As a new type of power compensation device, electric spring(ES) can ensure the stability of the critical load voltage by transferring the fluctuating power to noncritical loads. However, most of the ESs reported are limited by the operating voltage range of noncritical loads. In this paper, a new type of fractional-order ES is proposed, which can regulate the voltage of critical load without noncritical load. The fractional-order ES is based on the characteristic that fractional-order components can consume or release active power under different orders. The topology, operating principles and control method of the fractional-order ES are reported, firstly. Then, the differences in topology, installation location and control target of the fractional-order ES and the existing battery energy storage system(BESS) are compared. Finally, the effectiveness of fractional-order ES has been verified via the RT-Box semi-physical platform.