Journal: IEEE Open Journal of Power Electronics

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IEEE

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2644-1314

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2020 - 202526
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Publications 1 - 10 of 26
  • iGSE-C$_{\mathrm{x}}$ – a New Normalized Steinmetz Model for Class II Multilayer Ceramic Capacitors
    Item type: Journal Article
    Menzi, David; Heller, Morris; Kolar, Johann W. (2021)
    IEEE Open Journal of Power Electronics
    Ferroelectric Class II ceramic capacitors allow for highly compact converter realizations, but are showing relatively high losses for large-signal excitations which must be taken into account in the system dimensioning. Recent literature introduced the iGSE-C Q , a Steinmetz model based on the macroscopic capacitor Q-U hysteresis, allowing to accurately predict the losses of X7R capacitors. However, the model is specific for each single device, i.e., is insufficient to characterize losses in devices of the same series and manufacturer, which are employing the same dielectric material but with different voltage rating or nominal capacitance value. In this publication, based on basic physical properties we propose a new Steinmetz model, the iGSE-C X based on the relative dielectric material D-E hysteresis, which is applicable to all devices of a capacitor series. The iGSE-C X loss modeling technique is demonstrated for the TDK X7R, the TDK X7T, as well as the Knowles Syfer X7R series. Finally, the iGSE-C X is employed to estimate the large-signal losses of the capacitors of a three-phase inverter and shown to offer sufficient accuracy for a first power circuit design.
  • Fast and Accurate Data Sheet based Analytical Switching Loss Model for a SiC MOSFET and Schottky Diode Half-Bridge
    Item type: Journal Article
    Hu, Anliang; Biela, Jürgen (2024)
    IEEE Open Journal of Power Electronics
    Fast and accurate switching loss models that can be used for different devices are crucial for optimization-based converter design. This paper proposes a novel data sheet based, fully analytical loss model for a SiC MOSFET and Schottky diode half-bridge including parasitics. In the model, nonlinear device characteristics are approximated by multi-step piecewise constants. Furthermore, a small number of assumptions are used to derive and to solve the approximated nonlinear differential equations for obtaining the switching losses. To evaluate the model, a new accuracy measure is proposed for a fair accuracy comparison with existing models. The proposed model is also comprehensively verified by double pulse tests using 5 SiC MOSFET (with different structures) and Schottky diode pairs from different manufacturers. The proposed fully analytical model exhibits on average the best accuracy with a high computational efficiency (less than 1 millisecond per operating point) compared to state-of-the-art analytical switching loss models, as validated by using both data sheet information and measured device characteristics.
  • Hardware-Based Comparative Analysis of Multilevel Inverter Topologies for Integrated Motor Drives Considering Overload Operation
    Item type: Journal Article
    Rohner, Gwendolin; Gfrörer, Tino; Niklaus, Pascal; et al. (2023)
    IEEE Open Journal of Power Electronics
    With today's demand for increased industrial process automation a trend towards Integrated Motor Drives (IMDs) has evolved allowing a low complexity and compact installation of the drive system. Especially servo applications with high short-term overload requirements (e.g., three times the nominal current for several seconds) are a thermal challenge for the power electronics. Consequently, high efficiencies and power densities are key requirements of these motor-integrated Variable Speed Drives (VSDs). Multi-Level (ML) inverter topologies allow small LC output filter designs and benefit from utilizing low-voltage semiconductors with superior conduction and switching performance, and thus represent an interesting approach for future IMDs. In this work an experimental comparison between three different 800V DC link supplied drive systems is presented, namely between a 3L Flying Capacitor Converter (3L-FCC) (employing 650V GaN HEMTs), a 7L Flying Capacitor Converter (7L-FCC) (using 200V Si MOSFETs) and its promising alternative, a 7L Hybrid Active Neutral-Point Clamped Converter (7L-HANPC) (using both, 650V GaN HEMTs and 200V Si MOSFETs). All three systems are realized as hardware demonstrators for the same specifications, i.e., for integration into a Permanent Magnet Synchronous Motor (PMSM) with a case temperature of 90∘C , 7.5kW nominal output power at > 99% efficiency and a short-term overload capability of three times the nominal current for 3s . Thereby, the efficiencies and the thermally critical overload capability are experimentally verified. Overall, the 3L-FCC shows the best performance trade-off with lowest complexity and/or highest reliability and minimal control effort.
