High Power Density Applications Research Articles

Comparative Analysis of Two and Four Current Loops for Vector Controlled Dual-Three Phase Permanent Magnet Synchronous Motor

Dual three-phase (DTP) permanent magnet synchronous motors (PMSMs) are specialized machines which are commonly used for high power density applications. These machines offer the merits of high efficiency, high torque density, and superior supervisor fault tolerant capability compared to conventional three-phase AC-machines. However, the electrical structure of such machines is very complicated, and as such, control becomes challenging. In conventional vector controlled DTP-PMSMs drives, the components of the dq-subspace are associated with electromechanical energy conversion, and two currents, i.e., Id and Iq belonging to this subspace, are used in feedback-loops for control. Such orthodox control methods can cause some anomalies e.g., the voltage source inverter’s (VSI) dead time effect and other nonlinear factors, and can induce large harmonics. These glitches can be greatly alleviated by the introduction of the two-extra current loops to directly control the currents in Z1Z2-subspace in order to suppress the insertion of harmonics. In this paper, two approaches—one with two-current loops and other with four-current loops—for vector controlled DTP-PMSMs are investigated with the aid of different MATLAB-based simulations. Furthermore, in the paper, the influence of additional current loops is quantified using simulation-based results.

Mn substitution controlled Li-diffusion in single crystalline nanotubular LiFePO4 high rate-capability cathodes: Experimental and theoretical studies

Carbon-coated single crystalline nanotubular (NT) and nanoparticular (NP) LiFe1-xMnxPO4 (x = 0, 0.2, and 0.5) cathodes are fabricated to study the effect of compositional and microstructural changes on Li+ diffusion and electrochemical properties. Insight in to the compositional effect on Li+ diffusion is obtained from DFT facilitated climbing image nudged elastic band (CI-NEB) simulations. NT cathodes exhibit exceptionally good discharge capacities ∼60 (∼165) mAhg−1, ∼32 (∼110) mAhg−1 and ∼22 (∼82) mAhg−1 at 25C (1C) rate for x = 0, 0.2, 0.5, respectively. NP cathodes show capacity <5 mAhg−1 at 5C/2C-rate. The high-rate capability with two orders larger diffusion coefficient in nanotubes is due to improved access to Li+ intercalation channels. Whereas, nanoparticles are agglomerated, making b-axis inaccessible. While, Mn substitution affects the discharge capacity, it significantly improves capacity retention from ∼60% (x = 0) to ∼88% (x = 0.2) measured over 1000 cycles at ≥5C. From CI-NEB calculations we infer that Mn increases the activation barrier in its neighbourhood, thereby creating a steep potential hump (∼0.15 eV) for the Li+ diffusion. This largely impedes the ion transport and accounts for the steep loss of discharge capacity. We observe, while single crystalline nanotubular LiFePO4 are useful for high power density applications, Mn substitution in small quantities (x∼0.2) is ideal for cathodes with increased cyclic stability at high C-rates.

Recent Development in Ferrite Material for High Power Application [Passive Components

The most recent ferrite development is illustrated in material and in core shape. The highest Bs material is in focus for high power, i.e., SiC-driven application in high power for motion, automotive, and traction application associated with midvoltage dc grid propagation and high power density. The high Bs is desired according to Snoek's law, and while Bs is predominately influenced by chemistry, the loss mechanism is crystallind with an investigation into its morphological nature and its processing parameters, i.e., the densification process. Another trend in large -sized core shapes, about 8 in in height and 4 in in width, is also described, overcoming challenges to deliver perfect artificial ferrite ceramic to fulfill the needs of newest developments in power electronics. Today, ferrite, after nearly 100 years of development, is manufactured with a capacity of about 500,000 metric tons per year for diverse industries. This recent innovation is rooted in Snoek's formulation. Both high power density and high power application requires high Bs characteristics. It is crucial to understand both the chemical composition and the morphology engineering process to fully comprehend the impressiveness of the artificial ceramics.

