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LLC converter design optimization remains a challenging task for varying loads such as in battery chargers. There are numerous L-L-C combinations to choose from a design space that can satisfy the required voltage gains of the application. An accurate magnetic model is essential to optimally size the passive components according to the application needs. This paper provides a new design tool for gapped core magnetics to optimize the transformer and resonant inductor in LLC converters. Unlike conventional design algorithms, the proposed algorithm considers multiple distributed cores and selects the optimal magnetic flux density by minimizing a penalty function that includes power loss, cost and volume of the magnetic components using Big-Bang Big-Crunch Algorithm. The gapped core transformer and inductor design equations have been verified in Ansys Maxwell and Simplorer co-simulation environment for a 3700 W 48 V LLC and calculated power loss have been compared with experimental results. For the givenLmandLrpair of37.52μHand9.38μH, the proposed magnetic model designed a transformer with two-distributed cores, each one exhibiting a magnetizing inductance of17.73μHand leakage inductance of0.7μHon a EE422120 with 3F36 material. The total power loss of the transformers are measured as 12.44 W on a 3700 W prototype switched at 350 kHz.

Latest developments in low voltage wide-bandgap semiconductor technology have increased the popularity of single-phase multi-level (ML) totem pole (TP) power-factor correction (PFC) converters. Phase shifted flying capacitor based power stages offer several advantages, such as higher input current ripple frequency, smaller size inductor and differential mode (DM) filter, and usage of low voltage Gallium Nitride (GaN) devices with better figure-of-merit. Even though it has been proven that ML TP PFC converters have good power density and efficiency, the determination of optimal voltage levels and switching frequency requires a system-level optimization. This paper proposes an optimization framework for ML TP PFC converters, taking the power stage, thermal, DM filter, and magnetic designs, as well as practical design considerations, into account to determine the voltage-levels and switching frequency that minimize the power losses, cost and volume of the total system. To process output power of 3700W, the optimization tool suggests using a 4-Level GaN TP PFC topology switched at 45 kHz. The outcome of the tool has been compared with other fixed inductor current ripple designs, as well as optimized designs for 3-Level and 5-Level TP PFC converters in terms of cost, volume, and power losses. In accordance with the optimization results, a prototype of a 4L TP PFC rated at 3700 W is designed, which achieves a peak efficiency of 99.6% at 1 kW and >99.1% efficiency under the full power range.

Temperature sensitive electrical parameters (TSEP) provide an indirect and noninvasive method for on-line junction temperature estimation of power semiconductor devices. It is known that the fundamental of TSEP-based methods is to calibrate the relationship between TSEP and junction temperature in advance. However, the calibration methods in the literature need to open the module, require pretesting, or record the operating data of a converter in the entire power rating range, which are inconvenient in field applications. This article proposes an on-line and noninvasive calibration method by measuring the data at three operating states that are already existed in the regular converter operation. It is achieved by measuring the accessible heatsink/case temperature and TSEP during converter regular operation. The concept, implementation, and error analysis of the proposed method are presented in this article. Experimental verification is given to prove the effectiveness, accuracy, and convenience of the proposed method.

This article proposes a power routing approach for active asset management in power-electronic-based power systems. The proposed approach aims to expand the lifecycle of power converters as the key assets of modern energy systems. Moreover, it takes into account the operational costs of converter-based generation units in order to obtain economic dispatch in the system. As a result, the useful lifetime of converters is enhanced, thus improving the overall reliability of the system with respect to the operational costs of the generations. A numerical case study on a dc distribution system is presented to illustrate the effectiveness of the proposed approach.