  • Duty-Cycle Dependent Phase Shift Modulation of Dual Three-Phase Active Bridge Four-Port AC–DC/DC–AC Converter Eliminating Low Frequency Power Pulsations
    Item type: Journal Article
    Heller, Morris J.; Krismer, Florian; Kolar, Johann W. (2022)
    IEEE Open Journal of Power Electronics
    A recently introduced Dual Three-Phase Active Bridge Converter (D3ABC) provides two three-phase ac ports (ac₁ and ac₂), two dc ports (dc₁ and dc₂), and galvanic isolation between the ports ac₁, dc₁ (primary side) and ac₂, dc₂ (secondary side). Previously documented studies confirm that the D3ABC is generally capable of transferring power between all four ports. However, it has been found challenging to operate the converter if ac voltages with different line frequencies, ⨍₁ ≠ ⨍₂, are present at the ports ac₁ and ac₂. Such operation causes Low-Frequency (LF) power pulsations in the converter's dc links, leading to fluctuating dc link voltages and distorted phase currents. In this paper, a new duty-cycle dependent phase shift modulation scheme is proposed that eliminates such LF power pulsations and substantially increases the theoretical maximum transmittable power between primary and secondary sides compared to previous work. The new modulation scheme is developed on the basis of analytical considerations, which are supported by the results of numerical calculations, and verified by means of circuit simulations and experimental results. A hardware demonstrator originally designed for a rated power of 8 kW when operated from ac₁ to dc₂ at the European low-voltage ac mains ( V_ac,1 = 230V line-to-neutral rms, V_dc,1 = 800V , V_dc,1 = 400V ) is used for experimental verification. Since the operation with ⨍₁ ≠ ⨍₂ leads to an increase of the currents in the converter, the experimental verification is conducted at half voltages and for a reduced power of 2 kW that is transferred from ac₁ to ac₂ at substantially different primary-side and secondary-side line frequencies of ⨍₁ = 50 Hz and $f_{2} = \tex...
  • Analytical Model for HF-losses Caused by 2D Magnetic Fields in Litz Wire
    Item type: Journal Article
    Meng, Qinghao; Biela, Jürgen (2023)
    IEEE Open Journal of Power Electronics
    The 2D magnetic field effect arises when the winding height is lower than the window height due to isolation requirements and mechanical constraints. In this situation, most analytical models for calculating HF-losses in Litz wire fail to predict the winding losses accurately since they are normally based on a 1D magnetic field assumption. Although numerical or semi-numerical methods can accurately calculate the winding losses, they are too time-consuming to be integrated into the converter optimization routines. This paper provides a new loss model, which is validated to have a much lower error ( <10% ) than 1D field loss models (up to -45%) by numerical calculations and experiments. The model is presented for two winding transformers with layered windings and non-gapped cores with high permeability in the frequency range, where the strand diameter to skin depth ratio is equal to 1.2. Moreover, the model can also be extended for interleaved windings by separating the windings to multiple blocks. Furthermore, the computation time is less than 300μs using the algorithm provided in this paper. This new model achieves a good balance between accuracy and computational time and has great potential to improve the transformer as well as the converter design.
  • Novel ZVS S-TCM Modulation of Three-Phase AC/DC Converters
    Item type: Journal Article
    Haider, Michael; Azurza Anderson, Jon; Miric, Spasoje; et al. (2020)
    IEEE Open Journal of Power Electronics
    For three-phase AC-DC power conversion, the widely-used continuous current mode (CCM) modulation scheme results in relatively high semiconductor losses from hard-switching each device during half of the mains cycle. Triangular current mode (TCM) modulation, where the inductor current reverses polarity before turn-off, achieves zero-voltage-switching (ZVS) but at the expense of a wide switching frequency variation (15× for the three-phase design considered here), complicating filter design and compliance with EMI regulations. In this paper, we propose a new modulation scheme, sinusoidal triangular current mode (S-TCM), that achieves soft-switching, keeps the maximum switching frequency below the 150 kHz EMI regulatory band, and limits the switching frequency variation to only 3×. Under S-TCM, three specific modulation schemes are analyzed, and a loss-optimized weighting of the current bands across load is identified. The 2.2 kW S-TCM phase-leg hardware demonstrator achieves 99.7% semiconductor efficiency, with the semiconductor losses accurately analytically estimated within 10% (0.3 W). Relative to a CCM design, the required filter inductance is 6× lower, the inductor volume is 37% smaller, and the semiconductor losses are 55% smaller for a simultaneous improvement in power density and efficiency.
  • Calculation of the Inductance and Resistance Matrices of Medium Frequency Transformers
    Item type: Journal Article
    Korthauer, Bastian; Biela, Jürgen (2024)
    IEEE Open Journal of Power Electronics
    Due to the ever-increasing switching speeds of wide band gap (WBG) devices, the high-frequency behavior of magnetic components, such as medium frequency transformers, is becoming increasingly significant. To describe this complex high-frequency behavior, large multiconductor networks are commonly employed. The frequency-dependent parameters of these networks are typically represented as matrices. However, accurately calculating these matrices often necessitates time-consuming finite element analysis (FEA), which significantly limits the investigation of various geometries within a practical timeframe. This paper addresses this problem by proposing a model based on analytical formulations for the frequency-dependent resistance and inductance matrices of transformers with litz wire windings. The model is experimentally verified showing good agreement to the measurements over a wide frequency range. Compared to FEA only a marginal deviation of less than 2% is noticeable, whereas the calculation is more than 200 times faster.
