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Flow boiling with dielectric coolant is not only a highly desirable approach for effective electronic cooling but is also notorious for its poor scalability. Most current flow boiling enhancement strategies are based on silicon substrates with footprint areas less than 1 cm2, which greatly limits their applications to large-size electronics. This study developed a scalable channel configuration to facilitate efficient flow boiling on large copper substrates (∼10 cm2), in which the channel walls are formed by porous pin-fin arrays. This type of hybrid capillary wall makes up for the limitation of conventional machining in creating intricate features, making it scalable and feasible for developing large-size, two-phase cold plates. Moreover, effective two-phase separation and sustainable film evaporation have been realized in the current work. As a result, the proposed structure achieved a 512% increase in heat dissipation when the heating area scales up 480% from the silicon microchannels with micro-pin-fin arrays. Experiments showed a base heat flux of 106.1 W/cm2 was dissipated over a heating area of 9.6 cm2 using the dielectric fluid HFE-7100 at a mass flux of 247 kg/m2 s. It outperformed most existing metallic flow boiling heat sinks using the same coolant at a similarly high coefficient of performance as small-size enhanced silicon microchannels. [ABSTRACT FROM AUTHOR]

In modern dc microgrids, several feedback-controlled power electronic converters are connected to the common dc bus. Although the control loops of each individual converter are designed with good stability margins, the interconnection of multiple source and load converters can cause stability and performance concerns, due to potential interactions. Therefore, in order to ensure the desired dynamic performance of the interconnected power converter system, an interesting approach is to perform online stability monitoring of the dc bus, and to properly damp the dc bus impedance, which has been demonstrated to ensure system-level stability and performance. In order to accomplish that, this article first derives a representation of the dc bus impedance in terms of voltage (or droop) loop gain of the source-side converter. Second, under certain simplifying assumptions it provides an estimate for the peak value of bus impedance—an indicator of system dynamic behavior— based on the phase margin. Third, it proposes to continuously monitor the peak value of bus impedance by only injecting a single sinusoid in the voltage (or droop) loop. The monitored value can then be used to autotune the voltage regulator, in order to keep the bus impedance in a well-known allowable impedance region. The proposed monitoring and stabilization technique eliminates the need for the time consuming and memory intensive impedance measurement tasks. This technique is verified by simulation and experimental results on a laboratory prototype system of interconnected power converters. [ABSTRACT FROM AUTHOR]

Frequency-domain identification based on wideband techniques has become a popular method in the analysis and control of various dc power distribution systems. In the method, a single converter or a system is perturbed by an external wideband voltage or current injection, the resulting voltage or current responses are measured, and Fourier analysis is applied to extract the spectral information of the measured variables. Most often, the system or converter input and output impedances and the loop gain are the quantities of interest. One class of perturbation signals, pseudorandom binary sequences, has become widely used because most of such signals can be generated using simple shift-register circuitry. As the signals are deterministic and binary, they are well suited to perform measurements on power-converter systems in real time, allowing fast response to system variations through, for example, adaptive controllers. This article reviews the pseudorandom binary sequences applied to dc power distribution systems and discusses their advantages as well as limitations. The conventional maximum-length binary sequence, inverse-repeat binary sequence, discrete-interval binary sequence, and orthogonal binary sequences are considered. Several experimental results from various dc power systems are presented and used to demonstrate the applicability of the discussed methods. [ABSTRACT FROM AUTHOR]