Power system state-space models are often constructed by interconnection of their subsystems (converters, distribution lines, and grid). The interconnection between L-/LCL-filtered converters with the distribution lines subsystems is often realized through a virtual resistor, because they both have the voltage as input, introducing inaccuracy. Moreover, the parameters variations influence not only the eigenvalues, but also the equilibrium point. In this case, the small-signal model has to be reevaluated around the new equilibrium point. For the computation of the equilibrium point, an additional method, e.g., power flow, is conventionally used. However, the variables computed with power flow (e.g., {rm P},Q,{rm V},text{ and }theta) do not always coincide with the state-space model variables, required for the linearization. Furthermore, the traditional power flow does not consider the influence of the voltage-source-converter control system on the grid equilibrium point. This article proposes a nonlinear grid model that does not need the virtual resistor to be interconnected. The proposed model can be used both for equilibrium point computation through the Newton-Raphson method, and it can be linearized around the computed equilibrium point for small-signal analyses. Simulations and experiments are provided.

International audience; Modular multilevel converter (MMC) is an attractive topology in industrial applications such as high-voltage direct current (HVdc) transmission system where fast power control is required. The most conventional control method for MMC uses cascaded structures, where the power transmission and internal energy dynamic (outer loops) is limited by the ``frequency separation'' constraints since the dynamic choice of the currents (inner loops) must consider the tradeoff between rapidity and robustness. In this article, we present a new control method based on a differential flatness theory. The main interest of the proposed control is the possibility to obtain a very high dynamic performance of the MMC power flow, even under noisy measurements and parametric disturbances. Using the well-known average model of the MMC, a flat output is proposed, proving the differential flatness property of the MMC. Trajectory tracking controllers of ac grid active and reactive power are proposed using input-state full-order linearization. Simulation results, including losses corresponding to a realistic case of on-shore, point-to-point HVdc interconnection, are presented to show the performance of the proposed control scheme even with strong measurement noise.

Wide bandgap devices enable design of power converters with high power density. However, these power converters require compact printed circuit board (PCB) layouts with low power-loop stray inductance. Consequently, sensing device current in such layouts with minimal intrusion in power-loop remains a challenge. This article presents a PCB coil based current sensor design featuring power-loop stray inductance characterization. The PCB coil is designed on a double pulse test (DPT) board for current sensing of a discrete TO-247 packaged silicon carbide MOSFET. The design utilizes finite element method (FEM) simulations to determine a suitable position for the PCB coil on the DPT board. The coil placement also results in an increased power-loop stray inductance, which is estimated through FEM simulations. Further, these simulations are used for computation of mutual inductance between the PCB coil and the power-loop traces. Depending on this mutual inductance, a voltage is induced across the terminals of the PCB coil, which is then integrated using an op-amp based integrator circuit. Considering practical op-amp limitations, demonstrated with LTspice simulations, various guidelines for sensor design are established in this article. A sensor prototype is developed based on these guidelines, and experimental results from its evaluation are finally presented.

This letter proposes a converter-level method for measuring the on -state voltages of all power semiconductors in a single-phase inverter by using a single circuit only. The proposed circuit distinguishes itself by connecting to the middle point of each phase leg, instead of the two power terminals of individual devices as conventional methods do. It has the advantages of reduced circuit complexity, size, cost, and ease of connection. The principle and theoretical analysis of the proposed converter-level method are discussed. A case study on a single-phase full-bridge inverter is demonstrated to prove the concept.

Monte Carlo simulation has been widely used for reliability assessment of power electronic systems. In this approach, multiple simulations are carried out during the lifetime estimation of the components in power converter, e.g., power devices, where the parameter variations are considered. In the previous mission-profile based reliability assessment methods, the dynamic thermal stress profiles are usually converted into a set of static parameters. However, this simplification may introduce a certain uncertainty during the reliability assessment, since the static parameters may not be able to accurately represent the thermal stress under highly dynamic conditions. Moreover, the previous research did not take into account the correlation between the method of introducing the parameter variation and the required number of Monte Carlo simulations. This can significantly affect both the accuracy and computation burden of the Monte Carlo simulation. To address this issue, an in-depth analysis of Monte Carlo simulation applied to reliability assessment of power devices in power electronic systems is provided in this paper. Two additional Monte Carlo simulation approaches based on semi-dynamic and dynamic parameters are proposed, and their reliability evaluation results are compared with the traditional static parameter method. It is demonstrated in a case study of photovoltaic (PV) inverter application that the reliability of power converter can be overestimated up to 30% when using the static parameters.

