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 assessment of single-phase grid-connected PV microinverters considering mission profile and uncertainties

Abstract: Microinverters usually connect a PV panel to a Single-phase power grid. In such system, the input power is constant while the output power oscillates twice the line frequency. Thus, the input and output power differences should be stored in a storage component, which is typically an electrolytic capacitor. However, electrolytic capacitors are usually blamed for their short lifetime. Recently, some active power decoupling methods are introduced in the literature which can takes advantage of high reliable film capacitors. However, some extra switches and diodes are added to the microinverter which can influence the microinverter lifetime. This paper investigates the microinverter reliability according to mission profile where it is installed. To get more accurate results, uncertainties in both lifetime model and manufacturing process are considered. The effect of ambient temperature and solar irritation of two different places on the microinverter lifetime is studied.

Analysis of indirect rotor field oriented control-based induction machine performance under inaccurate field-oriented condition

Abstract: Indirect rotor field oriented control (IRFOC) plays an important role in the high performance induction machine drives. In the indirect rotor field oriented control — based induction machine adjustable speed control system, the rotor field angle is usually obtained by the rotor angular velocity and the slip angular velocity. The rotor angular velocity can be sensed by an encoder with sufficient accuracy. However, the slip angular velocity is affected by the rotor parameters variations and the current control performance degradation especially in the field-weakening region. Therefore, the field angle used in the indirect rotor field oriented control may have considerable error. In the paper, the angle error caused by rotor resistance variation is analyzed and the impact on the output torque and the rotor field intensity of the induction machine is studied. Simulations and experimental verification in base-speed region and field-weakening region are presented.

An active capacitor with self-power and internal feedback control signals

Abstract: This paper proposes a concept of two-terminal active capacitor implemented by power semiconductor switches and passive elements. The active capacitor has the same level of convenience as a passive one with two power terminals only. A control strategy that does not require any external feedback signal is proposed and a self-power scheme for gate drivers and the controller is applied to achieve the two-terminal active capacitor. The concept, control method, self-power scheme, efficiency, and impedance characteristics of the active capacitor are presented. A case study of the proposed active capacitor for a capacitive DC-link application is discussed. The results reveal a significantly lower overall energy storage of passive elements and a reduced cost to fulfill a specific reliability target, compared to a passive capacitor solution. Proof-of-concept experimental results are given to verify the functionality of the proposed capacitor.

Switching Characterization of SiC MOSFETs in Three-Level Active Neutral-Point-Clamped Inverter Application

Abstract: The switching characterization of power devices is critical for improving the efficiency and reliability of power electronic converters. In this paper, the switching characteristics of silicon carbide (SiC) MOSFETs in a three-level active neutral-point-clamped (3L-ANPC) inverter are investigated. A parasitic model of the 3L-ANPC phase-leg is proposed first based on a design case and its ANSYS/Q3D simulation. Then, two typical commutation modes for ANPC inverters, namely the outer mode and the inner mode, are studied, and the separate switching loops and parasitic inductances are identified according to the parasitic model. Knowing this, double-pulse tests (DPTs) for each type of commutation are conducted. The differences in terms of switching characteristics and switching dissipations are fully revealed. The conclusion drawn can be utilized for developing the next-generation highly efficient and reliable SiC MOSFET based 3L-ANPC inverters.

Modeling and Optimization of Displacement Windings for Transformers in Dual Active Bridge Converters

Abstract: The transformer in the dual active bridge converter (DAB) is the key element which provides galvanic insulation and voltage conversion. The parasitic parameters, including winding capacitance, ac resistance, and leakage inductance, are the primary considerations in its winding design. Without proper consideration of those parameters could result in issues on current ringing, high power loss, and overheating. In this paper, a comprehensive study is devoted to those parameters. A winding design method is presented by taking all those parameters into consideration. Special attention is paid to the impact of displacement winding, which is quite often in the manufacture and especially in prototype design phase. Both the normal and displacement winding will be studied and compared, with analytical, simulation, and experimental methods. Through comparison, additional coefficients are introduced to the simple analytical equations so that they could also be applied for displacement windings. Several considerations are given to control those parameters within a reasonable range in the design and manufacture phase. Finally, the analysis and design method are verified by finite element method and the experimental results on a 120 kHz prototype, and can be extended to other high-frequency magnetic designs.

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.