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Robustness Assessment of the EMI Filter in a Three-Level Inverter
... This paper evaluates the robustness of the EMI-filter in a 3L-ANPC inverter based on the mission profile of the operating environment. Our conference paper [46] investigates this procedure, while the mission profile to reliability stresses transformation, humidity modeling, attenuation shifting modeling, and comparison analysis are not studied. Extending the research in [46], this paper solves these issues and have four major contributions: ...
... Our conference paper [46] investigates this procedure, while the mission profile to reliability stresses transformation, humidity modeling, attenuation shifting modeling, and comparison analysis are not studied. Extending the research in [46], this paper solves these issues and have four major contributions: ...
The EMI filter is a critical component for power electronics to conform with the electromagnetic interference (EMI) standards, ensuring electromagnetic compatibility (EMC) and a safe operating environment. Yet, its attenuation capability can be shifted during the long-term operating period due to the passive components' degradation. A poorly designed EMI filter may fail to meet the standards' specifications and affect the robustness, leading to the converter's fault and even failure. This paper proposes a robustness assessment procedure of an EMI filter for a three-level active neutral-point-clamped (3L-ANPC) inverter. The mission profile is used to emulate the operating environment. The nonlinear degradations of film capacitors and nanocrystalline core chokes are modeled. Further, the Monte-Carlo-Based robustness assessment procedure is presented. It considers the uncertainties of model parameters and uses the filter attenuation capability as the failure criteria. Finally, an EMI filter for a 15 kW 3L-ANPC inverter is used as the demonstration and experimental verification of the evaluation procedure. The B10 lifetime of the EMI filter is obtained, which serves as a first step of the inverter-system-level EMI robustness evaluation and feedback for the robustness-oriented EMI filter design.
This paper proposes a general physics-based model for identifying the parasitic capacitance in medium-voltage (MV) filter inductors, which can provide analytical calculations without using empirical equations and is not restricted by the geometrical structures of inductors. The elementary capacitances of the MV inductor are developed, then the equivalent capacitances between the two terminals of the inductor are derived under different voltage potential on the core. Further, a three-terminal equivalent circuit, instead of the conventional two-terminal equivalent circuit, is developed by using the derived capacitances. Thus, the parasitic equivalent capacitance between the terminals and core are explicitly quantified. Experimental measurements show a close agreement with the theoretical calculations.
Faraday shields are widely used in highfrequency transformers to conduct the common-mode (CM) current to the ground. They are normally located in the high magnetomotive force (MMF) region, where severe eddy currents are induced and contribute considerable magnetic field losses. In this paper, an analytical procedure is presented for the magnetically-induced loss in Faraday shields. It is originally derived from shields of foil conductors. Then it is extended to different shields with round and Litz wire, and different configurations, e.g., multi-layer shields, interleaved windings, and coaxial transformers. It is verified by the finite element method (FEM) and experimental results in six case studies. Moreover, the criteria to determine the losses of Faraday shields is given and a design procedure is presented to reduce the shield losses at a certain level while keeping the functionality. Finally, a case study is provided to verify the shield design procedure on a 100 kHz transformer.
This paper proposes an improved analytical stray capacitance model for inductors. It considers the capacitances between the winding and the central limb, side limb, and yoke of the core. The latter two account for a significant proportion of the total capacitance with the increase of the core window utilization factor. The potential of the floating core/shield is derived analytically, which enables the model to apply not only for the grounded core/shield, but also for the floating core/shield cases. Based on the improved model, an analytical optimization method for the stray capacitance in inductors is proposed. Moreover, a global Pareto optimization is carried out to identify the trade-offs between the stray capacitance and ac resistance in the winding design. Finally, the analysis and design are verified by finite element method (FEM) simulations and experimental results on a 100 kHz dual active bridge (DAB) converter.
Capacitive DC links are an important part in voltage source power electronic converters, which contribute to cost, size and failure rate on a considerable scale. With more and more stringent constraints brought by industrial applications, the capacitive DC links encounter reliability aspect challenges. This paper presents a review on the reliability design and improvement of capacitive DC links from three aspects: 1) Quantitative reliability prediction for DC-link capacitors; 2) Reliability-oriented design of passive DC-link capacitor banks; and 3) Advanced active DC links to exceed the limits of passive DC-link capacitors. Key solutions for each aspect are highlighted and discussed with case studies. This review serves to provide a picture of state-of-the-art research on the reliability design and improvement of capacitive DC links, highlight the key milestones in this area, and identify the corresponding challenges and future research directions.
