Showing papers by "Huai Wang published in 2012"

Design for reliability of power electronic systems

Abstract: Advances in power electronics enable efficient and flexible processing of electric power in the application of renewable energy sources, electric vehicles, adjustable-speed drives, etc. More and more efforts are devoted to better power electronic systems in terms of reliability to ensure high availability, long lifetime, sufficient robustness, low maintenance cost and low cost of energy. However, the reliability predictions are still dominantly according to outdated models and terms, such as MIL-HDBK-217H handbook models, Mean-Time-To-Failure (MTTF), and Mean-Time-Between-Failures (MTBF). A collection of methodologies based on Physics-of-Failure (PoF) approach and mission profile analysis are presented in this paper to perform reliability-oriented design of power electronic systems. The corresponding design procedures and reliability prediction models are provided. Further on, a case study on a 2.3 MW wind power converter is discussed with emphasis on the reliability critical components IGBTs. Different aspects of improving the reliability of the power converter are mapped. Finally, the challenges and opportunities to achieve more reliable power electronic systems are addressed.

Dc link module for reducing dc link capacitance

Abstract: A dc link module for a power circuit comprising a first connector for connecting to a first power conversion circuit, a second connector for connecting to a second power conversion circuit, wherein the second power conversion circuit is connected to a load circuit arranged to at least intermittently operate as a power source to the power circuit, at least one dc link capacitors arranged between said first connector and said second connector for processing a voltage signal received at said first connector or said second connector, and at least one voltage compensation circuits arranged between said first connector and said second connector, said one or more voltage compensation circuits arranged to generate a voltage signal to compensate an ac ripple component in a dc voltage signal appearing across the at least one dc link capacitor.

A New Concept of High-Voltage DC–DC Conversion Using Asymmetric Voltage Distribution on the Switch Pairs and Hybrid ZVS–ZCS Scheme

Abstract: A new concept of high-voltage dc-dc power conversion is presented in this paper. Its distinctive feature lies in distributing the high input voltage asymmetrically between two primary-side series-connected switch pairs. This allows using switches of optimal ratings in their respective class: the low-voltage switch pair implemented with MOSFETs only, and the high-voltage switch pair implemented with insulated gate bipolar transistors (IGBTs) only. As the switches in a switch pair are of the same type and voltage rating, they are maximally utilized. With an active snubber on the secondary side of the isolation transformer, a hybrid zero-voltage-switching-zero-current-switching (ZCS) scheme, which is different from the zero-voltage and zero-current-switching technique, is realized and makes all IGBTs be zero-current-switched and all MOSFETs be zero-voltage-switched from very light load to full load condition with minimal circulating energy. The ZCS snubber energy is completely released to the load, leading also to a duty-cycle gain. The operating principles, dc analysis, and design guidelines will be given. A 2-kW, 1500/48-V experimental prototype has been built and evaluated. The measured efficiency of the converter is found to be 92.4% at the rated condition.

A novel concept to reduce the DC-link capacitor in PFC front-end power conversion systems

Abstract: A series voltage compensator is proposed for power factor corrector (PFC) in power conversion systems. The introduced concept can reduce the dc-link capacitors used for balancing input and output power, limiting voltage ripple and maintaining certain period of hold-up time if required. Therefore, it allows replacing aluminum electrolytic capacitors by alternative ones with long lifetime while achieving high power density and cost effectiveness. The voltage compensator processes the ripple voltage of the dc-link and supplies reactive power only. It can be implemented by low voltage switching devices and passive components. Simulated and experimental results of a boost PFC converter verify the theoretical predications.

Ontologies for intellectual property rights protection

Abstract: Pirating various forms of intellectual property (IP) causes great economic loss to intellectual property rights (IPR) holders. IPR protection is becoming a key issue in our highly networked world. In order to further deepen our understanding of how to protect IPR and enhance information interchange and knowledge sharing among related entities, ontologies for IPR protection are proposed. This study contains three parts, which are developed to deal with different perspectives in this domain. The first part presents a static ontology, i.e. a hierarchy framework for the domain language, including primarily classes of participants, classes of IP works, classes of activities, and relations between these classes. In the second part, a dynamic ontology is shown to illustrate the IPR protection process. Thirdly, a causal map is used to demonstrate how classes of IPR protection methodologies are causally related with classes of IP piracy methodologies. Finally, the case of Tomato Garden is offered to demonstrate how the proposed ontologies are used in the real world. In respect of the ontology, it is first helpful to gain a comprehensive understanding of domain knowledge of IPR protection; second, IPR protection systems' design and development in this domain are facilitated and supported by these ontologies; third, the proposed ontologies are united in the Ontology Web Language (OWL) and the OWL rules languages framework, both of which are machine readable.

Hold-up time analysis of a dc-link module with a series voltage compensator

Abstract: A dc-link module composed of dc-link capacitors and a series voltage compensator has been proposed. It has been verified that the module can reduce the dc-link capacitance to 10–20% while achieving a very low voltage ripple across its output terminals. This paper investigates the required dc-link capacitance when a certain period of hold-up time is considered. Trade-off design conditions are presented and the hold-up time is compared with the solution without the series voltage compensator. The analysis is crucial to power converters connected to critical loads when hold-up time is required. The theoretical predictions have been verified by experimental results.

Long Lifetime DC-Link Voltage Stabilization Module for Smart Grid Application

Abstract: Power converters enable efficient and flexible control and conversion of electric energy among different smart grid players (ie producers, energy storage systems, and loads) One of the expected features of smart grid is that it will be more reliable compared to conventional grid However, power converters are one kind of the lifetime limiting components applied in smart grid One of the major causes is the malfunction of electrolytic capacitors (E-Caps) which are widely used for stabilizing the dc-link voltage in various types of power converters applied in smart grid A dc-link module is therefore proposed in this paper with a reduced value of dc-link capacitor and a series voltage compensator It allows the replacement of the popularly used E-Caps with alternatives of longer lifetime, like power film capacitors The basic concept, implementation and operation principle of the dc-link module are given The theoretical analysis is verified by simulation and experimental results (6 pages)