Power Electronics Applications Research Articles

Design of an Optimal Fractional Complex Order PID Controller for Buck Converter

Dynamic and robust controllers are the inherent requirement of power electronic converters, which are subjected to dynamic variations and nonlinearities. The effectiveness of fractional order controllers in non-linear system control has been well-established by studies in the past few decades. Various forms of fractional order controllers have been used in power-electronic control. Recent research indicates that complex order controllers, extensions of fractional controllers, are more robust against uncertainties and non-linearities than their integer and fractional order counterparts. Though complex order controllers have been employed in various nonlinear plants, they have not been extensively tested on power electronic applications. Also, the design and tuning of the controller is difficult. This paper investigates the effectiveness of a complex order PID controller on a typical power electronic DC-DC buck converter for the first time. Two types of complex order controllers of the form PI^{a+ib}D^c and PI^{a+ib}D^{c+id} were designed for a power electronic buck converter. The complex order controllers were implemented in Simulink and the optimal tuning of the complex order controller parameters for various performance indices was performed using different optimization algorithms. The Cohort Intelligence algorithm was found to give the most optimal results. Both the complex controllers showed more robustness towards uncertainties than the linear and fractional PID controllers. The PI^{a+ib}D^c controller gave the smoothest and fastest response under non-linearities. The dynamic performance of the complex order controller is the best and can be expected to be useful for more power electronic applications.

Radiation damage in GaN/AlGaN and SiC electronic and photonic devices

The wide bandgap semiconductors SiC and GaN are commercialized for power electronics and for visible to UV light-emitting diodes in the case of the GaN/InGaN/AlGaN materials system. For power electronics applications, SiC MOSFETs (metal–oxide–semiconductor field effect transistors) and rectifiers and GaN/AlGaN HEMTs and vertical rectifiers provide more efficient switching at high-power levels than do Si devices and are now being used in electric vehicles and their charging infrastructure. These devices also have applications in more electric aircraft and space missions where high temperatures and extreme environments are involved. In this review, their inherent radiation hardness, defined as the tolerance to total doses, is compared to Si devices. This is higher for the wide bandgap semiconductors, due in part to their larger threshold energies for creating defects (atomic bond strength) and more importantly due to their high rates of defect recombination. However, it is now increasingly recognized that heavy-ion-induced catastrophic single-event burnout in SiC and GaN power devices commonly occurs at voltages ∼50% of the rated values. The onset of ion-induced leakage occurs above critical power dissipation within the epitaxial regions at high linear energy transfer rates and high applied biases. The amount of power dissipated along the ion track determines the extent of the leakage current degradation. The net result is the carriers produced along the ion track undergo impact ionization and thermal runaway. Light-emitting devices do not suffer from this mechanism since they are forward-biased. Strain has also recently been identified as a parameter that affects radiation susceptibility of the wide bandgap devices.

Characterization of GaN structures for power electronics by secondary ion mass spectrometry and atomic force microscope approach

This scientific paper describes the chemical study of different Al2O3/GaN interfaces found in the new generation of high electron mobility transistors developed for power electronics applications. The stake for these interfaces is the limitation, ideally the absence of an oxidized gallium layer hampering the good electrical behavior of the semiconductor. These structures have been studied through time-of-flight secondary ion mass spectrometry (ToF-SIMS), magnetic SIMS (M-SIMS), and atomic force microscopy (AFM) analyses. Two structures were considered: a bilayer Al2O3 10 nm–GaOx 2 nm on GaN and a Al2O3 10 nm single layer deposited on preliminary etched GaN. The first sample was used as a dedicated reference sample where an actual gallium oxide layer was grown, whereas the second one was a technologically relevant structure. Several experimental conditions were compared for the ToF- and M-SIMS analyses; in particular, three angles of incidence for the primary Cs+ sputter beam (65°, 61°, 45°) were used, leading to diverse depth resolutions and roughnesses, as revealed by surface topography analysis provided by AFM. Among the different incidence angles, it was found that the best experimental conditions were those obtained by ToF-SIMS analysis with an incidence angle of 45°, generating the least roughness.

