Power Density Of System Research Articles

A 50-kW Three-Phase Wireless Power Transfer System Using Bipolar Windings and Series Resonant Networks for Rotating Magnetic Fields

The mass and volume of wireless power transfer (WPT) systems for charging electric vehicles are directly related to the rated power of the system. The difficulties of high-power wireless charging are exacerbated by the need to meet the same practical constraints associated with vehicle integration as lower power systems. Therefore, more advanced techniques are necessary to improve power density and specific power of wireless charging systems for high-power applications. This article presents theory and analysis of three-phase inductive WPT systems with bipolar phase windings. Magnetic coupler topologies and the theoretical and practical aspects of series three-phase resonant compensation networks are discussed. The systems under consideration are designed to utilize rotating magnetic fields to achieve a power transfer characteristic that is temporally smoother than single-phase systems. Other benefits associated with rotating magnetic field based WPT, including reduced ferrite mass, filter component requirements, and electromagnetic field emissions, are discussed. Experimental results of a prototype system are presented in both aligned and misaligned configurations. The system is demonstrated transferring 50 kW with 95% dc-to-dc efficiency over a 150-mm airgap in the aligned case. Onaper-pad basis, the magnetic couplers achieve a power density of 195 kW/m 2 and a specific power of 3.65 kW/kg. This article is accompanied by a video of the rotating magnetic field produced by a simulated three-phase WPT system.

THERMAL VALIDATIONS OF ADDITIVE MANUFACTURED NON-METALLIC HEAT SPREADING DEVICE FOR HOT SPOT MITIGATION IN POWER MODULES

Abstract As energy demands and power electronics density scale concurrently, reliability of such devices is being challenged. Inadequate thermal management can cause system-wide failures due to thermal run-away, thermal expansion induced stresses, interconnect fractures and many more. Conventional techniques used to cool devices consist of heavy, metallic systems such as cold plates and large heat sinks, which can significantly reduce the overall system power density. Moreover, the manufacturing of such components is expensive and often requires custom-made cold plates for improved integration with the electronic system. Although used as a standard practice, these metallic thermal management systems have the potential to intensify electro-magnetic interference (EMI) when coupling with high frequency switching power electronics, and the material density increases the weight of the system, which is detrimental in mobile applications. Lastly, cold plates and heat sinks can create non-uniform cooling profiles in the electronics due to the insufficient management of hot-spots. To combat these drawbacks, a new heat spreader design has been proposed which reduces weight and EMI effects while eliminating hot-spots through localized fluid impingement. This current study describes the methodology and construction of the experimental test setup to characterize the performance of the heat spreading device compared to an off-the-shelf cold plate. Through infrared imagining, the viability of two heated test sections are evaluated in their ability to replicate power module temperature profiles during operation.

Upgrading the electrochemical performance of graphene oxide-blended sulfonated polyetheretherketone composite polymer electrolyte membrane for microbial fuel cell application

Abstract In the present study, composite polymer electrolyte membranes were synthesized by the incorporation of graphene oxide (GO) in sulfonated polyetheretherketone (SPEEK) for simultaneous wastewater treatment and electricity generation. A variety of techniques were applied to characterize the chemical, crystal and morphological structure of the as-synthesized membranes. In addition, the water uptake, mass transfer, and oxygen diffusion coefficients, proton conductivity, ion exchange capacity, internal resistance, power density, coulombic efficiency and COD removal of the MFC system applied with SPEEK, SPEEK/GO composite membranes were studied and compared with the commercial Nafion117. The incorporation of various GO contents caused a decrease in oxygen diffusion and mass transfer coefficients of 7.45 × 10-6 cm2 s-1 and 0.00048 cm s-1, respectively. This was also shown that the SPEEK/GO3 membrane with proton conductivity 2.88 mS cm-1, power density 53.12 mW m−2, voltage 883 mV, and CE 3.74% showed higher performance compared to Nafion 117 membrane as a separator in MFC. Furthermore, the MFC with SPEEK/GO3 membrane gave slightly higher COD removal (88.7%) than that of MFC incorporating the Nafion 117 membrane (81.9%). The ion exchange capacity (IEC) and WU of as-prepared membranes were found to vary from 1 to 2.21 meq g-1 and from 44.31 to 67.85%, respectively. The results obtained were revealed that the MFC assembled SPEEK/GO3 composite membrane is demonstrated significant improvement in cell performance compared with commercial Nafion 117 membrane that qualifies it to be a promising candidate as a proton exchange membrane in the lab-scale microbial fuel cells.