In This case report a surgical technique for vertical ridge augmentation is presented. The procedure, performed in a 30-year-on woman with an atrophied alveolar ridge in the anterior portion of the mandible, is based on the biologic concept of osteogenesis distraction previously introduced in orthopedic and maxillofacial surgery. After elevation of a full-thickness flap a horizontal osteotomy was performed 7 to 8 mm from the top of the ridge. Two vertical osteotomies were prepared with drills of increasing diameter (2, 2.8, and 3.25 mm), tapping was performed for the first 5 to 6 mm, and two distractor base plugs were placed at the base of the osteotomies with a repositioning tool. An intraosseous distraction implant was then inserted and 2 inward vertical cuts were mode in the bone to allow proper distraction to take place. Correct functioning of the device was checked by distracting the bone fragment 1 mm using the axial distraction screw. A latency distraction healing screw was inserted in each of the distraction implants and the area was left to heal for 5 days. Once primary healing had occurred, the distraction of the newly formed bone callus was activated each day for 10 days (1 mm per day). At the end of the distraction period a final distraction screw was left in place and a final healing screw was inserted. During this lime there were no complications and the patient on no occasion complained of discomfort. The distractor device was removed 30 days late, leaving the base plugs in place. One month later a vertical augmentation of 7 mm had been achieved; the base plugs were removed, 3 intraosseous implants were inserted, and a biopsy of the newly formed tissue was obtained. Histologic evaluation of the biopsy specimen showed woven bone formation approximately 75 days after the initial procedure. [ABSTRACT FROM AUTHOR]

This paper presents a unified physics-based insulated-gate bipolar transistor (IGBT) compact model for circuit simulation that predicts the performance of both Si and SiC, n- and p-channel devices. The model can predict the detailed switching waveforms of these technologies based on its charge-based formulation. Further, this compact IGBT model is presented alongside a unique datasheet-driven parameter extraction process. The parameter extraction process enables users to quickly extract model parameters from data typically published without the need of taking physical measurements. The model has been validated with both Si and SiC devices for static and dynamic characteristics. The SiC IGBTs used for validation are a 12.5-kV n-channel device and a 13-kV p-channel device, while the Si IGBT chosen was IXDH30N120 from IXYS Corp. (Milpitas, CA, USA). This is the only IGBT model that predicts the performance of both n- and p-channel, Si and SiC devices, providing more freedom for the development of complex power electronics circuit designs. The convergence of the model has been verified by implementing a complex circuit consisting of both a dc–dc converter and a dc–ac inverter. The results presented here show that the unified model can be used to describe the behavior of a wide range of Si and SiC IGBT circuits. This paper is accompanied by a Verilog-A source code and a power point file demonstrating the model parameter extraction sequence. [ABSTRACT FROM AUTHOR]

DC power distribution systems typically consist of several source converters supplying load converters through single or multiple dc buses. Such complex systems are prone to stability issues caused by the interactions among feedback-controlled converters. Additionally, dc interconnected systems typically undergo considerable changes in their operating points. This can cause a system that is well-stabilized at a certain operating point to go unstable for another operating condition. Therefore, a stabilization method that is capable of adapting to variations in system operating conditions is highly desirable. This paper presents an adaptive stabilization method implemented on the source-side. The system stability is periodically analyzed by real-time measurement of the system bus impedance, which is dominated by the source impedance. Accordingly, the source converter control is modified by the proposed method to guarantee stability and high performance of the entire system after system changes. The approach has several advantages, including ease of design and implementation, minimal deviation from the nominal controller, and robustness due to the real-time adaptive implementation. Simulation and experimental results are presented that confirm the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

DC distribution systems typically consist of several feedback-controlled switched-mode converters forming a complex power distribution system. Consequently, a number of issues related to stability arise due to interactions among multiple converter subsystems. Recent studies have presented methods such as passivity-based stability criterion, where the stability and other dynamic characteristics of an interconnected system can be effectively analyzed using bus-impedance measurement. Studies have presented online measurement techniques, where the bus impedance is obtained by combining together the measurements of input and output impedances of single converters in the system. Since the converters are coupled, the presented measurement techniques require several measurement cycles in order to sequentially measure the individual impedances to be combined to obtain the overall bus impedance. This paper presents a measurement technique based on injection of orthogonal binary sequences. Applying this method, all the impedances in the system can be simultaneously measured during one measurement cycle. Therefore, the overall measurement time of the bus impedance is reduced compared to conventional measurement techniques. Furthermore, the method guarantees that the system dynamics do not change between measurements, and therefore, the computed bus impedance is not distorted. Experimental results are presented and used to demonstrate the effectiveness of the proposed method in the design of a stabilizing controller for a notional dc system using positive feed-forward control. [ABSTRACT FROM AUTHOR]