This article presents an innovative technique for the black-box modeling of the conductive emissions of switching circuits from external observations. The proposed methodology relies on the robust and elegant theory of periodically switched linear systems, providing the user with a tool for the generation of frequency-domain augmented linear time-invariant equivalents. The obtained models offer both a remarkable accuracy for different supply conditions and a deep understanding of the inherent switching mechanisms of this class of devices. The proposed framework also enables the derivation of a simplified enhanced Norton representation which outperforms the classical state-of-the-art models based on linear time-invariant approximations. Model parameters are computed via a blind procedure based only on two measurements. The feasibility and strength of the proposed approach are demonstrated on a dc–dc boost power converter and on a dc electrical motor via the prediction of their conducted disturbances.

Power electronic converters will serve as the fundamental components of modern power systems. How-ever, they may suffer from poorer reliability if not properly designed, consequently affecting the overall performance of power systems. Accordingly, the converter reliability should be taken into account in design and planning of Power Elec-tronic-based Power Systems (PEPSs). Optimal decision-mak-ing in planning of PEPSs requires precise reliability modeling in converters from component up to system-level. This paper proposes model-based system-level design and maintenance strategies in PEPSs based on the reliability model of convert-ers. This will yield a reliable and economic planning of PEPSs by proper sizing of converters, cost-effective design of con-verter components, identifying and strengthening the con-verter weakest links, as well as optimal maintenance schedul-ing of converters. Numerical case studies demonstrate the ef-fectiveness of the proposed design and planning strategies for modern power systems.

The increase in the penetration of renewable energy sources (RES) has reduced the effective inertia of the power system dominated by synchronous machines. The reduction in inertia has paved the way to the development of inertia emulation techniques, which complements the increased penetration of RES. The synchronverter technology is one among the virtual inertia emulation techniques which resembles close to the synchronous machine. The advancements in control and adaptations of synchronverter for various applications demand a comprehensive yet critical review. Thus, the main objective of this paper is to present a critical review of synchronverter technology which could increase the inertial response of RES. A critical analysis of modifications made to original synchronverter and the stability assessment techniques is presented. The effect of parameter variation on stability and dynamic performance is brought out as a decision matrix by analysing the movement of eigenvalues presented in various works. Towards the end, a synoptic overview is presented to depict the research trend and emphasize the domain which requires further attention. Furthermore, a brief discussion of the research gaps perceived during the phase of review is presented to leverage future research in the field.

With the increasing penetration of renewable distributed generations (DGs), large numbers of “energy prosumers” are emerging rapidly. There will be severe impacts on the utility grid if these renewable DGs are not managed properly. Smart electrical power devices which enable high flexibility in energy management, alleviation in harmonic pollutions and friendly interactions with the utility grid are needed urgently. To meet all these requirements, a novel energy router which enables a unique parallel operation mode to the energy prosumer is presented. Facilitated with a bi-directional DC/AC converter, a switch array module and a fuzzy logic based hierarchical control strategy, the presented energy router enables plug-and-play connections and reliable energy management for the energy prosumer. The switch array and the parallel mode enable the loads to be flexibly scheduled to reduce energy cost and improve system performance. MATLAB/Simulink model of the energy prosumer is set up and a fuzzy logic based hierarchical control strategy is implemented for transient power balance control in various operation modes. Simulation results have demonstrated high flexibility, stability and feasibility of the proposed energy router in energy management of the prosumer, which will contribute to the better utilization of the ever-growing renewable energies.

