Junction temperature estimation via plug-in system for the design validation of IGBT industrial power converters

L'abstract è presente nell'allegato / the abstract is in the attachmen

Design Space Optimization of a Three-Phase LCL Filter for Electric Vehicle Ultra-Fast Battery Charging

State-of-the-art ultra-fast battery chargers for electric vehicles simultaneously require high efficiency and high power density, leading to a challenging power converter design. In particular, the grid-side filter, which ensures sinusoidal current absorption with low pulse-width modulation (PWM) harmonic content, can be a major contributor to the overall converter size and losses. Therefore, this paper proposes a complete analysis, design and optimization procedure of a three-phase LCL filter for a modular DC fast charger. First, an overview of the basic LCL filter modeling is provided and the most significant system transfer functions are identified. Then, the optimal ratio between grid-side and converter-side inductance is discussed, aiming for the maximum filtering performance. A novel design methodology, based on a graphical representation of the filter design space, is thus proposed. Specifically, several constraints on the LCL filtering elements are enforced, such that all feasible design parameter combinations are identified. Therefore, since in low-voltage high-power applications the inductive components typically dominate the overall filter volume, loss and cost, the viable LCL filter design that minimizes the total required inductance is selected. The proposed design procedure is applied to a 30 kW, 20 kHz 3-level unidirectional rectifier, employed in a modular DC fast charger. The performance of the selected optimal design, featuring equal grid-side and converter-side 175 µH inductors and 15 µF capacitors, is verified experimentally on an active front-end prototype, both in terms of harmonic attenuation capability and current control dynamics. A current total harmonic distortion (THD) of 1.2% is achieved at full load and all generated current harmonics comply with the applicable harmonic standard. Moreover, separate tests are performed with different values of grid inner impedance, verifying the converter control stability in various operating conditions and supporting the general validity of the proposed design methodology

Estimation of the Internal Junction Temperatures of Resin Encapsulated IGBT Power Modules

Power electronics converters used in applications requiring high reliability require an accurate thermal manage- ment for each component. Therefore, several methods for the estimation of the junction temperature of power devices are reported in the literature, having different features in terms of sensitivity, linearity and calibration process. Nevertheless, state of the art technologies in power modules packaging, such as the resin encapsulation technology, have shown that junction temperature estimation is still an open issue. In such modules, the lack of physical access to the die has led a growing interest in estimation methods based on thermo-sensitive electrical parame- ters. This paper proposes a non-invasive method for the junction temperature estimation of high current resin encapsulated IGBT power modules. The proposed solution is suitable for the thermal model validation of industrial converters thanks to the off-the- shelf components and the easiness of implementation

Digital Multi-Loop Control of an LLC Resonant Converter for Electric Vehicle DC Fast Charging

This paper proposes a digital control strategy for LLC resonant converters, specifically intended for EV battery charging applications. Two cascaded control loops, i.e. an external battery voltage loop and an internal battery current loop, are designed and tuned according to analytically derived expressions. Particular attention is reserved to the output current control analysis, due to its extremely non-linear behaviour. The well known seventh-order LLC small-signal model, derived with the extended describing function (EDF) method, is simplified to an equivalent first-order model at the resonance frequency. In theseconditions,whichareproventobethemostunderdamped, the current control loop is tuned taking into account the delays introduced by the digital control implementation. Moreover, the adoption of a look-up table (LUT) in the feed-forward path is proposed to counteract the system non-linearities, ensuring high dynamical performance over the full frequency operating range. Finally, the proposed control strategy and controller design procedure are verified both in simulation and experimentally on a 15 kW LLC converter prototype

Three-Level Unidirectional Rectifiers under Non-Unity Power Factor Operation and Unbalanced Split DC-Link Loading: Analytical and Experimental Assessment