Many applications require the use of RFI (Radio Frequency Interference) X2 capacitors with high stability in harsh environmental conditions e.g. general-purpose applications in series to the mains (capacitive voltage dividers, energy meters) and automotive ones (battery chargers). Although full agency approvals (UL, ENEC, CQC) are mandatory only on RFI components mounted in parallel to the line, customers often require X2 approval also for series-with-the-mains applications. While the electrical stress on components used in series and in parallel with the mains are comparable, the performance requirements in applications in series to the mains are much stricter. For both applications, environmental conditions (temperature and relative humidity) are the major factors affecting the expected life of components. Severe working conditions are simulated in KEMET's laboratories by means of accelerated life tests: climatic chambers replicate high temperature, high humidity and AC voltage stress. KEMET released recently a new fully-approved RFI X2 metallized film series, suitable for both series and parallel-to-the-mains connection, designed for high capacitance stability in harsh conditions. This paper identifies the main root cause of capacitance instability in harsh environment applications and shows the features and performances of the most advanced KEMET capacitors suitable for RFI X2 applications.
EMRIC project, a new research activity mixing integrated circuits electromagnetic compatibility (EMC) and integrated circuits (ICs) reliability, provides methods and guidelines to circuits and equipment designers to ensure EMC during lifetime of their applications. In order to improve the ICs electromagnetic robustness (EMR) this project studies the effect of ICs ageing on electromagnetic emission and immunity to radio frequency interferences, clarifies the link between IC degradations and related EMC drifts and develops prediction models and propose “time insensitive” EMC protection structures.
An improved calculation of ferrite core loss for nonsinusoidal waveforms separates a flux trajectory into major and minor loops via a new recursive algorithm. It is highly accurate and outperforms two previous methods for our measured data. The only characteristics of the material required are the standard Steinmetz-equation parameters.
Frequency responses are non-identical between the positive and the negative frequency range for symmetric three-phase systems modeled with complex transfer functions, which shows unbalanced stability margins. The unbalanced stability margins limit the system performance, as the system dynamics is restricted by the worst one. This paper extends the discussion of unbalanced stability margins to asymmetric three-phase systems, i.e. three-phase grid-tied inverters, which are described by transfer matrices. The reason for unbalanced stability margins is analytically investigated, and different impacts are analyzed. It is found that both the control delay and asymmetric control loops can lead to the unbalanced stability margins. To improve the performance limited by the worst stability margin, a margin balancing control is proposed. By implementing a phase correction term, the worst stability margin can be increased by reducing the best one. As a result, the overall stability margin of the system can be improved. The design procedure is elaborated based on a 2MW inverter system. Verifications are presented based on a 1 kW prototype including simulations, experimental results, and Nyquist analyses. This method applies to all types of grid-tied inverters with multiple control loops.
With the increasing penetration of power-electronic-based renewable generations, stability issues become challenging due to interactions between converters and the grid. This paper develops a framework to investigate the stability of grid-tied photovoltaic inverter systems using impedance models (IMs). IMs are developed considering the complete system dynamics for both proportional-integral (PI) control and proportional-resonance (PR) control structures. Different stability investigation methods are elaborated with a focus on the Bode plot and the generalized Nyquist criterion. Sensitivity analyses are conducted utilizing Bode plots to observe the impact of different factors in the frequency domain. Followed by that, an impedance-resonance analysis method is proposed to identify the cause of resonances according to the critical interactions of diagonal impedances and the frequency range of resonances. The performance of PI and PR controls is compared with a focus on the influence of the outer control loops. The analyses are validated through experiments in a down-scale test bench.
This paper characterizes the thermal behavior of a commercialized silicon carbide (SiC) power MOSFET module with special concerns on high-temperature operating conditions as well as particular focuses on SiC MOSFET dies. A temperature-dependent Cauer-type thermal model of the SiC MOSFET is proposed and extracted based on offline finite-element simulations. This Cauer model is able to reveal the temperature-dependent thermal property of each packaging layer and it is suitable for the high-temperature thermal-profile prediction with sufficient computational efficiency. Due to the temperature-dependent thermal properties of the SiC die and ceramic material, the junction-heatsink thermal resistance can be raised by more than 10% under high-temperature conditions (up to 200 ◦C), which can considerably worsen thermal estimations of the SiC die and its packaging materials. Furthermore, the experimental measurement of transient thermal impedance was conducted under operating temperature variations (with virtual junction temperature ranging from 60.5 ◦C to 199.6 ◦C), and the effectiveness of the proposed temperature-dependent Cauer model was fully validated.