Analysis of a Novel Transverse Laminated Rotor Flux Switching Machine

Flux-switching permanent magnet machines with a segmented rotor are attractive alternatives for high torque and power density and high-speed applications. However, the motor doubly salient structure generates high torque ripples. In order to mitigate this problem and enhance motor torque density, a new flux-switching machine topology with transverse laminated rotor segments is proposed in this paper. An analytical model of the proposed machine for calculation of d - and q -axis inductances and developed torque for various number of rotor segments laminations are presented, as well. A finite element model of the proposed motor with various number of segments laminations is simulated in order to evaluate the analytical results. The results are compared with analytical outcomes that show acceptable accuracy of the analytical model. It is also shown that torque ripple is seriously suppressed, whereas average developed torque and efficiency are considerably increased in this new proposed topology. Eventually, the proposed rotor structure mechanical robustness is evaluated by structural finite element analysis. It is shown that the proposed design is mechanically reliable for low- and high-speed applications.

(Battery Division Technology Award) Insight of Structures and Properties of Cathode Materials for Li-ion Battery

Insight into relationship between Crystal/Interface structure and properties of capacity, stability and rate capability are important for developing advanced Li-ion batteries. Using theoretical calculations combined with experimental in-situ tests, we did extensive studies on the kinetic of Li-ion diffusion for two representative cathode materials: layered Li(NixMnyCoz)O2 (NMC) (x + y + z = 1) and LiFePO4. We not only focus on the bulk kinetics, but also the kinetics across electrode/electrolyte solid-liquid interface and in the electrolytes. For example, we first proposed that "Janus" solid-liquid interface would facilitate the Li-ion transport in battery and introducing some disordering in non-active cathode materials would activate them for Li-ion storage.（Ref. 1） For high energy and power density applications (e.g., EVs), the safety becomes especially important. Using ab initio calculations combined with experiments, we clarified how the thermal stability of NMC materials can be tuned by the most unstable oxygen, which is determined by the local coordination structure unit (LCSU) of oxygen (TM(Ni, Mn, Co)3-O-Li3-x’): each O atom bonds with three of transition metal (TM) from the TM-layer and three to zero of Li from fully discharged to charged states from the Li-layer. Under this model, how the lithium content, valence states of Ni, contents of Ni, Mn, and Co, and Ni/Li disorder to tune the thermal stability of NMC materials by affecting the sites, content, and the release temperature of the most unstable oxygen is proposed. In NMC, insight of Ni/Li disorder has be investigated by theory and experimental e.g. neutron powder diffraction experiments and magnetization measurements. The spins of TM ions construct a two-dimensional triangular networks, which can be considered as a simple case of geometrical frustration. Remarkably, the frustration parameters of these compounds are estimated to be larger than 30, indicating the existence of strongly frustrated magnetic interactions between spins of TM ions, which give rise to lattice instability, the formation of Li/Ni exchange in NMC will help to partially relieve the degeneracy of the frustrated magnetic lattice by forming a stable antiferromagnetic state in hexagonal sublattice with nonmagnetic ions located in centers of the hexagons. Moreover, Li/Ni exchange will introduce 180° superexchange interaction, which further relieves the magnetic frustration through bringing in new exchange paths. Thus, the variation of Li/Ni exchange ratio vs. TM mole fraction in NMC with different compositions can be well understood and predicted in terms of magnetic frustration and superexchange interactions. (Ref. 2) Ref. (a)F. Pan el al., “Kinetics Tuning of Li-ion Diffusion in Layered Li(NixMnyCoz)O2”, J. Am. Chem. Soc., 2015, 137, 8364; (b) "Optimized Temperature Effect of Li-Ion Diffusion with Layer Distance in Li(NixMnyCoz)O2 Cathode Materials for High Performance Li-Ion Battery", Adv. Energy Mater., 2015, 1501309(1-9).(c) "Janus Solid–Liquid Interface Enabling Ultrahigh Charging and Discharging Rate for Advanced Lithium-Ion Batteries", Nano Lett,2015, 15 (9), pp 6102 (d)“Single-particle performances and properties of LiFePO4 nanocrystals for Li-ion batteries” Energy Mater., (Front page ) 2016, 1601894 (e) Nano Lett, 2017, 17, 6018 (f) Nano Energy 2017 37, 90 (g) Nano Lett., 2017, 17 (8), 4934(a) F. Pan el al., “Tuning of Thermal Stability in Layered Li(NixMnyCoz)O2”, J. Am. Chem. Soc., 2016, 138 (40), 13326, (b)“Aligned Li+ Tunnels in Core−Shell Li(NixMnyCoz)O2@LiFePO4 Enhances Its High Voltage Cycling Stability as Li-ion Battery Cathode” Nano Letters 2016, 16 (10), pp 6357; (c) Nano Letters, 2015, 15, 5590; （d）The Role of Super-Exchange Interaction on Tuning of Ni/Li Disordering in Layered Li (NixMnyCoz) O2, J. Phys. Chem. Lett., 2017, 8 (22), 5537; (e) Insight into the origin of Lithium/Nickel ions exchange in layered Li(NixMnyCoz)O2 cathode materials, Nano Energy 49 2018,49,77

