Power Electronics and Control of Renewable Energy Systems F. Iov, M. Ciobotaru, D. Sera, R. Teodorescu, F. Blaabjerg Aalborg University, Institute of Energy Technology Pontoppidanstraede 101, DK-9220 Aalborg East, Denmark fi@iet.aau.dk, mpc@iet.aau.dk, des@iet.aau.dk, ret@iet.aau.dk, fbl@iet.aau.dk Abstract – The global electrical energy consumption is still rising and there is a demand to double the power capacity within 20 years. The production, distribution and use of energy should be as technological efficient as possible and incentives to save energy at the end-user should also be set up. Deregulation of energy has in the past lowered the investment in larger power plants, which means the need for new electrical power sources may be very high in the near future. Two major technologies will play important roles to solve the future problems. One is to change the electrical power production sources from the conventional, fossil (and short term) based energy sources to renewable energy resources. Another is to use high efficient power electronics in power generation, power transmission/distribution and end-user application. This paper discuss some of the most emerging renewable energy sources, wind energy and photovoltaics, which by means of power electronics are changing from being minor energy sources to be acting as important power sources in the energy system. I. INTRODUCTION In classical power systems, large power generation plants located at adequate geographical places produce most of the power, which is then transferred towards large consumption centers over long distance transmission lines. The system control centers monitor and regulate the power system continuously to ensure the quality of the power, namely frequency and voltage. However, now the overall power system is changing, 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 [1], [2] and installed. A wide-spread use of renewable energy sources in distribution networks and a high penetration level will be seen in the near future many places. E.g. Denmark has a high power capacity penetration (> 20%) of wind energy in major areas of the country and today 18% 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 inexhaustible resources of the primary energy. However, the main disadvantage, apart from the higher costs, e.g. photovoltaic, is the uncontrollability. 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. This is further strengthened as no real large energy storage systems exist. The wind turbine technology is one of the most emerging renewable energy technologies. It started in the 1980’es with a few tens of kW production power to today with multi-MW size wind turbines that are being installed. It also means that wind power production in the beginning did not have any impact on the power system control but now due to their size they have to play an active part in the grid. The technology used in wind turbines was in the beginning based on a squirrel- cage induction generator connected directly to the grid. By that power pulsations in the wind are almost directly transferred to the electrical grid. Furthermore there is no control of the active and reactive power, which typically are important control parameters to regulate the frequency and the voltage. As the power range of the turbines increases those control parameters become more important and it is necessary to introduce power electronics [3] as an interface between the wind turbine and the grid. The power electronics is changing the basic characteristic of the wind turbine from being an energy source to be an active power source. The electrical technology used in wind turbine is not new. It has been discussed for several years [6]-[50] but now the price pr. produced kWh is so low, that solutions with power electronics are very attractive. This paper will first discuss the basic development in power electronics and power electronic conversion. Then different wind turbine configurations will be explained both aerodynamically and electrically. Also different control methods will be shown for a wind turbine. They are now also installed in remote areas with good wind conditions (off-shore, on-shore) and different possible configurations are shown and compared. Next the PV-technology is discussed including the necessary basic power electronic conversion. Power converters are given and more advanced control features described. Finally, a general technology status of the wind power and the PV technology is presented demonstrating still more efficient and attractive power sources for the future. PEDS 2007 1-4244-0645-5/07/$20.00©2007 IEEE P-6