Abstract

In medium and high power applications, two topologies have evolved for three-phase six-switch static power converters with an intermediate dc link, the voltage-source and the current-source. Despite the advantages of the current-source topology such as current limiting, higher reliability, and low ac-voltage harmonic distortion, voltage-source topologies are more widely used. This is in part due to the fact that current-source topologies present the following difficulties: (a) a lack of on-line modulating techniques that satisfy all the constraints of their gating signals and (b) the complexity of the control schemes for medium and high power applications. This thesis provides solutions to these problems. It proposes two enhanced on-line modulating techniques and three control schemes for three-phase six-switch current-source topologies, namely: (a) an on-line carrier-based PWM modulating technique, (b) an on-line PWM space-vector based modulating technique with reduced switching frequency, (c) an inner voltage control loop and an outer modulation index control loop for inverter topologies, and (d) a non-linear control scheme for rectifier topologies. The resulting power conversion schemes demonstrate the intrinsic advantages of the current-source topology and none of the disadvantages of the voltage-source topology. Moreover, they can be operated at reduced switching frequency, unity displacement power factor in the rectifier mode, minimum and constant load harmonic distortion, and allow the topology to provide high quality load waveforms and fast dynamic response. Simulated and experimental tests validate the theoretical considerations.