Efecto y eficiencia de los extractos botánicos sobre la población de Plutella

Figure 2.1: The power electronics hierarchy, from applications and systems to devices and materials.

2.2

The Systems

Renewable energy is the future of power generation and currently the only truly clean form of energy generation with Nuclear Fusion still a long way from fruition. Excluding biofuels, renewables including wind, solar, wave and hydro powers accounted for just 6 % of the global final energy consumption in 2009 [25]. Wind power accounts for a large proportion of the renewables market and at the time of writing, the UK had 3157 turbines, with a maximum output capacity of 5.2 gigawatts (GW) of power [26], some 5 %

2.2 The Systems

of the national requirement. Being ideally positioned for offshore wind generation, just under 4 GW of construction projects were under way, with another 5 GW given the go ahead, and 8 GW in the planning stages [26]. These impressive figures show that this is a huge, expanding industry, and power electronics plays an important role in optimising the turbines. Beginning with the hugely variable energy supply of the wind, energy must first be transferred from mechanical, rotational power to electrical power through a gearbox and generator. This must then be transformed onto the correct AC rating to be placed on the national grid, therefore requiring efficient bi-directional DC-AC converters at the systems level of Figure 2.1.

Once onto the grid, the efficient and appropriate distribution of electrical power is the next challenge. A recent buzz-word, the smart grid is an ideology that encompasses a number of technological challenges that have a common theme of providing power in a fashion that reduces cost, saves energy and improves reliability. At the forefront of this idea is the increased use of control systems, smart meters in homes that can communicate power requirements immediately back to the national grid and to the suppliers, thus regulating output with up-to-the-minute demand. This is the popular face of the smart grid idea; however, the true ”smart” network needs more. Power, like so much else, is becoming an international affair, with the national grids all over Europe connected up. However, each A.C. grid has its own requirements in terms of transmission frequencies and powers. This means that each nation’s grid must be joined to the next by converting the A.C. to D.C. and back to A.C. again. Seeing that DC power is generated at the power stations and that most domestic products are D.C., one has to ask, why are we not using a D.C. grid? Significant progress has been made in the field of high voltage D.C. (HVDC) distribution and it is now the most energy efficient way to transmit power over long distances. Many international HVDC cables already exist such as those linking

2.2 The Systems

Britain with France, Scotland with Northern Ireland, as well as many other connections across Europe and the globe. At the moment however, the significant cost of these systems has prevented HVDC being rolled out as a national grid. With a HVDC national grid off the cards for the foreseeable future, the use of more efficient, smaller, cheaper and lighter power conversion solutions is essential. Hence in a similar conclusion as the last paragraph, the efficiency of DC-AC, AC-DC and DC-DC converters are essential.

After the power has been generated, transmitted and distributed, we end up with it in our homes, and the role of power electronics does not end. It crops up in all our electronic equipment converting the 220 V 50 Hz A.C. supply down to the 5, 9 or 12 V DC the T.V., computer or radio requires. However looking again to the future, it is likely to be our domestic energy supply that powers our mobility, and it is the electric car in particular that has so much to be won and lost in the quality of its electronics. The biggest challenge currently facing the full electric car market is actually energy storage, as it is the absence of a small and lightweight, but high capacity battery that prevents the electric car getting further than their current 100 mile range [27]. As well as this so called “Range Anxiety”, the biggest criticism of electric cars is the fact that they are only as green as the electricity supply. This neatly brings us full circle in our demand for greener energy, reiterating the previous need for investment in renewables. Currently these limitations hold us back from using full electric vehicles, but hybrids are becoming ever more popular, with several on the market already [28]. In both full electrics and hybrids we return to our recurring need for efficient power conversion as these cars require an efficient inverter to convert stored D.C. charge into the A.C supply powering the motor. Of course in reverse, as the motor is acting as a generator, the opposite is true and the A.C. needs to be rectified to D.C. for storage.