Influence of Temperature on the Pressure Distribution Within Press Pack IGBTs

Press pack (PP) packaging technology has been applied to insulated-gate bipolar transistors (IGBTs) for high-voltage and high power density applications in recent years. The pressure distribution within PP IGBTs is very important because it affects both the electrical and thermal contact resistances, thermal cycling capability, and short-circuit current rating. Too much pressure will mechanically damage the chip and too little pressure will increase the thermal contact resistance, which eventually leads to chip thermal damage. In this paper, a finite-element multiphysics model cocoupled with an electrical field, thermal field, and mechanical field is proposed to analyze the collector current distribution, pressure distribution, and junction temperature distribution within PP IGBTs. The most important coupling variables, such as electrical and thermal contact resistances, for this cocoupled multiphysics model are calculated or measured by experiment through a single IGBT/fast-recovery diode chip submodule. Based on this multiphysics model, the influence of the high temperature generated by the chip's power dissipation on the pressure distribution within PP IGBTs (in the heating phase) is discussed, and then, compared with the pressure distribution in the clamping phase. The results show that the pressure distribution within PP IGBTs in the heating phase is extremely uneven and different from the value in the clamping phase. Furthermore, the mechanical model and its boundary conditions are verified through the pressure distribution experimental results in the clamping phase, which is measured based on the Fuji prescale film and the clamping test bench. Based on the simulation and experimental results, an optimization of the collector electrode and pedestal is proposed to improve the pressure distribution within PP IGBTs in the heating phase.

Multidomain Optimization of High-Power-Density PM Electrical Machines for System Architecture Selection

The power density of electrical machines for transport applications has become a critical aspect and target of optimization. This paper looks at the development of an intelligent, rapid, flexible, and multidomain tool to aid for system-level optimization of electrical machines within next-generation high power density applications. The electromagnetic, thermal, and mechanical aspects are wholly integrated, thus enabling the optimization including the nonactive mass. The implementation and overall architecture of the tool are described, and using a case study drawn from the aerospace industry, the tool is used to compare the power density of various surface permanent magnet topologies including single airgap and dual airgap machines, highlighting the particular suitability of the dual rotor topology in achieving the best power to mass ratio. Finally, the accuracy of the tool is highlighted by practical realization and experimental validation.

Optimal and Systematic Design of Current Controller for Grid-Connected Inverters

A design approach for grid-connected inverter controllers for distributed and renewable energy system applications is proposed, where a high number of controller gains can be designed optimally in a fairly systematic way. The linear quadratic regulator problem is first modified to accommodate sinusoidal signal tracking through a meaningful state-space transformation. The cost function is modified to explicitly include the tracking error, so that its weights are designed in a transparent and systematic way. The proposed technique is applied to the well-known control structure comprising the fundamental and harmonic resonant controllers. Second, the control structure is rearranged to reject the distortions from both the grid voltage and the reference signal, and the proposed design technique is applied to this new structure. It is shown that the desired features of active damping for $LCL$ filters and robust performance against system uncertainties, harmonics, and disturbances are achieved. Third, the controller and the systematic design procedure are extended for inverters with $LLCL$ filters. Proposed control structures are designed and simulated and then implemented on a digital signal processor. Results confirm features of the method and its ability to address control system challenges in high power density and efficient inverter applications.

