Journal: CPSS Transactions on Power Electronics and Applications

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China Power Supply Society

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ISSN

2475-742X

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2017 - 201912020 - 20215
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Publications 1 - 6 of 6
  • The Essence of the Little Box Challenge-Part B: Hardware Demonstrators & Comparative Evaluations
    Item type: Journal Article
    Neumayr, Dominik; Bortis, Dominik; Kolar, Johann W. (2020)
    CPSS Transactions on Power Electronics and Applications
    In order to expedite the development of power electronic systems towards higher power density and efficiency at a lower cost of implementation, Google and IEEE initiated the Google Little Box Challenge (GLBC) aiming for the worldwide smallest 2 kVA/450 VDC/230 VAC single-phase PV inverter with η > 95% CEC weighted efficiency and an air-cooled case temperature of less than 60 °C by using latest power semiconductor technology and innovative topological concepts. This paper, i.e. Part B of a discussion of The Essence of the Little Box Challenge, presents the hardware implementations and novel control concepts of two GaN-based inverter systems selected by the authors to counter the challenge: (i) Little Box 1.0 (LB 1.0), a H-bridge inverter with two interleaved bridge-legs both operated with Triangular Current Mode (TCM) modulation which features a power density of 8.18 kW/dm 3 (134 W/in 3 ) and a nominal efficiency of 96.4% and (ii) Little Box 2.0 (LB 2.0), an inverter topology with single bridgeleg DC/|AC| buck-stage operated with constant frequency PWM and a subsequent |AC|/AC H-bridge unfolder, which features a remarkable power density of 14.8 kW/dm 3 (243 W/in 3 ) and a nominal efficiency of 97.4% Implemented using latest GaN power semiconductor technology, Zero Voltage Switching (ZVS) throughout the AC period and a variable switching frequency in the range of 200 kHz-1 MHz in order to shrink the size of filter passives, the LB 1.0 was ranked among the top 10 out of 100+ teams actively participating in the GLBC. The LB 2.0 is the result of further research and considers lessons learned from the GLBC and achieves despite moderate 140 kHz constant frequency PWM and hard-switching around the peak of the AC output current a higher power density ρ and a higher efficiency η. For both implemented prototypes experimental results are provided to confirm that all GLBC technical requirements are met. The experimental results include steady-state and step-response waveforms, EMI and ground current measurements, as well as efficiency and operating temperature measurements. The reason for the ηρ-performance improvement of LB 2.0 over LB 1.0 are then discussed in detail. Furthermore, the solutions of other GLBC finalists are described and then compared to the performance achieved with the hardware prototypes presented in this paper. This leads to findings of general importance and provides key guideline for the future development of ultracompact power electronic converters.
  • Design and Experimental Analysis of a Three-Phase Active CM/DM Conducted EMI Noise Separator
    Item type: Journal Article
    Niklaus, Pascal; Bortis, Dominik; Kolar, Johann W. (2020)
    CPSS Transactions on Power Electronics and Applications
    This work investigates three-phase electromagnetic interference (EMI) conducted emission (CE) measurements with the aim to separate the noise voltages in their common-mode (CM) and differential-mode (DM) parts. By doing so, the converter input and/or output filter stages can be individually optimized to improve the CM or DM attenuation depending on the origin of the CE disturbances. An overview of various ways to achieve this separation is provided and an active three-phase noise separator is presented. The main advantage of the presented active solution is the absence of magnetic components in the signal path which drastically facilitates the matching at high frequencies. The influence of asymmetries and mismatches of the component parasitics as well as in the circuit board layout are analyzed. To assess the performance of the proposed system according to widely known metrics such as CM and DM transfer functions and rejection ratios, different test methods are established and the implied limitations regarding maximum measurable performance are considered. Finally, experimental results verifying the calculated separation capabilities are provided.
  • Input/Output EMI Filter Design for Three-Phase Ultra-High Speed Motor Drive GaN Inverter Stage
    Item type: Journal Article
    Antivachis, Michael; Niklaus, Pascal; Bortis, Dominik; et al. (2021)
    CPSS Transactions on Power Electronics and Applications
