Strategy for Reliability Enhancement of Parallel PFCs With LCC Restriction

Power flow controllers (PFCs), which adopt high voltage and large power converters, are the significant device of cophase traction power supply systems (TPSSs); therefore, it is important to enhance the reliability of PFCs. Due to the limited capacity of power semiconductor switches, parallel connection of PFC units has been encouraged, and system reliability can be enhanced by configuring standby PFC units. However, while the increase in the number of redundant modules is accompanied by higher investment, the reliability improvement also has a saturation effect. In addition, among the control techniques of parallel PFCs, one of the commonly employed methods is current-sharing control, but the thermal stress of converters is increased at low loads. Therefore, in this article, a PFCs’ cost model is built based on life cycle cost (LCC) theory, and the number of basic, redundant PFC units is determined with the constraint of the minimum average annual cost. Furthermore, an improved coordinated control strategy that can alleviate thermal stress is proposed. Under a high load, all the PFC units are operated simultaneously, while, under a low load, the units are operated by turns. Moreover, to ensure consistent reliability and maximize system reliability, the rotation working time of each unit and the load demarcation point are optimized considering negative sequence compensation constraints. Case studies show that the given control strategy can extend the life span up to 26.30% and achieve a 19.11% cost reduction.

GaN-on-Si: Monolithically Integrated All-GaN Drivers for High-Voltage DC-DC Power Conversion

This paper presents a novel integrated half-bridge driver architecture using GaN-on-Si process for high-speed and high-voltage DC-DC converters. The entire circuit includes only enhancement mode (E-mode) and depletion-mode (D-mode) GaN transistors. The high-side driver circuit adopts the E-stacked E/D-mode (EED) architecture, which can directly drive the gate of the high-side transistor with a low-voltage signal without using an additional level shifter, which simplifies the design and reduces propagation delay. In addition, the low-side power transistor is driven by stacking two D/E-mode devices. This architecture separates the high-side pulse from the low-side drive signal to prevent false triggering of the low-side driver. The designed fully integrated GaN driver can output a high-voltage pulse wave with an operating frequency greater than 1 MHz when the input voltage is greater than 200 V. The rise and fall times of the high-voltage pulse wave operating at a peak voltage of 200 V are 54.4 ns and 57.6 ns, respectively. The experimental results show that the circuit can effectively drive the half-bridge circuit and be applied to a buck converter. The designed buck converter can deliver up to 20.5 W of output power, and the maximum efficiency achieves 90.7%.

Adaptive Control and Formal Stability Analysis of Single-Phase Flying Capacitor Multicell DC-AC Inverters

Multicell converters and inverters using flying capacitors are usually used for high voltage power conversion applications. This study is carried out in a general context concerning an N-cell flying capacitors converter described by an (N + 1)th order average mathematical model. A nonlinear adaptive backstepping controller suitable for regulating the voltages across the N-flying capacitors is proposed with the aim to reach equitably distributed stresses on the converter switches. The controller also aims at generating a sinusoidal voltage with a desired amplitude and frequency at the output of the converter as well as to estimate, in real time, the load resistance. Special attention is devoted to the stability analysis of the whole closed-loop system with load estimation by using Lasalle’s invariance principle and Lyapunov method. The system performance is tested by means of numerical simulations showing that the proposed controller meets its objectives in terms of tracking, regulation, robustness and adaptation and demonstrating that it outperforms the classical backstepping controller.

Lightweight High-Voltage Power Converters for Electroaerodynamic Propulsion

Recent studies in electroaerodynamic (EAD) propulsion have stimulated the need for lightweight power converters providing outputs at tens of kilovolts and hundreds of watts <xref ref-type="bibr" rid="ref2" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[2]</xref> – <xref ref-type="bibr" rid="ref3" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"/> <xref ref-type="bibr" rid="ref4" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[4]</xref> . This article demonstrates a design of a lightweight high-voltage converter operating from a 160–225 V dc input and providing dc output of up to 565 W at 40 kV. It operates at around 500 kHz and achieves a specific power of 1.15 kW <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\cdot {\text{kg}}^{-1}$</tex-math></inline-formula> . High-voltage converters generally comprise an inverter, a step-up transformer, and a rectifier, with the large needed voltage gain distributed among these stages. Several means of realizing these stages are compared in terms of weight. The weight of the converter is minimized by properly selecting and optimizing the design and the voltage gain of each stage within the constraints of device limitations and losses. A prototype circuit is developed based on this approach and used to drive an EAD propulsion system for an unmanned aerial vehicle. Moreover, this article also presents approaches to further improve the specific power of such converters, including better diode utilization and more flexible high-voltage transformer design. In addition to addressing the needs for EAD, this research can potentially benefit the development of lightweight high-voltage converters in many other applications, where weight and size are important.

Customizing a self-healing soft pump for robot

Recent advances in soft materials enable robots to possess safer human-machine interaction ways and adaptive motions, yet there remain substantial challenges to develop universal driving power sources that can achieve performance trade-offs between actuation, speed, portability, and reliability in untethered applications. Here, we introduce a class of fully soft electronic pumps that utilize electrical energy to pump liquid through electrons and ions migration mechanism. Soft pumps combine good portability with excellent actuation performances. We develop special functional liquids that merge unique properties of electrically actuation and self-healing function, providing a direction for self-healing fluid power systems. Appearances and pumpabilities of soft pumps could be customized to meet personalized needs of diverse robots. Combined with a homemade miniature high-voltage power converter, two different soft pumps are implanted into robotic fish and vehicle to achieve their untethered motions, illustrating broad potential of soft pumps as universal power sources in untethered soft robotics.