CFD modelling of cooling channel geometry of PEM fuel cell for enhanced thermal performance

Proton exchange membrane (PEM) fuel cell has many distinctive features that make it an attractive alternative clean energy source, including low start - up, high power density, high efficiency, portability and remote applications. An approach to stem the the rmal build - up within the fuel cell structure that could lead to degradation of the system components is by integrating cooling channels as part of flow structure of the PEM fuel cell system. In this study, a numerical investigation was carried out to deter mine the impact of cooling channel geometry in combination with temperature dependent operating parameters on thermal management and overall performance of a PEM fuel cell system. The evaluation is performed using a computational fluid dynamics (CFD) code based on a finite volume approach. The systems performances are presented as a function of the system temperature, operating parameters and cooling channel geometry. The results obtained indicate that incorporating cooling channels within the fuel cell structures improves the PEM fuel cell system performance at higher temperature of operation and optimal aspect ratio of the cooling channels exist for maximised fuel cell performance for the fuel cell model considered. In addition, the parameters studied were optimized using a mathematical optimization code integrated with the CFD code. Keywords : PEM fuel cell; Cooling channel; Aspect ratio; Optimal performance; Higher temperature; Mathematical optimisation

SiC Trench MOSFET With Integrated Self-Assembled Three-Level Protection Schottky Barrier Diode

A silicon carbide (SiC) trench MOSFET (TMOS) with integrated three-level protection (TLP) Schottky barrier diode (SBD), named ITS-TMOS, is proposed and investigated by simulation. The device features the integrated TLP-SBD that remarkably improves body diode characteristics while guarantees excellent fundamental performance of TMOS. In the blocking state, the P-base region, the trench gate, and the P+ shield at the trench bottom serve as the TLP of the Schottky contact. Each protection assists in depleting the drift region beneath Schottky contact. Benefiting from the self-assembled TLP, the leakage current of the integrated body diode of the ITS-TMOS is significantly reduced. Moreover, the reverse turn-on voltage ( ${V} _{ \mathrm{\scriptscriptstyle ON}}$ ) and the gate charge ( ${Q} _{g}$ ) of the ITS-TMOS are 65% and 18% lower than those of the conventional TMOS, respectively. The improved overall performances make the SiC ITS-TMOS a competitive candidate for high-efficiency and high power density applications.

Effect of vanadium doping on electrochemical properties of carbon coated nano lithium iron phosphate for high rate applications

Lithium iron phosphate (LiFePO4) is a promising electrode material for the lithium ion battery technology as it has the potential to meet the requirements of the high energy density and power density applications. However, its limitations such as low conductivity and a low diffusion coefficient lead to high impedance due to which its application is restricted. The cationic substitution of vanadium in the native LiFePO4/C is one of the methods to enhance the conductivity. Here the work is focused on obtaining a cathode material with improved electrical performance by doping it with different compositions of vanadium in the lithium site of LiFePO4/C. Nano powders of LiFePO4/C and Li1–x V x FePO4/C (x = 0.05, 0.1, 0.15–0.2) were synthesized from precursors via the solid state vacuum synthesis. The solid solution formation up to Li1–x V x FePO4/C (x = 0.2) without impurity phases is confirmed by the XRD and FTIR results. The particles distribution of synthesized powders was followed by the SEM. Also, dc conductivities are measured on sintered pellets and activation energies are calculated using the Arrhenius equation. The dependence of conductivity and activation energy of LiFePO4/C on variation of vanadium doping is also investigated in this study. The CR2032 cells were fabricated and subjected to cyclic voltammetry studies, charge-discharges at different C-rates and cycle life. The electrochemical impedance spectroscopy was used to obtain the ac impedance and diffusion coefficients, and the effect of doping on these parameters is discussed. It was observed that the room temperature dc conductivity was improved by vanadium doping when compared to LiFePO4/C (2.141 × 10–2 S cm–1) and it was maximum for Li0.85V0.15FePO4/C (22.201 × 10–2 S cm–1). It was also observed that the diffusion coefficient of Li+ in Li0.85V0.15FePO4/C (12.89 × 10–9 cm2 s–1) improved by two orders of magnitude as compared to that of pure LiFePO4 (10–12 cm2 s–1) and carbon coated nano LiFePO4/C (0.626 × 10–11 cm2 s–1). Cells with Li0.85V0.15FePO4/C are able to deliver useful capacity of around 101 mAh g–1 at 10C rate. More than 1000 cycles were achieved with Li0.85V0.15FePO4/C at 20C rate.

