Direct load control for wind power integration

Output power fluctuation of high penetration of wind power causes demand and supply imbalance in electric power systems and results in frequency deviation if the fluctuation is not fully compensated by other regulable power plants. In Japan, some electric utilities have started to accept only the wind farms which disconnect and give up generating power during light-load periods with less adjustable reserve. Otherwise, wind farms are required to employ battery energy storage systems to charge the generated power during the light-load periods. Instead of these uneconomical solutions, this paper proposes direct control of loads such as electric water heaters (EWHs) for power system balancing. In the paper, the increase of acceptable wind power generation by the proposed load control has been evaluated quantitatively in the power system of the Hokkaido Island in Japan. The result indicates that the acceptable wind power generation increases almost three times higher by implementing the direct control on seven-tenth of EWHs in Hokkaido. However, the control interval of the direct load control is required to be shorter than or almost equal to the inertia constant of the power system.