Improvement of fault ride through capability of synchronous generators with excitation boosters

Excitation Boosters (EB) are aimed at improving Fault Ride Through (FRT) capability of synchronous generators equipped with bus fed static excitation systems by means of adding a supplementary voltage or current source to the rectifier. Alstom patented a voltage EB, whose main component is an ultracapacitor that is connected to the field winding in case of a fault by an onoff controller. The ultracapacitor is sized in such a way that the FRT capability is improved when the generator is connected to an infinite bus. However, the paper shows that EBs governed by on-off controllers may result in adverse effects in case of remote faults from generators that may occur in multi-machine systems. To sort this problem out, a controller that modulates the EB voltage using the generator speed deviation with respect to the speed of the Center Of Inertia (COI). The speed of the COI is obtained using a Wide Area Measuring System (WAMS).