An SiC-Based Half-Bridge Module With an Improved Hybrid Packaging Method for High Power Density Applications

SiC devices have the potential to structure high power density converters; however, SiC devices have high d i /d t during switching. Therefore, the parasitic inductances in the power loop and gating loop must be reduced to restrain the induced voltage. This paper proposes a SiC-based, half-bridge (HB) module with a hybrid packaging method. Such a module is based on printed circuit board (PCB) plus direct bonding copper (DBC) structure. The DBC provides part of power loops, and the SiC bare dies can be directly soldered on these loops; the PCB provides another part of the power loops, as well as the gating loops. Such a design allows the power loops on the PCB to be soldered with those on the DBC directly; in the meantime, the SiC bare dies soldered on the DBC can be connected to the PCB with bounding wires. Such a structure provides extra degrees of freedom for design so that the parasitic inductances can be minimized by optimizing the current communication loops, driver locations, and the gating connections, and the heat can also be dissipated through the direct cooling structure easily. A 1200 V/24 A SiC HB module is fabricated with the proposed method in the laboratory, and based on the fabricated module, a synchronous buck converter with power density of 379.3 W/in3 is also structured. The double pulse test shows that the fabricated module can be switched within 10 ns and that the drain-source voltage overshoot is only 2.5%. The highest efficiency of the converter based on the fabricated module is up to 99.46%.

Improved multiferroic properties of graded Mn doped BiFeO3 thin film

The compositionally graded BiFe1-XMnXO3 (0.0 ≤ x ≤ 0.3) thin film was deposited on LaNiO3 coated Si (100) substrate via pulsed laser deposition technique to investigate multiferroic properties. This thin film had a (l00) oriented perovskite structure without any secondary phases. Compared with the pure BiFeO3 film, the graded film not only exhibits out of plane magnetic anisotropy but also increases ferroelectric polarization and dielectric tunability. A large remanent polarization of Pr∼69.47 μC/cm2 and coercive field of HC∼86.95 kV/cm are observed in such a graded thin film. These improved responses could be due to spontaneous and induced polarization of individual layers. Moreover, electrostatic coupling, polarization gradient and elastic integration between layers also contributed for the enhancement of multiferroic properties in graded thin film. This work presents a feasible way to design a new kind of electronic devices based on graded multiferroic for developing high power and energy density applications.

Meso and Microstructural Interactions in Porous Lithium-Ion Batteries

Rechargeable batteries are porous electrochemical structures composed of secondary particles, which are aggregates of single crystal primary particles, pores, cracks, and processing-induced phases and features. The underlying meso and microstructural topology, including its size, size distribution, morphology and crystallographic orientation of each of the underlying phases impacts the delivered power and energy density. While it is clear that the component with the lowest efficiency will be the bottleneck to performance of the overall device, the understanding of the fundamentals associated to the different electrochemical and chemomechanical interactions of the underlying phases remains unclear. In this paper we will discuss the meso and microstructural limitations associated to porous cathode electrodes, and will outline strategies to tune the response of primary and secondary particle configurations for high power or energy density applications.

Experimental Comparison of High‐Speed Gate Driver Design for 1.2‐kV/120‐A Si IGBT and SiC MOSFET Modules

Silicon carbide (SiC) metal–oxide–semiconductor field-effect transistor (MOSFET) is regarded as an attractive replacement for Si insulated gate bipolar transistor (IGBT) in high-power density applications due to its high switching speed and low switching loss. However, to fully utilise these benefits, the gate driver of the SiC MOSFET needs to be optimised to meet its special driving requirements. Fundamentally, both gate drivers for Si IGBT and SiC MOSFET share similar design methodology since these two power devices have the same MOS-gated structure. However, one of the major challenges in the gate driver design for SiC MOSFET is overcoming the electromagnetic interference, which is resulted from the much higher dv/dt and di/dt ratios during the switching transition. In this study, high-speed gate drivers for Si IGBT and SiC MOSFET power modules of similar ratings of 1.2 kV/120 A have been designed. The performances of gate driver have been experimentally evaluated by a double pulse test. The design considerations of gate driver to enable the replacement of Si IGBT by SiC MOSFET have been conclusively investigated and presented in this study.

