We demonstrate the ratchet and phase locking effects in a two-dimensional overdamped Frenkel-Kontorova model with a square symmetric periodic substrate when both a longitudinal dc drive and a circular ac drive are applied. Besides the harmonic steps, the large half integer steps can also clearly be seen in the longitudinal (x) direction. These half integer steps are directly correlated to the a...

 Traditional high-frequency pulse width modulation (PWM) inverters for motor drives have several problems associated with their high frequency switching which produces high voltage change (dV/dt) rates. Multilevel inverters solve these problems because their devices switch at the fundamental frequency. Two different multilevel topologies are identified for use as a converter for electric drive...

Voltage sags originating in ac supply systems can cause nuisance tripping of variable speed drives (VSDs) resulting in production loss and restarting delays. In ac VSDs having an uncontrolled rectifier front-end, the effects of voltage sags on the dc link causing dc under-voltage or ac overcurrent faults initiate the tripping. This paper suggests modifications in the control algorithm in order ...

 Traditional 2-level high-frequency pulse width modulation (PWM) inverters for motor drives have several problems associated with their high frequency switching which produces common-mode voltage and high voltage change (dV/dt) rates to the motor windings. Multilevel inverters solve these problems because their devices can switch at a much lower frequency. Two different multilevel topologies a...

The application of flux-observer-based sensorless control to permanent-magnet brushless ac motor drives is described. Current methods of speed estimation are assessed, both theoretically and experimentally, and an improved method, which combines the best features of methods in which speed is derived from the differential of rotor position and from the ratio of the electromotive force to excitat...

This thesis focuses on controller design and analysis for induction motor (IM) drives, flux control for electrically excited synchronous motors with damper windings (EESMs), and to enhance voltage sag ride-through ability and analysis for a wind turbine application with a full-power grid-connected active rectifier. The goal is to be able to use the existing equipment, without altering the hardw...