Control strategy and dynamic performance of a doubly-fed flywheel generator-motor; Koryu reiji flywheel hatsudenki no seigyoho to kato tokusei

A doubly-fed flywheel generator-motor consists of a wound-rotor induction machine and a cycloconverter or a voltage-source PWM rectifier-inverter which is used as an ac exciter. Adjusting the rotor speed makes the generator-motor either release the kinetic energy to the power system or absorb it from the power system. Thus, the generator-motor has the capability of achieving, not only reactive power control, but also active power control based on a flywheel effect of the rotor. A 200-MJ flywheel generator-motor for the purpose of line-frequency regulation on a 132-kV bus has been installed and commissioned by the Okinawa Electric Power Company. However, little literature has been published on control strategy and dynamic performance analysis of doubly-fed flywheel generator-motors. This paper proposes a new control strategy for a doubly-fed flywheel generator-motor, which is characterized by the combination of vector control and decoupling control. The control strategy enables the flywheel generator-motor to perform active power control independent of reactive power control even in transient states. The validity of the theory developed in this paper; along with the effectiveness of the control strategy, is confirmed by computer simulations using EMTDC. In addition, this paper discusses the transient behavior of a magnetizing current of the flywheel generator-motor. The flywheel generator-motor based on leading edge power electronics and electric machine technologies shows promise as a versatile power conditioner, in particular, being capable of repetitively absorbing or releasing electric energy for a short period of time less than a minute. 18 refs., 9 figs., 1 tab.