  • Improved Analytical Triple-2D Leakage Inductance Model of Cone Winding Matrix Transformers
    Item type: Journal Article
    Schlesinger, Richard; Biela, Jürgen (2023)
    IEEE Open Journal of Power Electronics
    The transformer leakage inductance is one of the limiting factors for pulse shape quality in high voltage pulsed power (HVPP) converters that are essential in applications such as cancer treatment, particle accelerators, and free electron lasers. Cone winding matrix (CWM) transformers are commonly used in HVPP converters as they offer low leakage inductance and high insulation distance. This paper proposes an improved Triple-2D (iT2D) leakage inductance model for CWM transformers. The iT2D model identifies three basic cross sections of CWM transformers and calculates their associated leakage inductance contributions. The paper proposes an accurate and compact analytical formula of the leakage inductance contribution resulting from the magnetic energy stored in between the magnetic cores. For cross sections with cone windings, an expression is presented that computes the leakage inductance per unit length of non-parallel windings. The iT2D model is verified with measurements and finite element simulations of three transformer prototypes. The analytical solutions used in the iT2D model ensure applicability to arbitrary geometric aspect ratios and designs. Furthermore, the iT2D model is rapidly executable enabling its time-efficient integration in converter optimisations.
  • Models for a Fast Computation of Internal Overvoltages in Medium-Frequency Transformers
    Item type: Journal Article
    Korthauer, Bastian; Biela, Jürgen (2024)
    IEEE Open Journal of Power Electronics
    The fast switching of wide-bandgap (WBG) devices and the resulting harmonics in the switching waveforms can cause significant overvoltages in medium frequency transformers (MFTs). To enhance the reliability and lifetime of MFTs, fast and accurate models for these high frequency effects in the windings are necessary. The effects can be described using large multiconductor networks. However, computing the frequency-dependent parameters of such networks – namely the impedance and capacitance matrices – typically involves time-consuming finite element analysis (FEA), hindering the investigation of multiple designs in a reasonable timeframe. Therefore, this paper presents an analytical approach to compute impedance and capacitance matrices for the equivalent networks, focusing on an efficient algorithm to compute the capacitance matrix as well as an appropriate length scaling of the calculated per-unit-length matrices. Simulation and measurement results show that the proposed models can compute internal overvoltages more than 500 times faster than FEA, while predicting the maximum overvoltage with an error of less than 7%. The individual validation of all presented submodels not only confirms the applicability to overvoltage modeling, but also demonstrates a potential use of the models in other areas of high-frequency modeling.
  • New Figure-of-Merit Combining Semiconductor and Multi-Level Converter Properties
    Item type: Journal Article
    Azurza Anderson, Jon; Zulauf, Grayson; Kolar, Johann W.; et al. (2020)
    IEEE Open Journal of Power Electronics
    Figures-of-Merit (FOMs) are widely-used to compare power semiconductor materials and devices and to motivate research and development of new technology nodes. These material- and device-specific FOMs, however, fail to directly translate into quantifiable performance in a specific power electronics application. Here, we combine device performance with specific bridge-leg topologies to propose the extended FOM, or X-FOM, a Figure-of-Merit that quantifies bridge-leg performance in multi-level (ML) topologies and supports the quantitative comparison and optimization of topologies and power devices. To arrive at the proposed X-FOM, we revisit the fundamental scaling laws of the on-state resistance and output capacitance of power semiconductors to first propose a revised device-level semiconductor Figure-of-Merit (D-FOM). The D-FOM is then generalized to a multi-level topology with an arbitrary number of levels, output power, and input voltage, resulting in the X-FOM that quantitatively compares hard-switched semiconductor stage losses and filter stage requirements across different bridge-leg structures and numbers of levels, identifies the maximum achievable efficiency of the semiconductor stage, and determines the loss-optimal combination of semiconductor die area and switching frequency. To validate the new X-FOM and showcase its utility, we perform a case study on candidate bridge-leg structures for a three-phase 10 kW photovoltaic (PV) inverter, with the X-FOM showing that (a) the minimum hard-switching losses are an accurate approximation to predict the theoretically maximum achievable efficiency and relative performance between bridge-legs and (b) the 3-level bridge-leg outperforms the 2-level configuration, despite utilizing a SiC MOSFET with a lower D-FOM than in the 2-level case.
Publications 1 - 10 of 26