A Survey of Electromagnetic Influence on UAVs from an EHV Power Converter Stations and Possible Countermeasures

It is inevitable that high-intensity, wide-spectrum electromagnetic emissions are generated by the power electronic equipment of the Extra High Voltage (EHV) power converter station. The surveillance flight of Unmanned Aerial Vehicles (UAVs) is thus, situated in a complex electromagnetic environment. The ubiquitous electromagnetic interference demands higher electromagnetic protection requirements from the UAV construction and operation. This article is related to the UAVs patrol inspections of the power line in the vicinity of the EHV converter station. The article analyzes the electromagnetic interference characteristics of the converter station equipment in the surrounding space and the impact of the electromagnetic emission on the communication circuits of the UAV. The anti-electromagnetic interference countermeasures strive to eliminate or reduce the threats of electromagnetic emissions on the UAV’s hardware and its communication network.

Имитатор импульсных высоковольтных перенапряжений

The electrical circuit of a simulator of pulse high voltage overvoltages with an amplitude of up to 10 kV DC, which is intended for testing the stability of solid-state power converters to emergency conditions according to item 4.9.3.5 of State Standard GOST 33726-2016, is proposed. By using the developed simulator, a high voltage pulse with the required values of amplitude, duration, and rising and falling rates can be obtained. Analytical expressions are derived that describe, with sufficient accuracy, the transients in the electrical circuits of the proposed pulse high voltage overvoltage simulator, which is confirmed by computer simulation carried out in the MATLAB Simulink environment. Based on the obtained theoretical results, a mockup simulator for testing the stability of a high-voltage power converter to overvoltage of a given shape and amplitude has been developed. The results of practical use of the developed simulator on the example of testing the PSN110 U1 auxiliary converter are given. The article may be of interest to specialists who design equipment for carrying out overvoltage tests of solid-state high-voltage converters for both railway transport and industrial applications.

On-line fault diagnosis and fault-tolerant operation of modular multilevel converters — A comprehensive review

Modular multilevel converters (MMCs) have been one of the most broadly used multilevel converter topologies in industrial applications, particularly in medium-voltage motor drives and high-voltage dc power conversion systems. However, due to the utilization of large amount of semiconductor devices, the reliability of MMCs becomes one of the severe challenges constraining their further development and applications. In this paper, common electrical faults of the MMC have been summarized and analyzed, including open-circuit switching faults, short-circuit switching faults, dc-bus short-circuit faults, and single line-to-ground faults on the ac side. A thorough and comprehensive review of the existing online fault diagnostic methods has been conducted. In addition, fault-tolerant operation strategies for such various fault scenarios in MMCs have been presented. All the fault diagnosis and fault-tolerant operation strategies are comparatively evaluated, which aims to provide a state-of-the-art reference on the MMC reliability for future research and industrial applications.

(Invited) GaN Homoepitaxial Growth and Substrate-Dependent Effects for Vertical Power Devices

Vertical GaN power switch technology is expected to be utilized in next-generation medium to high voltage power converters due to the low ON-resistance and high breakdown voltage enabled by the improved critical electric field and mobility compared to Si and SiC-based devices. As large area substrates have become available by hydride vapor phase epitaxy (HVPE) and ammonothermal growth, the properties of nitrides are no longer dominated by defects introduced by heteroepitaxial growth, allowing recent realization of several fundamental vertical power devices, including diodes with edge termination, trench MOSFETs, and CAVETs. However, additional materials challenges are coming to the forefront that need to be understood and surmounted in order to allow vertical GaN power devices to achieve their full potential, notably the realization of repeatable thick drift layers with low background doping. To enable this, a deeper understanding of substrate preparation and the effects of the substrate and growth initiation on the characteristics of the epitaxial layers is required for MOCVD growth of homoepitaxial films. We investigate these effects on epi morphology, uniformity, and impurity incorporation by growing simultaneously on wafers from different vendors. The goal of this work is to detect and identify defects in GaN substrates with a series of quick, non-destructive, inexpensive techniques with capabilities of mapping whole wafers. We have characterized multiple substrates from over eight suppliers and the homoepitaxy grown on those substrates. All the substrates had nominally similar as-received specifications (resistivity, thickness, off-cut angle, bow, surface finish). The substrates were evaluated with a variety of techniques including Raman spectroscopy, photoluminescence, white light interferometry, and Nomarski imaging, enabling to detection of different concentrations of grain boundaries, sample impurities, point defects, v-shaped pits, polishing defects, crystal stress damage, and non-uniform insulating and conducive regions. The substrates can be characterized in two different categories: those with uniform characteristics, including carrier concentration, and those without. Comparing these results to those from homoepitaxial growth on the same wafers, the effects are both subtle and overt. Macroscopic surface morphology, which has shown a direct correlation to leakage current, copies and exaggerates that of the underlying substrate. Photoluminescence of the homoepitaxial surface along with Raman spectroscopy show that non-uniformities in the substrate carrier concentration can continue into the epitaxy. Following optical characterization, vertical Schottky diodes were fabricated to quickly evaluate device performance. While most of the films showed the ability to withstand high electric fields, those with more uniform properties in the substrate also showed more uniform electrical properties. These results show that the bulk substrates enable the path to high voltage vertical devices, but also show the significant influence that substrates can play in device performance.