풍력발전 출력보상을 위한 하이브리드 에너지저장시스템에 관한 연구

Abstract

Nowadays, to cope with the rapid exhaustion of the earth's fossil fuel resources and the climate change, the renewable energies have been researched in many countries such as wind energy, solar energy, tidal energy and so on. Especially, wind energy is the most significant renewable energy because of its capacity and friendly environment. With the development of advanced technologies, the wind turbine has been increasing in the capacity. Wind power has been given much weight in the electrical energy every year. But wind power systems may cause problems to system operation such as power fluctuation, frequency variation, voltage variation, and grid instability. Hence, wind farm can be no longer considered as a stable energy source. In the Jeju Island, wind power system is one of the main renewable energy source because wind speed is most strong in Korea. The total wind power capacity is almost 106 MW among 852 MW of Jeju power system in 2012. This power will be increased in the future when new wind farms are installed. The Jeju power system is considered as a weak-grid, thus it needs a support from other sources. Two LCC(Line Commutated Converter)- HVDC(High Voltage Direct Current) systems have built to connect between mainland and the Jeju power grid network (HVDC #1: 150 MW and HVDC #2: 250MW). The aims of LCC-HVDC systems are to supply the electrical energy and to make a stabilization in the Jeju power system. However, the Jeju power system will be able to be also in dangerous situation, such as frequency fluctuation, in case of maintenance or breakdown of HVDC systems. Therefore, a separated energy source should be connected to wind farm when a fault occurs. Many methods have been researched in literature to solve this problem. An ESS(Energy Storage System) using lithium ion battery is also one of the effective methods to stabilize the fluctuation of wind power system. Advanced battery technologies now allow extraordinary energy densities, but it is still insufficient for applications of large power impulses. Especially, in case of the fluctuation in wind power system, it requires a high power density in very short duration. This deficiency can be overcome by paralleling more batteries if that is allowed by system volume, weight, and cost constraints. On the other hand, a hybrid ESS-EDLC(Electric double layer capacitor) can solve the power deficiency at lower cost, space, and weight. Even though lithium-ion battery has high energy density, EDLC has much more energy density than former battery. The advantages of a hybrid ESS-EDLC are the extension of life cycle and the reduction of internal faults because EDLC does not have chemical variations on the electrodes. With smaller internal resistances, the internal losses and heating during extremely discharging term can be also reduced. In this dissertation, the different storage energy devices are first analyzed and compared each other. Then, a hybrid ESS is proposed to compensate for the Jeju power system in case of power fluctuation. The characteristics of battery is compared between real data and simulation data. This dissertation also proposes the method for calculating the adequate capacity of the hybrid ESS. This work is very important because the fluctuation of wind power will be depended on the characteristic of wind velocity. An proposed capacity depend on the capacity of wind farm will save energy, increase efficiency, and ensure economical operation. Finally, the simulation results will confirm the effectiveness of proposed method.