SCR harmonic correction topologies for VSI drives

The circuit topologies described in this paper contribute to the technology of converting three-phase AC power to DC, with the prime application being the input stage to commercial variable speed VSI drives. The power converter topologies examined are essentially SCR harmonic correction units (HCUs) suitable as a retrofit or as a drive option. The elementary HCU uses a three-phase switch network to sequentially access each line voltage. Current pulses are drawn from the selected line voltage and low distortion line currents are drawn as a result. Each HCU topology has a hard switched and a resonant soft-switch version. Since the HCUs are separate to the main drive structure, drive operation can be maintained even if the unit fails. Alternatively, when low current total harmonic distortion is not required, the drive can be installed without the HCU to lower the drive cost. The performance of the power converters described in this paper are illustrated with reference to simulated and experimental data.