Power electronics - key technology for renewable energy systems

The electrical energy consumption continues to grow and more applications are based on electricity. We can expect that more 60 % of all energy consumption will be converted and used as electricity. Therefore, it is a demand that production, distribution and use of electrical energy are done as efficient as possible. Further, the emerging climate changes is arguing to find sustainable future solutions. Of many options, two major technologies will play important roles to solve parts of those future problems. One is to change the electrical power production from conventional, fossil based energy sources to renewable energy sources. Another is to use high efficient power electronics in power generation, power transmission/distribution and end-user application. This paper discuss trends of the most emerging renewable energy sources, wind energy and photovoltaics, which by means of power electronics are changing and challenging the future electrical infrastructure but also contributes steadily more to non-carbon based electricity production. Most focus in the paper is on the power electronics technologies used. In the case of photovoltaics transformer-less systems are discussed as they have the potential to obtain the highest efficiencies

I. Introduction

In classical power systems, large power generation plants are located at adequate geographical places to produce most of the power, which is then transferred towards large consumption centers over long distance transmission lines. Now the power system is changing, as a large number of dispersed generation (DG) units, including both renewable and non-renewable sources such as wind turbines, wave generators, photovoltaic (PV) generators, small hydro, fuel cells and gas/steam powered Combined Heat and Power (CHP) stations, are being developed and installed all over the world [1]–[2]. A wide-spread use of renewable energy sources in distribution networks is seen. E.g. Denmark has a high power capacity penetration (> 30 %) of wind energy in major areas of the country and today 28 % of the whole electrical energy consumption is covered by wind energy. The main advantages of using renewable energy sources are the elimination of harmful emissions and the inexhaustible resources of the primary energy. However, the main disadvantage, apart from the higher costs is the uncontrollability as they are completely weather-based. The availability of renewable energy sources has strong daily and seasonal patterns and the power demand by the consumers could have a very different characteristic. Therefore, it is difficult to operate a power system installed with only renewable generation units due to the characteristic differences and the high uncertainty in the availability of the renewable energy sources without any load control. This is further strengthened as no real large scale electrical energy storage systems exist.

Major parts of this paper was presented at EPE-PEMC 2010, Ohrid, Macedonia.