Six block grafts harvested from the mandibular symphysis were used to augment partially atrophied ridges. Three maxillary detects and three mandibular defects were treated in five patients. Autologous bone grafts from the chin were stabilized in the recipient sites with resorbable pins and no membranes were used over the grafts. Healing proceeded without complications. At 3 to 4 months the external cortical surface of the grafts progressively resorbed and the profiles of the pins protruded from underneath the buccal tissue that covered the augmented areas. However, the pins never perforated the tissue and they were resorbed macroscopically within 4 to 6 months. At 6 months the areas treated showed successful ridge augmentation and, when exposed for stage 2 surgery remnants of the pin holes on the external surface of the repaired defects were detected. Radiographic evaluation of the block grafts was performed at 3 and 6 months and histologic specimens were obtained at 6 months; the specimens demonstrated incomplete pin resorption and encapsulation. A severe foreign-body reaction was detected in, one case. The presence of an acellular bone matrix in certain sections and a normal bone pattern with a cellular component in others was a consistant finding. ITI endosseous implants were placed with excellent primary stability in all treated cases. [ABSTRACT FROM AUTHOR]

The clinical and histologic responses to periodontal treatment of gingival enlargements, induced when cyclosporine and nifedipine were administered singly or in combination, were evaluated. A significant correlation was noted between plaque, gingivitis, and gingival overgrowth, Severity of enlargement appeared to be greater in patients on combined therapy. All treatment approaches such as scaling, root planing, gingivectomy, and periodontal flaps, and a combination of therapies, were effective in the management of gingival overgrowth up to 1 year after completion of treatment. Adjunctive use of chlorhexidine was found to be beneficial. [ABSTRACT FROM AUTHOR]

Grid impedance and the output impedance of grid-connected inverter are important parameters for the operation of grid-connected systems, such as solar, wind, and other distributed-generation resource systems. The impedance mismatch between the grid and the interfacing circuit often generates harmonic resonances that lead to reduced power quality and even instability. Since the impedances usually vary over time as a function of many parameters, online measurements are required for stability assessment and adaptive control of the inverters. Several methods have been proposed for quick, accurate measurements of impedances, but the use of multiple-input multiple-output (MIMO) identification techniques have not been considered. Applying the MIMO techniques, different components of the inverter output impedance or grid impedance can be simultaneously measured during a single measurement cycle. Therefore, the operating conditions of the system can be kept constant during the measurements, and the overall measurement time is significantly reduced. This paper shows the use of orthogonal binary sequences to simultaneously measure the “d” and “q” components of grid-connected inverter output impedance and/or grid impedance. Experimental results based on a three-phase grid-connected inverter are presented and used to demonstrate the effectiveness of the proposed methods. [ABSTRACT FROM PUBLISHER]

In this paper, a simple and accurate circuit-simulator compact model for gallium nitride (GaN) high electron mobility transistor is proposed and validated under both static and switching conditions. A novel feature of this model is that it is valid also in the third quadrant, which is important when the device operates as a freewheeling diode. The only measurements required for the parameter extraction are simple I–V static characteristics and C–V characteristics. A detailed parameter extraction procedure is presented. Furthermore, a double-pulse test-bench is built to characterize the resistive and inductive switching behavior of the GaN device. A simulation model is built in Pspice software tool, considering the parasitic elements associated with the printed circuit board interconnections and other test-bench components (load resistor, load inductor, and current shunt monitor). The Pspice simulation results are compared with experimental results. The comparison shows good agreement between simulation and experimental results under both resistive and inductive switching conditions. Operation in the third quadrant under inductive switching is also validated. [ABSTRACT FROM AUTHOR]

Recently, there has been an increase in the use of finite control set model predictive control (FCS-MPC) for power converters. Model predictive control (MPC) uses the discrete-time model of the system to predict future values of control variables for all possible control actions and computes a cost function related to control objectives. This control technique can provide fast dynamic response. However, MPC method implementation imposes a very high computational burden and causes significant hardware requirements for real-time implementation. In this paper, a fully field-programmable gate array (FPGA)-based real-time implementation of MPC is proposed for direct matrix converter (DMC). In the proposed method, all control calculations and the safe commutation scheme for DMC are fully implemented in the FPGA and the need for another digital control platform, such as digital signal processors (DSP) or dSPACE, is eliminated. The proposed scheme takes full advantages of the parallel computation capability of FPGAs. [ABSTRACT FROM PUBLISHER]