Development of two-phase interleaved synchronous rectification DC-DC for commercial vehicle engine ECU

The commercial vehicle diesel engine ECU and the electronically controlled common rail system power supply developed in this paper adopt the two-phase BUCK converter as the main loop. Considering the problems of large current fluctuation, high continuum diode loss and possible non-uniform current in parallel connection of traditional BUCK converter, a control strategy of two-phase staggered parallel synchronous rectifier BUCK converter is proposed. The relationship between current fluctuation and inductance, switching frequency and duty cycle of different operating modes is theoretically analyzed, and the current fluctuation of traditional BUCK converter is compared. The prototype test results show that the converter structure and control strategy effectively reduce the output current fluctuation and improve the system power density.

Review of Si IGBT and SiC MOSFET based on hybrid switch

SiC Hybrid switch (HyS) combines low conduction loss of Si IGBT and low switching loss of SiC MOSFET, and the cost is closer to that of Si IGBT. The promising high performances of HyS will bring considerable achievement in terms of enhancing power density of a converter system. By reviewing the gate drive pattern, gate drive hardware, current sharing, module design, converter design, and cost, this paper introduces state-of-the-art SiC HyS.

Boosting Energy Density of an All Solid-State Asymmetric Supercapacitor Based on rGO/Ni(OH)2 and Activated Carbon Via Model Guided Design

Supercapacitors are one of the promising energy storage devices because of their long life span and high power density, which leads to their advantageous application in regenerative braking system of electric vehicles (EVs). The major challenge that supercapacitors facing is their relatively lower energy density. There are two possible routes to overcome this shortcoming: first, increasing the capacitance by selecting electrode materials with a higher specific area, such as activated carbon (AC); second, enlarging the operable potential window by choosing two electrodes of different materials, forming the so called asymmetric supercapacitors (ASCs). Despite ASCs do enlarge the operable voltage window, most of the aqueous ASCs still suffer from the decomposition of water, limiting the maximum operation voltage to around 1.6 V. Capacitors employing aqueous electrolyte are also prone to leakage, leading to safety concerns. The gel polymer electrolyte (GPE), on the other hand, has higher electrochemical stability compared to aqueous ones. Their solid-state characteristics prevent the electrochemical system from leakage, which is advantageous for supercapacitors employed in portable electronics or EVs. In this work, we aim to construct an asymmetric supercapacitor, where rGO/Ni(OH)2 and AC are used as electrode materials and a LiClO4–based gel polymer is employed as the electrolyte, to achieve enhanced energy density. Cyclic voltammetry is first conducted on rGO/Ni(OH)2 and AC half-cells with GPEs to identify the operational voltage window, and the former is selected as the positive electrode and the latter as the negative electrode to optimize the utilization of electrical double layer capacitance (EDLC) of the system. With limited redox reactions involved, the cell can not only have longer cycle life but also endure higher current densities. The assembled ASC is further examined by galvanostatic charge-discharge (GCD) experiments. GCD examination is conducted with an upper voltage limit of 3 V and under a current density of 2 mA/cm2, and the results are shown in Figure 1. Figure 1 (a) shows charge/discharge curves of the first five and the last five of the recorded 10,000 cycles of our ASC, and the highly similar voltage-time behavior after the first cycle indicates high electrochemical reversibility of this ASC. Figure 1 (b) shows that the coulombic efficiency remains close to 100% after the initial activation cycles. The specific capacitance, energy density and power density of this ASC system are measured to be 2 F/g, 61.6Wh/kg, and 1800 W/kg, respectively. By exerting excess faradaic reaction of the rGO/Ni(OH)2 electrode, this ASC system can potentially have enhanced specific capacitance. We propose to conduct multi-physics simulations to better match the two electrodes when faradaic reaction is involved, as well as optimize the operation window of the ASC. COMSOL software is employed to simulate charge/discharge profiles under pseudo capacitive conditions, with the physical parameters measured by experiments. With the simulation guided design of the ASC, we anticipate to systematically enhance the functionality of this electrochemical device for future application such as in EVs. Figure 1

