Limited ride-through capabilities for direct frequency converters

摘要

Many solutions to provide continuous operation of adjustable speedndrives (ASDs) during power grid disturbances have been proposed, butnthey are all applied to DC-link ASD. In this paper a new solution tonprovide limited ride-through operation of a scalar controlled directnfrequency converter (DFC) for a duration of hundreds of milliseconds,nwithout any hardware modification, is presented. During the ride-throughnoperation, the drive is not capable of developing torque or to controlnthe motor flux. By recovering the necessary power to feed the controlnhardware, the DFC is able to keep the ASD operating. When normal gridnconditions are re-established, the DFC is also able to accelerate thenmotor from nonzero speed and flux by initializing the modulator with thenestimated frequency and initial voltage vector angle. The duration ofnthe ride-through operation depends on the initial motor flux, speednlevel, rotor time constant, load torque and inertia