Subsynchronous resonance (SSR) damping in fixed-speed wind turbine generator systems (FSWTGS) by using two series flexible ac transmission system (FACTS) devices, the thyristor-controlled series capacitor (TCSC), and gate-controlled series capacitor (GCSC) are studied in this paper. The former is a commercially available series FACTS device, and the latter is the second generation of series FACTS devices using gate turnoff (GTO) or other gate-commuted switches. The GCSC is characterized by a fixed capacitor in parallel with a pair of antiparallel gate-commuted switches enabling rapid control of series impedance of a transmission line. It is shown that the SSR damping with a GCSC is limited to changing the resonance frequency, in comparison with a fixed capacitor, which may not be adequate to damp out the SSR. Therefore, a supplementary SSR damping controller (SSRDC) is designed for the GCSC. Moreover, it is proven that the GCSC equipped with a well-designed SSRDC can effectively damp the SSR in FSWTGS. In order to verify the effectiveness of the GCSC in SSR damping, its performance is compared with the TCSC, which is an existing series FACTS device. In addition, time-frequency analysis (TFA) is employed in order to evaluate and compare the SSR time-varying frequency characteristics of the GCSC and TCSC. The IEEE first benchmark model on SSR is adapted with an integrated FSWTGS to perform studies, and extensive simulations are carried out using PSCAD/EMTDC to validate the result. [ABSTRACT FROM PUBLISHER]

Using both modal analysis and time domain simulations, it is shown that sub‐synchronous resonance (SSR) phenomena in a series‐compensated DFIG wind farms may cause system instability. In order to damp the SSR, both the rotor‐side converter (RSC) and grid‐side converter (GSC) controllers of the doubly‐fed induction generator (DFIG) are utilised. The objectives are to design an SSR damping controller (SSRDC) with an optimum input control signal (ICS), and to identify the optimum point within the RSC and GSC controllers where to introduce the SSRDC. The optimum ICS is identified using residue‐based analysis and root‐locus method. The criterion for choice of optimal ICS is that it should make the SSR mode stable without decreasing or destabilising the other system modes. Moreover, since the dynamics of the DFIG‐based series compensated wind farm change with varying operating point conditions, the operation of the SSRDC is optimised using the adaptive gain‐scheduling method. [ABSTRACT FROM AUTHOR]

This paper deals with subsynchronous resonance (SSR) phenomena in a capacitive series-compensated DFIG-based wind farm. Using both modal analysis and time-domain simulation, it is shown that the DFIG wind farm is potentially unstable due to the SSR mode. In order to damp the SSR, the rotor-side converter (RSC) and grid-side converter (GSC) controllers of the DFIG are utilized. The objective is to design a simple proportional SSR damping controller (SSRDC) by properly choosing an optimum input control signal (ICS) to the SSRDC block, so that the SSR mode becomes stable without decreasing or destabilizing the other system modes. Moreover, an optimum point within the RSC and GSC controllers to insert the SSRDC is identified. Three different signals are tested as potential ICSs including rotor speed, line real power, and voltage across the series capacitor, and an optimum ICS is identified using residue-based analysis and root-locus method. Moreover, two methods are discussed in order to estimate the optimum ICS, without measuring it directly. The studied power system is a \mathbf100\;MW DFIG-based wind farm connected to a series-compensated line whose parameters are taken from the IEEE first benchmark model (FBM) for computer simulation of the SSR. MATLAB/Simulink is used as a tool for modeling and designing the SSRDC, and power system computer aided design/electromagnetic transients including dc (PSCAD/EMTDC) is used to perform time-domain simulation for design process validation. [ABSTRACT FROM PUBLISHER]

Compact models of wide-bandgap power devices are necessary to analyze and evaluate their impact on circuit and system performance. Part I reviewed compact models for silicon carbide (SiC) power diodes and MOSFETs. Part II completes the review of SiC devices and covers gallium nitride devices as well. [ABSTRACT FROM AUTHOR]