Evaluation of DC-Link Voltage Switching Ripple in Multiphase PWM Voltage Source Inverters

This article presents a generalized approach toward the dc-link voltage switching ripple analysis in the two-level multiphase pulsewidth modulation (PWM) voltage source inverters with a balanced load. Since the voltage ripple is one of the crucial sizing criteria for a dc-link capacitor, a simple and practical equation for designing the dc-link capacitor, based on the maximum (peak-to-peak) value of the dc-link voltage ripple, has been proposed for the multiphase inverters. The amplitude of the dc-link voltage switching ripple is analytically derived as a function of operating conditions. The effect of the number of phases on the dc-link capacitor size is investigated as well. It is found that considering the same total output current, the dc-link capacitor size is reduced by increasing the number of phases up to seven. However, from the point of view of the dc-link capacitor size, there are no benefits of further increasing the number of phases. Reference is made to two commonly used modulation strategies—sinusoidal PWM and continuous symmetric centered PWM (i.e., space vector). The mathematical models are derived with an aim to provide the precise dc-link capacitor sizing and hence improve the power density of the whole system. The comparison of different phase numbers has been made. Proposed theoretical developments are verified by the simulation and experimental tests.

Energy management strategy for battery/supercapacitor/fuel cell hybrid source vehicles based on finite state machine

In recent years, fuel cell vehicles have attracted attention for their zero emission and environmental friendship. The sole fuel cell system cannot satisfy the dramatical change of motor power demands. In addition, the power fluctuations will damage the fuel cell stacks and shorten the cycle life of fuel cells. Therefore fuel cell systems are always combined with other energy storage devices like batteries and supercapacitors to increase the power density of the power system and fulfill the load power demands. The management strategy of the hybrid propulsion system is a significant technique for the vehicular power system. In this work, a finite state machine based management strategy is first proposed for both the battery/fuel cell and battery/supercapacitor/fuel cell system. The power capabilities of the battery and supercapacitor have been considered as important parameters in the management strategy. Moreover, an optimal oxygen excess ratio control is presented to maximize the fuel cell output net power. To evaluate the performance of the fuel economy and dynamic property, both the simulations and experimental verifications with the real physical system are given, and the real driving cycle of urban dynamometer driving schedule is utilized. The experimental and simulated results indicate that the proposed method is able to guarantee the required power during most of the driving cycles.

Design and test of a new two-stage control scheme for SMES-battery hybrid energy storage systems for microgrid applications

This paper proposes a novel control scheme for a hybrid energy storage system (HESS) for microgrid applications. The proposed two-stage control method is used to control the HESS to stabilize a microgrid’s voltage level and extend battery service lifetime during the coupling/decoupling of a microgrid from the main power grid. The conventional HESS control method (the filtration method) is not suitable to compensate for a microgrid’s power demand when it is decoupled from the main grid. This research focuses on using a superconducting magnetic energy storage (SMES) and battery HESS to assist with the microgrid coupling/decoupling process. To compensate for the instantaneous high power demand during decoupling, the battery will need to rapidly discharge. Moreover, batteries have difficulty supporting high discharging rates, which results in ineffective compensation of the power demand. In this paper, the high power density of the SMES system combined with the high energy density of a battery shows good performance on stabilizing microgrid bus voltage during the decoupling process. A novel energy management method for the HESS is proposed to improve the battery performance when the microgird coupled/decoupled from main grid. The sizing design is simplified based on the control methodology. Moreover, a SMES and battery HESS experimental platform is built to validate the proposed control methodology and its reliability.