Solid-state transformer (SST) is an emerging technology integrating with a transformer power electronics converters and control circuitry. This paper comprehensively reviews the SST topologies suitable for different voltage levels and with varied stages, their control operation, and different trends in applications. The paper discusses various SST configurations with their design and characteristics to convert the input to output under unipolar and bipolar operation. A comparison between the topologies, control operation and applications are included. Different control models and schemes are explained. Potential benefits of SST in many applications in terms of controllability and the synergy of AC and DC systems are highlighted to appreciate the importance of SST technologies. This review highlights many factors including existing issues and challenges and provides recommendations for the improvement of future SST configuration and development.

The design of an innovative converter for ohmic heating of fluid foods is presented. Application-specific requirements are addressed with new solutions and verified on a commercial-size 60-kW prototype. A multioutput high-voltage (0.8 to 4 kV) transformer with automatic tap change enriches a basic H-bridge topology, enabling processing of a wide set of foods and allowing grounding one of the outputs. High power density is achieved by power switches Pareto optimization in the reliability-efficiency objectives and by pushing the switching frequency up to 30 kHz, solving the electrode corrosion problem, too. Reproducible and reliable operation is assured by three different control strategies: load variability is dealt with high-dynamics power control, repeatable output is guaranteed by input voltage compensation, and optimal working point is ensured by control of the transformer primary current dc component. This last control also allows removing the output capacitors, improving density metrics with respect to the state-of-the-art. Analytical models for all control strategies are given to support dynamic performance tuning while guaranteeing stability.

The larger capacity of power converters increases with the size of wind turbines over the years, which implies more failures occur in the components of power converter. Meanwhile, the strategies of fault diagnosis of power converter in wind turbine are still under discussion and research. The main purpose of this paper is proposing a strategy containing wavelet transform, feature analysis, judgment and back propagation neural network (BPNN) classification (WT-FA-JD-BP) to identify the single and double power components open-circuit faults accurately, happen in grid-side converter (GSC) of permanent magnet synchronous generator (PMSG) wind turbine systems. First, as the original signals, the three-phase bridge legs voltage of the GSC are collected under different faults. Second, wavelet transform is used to decompose and reconstruct the signals. Third, a new method includes feature analysis and judgment is conducted to amplify the divergence of data obtained by wavelet transform. Finally, the data are used as the inputs of BPNN for decision-making and classification. The simulation and experimental results show that the proposed strategy can classify the single and double open-circuit faults, and the accuracy is higher than that without data feature analysis and judgment.

In previous studies, researchers used the fractional definition of Caputo to study fractional-order power converter. However, it is found that the model based on Caputo fractional definition is inconsistent with the actual situation. The fractional definition is crucial for the application of fractional-order theory into electric engineering, which directly influences the accuracy of model and operational characteristics of power converter. This paper analyzes fractional-order Buck converter according to the fractional definition of Riemann-Liouville. Firstly, the converter model operating in continuous conduction mode (CCM) is established under Riemann-Liouville fractional definition, and it shows that voltage gain and inductor current are relative with the order, but they are independent of order in the model of Caputo fractional definition. Secondly, the different steady-state characteristics of CCM Buck converter are researched under the models of Caputo and Riemann-Liouville derivative. Finally, the feasible simulations and experiments verify that the model derived by Riemann-Liouville fractional definition is more accurate and suitable for analyzing Buck converter.

The selection of electromagnetic interference (EMI) output filters in a power drive system can be a challenge that involves a “cut and try” process with several retro-designed EMI filters, which are often not optimized in term of size, weight, or cost. Key components of an EMI filter are common mode chokes. They are needed to reduce common mode currents which are the main source of radiated emission in power drive systems. Using a “static modification factor,” this paper analyses effects of its designable parameters on its final performance as if it was already in situ . All in situ impedances of the common mode current loop have been taken into account. Two test setups are used to validate effects related to changes of core material, size, number of turns, and wiring system.

