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.

Reliability Evaluation of DC-link Capacitors in Multi-drive Systems

Abstract: This paper proposes a time-efficient equivalent model for the ripple current analysis of DC-link capacitors in multi-drive systems and investigates the impact of number of drives and grid voltage unbalance on the capacitor lifetime. Firstly, a time-efficient equivalent model for multi-drive systems is proposed to obtain the electro-thermal stress of capacitor in individual drive. Then, applying the lifetime prediction method, the reliability of the DC-link capacitors in multi-drive systems considering the interactions among multiple drives are studied. Finally, the quantitative impact of number of drives and unbalanced grid conditions on the lifetime of DC-link capacitors are discussed. The outcomes support the model based sizing of DC-link capacitors for multi-drive systems considering the electro-thermal and lifetime aspect requirements.

Performance Evaluation of a Two-terminal Active Inductor in the DC-link Filter of a Three-phase Diode Bridge Rectifier

Abstract: A two-terminal active inductor implemented by power switches and energy storage elements is proposed recently to breakthrough the limitation of the commonly used passive inductor. It has the same level of convenience in use as passive inductors and could have the same impedance characteristic in the frequency of interest. As a further study of the proposed concept, this paper quantitatively evaluates the performance of the two-terminal active inductor in terms of power loss, inductive energy storage, volume, and weight. Comparative study between an active inductor and a passive inductor with the same rated current and equivalent inductance used for a three-phase diode bridge rectifier is presented. Experimental results are provided to verify the accuracy of the theoretical predictions.

Transient Voltage Stress Modeling for Submodules of Modular Multilevel Converters under Grid Voltage Sags

Abstract: The trend for the model-based design of modular multilevel converters (MMC) demands a better estimation of the submodule (SM) voltage stress. The transient voltage stresses of MMC SMs are important for the SM capacitor dimensioning and the robustness of power modules. This paper proposes an analytical model of the SM transient voltage stress under grid voltage sags. It is based on a simplified analysis of the MMC current control and circulating current control schemes. A case study reveals that a sufficient accuracy level can be achieved with the proposed model to estimate the transient voltage stress.

Reliability evaluation of a single-phase H-bridge inverter with integrated active power decoupling

Abstract: Various power decoupling methods have been proposed recently to replace the DC-link Electrolytic Capacitors (E-caps) in single-phase conversion system, in order to extend the lifetime and improve the reliability of the DC-link. However, it is still an open question whether the converter level reliability becomes better or not, since additional components are introduced and the loading of the existing components may be changed. This paper aims to study the converter level reliability of a single-phase full-bridge inverter with two kinds of active power decoupling module and to compare it with the traditional passive DC-link solution. The converter level reliability is obtained by component level electro-thermal stress modeling, lifetime model, Weibull distribution, and Reliability Block Diagram (RBD) method. The results are demonstrated by a 2 kW single-phase inverter application.

Benchmarking of Constant Power Generation Strategies for Single-Phase Grid-Connected Photovoltaic Systems

Abstract: With a still increase of grid-connected photovoltaic (PV) systems, challenges have been imposed on the grid due to the continuous injection of a large amount of fluctuating PV power, like overloading the grid infrastructure (e.g., transformers) during peak power production periods. Hence, advanced active power control methods are required. As a cost-effective solution to avoid overloading, a constant power generation (CPG) control scheme by limiting the feed-in power has been introduced into the currently active grid regulations. In order to achieve a CPG operation, this paper presents three CPG strategies based on a power control method (P-CPG), a current limit method (I-CPG), and the perturb and observe algorithm (P&O-CPG). However, the operational mode changes (e.g., from the maximum power point tracking to a CPG operation) will affect the entire system performance. Thus, a benchmarking of the presented CPG strategies is also conducted on a 3-kW single-phase grid-connected PV system. Comparisons reveal that either the P-CPG or I-CPG strategies can achieve fast dynamics and satisfactory steady-state performance. In contrast, the P&O-CPG algorithm is the most suitable solution in terms of high robustness, but it presents poor dynamic performance.

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.