Transient Thermal Analysis of HTS DC Cables Cooled With Gaseous Helium Using a Volume Element Method

Gaseous helium is being considered as a cryogen for a variety of high-power density applications. It is capable of reaching operational temperature levels as low as 20 K. This paper presents a time efficient method of designing and modeling a high-temperature superconducting dc cable. The analysis is an extension of a previously presented mathematical model in which the volume element method was used to characterize the fluid flow and heat transfer by conduction, convection, and radiation through a flexible cable cryostat. A system of ordinary differential equations was formulated using the fundamental principles of thermodynamics. The computational domain consists of volume elements distributed in three dimensions to account for the spatial dependence of the model. The pressure drop of the gaseous helium was calculated based on the Darcy-Weisbach correlation. Additionally, the temperature distribution was solved numerically using adaptive time-stepping. The obtained solutions converge within a timescale on the order of seconds to minutes, and the steady state results along with a transient analysis is discussed.

XLi2MnO3-yLiMn2O4-(1-x-y)LiNi0.5Mn0.5O2 for Lithium Ion Batteries

Lithium-ion batteries are considered as an important power source for electric and hybrid electric vehicles. Li2MnO3 based composite cathode materials are one of the most investigated cathode materials due to their ability to provide high discharge capacity and excellent rate capability. In this study, we have focused on synthesizing a lithium intercalated cobalt-free layered-layered-spinel composite cathode material xLi2MnO3-yLiMn2O4-(1-x-y) LiNi0.5Mn0.5O2 (LLNMO) by solvothermal synthesis technique. The structure of the compositions was characterized using X-ray Diffraction (XRD) and Raman Spectroscopy; peaks corresponding to layered and spinel structures were identified by both study methods. The surface morphology was studied by Scanning Electron Microscope (SEM). SEM images showed agglomerations of the nano-sized particles as well as the presence of the corresponding transition metals in the compositions which was confirmed with Electron Disperse Spectroscopy (EDS). The electrochemical performance was performed on coin cells, assembled in the Ar- filled glove box; we used Li as counter electrode, spread material as cathode and Celgard as separator. LiPF6 with EC:DMC in the 1:2 ratio was used as the electrolyte. Cyclic voltammogram (CV) was performed using a scan rate of 0.1 mV/s in a voltage range from 2.0-4.8 V. The charge discharge studies were performed using a current density of 10mA/g in the same voltage range. Finally, the Electrochemical Impedance Spectroscopy (EIS) was studied between cycles to understand the effect of cycling in the charge transfer resistance and also the internal resistance of the cells. The CV, charge discharge and EIS studies revealed that the lithium intercalated cathode material developed is a promising, structurally stable material for high energy and high power density applications.

A review of radioisotope batteries

As an important kind of energy source, radioisotope batteries are attracting more and more academic researchers and people from industry due to the high power density, long lifetime (equal to half life of the radioisotope source), outstanding reliability, without maintenance, miniaturization and wide application compared with traditional dry batteries, chemical batteries, fuel batteries and solar batteries. Based on the optimization of functional materials and energy conversion types, radioisotope batteries have been developed for more than 15 species since the first β battery invented by Henry Mosley in 1913. This review describes historical background and development, limitations of key techniques in radioisotope batteries. The radioisotope source loading methods and thermocouple materials of radioisotope thermoelectric generator (RTG), the semiconductor materials and energy conversion units of radiation voltaic isotope batteries (RVIB) are analysed in detail. After an introduction of the basic principles and design requirements of radioisotope batteries, we discuss the technical proposals of different energy conversions for radioisotope batteries. Then, the most recent experimental results for several configurations and experimental set-ups of radioisotope batteries are introduced detailedly, including static thermoelectric type radioisotope batteries, radiation voltaic effect radioisotope batteries, dynamic energy transformation radioisotope batteries and piezoelectric energy transformation radioisotope batteries. The figure for PCEs (Power Conversion Efficiencies) in different radioisotope batteries from 1913 to 2015 is first demonstrated in the end, which illustrates the PCEs of RTG, RVIB are close to 10% and DIPS (Dynamic Isotope Power System) is higher than 23%. Thus, the PCEs of radioisotope batteries will increase effectively if some various high efficient energy conversion types like RTG, RTPV (Radioisotope thermophotovoltaic) and RTIGs (Radioisotope Thermionic emission Generators) are assembled. In the future, four main trends for radioisotope batteries include the better safety and reliability, the higher output power and power matching, the micro/nano integration and module combination of battery structure, the production of radioisotope source. We believe that the research and application of radioisotope batteries will be much attractive with the break through of these aspects made by academic and industrial world.