Metallized film capacitors are used to reduce electromagnetic interference (EMI) in electric power mains due to their high voltage capability and their open circuit failure mode, which aids in safe operation. This paper presents a comprehensive review of metallized film capacitors used for EMI filtering and their failure modes and mechanisms. One of the major failure mechanisms discussed is the corrosion of the metallized film due to moisture ingress into the package. Safety, quality, and reliability standards for metallized film capacitors are also discussed. The paper concludes with recommendations for film capacitor selection and the proper qualification and accelerated life testing to ensure long-term reliable operation.
increasing the energy efficiency is one of the most important issues in modern power electronic systems. In aircraft applications, the energy efficiency must be associated with a maximum reduction of mass and volume, so a high components compactness. A consequence from this compactness is the increase of operating temperature. Thus, the magnetic materials used in these applications, have to work at high temperature. It raises the question of the thermal ageing problem. The reliability of these components operating at this condition becomes a real problem which deserves serious interest. Our work takes part in this context by studying the magnetic material thermal ageing. The nanocrystalline materials are getting more and more used in power electronic applications. Main advantages of nanocrystalline materials compared to ferrite are: high saturation flux density of almost 1.25 T and low dynamic losses for low and medium frequencies. The nanocrystalline Fe73.5Cu1Nb3Si15.5B7 alloys have been chosen in our aging study. This study is based on monitoring the magnetic characteristics for several continuous thermal ageing (100, 150, 200 and 240 °C). An important experimental work of magnetic characterization is being done following a specific monitoring protocol. Elsewhere, X-Ray Diffraction and magnetostriction measurements were carried out to support the study of the anisotropy energies evolution with ageing. This latter is discussed in this paper to explain and give hypothesis about the ageing phenomena.
In this work, the power density of a two-stage, i.e. LCLCL, EMI filter for a 10 kW three-phase, T-type threelevel, boost-type PWM rectifier system is optimized concerning construction volume. It is found that reasonable boundary conditions limit or define most component values and only few degrees of freedom are remaining. In this context, the ratio of the first filter stage’s common to differential mode inductance, kL = Lcm,1/Ldm,1, is identified to particularly affect the total filter volume. For given switching frequency and DClink voltage of fs = 48 kHz and Vdc = 700 V, a flat minimum of the overall filter volume results for 10 < kL < 40. The boxed volume of the filter realized for kL = 18 is 763 cm3 (46.6 in3), which corresponds to a filter power density of 13.1 kW/dm3 (215 W/in3). Measurements of conducted EMI confirm that the rectifier system complies with the considered limits of conducted EMI (CISPR 11, class A).
Photovoltaic (PV) energy conversion has been on the spotlight of scientific research on renewable energy for several years. In recent years the bulk of the research on PV has focused on transformerless grid-connected inverters, more efficient than traditional line transformer-based ones, but more critical from a power quality point of view, especially in terms of ground leakage current. Neutral point clamped (NPC) inverters have recently gained interest due to their intrinsically low ground leakage current and high efficiency, especially for MOSFET-based topologies. This paper presents an active NPC (ANPC) topology equipped with 650 V SiC MOSFETs, with a new modulation strategy that allows to reap the benefits of the wide-bandgap devices. An efficiency improvement is obtained due to the parallel operation of two devices during the freewheeling intervals. Simulations and experimental results confirm the effectiveness of the proposed converter.