Defect-mediated diffusion of implanted Mg in GaN: Suppressing dopant redistribution by sequential thermal and microwave annealing

The diffusion behavior of Mg in Mg/N co-implanted GaN is investigated in response to a set of annealing conditions and methodologies, namely, 1000 °C/30 min thermal anneal, by high-temperature pulsed gyrotron microwave annealing at 1420 or 1500 °C, or by thermal and microwave annealing, sequentially. After 1000 °C annealing, the diffusion of Mg in GaN is found to be negligible, as measured by secondary ion mass spectrometry. Annealing by gyrotron microwave annealing alone induces the diffusion of Mg at a rate on the order of 10−12 cm2/s. However, the use of a thermal anneal before microwave gyrotron annealing reduces this rate by an order of magnitude to 10−13 cm2/s. We find that a model that considers Mg diffusion from an inhomogeneous medium that contains a defect-rich implanted region near-surface to a relatively pristine region below the implant range better explains the observed diffusion behavior than a conventional model that assumes a homogeneous medium. By analyzing the diffusion behavior using the Boltzmann–Matano method, we present a discussion of reduction in [VGa] by thermal annealing at 1000 °C, leading to a suppressed diffusion coefficient during subsequent high-temperature annealing relative to diffusion after 1420/1500 °C annealing alone. This effect holds potential for improvement in the precision of selectively doped regions for future applications based on the (Al)GaN material system. An improved field profile control in real devices can increase the breakdown and current-handling capabilities in power electronic applications.

Laminated transient liquid phase preform and bond characterization for high-temperature power electronics application

Laminated transient liquid phase preform and bond characterization for high-temperature power electronics application

Efficient PEEC Iterative Solver for Power Electronic Applications

A new formulation of the partial element equivalent circuit (PEEC) is proposed that is well suited to be used along with fast Fourier transform (FFT)-based acceleration techniques. FFT-based techniques are used in conjunction with iterative solvers to accelerate matrix-vector products. Despite the significant memory saving and computational time reduction, these techniques may suffer at high frequencies due to the fine voxelization that they require. In this work, a new surface impedance-based formulation is presented and a novel preconditioner is proposed. Both contributions allow the frequency range of applicability of the FFT-accelerated PEEC method to be extended up to the gigahertz range. The accuracy and efficiency of the proposed solver are demonstrated by applying the proposed modeling strategy to a toy-problem and real-world structures comprising a printed circuit board and a transistor package, involving millions of unknowns.

Artificial neural networks controllers for three-phase neutral point clamped inverters

In this study, a new current control method consisting of proportional-resonant (PR) based artificial neural networks (ANN) has been developed for a neutral point clamped (NPC) inverter. The used NPC inverter circuit is three phase three level three leg and four wire. Current control in the inverter has been carried out primarily with PR and Hysteresis current controllers for comparison purposes. Then, a dynamic ANN structure is designed and trained using the PR current controller data from the simulation. The performance of this ANN current controller is investigated by simulation and experimental studies. The proposed ANN controller has been compared with other ANN controllers used in power electronics applications in the literature, based on the size and functions of the network structures. In addition, NPC inverters have a controller whose task is to balance the voltages of direct current (DC) bus capacitors. A separate static ANN based controller has been developed for this voltage balancing controller, which usually includes two proportional-integral (PI) controllers. The performance of these two types of ANN controllers has been experimentally verified with balanced/unbalanced, linear/non-linear loads.

Enhancement-mode vertical (100) β-Ga2O3 FinFETs with an average breakdown strength of 2.7 MV cm−1

In this work, we report on the realization of vertical (100) β-Ga2O3 FinFET devices for the use in power electronics applications. The experiments are carried out on structures consisting of highly conducting (100) β-Ga2O3 substrates with a doping concentration N D of 3 × 1018 cm−3, and epitaxially grown layers with N D of 5 × 1016 cm−3 for the drift and channel region. The fabricated FinFET devices feature enhancement-mode properties with a threshold voltage of +4.2 V and on/off-current ratio of 105. Moreover, breakdown measurements of these devices reveal an average breakdown strength of 2.7 MV cm−1. Additional device simulation indicates the presence of electric field peaks near the gate edge outside the active device as high as 7 and 5 MV cm−1 in the Al2O3 gate oxide and β-Ga2O3 semiconductor, respectively.