A hybrid system using Brayton cycle to harvest the waste heat from a direct carbon solid oxide fuel cell

A new hybrid system model is developed to evaluate the potentials of a Brayton cycle heat engine for waste heat recovery from a direct carbon solid oxide fuel cell (DC-SOFC). The maximum power density of the proposed system is up to 0.8675 W cm−2, which is approximately 1.8 times as large as that of the single DC-SOFC. Numerical calculations also indicate that the proposed hybrid system is an efficient approach to boost the fuel utilization, and the maximum power density of the proposed system is markedly better than that of the DC-SOFC/thermophotovoltaic cell, DC-SOFC/thermionic generator, and DC-SOFC/Otto heat engine hybrid systems except for the DC-SOFC/Stirling engine hybrid system. The optimum regions for power density, efficiency and operating current density of the proposed system are determined. The higher operating temperature and lower gap between the anode and carbon layer increase the power density and efficiency of the proposed system. Moreover, the higher heat transfer coefficient boosts the power density and efficiency at high current density. The compression efficiency, expansion efficiency and recuperator coefficient significantly affect the power density and efficiency.

Performance evaluation of a novel photovoltaic-electrochemic hybrid system

To harvest the relatively high wavelength sunlight, a novel hybrid system coupling a thermally regenerative electrochemical cycle to a dye-sensitized solar cell is proposed. Efficiencies and power outputs of dye-sensitized solar cell and thermally regenerative electrochemical cycle are calculated, and the mathematical relationship between the electric current of thermally regenerative electrochemical cycle and the working current density of dye-sensitized solar cell is deduced. The power output and efficiency of the hybrid system are also derived considering multiple irreversible losses. The feasibility and effectiveness of the proposed hybrid system will be assessed by comparing the performances between the hybrid system and the single dye-sensitized solar cell. Numerical calculations show that the maximum efficiency and power density of the hybrid system allow 32.04% and 32.18% greater than that of the single dye-sensitized solar cell, respectively. Comprehensive parametric studies are undertaken to examine the dependences of the hybrid system performance on some operating conditions and microstructure parameters, including electrode porosity, photoelectron absorption coefficient, Schottky barrier, film thickness and internal resistance of thermally regenerative electrochemical cycle. The derived results may offer new insights into design and optimization of such an actual hybrid system.

High-Power-Density Single-Phase Three-Level Flying-Capacitor Buck PFC Rectifier

Active pulsating power buffering (PPB) is an effective technique to reduce the energy storage requirement of a single-phase power-factor-correction (PFC) rectifier. Existing single-phase solutions with active PPB, however, generally suffer from high voltage stresses, leading to increased power losses as well as the need for high-voltage-rating semiconductor switches. Previous works have been focusing on two-level switching converter configurations, and thus have failed to address the high-voltage-stress problem. In this paper, a single-phase three-level flying-capacitor PFC rectifier with PPB-embedded switching is proposed. The flying capacitor not only clamps the voltage stresses of all power devices but also functions as a PPB capacitor. The operating principles, control methods, and design guidelines are detailed and the feasibility of the proposed converter is verified through a 48-W (48-V/1-A) hardware prototype. The proposed rectifier is shown to achieve nearly 50% reduction of the voltage stresses, 72% reduction of the buffering capacitor's volume, and 23.8% reduction of the magnetic core size, as compared to a state-of-the-art two-level solution recently proposed. This new approach of formulating single-phase PFC rectifiers with active PPB could dramatically boost the system's efficiency and power density whilst reducing cost.

Enhanced platinum utilization efficiency of polymer-coated carbon black as an electrocatalyst in polymer electrolyte membrane fuel cells

The utilization efficiency of platinum (Pt) in polymer electrolyte membrane fuel cells (PEMFCs) needs to be increased to lower the cost of PEMFCs to facilitate their widespread commercialization. Here we developed a novel method to improve the Pt utilization efficiency by coating of polybenzimidazole (PBI) on the surface of the carbon support material; Vulcan. Electrochemical experiments revealed that Pt nanoparticle-loaded PBI-coated Vulcan (denoted as Vulcan/PBI/Pt) electrode possessed a much larger electrochemically active surface area (ECSA) compared with that of Pt nanoparticles directly deposited on Vulcan (Vulcan/Pt).The power density of the cell with Vulcan/PBI/Pt was 1.16 kW g−1, which was ca. 20% higher than that of the control cell using Vulcan/Pt (0.97 kW g−1). We considered that the higher Pt utilization efficiency of Vulcan/PBI/Pt than Vulcan/Pt resulted in such an enhanced ECSA and power density of the PBI-coated system. Two possible reasons were considered for the improvement; namely 1) the polymer layer prevented the loading of Pt nanoparticles into inaccessible micropores of Vulcan and 2) the polymer layer improved the coating homogeneity of Nafion ionomer, and thus improved the proton accessibility for Pt nanoparticles.