Conventional voltage-source inverters used for induction motor drives generate a hexagonal space vector structure. In the overmodulation range, the hexagonal space vector structure generates low-order harmonics in the phase voltage resulting in low-order torque ripple in the motor. Inverter topologies with an octadecagonal (18 sided) space vector structure eliminate fifth-, seventh-, eleventh-, and thirteenth-order harmonics from the phase voltage, and hence, the dominant sixth- and twelfth-order torque ripple generation is eliminated. Octadecagonal space vector structures proposed in the past require multiple dc sources, which makes four-quadrant operation of the drive system difficult and costly. In this paper, the formation of a multilevel nine-concentric octadecagonal space vector structure using a single dc source is proposed. Detailed experimental results, using open-loop $V/f$ control and rotor field-oriented control, are presented to validate the effectiveness of the proposed drive scheme.

This paper describes the influence of an irradiance-dependent photo-induced leakage current through a semi-insulating GaAs substrate on the performance of photovoltaic monolithically series-interconnected multisegment laser power converters. A reciprocal relation between the resistivity of a semi-insulating GaAs substrate and irradiance of monochromatic light is experimentally observed. A reduced resistivity of the substrate with an increasing irradiation results in a substantial increase of a leakage current through the semi-insulating GaAs substrate between adjacent segments. For a multisegment laser power converter, this photo-induced leakage current is identified as a major shunting mechanism between adjacent segments that arises under high irradiances. Open-circuit voltage $V_{{\rm{oc}}}$ , fill factor (FF), and consequently conversion efficiency of a multisegment laser power converters are highly affected by the shunting mechanism. Based on a shading experiment, we observed that $V_{{\rm{oc}}}$ drops up to 21.5 mV per segment at a short-circuit current density $J_{{\rm{sc}}}= 47.3{\rm{\,A/ cm}}^{2}$ for the studied six-segment MIM specimen. For the same device, FF drops by 4.1% absolute at $J_{{\rm{sc}}}= 40.5{\rm{\,A/ cm}}^{2}$ . For the two-segment specimen, 5.8 mV drop of $V_{{\rm{oc}}}$ per segment and 1.5% absolute drop in FF is reported at $J_{{\rm{sc}}}= 47.3$ and $43.7{\rm{\,A/ cm}}^{2}$ , respectively.

Some couplings exist between the positive- and negative-sequence impedances of a voltage-sourced power converter especially in the low frequency range due to the nonlinearities and low-bandwidth control loops such as the phase-locked loop. In this paper, a new numerical method based on the harmonic transfer function for analysis of the linear time periodic systems is presented, which is able to handle these couplings. In a balanced three-phase system, there is only one coupling term, but in an unbalanced (asymmetrical) system, there are more couplings, and therefore, in order to study the interactions between these couplings a matrix-based method should be used. No information about the structure of the converter is needed and elements are modeled as black boxes with known terminal characteristics. The proposed method is applicable for both power quality (harmonic and interharmonic emissions) and stability studies, which is verified by simulations in this paper.

Power electronic systems have gradually gained an important status in a wide range of industrial applications such as renewable generation, motor drives, automotive, and railway transportation. Accordingly, recent research makes an effort to improve the reliability of power electronic systems to comply with more stringent constraints on safety, cost, and availability. The power devices are one of the most reliability-critical components in power electronic systems. Therefore, its condition monitoring plays an important role to improve the reliability of power electronic systems. This paper proposes a condition monitoring method of insulated-gate bipolar transistor (IGBT) modules. In the first section of this paper, a structure of a conventional IGBT module and a related parameter for the condition monitoring are explained. Then, a proposed real-time on-state collector-emitter voltage measurement circuit and condition monitoring strategies under different operating conditions are described. Finally, experimental results confirm the feasibility and effectiveness of the proposed method.