An Effective Control Technique to Implement an IUPQC Design for Sensitive Loads in a Hybrid Solar PV-Grid Connection

The recent innovation in power electronic application in the electrical power system (EPS) has given birth to an Improved Unified Power Quality Conditioner (IUPQC) that positively impacts the electrical power system (EPS). The previously available mitigation approaches with the application IUPQC are monotonous and are major designs for a particular power quality (PQ) issue which does not take care of the degree of impart. This paper presents an effective control architecture of an IUPQC design for sensitive loads in hybrid Photovoltaic Solar (PV) connected grid, concentrating on the voltage demand of loads that respond to slight changes. The objective of this work is to design a flexible controller that can respond to the different degrees of PQ challenges concerning voltage, variable load, and solar irradiation. It has combined the merits of an IUPQC and grid-integrated PV source. Effective controllers for Voltage Source Inverter (VSI) connected in series and Current Source Inverter (CSI) connected in shunt compensators of the UPQC are implemented to increase device strength for different voltage and current distortions. The series compensator was controlled using an enhanced Synchronous Reference Frame (SRF) technique based on adaptive notch filters. An Adaptive Logarithmic Absolute Algorithm (ALAL) was deployed for the parallel section of the proposed approach. The Mean Turning Filter (MTF) was used as a replacement for a low pass filter (LPF) for direct current node voltage management, leaving high and low-frequency ripples unaffected. To maintain a constant current on the grid side during grid disturbances, a feed-forward element has been introduced to the shunt CSI controller. Under various network situations, such as under-voltage, over-voltage, voltage distortion, harmonics, rapid load changes, and fluctuation in solar power, the control system performance is better as confirmed by experimental validation. Finally, it is observed that the voltage profile of 0.984 p.u. due to application control falling within the permissible limits. The proposed controllers are tested in the MATLAB Simulink on a developed distribution system model and validated experimental prototype.

Size-Controlled Low-Melting-Point-Alloy Particle-Incorporated Transient Liquid-Phase Epoxy Composite Conductive Adhesive with High Performances

With fast developments in the environmental-friendly industry, electrically conductive adhesive (ECA) composites with high electrical conductivity, mechanical strength, and electrochemical migration resistance as well as low cost are highly desirable for emerging power electronics applications. In this study, a category of ECAs, namely, size-controllable sonochemical low-melting-point-alloy (LMPA) particle-incorporated transient liquid-phase ECAs (TLP-ECAs), with excellent electrical conductivity, considerable mechanical strength, and high electrochemical migration resistance has been successfully demonstrated. Experimental results showed that the bulk resistivity of TLP-ECA decreased to a minimum value of 2.37 × 10–4 Ω-cm with the remaining filler content at a low level (the total content of metallic fillers, i.e., 70 wt % in TLP-ECAs), while the mechanical shear strength increased considerably (by 55.4%) compared with pure silver ECA with the same filler content, demonstrating that addition of sonochemical LMPA particles into ECA can simultaneously and considerably improve the electrical and mechanical properties. Moreover, the diffusional reaction mechanism of sonochemical LMPA particle-filled TLP-ECA was systematically investigated via differential scanning calorimetry (DSC), X-ray diffraction (XRD), and high-resolution scanning transmission electron microscopy in high-resolution high-angle annular dark-field mode (STEM-HAADF). The mechanism of the diffusion reaction of TLP-ECA with LMPA particles was rationalized, where Ag9In4 (γ phase, cP52, and P43m) and Ag3Sn (ε phase, oP8, and Pmmm) intermetallic compounds (IMC) and their corresponding nanostructures were responsible for the substantial enhancement in mechanical strength and the antielectrochemical migration property. The sonochemical method is the key to synthesize LMPA particles of desirable compositions and controllable size, thereby enhancing the overall performance of Ag-based TLP-ECAs. Accordingly, the sonochemical LMPA particle-incorporated-TLP-ECAs are the promising interconnection material candidates for power electronics packaging.

High performance trench diamond junction barrier Schottky diode with a sidewall-enhanced structure

The trench diamond junction barrier Schottky (JBS) diode with a sidewall enhanced structure is designed by Silvaco simulation. Comparing with the conventional trench JBS diode, Schottky contact areas are introduced on the sidewall of the trench beside the top cathode. The sidewall Schottky contact weakens the junction field-effect transistor effect between the trenches to realize a low on-resistance and a high Baliga’s figure of merit (FOM) value. In addition, the existence of the n-type diamond helps to suppress the electric field crowding effect and enhance the reverse breakdown voltage. With the optimal parameters of device structure, a high Baliga’s FOM value of 2.28 GW/cm2 is designed. Therefore, the proposed sidewall-enhanced trench JBS diode is a promising component for the applications in diamond power electronics.