Low pressure, modular compressed air energy storage (CAES) system for wind energy storage applications

The construction and testing of a modular, low pressure compressed air energy storage (CAES) system is presented. The low pressure assumption (5 bar max) facilitates the use of isentropic relations to describe the system behavior, and practically eliminates the need for heat removal considerations necessary in higher pressure systems to offset the temperature rise. The maximum overall system efficiency is around 97.6%, while the system physical footprint is less than 0.6 m3 (small storage room). This provides a great option for storage in remote locations that operate on wind energy to benefit from a nonconventional storage system. The overall size and capacity of the system can be changed by changing the number of active cylinders, which in this case are off-the-shelf, small pressure vessels used for fire protection. Moreover, the system operation is automated and capable of addressing both high energy and high power density applications with an infinite number of charge-discharge cycles by augmenting the capacity with the required number of storage cylinders. The system is eco-friendly and has low maintenance costs compared to chemical storage.

Investigation of the Direct Plating Copper (DPC) on Al2O3, BeO or AlN Ceramic Substrates for High Power Density Applications

Abstract In the high power module applications, the power increasing and the size shrinking becomes one of the major topics for the power module design. Due to both the power increasing and the size decreasing, the power density of the device will be much increased. Therefore, not only the thermal conductivity and stability of the substrate material but the long-term material reliability of the substrate have to be seriously considered. For these reasons, the ceramic PCB becomes one of the best solutions. The ceramic substrates now used are normally based on Ag-printed or direct bonding copper (DBC) technology. In the case of the Ag-printed ceramic substrate, the pattern resolution and metallization thickness are limited by the Ag-printed process. Also the combination strength of the silver and ceramic substrate by glass (which is normally mixed in the silver paste) is normally not good enough. A thermal dissipation barrier will then be formed between silver and ceramic substrate due to the poor thermal conductivity of the glass material. For the DBC ceramic substrate, DBC substrates are manufactured at 1065°C by the diffusion between ceramic and Cu/CuO layer. A thicker Cu layer thickness of normally more than 300 um is required in the thermal compressing bonding process. The Cu pattern resolution will then be limited by the thickness of the Cu layer. However, the about 5~10% of the voids exist randomly between ceramic and Cu layer is the other major issue. The resolution issues of the Ag-printed and DBC ceramic substrates make the limitation for the device density design (fine line/width and flip-chip device design become very difficult). The glass material in the Ag printed ceramic substrate and the 5~10% voids existence in DBC ceramic substrate may cause the reliability issue operating at a high power density applications. For high power density module applications, we introduce the DPC technology on the ceramic substrate. In DPC ceramic substrate system, the sputtered Ti is used as the combination material between Cu and ceramic substrate. And the first copper is then sputtered on the top of Ti layer as seed-layer for the following Cu electrode plating (second cupper layer). By the material and the sputtering process control, several ceramic substrate raw materials can be used, such as Al2O3, AlN, BeO, Si3N4 and so on. The Ti combined/buffer layer provides good adhesion strength and material stability. The second copper layer is plated by electrode casting plating to 3 to 5 oz. (100~150um) in thickness. The key technology of the metal trace plating is the material control of the sputter layers and the second copper layer stress release during plating. In the DPC system, the double layers design is available. The laser drilled via holes on the various ceramic substrates is introduced. The conducting of the front and back side is connected by the following plating process. The key technology of this process is the stability of the via-holes. We have to make sure the via-holes cleaning, impurity removing and material stability during high temperature laser drilled is well controlled. DPC ceramic substrates provide a better metal/ceramic interface uniformity and material reliability due to the stable Ti combination material and much less voids in the metal/ceramic interface. Also, the DPC ceramic substrates provide a gold pattern resolution of 50 um line space with tight tolerance of 20 um min. We believe the material characteristic make DPC a very suitable substrate material for high power module applications.