Microbial fuel cells: A fast converging dynamic model for assessing system performance based on bioanode kinetics

In this work, a dynamic computational model is developed for a single chamber microbial fuel cell (MFC), consisting of a bio-catalyzed anode and an air-cathode. Electron transfer from the biomass to the anode is assumed to take place via intracellular mediators as they undergo transformation between reduced and oxidized forms. A two-population model is used to describe the biofilm at the anode and the MFC current is calculated based on charge transfer and Ohm's law, while assuming a non-limiting cathode reaction rate. The open circuit voltage and the internal resistance of the cell are expressed as a function of substrate concentration. The effect of operating parameters such as the initial substrate (COD) concentration and external resistance, on the Coulombic efficiency, COD removal rate and power density of the MFC system is studied. Even with the simple formulation, model predictions were found to be in agreement with observed trends in experimental studies. This model can be used as a convenient tool for performing detailed parametric analysis of a range of parameters and assist in process optimization.

Performance assessment of an advanced triple-cycle system based upon solid oxide fuel cells, vacuum thermionic generators and absorption refrigerators

In addition to generate electricity, solid oxide fuel cells also produce a considerable quantity of high-quality waste heat. To harvest the waste heat, an advanced triple-cycle system based upon solid oxide fuel cells, vacuum thermionic generators and absorption refrigerators is theoretically put forward. Assuming that the main irreversible losses within the system are thermodynamic and electrochemical losses, the performance parameters mathematically evaluating the whole system are specified under different operating conditions. The effectiveness is also demonstrated through performance comparisons between the proposed system and the stand-alone solid oxide fuel cell system. Numerical calculations show that the maximum attainable power density and its corresponding efficiency allow 20.3% and 18.4% larger than that of the stand-alone solid oxide fuel cell system, respectively. Comprehensive parametric studies are further undertaken to reveal the influences of some decisive design parameters and operating conditions on the triple-cycle system performance. Results show that the microstructure parameters of the solid oxide fuel cell and the anode temperature of the vacuum thermionic generator can be optimally designed to maximize the power density of the triple-cycle system. The vacuum thermionic generator can be treated as the alternative intermediate cycle for SOFC based triple-cycle systems.

Mechanistic Theoretical Investigation of Self-Discharge Reactions in a Vanadium Redox Flow Battery.

Compared to the studies of new electrolyte and electrode chemistries aimed to push the energy and power density of battery systems, investigations of self-discharge reactions contributing to capacity fading are still very limited, especially at the molecular level. Herein, we present a computational study of oxidation-reduction reactions between vanadium ions in solution leading to battery self-discharge due to the crossover of vanadium species through the membrane in all-vanadium redox flow batteries (RFB). By utilizing Car-Parrinello molecular dynamics (CPMD) based metadynamics simulations in combination with the Marcus electron transfer theory, we examine the energetics of condensation reactions between aqueous vanadium ions to form dimers and their subsequent dissociation into vanadium species of different oxidation states after electron transfer has occurred. Our results suggest that multiple self-discharge reaction pathways could be possible under the vanadium RFB operation conditions. The study underscores the complexity of vanadium polymerization reactions in aqueous solutions with coupled electron and proton transfer processes that can lead to the formation of various mixed-valence vanadium polymeric structures.