Three-phase three-level unidirectional rectifiers are among the most adopted topologies for general active rectification, achieving an excellent compromise between cost, complexity and overall performance. The unidirectional nature of these rectifiers negatively affects their operation, e.g., distorting the input currents around the zero-crossings, limiting the maximum converter-side displacement power factor, reducing the split DC-link mid-point current capability and limiting the converter ability to compensate the low-frequency DC-link mid-point voltage oscillation. In particular, the rectifier operation under non-unity power factor and/or under constant zero-sequence voltage injection (i.e., when unbalanced split DC-link loading occurs) typically yields large and uncontrolled input current distortion, effectively limiting the acceptable operating region of the converter. Although high bandwidth current control loops and enhanced phase current sampling strategies may improve the rectifier input current distortion, especially at light load, these approaches lose effectiveness when significant phase-shift between voltage and current is required and/or a constant zero-sequence voltage must be injected. Therefore, this paper proposes a complete analysis and performance assessment of three-level unidirectional rectifiers under non-unity power factor operation and unbalanced split DC-link loading. First, the theoretical operating limits of the converter in terms of zero-sequence voltage, modulation index, power factor angle, maximum DC-link mid-point current and minimum DC-link mid-point charge ripple are derived. Leveraging the derived zero-sequence voltage limits, a unified carrier-based pulse-width modulation (PWM) approach enabling the undistorted operation of the rectifier in all feasible operating conditions is thus proposed. Moreover, novel analytical expressions defining the maximum rectifier mid-point current capability and the minimum peak-to-peak DC-link mid-point charge ripple as functions of both modulation index and power factor angle are derived, the latter enabling a straightforward sizing of the split DC-link capacitors. The theoretical analysis is verified on a 30 kW, 20 kHz T-type rectifier prototype, designed for electric vehicle ultra-fast battery charging. The input phase current distortion, the maximum mid-point current capability and the minimum mid-point charge ripple are experimentally assessed across all rectifier operating points, showing excellent performance and accurate agreement with the analytical predictions

Full Digital Control and Multi-Loop Tuning of a Three-Level T-Type Rectifier for Electric Vehicle Ultra-Fast Battery Chargers

The rapid development of electric vehicle ultra-fast battery chargers is increasingly demanding higher efficiency and power density. In particular, a proper control of the grid-connected active front–end can ensure minimum passive component size (i.e., limiting design oversizing) and reduce the overall converter losses. Moreover, fast control dynamics and strong disturbance rejection capability are often required by the subsequent DC/DC stage, which may act as a fast-varying and/or unbalanced load. Therefore, this paper proposes the design, tuning and implementation of a complete digital multi-loop control strategy for a three-level unidirectional T-type rectifier, intended for EV ultra-fast battery charging. First, an overview of the operational basics of three-level rectifiers is presented and the state-space model of the considered system is derived. A detailed analysis of the mid-point current generation process is also provided, as this aspect is widely overlooked in the literature. In particular, the converter operation under unbalanced split DC-link loads is analyzed and the converter mid-point current limits are analytically identified. Four controllers (i.e., dq-currents, DC-link voltage and DC-link mid-point voltage balancing loops) are designed and their tuning is described step-by-step, taking into account the delays and the discretization introduced by the digital control implementation. Finally, the proposed multi-loop controller design procedure is validated on a 30 kW, 20 kHz T-type rectifier prototype. The control strategy is implemented on a single general purpose microcontroller unit and the performances of all control loops are successfully verified experimentally, simultaneously achieving low input current zero-crossing distortion, high step response and disturbance rejection dynamics, and stable steady-state operation under unbalanced split DC-link loading

