Huai Wang

Bio: Huai Wang is an academic researcher from Aalborg University. The author has contributed to research in topics: Capacitor & Power electronics. The author has an hindex of 38, co-authored 328 publications receiving 7480 citations. Previous affiliations of Huai Wang include Yangtze University & City University of Hong Kong.

Capacitor Condition Monitoring for Modular Multilevel Converter Based on Charging Transient Voltage Analysis

Abstract: This article proposes a capacitor condition monitoring (CM) method for modular multilevel converter (MMC) in motor drive applications. The proposed method is based on wavelet decomposition of transient voltage signals, which is independent of modulation schemes and control strategies. The equivalent series resistance (ESR) change can be detected with a moderate computation requirement. Both simulation and experimental results have verified the performance of the proposed method.

A new concept of high input voltage to low load voltage (1500 V – 48V) DC-DC conversion with hybrid ZVS-ZCS and asymmetrical voltage distribution

Abstract: A new dc-dc converter with asymmetrical voltage distribution between two primary switch pairs is proposed. It allows an implementation with popularly used MOSFETs for the low-voltage switch pair and IGBTs for the high-voltage switch pair, giving the optimal option for a particular class of high-voltage applications. A new hybrid zero-voltage-switching (ZVS)-zero-current-switching (ZCS) technique, which is different from the ZVZCS solution, is proposed. A secondary-side snubber is used to achieve ZCS of all IGBTs in the IGBT pair; its resonant energy is fully released to the load. The energy used for achieving ZVS for the upper MOSFET in the low-voltage switch pair at the transition from the freewheeling to energy transfer stage is provided by the primary-side input capacitor and dc-blocking capacitor. All IGBTs and MOSFETs in the proposed structure are soft-switched from very light load to full load. The duty cycle of the upper switch in each pair determines the voltage distribution between the switch pairs. It is controlled by a simple PWM. A 2kW, 1500/48V experimental prototype has been built and evaluated. The experimental results confirmed the theoretical predictions.

A Minimum Viable Mission Profile Emulator for IGBT Modules in Modular Multilevel Converters

Abstract: Various methods have been presented to emulate the electrical behavior of Modular Multilevel Converters (MMCs). To meet the demands for reliability aspect study of MMCs, this paper proposes a minimum viable setup to emulate the thermal behavior and investigates its feasibility for reliability testing. The proposed mission profile emulator has three distinctive features: 1) capable of emulating and measuring the thermal stresses of power modules; 2) capable of implementing practical switching profiles as a full-scale MMC; and 3) with significantly reduced requirement for dc power supply compared to existing setups used for electrical aspect study. Theoretical discussions and experimental measurements are presented to demonstrate the capability of the mission profile emulator.

Approaching repetitive short circuit tests on MW-scale power modules by means of an automatic testing setup

Abstract: An automatic testing system to perform repetitive short-circuit tests on megawatt-scale IGBT power modules is presented and described in this paper, pointing out the advantages and features of such testing approach. The developed system is based on a non-destructive short-circuit tester, which has been integrated with an advanced software tool and a semiconductor device analyzer to perform stress monitoring on the considered device under test (DUT). A case-study is included in the paper concerning a 1.7 kV/ 1 kA IGBT module, which has been tested safely up to 30,000 repetitions with no significant damage. The developed system has been demonstrated to be very helpful in performing a large number of repetition tests as required by modern testing protocols for robustness and reliability assessment. The software algorithm and a demonstration video are available for download.

Analytical Modeling of 9-150 kHz EMI in Three-Phase Active Rectifiers

Abstract: In recent years, new challenging issues have been raised due to interaction among power electronic converters and other electronic devices such as mains communication systems connected to the distribution network within a 9-150 kHz frequency range. Since there is a lack of a general standard and also a fundamental study within this new frequency range, it is necessary to investigate power converter frequency behavior within 9-150 kHz. It not only enables the possibility of characterizing power converters behavior but also provides a suitable indication of designing proper Electromagnetic Interference (EMI) filters. Moreover, there are no fundamental studies and general standards despite some reported EMI noise issues in this frequency range. Therefore, it is necessary to investigate the power converter frequency behavior within this new frequency range, providing a guideline to design proper EMI filters. This paper proposes an analytical time-frequency domain approach for modeling Differential Mode (DM) EMI noise of three-phase active rectifiers within the 9-150 kHz frequency range. To develop an analytical frequency-domain approach, the switching function model of the converter is defined using a double Fourier analysis method, including its input estimated impedance model. Furthermore, the equivalent circuit model includes Line Impedance Stabilization Network (LISN) circuit, and EMI receiver due to EMI standard requirement. A 9 kW three-phase AC to DC grid-connected converter prototype is used to validate the proposed EMI modeling approach. The analytical approach is shown to successfully predict EMI emission within the 9-150 kHz frequency range with an error of 1.2 dB or less at most frequency ranges.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Ultracapacitors: Why, How, and Where is the Technology

Abstract: The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Light-emitting diodes

Abstract: Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.