Process-Factor Optimization of Small-Area Sintered Interconnects for Power Electronics Applications

AbstractPower electronics is concerned with the use of electronic devices to control and transfer electric power from one form to another. Power electronics can be found in laptop chargers, electric grids, and solar inverters. Die-attach interconnections form a critical part of power electronics devices. Silver sintering has been traditionally used for die-attach interconnections because of its high melting point and ability to form very thin thicknesses. However, the processing time compared with soldering is very long. Sintered layers might contain large voids that affect the mechanical stability of the structure. Stresses caused by mechanical and environmental conditions might cause degradation and possibly early failures. This work focuses on studying the combined effect of process factors on the shear strength of small-area die-attach interconnections in silver sintering. Design of experiments (DoE) tools were used to build an experimental matrix with a 95% confidence level. The results have shown that holding time has a considerable effect on the mechanical stability of the die-attach interconnections. Intermetallic compounds formed in the sintered joints at higher holding times resulted in fewer voids. Furthermore, the treatment level of the holding time highly affects the shear strength under other factors such as temperature and pressure.

Small Electron Polaron in Carbon-Doped Cubic Boron Nitride

Controllable and reliable doping of cubic boron nitride (cBN) is a critical challenge in its widespread application in power electronics. Recently, progress was made in this regard when an experiment reported successful n-doping of cBN with carbon, reaching carbon concentrations as high as 5%, which is beyond the thermodynamic solubility limit. However, the nature of carbon-based defects introduced within the cBN matrix remains unknown thus far. Here, we explore the electronic structure of carbon-doped cBN under nitrogen-rich conditions, which are conducive to the formation of donor-type defects (such as carbon substituents replacing boron), and predict several possible arrangements of carbon in clusters at experimentally relevant concentrations of 1.5–7.8%. Our theoretical calculations show that carbon dopants prefer to aggregate into small clusters with local ordering rather than distributing randomly in the bulk. Along with defects that result in easily ionizable defect states, we also report a distribution of carbon dopants, where the structure exhibits a defect-bound small electron polaron. The polaron can be identified via a split-off localized dopant band near the valence band edge. These findings not only shed light on identities of possible carbon-based defects but also predict additional carriers─defect-bound small polarons.

An Online Diagnosis Method for Sensor Intermittent Fault Based on Data-Driven Model

The intermittent fault (IF) is usually overlooked in power electronic applications. In this letter, an intelligent diagnosis method based on a data-driven model is proposed for sensor IFs. First, the manifestation of IF in the time domain is discussed to explore its distinctive characteristics. Then, a signal predictor is constructed in a data-driven way by utilizing the nonlinear autoregressive exogenous structure with the extreme learning machine algorithm. In addition, the residual is generated online by comparing the output of the devised data-driven predictor and that of the real sensor. The fault diagnosis decision-making scheme is finally designed based on the residual evaluation to identify the sensor IF and permanent fault simultaneously. The feasibility and effectiveness of the proposed method are demonstrated by offline tests and real-time experimental tests.

Selecting the Best Magnetic Core Geometry

Selecting the best core geometry for a given application can be challenging given all the options available. For high-frequency applications using ferrite and other low loss materials, many different shapes are available from core manufacturers. For power electronics applications, frequencies are not constrained to power line frequencies leading to more complex core designs. Proximity effects, nonlinear core excitation, and sensitivity to frequency are just some effects to consider for good designs. Whether designs are intended for 50 Hz or 100 kHz, the basic design equations are the same.

Comparisons and Evaluations of Silicon and Wide Band Gap Devices at Cryogenic Temperature

In this article, the static and dynamic characterizations for semiconductors with different materials, including silicon (Si), silicon carbide (SiC), and gallium nitride (GaN), are evaluated and compared at room temperature and cryogenic temperature (liquid nitrogen temperature). For static characterizations, the on-state resistance and threshold voltage are evaluated. For dynamic characterizations, the turn-on switching loss, turn-off switching loss, and dynamic on-state resistance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds(on)</sub> ) are evaluated. The results demonstrate that Si and GaN based semiconductors have improved performances with lower on-state resistance and faster switching speed at low temperature operations. For SiC based semiconductors, the on-state resistance increases significantly at cryogenic temperature. The switching speed is reduced dramatically for the evaluated 1.2 kV SiC metal oxide semiconductor field effect transistors (MOSFETs) at cryogenic temperature. This makes it less attractive for cryogenic applications. For the evaluated 650 V and 900 V SiC MOSFETs, the switching speed remains almost unchanged at low temperature. GaN high electron mobility transistor (HEMT) demonstrates a fast turn-on switching speed at low temperature, where the device's <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di/dt</i> are almost doubled when compared with room temperature. In addition, the dynamic <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds(on)</sub> of the evaluated GaN HEMTs also decreases at low temperatures. The evaluation results can serve as guidelines for cryogenic power electronics applications. Meanwhile, the future work for semiconductors cryogenic characterizations is discussed.