Wide bandgap power devices have emerged as an often superior alternative power switch technology for many power electronic applications. These devices theoretically have excellent material properties enabling power device operation at higher switching frequencies and higher temperatures compared with conventional silicon devices. However, material defects can dominate device behavior, particularly over time, and this should be strongly considered when trying to model actual characteristics of currently available devices. Compact models of wide bandgap power devices are necessary to analyze and evaluate their impact on circuit and system performance. Available compact models, i.e., models compatible with circuit-level simulators, are reviewed. In particular, this paper presents a review of compact models for silicon carbide power diodes and MOSFETs. [ABSTRACT FROM AUTHOR]

This paper presents application and control of the gate-controlled series capacitor (GCSC) for series compensation and subsynchronous resonance (SSR) damping in doubly-fed induction generator (DFIG)-based wind farms. The GCSC is a new series FACTS device composed of a fixed capacitor in parallel with a pair of antiparallel gate-commuted switches. The study considers a DFIG-based wind farm, which is connected to a series-compensated transmission line whose parameters are derived from the IEEE first benchmark model for computer simulation of the SSR. The small-signal stability analysis of the system is presented, and the eigenvalues of the system are obtained. Using both modal analysis and time-domain simulation, it is shown that the system is potentially unstable due to the SSR mode. Therefore, the wind farm is equipped with a GCSC to solve the instability of the wind farm resulting from the SSR mode, and an SSR damping controller (SSRDC) is designed for this device using residue-based analysis and root locus diagrams. Using residue-based analysis, the optimal input control signal to the SSRDC is identified, which can damp the SSR mode without destabilizing other modes, and using root-locus analysis, the required gain for the SSRDC is determined. MATLAB/Simulink is used as a tool for modeling, design, and time-domain simulations. [ABSTRACT FROM PUBLISHER]

Currently available wireless charging technology for portable electronics demonstrates several shortcomings. For the consumers, the two major shortcomings are limited receiver positioning flexibility and lower efficiency compared to hard-connected charging. For the industry, the major disadvantages are higher cost and complexity in design and control. To overcome these shortcomings and disadvantages, this paper presents a novel control method for unity-gain frequency tracking (UGFT) under coupling coefficient $(k)$ variation in a resonant converter containing a symmetrically implemented series–series (SS) resonant tank. An SS resonant converter employing the UGFT control provides several desirable features: the need for digital communication between the transmitter and the receiver to achieve leakage inductance compensation is eliminated, the design is robust against coupling (k)$ and load (Q)$ variations, the SS resonant converter can operate most of the time at the frequency of highest efficiency (unity-gain frequency ), and the downstream regulator commonly employed in a wireless charging system may be eliminated. Furthermore, in this paper, frequency-domain characteristics of SS resonant tank are explained in detail to illustrate various desirable characteristics. Detailed design criteria for SS resonant tanks are provided to achieve these characteristics. Throughout the analysis, various simulation results are provided to complement the discussion. The proposed UGFT control method is validated through experimental results. [ABSTRACT FROM AUTHOR]

This paper first presents a step‐by‐step tutorial on modal analysis of a doubly‐fed induction generator (DFIG)‐based series compensated wind farm. The model of the system includes a wind turbine aerodynamics, a sixth‐order order induction generator, a second‐order two‐mass shaft system, a fourth‐order order series compensated transmission line, an eighth‐order rotor‐side converter (RSC) and grid‐side converter (GSC) controllers, and a first‐order DC‐link model. Then, using modal analysis and time‐domain simulations, it is shown that a fixed‐series compensated DFIG is highly unstable due to the sub‐synchronous resonance (SSR) mode. In order to damp the SSR mode, the wind farm is interfaced with the gate‐controlled series capacitor (GCSC) ‐ which is a new series flexible AC transmission system (FACTS) device. A SSR damping controller (SSRDC) is designed for the GCSC using residue‐based analysis and root locus diagrams, and an effective input control signal (ICS) to the SSRDC is identified in order to simultaneously increase damping of both the SSR and super‐synchronous (SupSR) modes. The IEEE first benchmark model on SSR is adapted with an integrated DFIG‐based wind farm to perform studies. Matlab/Simulink is used as a tool for designing process, and PSCAD/EMTDC is used for time‐domain simulations. [ABSTRACT FROM AUTHOR]