01-06-2013, 02:54 PM
Seminar Report on A HIGH PERFORMANCE RECTIFIER FOR ELECTRICAL POWER GENERATION FROM MARINE CURRENTS
A HIGH PERFORMANCE.doc (Size: 1.55 MB / Downloads: 24)
ABSTRACT
The oceans represent a huge energy reservoir consistent of stored solar and gravitational energy in several forms, causing movements of enormous volume of water. This energy is generally diffuse but, in many cases, significantly more concentrated than other forms of renewable energy already being successfully exploited on land. Among the ocean energy resources, wave and marine current energy emerge as the most promising option for massive power generation with zero environmental impact. A power electronic rectifier is built for electrical power generation from marine currents, which guarantee both DC-side voltages with very low ripple and sinusoidal generator currents.
Each power generation unit consists of two turbines (and electrical generators) which are contextually used. Six conventional single-phase rectifiers are connected in series at their DC-side terminals, so achieving a DC-voltage with high mean value and very low ripple. The power factor of each single-phase rectifier is corrected by means of an effective passive network. After correction, ACside generator currents practically become sinusoidal, avoiding troublesome oscillating torques on generator and turbine boards. The efficiency of rectifier is improved by an electronic resistance emulator circuit which emulates the wasting behavior of resistors. The performance will be analyzed by using Pspice.
INTRODUCTION
Marine current power is a form of marine energy obtained from harnessing of the kinetic energy of marine currents, such as the Gulf stream. Although not widely used at present, marine current power has an important potential for future electricity generation. Marine currents are more predictable than wind and solar power.
A 2006 report from United States Department of the Interior estimates that capturing just 1/1,000th of the available energy from the Gulf Stream, which has 21,000 times more energy than Niagara Falls in a flow of water that is 50 times the total flow of all the world’s freshwater rivers, would supply Florida with 35% of its electrical needs.
Marine currents are caused mainly by the rise and fall of the tides resulting from the gravitational interactions between earth, moon, and sun, causing the whole sea to flow. Other effects such as regional differences in temperature and salinity and the Coriolis effect due to the rotation of the earth are also major influences. The kinetic energy of marine currents can be converted in much the same way that a wind turbine extracts energy from the wind, using various types of open-flow rotors. The potential of electric power generation from marine tidal currents is enormous.
WHY MARINE CURRENTS?
There are a number of market drivers making marine currents a more viable renewable alternative to traditional energy sources:
• The world-wide demand for electricity is expected to double within the next 20 years, with the strongest growth in the developing areas of Asia.
• The decommissioning of nuclear power stations and an increased reliance upon natural gas resulting in concerns over security of supply and an increased push for renewables.
• The introduction of the EC emissions trading scheme making renewables an attractive investment.
Marine current energy is a particularly attractive renewable energy source. The velocities in good tidal stream areas are a fraction of typical wind cut-out speeds, but they are steadier and accurately predictable. This means there should be less need of storage and easier integration within network planning.
In addition, the increased density of water in comparison to air means that it has higher energy intensity than most renewables (four times as much as wind).
The advantages of marine current energy over other renewables can be clearly observed in the table below, although actual characteristics will vary according to generator design. One of the major drawbacks of this technology however, is the high capital cost, as technology is in it’s infancy.
POWER CONVERTER
• Power converter is a power supply unit(PSU)that not only delivers energy to an electronic device from an electrical outlet ,but also regulates the current to meet the specific device requirements.
• Power converters specifically designed can improve electrical power generation from marine currents, improving plant reliability and flexibility, quality of generated voltages and currents and circuit efficiency.
• Conventionally the inverter is placed on the mainland, so that the design of the DC-section could assume a great relevance in minimizing power transmission losses.
NUMERICAL VALIDATION OF THE PROPOSED CIRCUIT
In order to give evidence of the effectiveness of the proposed circuit, without and with the resistance emulation technique, a case-study circuit of about 1.5 MW of active power is numerically analyzed with the help of several PSPICE simulations. For the sake of simplicity an equivalent resistive load, Rload, has been considered at the DC side terminals of the circuit.
With reference to the most complete circuit depicted in Fig.7, Tables I÷III report the values of the circuit parameters needed for simulations, calculated according also with the designing procedure of section IV.
CONCLUSION
Modern power generation units from marine currents can be profitably improved by utilizing power electronic converter specifically designed.
The proposed rectifier, with passive PF correction, makes generator currents quasi sinusoidal, so avoiding troublesome additional power losses and oscillating torques on generator and turbine boards; furthermore, the DC side voltage results with high quality waveform and very high mean value, so minimizing also transmission losses. The circuit efficiency can be improved by introducing a resistance emulator circuit.