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.

Reactive Power Impacts on LCL Filter Capacitor Lifetime and Reliability in DFIG Grid-Connected Inverter

Abstract: With the increasing penetration of renewable power, its reliable and cost-effective production is of more and more importance. A filter is normally inserted between the grid-connected inverter and the power grid to reduce the PWM switching harmonics. According to an electro-thermal stress evaluation, the time-to-failure distribution of the single LCL filter capacitor is investigated in detail. Aiming at the system-level reliability analysis, a Weibull distribution based component-level individual capacitor can be linked together by using the reliability block diagram. A case study of a 2 MW wind power converter shows that the lifetime is significantly reduced from the individual capacitor to the capacitor bank. Besides, the over-excited reactive power injection further reduces the lifetime of the LCL filter capacitors.

Thermal Modeling and Sizing of PCB Copper Pads

Abstract: In low power applications, a surface mounted device (SMD) is naturally cooled by attaching to a printed circuit board (PCB) copper pad. This paper proposes an analytical thermal resistance model and a sizing algorithm for PCB copper pads. Firstly, an axisymmetric thermal resistance model is developed for PCB copper pads where the heat conduction, convection and radiation all exist. Due to the interdependence of the conductive/radiative heat transfer coefficient and the board temperature, a new algorithm is proposed to fast obtain the thermal resistance and to predict the semiconductor junction temperature at different copper pad radii. The algorithm enables a fast sizing of copper pads based on different junction temperature limits. Finally, the developed thermal resistance model and algorithm are verified by computational fluid dynamics (CFD) simulations and experiments.

Robust Stability Assessment of Single-Phase Inverter With Multiparameter Distributions

Abstract: Grid-connected inverters inevitably operate under uncertain system parameters. These uncertain parameters such as inductance and capacitance are caused by device aging or uncertain grid conditions. And they will affect the stability margin of the inverter and bring an unstable operation risk even with a well initial design. The existing research articles mainly focus on robust stability analysis and control strategies while ignoring the influence of parameter distributions on operational risk. How to evaluate the instability risk of the inverter under multiparameter distribution is still an open question. In this article, the structured singular value (SSV) method is proposed to evaluate the robust stability of the inverter with multiparameter distributions. The distribution characteristics of uncertain parameters are briefly reviewed. The system model of a single-phase grid-connected inverter is established with the parameter distributions of the system key components. The probability of stable system operation can be quantified by the SSV method. Experiment and case study results verify the correctness and effectiveness of the proposed method.

Impact of Mission Profile Dynamics on Accuracy of Thermal Stress Modeling in PV Inverters

Abstract: Thermal stress modeling of power devices is a key factor that influences the design for reliability of Photovoltaic (PV) inverters under long-term operations, i.e., different mission profiles. Due to the requirement of long-term analysis for mapping the inverter reliability more accurately, a thermal model based on a lumped thermal network is normally employed due to its low computational burden. However, there is still a lack of validation in terms of modeling accuracy, e.g., comparing the simulation results against the experimental thermal stress in field operations. Besides, the impact of mission profile dynamics on the accuracy of different thermal modeling approaches have not been analyzed. To address this issue, the model accuracy of two thermal stress modeling approaches for PV inverters are evaluated in this paper by comparing the thermal stress estimated from a thermal model with the experimental results under various mission profile dynamics. According to the results, the average error of the junction temperature estimation is 1.51 % for a transient thermal model and 2.08 % for a steady-state thermal model, respectively. On the other hand, the computational efficiency of the thermal stress modeling can be improved by more than a factor of three when using the steady-state thermal model.

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.