Design route towards a PM machine for rotorcraft environments

This paper discusses the design route followed in the development of a permanent magnet (PM) machine for electrical power generation on board a rotorcraft (helicopter). The focus of the machine design is to optimise system power density, efficiency, and robustness – all of which are crucial considerations in aerospace applications. A matrix of designs was created consisting of two stators with different winding conductors – copper and aluminium – and three rotors, each using different containment sleeve materials. These include two semi-permeable metallic sleeves, which act to decrease the effective air gap. Combinations of the different materials will yield different system-level power densities and efficiencies. Here, all the designs are presented along with the initial test results for the baseline machine combination validating the design predictions.

Liquid Cooling of Compute System

The continued demand for increasing compute performance results in an increasing system power and power density of many computers. The increased power requires more efficient cooling solutions than traditionally used air cooling. Therefore, liquid cooling, which has traditionally been used for large data center deployments, is becoming more mainstream. Liquid cooling can be used selectively to cool the high power components or the whole compute system. In this paper, the example of a fully liquid cooled server is used to describe different ingredients needed, together with the design challenges associated with them. The liquid cooling ingredients are cooling distribution unit (CDU), fluid, manifold, quick disconnects (QDs), and cold plates. Intel is driving an initiative to accelerate liquid cooling implementation and deployment by enabling the ingredients above. The functionality of these ingredients is discussed in this paper, while cold plates are discussed in detail.

(Invited) Promises and Limitations of Fluoride in Next-Generation Batteries: From New Reactions to New Interfaces

Fluoride-containing additives, electrolytes, solid electrolyte interphases (SEI), and fluorinated materials represent a recurring motif in many proposed next-generation battery chemistries. Fluoride-enrichment at the surface of metallic anodes, such as Li, has been suggested to impart favorable stabilization of the SEI, permitting empirically enhanced round-trip efficiency and cycle life by mitigating dendrite formation. Meanwhile, fluorinated materials such as oxyfluoride intercalation cathodes, fluorinated carbons in primary battery cathodes, and metal fluoride conversion cathodes represent distinct approaches to tailor the behavior of bulk materials. In spite of this promise, precisely manipulating fluoride-based materials and reaction mechanisms remains challenging. In this talk, I describe our group’s exploration of several applications where fluoride-forming reactions can be tailored and harnessed for application in primary and secondary batteries. First, I describe our efforts to develop high-energy density primary batteries based on the electrochemical reduction of fluorinated gases. We show that fundamental knowledge and the experimental framework developed in the field of Li-oxygen batteries in recent years can be successfully translated to the development of new gas-to-solid conversion reactions with high energy densities. Molecular transformation mechanisms occurring during the discharge reactions, which involve atypically high electron transfer numbers (2<n<8), will be presented, and future strategies to improve power density of gas-based conversion systems will be discussed. Then, we shift gears to focus on how fluorinated reactions can be harnessed to modify metal interfaces. We discuss our findings on the reactivity of fluorinated gases with Li surfaces in the development of so-called “artificial SEI” layers on Li, and critically examine the role of LiF in imparting stability to modified interfaces. Finally, we highlight future challenges and opportunities in the modification of cathode materials enriched with fluoride derived from our gas-based reaction architecture.

Performance Analysis of a Hybrid System Consisting of a Molten Carbonate Direct Carbon Fuel Cell and an Absorption Refrigerator

By integrating an Absorption Refrigerator (AR), a new hybrid system model is established to reuse the waste heat from a Molten Carbonate Direct Carbon Fuel Cell (MCDCFC) for additional cooling production. Various irreversible losses in each element of the system are numerically described. The operating current density span of the MCDCFC that allows the AR to work is derived. Under different operating conditions, the mathematical expressions for equivalently evaluating the hybrid system performance are derived. In comparison with the stand-alone MCDCFC, the maximum attainable power density of the proposed system and its corresponding efficiency are increased by 5.8% and 6.8%, respectively. The generic performance features and optimum operating regions of the proposed system are demonstrated. A number of sensitivity analyses are performed to study the dependences of the proposed system performance on some physical parameters and operating conditions such as operating temperature, operating current density, and pressure of the MCDCFC, cyclic working fluid internal irreversibility inside the AR, thermodynamic losses related parameters and the anode thickness of the MCDCFC. The obtained results may offer some new insights into the performance improvement of an MCDCFC through a reasonable heat management methodology.