2) Adaptive Piezoelectric energy harvesting circuit

This paper describes an approach to harvesting electrical energy from a mechanically excited piezoelectric element. A vibrating piezoelectric device differs from a typical electrical power source in that it has a capacitive rather than inductive source impedance, and may be driven by mechanical vibrations of varying amplitude. An analytical expression for the optimal power flow from a rectified piezoelectric device is derived, and an “energy harvesting “ circuit is proposed which can achieve this optimal power flow. The harvesting circuit consists of an ac-dc rectifier with an output capacitor, an electrochemical battery, and a switch-mode dc-dc converter that controls the energy flow into the battery. An adaptive control technique for the dc-dc converter is used to continuously implement the optimal power transfer theory and maximize the power stored by the battery. Experimental result reveal that the use of the adaptive dc-dc converter increases power transfer by over 400% as compared to when the dc-dc converter is not used.

1) AC Cable Versus DC Cable Transmission for Offshore Wind Farms

A large interest in renewable energy systems has been developed to mitigate the green house effect. In Western Europe, the focus is thus, on wind power and especially on offshore locations, due to higher energy production, a longer expected life time and lack of suitable wind turbine sites on land. A DC cable is the preferred choice when connecting large offshore wind farms to the grid. The utilization of the Dc cables was enabled by the new HVDC transmission technology using voltage sourced converters.

The offshore wind farms that are being built today use an AC connection to shore and the distances to shore are also quite moderate. This paper describes three different solutions with a DC connection the shore and compares the cost and losses of a DC system with a traditional AC system that is used as a reference. DC systems will be competitive solutions in ten years and have several advantages compared with an AC system. This paper includes several reasons for selecting a DC cable is the preferred choice when connecting large offshore wind farms, to the grid.

The offshore wind farms that are being built today use an AC connection to shore and the distances to the shore are also quite moderate. This is a well-known technology and a natural step for the first off-shore wind farms. However in ten, years when the experiences from the first offshore wind farms have been evaluated and the next expansion starts, the alternatives with a DC grid will become cost-effective solutions. The future wind farms will becomes larger and will be situated at a farther distance from shore. The connection to the onshore transmission grid must be at a point with high short circuit capacity and the onshore distance, therefore is expected to be greater in the future.

The cost of power electronics will be significantly lower in the future and the losses will continue to decrease, so the advantages will outweigh the disadvantages.

New Technical Seminar Topics in Engineering

Wide Range of Seminar Topics and its abstracts for students in different branches in Engineering Field. (Electrical, Mechanical, Electronics, Civil, Chemical, Computer, Automobile etc).

About Seminar

A seminar is, generally, a form of academic instruction, either at a university or offered by a commercial or professional organization. It has the function of bringing together small groups for recurring meetings, focusing each time on some particular subject, in which everyone present is requested to actively participate. This is often accomplished through an ongoing Socratic dialogue with a seminar leader or instructor, or through a more formal presentation of research. Normally, participants must not be beginners in the field under discussion (at a university, seminar classes are generally reserved for upper-year students). The idea behind the seminar system is to familiarize students more extensively with the methodology of their chosen subject and also to allow them to interact with examples of the practical problems that always crop up during research work. It is essentially a place where assigned readings are discussed, questions can be raised and debates conducted. It is relatively informal, at least compared to the lecture system of academic instruction.