3D Printing and Supercritical Foaming of Hierarchical Cellular Materials

Hierarchical porous structures have been gathering interest in different fields owing to their unique properties associated with their multi-scale features. The observation of natural materials brought new insights into the functionality of cellular materials and inspired new processes to produce synthetic hierarchical structures. Such hierarchical cellular materials have shown significant potential in many applications, as filtering, tissue engineering and drug delivery. Polymers in particular gathered a burgeoning interest thanks to their ease of processing, which allows to produce structures at high strength/density ratio and high surface area with defined porosity. In the present study, it is proposed to develop novel technologies to manufacture polymer cellular structures. From the application of Supercritical Carbon Dioxide Foaming (ScCO2) to Fused Deposition Modelling / Fused Filament Fabrication (FDM / FFF), an extrusion based additive manufacturing technology, hierarchical porous structures were created. The material transformation phenomena and the processing window of this homothetic foaming processed were studied. The fine tuning of the foaming parameters allowed creating a micro cellular porosity with-in a 3D printed structure, without modifying the 3D topology. This allowed producing a wide range of cellular struc-tures with controlled multi scale porosity and stiffness reduced up to hundred times the stiffness of the 3D printed cellular structures. Homothetic foaming was then applied to biopolymers in order to create gradient hierarchical porous structures. In particular, articular cartilage and bone (osteochondral) defects were targeted. Cartilage repair is a challenging clinical problem because large defects do not regenerate. Tissue engineering offers a solution by implanting a material, defined as scaffold, loaded with cells to induce a regeneration in the tissue that otherwise would not occur. Multi material Poly(lactide-co-caprolactone) â Poly(lactide-BTCP) cellular structures were successfully processed into a scaffold able to replicate the complex gradient mechanical properties of the osteochondral tissue. In particular, the processing windows to process multi material 3D printed and foamed structures was established. The mechanical properties under compression of these scaffolds were compared to the values measured by nanoindentation on human articular cartilage, showing a good correlation between scaffold and target application. Furthermore, from the developed knowledge, a novel additive manufacturing method is proposed from the inte-gration of FDM/FFF and ScCO2 into a single process, named 3D Foam Printing. 3D Foam Printing was applied to process structures with hollow filaments or filaments with radial porosity with live porosity control during the process. The influence of processing parameters on foam morphology was investigated. Different cellular structures achievable by tuning the printing temperature and speed were described for different biomaterials. The processes described in this work allowed to mimic the complex mechanical properties of the osteochondral tissue, a natural hierarchical material. However, they demonstrated to be relevant to a wide range of materials, as polymers, blends and composites. This is particularly true for 3D Foam Printing, which could positively influence many engineering applications, as aerospace, medicine and energy, where tuneable cellular polymers are highly demanded

Iterative Design of a 60 kW All-Si Modular LLC Converter for Electric Vehicle Ultra-Fast Charging

This paper proposes an iterative design procedure for a high-power LLC resonant converter, taking part in a 60 kW modular DC/DC conversion stage for an electric vehicle (EV) ultra-fast battery charger. The basics of operation of the LLC converter are briefly recalled and the most relevant analytical expressions are reported. Due to the high-power requirement and the wide output battery voltage range (i.e. 250-1000 V), a modular design approach is adopted, leveraging the split input DC-link structure provided by a 3-level active front-end. A total of four modules, with at 15 kW nominal power and a 250-500 V output voltage regulation capability, are designed with a straightforward iterative procedure based on the first-harmonic approximation (FHA). Finally, the proposed methodology is verified experimentally on a 15 kW LLC converter prototype directly resulting from the design procedure

GW190521 as a dynamical capture of two nonspinning black holes

Gravitational waves from $\sim 90$ black holes binary systems have currently been detected by the LIGO and Virgo experiments, and their progenitors' properties inferred. This allowed the scientific community to draw conclusions on the formation channels of black holes in binaries, informing population models and -- at times -- defying our understanding of black hole astrophysics. The most challenging event detected so far is the short duration gravitational-wave transient GW190521. We analyze this signal under the hypothesis that it was generated by the merger of two nonspinning black holes on hyperbolic orbits. The best configuration matching the data corresponds to two black holes of source frame masses of $81^{+62}_{-25}M_\odot$ and $52^{+32}_{-32}M_\odot$ undergoing two encounters and then merging into an intermediate-mass black hole. We find that the hyperbolic merger hypothesis is favored with respect to a quasi-circular merger with precessing spins with Bayes' factors larger than 4300 to 1, although this number will be reduced by the currently uncertain prior odds. Our results suggest that GW190521 might be the first gravitational-wave detection from the dynamical capture of two stellar-mass nonspinning black holes.Comment: Version accepted for publicatio