Un objectif important des études de la compatibilité électromagnétique (CEM) est de rendre les produits conformes aux exigences CEM des clients ou les normes. Cependant, toutes les vérifications de la conformité CEM sont appliquées avant la livraison des produits finis. Donc nous pourrions avoir de nouvelles questions sur les performances CEM des systèmes électroniques au cours de leur vie. Les comportements CEM de ces produits seront-ils toujours conformes dans plusieurs années ? Un produit peut-il garder les mêmes performances CEM pendant toute sa durée de vie ? Si non, combien de temps la conformité CEM peut-elle être maintenue ? L'étude à long terme de l'évolution des niveaux CEM, appelée "robustesse électromagnétique», est apparue ces dernières années. Les travaux précédents ont montré que la dégradation causée par le vieillissement pourrait induire des défaillances de système électronique, y compris une évolution de la compatibilité électromagnétique. Dans cette étude, l'évolution à long terme des niveaux CEM de deux groupes de composants électroniques a été étudiée. Le premier type de composant électronique est le circuit intégré. Les courants de hautes fréquences et les tensions induites au cours des activités de commutation de circuits intégrés sont responsables des émissions électromagnétiques non intentionnelles. En outre, les circuits intégrés sont aussi très souvent les victimes d'interférences électromagnétiques. Un autre groupe de composants est formé par les composants passifs. Dans un système électronique, les circuits intégrés fonctionnent souvent avec les composants passifs sur un même circuit imprimé. Les fonctions des composants passifs dans un système électronique, telles que le filtrage et le découplage, ont également une influence importante sur les niveaux de CEM. Afin d'analyser l'évolution à long terme des niveaux CEM des composants électroniques, les travaux présentés dans cette thèse ont pour objectif de proposer des méthodes générales pour prédire l'évolution dans les temps des niveaux de compatibilité électromagnétique des composants électroniques.
Photovoltaic energy conversion has been on the spotlight of scientific research for several years. Special attention was paid to the grid-connected inverters that do not feature an insulation transformer (transformerless topologies). In this framework, Neutral Point Clamped inverters have gained interest due to the low ground leakage current. Recently, the research has been focused on high-efficiency MOSFET-based topologies. In this paper an Active-NPC topology is equipped with 650V ROHM SiC devices. A new modulation strategy that allows to exploit the characteristics of Sic MOSFETs, is proposed. It permits to obtain very high efficiency due to the parallel operation of the devices during the freewheeling phases of the inverter output current. Simulation and experimental results show the benefits of this choice.
The effects of eddy currents in transformer windings are considered, and a method is derived for calculating the variation of winding resistance and leakage inductance with frequency for transformers with single-layer, multilayer and sectionalised windings. The method consists in dividing the winding into portions, calculating the d.c. resistances and d.c. leakage inductances of each of these portions, and then multiplying the d.c. values by appropriate factors to obtain the corresponding a.c. values. These a.c. values are then referred to, say, the primary winding and summed to give the total winding resistance and leakage inductance of the transformer. Formulas are derived and quoted for calculating the d.c. resistances and leakage inductances of the winding portions. Theoretical expressions are derived for the variation with frequency etc. of the factors by which the d.c. values must be multiplied to obtain the corresponding a.c. values. These expressions are presented in the form of graphs, permitting the factors to be read as required.
Loss models of inductive components are thoroughly investigated, thereby all different aspects of loss modeling are considered. The impact of peak-to-peak flux density ΔB, frequency f, DC premagnetization HDC, temperature T, core shape, minor and major loops, flux waveform, and material on core loss calculation are considered. In order to calculate winding losses, formulas for round conductors and litz wires, each including skin- and proximity effects (including the influence of an air-gap fringing field) are included. A high level of accuracy is achieved by combining the best state-of-the-art approaches and by embedding newly-developed approaches into a novel loss calculation framework. The loss models are verified by FEM simulations and experimental measurements.
A test program that demonstrated that the electrical degradation
of a conductive elastomer-aluminum flange joint could be determined
using shielding effectiveness measurements is described. Two tests were
developed. One measures the degradation of shielding effectiveness of a
simulated gasketed enclosure seam (test set). Shielding effectiveness
measurements are made at frequencies up to 10 GHz. The second test
method yields a quantitative scale of conductive elastomer corrosivity
(galvanic compatibility) and a quantitative measure of DC electrical
degradation of the conductive elastomer. The tests demonstrated that a
Ag-Al gasket/aluminum flange joint was more stable than a nickel-coated
graphite gasket/aluminum flange joint after 192 h of sulfur dioxide salt
fog exposure. This result reflects the greater stability of the Ag-Al
gasket and the better galvanic compatibility of the Ag-Al gasket with
the aluminum flange
Capacitive dc links-design, control and its impact on the reliability of power electronic systems
- H Wang
H. Wang, "Capacitive dc links-design, control and its impact on the
reliability of power electronic systems," Ph.D. dissertation, Aalborg,
Denmark: Aalborg University, 2018.
True 1500 V technology for the new generation of PV power plants
SMA Solar Technology AG, "True 1500 V technology for the new
generation of PV power plants," Tech. Rep., 2020.
Nano-crystalline core datasheet
"Nano-crystalline core datasheet," U.S. Department of Energy -National Energy Technology Laboratory, Tech. Rep., 2018.