Power Electronic Applications in Power and Energy Systems

Modern environmental policies, carbon emission reduction targets, stimulus funding for economy recovery, end-use energy efficiency, objectives for higher reliability, and service quality in energy systems are a few of the factors driving forces behind the integration of advanced control and communication technologies into energy systems [...]

Zero Crossing Point Detection in a Distorted Sinusoidal Signal Using Decision Tree Classifier

Zero-crossing point detection in a sinusoidal signal is essential in the case of various power systems and power electronics applications like power system protection and power converters controller design. In this paper, 96 data sets are created from a distorted sinusoidal signal based on MATLAB simulation. Distorted sinusoidal signals are generated in MATLAB with various noise and harmonic levels. In this paper, a decision tree classifier is used to predict the zero crossing point in a distorted signal based on input features like slope, intercept, correlation and Root Mean Square Error (RMSE). Decision tree classifier model is trained and tested in the Google Colab environment. As per simulation results, it is observed that decision tree classifier is able to predict the zero-crossing points in a distorted signal with maximum accuracy of 98.3 % for noise signals and 100 % for harmonic distorted signals.

Quasi-vertical GaN merged PN Schottky diode by using the p-NiO/n-GaN heterojunction

In this study, a novel quasi-vertical GaN-on-sapphire MPS diode is fabricated by using the p-NiO/n-GaN heterojunction. The sputtered NiO covers the bottom and sidewall of trench region perfectly, presenting a hole concentration 2.2 × 1018 cm−3 and a mobility of 0.1 cm2/V•s. Compared with the Ni-anode SBD, the SBD and NiO/GaN heterojunction parts in the MPS diode turn on consecutively, resulting in a higher turn-on voltage of about 1.6 V (at the current of 1 A/cm2) and on-resistance of 3.5 mΩ·cm2. On the other hand, the depletion regions at the heterojunction interface suppress the electric field crowding and enhance the reverse breakdown voltage effectively. The TCAD simulation shows that the electric field modulation becomes weak slightly with the increasing p-NiO interval, resulting in the increasing electric field as well as the leakage current. Those results are beneficial to realize a high-performance GaN MPS diode for power electronic device applications.

Thermal Analysis of Flip-Chip Bonding Designs for GaN Power HEMTs with an On-Chip Heat-Spreading Layer

In this work, we demonstrated the thermal analysis of different flip-chip bonding designs for high power GaN HEMT developed for power electronics applications, such as power converters or photonic driver applications, with large gate periphery and chip size, as well as an Au metal heat-spreading layer deposited on top of a planarized dielectric/passivation layer above the active region. The Au bump patterns can be designed with high flexibility to provide more efficient heat dissipation from the large GaN HEMT chips to an AlN package substrate heat sink with no constraint in the alignment between the HEMT cells and the thermal conduction bumps. Steady-state thermal simulations were conducted to study the channel temperatures of GaN HEMTs with various Au bump patterns at different levels of current and voltage loadings, and the results were compared with the conventional face-up GaN die bonding on an AlN package substrate. The simulations were started from a single finger isolated HEMT cell and then extended to multiple fingers HEMT cells (total gate width > 40 mm) to investigate the "thermal cross-talk" effect from neighboring devices. Thermal analysis of the GaN HEMT under pulse operation was also performed to better reflect the actual conditions in power conversion or pulsed laser driver applications. Our analysis provides a combinational assessment of power GaN HEMT dies under a working condition (e.g., 1MHz, 25% duty cycle) with different flip chip packaging schemes. The analysis indicated that the channel temperature rise (∆T) of a HEMT cell in operation can be reduced by 44~46% by changing from face-up die bonding to a flip-chip bonding scheme with an optimized bump pattern design.