This letter proposes a concept of two-terminal active capacitor implemented by power semiconductor switches and passive elements. The active capacitor has the same level of convenience as a passive one with two power terminals only. It is application independent and can be specified by rated voltage, ripple current, equivalent series resistance, and operational frequency range. The concept, control method, self-power scheme, and impedance characteristics of the active capacitor are presented. A case study of the proposed active capacitor for a capacitive DC-link application is discussed. The results reveal a significantly lower overall energy storage of passive elements and a reduced cost to fulfill a specific reliability target, compared to a passive capacitor solution. Proof-of-concept experimental results are given to verify the functionality of the proposed capacitor.

The concept of a community grid is presented here. It involves the distribution grid and an increased use of renewable energy coming from distributed resources along with consumer/prosumer engagement in the energy trading mechanism. The possible operation and management with energy trading flexibility are briefly outlined. Under such scenario, the classical operation of the distribution grid is challenged by the issues brought about by the large penetration level of the new energy resources. This paper presents a status review of the technical issues that may appear under the community grid scenario. Building up on these surveyed issues, this paper also reviews and discusses approaches to solutions, which are required in order to make the community grid highly renewable and sustainable.

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting /republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works This paper focuses on the design of an active-damping controller that shapes the dynamics of an LCL grid connected voltage source converter (VSC) to mimic an L-filter connected VSC. This makes possible to use simpler classical proportional plus resonant or proportional plus integral controllers design methods to regulate the grid current with minimum penalties in both performance and stability margins. The active-damping design follows a model-reference approach and is synthesized through a (sub)optimal H 8 algorithm. The controller uses the grid current and point of common coupling voltage, although it allows the selection of a different set of measurements. Effectiveness of the method is demonstrated with timeand frequency-domain experimental results.

This paper deals with a low-cost diagnostic technique for polymer electrolyte membrane (PEM) fuel cells (FCs), which exploits the ripple produced by power converters to monitor the equivalent ohmic resistance. While the available literature on this topic is focused on constant-frequency control of the power converter (such as pulsewidth modulation), this paper discusses the measurement issues that arise when hysteresis current control is employed for a dc/dc boost converter, which represents the simplest solution from the implementation point of view, and therefore particularly suitable for low-cost applications. The classic frequency-domain analysis for ohmic resistance identification, based on the Fourier transform, is compared with a time-domain analysis based on a simple identification algorithm, and a real-time implementation of the latter is presented. The experimental results are obtained on a single PEM FC, but the extension to FC stacks for commercial applications is also discussed.

In this paper, a low-cost approach for polymer electrolyte membrane fuel cell (FC) drying and flooding diagnosis based on power converter ripple is presented, suitable to be implemented in commercial applications. If proper signal processing algorithms are employed, the high-frequency ripple inherently produced by switch-mode converters allows one to monitor the FC ohmic resistance, which is a good indicator for membrane drying, while an ad hoc switching control of the converter allows one to monitor also the low-frequency impedance, which is an indicator for cell flooding. This technique is tested with a dc/dc boost converter directly connected to a single cell, discussing how different FC operation modes (such as constant current or constant voltage) may affect the sensitivity required to the diagnostic algorithm to correctly recognize drying and flooding occurrences.

This paper is focused on the current quality of matrix converter controlled by space vector modulation (SVM) feeding inductive loads. The analysis carried out in this paper leads to the determination of the optimal use of zero vectors, i.e., the switching pattern leading to the minimum rms value of the load current ripple. The optimization of the switching pattern is based on the graphical analysis of the loci described by the ripple of the current vector in the alpha- beta reference frame. As a result, a set of analytical relationships that allow the online calculation of the duty cycles of the zero vectors is presented. Finally, simulation and experimental results confirm that the current ripple of the proposed modulation strategy is lower than that of traditional SVM strategies and, in some cases, with a reduced number of commutations.

This paper describes the realization of a high-performance drive based on stepping motors, with a specific reference to the optimal choice of pulsewidth modulation. An original modulation technique is proposed that allows, in conjunction with current feedback, to achieve high performances together with a reduced current ripple. A prototype digital signal processor-based drive was realized for a small-size stepping motor.