    Pairing wide-bandgap (WBG) inverters with highspeed motors results in compact and efficient motor drives, but requires special attention on electromagnetic interference (EMI) aspects. This paper focuses on electromagnetic compatibility (EMC) of high-speed motor drives, supplied by a DC source. In order to protect the nearby equipment from the EMI noise of the WBG inverter, a filter that complies with conducted EMI regulations is placed at the inverter DC input-side. However, there is no clear mandate requiring from inverters to comply with conducted EMI regulations at the AC output-side, where only the motor is placed. For this reason, there is no full consensus whether it is necessary to use an output filter, and if so, what type of output filter would be suitable, i.e., if differential-mode (DM), common-mode (CM) or both DM/CM output filter would fit best. A full sine-wave output filter (FSF) is proposed in this paper, that features both DM and CM attenuation, and capacitors connected to the DC link. Besides the several well established benefits of a FSF, such as purely sinusoidal motor currents and the protection of the motor against high dw/dt originating from the fast switching of the semiconductor devices, a FSF at the inverter output-side, also reduces the CM EMI emissions at the inverter input-side. Namely, since the inverter housing, the motor housing and the interconnecting shielded cable are all grounded, CM emissions generated at the inverter output-side are directly mapped to the inverter input-side, i.e., there is an input-to-output CM noise interrelation. A FSF reduces the output-side CM EMI emissions and thus mitigates the input-to-output CM noise mutual influence. Two types of FSF (c-FSF and d-FSF) are comparatively evaluated, in terms of volume, losses and EMI performance. The theoretical consideration are tested within the context of a high-speed 280 krpm, 1 kW motor drive, with 80 V DC supply. The experimental results validate the good performance of the proposed filter concept.
  • The Essence of the Little Box Challenge-Part A: Key Design Challenges & Solutions
    Item type: Journal Article
    Neumayr, Dominik; Bortis, Dominik; Kolar, Johann W. (2020)
    CPSS Transactions on Power Electronics and Applications
    In order to expedite the development of power electronic systems towards higher power density and efficiency at a lower cost of implementation, Google and IEEE initiated the Google Little Box Challenge (GLBC) aiming for the worldwide smallest 2 kVA / 450 V DC / 230 V AC single-phase PV inverter with η > 95 % CEC weighted efficiency and an air-cooled case temperature of less than 60 °C by using latest power semiconductor technology and innovative topological concepts. This paper, i.e., Part A of a discussion of The Essence of the Little Box Challenge, documents all important R&D activities and engineering considerations of the authors endeavor to implement the world's most compact inverter; Part B is intended to convey the main findings and lessons learned from the participation in the GLBC. First, the key technical challenges of the GLBC are discussed and the technologies and concepts selected by the authors among different options are described in detail. Relevant design considerations, such as constant frequency pulse width modulation (PWM) or triangular current mode (TCM) operation of the bridge-legs, selection of power semiconductor technology, interleaving of bridge-legs, sizing of the power buffer capacitor, limitation of ground/leakage currents, etc., to achieve an ultra-compact implementation are discussed. Based on this overview, two promising inverter concepts to tackle the GLBC, (i) an H-bridge based inverter with DC-link referenced output filter and (ii) a DC/|AC| buck-stage with series-connected low-frequency (LF) |AC|/AC unfolder inverter, are then analyzed in detail. Based on the results of a multi-objective ηρ-Pareto optimization, a comparative evaluation of the performance in terms of efficiency (η) and power density (ρ) of the two considered inverter concepts is provided. It is shown that with the DC/|AC| buck-stage and |AC|/AC H-bridge unfolder inverter operated with 140 kHz PWM a power density of 14.7 kW/dm 3 (240 W/in 3 ) with a maximum efficiency of 98.1% at 2 kW output power can be achieved. These claims are then verified in Part B by means of experimental results obtained from prototype realizations and compared to the achievements of other GLBC finalists. The conclusions are of general importance and are providing key guidelines for the future development of ultra-compact power electronic converters.
  • Medium-Frequency Transformer Scaling Laws: Derivation, Verification, and Critical Analysis
    Item type: Journal Article
    Guillod, Thomas; Kolar, Johann W. (2020)
    CPSS Transactions on Power Electronics and Applications
    Medium-frequency transformers (MFTs) are one of the fundamental building blocks of modern power electronic converters. The usage of increased frequencies leads to improved characteristics, i.e., efficiency and power density (volumetric and gravimetric) but also to design challenges and constraints. This paper reviews the analytical modeling of MFTs. More particularly, the mapping between the design space and the performance space is analyzed. It is found that wide regions of the design space are mapped to a narrow region in the performance space, i.e., the optimum is flat and designs with very different parameters features similar performances (design space diversity). Scaling laws are derived for optimal MFTs operated at different power ratings and power densities, which provide a comprehensive and general insight on the achievable performances. In a next step, the results obtained with the analytical model are compared to numerical simulations. It is concluded that the derived scaling laws capture qualitatively and quantitatively the behavior of MFTs, but should be used with caution for accurate design processes.
  • 99% Efficient Three-Phase Buck-Type SiC MOSFET PFC Rectifier Minimizing Life Cycle Cost in DC Data Centers
    Item type: Journal Article
    Schrittwieser, Lukas; Kolar, Johann W.; Soeiro, Thiago B. (2017)
    CPSS Transactions on Power Electronics and Applications
Publications 1 - 6 of 6