A novel method for improving the overload capability of stand-alone power generating systems based on a flywheel induction motor

Flywheel energy storage systems are good power stabilizers for stand-alone power systems, especially for highly fluctuating load or inrush power demand. In this investigation, a simple setup of a flywheel induction motor device is proposed which is composed of a flywheel and an induction motor directly connected in parallel to the inverter-controlled load. Also, a novel control method to improve the overload capability of the stand-alone power systems is presented by applying frequency control to the load side inverter. Compared to the conventional flywheel energy storage system, the proposed system has the following advantages: 1) simple configuration due to less number of inverters in the proposed system; 2) not only an improved overload capability of the stand-alone power system, but also a decreased capacity of the load-side inverter; 3) simple control and low cost. Although the changes of the flywheelpsilas speed would lead to frequency variations, a survey reveals that a small frequency variation is permitted for quite a lot of industrial machines. The requirement for the frequency variation can be satisfied by a proper capacity design of the flywheel induction motor. A design method to meet the utilitypsilas demand is introduced in this paper. Some experiments are conducted to verify the proposed system and the frequency control method. The experimental results show that the proposed system is easy and practical as an overload improvement method.